Non-destructive estimation of canopy gap fractions and shrub canopy volume of dominant shrub species in the Mojave desert

Variability of desert shrub canopy volume or above ground biomass can provide a useful metric for assessment of the response of desert shrubs to vehicular impacts, and can be used to determine the recovery and resiliency of different desert plant communities to such impacts. Traditional methods for measuring desert shrub canopy volume are inefficient and require destructive sampling. Field sampling methods that eliminate the need for destructive sampling are required to measure the vertical structure of desert shrubs for the purpose of measuring shrub volumes. Plant canopy analyzers and hemispheric photographs have been analyzed for the purpose of estimating canopy characteristics in forested and agricultural environments, but the utility of such instruments for measuring vertical structure of desert shrubs has not been fully explored. In this research, plant canopy gap fractions were estimated for 96 shrubs in the Mojave Desert using both a Li-Cor LAI 2000 Plant Canopy Analyzer and skyward looking hemispheric photographs collected with a digital camera with a fisheye lens attached. Gap fraction estimates from both estimates were comparable and no significant difference was found between estimates collected with both instruments. The LAI was identified as the preferred method for measuring gap fractions due to superior efficiency in data collection and processing. Using gap fractions recorded with the LAI, a model was developed to estimate the volume of desert shrub canopies that utilizes a combination of non-destructive, in situ measurements of plant canopy height and width and estimates of canopy area derived from remotely sensed imagery.