Environmental determinants of recruitment success of subalpine fir (Abies lasiocarpa) in a mixed-conifer forest
Stephens, E.Z., C.P. Murar, D.B. Tinker and P.E. Copenhaver-Parry. 2019.
Abstract
Understanding the processes that underlie forest resilience is of increasing importance as climate
change and shifting disturbance regimes continue to impact western forests. Forest research and management efforts
within the low-diversity conifer forests of the U.S. Rocky Mountains have typically focused on relatively monotypic
stands dominated by a single cohort, but mixed-conifer stands, such as those codominated by Abies lasiocarpa and
Pinus contorta have been less widely studied. The presence of A. lasiocarpa may enhance resilience to fire- and mountain
pine beetle-induced mortality and depends on successful A. lasiocarpa recruitment under a range of environmental
conditions. The purpose of this study was to quantify the effects of key forest structural characteristics and environmental conditions on recruitment of A. lasiocarpa in a midelevation mixed-conifer forest in the central Rocky Mountains. To address this aim, A. lasiocarpa seedling density, light availability, neighborhood basal area, and soil fertility
were measured across 24 plots, and the relative effects of each measured variable, temperature, and precipitation on
seedling density were quantified within a Bayesian multilevel regression model. Model results showed nonsignificant
effects of climate, light availability, and neighborhood index on seedling density; a significant positive association
between seedling density and the interaction between soil fertility and neighborhood index; and a strong negative relationship between seedling density and soil fertility. We posit that the negative association with soil fertility in these
nutrient-poor forests reflects an underlying gradient in soil moisture availability that corresponds with water flux pathways. Ultimately, much of the variance in seedling densities was explained by latent plot and year effects, indicating
that A. lasiocarpa establishment in this mixed-conifer forest is likely governed by a complex suite of environmental
factors that vary across fine spatiotemporal scales.
