Boreal tree regeneration after fire and fuelwood harvesting in coastal Nunatsiavut

Abstract

Consecutive landscape-scale disturbances are known to influence boreal forest regeneration, yet few published data exist on the compounding effects of natural and anthropogenic disturbance on regeneration in subarctic forests. We conducted a dendroecological study of eastern coastal boreal forest regeneration two decades after fire at three subarctic forest stands that are important sources of fuelwood for the people of Nunatsiavut (Labrador, Canada). We quantified spruce (Picea spp.) and balsam fir (Abies balsamea (L.) Mill.) seedling regeneration, standing dead tree density, trees harvested within burned forests, and aged proximal unburned stands. Age of unburned forest varied with site; however, each exhibited continuous regeneration over several decades. Despite low seedling regeneration at each site (stems·m−2; less than 35% of pre-fire stem density), model results indicated harvesting post-fire did not impact seedling regeneration. Findings suggest a negative pressure on seedling abundance from increased presence of tall multi-stemmed shrubs, yet we argue that because stands exhibit a range in tree age, shrubs may be a set of early successional species rather than indicating a change in successional trajectory. Examination of a larger chronosequence within coastal forest stands of Nunatsiavut is warranted to further understand forest regeneration in the eastern subarctic under changing disturbance regimes.

Anthropogenic and climate impacts on subarctic forests in the Nain region, Nunatsiavut: Dendroecological and historical approaches

“…Although wood harvesting seems to have been a primary factor affecting these forest ecosystems, some other disturbances have been observed, especially at the Dog Island site, where bark beetle outbreaks were documented during 1790, 1910, 1920and 1970-2000(Roy et al 2017. At the Nain site, no evidence of insect damage or fire was found (Lemus-Lauzon et al 2018) and no evidence of fire was noted at Kammasûk and Webb's Bay although a forest fire of moderate size did occur in the latter region in 2004 (Brehaut and Brown 2020).…”

Thermal Modelling Of Post-Fire Permafrost Change Under A Warming Coastal Subarctic Climate, Eastern Canada

“…At WB, loss of permafrost following fire is modelled to occur at least 24 years earlier when compared to undisturbed simulations, at a rate that is three to four times faster than that reported for the West. This accelerated degradation is likely due to the warmer, less ice-rich permafrost (i.e., with lower latent heat) at our site compared to conditions in the central Northwest Territories (Smith et al 2015) and may also reflect the slower post-fire forest regeneration processes reported for WB (Brehaut and Brown 2020) compared to the pulse recruitment that has been documented following fire in the West (Johnstone et al 2004).…”

“…Our simulations relate to ground conditions at a burned site located on a north-facing slope along Webb Bay (WB; 56.706°N, 62.209°W), ~25 km northwest of Nain (Figure 1-C). The WB burn was a small (1 km 2 ) low severity fire that occurred in summer 2004 (Brehaut and Brown 2020). The site is located on a series of raised beaches, although erratics are also present.…”

“…The site is located on a series of raised beaches, although erratics are also present. Unburned stands are of mixed composition, with an average tree age of 227 years (Brehaut and Brown 2020).…”

A critical review of successional dynamics in boreal forests of North America

“…As a result, interest in quantitatively characterizing forest successional dynamics is increasing . Empirical models, such as logistic (e.g., Taylor and Chen 2011;Boucher et al 2014), linear (e.g., Bose et al 2014;Brehaut and Brown 2020) and nonlinear (e.g., Brown et al 2015) mixed effects, and Markov (e.g., Baasch et al 2010), are widely used with observational data. Mechanistic models rely on knowledge of underlying ecological processes to simulate succession (e.g., Boulanger et al 2018Boulanger et al , 2019.…”