Changes in grassland canopy structure across a precipitation gradient

Abstract

In temperate grasslands, the relative importance of above-ground competition for light compared to belowground competition for water and nutrients is hypothesized to increase with increasing precipitation. Thus, competition for light is likely to exert an increasing influence on canopy structure and species composition as precipitation increases. We quantified canopy structure, light availability and changes in species composition at seven sites across the central grassland region of the United States to determine how these properties change across a precipitation gradient. Across the region, there was a disproportionate increase in leaf area and canopy height with increasing precipitation, indicating that plants become taller and leafier across the gradient. Leaf area index increased by a factor of 12 across the gradient while above-ground net primary productivity increased by a factor of only 5.5. As precipitation increased, there was decreased light availability at the soil surface, increased seasonal variability in light transmission, increased biomass and leaf area at higher canopy layers and an increased proportion of tallstatured species. These observed changes in canopy structure support the prediction that competition for light increases in importance with increasing precipitation.Nomenclature: Barkley (1986).Abbreviations: ANPP = Above-ground net primary productivity; CO = Colorado; LAI = Leaf area index; MAP = Mean annual precipitation; NE = Nebraska; NMP = Northern mixed prairie; PAR = Photosynthetically active radiation; SGS = Short-grass steppe; TGP = Tallgrass prairie.

Environmental control of leaf area production: Implications for vegetation and land‐surface modeling

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Simple physics-based models of compensatory plant water uptake: concepts and eco-hydrological consequences

“…Both aboveground biomass and leaf area index of temperate grasslands in the continental USA are known to be strongly and more or less linearly dependent on precipitation (e.g. Sala et al, 1988;Lane et al, 2000;Polley et al, 2011). The maximum leaf area index at the eight sites (Table 3) was therefore estimated from a linear regression equation (=0.00344 times annual precipitation in mm; R 2 = 0.6, p < 0.0001) fitted to data on temperate grasslands in the USA (Asner et al, 2003;www.daac.ornl.gov).…”

Comparison of different methods for measuring leaf area index in a mixed grassland

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