No increase in colonization rate of boreal bryophytes close to propagule sources

Abstract

Knowledge of the process of recolonization, and which temporal and spatial scale it operates on, is central to our understanding of species distributions, metapopulation dynamics, regional extinction risks, and ecosystem resilience. In this study the recolonization pattern of boreal forest bryophytes was investigated in stands that had been clear-cut approximately 50 years ago. Species known to be sensitive to clear-cutting were inventoried in 23 mature forest stands and in adjacent young stands at 10, 20, 40, and 80 m from the former forest-clear-cut edge. Based on previous studies showing that bryophytes tend to be dispersal limited at local population levels, it was hypothesized that the recolonizaton of many bryophyte species should be higher closer to the mature forest edge. It was also hypothesized that some species would show full recovery, while for others the young stands would still be inhospitable. All these patterns were found for individual species, but the main pattern was, however, quite different. Most species had started to recolonize the young stands (i.e., little or much, depending on species), but without any tendency of a higher colonization rate close to the mature stands. Possible explanations for the limited signs of positive influence of local propagule sources might be microsite limitation or that the local propagule availability displays a rapid decline from its sources and is masked by a higher regional propagule rain. For organisms with light propagules able to build up a regional background level, the role of mature forest stands in the recolonization process of the matrix may rather be to contribute to the regional background level of spores in the landscape than to affect the adjacent stands directly.

Boulders increase resistance to clear-cut logging but not subsequent recolonization rates of boreal bryophytes

“…The tail of the dispersal curve might, at least for common species, generate regional propagule clouds, capable of supplying the majority of potential microsites in a region. Such a mechanism operating at a regional rather than a local scale might explain the lack of influence from local propagule sources on bryophyte colonization found in two recent studies (Sundberg et al 2006;Hylander 2009) as well as in this study.…”

“…However, although deposition rates of spores are very high close to the source population, a substantial portion of the spores are frequently dispersed further away (e.g., Stoneburner et al 1992). It is possible that this dispersal, comprising the tail of the dispersal curve, is important in maintaining metapopulation and metacommunity dynamics in landscapes for certain bryophytes (e.g., Sundberg et al 2006;Hylander 2009). The tail of the dispersal curve might, at least for common species, generate regional propagule clouds, capable of supplying the majority of potential microsites in a region.…”

Biological control as an invasion process: disturbance and propagule pressure affect the invasion success of Lythrum salicaria biological control agents

“…When assessing the importance of propagule pressure at finer scales models containing propagule pressure had high probabilities of being selected and a positive trend with invasion success in the colonization stage for one species and the population increase stage for the other. If the regional propagule pool is large, as it is for Galerucella, the influence of local propagule variation may be undetectable (Hylander 2009). However, this is unlikely to explain the low importance of propagule pressure in Galerucella persistence models, as similarly low selection probabilities occurred for N. marmoratus, which had a much smaller overall release size.…”

Understory plant assemblages present distinct short-term responses to the clear-cutting of an old-growth spruce forest near an alpine timberline

“…First, the colonization and establishment might be affected by the loss of vital substrates and exposed soil. Second, the growth of these mosses might be limited by the microhabitat (Hylander 2009). Successional pattern analysis also indicates that the lowest coverage of mosses occurred in the early successional stage and that competitive AMs, which are followed by PMs, rise in the later succession (Uotila and Kouki 2005).…”

“…According to the disturbance impacts, Roberts (2007) has proposed a three-dimensional conceptual model to illustrate the immediate physical disturbance condition. Environmental alterations can exert a significant effect on understory plant growth, regeneration, and community development (Fenton and Frego 2005); thus the survival of many forest species is climate-limited (Hylander 2009). The dramatic environmental alteration produced by clear-cut logging indirectly affects the understory plant community according to the species' biological characteristics (Decocq et al 2004), although the responses of different understory plant species groups may lag behind those of other environmental changes (Bergstedt and Milberg 2001).…”