by Claire Morin | 24 August 2022
Published in Frontiers in Forests and Global Change 5: 879382. https://doi.org/10.3389/ffgc.2022.879382
Under climate change, drought conditions are projected to intensify and soil water stress is identified as one of the primary drivers of the decline of forests. While there is strong evidence of such megadisturbance in semi-arid regions, large uncertainties remain in North American temperate forests and fine-scale assessments of future soil water stress are needed to guide adaptation decisions. The objectives of this study were to (i) assess the impact of climate change on the severity and duration of soil water stress in a temperate forest of eastern North America and (ii) identify environmental factors driving the spatial variability of soil water stress levels. We modeled current and future soil moisture at a 1 km resolution with the Canadian Land Surface Scheme (CLASS). Despite a slight increase in precipitation during the growing season, the severity (95th percentile of absolute soil water potential) and duration (number of days where absolute soil water potential is greater than or equal to 9,000 hPa) of soil water stress were projected to increase on average by 1,680 hPa and 6.7 days in 80 years under RCP8.5, which correspond to a 33 and 158% increase compared to current levels. The largest increase in severity was projected to occur in areas currently experiencing short periods of soil water stress, while the largest increase in duration is rather likely to occur in areas already experiencing prolonged periods of soil water stress. Soil depth and, to a lesser extent, soil texture, were identified as the main controls of the spatial variability of projected changes in the severity and duration of soil water stress. Overall, these results highlight the need to disentangle impacts associated with an increase in the severity vs. in the duration of soil water stress to guide the management of temperate forests under climate change.
by Claire Morin | 24 August 2022
Published in Agricultural and Forest Meteorology 323(18): 109041. https://doi.org/10.1016/j.agrformet.2022.109041
Global warming advances bud break, mismatches plant phenology from the local climate, and exposes the developing leaves to higher risks of frost damage. Bud break of sugar maple [Acer saccharum (Marsh.)], a species included in recent programs of assisted migration, is sensitive to nighttime spring temperatures. This suggests a link between frost events and leaf development. In this study, we raise the hypothesis that late frost is an evolutionary driver of growth reactivation in sugar maple provenances. We investigated the ecotypic variation of bud phenology in 30 provenances planted in two common gardens within and at the northern limit of the species range, in the Province of Quebec, Canada. Eight phases of bud break were assessed twice a week during 2020 on 252 and 272 seedlings in southern and northern sites, respectively. In the southern site, bud break occurred in May, starting on average 12 days earlier and ending 3 days earlier compared to the northern site. Logistic regression was used to estimate the probability of late frost and the results showed that regions located in the north, at higher elevations, and along the northeastern coast of the native maple range showed the latest occurrences of frost events in spring. This pattern mirrored the timing of bud break. When planted in the same common garden, provenances originating from sites with later spring frosts leafed out earlier. Such differences were maintained across the eight bud phenological phases and between the two common gardens, which indicates a similar response of the provenances to changing growing conditions. To avoid frost damage to sugar maple plantations, assisted migration should account for phenotypic traits in bud phenology, ensuring that the frost regime at the origin of the provenances is compatible with that of plantations.
by Claire Morin | 24 August 2022
Published in European Journal of Forest Research 141: 629–639. https://doi.org/10.1007/s10342-022-01465-5
Clear-cutting is one of the most widespread forestry practices used in boreal forests. Clear-cutting of boreal forests in late successional stages could trigger reversion of successional trajectories back toward forests of earlier stages. Such successional setbacks could generate sustainability issues by prolonging the expected time to compositional recovery after clear-cutting. This could lead to overestimation of allowable cuts of economically important late-successional species if the occurrence of successional setbacks remains unassessed. Our objective was to assess whether clear-cutting without additional regeneration treatments has triggered successional setbacks. We studied post-clearcut successional trajectories by using forest inventory data in post-clearcut stands, in light of conceptual successional dynamics models. These data covered the actively managed boreal forest region of Quebec, eastern Canada, which is classified into two ecological regions, themselves subdivided into eastern (cool–wet) and western (warm–dry) sub regions. Clear-cutting triggered successional setbacks in half of these regions. Such setbacks could prolong, by at least an additional century, the expected time to compositional recovery after clear-cutting. To prevent the overestimation of allowable cuts of economically important late-successional species, foresters could monitor post-clear-cut successional trajectories to assess whether setbacks were triggered. Post-clear-cut successional setbacks occurred in the two western ecological regions where climatic conditions are warmer and drier than in their eastern counterpart where no setbacks occurred. Hence, sustainability issues brought on by successional setbacks may be exacerbated by climate change. Finally, furthering our understanding of the transformation of successional dynamics by anthropogenic disturbances will be essential to insure sustainable forestry practices.
by Audrey Verreault | 14 June 2022
Published in Forest Science. https://doi.org/10.1093/forsci/fxac019
The North American temperate deciduous forests are an important source of hardwoods sought after by the appearance wood products industries. The purpose of this study was to model the relationships between log characteristics and sawn board attributes in sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britt.). We harvested sixty-four sugar maple and thirty-two yellow birch trees from two locations in southern Quebec, Canada, which were then processed into 189 sawlogs and 2,236 boards. We developed statistical models linking log characteristics to the volume recovery of the various lumber grades and color specifications according to the National Hardwood Lumber Association rules. In both species, board grades were strongly related to log length, position of the log in the stem, and small-end diameter and decay of the log. Color classes were related to small-end diameter of the log and red heartwood diameter of the log at both ends for sugar maple, and to log length, diameter of the log at the small-end, and red heartwood diameter at the large-end of the log for yellow birch. These models outperformed a log classification used in practice for predicting lumber volume recovery from different log grades.
by Audrey Verreault | 14 June 2022
Published in GCB Bioenergy. https://doi.org/10.1111/gcbb.12951
In the context of global change, a better understanding of the dynamics of wood degradation, and how they relate to tree attributes and climatic conditions, is necessary to improve broad-scale assessments of the contributions of deadwood to various ecological processes, and ultimately, for the development of adaptive post-disturbance management strategies. The objective of this meta-analysis was to review the effects of tree attributes and local climatic conditions on the time since death of coarse woody debris ranging in decomposition states. Results from our meta-analysis showed that projected warming will likely accelerate wood decomposition and significantly decrease the residence time in decay stages. By promoting such a decrease in residence time, further climate warming is very likely to alter the dynamics of deadwood, which in turn may affect saproxylic biodiversity by decreasing the temporal availability of specific habitats. Moreover, while coarse woody debris has been recognized as a key resource for bioenergy at the global scale, the acceleration of decay-stages transition dynamics indicates that the temporal window during which dead trees are available as feedstock for value-added products will shrink. Consequently, future planning and implementation of salvage harvesting will need to occur within a short period following disturbance, especially in warmer regions dominated by hardwood species. Another important contribution of this work was the development of a harmonized classification system that relies on the correspondence between the visual criteria used to characterize deadwood decomposition stages in locally developed systems the literature. This system could be used in future investigations to facilitate direct comparisons between studies. Our literature survey also highlights that most of the information on wood decay dynamics comes from temperate and boreal forests, whereas data from subtropical, equatorial and subarctic forests are scarce. Such data are urgently needed to allow broader-scale conclusions on global wood degradation dynamics.
