....and forest management in Sabah, Malaysia
Stingless bees (meliponines) are social bees that live in perennial colonies of a few hundred to several thousand workers. Although they are only moderately diverse (~ 30 species in Borneo), they are among the most predominant flower-visiting insects in tropical forests and likely pollinators of many timber trees. As a consequence their conservation in commercial forests should be of concern to forest managers.
The Malaysian-German-Sustainable Forest Management Project was founded as a cooperation between the Sabah Forestry Department and the Gesellschaft für Technische Zusammenarbeit (GTZ). It is aimed at introducing sustainable forest management to Sabahs' commercial forests. Management concepts and Reduced Impact Logging (RIL) techniques are developed and tested in the Deramakot Forest Reserve in central Sabah, the model area of the project. Ecological impact assessment using faunal indicators is seen as an integral part of judging long-term sustainability. In that framework I conducted my PhD project on stingless bees populations and communities, funded by the GTZ's Tropenökologisches Begleitprogramm (TÖB).
A potential conflict between timber harvest and bee conservation in managed forests arises from the bees' nesting biology. In Southeast Asia the vast majority of nests is found in hollows in or under large timber trees. I analyzed size, taxonomic affiliation and expected timber quality of 142 nest trees in Sabah, Borneo, and estimated that more than one third of nest trees (and nests) would be killed during an average selective logging operation (Eltz et al. 2002). As meliponine colonies are long-lived and have low fecundity, direct impact from logging may have lasting effects on bee populations and community composition.
In addition to causing direct mortality to bee colonies, logging may also indirectly affect bee populations by reducing the number of nesting opportunities available for recolonization. Limitation of nest cavities may be especially severe in heavily degraded forests that almost completely lack large trees. To investigate the factors that limit stingless bee populations we measured nest density and species diversity in undisturbed and older logged-over forests in Sabah (Eltz et al. 2002). Per-area nest density (and, closely correlated, bee species diversity) varied twenty-fold across 14 forest sites and was significantly affected by locality, but not by the degree and history of disturbance. The presence of potential nest trees (large trees), though positively correlated with nest density, explained only a minute fraction of the observed variation. Nest density was better explained by differences in the pollen resources available to the bees (quantified by analysis of pollen in bee garbage). Across five selected sites the amount of non-forest pollen (from mangrove or crop plants) included in bee diets was positively correlated with nest density. External pollen sources are a likely supplement to bee diets at times when little flowering occurs inside the forest, thus increasing overall bee carrying-capacity. Pollen limitation was also indicated by direct measurements of pollen import and foraging activity of Trigona collina in three selected sites: Pollen traps installed at nests in high-density areas captured significantly more corbicular pollen than colonies in low-density sites. At the same time, the foraging activity (measured by electronic bee counters) was also greater in Sepilok, indicating a regulatory increase of foraging in response to high pollen availability. It is concluded that the abundance and diversity of stingless bees in forests in Sabah is chiefly dependent on the local availability of food resources and only to a lesser degree on the availability of nest trees. Therefore, stingless bee communities are likely to recover from the effects of single selective logging events, provided that sufficient time is given for regeneration (Eltz & Brühl 2001).
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