Overstory #97 - Genetic Conservation of Tropical Trees
Genetic erosion is the loss of genetic diversity within a species caused by human activities and environmental changes. Unsustainable forestry practices and high rates of land clearance for agriculture are causing genetic erosion of valuable tree species in the tropics. This process endangers the economic sustainability of rural communities and limits opportunities for the development of new timber and non-timber forest products. With a focus on local community involvement, this article covers potential utility and limitations of six low-input interventions to help forestall further tree genetic erosion.
"The first rule of intelligent tinkering is to keep all the pieces."--Aldo Leopold
The tropics have the highest tree species diversity in the world (Gentry and Ortiz 1993). For example, over 200 tree species (10 cm in diameter at breast height) per hectare have been recorded in parts of the upper Amazon (Gentry 1988). Tropical cultures are often heavily dependent on the many products and services these species provide: in a survey in the Peruvian Amazon, local farmers used more than 250 tree species and considered 155 of these as priorities for agroforestry (Sotelo-Montes and Weber 1997). In addition, numerous tropical tree species have promising national and international markets for fruit (Prance 1994; Villachica 1996), medicinal (Estrella 1995; Mejía and Rengifo 1995) and lumber products (Toledo and Rincon 1996). If appropriate cultivation techniques and markets were developed, these species could greatly assist in the economic development of some tropical regions (Anderson 1989; Castillo 1995; Leakey and Simons 1998).
Despite this, over-harvesting and other poor forestry practices in many areas of the tropics are reducing tree genetic diversity, thereby limiting the ability of both tropical and non-tropical societies to capitalize upon these valuable genetic resources. This note attempts to foster a dialogue regarding the potential utility and limitations of six interventions (agroforestry, domestication, woodlots, collection systems, seed zoning and in situ conservation areas) which aim to forestall further tree genetic erosion in the tropics - i.e., to "keep all the pieces," as Aldo Leopold has said. Where possible, attention has been placed on maximizing the role of farmers and other community members in interventions, so as to capitalize upon their knowledge and ensure their involvement.
Expanding slash-and-burn agriculture by migration into forest areas is the primary cause of deforestation in many parts of the tropics (Brown and Pearce 1994). The increased, continuous and more diverse agricultural harvest associated with agroforestry (Denevan and Padoch 1987; Montagnini and Mendelsohn 1997) can increase farm productivity and profits, and thereby reduce subsistence land needs and forest encroachment by farmers (Portillo 1994; Scherr and Current 1997). For example, in Central America, farmers' profits were at least 10% greater in agroforestry systems relative to alternative land uses in 90% of cases examined.
Although the agronomic benefits of agroforestry systems have been demonstrated in many areas of the tropics, systems have often not been widely adopted (Scherr and Current 1997; Vosti et al. 1997). Farmers' perceptions of food security risks, a lack of labour (Barton 1994), opportunity costs (Christoffersen 1989) and the potential lack of profitability (Current et al. 1995) associated with agroforestry systems have been cited as factors inhibiting their adoption. In the Amazonian lowlands of Ecuador, lack of extension, credit, and product marketing have also been implicated (Follis and Nair 1994). In Central America, government regulation of tree harvesting and land tenure insecurity are disincentives for adoption (Current et al. 1995). In order for the benefits of agroforestry to be realized, therefore, the causes of slow adoption will need to be addressed.
By selecting and propagating the phenotypes that best suit their needs, farmers have been slowly domesticating trees for millennia. Modern domestication strategies can help meet the changing needs of farmers, resulting from increased land pressures and changing socio-economic conditions by increasing the productivity of tree plantings. Strategic approaches to domestication can help avoid the potential pitfalls of traditional methods, such as introducing narrow genetic bottlenecks, using maladapted materials or focusing on exotics (Weber et al. 2001).
By conducting genetic trials on-farm, farmers may be more inclined to participate in them, particularly if the trials are designed in a way that they can be converted into seed production stands or produce other valuable products after the evaluation phase. Converting appropriately designed trials to seed production stands can also reduce the time required for improved germplasm to reach users, and stands can serve as ex situ genetic conservation sites.
The major limitation in using tree domestication to reduce genetic erosion may be the availability of sufficient quantities of high-quality planting stock (Simons 1996). Few national government organizations and NGOs in the tropics are involved in tree domestication, and those efforts meet the needs of only a small fraction of tropical farmers. Larger-scale endeavours and the engagement of national organizations must be sought if tree domestication is to significantly reduce tree genetic erosion.
Selective extraction is the major form of logging practiced in much of the tropics. Logging of phenotypically superior individuals of commercial species removes the best genotypes from a population, leaving the poorest individuals of the least profitable species to produce seed for future generations.
Community- or farmer-based woodlot enterprises based on intensively managed tree plantations could supplant selective extraction as plantations are potentially more profitable. In addition, woodlot forestry may be more environmentally and economically sustainable than selective extraction or natural forest management (Bawa and Seidler 1998). Since most commercial tree species in the tropics are found at low-densities, woodlots, which have high marketable volume per hectare, could provide a timber supply with substantially lower extraction costs. In addition, management operations such as pruning, that add further value to timber, could be introduced. Investment costs could be reduced, and income and adoption rate increased, by locating woodlots on abandoned or degraded farms.
By promoting planting of well-known native timber species for the export market and developing markets for lesser-known native timber species, some of the logging pressures on the principal commercial species in wild stands may be deflected (Toledo and Rincon 1996). However, a number of issues remain to be addressed. First, if highly profitable, the promotion of woodlot forestry may actually increase deforestation if governments can not control activities on public land. Second, the long time required for most tree species to attain economic maturity may be a significant deterrent for poor farmers to adopt woodlot forestry. In order for woodlot forestry to reduce overall and selective extraction, therefore, several factors, including credit availability and land tenure, will need to be addressed (Current et al. 1995).
Improved seed collection systems
Seed collections for reforestation are frequently made from an insufficient number of trees, resulting in reduced genetic diversity. Moreover, seeds are often collected from trees that are the easiest to climb (i.e., the shortest and most crooked), which may result in slow-growing or poorly shaped progeny.
Seedlots collected from wild stands will continue to be of low quality unless regulation, training and monitoring programmes are established. National systems of tree seed registration should consider minimum standards for a) number of parent trees in each seedlot and seed bulking methods (Marshall and Brown 1975), b) separation distance between parent trees to minimize genetic relatedness (Dawson and Were 1997), c) yield and physiological quality of the harvested seed, d) health of the mother trees, and e) location data.
Strict standards for the documentation of collection localities will facilitate return to populations that perform well in particular environments, while populations that perform poorly can be avoided. Regulation of seed collection in this manner, however, will increase the cost of seed to consumers and requires substantial investment in training and monitoring of collectors.
Cooperative seed collection is one approach to address the financial and logistical difficulties of implementing improved seed collection systems. For example, a cooperative invites farmers to collect seed from one or more of their 'best' trees for a set of priority species. Collected seed is pooled by the cooperative and the genetically diverse pooled seedlots are then apportioned to contributors.
Demonstration plots that indicate the different performance of progeny collected from 'good' or 'bad' parental trees, or that illustrate the effect of genetic bottlenecks leading to inbreeding depression, can also be effective in illustrating to farmers and policy-makers the value of good collection practices.
When seed is planted away from its native environment, it may suffer from maladaptation, leading to pest attack, slow production or poor form, due to the new growing conditions. With the large investment in time and land area that tree planting demands, it is essential to ensure that planted germplasm is adapted to its planting environment.
Although the extent of maladaptation in most tropical plantations cannot be assessed because the original sources of seed are usually unknown, in some cases it is expected to be extensive. A seedlot registration system provides a simple method to minimize maladaptation by classifying administrative regions into ecologically similar "seed zones" and discouraging the transfer of seedlots across zones (Conkle 1997). In the absence of a well-defined ecological classification system, seed zones can be characterized based on climatic or elevation data.
Although natural forest areas are contracting, in situ reserves remain an important means of conserving intraspecific variation. Such reserves conserve ecosystem interactions, function as 'workshops' for natural selection, and are sources of germplasm for recolonisation following catastrophic events. While establishment and management of in situ reserves has traditionally been the domain of formal national authorities, provincial and community delineated and managed reserves may significantly complement such schemes. A community approach may have particular value because indigenous resident managers may have an intimate knowledge of local biota and ecology (Pimbert and Pretty 1995) and recognise the value of conservation. Local knowledge may be applied in the identification of corridors between reserves or areas of high habitat value for target species. It may also be employed in designing management practices to produce conditions optimal for reproduction of target species.
Regardless of the mode of control of a reserve or reserve system, careful planning of the size, shape, location and composition of conservation areas can improve their integrity and viability (Harris 1984). Since many tropical forest trees, particularly in lowland rainforests, occur at very low densities, their effective conservation in situ will require areas in the order of 2500 km2 (Lawrence and Marshall 1997). Identification and management of areas of this size may require the support of national government and should be considered within the larger framework of integrated natural resource planning and economic and agricultural development policies.
Current land-use patterns and unsustainable forestry practices are eroding tree genetic resources in the tropics, reducing the economic options and food security of peoples in many developing nations. The interventions proposed in this article focus mainly on technical innovations to involve farmers and forest-dependent communities in conservation. However, social, political and economic factors (such as population growth, inequitable land and wealth distribution, and conflicting policies) may pose a greater threat to the conservation of genetic resources than do technical deficiencies (Ledig 1986). The challenge for the future, therefore, will be to engage all players - farmers, communities, governments and policy-makers - in approaches that protect these precious and often intangible genetic resources.
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This article has been abridged from the original by the authors with the permission of Kluwer Academic Publishers:
O'Neill, G.A, I. Dawson, C. Sotelo-Montes, L. Guarino, and J.C. Weber. 2001. Strategies for genetic conservation of trees in the Peruvian Amazon. In: Biodiversity and Conservation 10: 837-850.
About the Authors
Greg O'Neill is a professional forester who works as a tree breeder in the Research Branch of the British Columbia Ministry of Forests in Canada. He has interests in community forestry and tree genetic resource management in Latin America. His current research focuses on tree seed transfer and adaptation. Address: Kalamalka Forestry Centre, 3401 Reservoir Road, Vernon BC V1B 2C7, Canada; Tel: 250-260-4776.
Luigi Guarino is Senior Scientist at the Regional Office for the Americas of the International Plant Genetic Resources Institute (IPGRI). He has previously worked in IPGRI regional offices in Africa and the Middle East, and as an FAO consultant on genetic resources in the Pacific. He has co-edited a book on "Collecting Plant Genetic Diversity" published by CAB International. He can be reached at: International Plant Genetic Resources Institute, Regional Office for the Americas, AA 6713, Cali, Colombia; Tel: 57-2-445-0029; Fax: 57-2-445-0096.
Ian Dawson is a germplasm specialist in the Tree Domestication Programme at the International Centre for Research in Agroforestry (ICRAF), Nairobi, Kenya. His main concern is optimising the genetic resource management of tree species in agroforestry systems by assessing the genetic composition of natural and cultivated tree populations. In addition, he works as part of a team at ICRAF undertaking seed production research and constructing databases on agroforestry trees.
Carmen Sotelo Montes is a forester and John Weber is a forest geneticist working with the International Centre for Research in Agroforestry. They conduct research and training on participatory domestication of agroforestry trees in the Peruvian Amazon Basin. Their research focuses on the management and conservation-through-use of tree genetic resources for community development. They have conducted studies of farmers' preferences for tree species, farmers'use and management of tree germplasm, the efficiency of phenotypic selection in the field, intraspecific variation in wood-quality and other traits, and methods for the production of improved tree seed in farming communities. They can be reached at: ICRAF, INIA Estación Experimental, Carretera Federico Basadre Km 4.2, Pucallpa, Peru.
Related Editions to The Overstory
- The Overstory #90--Biodiversity and Protected Areas
- The Overstory #77--Tropical Forest Conservation
- The Overstory #58--Guidelines for Seed Production of Agroforestry Trees
- The Overstory #31--Tree Domestication
- The Overstory #21--Agroforestry and Biological Diversity
- The Overstory #19--Selected Tree Seed