Comparing the predictive capacity of allometric models in estimating grass biomass in a desert grassland

Authors: NAITO, A.T. - Northern Michigan University; ARCHER, S.R. - University Of Arizona; Heilman, Philip - Phil

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2024
Publication Date: 1/25/2024
Citation: Naito, A.T., Archer, S., Heilman, P. 2024. Comparing the predictive capacity of allometric models in estimating grass biomass in a desert grassland. Rangeland Ecology and Management. 93:72-76. https://doi.org/10.1016/j.rama.2024.01.004.
DOI: https://doi.org/10.1016/j.rama.2024.01.004

Interpretive Summary: Quantifying rangeland production is difficult and time consuming. One approach is using so-called “allometric” models that relate easy to perform measurements of plant shape to an estimate of aboveground biomass for an individual plant. The method is a rapid and nondestructive tool appropriate for perennial grass species. In this study, we compared allometric relationships developed on different soils on the Sonoran Desert Santa Rita Experimental Range in southern Arizona, USA in 2005 and 2015. We used peak growing season field measurements to develop single- and multi-species regression models based on basal diameter and height to predict the current year’s aboveground biomass for seven perennial grass species. Basal diameter exhibited the strongest relationship among single-species (adjusted R2 = 0.54 to 0.87) and multi-species models (adjusted R2 = 0.73). Our models generally underestimated observed 2015 AGB on our loamy site, whereas models developed in 2005 on a sandier site overestimated the 2015 biomass on our site. Our results suggest site-specific allometric models should be used when possible. However, in lieu of such models, relationships developed at other sites or at other times may be appropriate depending upon the level of precision needed to address a specific research question.

Technical Abstract: Allometric models provide a rapid, nondestructive means for estimating aboveground biomass (AGB) of perennial grass species. In the absence of site-specific models, allometric relationships developed at other sites at other times are often used. This implicitly assumes that size-biomass relationships are highly robust. In this study, we assess the comparability of allometric relationships developed at two points in time (2005 and 2015) on different soils on a Sonoran Desert savanna in southern Arizona. We used peak growing season field measurements to develop single-species and multispecies regression models using basal diameter and height to predict the current year's AGB for seven perennial grass species. Basal diameter exhibited the strongest relationship with AGB among single-species (adjusted R2'='0.54 to 0.87) and multispecies models (adjusted R2'='0.73). Inclusion of height did little to improve biomass predictions. Our models generally underestimated observed 2015 AGB on the loamy site, whereas models developed in 2005 on a sandier site overestimated the 2015 AGB. Results suggest site-specific allometric models should be used when possible. However, in lieu of such models, relationships developed at other sites or at other times may be appropriate depending on the level of precision needed to address a specific research question.