My recent article (and photo taken on Volcan Cacao) made the cover of Journal of Vegetation Science in a special issue about plant functional diversity. This article highlights the bulk of my PhD research, most of which I spent running around in ACG backyard setting up vegetation plots and collecting plant traits everywhere from coastal mangroves to cloud forest volcanoes.
At the heart of this study, I was interested in testing a simple idea in ecology: at high latitudes and elevations the limiting factor for plant life includes abiotic conditions like cold temperatures whereas at low latitudes and elevations the limiting factor for plant life includes increased competition between plants for nutrients, light, and water. To test this idea we can compare plant functional diversity across elevational and latitudinal gradients.
Functional diversity can be defined as the different types of ecological strategies within a community. For example, plants can grow along a spectrum from very fast (Cochlospermum vitifolium; poroporo) to very slow (Hymenea courbaril; nispero). But how can we quantify functional strategies within plants? Fortunately, several leaf traits reveal a plant’s ecological strategy. Both leaf area and leaf mass provide an index of where a plant species falls along the spectrum of fast to slow growth.
By measuring these leaf traits in plant communities across elevational gradients (like the one in ACG) we can start to develop a picture of how plant communities are functioning which, in turn, can reveal the main factors limiting plant functional diversity.
In this study, I showed that in the tropics functional diversity tends to be higher than expected at low elevations. In contrast, at high elevations and at high latitudes functional diversity tends to be lower than expected. These signatures are thought to reflect biotic and abiotic limitations, respectively, on plant communities.
So what does this mean in ACG? Well, for starters, tropical dry forests appear to have some of the highest functional diversity compared to other wetter habitats. Is that because competition for water is more intense here? Maybe. But I am beginning to think that it may have more to do with the higher topographical heterogeneity and mosaic of forest types within tropical dry forests. The contrast between mesic and xeric forests allows very different species to coexist within the tropical dry forest habitat. I explore this idea in a recent book chapter too and in ongoing projects with UNAM collaborators Angelina Martínez-Yrízar and Alberto Búrquez. Questions? Contact me!