Modelling Post-Disturbance Successional Dynamics of the Canadian Boreal Mixedwoods

Abstract

Natural disturbances, such as fire and insect outbreaks, play important roles in natural forest dynamics, which are characterized over long time scales by changes in stand composition and structure. Individual-based forest simulators could help explain and predict the response of forest ecosystems to different disturbances, silvicultural treatments, or environmental stressors. This study evaluated the ability of the SORTIE-ND simulator to reproduce post-disturbance dynamics of the boreal mixedwoods of eastern Canada. In 1991 and 2009, we sampled all trees (including seedlings and saplings) in 431 (256 m 2 ) plots located in the Lake Duparquet Research and Teaching Forest (western Quebec). These plots were distributed in stands originating from seven wildfires that occurred between 1760 and 1944, and which represented a chronosequence of post-disturbance stand development. We used the 1991 inventory data to parameterize the model, and simulated short-to long-term natural dynamics of post-fire stands in both the absence and presence of a spruce budworm outbreak. We compared short-term simulated stand composition and structure with those observed in 2009 using a chronosequence approach. The model successfully generated the composition and structure of empirical observations. In long-term simulations, species dominance of old-growth forests was not accurately estimated, due to possible differences in stand compositions following wildfires and to differences in stand disturbance histories. Mid-to long-term simulations showed that the secondary disturbance incurred by spruce budworm did not cause substantial changes in early successional stages while setting back the successional dynamics of middle-aged stands and accelerating the dominance of white cedar in late-successional post-fire stands. We conclude that constructing a model with appropriate information regarding stand composition and disturbance history considerably increases the strength and accuracy of the model to reproduce the natural dynamics of post-disturbance boreal mixedwoods. Forests 2020, 11, 3 * Evaluations show the significant differences (p-value >0.05) between 2009 empirical data and short-term simulation output. Old values are the model parameters at the beginning of simulations and model parameterizations. New values are the final adjusted values for model parameters.

Advancing and reversing succession as a function of time since fire and insect outbreaks: An 18 year in situ remeasurement of changes in forest composition

“…When these more vulnerable conifers are killed by the SBW large openings are created, which permit the recruitment of shade-intolerant hardwoods (Kneeshaw and Bergeron, 1998;Vepakomma et al, 2010). In other words, our results demonstrate that SBW outbreaks are a mechanism for forest diversification by interrupting successional processes based strictly on ageing and replacement of shade-intolerant species by more shade-tolerant species (Sánchez-Pinillos et al, 2019;Maleki et al, 2020). Accordingly, gaps created by the SBW lead to three different compositional pathways: they continue to advance succession, they maintain current composition (30%-36% of quadrats) or succession returns to earlier phases (34%45% of quadrats).…”

Competitive interactions under current climate allow temperate tree species to grow and survive in boreal mixedwood forest

“…Alternatively, the position of each tree can be specified. We consider SORTIE is a good candidate model to address our research objectives as it is flexible, permitting us to capture more realistically tree allometry, growth, dispersion and mortality using non‐linear relationships and stochastic processes (Bose et al 2015, Maleki et al 2019, Benson et al 2022).…”

“…Such models, which simulate the demographics of individual trees in a stand, are capable of simulating forest succession by considering competitive interactions for resources between trees (e.g. light and space) (DeAngelis and Grimm 2014, Maleki et al 2019). Spatially explicit stand simulators model direct interactions between trees by considering their specific spatial positions, thus directly accounting for competition for light and space among trees.…”

Evaluating the Performance of a Forest Succession Model to Predict the Long-Term Dynamics of Tree Species in Mixed Boreal Forests Using Historical Data in Northern Ontario, Canada

“…As a result, agreement between observations and predictions may be high for some simulation periods, but low for other periods. For the boreal forest, the performance of gap models with repeated measurements was evaluated in studies that used a variety of models, such as SORTIE-ND, FAREAST, FORSKA-2V, BO-REALIS, ForClim, and SIBBORK [26,28,[30][31][32][33][34][35][36]. These studies provided invaluable results for the evaluation of gap models, but they had some limitations.…”