Abstract:

Gallery forests within grasslands have natural edges with open environments and offer a unique opportunity to examine how species performances vary across environmental gradients. Here, we asked if demographic rates of tree functional groups varied along the edge, if we could explain differences in plant strategies and performance through functional traits and which traits increase growth and survival in natural edges.

We examine mortality and recruitment within the first 10 m of natural edges of eight gallery forests using demographic data from five annual inventories. We defined a priori plant strategies using tree functional groups: light demanding, pioneer and shade tolerant.

The shade-tolerant group had the lowest mortality rates and basal area (BA) loss, while pioneer and light-demanding species had similar behavior for these rates. The survival and growth of functional groups were affected differently by the distance from the edge. The pioneer group survived more near the edge, while light-demanding and shade-tolerant groups toward the forest interior. All groups had higher growth in the grassland. Those differences could be explained by functional traits since most species have an acquisition strategy: higher specific leaf area and growth, lower leaf dry matter content, lighter stem density, deeper crowns and less slender stems. Acquisitive traits enhanced growth. However, mortality selected both strategies, but in distinct edge’s zones. Our study showed that the high diversity found in natural edges can be explained by a niche and functional perspective, where differences in functional traits lead to differential performance along the environmental gradient.

Key words: edges diversity, gradient, niche hypothesis, SLA, LDMC