Effects of substrate availability and competing vegetation on natural regeneration of white spruce on logged boreal mixedwood sites

Abstract

Given a seed source, the quality of available substrates is a key factor in determining the success of white spruce (Picea glauca (Moench) Voss) natural regeneration. We examined the influence of substrate and competing vegetation on survival and growth of natural regeneration of white spruce up to 4 years following harvesting in deciduous-dominated upland boreal mixedwood sites. Feather moss, thick soil surface organic layers, litter, and solid wood were poor substrates for establishment. Early successional mosses establishing on mineral soil, thin organics, and rotten wood were generally favourable microsites but were not highly available on postharvest sites. Mineral soil substrates were not as suitable as expected, likely because on a postlogged site, they are associated with unfavourable environmental characteristics (e.g., low nutrient availability, exposure). There was some evidence that survival and growth of seedlings were improved by surrounding vegetation in the first years, but heavy competing vegetation had a negative impact on older seedlings. Burial by aspen litter greatly increased seedling mortality, especially when combined with a brief period of submergence due to heavy spring snowmelt. The results provide insight into conditions under which natural regeneration could be an option for establishing white spruce following harvesting of deciduous-dominated boreal mixedwood forests.Key words: natural regeneration, white spruce, substrate, seedling survival, competing vegetation, forest management.Résumé : Pour une source de graines donnée, la qualité des substrats disponibles est un facteur clé pour le succès de la régénération naturelle d'épinette blanche (Picea glauca (Moench) Voss). Nous avons étudié l'influence du substrat et de la végétation concurrente sur la survie et la croissance de la régénération naturelle d'épinette blanche jusqu'à 4 ans après la coupe de peuplements mixtes boréaux dominés par des espèces décidues et établis sur des stations bien drainées. Les mousses hypnacées, les couches épaisses de matière organique sur le sol, la litière et le bois massif constituaient de mauvais substrats pour l'établissement des semis. Les mousses de début de succession établies sur le sol minéral, les couches minces de matière organique sur le sol et le bois décomposé constituaient généralement des microsites favorables, mais étaient peu disponibles sur les stations récoltées. Les substrats formés de sol minéral n'étaient pas aussi appropriés que prévu, probablement parce que sur une station qui a été récoltée, ils sont associés à des caractéristiques environnementales défavorables (p. ex. : faible disponibilité des nutriments, exposition). La survie et la croissance des semis ont montré des signes d'amélioration liés à la présence de végétation environnante au cours des premières années, mais une forte compétition exercée par cette végétation a eu un impact négatif sur les plus vieux semis. L'ensevelissement des semis par la litière de peuplier a considérablement augmenté leur mortal...

Natural regeneration potential and dynamics in boreal lichen woodlands of eastern Canada following soil scarification

“…In any case, the biomass of the planted seedlings would add up to the one of the naturally regenerated seedlings as it is unlikely that the two types of seedlings engage in a strong competition, at least in this time frame. The planted seedlings may even have a protective effect (mainly against wind) and thus increase the survival and the growth of the natural seedlings in the first years (Kokkonen et al, 2018). Therefore, afforestation seems to be necessary to accumulate enough biomass in the mid-term to compensate for soil C emissions resulting from soil scarification.…”

“…Mosses, however, can have contrasting effects on seedling establishment and growth depending on species and locations. For instance, early successional mosses developing on mineral soil patches have been shown to facilitate white spruce seedling establishment at several Canadian boreal sites, whereas feather mosses had the opposite effect (Kokkonen et al, 2018). More specific research must be conducted to assess the rate of colonization by both lichen and moss species, and their specific effect on the dynamics of seedling establishment in the LWs of the study area.…”

“…However, natural regeneration is not always limited by seed production. In this case, natural regeneration may rather depend on seedbed quality and availability (Fleming and Mossa, 1994;Peters et al, 2005;Wang and Kemball, 2005;Kemball et al, 2006;Madec et al, 2012;Kokkonen et al, 2018), or seedlings' vigor, which is known to increase with seed size in black spruce (Skeates and Haavisto, 1995). For instance, Madec et al (2012) have shown that the density and the distribution of seed trees were not a limiting factor for seedling establishment in scarified LWs, which was rather mostly controlled by exposed mineral soil surface area (thereafter 'scarification intensity' in m 2 ha −1 or %).…”

“…The natural regeneration dynamics following wildfires (Filion and Morin, 1996;Wang and Kemball, 2005;Kemball et al, 2006;Johnstone et al, 2009;Brown and Johnstone, 2012) or logging (Béland et al, 2000;Downey et al, 2018;Kokkonen et al, 2018;Prévost and Dumais, 2018;Laine et al, 2020;Rosenvald et al, 2020;Sikström et al, 2020;Kyrö et al, 2022) have been well documented in boreal forests but available data are much scarcer for scarified LWs, characterized by low seed tree density, low fertility and the presence of a competing cryptogamic vegetation (lichens and bryophytes). A few studies have shown the benefits of soil scarification in LWs for both natural seeding (Madec et al, 2012) and the growth of planted seedlings (Hébert et al, 2006(Hébert et al, , 2013, but as afforestation experiments in LWs started only a few decades ago, our long-term knowledge of natural regeneration dynamics in this habitat is limited.…”

Understory functional groups and fire history but not experimental warming drive tree seedling performance in unmanaged boreal forests

“…This may indicate different mechanisms for seedling survival and growth, as well as different modes of action for mosses and shrubs, such as facilitation or competition. Earlier findings have shown that the presence of mosses can be a great barrier for seedling germination and survival in the boreal forest (Valkonen and Maguire, 2005;Hypponen et al, 2013;Kokkonen et al, 2018) and relate that to changes in moisture (Lindo and Gonzalez, 2010;Soudzilovskaia et al, 2013) and competition for space as mosses can also suffocate tree seedlings (Stuiver et al, 2014). Shrubs have also been shown to suppress seedling growth (Wardle et al, 2008), e.g., E. hermaphroditum is known to produce poor quality litter with allelopathic compounds hampering seedling establishment (Nilsson and Zackrisson, 1992).…”