Structural diversity and dynamics of boreal old-growth forests case study in Eastern Canada

Abstract

Old-growth stands are considered as key components of boreal forest diversity and their preservation is largely integrated into management plans. However, while the differences between old-growth and young forests have largely been studied, little is known about the diversity of boreal old-growth forests. In managed landscapes, the efficacy of old-growth conservation plans may be reduced depending on how these old-growth forests are considered: as a single, homogeneous and steady-state forest type or as multiple, diverse and dynamic forest types. To fulfil this gap, our objectives were: (1) to create a typology of old-growth boreal structures; (2) to observe how these structures are influenced by environmental and temporal parameters; and (3) to elaborate a succession model of old-growth structural dynamics along temporal and environmental gradients. Seventy-one mature and overmature stands were sampled within a 2200 km 2 territory situated in Eastern Canada. Cluster analysis divided the sampled stands into two even-aged types, three transition old-growth types and six true old-growth types. Slope, minimum time since last fire and organic horizon depth were the three environmental and temporal parameters influencing the oldgrowth structures. Paludification-related productivity decline was present in only one old-growth forest type, while the other sites remained productive. These results allowed the creation of three succession models of the dynamics of old-growth stands in the boreal forest of eastern Canada. Boreal stands can undergo numerous structural changes once the old-growth succession process is initiated. An increase in structural diversity when the true old-growth stage is reached, coupled with a variety of secondary disturbance characteristics, favours multiple pathways of structural evolution of these ecosystems over time. Therefore, forest management planning should incorporate this complexity to improve the preservation of old-growth forests in managed territories.

The climate sensitivity of carbon, timber, and species richness covaries with forest age in boreal–temperate North America

“…Moreover, the climate sensitivity of ESB may vary with structural and compositional changes induced by forest aging (Boulanger, Taylor, Price, Cyr, & Sainte-Marie, 2018;Pan et al, 2011). For instance, older forests, being more structurally and functionally complex (Becknell & Powers, 2014;Martin, Fenton, & Morin, 2018;Tyrrell & Crow, 1994), are potentially better at buffering against undesired climate change effects on ESB than younger forests of lower complexity (Lindner et al, 2010;Urbano & Keeton, 2017). Large uncertainties about the effects of aging forests on ESB associations and their climate sensitivities hinder the design of the robust adaptive forest management strategies needed to sustain a broad range of species and ecosystem services under a changing climate.…”

Driving factors of conifer regeneration dynamics in eastern Canadian boreal old-growth forests

“…We applied the following equation to estimate regeneration attributes, i.e., seedling and sapling density, for black spruce and balsam fir: where D corresponds to the density per hectare, R is the number of seedlings or saplings sampled in each of the n plots surveyed, and S represents the surface (in m 2 ) of each of the n plots. (40) had previously computed several structural and environmental attributes for each of the sampled sites used in this study ( Table 1 ). Some of these attributes relate to stand structure, including merchantable tree density, basal area, Weibull’s shape parameter of diameter distribution (49), and gap fraction, i.e., the ratio between gap length and total transect length, sensu (50).…”

“…From the abovementioned observations, stands in the old-growth forests in eastern Canada are expected to shift between black spruce–dominated stands and black spruce–balsam fir mixed stands over time (21,28,40). As well, the structure of these stands varies over time (decades and centuries), even though tree species’ composition remains the same (40, 41).…”

“…From the abovementioned observations, stands in the old-growth forests in eastern Canada are expected to shift between black spruce–dominated stands and black spruce–balsam fir mixed stands over time (21,28,40). As well, the structure of these stands varies over time (decades and centuries), even though tree species’ composition remains the same (40, 41). At a decennial scale, it is therefore likely that the characteristics of the understory, e.g., tree density or tree species composition within the regeneration layer, will change significantly and rapidly due to the succession of tree-mortality and canopy closure phases.…”

Ecosystem management in paludified boreal forests: enhancing wood production, biodiversity, and carbon sequestration at the landscape level

“…where no species replacement occurs during succession), such as is the case in the black spruce-dominated Clay Belt, old-growth forests can be best described by their complex structure. At the stand level, such complex structures are the result of time since fire (Martin et al 2018) and secondary disturbance (such as insect outbreaks or windthrow), which allow for the recruitment of younger and smaller tree in the canopy (Kneeshaw and Gauthier 2003). As a result, the complex structures of old-growth stands are expressed by their irregular, uneven-aged character (Kneeshaw and Gauthier 2003).…”