Relative contribution of biotic and abiotic factors to stemflow production and funneling efficiency: A long-term field study on a xerophytic shrub species in Tengger Desert of northern China

Abstract

Stemflow production has been reported to be influenced by a suite of biotic and abiotic factors. Nevertheless, relative contributions of biotic and abiotic factors to stemflow production and funneling efficiency were largely unclear due to complex interactions among those factors. In this study, stemflow of nine xerophytic shrubs of Caragana korshinskii were measured in nearly nine growing seasons from 2010 to 2018 within a desert area of northern China, accompanying with observing on six biotic variables (shrub morphological attributes) and ten abiotic variables (meteorological conditions). We performed boosted regression trees (BRT) model to evaluate the relative contribution (θ) of each biotic and abiotic variable to stemflow volume (SFv), stemflow percentage (SFp), and funneling ratio (FR), associating with partial dependence plots (PDPs) to visualize the effects of individual explanatory variables on SFv, SFp, and FR, respectively. Generally, we observed that larger shrubs generated more SFv, while had lower SFp and FR. BRT analysis demonstrated that biotic variables outweighed abiotic variables by 1.5-fold as to their contribution to SFv, whereas abiotic variables prevailed for SFp and FR, respectively. Differences in θ between variables for SFv (CV = 146%) were much pronounced than for SFp (CV = 57%) and FR (CV = 26%), with the foremost three influential variables for SFv ranking in descending orders of θ by rainfall amount (33.2%), basal area (20.9%), projected canopy area (15.1%), and that for SFp by projected canopy area (13.2%), rainfall amount (13.0%), and air temperature (11.1%), and that for FR by antecedent dry period (9.1%), rainfall amount (8.4%), and wind speed (8.3%). The quantitative and mechanistic explanations regarding the effects of biotic and abiotic variables on three stemflow parameters from the present study are expected to be applicable to other shrub species within arid and semi-arid ecosystems.