Can sugar maple establish into the boreal forest? Insights from seedlings under various canopies in southern Quebec

Abstract

Abstract. Understanding tree recruitment dynamics in various growth environments is essential for a better assessment of tree species' adaptive capacity to climate change. We investigated the microsite factors influencing survival, growth, and foliar nutrition of natural and planted sugar maple seedlings (Acer saccharum) along a gradient of tree species that reflect the change in composition from temperate hardwoods to boreal forests of eastern Canada. We specifically tested whether the increasing abundance of conifers in the forest and its modifications on soil properties negatively affects foliar nutrition of natural seedlings as well as the survival and growth of seedlings planted directly in the natural soil and in pots filled with enriched soil. Results of natural seedlings indicate that under conifer-dominated stands, lower soil pH, accelerated dissolution of some minerals, lower temperature and moisture, and higher levels of phenolic compounds have created microsites that are less suitable for sugar maple foliar nutrition and regeneration. These conditions were omnipresent under hemlock. The growth of seedlings planted in the natural soil was negatively impacted by the overall low soil quality under all forest types (as compared to seedlings planted in pots with enriched soil). However, survival and growth of the seedlings were not negatively affected by conifers, regardless of planting type, likely because of stored nutrients from the nursery. Also, lower survival was found under maple-birch stands for seedlings planted both in the natural soil and in pots with enriched soil due to higher shading. This study has identified key microsite factors created by specific conifers that may impede or benefit the potential of sugar maple to maintain its current range or expand its range northward under climate change.

Low Light Availability Associated with American Beech Is the Main Factor for Reduced Sugar Maple Seedling Survival and Growth Rates in a Hardwood Forest of Southern Quebec

“…stands and maple-beech stands, thus suggesting a greater effect of phenols than other soil properties. However, the levels of phenolic compounds measured in 2013 were in the same range as those observed in conifer-dominated stands with maple regeneration [36]. In addition, these stands had a mean canopy openness and light availability of 29% and 12 mol·m 2 ·day −1 , respectively.…”

“…It is possible that the rapid change in growing conditions during transplantation may have caused a stress that led to the high mortality. Light availability under the deciduous stands at the SBL (below 22% of canopy openness, Table 2) is a potential candidate for creating the high mortality because the survival rate of the same maple seedlings planted under mixedwood forests at the SBL with similar soil conditions but with a canopy openness of 30% was, on average, 83% [36]. A potential alternative explanation relates to below-ground fungal pathogens, not completely controlled in this study, and which were shown to be density-dependant and responsible for high mortality in maple stands [56].…”

“…As such, plots of maple-birch spp. stands that were used in this experiment are the same as those reported in Collin et al [36]. Environmental data such as elevation, slope, and exposure were noted to characterize each plot.…”

Priority effects will impede range shifts of temperate tree species into the boreal forest

“…The primary boreal type of substrate, needle cover, was particularly efficient at inhibiting recruitment of temperate tree species, in particular for Acer species ( f = 0.115). Typically, boreal forest substrates are characterized as being thick, acidic and drier when compared within other forest floors (Collin et al, ). The acidification of soils under conifer stands is a general phenomenon (Cole, ).…”

“…More specifically, novel edaphic effects could arise, where the absence of key symbiotic microbial and fungal communities and/or nutrients (e.g. calcium and magnesium) could impact seedling emergence and survival (Collin, Kembel, Messier, & Bélanger, ; Lafleur, Paré, Munson, & Bergeron, ). Furthermore, as microclimate (i.e.…”