Assessment, Conservation and Sustainable Use of Forest Biodiversity

Keynote Addresses
Recent research and development work being carried out by CATIE and its national partners in natural
Central American timber production forests has the goals of increasing knowledge of forest management
effects on biodiversity – with emphasis on the surprisingly poorly-documented area of species- and geneticlevel
diversity of tree communities and populations – and on the development of adaptive ecological
components of national standards for sustainable forest management at the fmu level. This work, possibly
uniquely in the tropics, takes into account that Central American production forests are also, increasingly,
fragmented forests. Work towards the twin goals is closely integrated. The focus is on two moist forest
ecoregions as defined by Dinerstein et al. (1995): the Central American Atlantic forest and the Tehuantepec
forest. Besides embracing some of the largest remnant forest areas of Central America, these ecoregions are
major sources of forest products and are a key component of the area of the Mesoamerican Biological
Corridor, a major conservation strategy currently being implemented with support from governments and
international organizations. We emphasize that this research focuses on managed forests, not on forests
subjected to conventional logging.
Taxonomic biodiversity at the species level is usefully characterized in terms of both the species diversity and the
species composition of the forest community and our work is carried out in permanent sample plots with
planning for the long term. As a large proportion of the plant diversity of tropical rain forests is found among
life forms other than large trees, this characterization should embrace a broader spectrum of the community
than is the case in traditional permanent sample plot studies. CATIE has introduced methodological
innovations to take this latter necessity into account, sampling the forest understorey as well as individuals ≥ 10
cm dbh.
For the analysis of management effects on plant taxonomic biodiversity, our results show that in general, it is
convenient to identify both direct and indirect effects. Direct effects are immediate consequences of
management operations and occur simply because some plants in sample plots are killed by those operations.
Indirect effects of management operations on plant biodiversity may occur as consequences of managementinduced
changes in forest environmental conditions or in ecological processes such as pollination or seed
dispersal. These effects will evolve over time and may be long-lasting.
Direct effects of management on plant species richness are relatively simple to demonstrate. Speciesabundance
distributions in our permanent sample plots are typical of those for tropical forests in that they
show large numbers of species represented by few or single individuals. Some of these individuals are killed
when forests are logged or silvicultural treatments applied, these deaths bringing about immediate reductions
in the species-richness and diversity of the vegetation in the plot. It is important to point out that such
reductions of diversity are to an extent artefacts of the permanent sample plot techniques used and by their
very nature, certainly do not mean that species are being locally extinguished. Indirect effects require
demonstration by more detailed studies, though it may be inferred that such changes are taking place
especially if appropriate methodologies for the study of mortality are used. In intensive research in three
different floristic types of production forest in the Central American Atlantic moist forest CATIE has found,
however, that in spite of the array of factors which may influence it in timber production forests, plant species
diversity is not reduced during the first decade of management. This conclusion applies over a range of
harvesting intensities from 10 – 30 m 3 ha -1 and to forest stands where silvicultural treatment has produced
major changes in forest structure and marked increases in the growth of potential crop trees. Two hundredyear
simulations using Gavilán, an individual-tree computer model developed at CATIE (Sitoe 2000), further
support the tentative conclusion that plant species diversity is a robust forest characteristic in the context of
management interventions typical of Central American production forests, and that sustainable production
and the conservation of a large proportion of the original plant taxonomic biodiversity are compatible.
Forest composition and forest diversity may vary independently (Finegan 1996) and it remains a possibility
that compositional change occurs, for example if populations of plant species typical of the original forest
decline or are locally extinguished under management, even if forest diversity is maintained. Speciesabundance
distributions again rear their heads in the analysis of compositional change using permanent
sample plot data, as changes in relative abundance can only be reliably identified for that minority of species
which are, or become, relatively common. Our results for such species show that as may be expected, forest
13