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Changes in tree community structures in defaunated forests are not driven only by dispersal limitation

Citation

Hazelwood, Kirstie et al. (2021), Changes in tree community structures in defaunated forests are not driven only by dispersal limitation, Dryad, Dataset, https://doi.org/10.5061/dryad.wpzgmsbhg

Abstract

1. Bushmeat hunting has reduced population sizes of large frugivorous vertebrates throughout the tropics, thereby reducing the dispersal of seeds. This is believed to affect tree population dynamics, and therefore community composition, because the seed dispersal of large-seeded trees depends upon large-bodied vertebrates.

2. We report on a long-running study of the effect of defaunation on a tropical tree community. In three censuses over 11 years, we compared sapling recruitment between a hunted and a nonhunted site, which are nearby and comparable to one another, to determine the extent to which species composition has changed through time following defaunation. We expected to find a reduced abundance of tree species that rely on large frugivores for dispersal at the hunted site, and altered community structure as a consequence.

3. Although community composition at the hunted site diverged from that at the nonhunted site, the changes were independent of dispersal syndrome, with no trend towards a decline in species that are dispersed by large, hunted vertebrates. Moreover, the loss of large-bodied dispersers did not generate the changes in tree community composition that we hypothesised. Some species presumed to rely on large-bodied frugivores for dispersal are effectively recruiting despite the absence of their dispersers.

4. Synthesis: The presumption that forests depleted of large-bodied dispersers will experience rapid, directional compositional change is not fully supported by our results. Altered species composition in the sapling layer at the hunted site, however, indicates that defaunation may be connected with changes to the tree community, but that the nature of these changes are not unidirectional as previously assumed. It remains difficult to predict how defaunation will affect tree community composition without a deeper understanding of the driving mechanisms at play.

Methods

Data was collected between 2004 and 2015 from a hunted site (Boca Manu) and a non-hunted site (Cocha Cashu). Tree plots covered one 4-ha plot at each site, with a central square 1- or 1.08-ha sapling plot at the hunted and nonhunted sites, respectively. In each census, every individual was identified, tagged and mapped, DBH was measured for trees (≥10 cm DBH) and large saplings (>1 cm DBH, <10 cm DBH), and height was measured for smaller saplings (>1 m height, <1 cm DBH).

Four data sets are provided, two for mature trees at each site and two for saplings at each site.

Usage Notes

Metadata tabs provides detailed information on columns. Data may be missing if tree measurements were not obtained in unusual circumstances. If the tree was dead or not yet recruited into the study no height or DBH measurements are provided.

Funding

Natural Environment Research Council, Award: PhD Scholorship