Regeneration plays a critical role in long-term forest dynamics, particularly in forests that are structured by recurring disturbances like fire. In Rocky Mountain forests, the variation in fire frequency and severity across different forest types generates distinct establishment trends and successional trajectories. Although establishment following fire has been well-studied in Rocky Mountain forests, non-disturbance influences on establishment patterns have not been investigated as widely; some evidence suggests that the independent effects of climate on seedling establishment in Rocky Mountain forests are significant and may even exceed those of disturbance. Here, we evaluate long-term establishment trends of seven dominant Rocky Mountain tree species in relation to climate and fire to clarify the relative influences of climate and disturbance on seedling establishment. Specifically, we evaluated tree ring series from a mixed-species stand to identify establishment years, and then used a Bayesian regression modelling approach to relate establishment to a range of climate factors and fire occurrence in the year of establishment and the two preceding years. We then performed a Bayesian sensitivity analysis to estimate the relative importance of each climate factor and disturbance.
Results/Conclusions
Across all climate variables and all seven tree species studied, 33% more trees on average established during years with rainfall that exceeded average decadal precipitation than within two years following a disturbance, and mean monthly growing season precipitation had a greater relative influence on establishment success than temperature. On average, 12% more trees established when precipitation two years prior to establishment exceeded decadal averages than when precipitation one year prior to establishment exceeded decadal averages. These findings indicate that establishment trends may be closely tied to climatic controls on seed production, and that success of Rocky Mountain tree seedling establishment is highly dependent upon moisture availability. Seedlings across all species appear to establish independently of disturbance, underscoring the importance of independent climatic influences on seedling establishment, even in fire-adapted species.