Dry-weight-rank method assessment in heterogenous communities

Assessment of herbaceous standing crop in heterogeneous range plant communi ties requires large numbers of samples to account for inherent variability. The dry-weight-rank method (DWR) was developed to eliminate the need for c lipping and sorting of herbage to determine relative proportions on a dry w eight basis. The technique was assessed for applicability and accuracy in t he mixed prairie of the Texas Rolling Plains. Much of the herbage within th e communities investigated occurred in monospecific patches that resulted i n only 15% of qnadrats having 3 species ranked for which DWR was designed. Non-harvest methods of determining grass proportion by species were compare d to harvested proportions in mesquite (Prosopis glandulosa Torr.) and redb erry juniper (Juniperus pinchotii Sudw.) communities. Estimation methods ev aluated were 1) harvest by species, 2) weight estimation by species, 3) DWR with quadrat weighting, 4) unweighted estimated proportion by species, and 5) unweighted DWR. Correlations of non-harvest to harvest proportions were improved with quadr at weighting. Weighting improved values more in the juniper than in the mes quite communities. Although cumulative ranking of DWR multipliers was neces sary in 85% of sample quadrats, there was a high correlation (r(2)>0.995) b etween weight estimation and weighted DWR and between estimated proportion and unweighted DWR. This indicates that cumulative ranking with the origina l DWR multipliers was virtually the same as evaluator estimation. Analysis of variance indicated significant differences in non-harvest metho ds compared to harvesting. Quadrat weighting with DWR was necessary to draw the same statistical conclusions between means that harvest data provided. Ranks are easier to apply and more likely to be applied similarly by indiv idual evaluators than estimated proportions. For sites with high standing c rop variation and patchiness of species that require considerable nse of cu mulative ranking, DWR with quadrat weighting provides adequate determinatio n of species proportions of biomass.