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

Abstract

28des bourgeons de l'épinette sur la variabilité des paysages en zone boréale," as well as a new 29 professor start-up fund at University of Québec in Abitibi Temiscamingue (UQAT) and a 30 silvicultural research grant from MRC-Abitibi that were both obtained by MMG.Abstract 35 Old-growth forests play a major role in conserving biodiversity, protecting water resources, 36 sequestrating carbon, and these forests are indispensable resources for indigenous societies. To 37 preserve the ecosystem services provided by these boreal ecosystems, it becomes necessary to 38 develop novel silvicultural practices capable of emulating the natural dynamics and structural 39 attributes of old-growth forests. The success of these forest management strategies depends on 40 developing an accurate understanding of natural regeneration dynamics. Our goal was therefore 41 to identify the main patterns and the drivers involved in the regeneration dynamics of old-growth 42 forests, placing our focus on boreal stands dominated by black spruce (Picea mariana (L.) Mill.) 43 and balsam fir (Balsam fir (L.) Mill.) in eastern Canada. We sampled 71 stands in a 2200 km 2 44 study area located within Quebec's boreal region. For each stand, we noted tree regeneration 45 (seedlings and saplings), structural attributes (diameter distribution, deadwood volume, etc.), and 46 abiotic (topography and soil) factors. We observed that secondary disturbance regimes and 47 topographic constraints were the main drivers of balsam fir and black spruce regeneration. 48 Furthermore, the regeneration dynamics of black spruce appeared more complex than those of 49 balsam fir. We observed distinct phases of seedling production first developing within the 50 understory, then seedling growth when gaps opened in the canopy, followed by progressive 51 canopy closure. Seedling density, rather than the sapling density, had a major role in explaining 52 the ability of black spruce to fill the canopy following a secondary disturbance. The density of 53 balsam fir seedlings and saplings was also linked to the abundance of balsam fir trees at the stand 54 level. This research helps explain the complexity of old-growth forest dynamics where many 55 ecological factors interact at multiple temporal and spatial scales. This study also improves our 4 56 understanding of ecological processes within native old-growth forests and identifies the key 57 factors to consider when ensuring the sustainable management of old-growth boreal stands. 58 59 Introduction 63The global extent of native old-growth forest has declined markedly over the past few centuries 64 through a cumulative and increasing impact from anthropic activities within these forest 65 landscapes (1-3). The boreal forest, most of which is situated in Canada and Russia, is currently 66 the largest reserve of natural forest on our planet (3). Boreal old-growth forest has also 67 experienced rapid loss over the last centuries (1,4,5). The remaining old-growth forests are 68 critically important to biodiver...

Compared to Wildfire, Management Practices Reduced Old-Growth Forest Diversity and Functionality in Primary Boreal Landscapes of Eastern Canada

“…It is thus possible that Forest type 2 grouped together recently disturbed forests, explaining this more open structure despite the similarities with more productive forest types. A relatively open structure caused by secondary disturbances is often temporary, as shade-tolerant regeneration quickly reach the canopy and fill the gaps (Pham et al, 2004;Aakala et al, 2007;Martin et al, 2020d). Yet, compound disturbances (i.e., a succession of multiple disturbances of low and moderate severity in a short period of time) may overwhelm stand resistance and resilience.…”

The Abundance and Structure of Deadwood: A Comparison of Mixed and Thinned Chinese Fir Plantations

“…Different types of deadwood are formed following tree death, including standing dead trees (snags), fallen wood (logs), and broken wood ( Girona et al, 2019 ). Natural forests, especially those in temperate regions, have an abundance of deadwood that supports the growth and vitality of retained and regenerating trees ( Martin et al, 2020 ). Deadwood also provides resources, such as food and habitat, for small animals (e.g., birds, insects, and arthropods) as well as saprophytes and parasitic plants (e.g., lichens, mosses, fungi, and mushrooms) ( Franklin et al, 1987 ; Dittrich et al, 2014 ; Kim et al, 2020 ; Monaco et al, 2020 ; Oettel et al, 2020 ), and has been analyzed in studies of forest carbon stocks, soil development, and climate change (e.g., Bölöni et al, 2017 ; Farahat et al, 2017 ; Zhang et al, 2020 ).…”

Does the type of silvicultural practice influence spruce budworm defoliation of seedlings?

“…Stand type—in this study referring to pure black spruce or black spruce–balsam fir stands—plays a major role in determining a forest's resilience to natural disturbances, such as fire, windthrow, and insect outbreaks (MacLean and MacKinnon 1997, Martin et al 2020). Stand type has a major influence on mature tree susceptibility and vulnerability to SBW defoliation, also confirmed by our observations of defoliation in mature trees and the resulting NDVI values (Appendix : Fig.…”