by Svetlana Savin | 30 January 2019
Published in New Forests 50: 573–592. https://doi.org/10.1007/s11056-018-9680-2
Advance regeneration of red spruce (Picea rubens Sarg.) is scarce in many forest stands, due to past clearcuts and heavy harvesting of large seed trees in partial cuts. Understory enrichment planting has been proposed as a means to reintroduce the species in managed stands in which regeneration is deficient. Here, we present 5-year results regarding survival and growth dynamics of red spruce seedlings planted under hardwood, mixedwood, and coniferous forest covers following various cuts (each made on 0.5–1.2 ha square area): hybrid single-tree and group-selection, irregular shelterwood (two variants: continuous cover and extended irregular shelterwood), uniform regular shelterwood, harvesting with advance regeneration protection (HARP), and careful logging around advanced growth (hereafter referred to as ‘patch clearcut’). Five-year seedling survival did not vary among cuts except under the coniferous cover, where it was better in the heavier cuts (HARP and patch clearcut; 67%) than under continuous cover shelterwood cuts (24%), in which browsing occurrence was high (around 80%). Under the hardwood cover, height, diameter and biomass growth were greater in the extended irregular shelterwood cut than in other treatments. Under the mixedwood and coniferous covers, seedling growth was greater in patch clearcut, likely because transmitted light (90–100% full sunlight) was higher than in other cuts (around 30%). Results suggest that red spruce could be reintroduced using enrichment planting under a partial forest cover, but that additional treatments could be necessary to manage light and to limit browsing pressure in order to optimize long-term survival and growth performance.
by Claire Morin | 30 January 2019
Published in Forest Ecosystems 5(1): 30 https://doi.org/10.1186/s40663-018-0148-9
Background: In the context of ecosystem management, the present study aims to compare the natural and the present-day forested landscapes of a large territory in Quebec (Canada). Using contemporary and long-term fire cycles, each natural forest landscape is defined according to the variability of its structure and composition, and compared to the present-day landscape. This analysis was conducted to address the question of whether human activities have moved these ecosystems outside the range of natural landscape variability.
Methods: The study encompassed a forested area of 175 000 km2 divided into 14 landscapes. Using a framework that integrates fire cycles, age structure and forest dynamics, we characterized the forest composition and age structures that resulted from three historical fire cycles (110, 140, and 180 years) representative of the boreal forest of eastern Canada. The modeled natural landscapes were compared with present-day landscapes in regard to the proportion of old-growth forests (landscape level) and the proportion of late-successional forest stands (landscape level and potential vegetation type).
Results: Four landscapes (39%) remain within their natural range of variability. In contrast, nine landscapes (54%) show a large gap between natural and present-day landscapes. These nine are located in the southern portion of the study area, and are mainly associated with Abies–Betula vegetation where human activities have contributed to a strong increase in the proportion of Populus tremuloides stands (early-successional stages) and a decrease of oldgrowth forest stands (more than 100 years old). A single landscape (7%), substantially changed from its potential natural state, is a candidate for adaptive-based management.
Conclusion: Comparison of corresponding natural (reference conditions) and present-day landscapes showed that ten landscapes reflecting an important shift in forest composition and age structure could be considered beyond the range of their natural variability. The description of a landscape’s natural variability at the scale of several millennia can be considered a moving benchmark that can be re-evaluated in the context of climate change. Focusing on regional landscape characteristics and long-term natural variability of vegetation and forest age structure represents a step forward in methodology for defining reference conditions and following shifts in landscape over time.
by Claire Morin | 30 January 2019
Published in Forest Ecology and Management 375: 172-181. https://doi.org/10.1016/j.foreco.2016.05.037
Fire is considered the major disturbance in boreal forests. Nonetheless, in several areas logging has become the primary driver of forest dynamics. In many areas of the boreal forest, stands may undergo paludification (i.e. the accumulation of thick, poorly decomposed organic layers over the mineral soil) in the prolonged absence of fire, which reduces forest productivity. Whereas high-severity fires (HSF) may restore forest productivity by burning the soil organic layer (SOL), low-severity fires (LSF) mainly burn the soil surface and do not significantly reduce SOL thickness. In the Clay Belt region of eastern Canada, an area prone to paludification, forest stands have historically been harvested by clearcutting (CC), but concerns about the protection of soils and tree regeneration lead to the replacement of CC by careful logging (CL). Whereas CC disturbs the SOL and is thought to favor tree growth, CL has little impact on the SOL. Furthermore, it has been suggested that prescribed burning after clearcut (CCPB) could also be used to control paludification. Using a retrospective approach, this study sought to understand how CC, CL, and CCPB compare to LSF and HSF with respect to soil properties, SOL thickness, vegetation ground cover, tree nutrition, and stand height in paludified black spruce stands of the Clay Belt region. HSF led to significantly taller trees than CL and LSF, but did not differ from CC and CCPB. Foliar N was significantly higher in HSF and CCPB sites relative to CL and LSF, with an intermediate value in CC sites. Ground cover of Rhododendron groenlandicum was significantly lower in HSF and CC sites relative to LSF, with intermediate values in CL and CCPB sites. Sphagnum spp. ground cover was significantly lower in HSF and CCPB sites relative to CL, with intermediate values in CC and LSF sites. High-severity fire sites had a significantly thinner SOL than the four other disturbances. Finally, regression tree analysis showed that SOL thickness represented the best predictor of tree height, whereas segmented regression showed that tree height was negatively correlated to SOL thickness and revealed a cut-off point circa 23 cm, which suggests that tree growth is impeded beyond this threshold. These results support the idea that management strategies intending to regenerate paludified forests should primarily aim at reducing organic layer thickness, either through mechanical disturbance or combustion.
by Claire Morin | 30 January 2019
Published in Global Ecology and Biogeography 27(12): 1507-1519. https://doi.org/10.1111/geb.12829
Major taxa studied : Trees.
Methods : We investigate experimentally a series of factors thought to constrain the seedling phase at the leading edge of the distribution of a dominant tree species, sugar maple (Acer saccharum Marshall.). We established a seed transplant experiment using six provenances, representing the latitudinal species range, and transplanted them to 12 sites within, at and beyond the current northern species range margin.
Results : At present, northern provenances provide the best opportunity for establishment beyond the current range, where climatic conditions are more similar than those of the warmer central or southern portions of the species range. Establishment was highest within the species range, but survival rates were comparable to those at the range margin and beyond, regardless of provenance. We also found that the local climate was the most influential factor for early seedling establishment and survival; however, a lack of suitable microsites also significantly constrained recruitment.
Main conclusions : Our study highlights the complex interaction between provenance, climate and microsite conditions that is required to ensure successful seedling recruitment. Although sugar maple is currently displaying evidence for local adaptation to facilitate range shifts, it could risk maladaptation in the future if the local climate warms beyond a threshold required to ensure seed germination and a lack of favourable microsite conditions beyond the range.
by Claire Morin | 30 January 2019
Published in Canadian Journal of Forest Research 45: 529-539. https://doi.org/10.1139/cjfr-2014-0338
Constraints of the physical environment affect forest growth and forest operations. At a local scale, these constraints are generally considered during forest operations. At regional or continental scales, they are often integrated to larger assessments of the potential for a given land unit to be managed. In this study, we propose an approach to analyze the integration of physical environment constraints in forest management activities at the regional scale (482 000 km2). The land features that pose constraints to forest management (i.e., hydromorphic organic deposits, dead-ice moraines, washed till, glacial block fields, talus, and active aeolian deposits, slopes > 40%) were evaluated within 1114 land districts. To distinguish land districts that can be suitably managed from those where constraints are too important for sustainable timber production, we carried out a sensitivity analysis of physical constraints for the 1114 land districts. After analysis of two portions of the study area under management, a land district was considered suitable for management when more than 20% of its land area consists of features imposing few constraints or, for mountain-type relief districts, when more than 40% of the land area consists of features imposing few constraints. These cutoff values were defined by expert opinion, based on sensitivity analyses performed on the entire study area, on analyses of two different sectors with different types of constraints and on a strong understanding of the study area. Our results show that land districts where the physical environment posed significant constraints covered 7.5% of the study area (36 000 km2). This study shows that doing an a priori classification of land units based on permanent environmental features could facilitate the identification of areas that are not suitable for forest management activities.
