Recent efforts to restore western mixed-conifer forests to ecosystem structure and function that approximates historical conditions have contributed to the initiation of large-scale and long-term ecological research and monitoring projects. The interdisciplinary National Fire and Fire Surrogate Network Study is among the most comprehensive of these studies, but finer-scale vegetative response parameters were not included in the original network study design. For example, it is not yet clear how these large-scale stand manipulations (prescribed fire alone, mechanical thinning with an emphasis on retaining P. ponderosa [MechPine], mechanical thinning with an emphasis on retaining large trees regardless of species [MechSize], the combination of prescribed fire and MechPine, and an untreated control) differentially affect the foliar nutrient concentrations of the historically or currently dominant tree species, nor how long such effects persist. In order to address this question, I analyzed foliar N and P concentrations in Pinus ponderosa and Abies concolor for 6 and 10 years of needle cohorts, respectively.

Results/Conclusions

Preliminary analyses show that treatment differences were evident 3 yrs post-fire for A. concolor and 1 yr post-fire for P. ponderosa. For those needle cohorts, the combination of thinning and burning increased A. concolor foliar P relative to the control, whereas neither of the thinning treatments nor prescribed fire alone affected P relative to the control, suggesting that there is a synergistic effect of thinning and prescribed fire. In contrast, P. ponderosa foliar P decreased in all treatments relative to the control. Foliar P concentration was greater in the MechSize than the MechPine thinning treatment for both A. concolor and P. ponderosa. The combination of thinning and prescribed fire decreased P. ponderosa foliar N concentration relative to the control, but these effects were evident only in needles formed in the first two growing seasons following the prescribed fire. Foliar N concentrations for A. concolor will be included in the final analysis. These preliminary results suggest that the effects of large-scale forest restoration treatments on foliar N and P differ between two California conifer species, and become evident for each species at different times following treatment.