Assessing the potential of natural woody species regeneration for the conversion of Norway spruce plantations on alluvial soils

Abstract

-In the perspective of the conversion of Norway spruce plantations, there is a need for foresters to assess the potential of the natural woody species regeneration. We studied 50 Norway spruce plantations on alluvial soils throughout the Grand-duché de Luxembourg and compared the regeneration characteristics (species composition, spatial heterogeneity) with 42 riverine deciduous stands (the target communities). Within the Norway spruce plantations, Fraxinus excelsior and Acer pseudoplatanus were the main regenerating species, probably because of their very good dispersal abilities. Norway spruce seedlings were quasi-absent. Low Norway spruce densities and baserich soils (local factors) as well as proximity of riverine deciduous forests (regional factor) strongly favoured the regeneration of a suite of broad-leaved species. The thickness of Norway spruce litter did not appear to be a limiting factor, at least for large-seeded tree seedlings. The spatial heterogeneity of the woody regeneration was rather similar in coniferous and deciduous stands. We conclude that for the development of multifunctional forests, the spontaneous regeneration under low-dense Norway spruce stands on base-rich soils provides a valuable starting point. Picea abies / floodplain / spontaneous rejuvenation / spatial heterogeneity / LuxembourgRésumé -Évaluation des potentialités de régénération naturelle pour la conversion des plantations d'épicéas sur sols alluviaux. Dans une perspective de conversion des plantations d'épicéas, les forestiers ont besoin d'évaluer les potentialités de régénération naturelle. Nous avons étudié 50 plantations d'épicéas sur sols alluviaux au grand-duché de Luxembourg et comparé les caractéristiques de cette régénération naturelle (composition, hétérogénéité spatiale) à 42 forêts riveraines de feuillus (communautés de référence). Dans les plantations d'épicéas, Fraxinus excelsior et Acer pseudoplatanus sont les principales espèces qui régénèrent, probablement en raison de leur grande capacité de dispersion. Les jeunes épicéas sont quasiment absents. La régénération des essences feuillues est fortement favorisée par de faibles densités d'épicéas, par des sols riches en bases (facteurs locaux) et par la proximité de forêts alluviales (facteur régional). La litière de l'épicéa ne semble pas être un facteur limitant à la régénération, au moins pour les essences à grosses graines. L'hétérogénéité spatiale de la régénération est très similaire dans les peuplements de feuillus ou d'épicéas. En conclusion, la régénération spontanée d'essences feuillues sous les plantations d'épicéas peu denses et établies sur des sols basiques est un point de départ très intéressant dans un processus de conversion de ces plantations vers des forêts multifonctionelles.Picea abies / plaine alluviale / régénération naturelle / hétérogénéité spatiale / Luxembourg

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

“…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].…”

Sycamore maple (Acer pseudoplatanus L.) stands on former agricultural land in the Sudetes – evaluation of ecological value and production potential

“…Individual trees can produce up to 170,000 seeds that are easily carried by wind, mostly within 200 m distance of the parent tree (Rusanen & Myking, 2003;Hérault et al, 2004;Thies et al, 2009). Seedlings are very vulnerable to competitive herbs (Diaci, 2002;Modrý et al, 2004;Vandenberghe et al, 2007).…”

Restocking with broadleaved species during the conversion of Tsuga heterophylla plantations to native woodland using natural regeneration

“…Seeds can be dispersed by wind or alternatively a combination of animals and gravity (Farmer 1997). Observations on the distribution of tree seedlings has shown that seed of some species can disperse 100 m or more, but most seed falls much closer to the parent tree (Johnson 1988;Karlsson 1996;Farmer 1997;Herault et al 2004). Investigations into seed dispersal into a Norway spruce clearcut found that only a small proportion of seed from wind-dispersed species penetrated more than 20 m into the clearcut and that birch spread the furthest of the seven species studied (Karlsson 2002).…”

“…Whilst there were some differences between the forest types observed in this study and the relationships between vegetation, the occurrence of regeneration, the number of seedlings always was positively related to the proximity of parent trees. Consequently, whether conversion takes place gradually or by clearfelling, a species is unlikely to regenerate if it is distant from a parent tree and the probability of restocking is reduced at areas of a site remote from any parent trees (Herault et al 2004;Jonášová et al 2006). The potential for natural regeneration will vary and at most sites with few parent trees those species with light, wind-dispersed seeds such as birch and willow (Salix spp.)…”