Research Note<br><br>Volume–biomass functions reveal the effect of browsing on three Moroccan dwarf shrubs

Abstract

We studied the effects of browsing on the plant architecture and volume-biomass relationships of three dominant dwarf shrubs – Artemisia herba-alba, A. mesatlantica and Teucrium mideltense – in a sagebrush steppe in the Central High Atlas Mountains, southern Morocco. For this purpose, we developed power-law volume-biomass functions based on nonlinear regressions for each of these species, under both browsed and unbrowsed conditions. These functions were then applied to individual-based annual monitoring data from inside and outside a browsing exclosure to calculate standing biomass for each of the years from 2004 to 2009. The biomass of the three species was well predicted by the allometric functions, and different functions for the browsed and unbrowsed conditions reflected changes in plant architecture. Browsing had a significant negative impact on biomass for A. herba-alba but not for A. mesatlantica, whereas its effects on T. mideltense were inconsistent between years. The fact that the latter two species hardly benefited from browsing exclusion might be because of increased competition from the more dominant A. herba-alba. During the study period, the standing biomass increased whether or not there was browsing, which might be because of the recovery of the shrubs after a preceding severe drought. Further studies are needed in order to investigate the generality of the findings.

Keywords: allometric function, Atlas Mountains, nonlinear regression, permanent plot, plant architecture, standing biomass

African Journal of Range & Forage Science 2012, 29(1): 31–36