Data from: Forest loss and treeless matrices cause the functional impoverishment of sapling communities in old-growth forest patches across tropical regions

Landscape-level disturbances, such as forest loss, can profoundly alter
the functional composition and diversity of biotic assemblages. In fact,
the landscape-moderated functional trait selection (LMFTS) hypothesis
states that landscape-level disturbances may act as environmental filters
that select a set of species with disturbance-adapted attributes while
causing the loss of species with disturbance-sensitive attributes,
ultimately compromising ecosystem functioning. However, the impact of
landscape patterns on the functional composition and diversity of tropical
regenerating trees (saplings) is unknown. Using a multiscale approach to
identify the best spatial scale (i.e. the scale of effect), we tested the
effect of forest cover, matrix openness and forest patch density
(fragmentation) on functional composition and functional diversity of tree
saplings in old-growth forest patches (n = 59) in three Mexican rainforest
regions with different degree of deforestation. For 368 species and
~23,000 individuals, we compiled information from global and national
databases on six functional traits related to seed dispersal and plant
establishment and calculated their community abundance-weighted mean
(CWMs) and three complementary functional diversity indices. Forest loss
and matrix openness reduced functional richness and evenness, but only in
the two most deforested regions. Overall, fragmentation had contrasting
effects on functional diversity and composition, but correlated negatively
with some functional traits in the most deforested region. Importantly, in
the regions with high-to-intermediate degree of deforestation, functional
composition experienced major changes: maximum height, seed mass, fruit
size and wood density decreased, and SLA increased, in forest patches
surrounded by open matrices in highly deforested and fragmented
landscapes. This caused a shift of community traits towards more
disturbed-adapted attributes. Synthesis and applications. In agreement
with the LMFTS hypothesis, our results confirm that landscape
modifications in regions undergoing high and long-lasting deforestation
greatly impoverish the functional composition and diversity of sapling
communities. The shift from communities composed mainly by conservative
attributes towards communities with a higher prevalence of
disturbance-adapted attributes disrupts the future community structure and
jeopardizes critical ecosystem functions. Management practices focused on
preventing deforestation, increasing forest cover, and promoting treed
matrices are necessary to preserve the functionality of these species-rich
but increasingly threatened rainforests.