Long-term Herbivore Exclusion for Recovery of Buckbrush (Ceanothus fendleri ) Populations During Restoration of Ponderosa Pine Forests in Northern Arizona

Abstract

Open conditions created by restoration activities in ponderosa pine ( Pinus ponderosa ) forests of the American Southwest can lead to increases in understory plant productivity but also attract large ungulate herbivores. In this study, we remeasured buckbrush ( Ceanothus fendleri ) plants on permanent plots to determine effects of long-term herbivore exclusion on population abundance and potential reproduction. Results showed that survival of buckbrush was significantly lower on unprotected plots compared with plants given long-term herbivore protection. A greater proportion of the highest stem density class ( 50 stems m−2 ) was found on long-term protection plots compared with short-term protection or unprotected groups. The unprotected group was overwhelmingly (90%) made up of plots with less than 10 aerial stems m−2 . Plots with long-term protection had a significantly greater proportion of plots in the highest flowering class ( 50% of aerial stems flowering) than unprotected plots. Logistic regression showed a strong, positive relationship ( p = 0.61) between the probability of flowering and plant height. Results indicated that short-term protection following forest restoration treatments marginally improves survival of buckbrush in these ecosystems. However, herbivory pressure remained high over the 12-year study period and detrimentally affected potential reproduction of plants exposed to large herbivores. These findings generally suggest that short-term protection may not be sufficient to conserve buckbrush populations over time and high herbivory pressure may be constraining understory responses and slowing restoration success.