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Working with nature: technical and social dimensions of assisted natural regeneration - Percy Sajise

Percy Sajise

Regional Director, International Plant Genetic Research Institute - Regional Office for Asia, the Pacific and Oceania APO, Serdang, Malaysia


Around the world today, especially in the tropics, deforestation has become one of the most serious threats to biodiversity conservation, livelihood systems, ecosystem functions, peoples’ welfare and sustainable development. On average, the global figure of deforestation has been 14.6 million hectares per year between 1990 and 2000. Most of this occurred in the tropics due to the conversion of forest to agriculture (FAO, 2001). As a result of this conversion process and the dynamics associated with vegetation transformation, secondary forests are increasingly prominent in the landscape in tropical countries (UNESCO, 1978; FAO, 1996; Smith et al., 1999). In situations where forest conversion is accompanied by highly degraded conditions, “green deserts” or grassland disclimax stages of low quality and productivity predominate. There is an urgent need for forest restoration, which has been a subject of intense interest worldwide.

FAO defines deforestation as the conversion of forest to another land use or the long-term reduction of the tree canopy cover below the minimum of 10 percent threshold. Forest restoration, on the other hand, involves both reforestation and afforestation. Afforestation is the establishment of forest plantations in areas that were not previously covered by forest and denotes a change from non-forest to forest. Reforestation is the establishment of forests through planting, seeding or other means after a temporary loss of the forest cover (FAO, 2001). In the context of these definitions, most of the forest restoration process in the tropics will, therefore, involve reforestation, as opposed to afforestation.

Reforestation as a national, regional or global task is not easy to achieve, as shown by past experiences. It can be expensive, ineffective and even a constraint to enhancing biodiversity, depending on how it is implemented and the objectives of the reforestation process. In the Philippines, for example, the cost of reforestation varied from US$500-1000 per hectare, at 1983-85 price levels (Castillo, 1986). Thus, there is a need to look for options which will effectively and efficiently bring back the forest, with as much of its original characteristics and functions of productivity, stability and sustainability, as possible. This is one of the major reasons for the formation of the FAO-FORSPA-initiated network known as the Asia Pacific Forest Rehabilitation Network (APFReN). APFReN was established in 1997 to foster the distribution of information on forest rehabilitation in the region. This network provides technical support on how to implement rehabilitation activities in practice and has demonstration sites in Lao PDR, Viet Nam, Sri Lanka, Cambodia and Papua New Guinea.

Assisted natural regeneration and forest restoration

Deforestation in the tropics is, most often, the result of human activities such as exploitative logging, land conversion to other uses (such as grazing), frequent occurrence of fire, disruptive agricultural practices in open access land, fuel wood collection, and others (Lanh, 1994; Schmidt-Vogt, 2000). At present there have been a number of priority areas identified for the reforestation of deforested and degraded areas, in the Asian region. These priority areas include: upland watershed development, developing biological diversity, amelioration of environmental problems such as soil erosion, flooding and drought, providing forest products such as fuelwood and fodder for local communities and reducing subsistence pressures on other forests (Chokkalingam, 2001).

There has been some degree of success with reforestation in the region by assisting the natural tendency and process of ecological succession. Ecological succession is an apparently orderly process of community changes, which is directional and often predictable. It can be described in terms of plant community changes, referred to as plant succession. In the tropics, an area where the tropical rainforest vegetation has been removed will have this natural tendency to revert back to forest cover. In general, depending on the level of degradation, this process will involve the replacement of annuals, which have a relatively short life cycle, by perennials and pioneer or gap species, which have longer life cycle; finally these are replaced by climax-based tree species.

This fundamental ecological process has been used as a forest restoration strategy in the Philippines (Sajise, 1989), Brazil (Goetsch, 1992) and Thailand (Pakkad et al., 2002). There could be more cases of this type of strategy in forest restoration, as it is given different names in different countries, although the principles are almost the same. Assisted natural regeneration (ANR) in the Philippines, forest restoration in Thailand and imitating nature in Brazil, are a few examples of this principle being implemented.

The advantages of ANR or similar strategies in forest restoration can be summarized as follows (Sajise, 1989):

faster and cheaper (it may not be necessary to establish a nursery);

promotes and conserves biodiversity;

maintains the original vegetation stand and corresponding ecosystem functions;

maintains the integrity of the soil and involves minimum soil disturbance;

labor intensive and provides employment for the local community and promotes use of indigenous knowledge (IK);

can promote people empowerment if IK and traditional institutions are used and valued; and

promotes hydrologic integrity and biotic functions.

Based on experience in the Philippines, ANR is most suited for areas where the objective is to establish a protection forest cover as quickly as possible, such as:

ecologically vulnerable areas such as steep slopes, i.e., greater than 30 percent in critical watersheds;

areas where biological diversity and maintenance of the original flora and fauna is needed, i.e., national parks and reserves; and

community forestry or social forestry areas where communal reforestation is needed and where bio-physical and social conditions for ANR are favorable.

Preference for ANR may also be given to areas where enrichment planting is carried out, favoring natural and local species used as sources of premium wood or non-timber forest products such as rattan, resin, honey and other valuable products. The use of ANR in agroforestry systems has also been reported in Brazil (Goetsch, 1992).

Like any other forest restoration interventions, ANR has technological, bio-physical and socio-cultural (including economics and institutional) dimensions (Figure 1). These three dimensions must work in a complementary manner to ensure success.

Figure 1: Conceptual Framework of assisted natural regeneration strategy for forest rehabilitation

Ecological principles of ANR

The basic ecological principles of community succession involved in ANR were described by Sajise (1984). Succession initially developed as a botanical concept and is apparent in the early writings of plant geographers and taxonomists such as Von Humboldt and de Candolle. It was Clements (1916) who first developed a comprehensive theory on plant succession, which involved the recognition of successional stages and their associated habitat factors. Since then, succession has been defined in many different ways showing varied emphasis by different workers; vegetation composition (Mueller-Dombois, 1974), vegetation composition and disturbances (Horn, 1974) and reciprocity between plants and their environment (Margalef, 1968).

There are two basic assumptions inherent to the concept of plant succession: a) that species replacement during succession occurs because populations tend to modify the environment, making conditions less favorable for their own existence, thus leading to progressive substitutions; and b) climax is the end point consisting of a plant community that is self-perpetuating and in equilibrium. There are also two types of succession: a) autogenic, in which changes are internally generated or self-propelled; and b) allogenic, in which changes are brought about by external factors such as fire, volcanic eruption, earthquakes and even climatic change. Succession that begins on bare rock and reaches a climax is known as primary succession. Succession that occurs after the disruption of a previously well-developed community is known as secondary succession. In the tropics, most types of plant succession are secondary plant succession.

The distinct and recognizable stages of plant succession are known as seral stages. The final steady state is a climax which, in the humid tropics, is tropical rainforest. The climax is generally believed to be a function of the prevailing climate or edaphic conditions. In certain instances, however, the climax is not reached because of the occurrence of a dominant external factor such as regular burning, grazing and others. In such instances, a particular plant community will persist that is quite different from the climatic or edaphic climax. If these regularly occurring disturbances are prevented, then the normal course of succession will take place leading to the formation of a climatic or edaphic climax.

It is in this area where the socio-cultural and institutional dimensions interact with the natural resource base, because many of these disturbances are human-induced and their prevention is also a function of human interventions. The decision as to what kinds of human-induced disturbances or interventions will prevail depends on: knowledge (both indigenous and formal knowledge); technological availability; cultural beliefs and practices; economic incentives or disincentives; and the prevailing policy, or lack of it, including the effectiveness of its implementation.

It is also important to recognize that ecological succession as an ecological process is not only confined to changes in plant community composition in a given area. During community succession, there is an interaction between the biotic (plants, animals, microbial organisms and other living organisms) as well as with its abiotic environment. For example, a recent report on the effect of logging in a primary forest in Ulu Muda Forest Reserve, Kedah, Malaysia, indicated that the arboreal foliage-gleaning insectivore guild of bird species declined immediately after logging, while the seed feeders increased, indicating their importance in seed dispersal for plant succession (Rosli and Zakaria, 2002). Bird perches were found to promote accelerated plant colonization in landslides in Puerto Rico, indicating the importance of the role of biotic seed dispersal agents (Shiels and Walker, 2001). Native earthworm species which are litter-feeding were found to dominate in a forest area, compared to a disturbed area in Puerto Rico (Sanchez et al., 2001).

Succession as an ecological concept has dominated the thinking of ecologists for many years. However, it has also been subjected to criticism on two points: a) implications within the concept of a purposive or directed change, which reminds one of some teleological concept; and b) the debate on whether there really is a climax. Nevertheless, a common and readily accepted notion is that plant succession is initiated and sustained by some disturbances that create change and destabilization in the system. This becomes the window for management to use these ecological processes, provided these changes and the long-term consequences in terms of forest ecosystem characteristics are well understood.

ANR Technology

Based on the conceptual framework of the relationships between the technological, the natural resource base and the socio-cultural dimensions, it is necessary that the technology for ANR conforms to or enhances the ecological principles involved in the process. These technological interventions must be socially acceptable and institutionally supported. In general, the ANR technologies comprise site selection, site assessment, site-species matching, site modification such as shade opening, supplemental or enrichment planting of appropriate species, protection and maintenance and monitoring.

Site selection and site assessment

Site assessment is an important first step in ANR, as it determines the seral stage of plant succession which is going to be used as the starting point for forest restoration. It also identifies the type of site enhancement which will be applicable to enhance plant succession. In general, ANR will mainly be implemented in areas where the main objectives are protection forest, biodiversity conservation, quick establishment of protection cover for hydrologically critical areas and for soil conservation. However, for economic reasons, site assessment should also determine the cost of forest restoration, as the more retrogressive the seral stage is, the more expensive it will be to restore. For example, if the initial seral stage is a degraded grassland area, it will take longer and require more inputs to push it to an advanced stage of plant succession, like secondary forest. If seedlings of the appropriate species are no longer present in the area and the biotic components for seed dispersal no longer exist, then collection, transport and distribution of these materials will entail higher costs. For a successful ANR project, it is important to ensure that there are sufficient numbers of seedlings of natural species in the area and the appropriate soil conditions. This will enable enhancement of the regeneration without additional external inputs. It is also important to have sufficient seed dispersal agents (both biotic and abiotic) so that the natural process of forest restoration can proceed by protection alone.

Site-species matching

This is the weakest part of ANR, as there is limited knowledge of the specific ecological requirements of natural forest tree seedlings (Kartawinata et al., 2001). In the absence of any information on the niche requirements of the various seedlings and saplings located in the area, it is possible to make use of local knowledge. This type of information can be obtained by means of discussions with some key members of the community. Site-species matching in ANR is critical because a mismatch will result in the loss of propagules and regeneration materials. It will also result in a waste of time and money invested in the ANR sites. Several earlier studies have suggested that local people possess more knowledge concerning their local resources than is often appreciated by experts or accepted by government officials (Leach et al., 1999).

This technological step will also require good information on site characteristics such as biotic agents of dispersal, soil characteristics in relation to nutrient and moisture status, light quality and quantity, temperature, rainfall, organic matter and others. The key factor to this process is to be able to characterize site quality in terms of some key edaphic, hydrologic, biotic and other abiotic conditions.

Site modification

This part of the ANR technology is designed to favor the species that will catalyze an autogenic change to move the plant succession process to a higher seral stage. However, it should be designed to bring about an intervention that will enhance the growth of the preferred species, based on the ecological requirements of these species in the ANR site. For example, liberation thinning or canopy opening stimulated the growth of Eusideroxylon zwageri, Shorea leprosula and S. bracteolate seedlings and saplings in a secondary forest in Indonesia. However, poor performance was shown by Dipterocarpus spp. (Sastrawinata and Effendy, 1991). The pruning of pioneer tree species in a Brazilian secondary succession area enhanced the growth of both natural and agricultural crops, as the faster recycling of vegetation promoted nutrient enrichment (Goetsch, 1992).

In rehabilitating Imperata grasslands in the Philippines, plant competition between this grass species and tree seedlings is reduced by pressing the grass stand. This reduces the apical dominance of Imperata, thereby reducing its tillering regeneration capacity. If this were done by cutting, it would enhance tillering and increase competition between the grass and the tree seedlings (Sajise, 1972). This process also enhances the return of organic matter to the soil, while dramatically reducing labor requirements and expenses.

Enrichment or supplemental planting

This step in the ANR technology is derived from site-species matching. It involves species identification, assessment of appropriate planting density and site treatments. In some cases, depending on site conditions, leguminous species are planted to enrich the soil and pioneer species such as Trema, Macaranga and Erythrina are planted for both shade and soil enrichment. In Brazil, the herbaceous species capeba (Pothomorphe umbellate L.) is planted to stimulate earthworm activities and the bean feijao de porco (Canavalia ensiformis L.) serves as an effective repellent for the notorious leaf cutter ants (Goetsch, 1992).

Protection and maintenance

If adequately protected from significant disturbances such as fire, grazing, fuelwood cutting and others, a regenerating area will undergo ecological succession (Figure 2). In relatively wet areas in the Philippines, Sajise and Orlido (1973) observed that Imperata-dominated grassland is replaced by a shrub community of the Mikamia-Melastoma-Solanum association, after three years without fire and agricultural cultivation. Sajise (1972) demonstrated that 50 percent shading of Imperata reduces its net photosynsthesis capacity and consequently its rhizome production. This effect of shading is important because 60 percent of the total dry matter produced by this grass species is stored below the ground in the form of rhizomes, which are the main source of energy for rapid regeneration after burning and cutting. The shrub communities persist for four to six years and are gradually replaced by softwood species such as Ficus spp., Mallotus spp., Trema orientalis and Homolanthus populneus (Figure 2).

In order to succeed, ANR areas must have adequate protection and maintenance procedures, which involve both technological and social considerations. In the Philippines, successful social forestry projects will have more success with reforestation, as the community can effectively protect their areas from grassland and dry season fires. In India and Nepal, successful forest regeneration is also evident in community-based forestry programs.

Figure 2: Pattern of plant succession in a Philippine grassland ecosystem. Source: Sajise et al., 1976

Socio-cultural and institutional aspects of ANR

The third and equally important element in the triangle of a successful ANR project are the socio-cultural and institutional elements. These elements comprise the socio-cultural values of communities involved and the prevailing policies regarding the use of natural resources. These values can be in the form of the relationships that exist between the human communities and the natural resource base such as, the economic products and services provided by the restored forest ecosystem. It can also be in the form of human activities which are protective and promote the efficient restoration of the forest ecosystem.

The report of the World Commission on Forests and Sustainable Development (WCFSD) reported that these relationships can be promoted by the following (Poffenberger, 2000):

The process of decision making about the disposition of the forest should be open to widespread participation of the most affected, including women and indigenous people.

Land and resource tenure arrangements should be reviewed to make them more conducive to conservation.

Mechanisms need to be created that involve communities in monitoring what goes on in their local areas.

Local communities should be involved in all stages of planning and implementing forestry projects.

National and global governance structures need to be created that encourage transparency and redress corrupt practices.

These socio-economic and institutional arrangements are designed to ensure that local communities will have both the responsibility and accountability for protecting and enhancing forest restoration through ANR or other appropriate means, while at the same time securing the benefits that should accrue to them in a more sustainable and equitable manner. For example, at the national level in the Philippines, the implementation of ANR was facilitated by the issuance of Memorandum Circular Number 17, Series of 1989, which prioritized the application of the ANR method in the development of watersheds, protection and production forests. In the International Convention on Biological Diversity (CBD) and the recently adopted FAO-initiated International Treaty on Plant Genetic Resources for Food and Agriculture (PGRFA), these rights of communities to equitably share the benefits derived from use of these local plant genetic resources and indigenous knowledge are also secured. At the local level, the use of appropriate local and traditional institutions to support and implement ANR or any other community-based natural resource management has also proved to be effective in many situations.

Implementation constraints of ANR

There are some constraints in the application of ANR as a forest restoration strategy. These include:

A lack of basic knowledge of ecosystem dynamics, which would facilitate the application of ANR technology, including the ecological requirements of natural regeneration species.

The labor and knowledge intensive nature of the strategy, which can make it costly if not done properly.

Weak policy and incentive systems associated with the need for appropriate land tenure and benefits derived from the restoration of forest diversity.

Ecological knowledge limitations

The current level of knowledge about the interrelationships among components of the ecosystems where ANR is to be applied is very limited. For example, neither the intra- and inter plant species interactions, nor the plant-animal interactions, including soil microbial organisms, are understood clearly. More directly, the knowledge of the ecological requirements of the species involved in ANR is inadequate. For ANR to succeed, this basic ecological knowledge must be strengthened as forest restoration must meet the objectives of attaining not only a desirable level of biodiversity, but more significantly a functional type of diversity. This functional diversity should enhance productivity, the protective character of the forest cover and the sustainability of the products and services it generates.

An immediate and long-term concern is the impact of ANR on plant genetic diversity. In forest restoration, a key element of long-term significance to the productivity and sustainability of this ecosystem is plant genetic diversity. For example, the study of Wickneswari and Lee (2001) indicates that there is an apparent decline in the genetic diversity of Scapium macropodum in the logged areas in Malaysia. This aspect is very important to consider as one of the objectives of ANR is the restoration of the genetic diversity of the ecosystem. Genetic diversity forms the basis of adaptive flexibility in populations and the ultimate evolutionary potential of a particular species.

This lack of knowledge of the ecological processes in plant succession makes it difficult to operationalize ANR. For example, site assessment, which is an important aspect of ANR, entails an extensive analysis of the above and below ground processes (soil, light temperature). This analysis is both time consuming and expensive and forms a barrier to the simple implementation of ANR. There is a need to look for simple indicators of tree seedling density and soil conditions using specific biotic indicators (plant species, arthropods or insects and other animals). The monitoring and assessment of the effectiveness of ANR can also be a labor-intensive and costly process. This is especially so if there is a regular survival monitoring process, instead of just a total protection approach, combined with fast but effective monitoring. Such monitoring could be achieved through an indicator such as canopy development, provided that the macro-level site conditions are closely associated with the requirements of the key species in the ANR area.

Socio-cultural and institutional constraints

The biggest challenge is to overcome the constraints of inappropriate or lack of economic incentives, land tenure and national policies, which limit the benefits derived by communities in forest restoration through ANR. In this regard, the provision of mechanisms for community participation and the use of local knowledge in the implementation of ANR is critical. If the communities are to become effective implementers of ANR, they must have some security and assurance that they will benefit from this ecosystem restoration process, especially with regards to its long-term products and services. This can be in terms of promoting high value and market-oriented products such as medicinal plants, as long as this is done in a sustainable manner. For protection forest, local communities can be contracted by the government for the establishment of forest cover through ANR. However, their relationship to the accruing benefits should also be discussed and agreed upon on a long-term basis. An appropriate national land-use policy which contextualizes the appropriate use of ANR technologies for forest restoration will provide an overall framework to enhance its effectiveness and efficiency.

Another urgent need is to systematically document and assess the experiences and lessons learned from the implementation of ANR in other regions. This can be used as a source of feedback for the identification of priority research and the improvement of future implementation of similar strategies for forest restoration.


Forest restoration is needed in many areas in the tropics and poses a big challenge for national governments and international organizations. In many instances, this process is not only expensive but also ineffective. One option or strategy for forest restoration is ANR. ANR is beginning to gain ground because it works with or mimics nature, which makes it less costly, enhances biodiversity and is more effective.

However, to be effective, the ANR strategy should develop as a result of the synergistic and complementary interactions between the technological factors, socio-cultural elements and the natural resource base, with the ecological process of plant succession. These interactions and relationships must be well understood and used as the basis for the application of this forest restoration strategy.

The constraints to effective implementation of ANR require more research, especially on the basic ecological relationships which drive plant succession. It is only through an improved understanding that one can enhance the effectiveness of ANR. Similarly, the socio-cultural and institutional context of ANR should also be studied and effectively used as leverage for its effective implementation. After all, it is still people and human societies who must work with nature to fully benefit from this nature-people relationship in support of sustainable development.


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