Abstract
The aim of this resurvey study is to check if herbaceous vegetation on the forest floor exhibits overall stability at the stand-scale in spite of intensive dynamics at the scale of individual plots and stand dynamic events (driven by natural fine scale canopy gap dynamics). In 1996, we sampled a 1.5 ha patch using 0.25 m² plots placed along a 5 m × 5 m grid in the best remnant of central European montane beech woods in Hungary. All species in the herbaceous layer and their cover estimates were recorded. Five patches representing different stand developmental situations (SDS) were selected for resurvey. In 2013, 306 plots were resurveyed by using blocks of four 0.25 m² plots to test the effects of imperfect relocation. We found very intensive fine-scale dynamics in the herbaceous layer with high species turnover and sharp changes in ground layer cover at the local-scale (< 1 m2). A decrease in species richness and herbaceous layer cover, as well as high species turnover, characterized the closing gaps. Colonization events and increasing species richness and herbaceous layer cover prevailed in the two newly created gaps. A pronounced decrease in the total cover, but low species turnover and survival of the majority of the closed forest specialists was detected by the resurvey at the stand-scale. The test aiming at assessing the effect of relocation showed a higher time effect than the effect of imprecise relocation. The very intensive fine-scale dynamics of the studied beech forest are profoundly determined by natural stand dynamics. Extinction and colonisation episodes even out at the stand-scale, implying an overall compositional stability of the herbaceous vegetation at the given spatial and temporal scale. We argue that fine-scale gap dynamics, driven by natural processes or applied as a management method, can warrant the survival of many closed forest specialist species in the long-run. Nomenclature: Flora Europaea (Tutin et al. 2010) for vascular plants; Soo 1968–1980 for syntaxa
Highlights
The significance of the herbaceous layer in forest biodiversity and ecosystem functioning has been widely appreciated (Whigham 2004, Gilliam 2014), generating an interest in its dynamics
We found that intensive local-scale extinction and colonization episodes were balanced at the stand-scale, resulting in overall stability of the species pool in the herbaceous layer vegetation
The observed stand dynamics driven changes of vegetation indicate that the use of small regeneration areas in forest management can prevent competitive ruderal species (e.g. Calamagrostis epigejos) from causing serious problems in regeneration (Gálhidy et al 2006, Kelemen et al 2012)
Summary
The significance of the herbaceous layer in forest biodiversity and ecosystem functioning has been widely appreciated (Whigham 2004, Gilliam 2014), generating an interest in its dynamics. The observed changes were attributed to different background causes, such as combined effect of temperature increase and canopy opening (De Frenne et al 2013, 2015), abandonment of former forest management practices (Hédl et al 2010, Heinrichs et al 2014), lack of disturbance (Brewer 1980, Taverna et al 2005), deer herbivory (Rooney and Dress 1997, Taverna et al 2005, Wiegmann and Waller 2006), increased soil acidity (Falkengren-Grerup and Tyler 1991, Durak 2010, Šebesta et al 2011), nitrogen deposition (Verheyen et al 2012) and often the intermingled influence of several factors (Heinrichs et al 2014, Vanhellemont et al 2014, Bernhardt-Römermann et al 2015, Naaf and Kolk 2016). A loss of rarer native plants (Hédl 2004) and the homogenization of the herbaceous layer was detected, and was attributed to high browsing pressure by deer herbivory (Wiegmann and Waller 2006), acidification (Durak 2010) and light deficit (Davison and Forman 1982, Heinrichs et al 2014)
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