Regional Instability in the Abundance of Open Stands in the Boreal Forest of Eastern Canada

Abstract

Abstract:Fires are a key disturbance of boreal forests. In fact, they are the main source of renewal and evolution for forest stands. The variability of fire through space and time results in a diversified forest mosaic, altering their species composition, structure and productivity. A resilient forest is assumed to be in a state of dynamic equilibrium with the fire regime, so that the composition, age structure and succession stages of forests should be consistent with the fire regime. Dense spruce-moss stands tend, however, to diminish in favour of more open stands similar to spruce-lichen stands when subjected to more frequent and recurring disturbances. This study therefore focused on the effects of spatial and temporal variations in burn rates on the proportion of open stands over a large geographic area (175,000 km 2 ) covered by black spruce (Picea mariana (Mill.) Britton, Sterns, Poggenb.). The study area was divided into 10 different zones according to burn rates, as measured using fire-related data collected between 1940 and 2006. To test if the abundance of open stands was unstable over time and not in equilibrium with the current fire regime, forest succession was simulated using a landscape dynamics model that showed that the abundance of open stands should increase progressively over time in zones where the average burn rate is high. The proportion of open stands generated during a specific historical period is correlated with the burn rate observed during the same period. Rising annual burn rates over the past two decades have thereby resulted in an immediate increase in the proportion of open stands. There is therefore a difference between the current proportion of open stands and the one expected if vegetation was in equilibrium with the disturbance regime, reflecting an instability that may significantly impact the way forest resources are managed. It is apparent from this study that forestry planning should consider the risks associated with the temporal variability of fire regimes on the forest ecosystem, as the resulting changes can have a significant impact on biodiversity and allowable cut estimates.

Detecting Local Drivers of Fire Cycle Heterogeneity in Boreal Forests: A Scale Issue

“…On the one hand, zones where FC is short are especially vulnerable to the expected increase in fire frequency due to climate change (e.g., [17,96,97]). The resilience of these forests should be a main management concern, as successive disturbances lead closed forests to turn into open lichen woodlands [98][99][100][101]. On the other hand, zones where FC is long face issues associated with old-growth forest depletion, due to a shorter time lapse between harvests than between natural fires [21,22,102].…”

Soil carbon, available nutrients, and iron and aluminium crystallinity vary between boreal closed-canopy forests and open lichen woodlands

“…In the central portion of Quebec's boreal zone, Canada, a southward expansion of open black spruce-lichen woodlands (hereafter LW) is currently being observed at the expense of more closed black spruce-moss forests (hereafter MF) (Bernier et al, 2011;Girard et al, 2008Girard et al, , 2009Rapanoela et al, 2016). The current ecosystem shift could be due to a change in the regional fire regime (Ali et al, 2012;Rapanoela et al, 2016) that likely occurred several thousand years ago (Richard 1979; Asselin and Payette, 2005) and constitutes a hot stake raised by forest ecologists and forest managers in so far as open black spruce-lichen woodlands are less productive and, consequently, sequester less carbon than closed moss forests (Rapanoela et al, 2016;Van Bogaert et al, 2015). MF are characterised by dense stands mainly composed of black spruce (Picea mariana) with a ground layer dominated by feathermosses (Pleurozium schreberi and others) and sphagnum (Sphagnum spp.).…”

Boreal coniferous forest density leads to significant variations in soil physical and geochemical properties

“…9) that synthesises our interpretations of the possible feedback processes between climate, vegetation and soil biogeochemistry that can be considered to result from successive fires. Indeed, the progression of opencanopy forests could be due to a greater fire frequency resulting from the changing climate (Rapanoela et al, 2016). Differences in fire events may lead to direct and indirect consequences at the soil level arising from fire impacts on vegetation structure and soil properties (Certini, 2005).…”

“…In the central portion of Quebec's boreal zone, Canada, a southward expansion of open black spruce-lichen woodlands (hereafter LW) is currently being observed at the expense of more closed black spruce-moss forests (hereafter MF; Bernier et al, 2011;Girard et al, 2008Girard et al, , 2009Rapanoela et al, 2016). The current ecosystem shift could be due to a change in the regional fire regime (Ali et al, 2012;Rapanoela et al, 2016) that likely occurred several thousands of years ago (Richard, 1979;Asselin and Payette, 2005) and constitutes a hot stake raised by forest ecologists and forest managers in so far as open black spruce-lichen woodlands are less productive and, consequently, sequester less carbon than closed moss forests (Rapanoela et al, 2016;Van Bogaert et al, 2015).…”

“…The current ecosystem shift could be due to a change in the regional fire regime (Ali et al, 2012;Rapanoela et al, 2016) that likely occurred several thousands of years ago (Richard, 1979;Asselin and Payette, 2005) and constitutes a hot stake raised by forest ecologists and forest managers in so far as open black spruce-lichen woodlands are less productive and, consequently, sequester less carbon than closed moss forests (Rapanoela et al, 2016;Van Bogaert et al, 2015). MF are characterised by dense stands mainly composed of black spruce (Picea mariana) with a ground layer dominated by feather mosses (Pleurozium schreberi and others) and sphagnum (Sphagnum spp.).…”