Surface fuel accumulation and decomposition in old-growth pine-mixed conifer forests, northwestern Mexico.

Background: Stand-level forest structure varies spatially and surface fuels would be expected to vary as well. We measured surface fuel deposition and decomposition within old-growth Jeffery pine (Pinus jeffreyi Balf.)-mixed conifer forests to quantify rates of change and examine relationships with overstory structure and composition. Results: Annual fuel deposition ranged from 0.7 to 20.1 Mg ha⁻¹ for litter and 0.2 to 0.8 Mg ha⁻¹ for woody fuels, exhibiting large temporal and spatial variation, and corresponded with annual precipitation during the study period. Surface fuel deposition had high spatial heterogeneity and was predicted by stand structure such as basal area and canopy cover, particularly for litter deposition, which was the main contributor to total fuel loadings in this system. Jeffery pine litter decomposition rate of 7 to 11% yr⁻¹ over the six-year study period is among the lowest compared to other conifer forests in western North America. Conclusions: Two sites were distinguished by edaphic and structural characteristics, but exhibited similarities in fuels dynamics. Incorporating within-stand variation into fuel modeling could improve the accuracy in predicting fire behavior, fire effects, and stand progression. [ABSTRACT FROM AUTHOR]