Received: 4 November 2019 | Revised: 14 October 2020 | Accepted: 22 October 2020 DOI: 10.1111/avsc.12543 RESEARCH ARTICLE Applied Vegetation Science Long-term exclosure of sheep-grazing from an ancient wood: Vegetation change after a sixty-year experiment Ondřej Vild1 | Ian Douglas Rotherham2 1Institute of Botany, Czech Academy of Sciences, Průhonice, Czech Republic Abstract 2Faculty of Development & Society, Question: An ancient woodland site with a long history of coppicing and heavy Sheffield Hallam University, Sheffield, UK grazing was protected from domesticated stock in 1955. Results of a vegetation- Correspondence monitoring experiment were subsequently published in 1983. This study followed Ondřej Vild, Institute of Botany, Czech up the original research to investigate whether observed trends were as predicted. Academy of Sciences, Zámek 1, CZ-252 43 Průhonice, Czech Republic. These included a shift in tree species composition in favour of shade-tolerant spe- Email: [email protected] cies, beech (Fagus sylvatica) and rowan (Sorbus aucuparia), at the expense of light- Funding information demanding birch (Betula spp.) and oak (Quercus petraea agg.), and progress towards a The research leading to these results received funding from the European typical woodland ground flora. Research Council under the European Location: Peak District National Park, United Kingdom. Union's Seventh Framework Program (FP7/2007-2013)–ERC Grant agreement no. Methods: The mixed oak–birch woodland was re-surveyed in 2011. Two enclo- 278065 and the Czech Science Foundation sures (1955 and 1980s) and an unenclosed control area were investigated. Overstorey project No. 17-09283S. Additional funding was provided by the long-term research structure and composition was assessed by measuring canopy openness and the development project of the Institute of girths of all trees and saplings. Herb layer species composition was also recorded in Botany, Czech Academy of Sciences, RVO 67985939. 28 vegetation plots. Results: We demonstrated a progressive decline in the number of mature oaks and Co-ordinating Editor: Ralf Ohlemuller birch in the old enclosure although they still regenerated successfully. Only a few individuals of beech and rowan appeared. Herb layer species composition differed between the subareas but since the 1980s, the temporal change in the old enclosure was negligible. The new enclosure followed a similar pattern in both canopy and herb layer as observed in the early years in the old enclosure. However, the control sub- area had no regeneration of woody species and limited ground flora. Conclusions: After nearly 60 years, the replacement of light-demanding dominants by shade-tolerant trees was still limited, probably by low pH and stable light condi- tions. The findings are pertinent to the impacts of large herbivore grazing (domestic stock or wild) on woodland dynamics. KEYWORDS ecological succession, forest management, grazing intensity, herbaceous layer, long-term change, species diversity, temperate woodland, tree regeneration, vegetation monitoring © 2020 International Association for Vegetation Science Appl Veg Sci. 2020;00:1–10. wileyonlinelibrary.com/journal/avsc | 1 2 VILD AND DOUGLAS ROTHERHAM | Applied Vegetation Science 1 | INTRODUCTION unfavourable soil conditions and harsh climate. The experiment was one of the first of its kind, and therefore attracted the atten- Many European landscapes have been shaped by impacts of grazing tion of local researchers who subsequently investigated aspects of animals for millennia (Bakker and Londo, 1998), firstly by wild grazers woodland changes (Jarvis, 1960; Anderson, 1978). Following sheep and then by domestic stock. The impacts of large, grazing herbivores exclusion the most detailed surveys up to the 1980s were led by at landscape scale, of fluctuations between domestic and wild stock Dr Donald Pigott. Details of the early research were described by over time, and of protection of woods from grazing, are currently Pigott (1983), and the major findings are summarised for the current debated (e.g.Vera, 2000; Rotherham, 2013a; Plieninger et al., 2015). study. In the first two years after sheep exclusion Deschampsia flex- Relevance of this debate is further discussed in Appendix S1 of ESM. uosa, Vaccinium vitis-idaea and Vaccinium myrtillus quickly recovered. Recent recognition of detrimental impacts of over-grazing by do- Within a year, Deschampsia flexuosa was outcompeted by Vaccinium mestic stock on woodland regeneration led to conservation-oriented myrtillus and Pteridium aquilinum. Other species, including wood- attempts to reduce stocking densities or completely eliminate graz- land specialists such as Luzula pilosa, gradually started to appear. ing by larger herbivores from European temperate woodlands using By 1981, there was successful recruitment of dominant trees, oak fencing exclosures (e.g. Hester et al., 1996; Latham and Blackstock, (Quercus petraea agg.) and birch (Betula pendula, Betula pubescens 1998; Cooper and McCann, 2011; Newman et al., 2014). However, and hybrids) along with a few saplings of previously absent woody the roles of grazing herbivores in woodland dynamics remain con- species, such as beech (Fagus sylvatica) and rowan (Sorbus aucu- tentious in conservation management (Pereira and Navarro, 2015). paria). Vegetation changes were accompanied by soil development, Grazing impacts on tree regeneration vary with different tree the humus layer becoming less compact, better structured and with life stages. Grazers may be vectors of seed dispersal and through enhanced moisture regime. Pigott (1983) concluded that absence of soil disturbance create patches for seedling establishment. Seedling sheep-grazing was important in influencing both herb layer species growth may be facilitated by reduced competition from ground veg- composition and woody species recruitment and establishment. The etation. On the other hand, it may be reduced due to direct damage present study aimed to determine whether the originally observed (Mitchell and Kirby, 1990; Hester et al., 1996; Perrin et al., 2006). successional trends had continued along predicted pathways or had Furthermore, different responses of tree species to herbivore im- slowed, stopped, or changed direction. The specific focus was on pact have implications for woodland dynamics and exclusion of tree regeneration and herb layer composition. An additional, adja- grazing may eventually lead to replacement of forest dominants. For cent area was enclosed in the early 1980s and surveyed to inves- example, in an exclosure experiment in oak-dominated woodland in tigate whether the succession had been similar to that in the old North Wales, Linhart and Whelan (1980) observed increased regen- enclosure. A small adjacent area remains unenclosed and allows eration of highly palatable and shade-tolerant sycamore (Acer pseu- observation of the still-grazed wood, albeit with reduced intensity doplatanus) in fenced plots. Similarly, in a 20-year old exclosure in since the 1980s. alder (Alnus glutinosa)-dominated wood in the same area, there was Most research on animal exclosures focused on impacts of wild no alder regeneration but high densities of ash (Fraxinus excelsior) ungulates (Russell et al., 2001; Habeck and Schultz, 2015), and saplings were recorded (Latham and Blackstock, 1998). studies of domestic animals are rarer and often span under two de- Ground flora species composition is influenced by similar mech- cades (e.g. Linhart and Whelan, 1980; Latham and Blackstock, 1998; anisms leading to the increase in palatable species such as Rubus Cooper and McCann, 2011). In this paper, we evaluate the following fruticosus and the decline of less-competitive, low-growing spe- hypotheses: (a) in the old enclosure protected for 56 years, light-de- cies (Latham and Blackstock, 1998; Perrin et al., 2011; Newman manding oak and birch will be gradually replaced by shade-tolerant et al., 2014). Shifts in species composition are often accompanied by beech and rowan; (b) ground flora composition will further develop changes in species richness; frequently with an initial increase fol- towards shade-tolerant communities due to increased canopy shad- lowed by decline as competitive species become dominant (Cooper ing and competition from regenerating trees; and (c) in the new and McCann, 2011; Perrin et al., 2011; Newman et al., 2014). (1980s) enclosure, changes in tree regeneration and ground flora will Yarncliff Wood, situated in the Peak District National Park, is an follow trajectories originally observed in the old (1955) enclosure. excellent example of semi-natural, South Pennine, oak–birch wood- Preliminary results based on a subset of plots were published in Vild land (Clapham, 1969). The woodland is on rough boulder-strewn and Rotherham (2011). peri-glacial talus slopes and by the 1950s, was regarded as a char- acteristic presentation of such woodland with oak-dominated can- opy, “naturally depauperate ground flora,” and little regeneration of 2 | METHODS trees and shrubs. Surveys indicated that since at least 1852, there had been almost no tree or shrub regeneration (Pigott, 1983). In 2.1 | Study area 1955, in order to investigate the significance of sheep-grazing on tree and shrub regeneration in the wood, an enclosure of 1.12 ha The study site is located in Yarncliff Wood (Padley Gorge; 53°18' was erected around a part of the then open grazed woodland. One N, 1°37' W) in the Peak District Nation Park, UK. In 1972, the possibility