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Country report on forest invasive species in the Philippines

N.T. Baguinon, M.O. Quimado and G.J. Francisco
University of the Philippines, Los Baños
Forest Management Bureau, Department of Environment and Natural Resources (DENR)

The natural forest types of the Philippines

The types of forests in the Philippines were first enumerated by Whitford (1911) who recognized mangrove, beach, dipterocarp, molave, pine, montane and mossy forest types. The Palawan Botanical Expedition by Hilleshog AB (1984) recognized within Palawan many types of vegetation, for example, ultramafic and ultrabasic forests, karst limestone forests, riverine forests, semi-evergreen dipterocarp forests, evergreen dipterocarp forests and lake-margin forests. There could be more actual forest types than the number already published. Stereotyping a continuum of unique forest ecosystems into just a few lists may not render justice to the wonders of evolution and the complex Philippine bio-geological history.

However, the latest classification of Philippine ecosystem diversity types in the terrestrial setting (DENR-NBSAP 1997) are the following: (1) lowland evergreen rain forest, (2) lower montane forest, (3) upper montane forest, (4) subalpine forest, (5) pine forest, (6) forest over limestone, (7) forest over ultrabasic soils, (8) semi-deciduous forest, and (9) beach forest.

The lowland evergreen rain forests are located on volcanic soils with even distribution of rainfall and correspond with Whitford’s dipterocarp forests excluding the apitong-lauan subtype, which corresponds with semi-deciduous forest. The importance of the members of the Dipterocarpaceae is most notable in lowland evergreen rain forests (Newman et al, 1996).

Beyond 1000 metres in altitude, lower montane forests are encountered. In these forests, Fagaceae (the family of oaks) increase in number of species, as do species in families such as Araliaceae, Staphyleaceae, and Lauraceae. Many tree ferns, epiphytes such as orchids, ferns and allies, increase in importance. As elevation is gained, upper montane forest begins to occur (at about 2000 metres). Members of the Ericaceae (e.g. Rhododendron quadrasianum, Vaccinium myrtoides, etc.), Myrtaceae (such as Leptospermum flavescens) and Theaceae (such as Eurya, Cleyera, Schima, Adinandra, and Camellia species) families are encountered (Merrill and Merritt, 1910).

In regions with seasonal monsoon climates, the montane forests when disturbed into a gap by fire is readily succeeded by disclimax vegetation dominated by benguet pine (Pinus insularis) (Kowal, 1975). In Mindoro Island, only tapulau pine forest exists. Pine forests are perpetuated by fire and therefore also known as fire disclimaxes.

In limestone forests, below 1000 metres, the keystone species are molave (Vitex parviflora), lingo-lingo (Viticipremna philippinensis), alagao (Premna odorata), and batete (Kingiodendron alternifolium).

Beach forests above the intertidal zone vary depending upon the substrate (Merrill, 1945). Beach forests exist as Casuarina subtype or Barringtonia subtype. In one extreme, on sand dunes, pure stands of agoho (Casuarina equisetifolia) would be characteristic. At the other extreme, on rocky shores, is mixed vegetation of the Barringtonia subtype.

Forests on ultrabasic soils (Hilleshog Forestry AB, 1984) are not as dense and tall as the mixed dipterocarp forests, simply because they develop on unhealthy serpentine and basic soils. This type of forest features hardwoods such as mancono (Xanthostemon verdugonianum), bagoadlau (X. philippinensis), malabayabas (Tristaniopsis decorticata), Brackenridgea palustris, mountain agoho (Gymnostoma rumphiana), and Scaevola micrantha.

The introduction of exotic species

Merrill’s "Enumeration of Philippine flowering plants" (1921-26) and subsequent revisions in the "Flora Malesiana" (1954-present) are good references to determine which species are indigenous and exotic (Rojo, 1999). Exotic species are indicated with asterisks.

Prehistoric introduction of trees (probably by Malayo-Polynesian settlers) were first noted and may have included common agricultural tree crops such as the katurai (*Sesbania grandiflora), malunggai (*Moringa oleifera), mango (*Mangifera indica), nangka (*Artocarpus heterophyllus), breadfruit (*A. altilis), santol (*Sandoricum koetjape), rambutan (*Nephelium lappaceum), karamai (*Cicca (Phyllanthus) acida), bignai (*Antidesma bunius), kamias (*Averrhoa bilimbi), balimbing (*A. carambola), duhat (*Syzygium jambolana) and other *Syzygium spp., kawayan kiling (*Bambusa vulgaris), kawayan tinik (*B. spinosa) and many others. Most of these are Indo-Malayan in origin. A few escaped into the wild like the bignai, duhat and santol. However, these have not grown and established themselves as persistent gregarious stands.

The Spanish regime, through the Acapulco trade, brought additional exotic tree species, mostly agricultural crops such as the *Anona spp. (atis, cherimoya, guyabano, anonas), biriba (*Rollinia deliciosa), zapote (*Diospyros digyna), cacao (*Theobroma cacao), siniguelas (*Spondias purpurea), chico (*Manilkara sapota), tiesa (*Pouteria campechiana), cashew (*Anacardium occidentale), avocado (*Persea americana), kamatchile (*Pithecellobium dulce) and datiles (*Muntingia calabura). Woody trees such as the monkey-pod tree (*Samanea saman), *ipil-ipil (Leucaena leucocephala), kakawate (*Gliricidia sepium) and kalachuchi (*Plumiera rubra) were also introduced. Coffee (*Coffea spp.) was introduced by the Spanish from Africa. Some of these escaped into the field, for example ipil-ipil, datiles, and kamatchile. Of the tropical American exotic trees, ipil-ipil may be singled-out as bio-invasive, as the species forms pure stands in open areas. Kamatchile and datiles have been dispersed but their numbers are limited, compared with ipil-ipil.

During the American regime, more exotic tree species found their way to the Philippines as Caguioa (1953) recounts:

"After the Spanish-American war, plants have been introduced into the Philippines generally by exchange between the governments of foreign countries and the Philippine Government, through the Bureau of Forestry and Bureau of Plant Industry and by purchase from foreign countries by private citizens. Introduced plants came into the Philippines during the Spanish regime, the Philippines introduced plant materials from Central American countries through missionaries and others who came to the Philippines by way of galleon from Mexico to the Orient, and from the neighbouring countries or islands through traders and travellers who came to visit this country by water transportation. During the first half of the present century, many countries in both the western and the eastern hemisphere have exchanged planting materials with the Philippines."

Exotic species were added as a result of the agricultural and forestry schools that were opened (Buenaventura, 1958). In 1910, the School of Forestry site consisted of grass and brush at the base of Mount Makiling. Laguna, Luzon and American administrators initiated the reforestation of the school grounds mainly by planting indigenous tree species, as well as the tropical American species mahogany (*Swietenia spp.), rubber (*Hevea brasiliensis), and ipil-ipil (*Leucaena leucocephala). Then other exotics followed such as kakawate, palosanto (*Triplaris cumingiana), Anchoan dilaw (*Cassia spectabilis), golden shower (*C. fistula), and teak (*Tectona grandis). Note that they also introduced dipterocarps from other parts of the country to enrich the native Makiling dipterocarps, namely, white lauan (Shorea contorta), bagtikan (Parashorea malaanonan) and guijo (Shorea guiso) (Brown, 1919). African tulip (*Spathodea campanulata) was introduced in 1925 to the Forestry School campus (Anonymous, 1930) and it has since spread deep in natural stands.

Ponce (1933) documented the introduction of the American mahoganies. Small leaf mahogany (*Swietenia mahogani) was introduced as early as 1911, and by batches in 1913, 1914, 1920 and 1922, from tropical America. Large leaf mahogany (*S. macrophylla) was first planted in Manila in 1907, then at the Forestry School at Mt. Makiling in 1913. Lizardo (1960) reviewed the introduction of Eucalyptus in the Philippines. Spanish friars introduced (*Eucalyptus globulus) at Alcala, Cagayan as early as 1851 and in 1939, the first trial plantings for *E. robusta were initiated. Other plantings were *E. rostrata in 1918, *E. tereticornis 1910, *E. citriodora 1936, *E. viminalis 1918, *E. pulverulenta 1916, and *E. saligna 1947. The paper mulberry (*Broussonetia papyrifera) was introduced in 1935 to augment bast fibre-producing tree crops at the Makiling Forestry School campus and - as did coronitas (*Lantana camara) from Hawaii - escaped to become serious pests. Both species invade young secondary forests, thickets, orchards and farms. These two species and mahogany have spread throughout the Philippine archipelago.

Post-war introduction of exotics continues and planting them has almost become synonymous with reforestation. Yemane (*Gmelina arborea) was introduced in 1960 and planted in Minglanilla, Cebu by the Bureau of Forestry (Binua and Arias, 1966). Mangium (*Acacia mangium) was introduced in 1960 from Sabah. The Philippines Forestry Statistics (1984) record that out of a total 52 487 seedlings produced by the Philippines Government forest agency, 82.4 percent (43 234 seedlings) of seedlings were exotics. These were distributed across giant ipil-ipil (41 percent), large leaf mahogany (33 percent), yemane (17 percent), teak (4 percent), and others (5 percent). Seedlings of indigenous tree species contributed 17.6 percent.

Current foresters’ notion of reforestation

Based on the forest definition by American mentors as artificial or natural, Tamesis and Sulit (1937) define "reforestation" as the restoration of an area to forest either by artificial or natural means and "afforestation" applies to the planting of a forest on land that has not previously borne forest. They mention planting exotics in Bukidnon including chinchona, large leaf mahogany, *Araucaria bidwillii, *Pinus massoniana, Anchoan dilaw, *Adenanthera microsperma, *Thuja orientalis, black wattle (*Acacia decurrens), and *Cryptomeria japonica. In Baguio, *Eucalyptus spp. and Alder (*Alnus spp.) were planted. Tamesis and Sulit cite that good reforestation species are of:

There is also the mindset among foresters that artificial forests are as ecological as the natural forest they replace. For example, Domingo (1983) wrote during the First ASEAN Congress,

"... when we convert a dipterocarp forest to pulpwood plantation, what we are doing is just transferring the jungle regrowth onto a tree species of our choice for pulpwood. Substituting the economically unnecessary but ecologically necessary jungle regrowth with an economically important pulpwood plantation does not change, it might even enhance, the normal ecological pattern. The same ecological benefits that the jungle regrowth provides can be provided by the plantation...."

In short, this goes in line with most foresters’ pragmatism that if the natural forest is gone or nearly gone, enrichment planting with fast-growing commercial exotic tree species is better than restoring natural forests for two reasons. One, because a return of investment at the earliest possible time is provided by the artificial forest, and two, artificial forests also provide the same environmental services as natural forests, particularly, on watershed function and carbon-sequestration. Other foresters also claim that analogue forests and agroforest zones can also be as rich in floral diversity as or even richer than are natural forest ecosystems. Thus, during the ASEAN Regional Centre for Biodiversity Conservation (ARCBC) Symposium-Workshop on Facing the Challenge of Sustaining Biodiversity Conservation in Mt. Makiling, Gruezo (2000) reports

"...Comparison of floral diversity in these four zones (Mossy forest zone, Dipterocarp mid-montane forest zone, Grassland zone and Agroforestry Zone) reveals that the agroforestry zone had the highest diversity value using the Shannon-Weiner formula, with H’ = 4.2869 followed by the dipterocarp-mid-montane forest zone, H’ = 3.8913, ...".

Man can cram many exotic crops including their exotic weeds in one place, then make statements to the effect that agro-ecosystems are more diverse than natural forest ecosystems.

Bio-invasive species and natural forests

As far back as the pre-war period, exotic trees have been used in reforestation. Projects of the Reforestation Administration used exotic species as showcases, e.g. reforestation at Minglanilla in Cebu, the Nasiping Reforestation Project in Cagayan, Paraiso reforestation in Ilocos Norte, Canlaon reforestation in Negros, and Impalutao reforestation in Bukidnon. The reforestation projects of the Bureau of Forestry were well spread throughout the archipelago. Seedlings from these projects found their way into national parks and for this reason mahogany can be found in most of the country’s nature parks. However, no studies have yet been done on the rate of bio-invasion of these nature reserves and parks. The planting of exotics in the Integrated Protected Area System (IPAS) of the Philippines has now been prohibited under the present DENR’s PAWB (Park and Wildlife Bureau). No definite policies are in place yet on what to do with mature exotic trees, should they become bio-invasive. This issue is now being seriously considered by the College of Forestry and Natural Resources, for the Makiling Forest reserve.

Because there was a law requiring replanting of logged-over dipterocarp forests during the 1960s to 1980s, many timberlands have had been reforested with exotic trees, among them mahogany, yemane, mangium, bagras and teak. Of these tree species, only mahogany is a potential bio-invasive species in the logged-over forest and is threatening to out compete the indigenous dipterocarp and non-dipterocarp tree species.

Mahogany is successful at invading natural forests due to the following attributes of the species. The fruit of mahogany is a capsule and contains an average of 62 winged seeds (Anonymous, 1930). The number of seeds a mahogany mother tree can disperse is considerable. Assuming 50 capsules, 3000 seeds can be blown away from the mother tree. The seeds can be blown some 20 to 40 meters from the mother tree. The seeds, being recalcitrant, germinate in less than a month. Mahogany seeds contain food reserves and germinate hypogeal. This means that even if the initial light is relatively poor, the young mahogany plant develops even without initial photosynthesis. The first young leaves of mahogany are scale leaves and not green. True photosynthetic leaves come later and are adapted to sun-flecked shade and partial shade. Hardened mahogany seedlings can tolerate open fields as long as soil moisture is not limiting. The leaves of mahogany are rarely attacked by herbivores. Thus, a mahogany plantation is like a "green desert" to wildlife. Dipterocarps fruit and seed irregularly in intervals of four to five years and therefore stand no chance competing with mahogany.

When mother trees shed their leaves during the months of February, they form a thick litter mat. Dry mahogany leaves are red and can be very rich in tannin. The leaves are intact during the whole length of the dry season. This litter mat could be one reason why very few seedlings are recruited under the mahogany plantation, including their own seedlings. Dispersed recalcitrant seeds rest on top of the litter mat instead of reaching the moist soil and hence die due to desiccation.

They may also be allelopathic (Thinley, 2002). Extracts from the leaves of mahogany were shown to retard the growth of narra (Pterocarpus indicus) test seedlings. Recruits increase away from the mahogany plantation and this increase is proportional to the competition offered by mahogany wildlings (Alvarez, 2001; Castillo, 2001). The importance of mahogany seedlings is negatively correlated with the Shannon-Weiner Diversity Indices of quadrats positioned from the mahogany plantation and away from it. In other words, diversity of the quadrats decreases as the importance of mahogany increases.

While mahogany invades regenerating dipterocarp forests and may give the dipterocarps a hard time in competition, the paper mulberry (*Broussonetia papyrifera) also gives indigenous gap and pioneer tree species very keen competition. Ocular observation shows that where paper mulberry forms pure stand thickets, the usual indigenous pioneer tree species such as anabiong (Trema orientalis), binunga (Macaranga tanarius), alim (Melanolepis multiglandulosus), banato (Mallotus philippinensis), tibig (Ficus nota), hauili (F. septica), isis (F. ulmifolia), sablot (Litsea sebifera), paguringon (Cratoxylon sumatranum), and malapapaya (Polyscias nodosa) are not present.

The combination of mahogany and paper mulberry is therefore a big blow for the ecological succession of the landscape, at the gap and building-up phases. This can be a serious problem for Assisted Natural Regeneration (ANR) practitioners. Other important bio-invasive species in the general landscape of rural Philippine settings are hagonoy (*Chromolaena odorata) and coronitas (*Lantana camara). These two species retard the succession process in open grasslands, where they can become very gregarious, thus offering no ground for indigenous gap species. Where paper mulberry cannot establish, the equally important bio-invasive species ipil-ipil (*Leucaena leucocephala) can usurp steep bare slopes and form pure stands of ipil-ipil. At the back of beaches and along beaches, two exotic mimosoid legumes also form gregarious thickets of aroma (*Acacia farnesiana) and mesquite aroma (*Prosopis juliflorae), respectively.

In the gaps of lower and upper montane forests of the Cordillera Highlands, the prolific and gregarious alders *Alnus maritima and *A. nepalensis also tend to form pure stands and these could also potentially be bio-invasive species in these parts of the country.


Tree plantations and natural forest stands should be distant and dispersal of bio-invasive propagules should be avoided. Bio-invasive species that have very long dispersal abilities and with allelopathic properties should be checked and banned in all successional stages of natural forests, for example paper mulberry and mahogany. Dispersal radius of suspect bio-invasive exotic tree species should be studied, so that plantations that are safe from becoming sources of bio-invasive species may be designed.


Agroforestry Research Center - FORI. 1980. Introducing a fast-growing Acacia species. Canopy, 6(8): 1.

Alvarez E.M. 2001. Monitoring the spread of large leaf mahogany (*Swietenia macrophylla King) in lowland dipterocarp forest in Mt. Makiling, Laguna. Unpublished B.S. Forestry Thesis, UPLB-CFNR.

Anonymous. 1930. Notes and jottings from the Bureau of Forestry Plantations. Makiling Echo, January 23, 1930.

Baguinon N.T. 2000. ENRM 202: Forest and terrestrial ecosystems. Published by U.P. Open University. 409pp.

Bakuzis E.V. 1969. Forestry viewed in an ecosystem perspective. In: The Ecosystem Concept in Natural Resource Management. Ed. by. George M. Van Dyne. pp. 189-254.

Arias S.C. and Binua T.M. 1966. Exotic Gmelina: another fast-grower. Reforestation Monthly 6(1 and 2): 3.

Brown W.H. 1919. Vegetation of Philippine mountains. Manila: Bureau of Printing.

Caguioa V. 1953. Planting exotic species in the Philippines. Soil resources and forestry, Pacific science congress, vol. 5, p. 499-532.

Castillo R.R. 2001. Vegetation analysis of undergrowth plants in lowland forest of Mt. Makiling as a tool in assessing the advance and spread of big leaf mahogany (*Swietenia macrophylla King). Unpublished B.S. Forestry Thesis, UPLB-CFNR.

DENR-NBSAP. 1997. Philippine biodiversity: An assessment and plan of action. Bookmark, Inc., Makati City, 298 p.

Domingo I.L. 1983. Industrial Pulpwood Plantations. First Asean Forestry Congress, 10-15 October 1983, PICC, Manila, Philippines. P. 18.

Gruezo W.S. 2000. Floral Diversity Profile of Mt. Makiling Forest Reserve, Luzon, Philippines. ASEAN Regional Conference on Biodiversity Conservation, 20-21 September 2000, College of Forestry and Natural Resources, U.P. at Los Baños, College, Laguna, PHILIPPINES. p. 3.

Hilleshog Forestry AB. 1984. The Palawan botanical expedition, final report. IPAS Final Report, June 1, 1992.

Jacobs M. 1975. The world on Luzon’s highest mountains. Lecture in UNESCO-MAB, BIOTROP, Bogor, Indonesia.

Kowal N.E. 1975. Shifting cultivation, fire, and pine forest in the Cordillera Central, Luzon, Philippines. Lecture in UNESCO-MAB, BIOTROP, Bogor, Indonesia.

Lizardo L. 1960. Results of trial planting of Eucalyptus in the Philippines. The Philippine Journal of Forestry. 16(1-2): 31.

Merrill E.D. 1921-26. An enumeration of Philippine flowering plants. Manila: Bureau of Science, vol. 4.

Merrill E.D. 1945. Plant life of the Pacific world. New York: MacMillan Co., 295 pp.

Merrill E.D. and Merritt M.L. 1910. Flora of Mount Pulog. Philippine Journal of Science 5(4-5): 287-403.

Newman M.F., Burgess P.F. and Whitmore T.C. 1996. Manuals of dipterocarps for foresters - Philippines. Published by Royal Botanic Garden, Edinburgh and CIFOR, Jakarta. 124 pp.

Ponce S.S. 1933. Mahogany as a reforestation crop. The Makiling Echo 12 (1): 7.

Rojo J.P. 1999. Revised lexicon of Philippine trees. Forest Products Research and Development Institute, Department of Science and Technology. 484pp.

Tamesis F. and Sulit C. 1937. Reforestation and flood control. The Makiling Echo 16(2): 80-97.

Thinley P. 2002. Negative interaction between large leaf mahogany (*Swietenia macrophylla King) and some indigenous tree secies in lowland forest of Mt. Makiling - allelopathy, a possible cause? Unpublished B.S. Forestry Thesis, UPLB-CFNR.

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Status of forest invasive species in Sri Lanka

N.D.R. Weerawardane and J. Dissanayake
Forest Department
Ministry of Environment and Natural Resources


Sri Lanka has a land area of about 6.5 million hectares. Sri Lanka is a small but biologically diverse country that is recognized as a biodiversity hotspot of global importance for plants. Its varied topography and tropical conditions have given rise to this high level of biodiversity. There are many plant and animal species endemic to the country. Much of the diversity is found in the wet zone located in the southwest parts of the country. Human threats to biodiversity are greatest in this part of the country, due to the dense human population. It has been noted in the past that bio-invasions can have serious negative impacts on the function of these ecosystems. The direct economic consequences are more prominent in the agricultural sector, while the indirect economic consequences will be the loss of biodiversity. The agricultural sector has suffered a lot in the past from intentional or unintentional introductions of alien pests and diseases, including weed species. However, in more recent times attention has been given to the introduction of invasive species and their impacts on biodiversity in the country.

General overview of forest types in the country

According to the forest cover map prepared in 1992, Sri Lanka’s closed natural forest cover was 23.9 percent of the total land area, which amounts to about 1.5 million hectares. Including sparse forests, the total natural forest cover is 30.9 percent of the land cover, which is around two million hectares. The average rate of deforestation during the past few decades, both planned and unplanned, has been around 42 000 hectares per year (Bandaratillake, 2001). The major natural forest ecosystems and their extent are presented in Table 1.

Table 1: Natural forests in Sri Lanka, 1992

Forest type

Total area

Percentage of
total land area

Bio-climatic zone

Closed canopy montane

3 108


Montane zone

Sub montane

68 616


Submontane zone

Lowland rain

141 506


Low/mid country wet

Moist monsoon

243 886


Low/mid country intermediate

Dry monsoon

1 090 981


Low country dry


22 435


Low country wet and dry


8 688


Coastal areas, lagoons


1 579 220


Open canopy sparse

464 076


Low country dry and arid


2 043 296


The forests in the montane and submontane areas occur at high elevations, located in the central parts of the country. In the montane zone, the height of the canopy is low. The trees are of poor form with dense, spreading, flat-topped crowns. The forest is not of commercial value, rather it is left undisturbed, to serve as protection forest preventing soil erosion and flash flooding in the catchment areas. The genera in both zones include Syzygium, Calophylum, Gordonia, Michelia, etc. Lowland rain forests are rich in biodiversity and represent tropical rain forests that receive a well-distributed rainfall throughout the year. As a result, they develop multi-storey canopy structure with dense understorey. Climbers and epiphytes are prevalent in these forests. Common genera include Dipterocarpus, Mesua, Doona, Shorea, Campnosperma, Vitex, Wormia, Chetocarpus, Anisophyllea, etc. Moist monsoon forests are in the intermediate zone areas, which form a transition zone between the dry and the wet areas. Dry monsoon forests cover a large area of two-thirds of the country. In these forest areas, there is a pronounced moisture deficit period of about four months. Some of the timbers produced in these forests are highly priced. The major genera include Manilkara, Drypetes, Chloroxylon, Berrya, Diospyros, etc. Riverine forests are small in extent and distributed along major rivers in low lying areas. Mangrove forests are comparatively small, but play an important ecological role stabilizing the estuaries and lagoons and providing shelter and breeding grounds for fish, crustaceans and other marine life.

Importance and relevance of forest invasive species issues in the country

Invasive species are generally exotic or alien species having the ability to compete with and replace native species in natural habitats, thereby threatening native biological diversity. They have special characteristics that enable them to spread rapidly and aggressively and compete with native flora and fauna, to form a dense population that interferes with the natural development of biotic communities.

In order to protect biodiversity in the country, Sri Lanka became a signatory to the Convention on Biological Diversity in 1992 and ratified it in 1994. The Ministry of Forestry and Environment was identified as the focal point for activities related to biological diversity. The introduction of alien invasive species - intentionally or unintentionally - can cause a tremendous negative impact on biodiversity in a country like Sri Lanka. A large number of species extinctions can occur through the introduction of invasive species. In addition, some invasive species can contribute to degradation of catchment areas and irrigation systems, incurring severe economic losses. Intentional introductions include deliberate introductions for use in agriculture, forestry, horticulture, fisheries, aquaculture, landscaping, zoos, pet trade, etc. Unintentional introductions include accidental introductions of species through transport, trade, travel, tourism, etc. In Sri Lanka, alien invasive species are particularly important due to following factors (IUCN, 2000):

As some invasions have the potential to become irreversible, the prevention of new introductions is of primary importance, followed by the management of already established species that may pose a conservation threat.

Most significant forest invasive species in the country

The most significant invasive species and their mode and source of introduction, distribution and affected habitats/ecosystems are presented in Table 2 and Table 3.

Table 2: Invasive fauna in forest ecosystems in Sri Lanka


Mode/source of introduction


Affected habitats/ecosystems

Bubalus bubalis (Domestic/feral buffalo)

Deliberate; animal husbandry



Oncorhynchus mykiss
(Rainbow trout)

Deliberate; sport fishery

Montane zone


Chitala chitala
(Clown knife fish)

Negligence; ornamental fish trade

Lowland wet zone

Ponds, slow-flowing rivers, marshes

Hypostomus plecostomus
(Plectosomus catfish)

Negligence; ornamental fish trade

Lowland wet zone

Ponds, slow-flowing rivers, marshes

Clarias batrachus
(Walking cat fish)

Negligence; ornamental fish trade

Lowland wet zone

Marshes, streams

Gambusia affinis
(Mosqito fish)

Deliberate; mosquito control

Lowland wet zone

Marshes, ditches, streams

Poecilia reticulata

Deliberate; mosquito control

Lowland wet zone

Marshes, ditches, streams

Oreochromis mossambicus

Deliberate; commercial fishery


Rivers, marshes, lagoons and estuaries

Table 3: Invasive flora in forest ecosystems of Sri Lanka


Mode/source of introduction


Affected habitats/ecosystems

Weldelia triloba(runner)

Negligence; ornamental plants

Wet and intermediate zone

Forest edges

Mikania micrantha(wine)

Negligence; ornamental plants

Montane zone

Montane forests

Opuntia stricta(shrub)

Negligence; ornamental plants

Arid zone

Thorn scrublands

Lantana camara(shrub)

Negligence; ornamental plants


Scrublands, degraded open forests

Ulex europaeus(shrub)

Negligence; ornamental plant

Montane zone

Montane forests, wet patana grasslands

Eupatorium riparium(shrub)

Negligence; ornamental plants

Montane zone

Montane forests

Clidemia hirta(shrub)


Lowland wet zone

Rain forests

Eupatorium odoratum(shrub)

Negligence; ornamental plants

Lowland dry and wet zone

Forest edges and pathways

Mikania calvescens(shrub)

Negligence; ornamental plant

Submontane zone

Disturbed forests

Dillenia sufruticosa(shrub)

Negligence; horticulturists

Lowland wet zone,Riparian areas

Marshes, low lying areas

Millingtonia hortens(shrub)

Negligence; ornamental plant

Southern dry and intermediate zone

Disturbed forests and scrublands

Prosopis juliflora(small tree)

Deliberate; afforestation

Arid zone

Thorn scrublands

Annona glabra (small tree/shrubs)


Lowland wet zone

Coastal lagoons, marshes

Swietenia macrophylla(large tree)

Deliberate; forestry/ timber

Lowland wet zone

Disturbed forests

Leucaena leucocephala(small tree)

Deliberate; fodder plant, soil rehabilitation

Intermediate zone

Dry mixed evergreen forests

Psidium littorale(treelet)

Negligence; ornamental plants

Montane zone

Montane forests

Myroxylon balsamum(tree)

Deliberate; forestry

Wet and Intermediate zone

Forest edges

Alstonia macrophylla(tree)

Deliberate; forestry

Wet and Intermediate zones

Secondary forests

Mimosa pigra(small tree)


Mid country wet and intermediate zones

Wastelands, along river banks

Imperata cylindrica(grass)



Disturbed forests and scrublands

Panicum maximum(grass)

Deliberate; fodder


Disturbed forests and scrublands

Bambusa bambos(bamboo)


Mid country areas

Disturbed forests and scrublands

Ochlandra stridula(bamboo)


Wet zone

Disturbed forests

Acrostichum aureum(fern)


Lagoon areas

Mangrove forests

Najas marina(submerged plant)


Coastal areas

Lagoons and estuaries

Source: Bambaradeniya et al. (1999) and authors’ own observations

Biology and life history of the most significant invasive species


Imperata cylindrica, Graminae

Imperata is a rapidly spreading, noxious perennial weed in agricultural, forest and wastelands. Once this weed colonizes the land its subsequent propagation takes place by stolons. It poses serious problems to many agricultural crops and forest seedlings in plantation establishment. It is found in most parts of the country. It grows year round and up to 1 metre in height. Propagation is by wind dispersal of seeds and by underground stem parts. Manual control is very difficult and chemical control is fairly successful.

Panicum maximum (Guinea grass), Graminae

Guinea grass is a ubiquitous perennial weed. It poses a major problem in agriculture and forestry plantation establishment. It has spread to most parts of the country including natural ecosystems, abandoned or degraded lands, forest plantations, etc. When growth is uncontrolled, it can grow up to about 2 metres in height, shading out and out-competing natural or planted seedlings in forests and retarding their establishment and growth. Taller stands can block the access of humans and vehicles. Its faster spread, both by seeds and underground stem parts, threatens natural ecosystems by replacing native plants. In addition, it creates a fire hazard in dry periods, which can also replace natural vegetation in an area. When Guinea grass is burned it re-sprouts and grows rapidly, dominating the area. Its control is extremely difficult unless long-term control measures are taken. Cattle-grazing is somewhat effective in controlling this grass, although this does not eradicate it.


Lantana camara, Verbanaceae

Lantana camara is a plant introduced to Sri Lanka in 1926 through the Royal Botanic gardens of Sri Lanka. Currently a major weed found throughout the country, it has invaded natural ecosystems particularly when open conditions are prevalent. This species is commonly found in dense stands along roadsides and abandoned lands. It is a fast-spreading, thicket-forming, perennial shrub and is somewhat shade tolerant. The weed has invaded the Udawalawe National Park, which is a leading elephant sanctuary of the island, significantly reducing the grazing lands available for the elephants. It has also spread in forest plantations and degraded natural forests interfering with natural regeneration. The spread is influenced by birds eating the fruits. Manual methods are somewhat successful in controlling this grass.

Prosopis juliflora (Mesquite), Fabaceae

Mesquite was first introduced to Sri Lanka in 1880 and is currently found spreading rapidly in the coastal belts of Southern and Western provinces in the country. It was introduced in the early 1950s to Southern province to improve the saline soils and as ground cover. The species has now become invasive and is a serious threat to natural habitats. This species has severely affected the Bundala National Park, the only wetland in Sri Lanka listed under the Ramsar Convention, affecting all types of vegetation, except sand dunes. It invades disturbed open areas and gradually encroaches on forest interiors. The most seriously invaded vegetation is lagoon marsh, where more than 75 percent of vegetation has been replaced by this species. Some positive aspects have also been observed in this species: it reduces erosion around lagoons, provides resting, feeding and nesting places for the birds and provides fodder for cattle, elephants, birds and monkeys in periods of drought (Seneviratne and Agama, 2001).

Ulex europaeus (Gorse), Fabaceae

This species was introduced to Sri Lanka in 1888 and has invaded natural ecosysytems in the hill country of Sri Lanka. It is a prickly evergreen shrub with profuse yellow flowers. It reproduces by re-sprouting from stumps and by seed. Heavy seed production and long seed viability make it troublesome to control. It is confined to high altitude areas in the country. The biodiversity of the Horton Plains, a nature reserve, has been significantly affected due to the spread of this invasive plant. Several attempts have been made by community organizations to eradicate this weed by uprooting and burning, however, these efforts have only been marginally successful.


Myroxylon balsamum, Fabaceae

First reported in the 1920s, Myroxylon has recently been identified as colonizing natural and semi-natural habitats in some parts of the country. It has been planted as a shade tree along roadsides, as windbreaks and in plantations. It has been reported to damage the composition, structure and functions of natural ecosystems. In certain forests, it has developed into mono-specific stands, for example, in Udawattakele Nature Reserve and in some mixed mahogany forests.

Specific efforts to manage and control invasive species

At present, the identification and prioritization of species is done on an ad hoc basis. There is a lack of proper institutional and legal frameworks to deal with invasive species. Furthermore, there is no coordination among various government institutions that are directly or indirectly involved in dealing with alien invasive species. Currently, there are no concerted efforts to manage invasive species in Sri Lanka, except several isolated attempts to control such species.

To deal with this situation, the Biodiversity Secretariat of the Ministry of Environment and Natural Resources organized a national workshop on Alien Invasive Species (AIS) of Sri Lanka in October 1999. Some of the important recommendations in this workshop are given below:

A follow-up workshop was held in September 2000 to make an in-depth analysis of the problem. It recommended the development of a national invasive species action plan (NISAP) to overcome the problems of AIS (Marambe, 2000). The workshop participants identified strategies to be included in the NISAP.

Certain invasive species have the potential to be utilized in various ways. For example, water plants such as Eichornia, Salvinia, Hydrilla species and grasses such as Imperata and Panicum have the potential to be used as compost manure and mulch. Some are useful in making bio-gas. Species such as Colocasia and Tithonia can be used as organic manure in agricultural fields. Dillenia and Clusia species can be used as good fuelwood sources. Natural forest invasive species such as mahogany and Alstonia are good timber species and used widely in local markets.

For prevention, eradication and control of alien invaders, Bambaradeniya (2000) suggested the following actions:

1. Coordination, policy and legislative initiatives:

2. Actions to prevent future detrimental introductions:

3. Actions to control/eradicate established invaders:

Assessment of costs associated with specific pest and disease incursions

In the case of forestry, no assessments have been carried out with regard to the costs of damage caused by the alien invasive species. In general, no special pest or disease invasions have been recorded in the past, except some common pests found in teak and mahogany.

Forest health, quarantine and sanitary/phytosanitary regulations and procedures

In Sri Lanka, the legal basis for plant protection and plant quarantine (Plant Protection Ordinance) dates as far back as 1924. Plant quarantine ordinance is enacted by the Department of Agriculture in Sri Lanka. It makes provisions against the introduction of weeds, pests and diseases and for the sanitation of plants in the country. The ordinance has been progressively amended in 1956 and 1981. However, several devastating pests have established themselves in the country during the last decade. Therefore the ordinance was totally revised in 1999 to make adequate provisions to cope with current trends in the movement of flora and fauna, as a result of the increase in international trade and traffic. The plant protection ordinance of Sri Lanka aims to prevent the introduction of exotic pests including insects, diseases and weeds, but places less emphasis on plant species that can have serious negative effects on biodiversity of natural habitats.

The Fauna and Flora Act was amended in 1964, and again in 1970. It makes provisions for the establishment and maintenance of national reserves, national parks and jungle corridors.

The policy on imports of seed and planting material was revised by the Department of Agriculture in 1991, and the New Seed Act was formulated in 1999.

Key institutions involved with invasive species

In Sri Lanka, there are several institutions involved with alien invasive species - mainly those involved with biodiversity conservation. These are listed below:

1. Ministry of Environment and Natural Resources
2. Forest Department
3. Agriculture Department
4. University of Peradeniya
5. University of Sri Jayawardanepura
6. IUCN, Sri Lanka
7. National Science Foundation


Bambaradeniya C.N.B., Ekanayake S.P. and Gunawardane J. 1999. Preliminary observations on the status of alien invasive biota in natural ecosystems of Sri Lanka. Report on alien invasive species, GBF-SSEA. Colombo. IUCN Regional biodiversity programme, Asia, Colombo, Sri Lanka.

Bambaradeniya C.N.B. 2000. Alien invasive species. Loris. 22: No 4, pp 3-7.

FAO. 2001. Forests out of bounds: Impacts and effectiveness of logging bans in natural forests in Asia-Pacific. RAP publication 2001/08. FAO: Bangkok.205p.

Marambe B. 1999 (Ed). Proceedings of the National Workshop on Alien Invasive Species in Sri Lanka. Ministry of Forestry and Environment: Sri Lanka.

Marambe B. 2000 (Ed). Proceedings of the Symposium "Alien Invasive Species of Sri Lanka": Impacts on Ecosystems and Management. Ministry of Forestry and Environment: SriLanka.

Seneviratne G.I., and Algama A.L.M.N.S. 2001. Invasive species Prosopis juliflora in the coastal regions of Hambantota district. Sri Lankan Biodiversity Review. Volume 1:79-83.

Invasive species in the United States of America - 2003

David F. Thomas
Forest Health Protection, USDA Forest Service

Scope of problem

The threat of aquatic and terrestrial invasive species[4] is one of the greatest natural resources concerns in the United States of America. Their prevention and control is operationally critical to meeting the stewardship mission of the USDA Forest Service. Thousands of species of invasive plants, invertebrates, fishes, diseases, birds, and mammals threaten ecosystem function, economic stability, and human health. Second only to direct habitat destruction, invasive species are the greatest threat to native biodiversity and native communities, nutrient cycling, hydrology, and natural fire regimes. Direct and indirect impacts of invasive species have contributed to the decline of approximately 46 percent of all listed threatened and endangered species. Public recreational opportunities and experiences have been severely degraded by rapid infestations of invasive species, in many cases hampering access, reducing recreational quality and enjoyment and decreasing the aesthetic values of public use areas.

Nationally, invasive species cost Americans over US$137 billion each year, with a large portion of the impacts affecting public lands and agriculture. As the largest land managing agency within the Department of Agriculture, the Forest Service has a significant role in battling these insidious invaders and has stepped forward to work collaboratively at the local, state and national levels. The economic threats from invasive species to Forest Service timber and other production operations are significant and cannot be marginalized, and the linkage between the spread of invasive species and increased wildfire frequency and intensity has been well documented. It has been estimated that invasive plants occupy nearly 133 million acres (53.8 million hectares) of national forests and rangelands, other federal ownerships, state, tribal and private lands, and are spreading at a rate of nearly 1.7 million acres (688 000 hectares) per year. It is estimated that annual losses associated with invasive plants total US$13 billion. Insect and disease problems continue to increase and plague millions of acres of private, state, and national forests in nearly every region of the nation.

Due to the broad range of pathways for invasive species to enter and become established within our nation’s forests and rangelands, the rate of new infestations is growing exponentially. Also, due to overstocking of many forested areas, the threat of infestations by insects, pathogens and invasive plants is greatly enhanced. It is estimated that 70 million acres (28.3 million hectares) of the nation’s forests are threatened by infestations of insects and disease mortality, including 21 million acres (8.5 million hectares) by western bark beetles. Compliance with the requirements of the National Environmental Policy Act governing agency actions, and subsequent appeals and litigation have slowed the USDA Forest Service efforts in completing many projects designed to improve forest health.


America’s forests cover 747 million acres (302 million hectares), of which 20 percent are on National Forest System lands, 49 percent are owned by non-industrial landowners, 8 percent by states, 13 percent by other federal agencies and 10 percent by industrial landowners (Figure 1). This forest land is an invaluable asset to the American people, providing water, recreation, wildlife habitat, and future timber. Maintaining the health and sustainability of natural resources is a national security issue and the United States Department of Agriculture (USDA) Forest Service remains committed to the protection of these resources. America’s forests continue to face many catastrophic risks, including fires, invasive species and fragmentation.

The Forest Service definition of a healthy, sustainable forest is:

a condition wherein a forest has the capacity, across the landscape, for renewal, for recovery from a wide range of disturbances, and for retention of its ecological resiliency while meeting current and future needs of people for desired levels of values, uses, products, and services.

The USDA Forest Service works collaboratively with state foresters, state departments of agriculture, and other USDA agencies, including the Animal and Plant Health Inspection Service (APHIS) to protect America’s forests from native and introduced insects, pathogens and invasive plants. The FHP programme provides services to federal, state, tribal, and private managers of forest lands. Services include technical information and assistance in management and control of forest insects, diseases, and invasive plants; forest health monitoring; technology development; and pesticide use.

This report provides a summary of current forest ecosystem health issues in America’s forests. There are three general areas of concern:

Non-native invasive insects and pathogens

Global trade and travel are causing an unprecedented movement of animals, plants and micro-organisms across continents and oceans. All too often, these non-native species are invasive and can cause impacts that are extremely costly to both the U.S. economy and environment. When brought into new ecosystems, non-native invasive species have no natural enemies and can cause extensive damage. Nearly 50 percent of the plants and animals on the federal endangered species list have been negatively impacted by non-native invasive plants, animals, insects and microbes. These species threaten biodiversity and have caused catastrophic damage to agriculture, forest products, recreation and natural resources across North America. Examples include yellow star thistle, leafy spurge, gypsy moth, American chestnut blight and white pine blister rust.

Figure 1: United States of America forest cover types

In February 1999, the President issued Executive Order 13112 on Invasive Species, establishing the National Invasive Species Council. The council provides, for the first time, a coordinated effort by its 10 member departments. In October 2001, the council completed a management plan, Meeting the Invasive Species Challenge, to address the Executive Order. The plan is designed to raise public awareness and control the introduction and spread of non-native invasive pests. According to the plan, the economic cost of invasive species is estimated at US$137 billion every year.

The USDA Forest Service alone spends more than US$40 million annually to control the introduction and spread of non-native species and approximately US$40 million for native species. The control efforts include refining, developing and deploying a broad array of technologies to minimize the impacts of invasive species. Technology includes remote sensing, computer modeling, mechanical treatments, bio-pesticides, biological controls and conventional pesticides. The USDA Forest Service and APHIS have started an early detection and rapid response programme to detect and promptly eradicate any new invasive species. Invasive pests are dealt with as aggressively as possible, within budget constraints, before they become well established.

Selected examples of major invasive insects affecting U.S. forests

Emerald ash borer

The invasive emerald ash borer, a recently introduced pest, is threatening ash trees (Fraxinas spp.) in North American forests, urban plantings and shelterbelts. Critical, time-sensitive research is needed on the borer’s basic biology, ecology and management. At the present time, information is insufficient to support ongoing detection efforts and to develop effective strategies for containing the infestation, reducing beetle density, or eradicating this pest.

In 2002, the emerald ash borer (Agrilus planipennis) was discovered in dead and dying ash in a 5-county region around Detroit, Michigan and in neighbouring Windsor, Ontario, Canada. In August 2003, Forest Service research confirmed its presence in Toledo, Ohio. The borer, which was introduced into Michigan about five years ago, is native to China, Korea, Japan and other Asian countries.

A recent federal and state survey of ash in southwest Michigan determined that the outbreak covers over 2000 square miles (518 000 hectares). In southwest Michigan, 49.1 percent of the trees surveyed, and an estimated 5.2 million ash trees, are dead or declining. The State of Michigan has quarantined movement of ash trees and ash wood products from the five counties around Detroit to reduce the chances of transporting emerald ash borer outside the currently infested area.

In Michigan, only ash has been attacked - in Asia, elm, walnut and chestnut may be attacked. The borer may have a major impact on forests across the United States of America. Ash is a major component of natural and urban forests in the east and central United States of America and urban areas in the west. The potential value loss in nine major urban centres is estimated at US$20-60 billion for 30-60 million ash trees. Losing urban ash is also critical, because ash has been the primary replacement tree for American elm.

Information on biology, detection and control of emerald ash borer is limited to less than a paragraph in the Chinese literature. Currently, infestations are detected by visually examining each tree for exit holes left by emerging adults. "Control" is limited to removal and destruction of infested trees, although preliminary tests conducted this year indicate that tree injections or aphids may work. More research is necessary to obtain information on the basic biology and ecology of emerald ash borer and tools for assessing ecosystem risk, detection and control that managers must have to formulate effective management strategies.

The Undersecretary of Natural Resources and Environment at USDA and Chief of the Forest Service are aware of the urgency of the problem and the need for emergency research funds to obtain vital information. APHIS and the Forest Service are planning to submit a request to the Secretary for authority to use Commodity Credit Corporation (CCC) emergency funds.

Scolytus schevyrewi

Scolytus schevyrewi is native to eastern Russia, China and Korea. The beetle was first collected in rapid detection bark beetle pheromone traps set in Aurora, Colorado (a suburb of Denver) and Ogden, Utah, starting in late April 2003. It is considered very invasive. Dr James LeBonte, Oregon Department of Agriculture, first identified the beetle as new to the United States of America. At this time, there is no common name for this beetle and it is currently not known how damaging this insect can potentially be.

APHIS has increased its detection effort for this bark beetle in Colorado, Utah, and several adjacent states. The Forest Health Protection (FHP) rapid detection group along with staff of other FHP offices in the West and the Colorado State Forest Service are assisting APHIS.

In Colorado, S. schevyrewi has been collected all along the Front Range from Pueblo to Fort Collins and has been found in Durango in the southwest and in Lamar, a town in southeastern Colorado. In Utah, the bark beetle has been found in Ogden, Salt Lake City, and in eastern Utah. The beetle was found in samples of fresh wood from American elm, rock elm and Siberian elm.

The biology of S. schevyrewi is similar to that of S. multistriatus. The beetle completes a generation in about two months (fresh attacks in late-April and early-May in the Denver area, and brood emergence by early-July). The USDA Forest Service expects that S. schevyrewi will complete two to three generations per year in the Denver area. The literature suggests that the beetle has a feeding period on branch junctions like that of S. multistriatus. The egg galleries are very similar between these two bark beetle species.

Sudden oak death

Sudden oak death (SOD) - a disease caused by Phytophthora ramorum, a newly discovered pathogen of uncertain origin - has killed thousands of trees in coastal, mixed evergreen forests and urban-wildland interfaces in California and southern Oregon. It kills a range of tree species - including coast live oak, California black oak, shreve oak, tan oak, and madrone - and infects several other plant species including rhododendron, manzanita, California bay laurel, buckeye, evergreen huckleberry, and big leaf maple. The disease degrades ecological processes and watershed functions, and lowers forest productivity. It reduces aesthetic, recreational and economic values and leaves forests susceptible to invasive plant infestations. Dead trees add fuel to an already high fire risk.

There is presently insufficient knowledge of how the disease spreads and its biology. It is known to be spreading rapidly and has been found in nursery stock (particularly rhododendrons) in a few ornamental nurseries, raising concerns that it could be transported to and infect the extensive, susceptible oak forests of the Eastern United States of America. The oak-hardwood forest is the largest forest type in the United States of America.

The USDA Forest Service has spent over US$5 million to research, monitor, manage, and educate the public about SOD. The USDA Forest Service is also working closely with APHIS to assist in implementing quarantine and to regulate the transportation of wood, bark, and nursery stock that might harbor the SOD pathogen.

California and Oregon implemented state regulations, prior to the release of federal regulations, to prevent the spread of this disease. The states are coordinating their respective regulations with APHIS. The USDA Forest Service (through the California Oak Mortality Taskforce, a public-private coalition) is leading federal, state, and local partners in implementing effective SOD research, monitoring, management and education programmes to protect the nation’s oak forests.

In 2000, USDA Forest Service provided funds to help investigate the cause of this disease. Investigations led to the discovery that the primary cause of SOD is a previously undescribed species of Phytophthora. In 2001, the USDA Forest Service provided additional funds to determine the extent and severity of SOD in oaks and other native plants in California and Oregon. The funds were also used to develop diagnostic and survey methodologies for the SOD pathogen, evaluate fungicide treatments and other management strategies, and assess the fire risk and other ecosystem effects of accelerated oak mortality. The USDA Forest Service continues to support cooperative efforts in 2002 to monitor the disease development and spread. Forest health monitoring surveys detected the pathogen in southwestern Oregon. In the autumn of 2001, the Oregon Department of Forestry attempted to eradicate the pathogen. Monitoring efforts to determine the effectiveness of the eradication treatment are underway.

White pine blister rust

White pine blister rust (WPBR), an introduced fungus from Asia, has decimated several species of native white pines across the American West and Canada. Native white pines are an integral part of the natural biodiversity of western forests. The ecological and economic impacts have been most acute on the two largest commercial species - western white pine and sugar pine. WPBR entered North America through the east and west coasts on European nursery stock around 1910. In the west, it quickly spread from Vancouver, British Colombia, Canada, south through the Cascades and Sierra Nevada, and east into the Rocky Mountain States of Idaho, Montana, Colorado, Wyoming, and New Mexico. The pest has also inflicted severe ecological damage in high-altitude whitebark and limber pine forests. In susceptible stands, WPBR can kill over 95 percent of mature trees, effectively altering a forest ecosystem forever. Strategies for control include:

Gypsy moth

Since 1930, gypsy moth has defoliated more than 80 million acres (32 million hectares) of forests in the eastern United States of America, with most of this damage occurring during the past 20 years. A hardwood defoliator native to Europe and Asia, gypsy moth arrived in the United States of America in the 1800s, established itself in the oak forests of southern New England, and then spread south and west across 19 states. Occasionally, it appears in western forests, but has been successfully eradicated each time. Unfortunately, gypsy moth is now a permanent resident of eastern forests.

During outbreaks, moth populations often outpace the few natural enemies, parasites, predators, and pathogens that attack them. The gypsy moth feeds on the delicate first flush of leaves in the spring. It prefers oaks, but it will feed on 500 species of woody plants. The attacked trees become highly susceptible to secondary attacks from other insects and pathogens, often resulting in death. The deaths alter the forest ecosystem dramatically; usually dead oaks are replaced not with more oaks, but with other species that do not produce as much mast for wildlife. In response to this pest, the USDA Forest Service adopted the following strategies:

A gypsy moth virus and aerial treatments with biological and chemical insecticides conducted over 460 000 acres (186 155 hectares) in 2001 have effectively suppressed or slowed the spread of gypsy moth in nine northeastern states. The USDA Forest Service’s gypsy moth slow-the-spread programme slows the southwesterly spread of the insect by 60 percent through concentrated monitoring and by using environmentally benign mating disruption techniques. After discovering adult gypsy moths in pheromone traps in seven western states in 2000, steps were taken that eradicated the pest from these states. The USDA Forest Service and many other cooperators continue to develop new controls and delivery methods to use against this pest.

Hemlock woolly adelgid

The hemlock woolly adelgid (HWA) is one of the most serious forest pests threatening eastern forests. The insect defoliates eastern hemlock; trees can die within four years of infestation. Native to China and Japan and introduced to the American Northwest in the 1920s, it has spread quickly across the northern United States of America. Fortunately, western hemlock proved resistant to HWA. Unfortunately, eastern hemlock is highly susceptible to HWA. Beginning in the 1950s, the pest began a destructive march north and south through eastern forests. Today, it infests nearly half of the hemlock forests across 11 states from Massachusetts to South Carolina, and as far west as the southwest tip of West Virginia.

Eastern hemlock is a pivotal species in eastern forest ecosystems. It is especially important along streams and creeks, where its shade helps control water temperatures - thereby helping to sustain aquatic ecosystems. Eastern hemlock spans the eastern United States of America from Maine, west to northern Wisconsin, and south along the Appalachians to north Georgia. The span also includes small pockets in Indiana and Mississippi. To arrest the pest’s advance, the USDA Forest Service has:

The USDA Forest Service identified a number of pathogens and predators native to the United States of America that would attack HWA. The most effective to date is the Japanese ladybird beetle (Pseudoscymnus tsugae). This predator attacks only HWA, will feed on all stages (egg to adult) of HWA and, in sufficient numbers, will consume up to 97 percent of a HWA population. Since 1999, the USDA Forest Service has raised and released over half-a-million beetles in nine states. Additional research, development, and subsequent management actions are expected to reduce the impacts of this destructive pest.

Invasive plants

Thousands of invasive plant species have been introduced in the United States of America. About 1 400 are recognized as pests that pose significant threats to the biodiversity of forest and grassland ecosystems. Federal natural resource agencies list 94 species of exotic plants as noxious weeds, and many more appear on state lists. Experts estimate that well over 100 million acres (40 million hectares) are infested with invasive plants, and that as much as 20 million additional acres (8.1 million hectares) are being added every year. An estimated 3.6 million acres of National Forest System lands are infested.

Many of the invasive plants are not native to the United States of America. Therefore, they have no natural enemies to limit their reproduction and spread. Although rangelands are the primary targets of many invasive plants, they are showing up everywhere - in forests, parks, preserves, wilderness areas, wildlife refuges, croplands and urban spaces. Invasive plants threaten two-thirds of the habitat of all threatened and endangered species.

Two federally coordinated efforts are:

In 2001, the USDA Forest Service spent over US$27 million in implementing provisions of the National Fire Plan to prevent and control the spread of noxious weeds on more than 145 000 acres (58 000 hectares) of National Forest System lands. Part of these funds, US$3.5 million, was allocated to Idaho and Montana to protect approximately 93 000 acres (37 635 hectares) of state and private lands from invasive weeds.

The USDA Forest Service and its cooperators are conducting extensive research and development on biological control agents for use against many invasive plants, such as mile-a-minute weed, a major problem in five northeastern states. Biological control agents are showing some success in slowing the spread of invasive plants, such as leafy spurge in the West.

Selected examples of invasive plants affecting U.S. forests

Leafy spurge

Leafy spurge is a classic non-native, invasive plant. Arriving in North America from Eurasia in the 1890s, it now infests over 2.5 million acres (1.01 million hectares) of rangeland in southern Canada and the northern United States of America. At maturity, it can reach heights of 7 feet (2 meters). Leafy spurge can kill cattle and horses, and its sap can cause irritation to the eyes, mouths, and digestive systems of all domestic and wild grazing animals, except goats and sheep. The sap can also cause blistering, severe dermatitis and permanent blindness among humans. Seedpods explode when touched, scattering seeds up to 15 feet. It has a nutrient-storing taproot system that can reach soil depths of 20 feet (6.1 meters). Pulling the plant actually encourages it to spread.

Although conventional herbicides are effective against leafy spurge, they have a limited use. Due to this limited use, the USDA Agricultural Research Service, in cooperation with APHIS, developed and evaluated integrated approaches to managing leafy spurge. Now a cooperator, the USDA Forest Service, is researching and applying several biological control agents to suppress the pest’s spread, including:

Of these three, the flea beetles appear to be most effective against this pest, especially when used as an integral part of a pest management approach that includes grazing by sheep and goats and use of conventional herbicides, wherever possible. Imported from Asia, beetle populations have been established in Montana, the Dakotas, and Wyoming. Adult insects weaken the plants by attacking leaves and stems, and the larvae feed upon the roots. The USDA Forest Service and other cooperators are refining laboratory techniques so that the beetles can be mass-produced.

Mile-a-minute weed

Mile-a-minute weed is a prickly, annual vine that, true to its name, grows very rapidly and overpowers virtually all vegetation in its path. Originally from Asia, it first appeared on the west coast in the 1890s. In 1946, it was found in nurseries in Pennsylvania. It has spread to New York, Ohio, Maryland, New Jersey, Virginia, West Virginia, Delaware, and the District of Columbia. Seeds are spread by birds and rodents and are carried in rivers and streams. The plant is an excellent climber and easily overpowers, engulfs, and displaces much of the native flora in its path. It invades nurseries, forest openings, railroads, utility rights-of-way, roadsides, and riverbanks. It also threatens forest regeneration and recreational activities. In short, mile-a-minute weed is degrading plant diversity in North America.

Controlling the spread of mile-a-minute weed presents a tremendous challenge to forest and rangeland managers. The USDA Forest Service and its cooperators are working diligently to identify and apply effective biological controls to use against this non-native pest, including:

Outbreaks of native insects

Although native insects don’t fall into the definition of invasives species, they are an important damaging agent in the United States of America. Examples including southern pine beetle and western bark beetles are causing significant mortality.

Native insects such as bark beetles, in the West, and southern pine beetle, in the South, act as "agents of change" in coniferous forests. At the endemic level, they play a critical role in the development, aging, and rebirth of entire forests. At the landscape level, insect-caused mortality contributes to structural and mosaic diversity within ecosystems. Insects can also cause major disturbances within U.S. forests. For example, tree mortality due to bark beetle outbreaks can be extensive, affecting thousands of acres.

Certain circumstances can exert uncommon stress on forests and predispose them to extraordinary insect outbreaks and damage. These circumstances include drought, overstocking, and large areas of aging forest. During the last decade, several of these circumstances have arisen simultaneously, causing extensive tree mortality. In turn, that mortality has threatened wildlife, endangered and threatened species habitat, and degraded recreational quality. The increased mortality has contributed to considerable fuel accumulation, which in turn increases the risk of catastrophic fires.

In 2001, the USDA Forest Service spent about US$10 million to suppress and prevent bark beetle outbreaks. The USDA Forest Service has developed management plans to address the problem in an integrated manner and will implement these long-term plans as funding permits.

Southern pine beetle

Southern pine beetle (SPB) (Dendroctonus frontalis) is the most destructive forest pest in the South. Over 90 million acres (36 million hectares) of southern forests are at a moderate-to-high risk of SPB infestation. In 2001, due to a combination of a mild winter and a prolonged drought, the South experienced its most severe and prolonged SPB outbreak in history. SPB infested tens of thousands of acres and caused over US$200 million in damages. A single SPB "spot" (outbreak) can spread very quickly and cover up to 1 000 acres in one season. The situation has been especially dire in Alabama, where more than 25 000 SPB spots have been detected. In the Southern Appalachian Mountains, SPB has killed thousands of acres of pines. It has killed more than 70 percent of the pine forest habitat of the red cockaded woodpecker, a federally listed endangered species, in the Daniel Boone National Forest in southern Kentucky. In response, the USDA Forest Service has:

In 2001, the USDA Forest Service doubled its financial commitment from the previous year and provided over US$13 million to fund SPB suppression projects on federal, state, and private lands across the South. A comprehensive plan focusing on prevention and restoration has been developed and will be implemented as funding permits.

Mountain pine beetle in Colorado

The native mountain pine beetle (MPB) (Dendroctonus ponderosae) kills more pines in the American West than any other bark beetle. A regional assessment conducted by USDA Forest Service staff of the forests around the wildland-urban interface near Vail found that almost all of the 34 000 acres (13 759 hectares) of lodgepole pine in the area were at moderate to high risk of MPB infestation because of tree age, density and drought.

Vail, Colorado, the site of the 1999 World Alpine Ski Championships, is a world-class recreation setting. Vail also has some of the most valuable real estate in the United States of America. Among Vail’s natural treasures is the nearby White River National Forest - a large, and mostly wild, expanse of forest land. Increases in MPB infestations among Vail’s lodgepole pine forests started in 1996. Increases in MPB infestation were also detected in the forest around the Steamboat Springs area. The management of these outbreaks highlighted the importance of early communication and better understanding of science-based management methods to implement suppression and restoration practices within the wildland-urban interface. Sensitive to community concerns, while recognizing the urgent need to address the growing MPB problem, the USDA Forest Service:

Since 1997, the USDA Forest Service has provided technical assistance through the Colorado State Forest Service. This assistance has helped implement prevention and suppression programmes on private property, within the White River National Forest, and on property owned by the Town of Vail. The USDA Forest Service has also conducted programmes to peel and remove bark from beetle-infested trees in isolated locations, conducted field trials to identify and deploy pheromones effective against MPB, and applied insecticides to select individual trees. In April 2002, the USDA Forest Service published a "Western bark beetle report: a plan to protect and restore Western forests", which addresses the prevention, suppression and restoration needs related to bark beetle outbreaks.

The USDA Forest Service is an active member of the Bark Beetle Information Taskforce that helps residents of Routt County and surrounding areas understand the potential effects of bark beetles on national forests and state and private lands. The taskforce was formed in 1999 to provide the public with information about bark beetles and potential tree mortality so that they can make informed decisions about protecting their private property and provide meaningful input on proposed actions on public lands.

Risk map

A risk map for insect and disease potential within the United States of America is presented in Figure 2. It depicts where USDA Forest Service scientists predict mortality will occur over the next 15 years. Areas in dark gray will experience at least 25 percent mortality over and above normal levels (under 1 percent per year) due to the actions of insects and pathogens. It is a coarse-filtered map and, with other data, is used to plan where treatments will take place. Based upon our definition of risk, it depicts about 70 million acres (28 million hectares) at risk out of a total of 749 million acres (303 million hectares) of forest land in the United States of America. Four pests are responsible for 66 percent of the risk acres: gypsy moth in the East, southern pine beetle in the South, root disease in the Interior West and bark beetles in the West.

Figure 2: Risk map

Forest Service budget for 2004

The budget for combating invasive species is presented in Table 1. The figures are in thousands of dollars and include both native and non-native invasive species.

Table 1: USDA Forest Service 2004 budget for combating invasive species

Forest Service programmes

2001 Actual

2002 Current Estimate

FY2003 President’s Budget

FY2004 President’s Budget

Forest and rangeland research

13 183

10 034

7 940

14 540

International programmes





State and private forestry

· Forest health


40 121

45 000

59 152

· Pest mgmt. emergency

12 472




· Emerging pest and pathogen fund



11 968


Total Forest Service

54 830

61 130

81 683

95 535

[4] Definition of Invasives Species: An invasive species is defined as a species that is 1) non-native to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health (Executive Order 13112).

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