The Persisting Influence of Edge on Vegetation in Hemiboreal Alnus Glutinosa (L.) Gaertn. Swamp Forest Set-Asides Adjacent to Recently Disturbed Stands

Abstract

To increase set-aside areas and protect biodiversity values in managed hemiboreal forest landscapes, small forest parcels called Woodland Key Habitats have been designated in Baltic and Nordic countries. The aim of this study was to investigate the persisting influence of the edge on vegetation dynamics for young, medium-old and old edges in Alnus glutinosa (L.) Gaertn. Woodland Key Habitats. All of these edges are adjacent to recently disturbed (clear-cut) stands. We surveyed edge influence on vegetation in bryophyte, herbaceous, shrub and tree layers in 90 plots in 30 set-aside forest stands in Southern Latvia. We tested the differences in the number of species and projective coverage in all vegetation layers, but plant functional types were examined—separately in the herbaceous layer. We found that edge influence in protected forest stands of A. glutinosa swamp forests reflects strong changes in vegetation and plant functional types in the herbaceous layer mostly up to 20 years after clear-cut disturbance in adjacent stands. The greatest differences were between young edges (≤20 years) and old edges (≥41 years), but there were very few significant differences between medium-old (21–40 years) and old edges which signifies more rapid changes in the early stages of edge influence and gradual stabilization of vegetation later on. We found that in edges adjacent to recently disturbed stands (up to 20 years), significantly less rare and indicator epiphytic lichen species occur, but this occurrence increases over time and edge influence is no longer present beyond 20 years after disturbance. Changes in vegetation and species occurrence found in our study indicated the need to plan the allocation of set-aside patches in production forest landscapes to ensure connectivity over longer period of time. Careful planning of clear-cuts in neighboring areas over time can significantly reduce the impact of edge effect on these set-asides.

External management effects on the stand structure of protected forest patches

“…Our study supports such a pulse in the subcanopy development in mixed woods (but not in pine forests), while shrubs tended to decline in both forest types. Opposing trends in tree vs shrub cover have also been reported in swamp‐forest fragments in Latvia (Liepa et al, 2020).…”

“…Opposing trends in tree vs shrub cover have also been reported in swamp-forest fragments in Latvia (Liepa et al, 2020).…”

Long term effects of total biomass harvesting on understory vegetation and tree stand in Norway spruce stands

“…The same pattern was also seen in the Myrtillososphagnosa forest type, where the FBR and SAC stand had the highest resemblance (R=0.11) (Table 2). Although FBR management and clear-cutting are different, the difference is not substantial (Berķis et al, 2013;Liepa et al, 2014;Olsson & Staaf, 1995). This resemblance between FBR and SAC stands is mostly due to the strong shade provided by spruce forests, which inhibits the growth of species that cannot tolerate shade (Huston, 1994).…”