Population Dynamics in Lodgepole Pine‐Engelmann Spruce Forests

Pinus contorta var. latifolia and Picea engelmannii recruitment and mortality were reconstructed in 13 lower subalpine stands from age—height curves of live trees, saplings, and seedlings, and from cross—dated dead standing, fallen, and buried stems. Bole decomposition rates indicated the populations could only be reconstructed without bias during approximately the second half of a stand's history, irrespective of the stand's age. All stands traced similar recruitment and mortality patterns for the overlapping parts of their histories. Fire and understory regeneration cohorts were recognized based on risk histories. The lodgepole pine fire cohort established in the first decade after fire. Its mortality was high but decreasing in the first 10 yr, low and constant until thinning began at °25 yr, and increasing for the next °200 yr. The understory cohort recruitment started °15 yr after fire and its mortality was high, and constant with <0.5% chance of reaching the canopy. As with pine, Engelmann spruce recruited mostly in the first decade after fire, followed by low and sporadic recruitment for the next 200 yr. The mortalities of the Engelmann spruce fire and understory cohorts were constant, with the understory mortality slightly higher than the mortality of the fire cohort. As with pine, the chances of the understory reaching the canopy were small. Since the recruitment of both pine and spruce does not compensate for their mortality, the population is not self—reproducing. The population is not transient, however, because the calculated fire frequency of the area ensures burning within the life—span of the fire cohort, allowing regeneration. Consequently the long—term population dynamics of pine and spruce appear to be controlled by fire frequency.