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 < 0.001; R2 = 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.
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