Ungulate herbivory on buckbrush in an Arizona ponderosa pine forest

Abstract

Monitoring processes that affect plant population dynamics and determine community structure is central in forest restoration ecology. To study effects of mule deer (Odocoileus hemionus) and elk (Cervus elaphus) on buckbrush (Ceanothus fendleri Gray), we built exclosures around 90 plant-centered plots in 3 ponderosa pine (Pinus ponderosa Laws.) forest restoration management units and compared vegetative and flowering characteristics with unprotected plots for 2 years. On unprotected plots, 69% of the current-year branches were browsed during the first year and 44% were browsed the second year. There was no difference in number of aerial stems or current-year branches in the first year, yet stems on protected plots were longer (24.1 cm; P < 0.01) and retained more than 4 times the current-year biomass (1.4 g stem-1; P < 0.01) than those on unprotected plots (12.9 cm and 0.3 g stem-1, respectively). Stem number, length and diameter, number of current-year branches, and current-year biomass on protected plots were all greater (P < 0.01) than on unprotected plots in the second year. Stems on protected plots had significantly higher (P < 0.01) length-diameter ratios and had fewer current-year branches per unit length (P < 0.05) than unprotected stems. Flowering stems were found on significantly (P < 0.05) more protected plots (55%) than unprotected plots (8%) in the second year. Effects of ungulate herbivores on buckbrush size, stem recruitment, morphology, and flowering represent important constraints to early understory development and restoration in this Southwest ponderosa pine forest.