Quantifying woody plant abundance has often proven difficult in the field for reasons that include irregular plant morphology, between observer variability, and lack of standardized techniques. One potential solution to these challenges is the use of ground-based photographic technology. We developed a photo-based technique could to monitor changes in willow abundance over time and estimate changes in abundance associated with herbivory. We focused on young willows (< 2m in height) because this size class represents a critical life history stage for establishment of willow clumps. In August of 2000 and 2001 we harvested 25 willow clumps and clamped them in front of a 150 x 200cm fluorescent orange photoboard. Clumps were defoliated of photosynthetically active tissue (leaves and tips of current annual stem growth – PAT) by hand in 4 to 7 increments and photographed before and after each removal. Images were scanned to digital format and the degree of photoboard obstruction was determined using Adobe Photoshop 4.0 software. Regression analysis indicated that visual obstruction of the photoboard was a good predictor of both total clump PAT weight as well as PAT weight remaining following sequential defoliations. These results suggest our technique provides a reliable index of both willow abundance and utilization within the size class of willow tested. Results may differ using larger willows with increased woody biomass and additional research is needed to determine inter-species variability in the relationships described above.

Related publications

Boyd, C.S. and T.J. Svejcar. 2005. A visual obstruction technique for photo monitoring of willow clumps. Rangeland Ecology and Management 58:434-438.

Boyd, C.S. and T.J. Svejcar. (in press). A visual obstruction-based technique for photo monitoring of willow clumps. In 2004 Progress Report. Eastern Oregon Agricultural Research Center, Burns, OR.

If you are interested in this study, contact Chad Boyd