Forest diversity and structure in regenerating secondary forests after shifting cultivation abandonment in the Philippines uplands

We investigated parameters of forest diversity and structure along a
fallow age gradient in secondary forests regenerating after shifting
cultivation abandonment. We first measured the tree diversity and forest
structure indices in regenerating secondary forests and old-growth forest.
We then measured the recovery of tree diversity and forest structure
parameters in relation to the old-growth forest. Finally, using linear
mixed effect models (LMM), we assessed the effect of different
environmental variables on the recovery of forest diversity and structure.
Species density was significantly higher in the oldest fallow sites, while
Shannon’s index, species evenness, stem number, basal area and leaf area
index were higher in the old-growth forest. A homogeneous species
composition was found across the sites of older fallow age. Multivariate
analysis revealed patch size as a strong predictor of tree diversity and
forest structure recovery after shifting cultivation. Secondary forests
regenerating after shifting cultivation abandonment can recover rapidly
after five years. Although recovery of forest structure was not as rapid
as the tree diversity, our older fallow sites contained a similar number
of species as the old-growth forest. Many of these species are also
endemic to the Philippines. Novel and emerging ecosystems like tropical
secondary forests are of high conservation importance and can act as a
refuge for dwindling tropical forest biodiversity.