DOI: 10.5061/dryad.gxd2547pg
title: Data from: Forest loss and treeless matrices cause the functional impoverishment of sapling communities in old-growth forest patches across tropical regions

description: 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.
description: We worked in three rainforest regions from southeastern Mexico
 with different patterns and history of land-use change: (1) Marqués de
 Comillas region (in Selva Lacandona rainforest, Chiapas) and labeled as
 low-deforestation region (LDR) in the database; (2) Los Tuxtlas rainforest
 (Veracruz), labeled as intermediate-deforestation region (IDR); and (3)
 Northern Chiapas, labeled as high-deforestation region (HDR). In each
 region, we selected 20 old-growth forest patches (i.e. 60 forest patches
 in total). Sampling was conducted in the dry season, from January to May
 2018. At the centre of each forest patch, we established 25 circular plots
 of 1.60 m radius (8 m<sup>2</sup> each, which represents 200
 m<sup>2</sup> sampled in each patch), in a grid of 5 × 5 plots
 with a 30 m separation between them. In each plot, all saplings (excluding
 palms and lianas) ≥ 30 cm in height and &lt; 1 cm of diameter at
 breast height (DBH) were identified and counted. Then, we summed up the
 values obtained for the 25 plots to obtain a single value for each forest
 patch (i.e. sampling unit). For each forest patch (i.e.
 community), we collected six functional traits that represent the whole
 plant trait economic spectrum, play a key role in plant regeneration and
 are sensitive to environmental modifications: tree maximum height (Hmax,
 m), seed mass (SM, mg), specific leaf area (SLA, mm2/mg), fruit size (FS,
 mm), wood density (WD, g/cm3) and dispersal syndrome (DS). We then
 calculated the community abundance-weighted mean (CWM) for each of the
 afore-mentioned functional traits. We also calculated three complementary
 indices of functional diversity (Villéger et al., 2008): functional
 richness (FRic), functional evenness (FEve) and functional divergence
 (FDiv). FRic represents the amount of functional space occupied by the
 community and is based on the convex hull concept, which is the minimum
 convex hull that includes all species considered. FEve represents the
 homogeneity in the distribution of species trait abundances of a
 community, so FEve decreases when species trait abundances are distributed
 less uniformly among the included species or when functional distances
 among species are less regular. Finally, FDiv measures how far the
 abundances of the different species are from the centre of the functional
 space. Concerning the landscape variables, we estimated
 four landscape metrics: two metrics of landscape composition (i.e., FC =
 forest cover, MO = matrix openness) and two metrics of landscape
 configuration (i.e., PD = patch density, ED = forest edge density).
 Landscape variables were assessed in 13 concentric landscapes (i.e.
 buffers or landscape areas) of 100- to 1300-m radius (at 100-m intervals)
 from the centre of each sampling site. This multi-scale approach was used
 in order to identify the spatial scale at which the relationship between
 each response variable and each landscape metric is strongest (i.e. scale
 of effect; Jackson & Fahrig, 2015). Forest cover was estimated by
 dividing the total amount of old-growth forest area in the landscape by
 the landscape area × 100 (%). Matrix openness was calculated as the
 percentage of the matrix covered by open areas (i.e. cattle pastures,
 annual crops, water bodies and human settlements). Patch density was
 calculated as the number of old-growth forest patches in the landscape
 divided by the landscape area (<em>n</em>/ha). Edge density
 was estimated as the length of the perimeter of all old-growth forest
 patches in the landscape divided by the landscape area (m/ha).
 References: Jackson, H. B. & Fahrig,
 L. 2015. Are ecologists conducting research at the optimal scale? Global
 Ecology and Biogeography, 24, 52–63. Villéger, S.,
 Mason, N. W. H., & Mouillot, D. (2008). New multidimensional
 functional diversity indices for a multifaceted framework in functional
 ecology. <em>Ecology</em>, <em>89</em>,
 2290–2301.