Community assembly and functional traits

Can we use functional trait relationships to better optimize multiple ecosystem services in complex landscapes? Can it guide species selection in restoration plantings?

Community assembly research asks questions of species diversity and distribution. Why is a species present in one place but not another? Are there rules we can use to predict community composition? In relation to environmental restoration and management, can we manipulate community assembly to achieve our goals?

A community is composed of species that have arrived at the site, survived its environment and interacted successfully with other species. If this process is not random, then patterns of functional traits across a landscape can help us understand species distributions. Differences in seed size might limit species arrival, for example, whereas different nitrogen uptake strategies and growth rates may control species survival. Relating dispersal and environmental constraints to functional traits can indicate the mechanisms of community assembly.

Species also modify their environments, and a trait-based approach can describe these processes. Describing traits that affect the environment helps both to predict patterns of community assembly – nitrogen fixers, for example, may facilitate other species entering community – and to anticipate the ecosystem functions and services a species is likely to provide – plant with nitrogen-rich leaves, for example, are likely to make good forage for cattle.

We apply a trait framework in several lines of research:

Multiple ecosystem services in California rangelands

Rangelands support a billion dollar cattle industry in California, but are increasingly being valued as potential carbon sinks. Will the same species assemblages maximize both carbon sequestration and forage production? We tested this question by screening the traits of fifty rangeland plant species and pairing these data with above and belowground biomass and soil carbon measurements from pastures across the Sierra Foothills Research and Extension Center. Forage production was greatest in pastures with tall grasses that had high leaf quality (low C:N ratios), whereas soil carbon was greatest in pastures where plant species had a diversity of rooting strategies. These traits were not mutually exclusive, however, and so pastures that had tall plants with diverse root morphologies were hotspots of carbon storage and forage production. These results are currently in press at Journal of Ecology and more research with this trait database is ongoing.

People involved: Dr. Brad Butterfield, Northern Arizona University, Hui Gao, visiting student from China, and Dr. Marko Spasojevic, University of California, Davis

Filling the “weed-shaped hole” at Strawberry Creek

Strawberry Creek, which cuts through the UC Berkeley campus, has long been a focus of restoration efforts for the campus community. Much of this work has involved removing invasive ivy that coats the Creek’s banks. Removing invasive species without establishing other species however can leave a “weed-shaped hole” that invasive species can easily recolonize. In response recent restoration work on the Creek has included native planting. Based on the principle of “limiting similarity,” which suggests that two species cannot coexist if they have very similar traits and resource strategies, we hypothesized that these plantings will be most effective if they include species that have similar traits to ivy. We are currently screening the traits of fifty riparian and woodland plant species, and will use this information to out-plant experimental assemblages that vary in their trait similarity to ivy. This work is funded by the Green Initiative Fund and is in collaboration with the Strawberry Creek Restoration Program.

People involved: Nathan Bickart, Lawrence Fernandez, Lauren Hallett