Microclimatic buffering by logging residues and forest edges reduces clear‐cutting impacts on forest bryophytes

Abstract

Question: The practice of extracting logging residues after clear-cutting for bioenergy purposes is spreading. Logging residues constitute a shelter in clear-cut areas and therefore concerns have been expressed that their removal could make the ground and its vegetation more exposed to extreme microclimatic conditions. We asked whether logging residues and forest edges can protect ground-dwelling forest bryophytes from fatal microclimate events following clear-cutting. Location: Boreal forests of central Sweden. Methods: Using transplants of eight forest floor bryophyte species we experimentally analysed the sheltering effect (less solar radiation and less wind) of logging residues and forest edges in seven clear-cut areas. Transplants were placed in two contrasting positions in each area; near a north-facing forest edge and in the centre of the clear-cut area. In each position, half of the transplants were covered by a layer of spruce branches and the other half was left uncovered. We estimated proportion of apparently living shoots (apparent vitality) and measured radial growth of transplants during one growing season. Results: Position in the clear-cut area, but not cover of spruce branches, clearly influenced radial growth. Vitality scores were higher among transplants covered with branches and the lowest apparent vitality was observed in uncovered transplants in the middle of clear-cut areas. The change in area of apparently living shoots during the course of the experiment (growth minus mortality) was unaffected by branch cover close to the edge but positively affected in the centre of the clear-cut area. In general, the effect of branch cover on bryophytes was higher in the centre of clear-cut areas. Here, climatic measurements showed that branch cover buffers during periods of extreme microclimates. Conclusions: Extraction of logging residues after clear-felling may reduce the survival of some ground-dwelling forest organisms. The additional sheltering provided by branches was unimportant close to forest edges. We suggest smaller clear-cut areas, green-tree retention and other ways to make logged areas shadier and less windy to mitigate the reduced shelter caused by harvest of logging residues.

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

“…The quadrats with intense physical disturbances and interplay effects were defined as those that had more harvest residue cover, including remnant branches and twigs, than 75%; those quadrats only affected by environmental alteration were defined as those that were covered less than 5% by harvest residue. Dynesius et al (2008) also used this 5% threshold (i.e., 95% logging residue cover) for logging residue cover in their experiment. Hence, all quadrats in each clear-cut plot were placed into three groups: (1) quadrats with intense physical disturbance, the plants in the quadrats were affected by the total (combined) effect of physical disturbances and interplay effects, as well as environmental alterations; (2) quadrats without physical disturbances, the plants in the quadrats were affected by the environmental alterations alone; and (3) the other quadrats, the plants in the quadrats were affected by the combination of less intense physical disturbances and environmental alterations.…”

“…The interplay effects may also have substantial influences on understory bryophytes. For example, logging residue left on clear-cuts can be helpful to the survival of some bryophytes (Dynesius et al 2008). However, in areas covered by dense piles of logging residue, where nearly no sunlight can penetrate, the bryophytes are unlikely to survive (Schmalholz and Hylander 2011b).…”

Monthly microclimate models in a managed boreal forest landscape

“…Finally due to the large effects of forest edges on maximum temperatures in forests (Fig. S4), fragmentation and a high density of forest edges due to the intensive forestry may impede harmful effects of global climate warming, and the spatial arrangement and size of these clearings need careful planning (Dynesius et al, 2008). At the same time, mature forests positively influence conditions on adjacent regenerating forest patches and various forms of retention forestry have been suggested to "promote re-colonization of mature-forest species" (Baker et al, 2014).…”

Nutrient concentrations in coarse and fine woody debris of <i>Populus tremuloides</i> Michx.-dominated forests, northern Minnesota, USA

“…Although less studied, smaller woody debris, termed 'fine' woody debris (FWD) has recently received more attention, and its function in forested ecosystems is becoming better recognized (Juutilainen et al 2011). For example, FWD provides important microclimates for bryophytes (Dynesius et al 2008), substrate for fungi (Brazee et al 2012), and habitat for deadwood-dependent insects (Jonsell et al 2007). …”