by Marie-Claude Boileau | 14 July 2021
Published in Forests 12(6): 740. https://doi.org/10.3390/f12060740
Research Highlights: The spatial distribution of trees results from several ecological processes that can be difficult to measure. We applied a point process modelling approach that uses the diameter and species of neighbouring trees to represent inter-tree interactions through repulsive and attractive processes. Thinning treatments slightly influence the tree spatial distribution of trees in white spruce plantations. Integrating this “spatialiser” into growth models could help improve stand simulations following various thinning treatments over larger areas and longer periods. It could also allow for the use of spatially explicit models when tree position is not available. Background and Objectives: Tree spatial patterns result from several ecological processes and have important implications in forest ecology and management. The use of spatial information can significantly improve our understanding of forest structures. However, this implies intensive field work that is rarely integrated into forest inventories. The aims of this study were to develop a spatial distribution simulator of trees in white spruce plantations and to evaluate the influence of thinning treatments. Materials and Methods: A point process modelling approach was used to represent inter-tree interactions through repulsive and attractive process in white spruce (Picea glauca (Moench) Voss) plantations in eastern Quebec, Canada, that had been commercially thinned five years ago. Balsam fir (Abies balsamea (L.) Mill.) and hardwoods together can represent 30–40% of the basal area of these plantations. Results: The diameter and species of each tree’s two closest neighbours were found to be the most important predictors in explaining the observed distances between trees. Despite the short period since thinning treatments, results showed that the treatment had slight significant effects on tree interactions. However, their impact on the global spatial distribution of stands is quite limited. Conclusions: Using only a few readily-available variables (species and diameter of trees), this “spatialiser” will make it possible to assign spatial coordinates to trees and generate realistic stand spatial structures even after various silvicultural treatments.
by Audrey Verreault | 17 June 2021
Published in Can. J. Soil Sci. 98(3): 458-468. https://doi.org/10.1139/cjss-2018-0017
We studied mature and adjacent open lichen–spruce woodlands (LWs) and closed-canopy spruce–feathermoss stands (FMs) growing under similar edaphic conditions in the continuous boreal forest zone in Quebec (Canada). A total of six pairs of stands were investigated by profile sampling. Stem density, basal area, and biomass were about four times greater in FMs than in LWs on an area basis. In the humus layer, total stocks of C and N and of exchangeable K, Ca, Mg, Al, and Na were 1.4–2.3 times larger in FM than in LW soils. The first 30 cm and the first metre of mineral soils in LWs and FMs displayed similar available nutrient pools except for total C stocks, which were more than twice as large in FM as in LW soils in these soil layers. For the whole profile, total stocks of C and N and stocks of exchangeable Ca and Mg were 1.3–2.6 times larger in FM than in LW soils. These results highlight the low intrinsic fertility of LW soils, primarily due to the humus layer, but also the importance of the biological control of C, N, and mineral nutrients in these boreal soils.
by Audrey Verreault | 17 June 2021
Published in Journal of Experimental Botany. https://doi.org/10.1093/jxb/erab127
Mesophyll conductance (gm) determines the diffusion of CO2 from the substomatal cavities to the site of carboxylation in the chloroplasts and represents a critical component of the diffusive limitation of photosynthesis. In this study, we evaluated the average effect sizes of different environmental constraints on gm in Populus spp., a forest tree model. We collected raw data of 815 A–Ci response curves from 26 datasets to estimate gm, using a single curve-fitting method to alleviate method-related bias. We performed a meta-analysis to assess the effects of different abiotic stresses on gm. We found a significant increase in gm from the bottom to the top of the canopy that was concomitant with the increase of maximum rate of carboxylation and light-saturated photosynthetic rate (Amax). gm was positively associated with increases in soil moisture and nutrient availability, but was insensitive to increasing soil copper concentration and did not vary with atmospheric CO2 concentration. Our results showed that gm was strongly related to Amax and to a lesser extent to stomatal conductance (gs). Moreover, a negative exponential relationship was obtained between gm and specific leaf area, which may be used to scale-up gm within the canopy.
by equipewp | 17 June 2021
Published in Forests 12(5): 583. https://doi.org/10.3390/f12050583
Using residual biomass from forest harvesting to produce energy is viewed increasingly as a means to reduce fossil fuel consumption. However, the impact such practices on soil and future site productivity remains a major concern. We revisited 196 forest plots that were subject to either whole-tree (WTH) or stem-only (SOH) harvesting 30 years ago in the boreal forest in Quebec, Canada. Plots were stratified by four soil regions grouped by so-called ‘soil provinces’. Soil analyses indicated that after 30 years, the forest floor of WTH sites had smaller pools of N (−8%), exchangeable Ca (−6%) and exchangeable Mn (−21%) and a higher C/N ratio (+12%) than that of SOH sites. Mineral soil responses to the two harvesting intensities differed among soil provinces. In the two coarse-textured granitic soil provinces, organic matter, organic carbon, and nitrogen pools over the whole solum (0–60 cm soil depth) were at least 28% smaller after WTH than after SOH. Site productivity indicators followed differences between soils and were lower after WTH than after SOH in the two granitic soil provinces. The study shows that soil characteristics greatly influence a soil’s sensitivity to increased forest biomass harvesting in the long term.
by Audrey Verreault | 29 April 2021
Published in Soil Systems 4(3). https://doi.org/10.3390/soilsystems4030054
As acidic deposition has decreased across Eastern North America, forest soils at some sites are beginning to show reversal of soil acidification. However, the degree of recovery appears to vary and is not fully explained by deposition declines alone. To assess if other site and soil factors can help to explain degree of recovery from acid deposition, soil resampling chemistry data (8- to 24-year time interval) from 23 sites in the United States and Canada, located across 25° longitude from Eastern Maine to Western Ontario, were explored. Site and soil factors included recovery years, sulfate (SO42-) deposition history, SO42- reduction rate, C horizon pH and exchangeable calcium (Ca), O and B horizon pH, base saturation, and exchangeable Ca and aluminum (Al) at the time of the initial sampling. We found that O and B horizons that were initially acidified to a greater degree showed greater recovery and B horizon recovery was further associated with an increase in recovery years and lower initial SO42- deposition. Forest soils that seemingly have low buffering capacity and a reduced potential for recovery have the resilience to recover from the effects of previous high levels of acidic deposition. This suggests, that predictions of where forest soils acidification reversal will occur across the landscape should be refined to acknowledge the importance of upper soil profile horizon chemistry rather than the more traditional approach using only parent material characteristics.
