Aboveground and Belowground Patterns in Pyrogenic Boreal Ecosystems: What Governs Nutrient Availability?.

Corresponding author: S. Das Gupta (sanatan@ualberta.ca)

Wildfire in forest ecosystems has a major influence on biogeochemical processes that mediate the distribution of plant available nutrients. However, spatial information on post-fire recovery of nutrient availability and their mechanistic relationships with aboveground and belowground processes in boreal ecosystems is limited. We examined spatial variability in aboveground and belowground properties in a boreal fire chronosequence of aspen (Populus tremuloides Michx.) stands in northern Alberta, and modelled their combined effect on nutrient availability. We hypothesized that fire would create a uniform distribution in nutrients, and that a patchy spatial pattern might develop overtime due to structural heterogeneity. A variogram-based geostatistical approach was used to quantify spatial variability. Spatial autoregressive and random forests models were used for decomposing spatial, aboveground and belowground controls to nutrient availability. Most of the macronutrients, stand and soil properties in the post-fire (PF) stand either had a large scale spatial pattern (> 14 m) or did not show any spatial structure (nugget model), while the canopy closure (CC) and mature (MA) stands had fine scale spatial patterns (≤10 m). Resource congruence as measured by Kendall's W indicated a weak spatial coupling between aboveground and belowground properties in the PF stand which gradually increased in the CC and MA stands. Enzyme activities and nutrient interactions appeared to be the most significant predictors of nutrient availability in the PF stand, whereas organic matter quality (DOC, DON and C:N) and stand characteristics (organic layer depth, understory vegetation cover and tree location) were significant in the CC and MA stands. The current findings suggest that nutrient availability in pyrogenic boreal aspen ecosystems of northern Alberta might evolve from belowground (heterotrophic) dominance to a synergistic aboveground and belowground control.