DEFINING PLANTS BY THEIR EFFECTS ON ECOSYSTEM FUNCTIONS

Authors: Comas, Louise; Goslee, Sarah; Skinner, Robert; Sanderson, Matt

Submitted to: Ecological Society of America Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2004
Publication Date: 8/6/2004
Citation: Comas, L.H., Goslee, S.C., Skinner, R.H., Sanderson, M.A. 2004. Defining plants functional types by their potential effects on ecosystem properties. Proceeding of the Ecology Society of America, August 1-6, 2004, Portland, Oregon p. 102.

Interpretive Summary: The plant species present in Northeastern pastures fill a variety of different roles. The more clearly we understand these roles, the more effective our selection and management of plant species composition will be. We identified six plant functions (early spring productivity, spring productivity, fall productivity, drought avoidance, gap colonization, and growth response to low nitrogen) that are important for maintaining production in grazed ecosystems. We measured a wide variety of traits related to ecosystem functions of 21 different pasture plant species. Most research has attempted to group species based on similarities in their traits but we found that this did not work well. Instead, we developed a new approach to identify important functions performed by each species, as well as trade-offs among different functions that species can serve. The approach we developed can be used to select the appropriate species to provide the mix of functions needed to maintain forage production in Northeastern grazing lands.

Technical Abstract: Interest in defining plants by their ecosystem effects is growing as ecologists strive to understand ecosystems from a functional perspective. We used plant physiological, morphological, and seasonal growth measurements of 21 species from a combination of greenhouse and field studies to identify ways plants can directly affect productivity of temperate managed grasslands. We explored the use of standard multivariate methods to distinguish plant functional types (PFTs) among species. Species distributions were continuous across all axes, thus we did not find discrete clustering needed to identify PFTs. Analyses could not clearly distinguish general forb, grass and legume classifications, indicating these classifications were not adequate to describe functional differences among these plants. Consequently, a new perspective on PFTs was needed. Rather than identify PFTs, we identified six individual ecosystem functions of the plant community with potential value to managed grasslands: early spring productivity, spring productivity, drought avoidance, fall productivity, gap colonization and growth maintenance under low N. The ability of species to serve individual functions and trade-offs in service of functions was examined using factor analysis. This new approach offers a realistic view of the multiple functions of plants and a perspective that will allow us to mechanistically examine how different plants affect ecosystem performance.