Edge-related loss of tree phylogenetic diversity in the severely fragmented Brazilian Atlantic forest

Abstract

Deforestation and forest fragmentation are known major causes of nonrandom extinction, but there is no information about their impact on the phylogenetic diversity of the remaining species assemblages. Using a large vegetation dataset from an old hyper-fragmented landscape in the Brazilian Atlantic rainforest we assess whether the local extirpation of tree species and functional impoverishment of tree assemblages reduce the phylogenetic diversity of the remaining tree assemblages. We detected a significant loss of tree phylogenetic diversity in forest edges, but not in core areas of small (<80 ha) forest fragments. This was attributed to a reduction of 11% in the average phylogenetic distance between any two randomly chosen individuals from forest edges; an increase of 17% in the average phylogenetic distance to closest non-conspecific relative for each individual in forest edges; and to the potential manifestation of late edge effects in the core areas of small forest remnants. We found no evidence supporting fragmentation-induced phylogenetic clustering or evenness. This could be explained by the low phylogenetic conservatism of key life-history traits corresponding to vulnerable species. Edge effects must be reduced to effectively protect tree phylogenetic diversity in the severely fragmented Brazilian Atlantic forest.

Figure 1. Study landscape at the Brazilian Atlantic forest.

(A) Northeastern Brazil, where this study was conducted. (B) Distribution of the Atlantic forest of northeast Brazil ( =  Pernambuco Center of Endemism), note original (grey) and current (black) distribution of this forest in the region; white rectangle represents the study landscape (amplified in C). (C) Study landscape showing the location of 75 plots of 0.1 ha sampled to describe the phylogenetic diversity of tree assemblages in forest edges, small forest fragments, secondary forest patches and old-growth interior forests. Dark shaded polygons represent the forest fragments sampled; lightly shaded and white areas represent the remaining Atlantic forest remnants that were not sampled and a uniform matrix of sugarcane monoculture, respectively.

Figure 2. The relationship between forest age and phylogenetic diversity metrics.

The relationship between the age of 25 secondary forest patches within the Coimbra Forest and (A) the mean phylogenetic distance (MPD), (B) mean nearest taxon phylogenetic distance (MNTD), (C) net relatedness index (NRI), and (D) nearest taxon index (NTI) at Serra Grande, northeastern Brazil. R² values are shown for significant relationships. The mean (solid line), median (thin line), 25th and 75th percentiles (boundaries of boxes), 10th and 90th percentiles (whiskers above and below box plots), and each outlier (points outside 10th and 90th) are also indicated for equal-sized plots within small forest fragments (F, n = 20), forest edges (E, n = 10) and old-growth forest interior areas (C, n = 20). Values outside the area delimited by dotted lines in plots C and D indicate significant phylogenetic clustering (>1.96) and overdispersion (< −1.96).

Figure 3. The relationship between functional attributes of tree assemblages and phylogenetic diversity metrics.

The correlation between the proportion of species within vulnerable functional groups and the mean phylogenetic distance (MPD), mean nearest taxon phylogenetic distance (MNTD), net relatedness index (NRI), and nearest taxon index (NTI) at Serra Grande, northeastern Brazil. Triangles, open circles, and dark shaded circles represent plots in small forest fragments (n = 20), forest edges (n = 10), and old-growth forest interior areas (n = 20), respectively. Pearson product-moment correlation coefficients are shown for significant relationships (P<0.05).