Abstract
Forest understory vegetation is largely influenced by disturbances and given local abiotic conditions. Our research focuses on the early response of understory vegetation to various forest management intensities in Dinaric fir-beech forests in Slovenia: (i) control, (ii) 50% cut of stand growing stock, and (iii) 100% cut of stand growing stock. Apart from identifying overstory removal effects, we were interested in fine-scale variation of understory vegetation and environmental determinants of its species composition. Vegetation was sampled within 27 karst sinkholes, which represent a dominant landform in studied forests. Within each sinkhole, five sampling plots, varying in slope aspect (centre, north, east, south, west), were established (135 in total), where pre-treatment (in 2012) and post-treatment (in 2014) floristic surveys were conducted. The sampled understory species were characterized in terms of Ellenberg’s indicator values (EIVs) and plant functional traits (plant height, seed mass, specific leaf area, leaf dry matter content). Diversity metrics (species richness, total cover, Shannon index) increased in plots where the silvicultural measures were applied. Tree species richness also increased in 100% cutting. A redundancy analysis revealed that species composition was related to environmental variables, which are directly influenced by management interventions (overstory canopy cover, microclimate—maximum daily temperature, soil properties—thickness of organic soil layer) as well as by topographic factors (slope inclination and surface rockiness). EIVs for light were significantly affected by treatment intensity, whereas soil-related EIVs (moisture, reaction, nutrients) depended more on the within-sinkhole position. Canopy gaps, compared with uncut control plots, hosted a higher number of colonizing species with a higher plant height and smaller seeds, while leaf traits did not show a clear response. We found a negative correlation between pre-treatment species (functional) richness and post-treatment shifts in floristic (functional) composition. Plots with higher richness exhibited smaller changes compared with species-poor communities. Incorporating different perspectives, the results of this study offer valuable insights into patterns of understory vegetation response to forest management in fir-beech forests.
Highlights
One of the main ideas of sustainable, close-to-nature forest management is to mimic the natural disturbance regimes and forest dynamics as close as possible [1,2,3]
The highest species richness was on average observed in the southern plots in canopy gaps and the lowest in the western control plots (16.4 ± 5.7)
This study confirms that forest management intensity is the main determinant of understory diversity, abundance, and composition in managed forests
Summary
One of the main ideas of sustainable, close-to-nature forest management is to mimic the natural disturbance regimes and forest dynamics as close as possible [1,2,3]. Comparisons of unmanaged and managed European forests with varying management types and intensities (e.g., [2,8,9]) have led to a general conclusion that plant species and functional diversity in the understory layer tend to be higher in sustainably managed forests. This is mainly because of the co-existence of species with different ecological requirements and resource acquisition strategies, for example, shade-tolerant forest specialists versus shade-intolerant open-habitat species [10,11,12]. High plant species richness indicates management-related disturbances rather than the conservation status of forests [5]
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