Regeneration of Picea engelmannii and Abies lasiocarpa in high-elevation forests of south-central British Columbia depends on nurse logs

Abstract

We studied the regeneration niche of Picea engelmannii and Abies lasiocarpa in wet sub-zones of the Engelmann spruce-subalpine fir (ESSF) zone of southern British Columbia. We characterized the niche on transects from clearcuts into adjacent old-growth stands, in terms of aspect, elevation, micro-relief, light, seedbed, canopy cover, and competing vegetation. Fourteen transects were sampled at four watersheds. The sampling design ensured similar representation of small (1-30 cm), medium (31-100 cm) and tall (101-300 cm) saplings, and of both species. In total, 465 Picea and 623 Abies saplings were sampled. For every third sapling, an adjacent microsite with no sapling was selected using a random procedure and correspondingly characterized, enabling a pairwise comparison of microsites with and without saplings. Recruitment of both species was related to rotten wood seedbeds, i.e., mainly logs, but also stumps and root plates. This effect was stronger for Picea saplings, and it decreased with increasing sapling size, suggesting lower survival on rotten wood seedbeds. A higher occurrence of tall Abies saplings, in comparison to small ones, under the cover of canopy trees suggests higher survival under canopy than in gaps. Levels of direct light did not generally differ either between microsites with and without regeneration, or between Picea and Abies saplings. The microsite effects on sapling occurrence were quite consistent across gentle south-and north-facing slopes, upper and lower ESSF forests, sites, and along clearcut -old-growth gradients. The results suggest a strong dependence of Picea and Abies establishment on logs in ESSF forests.Key words: seedling establishment, microsite, seedbed, nurse logs, direct light, advance regeneration, ecological niche Nous avons étudié la niche de régénération de Picea engelmannii et d'Abies lasiocarpa dans les sous-zones humides de la zone de l'épinette d'Engelmann -sapin sub-alpin (ESSF) dans le sud de la Colombie-Britannique. Nous avons caractérisé la niche selon des tracés transversaux allant des coupes à blanc vers les vieux peuplements adjacents, au niveau de l'aspect, de l'altitude, du micro-relief, de la luminosité, du milieu de germination, du couvert des cimes et de la végétation concurrente. Quatorze tracés ont été échantillonnés dans quatre bassins versants. La conception de l'échantillonnage assurait une représentation similaire des semis de petite taille (1 -30 cm), de taille moyenne (31 -100 cm) et de grande taille (101 -300 cm) et des deux espèces. Au total, 465 semis de Picea et 623 semis d'Abies ont été échantillonnés. À chaque troisième semis, un microsite adjacent sans semis a été sélectionné au moyen d'une procé-dure aléatoire et caractérisée de la même façon, permettant une comparaison par éléments pairés des microsites ayant et n'ayant pas de semis. Les recrues des deux espèces étaient reliées à un milieu de germination composé de bois en décomposition, c'est-à-dire, principalement des billots, mais également des souches et des mottes. Cet effet étai...

Early development and nutrition of Norway spruce (Picea abies(L.) Karst.) seedlings on different seedbeds in the Bavarian limestone Alps – a bioassay

“…seedling development in natural forests [5,14,34]. It has recently been shown that the recruitment of a new spruce generation strongly depends on the quality of the seedbed [14,15,46]. This applies in particular for spruce, because spruce is a species with small seeds and therefore is more substrate-restricted than other tree species [27,35,37].…”

“…Former clear cuts and impact of grazing with regard to the benefits of decayed wood on spruce nutrition is insufficiently known [15,22]. Furthermore, the positive properties of humus layers on seedling establishment of spruce are at the moment not fully understood [30,31].…”

Wood Microsites at Timberline-Alpine Meadow Borders: Implications for Conifer Seedling Regeneration and Alpine Meadow Conifer Invasion

“…Wood microsites are key substrates in subalpine forests (Veblen 1989;Gratzer et al 1999;Zielonka and Niklossen 2001;Brang et al 2003;Narukawa et al 2003;Motta et al 2006;Baier et al 2007). A reconnaissance study of wood microsites in the Pacific Northwest found that mature trees, typically Abies lasiocarpa, which commonly fell directly into alpine meadows from the forest line via blow-down and wind snap, decayed and created warmer and moister conditions that produced greater seedling density and seedling survival than the adjacent soil substrates (6.85 seedlings per meter squared on wood versus 3.64 seedlings per meter squared on soil, P ¼ 0.026; Johnson and Yeakley 2013).…”

Effects of gap microsites and bamboo onAbies faxonianaregeneration in a subalpine forest, China

“…As described by Bace et al (2012), with the decaying logs become more rotten, these raised surfaces get closer to the forest ground, the litter layer is increasingly thicken (Harmon & Franklin 1989), and thereafter the positive effect of surrounding plants turns to be the negative one. Meanwhile, if sapling roots do not reach the forest ground, decaying logs would also be increasingly instable and lack of nutrients (Brang et al 2003). All these changes would contribute to an unfavorable environment on decaying logs.…”