Submitted to: Oikos
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/29/2013
Publication Date: 8/26/2013
Citation: Polley, H.W., Isbell, F.I., Wilsey, B.J. 2013. Plant functional traits improve diversity-based predictions of temporal stability of grassland productivity. Oikos. 122:1275-1282. Interpretive Summary: Plant growth varies among years in response to inter-annual variation in precipitation. Variability in plant growth (biomass production) usually is smaller and the stability of annual production is greater when many rather than few plant species are present in grassland and other multi-species plant communities. But stability of plant production likely also depends on the relative abundances of and growth-related traits possessed by species in communities. We determined effects of species number (richness), abundances, and traits on inter-annual stability of aboveground biomass production of grassland communities over an 11-year period in central Texas, USA. Annual precipitation varied by greater than a factor of three leading to large inter-annual variation in aboveground production of communities with different numbers and species of grassland plants. Inter-annual variation in production was least and stability was greatest in communities that were not strongly dominated by only two species, contained many rather than few species, and in which dominant species either rooted shallowly, had dense leaves with little water content relative to dry weight, or responded to the wettest year with a minimal increase in production. Our results indicate that land managers may reduce inter-annual variability in grassland production by introducing species that root shallowly or have dense leaves and managing so as to prevent one or two species from producing the bulk of community biomass.
Technical Abstract: Aboveground net primary productivity (ANPP) varies in response to temporal fluctuations in weather. Temporal stability (mean/standard deviation) of community ANPP may be increased, on average, by increasing plant species richness, but stability also may differ widely at a given richness level implying that stability depends partly on relative abundances and functional properties of species present in communities. We measured temporal stability in ANPP over an 11-year period in field plots in central Texas, USA in which we varied the richness and relative abundances of perennial grassland species at planting. We sought to identify species relative abundance patterns and functional traits that could be used to predict the temporal stability of community ANPP in lieu of or addition to information on species richness. Annual precipitation varied by greater than a factor of three leading to large inter-annual variation in ANPP. A quadratic function of richness explained 32% of the variance in community stability. Regression models that included richness plus the fraction of community ANPP produced by the two dominant species in combination with abundance-weighted values of either the responses of dominant species to greater-than-average precipitation, the fraction of sampled root biomass at 20-45 cm depth, or the leaf dry matter content (LDMC; leaf dry mass/saturated weight) of species grown in monocultures explained 59%-69% of the variance in community stability. Stability was greatest in communities that were not strongly dominated by only two species and in which dominant species rooted shallowly, had high values of LDMC, or responded to the wettest year with a minimal increase in ANPP when grown in monoculture. Our results indicate that the temporal stability of grassland ANPP may depend as much on species abundance patterns and functional traits linked to plant responses to precipitation variability as on species richness per se.