Individual study: Woodland regeneration in relation to cattle and sheep grazing and livestock exclusion in Coed Gorswen NNR, Clwyd, Wales
Linhart Y.B. & Whelan R.J. (1980) Woodland regeneration in relation to grazing and fencing in Coed Gorswen, North Wales. Journal of Applied Ecology, 17, 827-840
The UK is one of the least forested countries in Europe. Regeneration of native Quercus woodland is being attempted in some areas but natural regeneration is absent or severely deficient in many oak-dominated woodlands. Overgrazing by livestock (sheep and cattle) is considered a problem at some sites. In this study, seedling regeneration of tree species was studied in a deciduous woodland in fenced and unfenced plots in a nature reserve in North Wales.
The study was undertaken in Coed Gorswen (National Grid ref. SH 755709), a 13 ha National Nature Reserve in Clwyd. The oak-dominated (Q.petraea and Q.robur) woodland was fenced in 1960 but small parts remained outside the reserve boundaries and grazing, primarily by sheep and cattle, continued. Other native trees present included alder Alnus glutinosa, ash Fraxinus excelsior, rowan Sorbus aucuparia and hawthorn Crataegus monogyna, and also non-native sycamore Acer pseudoplatanus.
At each of two sites, a 0.1 ha plot within the reserve ('fenced') paired with an adjacent 0.1 ha plot ('unfenced') were established. Within each plot all individuals of woody species above 1 m tall were counted and basal diameter measured. Individuals over 1 m tall but not yet reproductive were classified as saplings. For hazel Corylus avellana (due to the many basal stems) total numbers of shrubs was only recorded. Tree seedlings were counted in randomly placed rows of adjacent 0.5 x 0.5 m (0.25 m²) quadrats. Presence or absence of grazing damage was recorded for a subsample of seedlings in each plot. A comparison was also made between current and past regeneration by analysing previously collected data.
Tree species diversity and abundance of seedlings and saplings did not reflect the relative abundances of mature trees. Most seedlings were of ash but most saplings were sycamore (sometimes invasive in British woodlands) and ash. Oak regeneration was almost non-existent despite it being the dominant tree species; of 160 mature trees in the plots, 50 were oaks. However, no oak saplings were found, with only three seedlings recorded in the entire 200 m² study area. Transect samples gave an estimate of 189 oak trees/ha, but (in this 0.63 ha transect) only one seedling and two saplings were located.
There were many seedlings of various other species in the plots but in the plots open to livestock, few survived beyond 2 years. Sycamore seemed most susceptible to grazing and hawthorn least. There were four times more saplings in fenced than in the unfenced plots. In addition to apparent preferential grazing of sycamore, grazing stock also eliminated bramble Rubus fruticosus. Bramble was very abundant in the fenced area. In the fenced plots, sycamore and ash saplings were most prevalent in gaps caused by death of mature trees. In unfenced grazed areas, saplings of hawthorn and ash appeared most likely to replace mature trees.
Conclusions: Excessive grazing is known to inhibit oak regeneration but at this locality protection from grazing did not enhance regeneration. Factors important for oak regeneration such as periodic ground disturbance by large animals and burial of acorns were lacking, and brambles (colonising as a result of stock exclusion) were shading much of the ground (seedlings of Q.petraea and Q.robur are not particularly shade tolerant).
Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28198012%2917%3A3%3C827%3AWRIRTG%3E2.0.CO%3B2-V