Influence of Oak in Pine Forests of Central Arizona on Selected Nutrients of Forest Floor and Soil

Abstract

AbstractThis study focused on the effect of Gambel oak (Quercus gambelii Nutt.), a common subdominant and understory species in a ponderosa pine (Pinus ponderosa Laws.) forest in central Arizona, on selected nutrient properties of the forest floor and soil. Samples of the L, F, and H layers (Oi, Oe, and Oa horizons, respectively) of the forest floor and the 0‐ to 5‐ and 5‐ to 15‐ cm layers of mineral soil from 33 randomly selected stands of ponderosa pine with varying amounts of Gambel oak (from 0 to about 75% of total basal area) were collected and analyzed for total N, P, S, total and exchangeable Ca, Mg, and K, and organic C. Chemical properties of fresh litterfall suggested the potential for oak to strongly influence soil fertility of the pine forest. In the forest floor as a whole, only C and Mg concentrations were not positively correlated with oak basal area. In separate layers (L, F, and H) of the forest floor, the concentration of all measured nutrients increased with oak. Increases in nutrient concentration for these layers ranged up to 133% for K in the H layer at 70% oak basal area. Increased oak influenced C and N concentration more than other nutrients in the 0‐ to 5‐ and 5‐ to 15‐ cm soil layers. Increase in oak basal area to 70% resulted in a downward shift (i.e., redistribution) of C, N, P, and S within the forest floor. Hence, these nutrients were more heavily concentrated in the H than in the L and F layers with increases in oak from 0 to 70% of total basal area. Elemental ratios (C/N, C/P, C/S, C/Ca, C/Mg, and C/K) for all layers of the forest floor declined sharply as percentage oak basal area increased.