Population Dynamics in Lodgepole Pine‐Engelmann Spruce Forests

Abstract

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.

Minireviews: Neighborhood Effects, Disturbance Severity, and Community Stability in Forests

“…Lodgepole pine (Pinus contorta) in the United States and Canadian Rockies also displays these dynamics (Romme 1982;Johnson and Fryer 1989;Turner and others 1997).…”

“…In contrast, others point out that forests dominated by shade-tolerant species appear to be self-replacing, although acknowledging that rare catastrophic disturbances upset the temporary equilibrium (Clements 1936;Hough and Forbes 1943;Lorimer 1977). From yet another perspective, some also point out cases where canopy-killing disturbances cause great changes in biomass and nutrient status of an ecosystem, but the species composition of the subsequent canopy remains similar to that before the disturbance (Dix and Swan 1971;Heinselman 1973;Johnson and Fryer 1989). Such examples bring into question the idea that compositional succession necessarily follows canopy-killing disturbance.…”

Climate and wildfires in the North American boreal forest

“…Johnson & Fryer 1989;Johnson 1992). This would probably have implications for species distribution, for example, favouring species with earlier reproductive ages.…”

Tree-line Dynamics: Adding Fire to Climate Change Prediction

“…In the western boreal forest of North America, historic fire-return intervals have been estimated as typically 80 -120 years between fires (Johnson, 1992). Tree establishment occurs most rapidly in the first years following fire, when the availability of viable seed and nutrients is at its highest (Johnson and Fryer, 1989;Johnstone et al, 2004). In a typical fire cycle of one to two centuries, the individuals that germinate in the first few years following a fire are the same individuals that reach reproductive maturity and are burned in the next fire, continuing the cycle of post-fire self-replacement.…”