Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2004
Publication Date: 10/15/2004
Citation: Northup, B.K., Zitzer, S.F., Archer, S.A., McMurtry, C.R., Boutton, T.W. 2004. Aboveground biomass, C and N contents of woody species in a subtropical thornscrub parkland. Journal of Arid Environments. 62(1):23-43. Interpretive Summary: Accurately describing the amounts of stems and leaves in canopies of woody plants is a difficult process. Traditionally, it has required the harvest of plants and their division into different size classes of stems and leaves. However, this is a time-consuming and costly process that can seriously affect the remaining plants, and points to the need for fast, accurate methods that do not require harvesting. A different approach is to use sets of equations that predict amounts of stems and leaves using simple measurements of plants. In this study, we described how weights and nutrient contents of 10 common woody species of southern Texas could be estimated with regression equations. Fifteen to 38 plants of each species were measured to describe plant canopies. We then harvested these plants to ground level, divided them into different stem size classes and leaves, defined dry weights, and analyzed samples for carbon and nitrogen. Measures of canopy area and total diameter of stems at the soil surface were then related to amounts of leaves, stems, carbon and nitrogen in plants to build the necessary equations. Canopy area was more accurate at predicting amounts of wood, leaves, carbon and nitrogen than the total diameter of stems. However, this improvement was not large, and either canopy area or basal diameter could be used. These equations are potentially useful for future estimates of the amount of browse available to animals, estimating plant materials by remote sensing data, or evaluating models of the function of nutrient cycles.
Technical Abstract: Biomass production and accumulation of woody plants integrates responses to biotic and abiotic features of their environment, and are important metrics to understanding and managing plant communities in southern Texas and modeling ecosystem processes. Direct assessments of shrub biomass is labor-intensive, a major disturbance to study sites, and often infeasible in remote areas or when plants are large, pointing to the need for fast and accurate non-destructive techniques. In this study, we developed predictive equations to describe aboveground biomass and nutrient contents of 10 common tree and shrub species in subtropical thorn parkland of southern Texas. Plant canopies were measured (n=15 to 38 per species) to describe total stem basal diameter at the soil surface and projected canopy area as predictors. Measured plants were harvested to ground level, divided into three stem (two live stem size classes and dead stems) fractions and leaves, and representative sub-samples collected and dried to develop multipliers for describing dry biomass. Samples were also collected and analyzed for carbon and nitrogen contents. Linear regressions were applied to Ln transformed variables to predict biomass fractions, and best-fit non-linear equations were applied to predict nutrient contents. Projected canopy area yielded slightly more precise estimates of biomass and nutrient concentrations than stem basal diameter, though all equations (except dead stems) had r2>0.75 (P<0.05). These equations are potentially useful for: (a) estimating availability of browse; (b) estimating woody biomass and nutrient content from remotely sensed data, and (c) parameterizing and evaluating models of ecosystem biogeochemistry.