Plant Parameters for Plant Functional Groups of Western Rangelands to Enable Process-based Simulation Modeling

Aims: To quantify western rangeland plant parameters for a wide range of representative species in the region.

Study Design: Use field measurements to quantify leaf area index (LAI), light extinction coefficient (k), radiation use efficiency (RUE), and nutrient concentrations of representative plant species. Measure fraction of intercepted photosynthetically active radiation, leaf area index, and dry matter during the growing season. Use these plant parameters to simulate five representative ecological sites in the region.

Place and Duration of Study: Beaver, UT, Fillmore, UT, Stone, ID, Logan, UT, Bridger, MT, Aberdeen, ID, Lockeford, CA, and Meeker, CO in 2011 and 2012.

Methodology: Fraction of light intercepted was measured repeatedly above and below the plant canopy. Plant samples were harvested, dried until constant weight, then weighed. Nitrogen and phosphorus concentrations were determined using standard protocols.

LAI and RUE were calculated from the destructive samples, the leaf area estimates, the light interception, and the dry weights.

Results: LAImax of grass generally ranged from 1.0 to 2.1. Values for k generally ranged from -0.50 to -0.85. RUE generally ranged from 0.70 to 1.3g MJ-1. For forbs, values for LAImax of the two leguminous forbs were 0.6 and nearly 3.0. Values for LAImax for the non-leguminous forbs ranged from 0.5 to about 1.1. Correspondingly, among the five genera, k varied from -0.3 to -0.6 and RUE varied from near 1.1 to 4.4g MJ-1.

For shrubs, Prunus and Cleome values of LAImax were 0.2 and 1.5; values for k were -0.5 and -1.65, respectively.

Conclusion: Results demonstrated that assessments with process-based models such as ALMANAC are feasible with realistic estimates of plant parameters for plant functional groups in a region. Our measurements of individual species within these groups provide estimates for the needed parameters for the group for these assessments