Natural regeneration and stand dynamics in a managed pine-oak forest in the Sierra Madre Occidental, Mexico

The pine-oak forests of Mexico's Sierra Madre Occidental have been subjected to industrial logging for less than 50 years. They retain many pre-European settlement characteristics, including uneven-aged stand structures and surface fires. However, logging is increasingly intensive, and the forests may be on the cusp of permanent change.; The goals of this thesis were to (1) explore environmental and logging effects on regeneration dynamics and stand structures in a managed Madrean forest, and (2) assess these effects in relationship to Forest Stewardship Council (FSC) certification principles for the management of natural forests. Natural regeneration dynamics were explored in relationship to logging and environmental influences. Microsite affinities of seedlings and spatial relationships between mature oak and pine trees were investigated under different fire regimes. Finally, the effects of logging on stand structure trajectories was modelled under a variety of fire regimes.; Environmental factors, particularly evidence of fire, accounted for four times more variation in species composition and abundance than year of harvest. Steep topography, mineral soil exposure, the occurrence of surface stones and widespread evidence of fire were associated with regeneration of fire-adapted pine species. Oaks and shade tolerant pines were associated with fine-textured soils, deep litter layers and extensive crown cover. Patches of fire-resistant pine seedlings were associated with spatially heterogeneous mineral soil and surface stone microsites in frequent fire stands. In contrast, oaks had weaker associations with deep litter and shade, and tended to be distributed randomly. Different diameter classes of adult pines were spatially dissociated in frequent fire stands, but clustered or distributed at random in stands with longer fire-free intervals. Longer fire-free intervals may also foster the formation of near-monospecific tree neighbourhoods.; Many larger diameter trees are cut during logging. Residual diameter distributions are therefore skewed towards smaller diameter classes. However, models suggested that trees would grow into the larger diameter classes and forest productivity would be maintained under an intermediate (15 year) fire regime. Overall, while natural processes continue and natural regeneration was abundant on most sites, high grading and plans for fire suppression may impede any attempt to certify this community owned forest.