Spatial and temporal patterns in structure, regeneration, and mortality of an old-growth ponderosa pine forest in the Colorado Front Range

Effective management and restoration of ponderosa pine forests requires an understanding of the heterogeneity of contemporary and historical stand structures. We assessed spatial and temporal patterns of tree establishment, mortality and size structure over a 30-year period in an old-growth ponderosa pine stand in the mid-montane zone of the Colorado Front Range. We analyzed spatial patterns and spatial associations using Ripley's K(t) and K12(t) and then modeled the patterns using point process models. Forest age structure was estimated by aging a sub-sample of trees in the stand. Climate appeared to play a significant role in the coarse-scale temporal pattern of regeneration events. Stand structure (distribution of patches, light availability, and seed trees) influenced the spatial and temporal pattern of more recent regeneration events. Patchy regeneration resulted in spatial independence and some segregation of size classes. Older trees in the stand (40-55 cm dbh) exhibited some regularity in their spatial distribution at short distances indicating that patterns of mortality had been historically patchy. Contemporary patterns of mortality were mostly patchy, and mountain pine beetles caused a significant amount of mortality in the 1970s and 1980s. Both establishment and mortality retained spatial patterns that were somewhat consistent with pre-settlement forests, despite changes in driving processes.