There has been a significant reduction in the natural forest cover in Sri Lanka during the recent past. The main causes of this have been clearing of forests for agricultural development, shifting cultivation and settlements. At present, a moratorium has been imposed on all harvesting activities in natural forests in the country until management plans are prepared for them. Preparation of these management plans has been started recently under the ongoing Forest Resources Management Project.
Forest plantation activities started in Sri Lanka as far back as 1680 with the introduction of teak to the country. During the period of 1680-1890 several other exotic species were included in planting programmes. During the subsequent years, a substantial area was planted with of exotic species to compensate the loss of timber production from natural forests.
With the rapid development of plantation forestry and the introduction of exotic species, a need for genetic improvement was felt and activities leading to tree improvement were initiated. Early tree improvement work was carried out on four species used widely in plantation establishment, namely teak, Pinus caribaea, Eucalyptus grandis and E. microcorys. The activities included provenance trials, establishment of seed production areas, selection of plus trees and establishment of clonal seed orchards. However, due to the small-scale nature of these experiments, it was not possible to produce sufficient amount of improved planting materials for commercial planting.
According to the latest satellite imagery and aerial photographs the total area of natural forests is 1 942 219 ha of which 1 470 636 ha are identified as dense canopy forest, while the remaining area is sparse forest. The total extent of forest plantations is estimated to be 93 000 ha. The natural forests of Sri Lanka contain more than 100 indigenous timber species. Majority of them are found in the Wet Zone while the Dry Zone and the drier parts of the Montane Zone contain fewer valuable species and the stocking is very poor (Vivekanandan 1975). With regard to the conservation of forest genetic resources (FGR) in natural forests, the Forest Department (FD) is implementing a World Bank-funded Medicinal Plant Project, in which conservation measures are taken with respect to plants with medicinal value occurring in natural forests.
The FD has been experimenting with a number of indigenous species as well as some exotic species since the inception of plantation establishment. The following species have been given priority in plantation establishment during the recent past based on the field experience gained so far:
• Teak
Teak, an exotic species, has been considered the highest priority species, considering its importance as a high value furniture timber with relatively fast growth. It is therefore the most popular species planted by private tree growers. In the 1960s and 1970s planting of teak increased in the Dry Zone when degraded natural forests were planted using a modified form of the Taungya system. Many of the mature teak plantations seen today in Sri Lanka are a result of the efforts made under this programme. Presently, 28 115 ha of teak plantations have been inventoried and are managed by the FD. Majority of these plantations are located in the Dry Zone.
• Eucalypts
Eucalypts, another group of exotics, have been the dominating species in the uplands since the time of the British colonization. Among the successful introductions have been Eucalyptus grandis, E. microcorys, E. robusta, E. pilularis, E. camaldulensis, E. torelliana and a few others. In the Dry Zone introductions have been relatively recent and among the several species tested E. camaldulensis and E. tereticornis have been the most promising ones.
• Pines
The bulk of the early planting activities in the highlands consisted of Pinus patula. In the 1970s, with a growing interest in planting tropical pines such as P. caribaea and P. oocarpa, the FD, after a number of field evaluations, initiated large scale planting of P. caribaea var. hondurensis in the montane and lowland Wet Zone especially in fern lands and degraded tea cultivation areas. In fact, it was the principal species used in reforesting the upland watersheds. The original objective of pine planting was to create a resource for the production of long-fibre pulp; however, local pulp industry never used this raw material for making pulp. Pines were also planted in upcountry watershed areas with the primary objective being prevention of soil erosion, reduction in sedimentation of reservoirs and regulation of flow of water to Dry Zone reservoirs. Tapping pines for oleoresins is a fast-growing industry and currently 5300 ha of pine plantations have been leased out to the private sector for resin tapping.
• Acacias
Acacias were first introduced in the highlands mainly to meet the fuelwood requirements of tea estates and the main species planted were Acacia melanoxylon, A. decurrens and a few others. The introductions of acacias in the Dry and lowland Wet Zones have been relatively recent. Several field trials have been conducted by the FD with assistance mainly from the Australian Tree Seed Centre, which generously provided the seeds for the trials. Based on the results of the trials, Acacia auriculiformis has proved to be an ideal species for the degraded sites in the Dry Zone and is now extensively planted. A. mangium has performed well in the intermediate and lowland Wet Zone and it is planted on a limited scale. In addition to these, A. aulacocarpa, A. crassicarpa, and A. leptocarpa have shown promising performance in field trials.
• Mahogany
Swietenia macrophylla has been planted rather extensively in the Wet and Intermediate Zones. One of the African mahoganies, Khaya senegalensis has shown promising performance in the Dry and Intermediate Zones and is planted on a limited scale.
• Other species
The FD has been experimenting with a number of indigenous as well as some exotic species since the inception of the silvicultural research branch in 1937. Many of the species trials have been replicated both in time and species and some species have proven to be suitable for specific sites. Of particular interest are Azadirachta indica (neem) and Casuarina equisetifolia for drier sites and coastal areas, Melia dubia for Dry and Intermediate Zones, Terminalia arjuna (kumbuk) for waterlogged lowland areas, Berrya cordifolia (halmilla) and Madhuca longifolia (mee) for relatively fertile lowland dry sites.
The Medicinal Plant Project has selected natural forests from different ecological zones in the country, with one of these forests located in the Dry Zone, two forests in the Wet Zone and two forests in the Intermediate Zone. In situ conservation in natural forests as well as ex situ conservation measures such as establishment of nurseries, home gardens and demonstration plots were initiated under this project. The most important tree species in the Medicinal Plant Project include Diospyros melanoxylon, Litsea glutinosa, Phyllanthus emblica, Pterocarpus marsupium, Salacia reticulata, Terminalia belerica and Terminalia chebula.
Most of the natural forests and some of the forest plantations in the country have faced threats from the growing human population. These forests are gradually losing their quality in terms of species and stocking mainly due to illegal harvesting and clearing for agricultural activities.
Considerable attempts are being made to protect, enrich and reforest those forest areas wherever necessary in order to provide benefits to the present and future generations. The attempts made towards conservation of forest resources by the FD include enactment of forest ordinance, revision of forest policies, imposing logging bans in natural forests, establishment of biosphere reserves and other protected areas, implementing programmes of reforestation and forest management, forest protection, forestry research, social forestry and environmental management.
In the Dry Zone damages caused by forest fires and cattle and elephants are also significant. Fire lines are opened in fire-prone areas as a measure of protection, but there are occasions where the fire has spread during acute dry weather in spite of fire lines.
Invasive plants are a major threat to conservation of biodiversity. These plants are capable of replacing diverse ecosystems with few species, which is a direct threat to native flora and fauna.
Udawattakele is a wet semi-evergreen forest in the central hilly region of Sri Lanka, located in Kandy, the hill capital of the country. This forest is reserved as a sanctuary in Sri Lanka and the extent of the forest is about 100 ha, with high species richness. The ecological and social value of the Udawattakele is also significant to Kandy since it acts as a watershed, and creates a pleasant microenvironment. However, the introduced tree species Myroxylon balsamum has become invasive and is threatening the biodiversity in this forest (Pushpakumara and Hitinayake 2001).
Prosopis juliflora, a leguminous species native to Central and Northern South America has been introduced to the arid areas of the country in the 1950s to improve the salt-affected soils as well as for firewood and to provide vegetative cover. A variety of this species is found to be naturalized and it has now become invasive. The Wetland Site Report published by Central Environmental Authority in 1993 indicates that this species is a serious threat to the Bundala National Park in Hambantota district (Seneviratne and Algama 2001).
