The study examined the damage caused to naturally regenerated Scots Hue by red deer and certain other mammals and birds, and its effect on the development of natural woodland. Investigations were concentrated in three areas, which carried high, moderate and low stockings of red deer, in the upper Dee valley in Aberdeenshire. Most marked trees, above 2-3 inches in height, suffered some degree of browsing during the study period. Simulated browsing experiments, supported by data from study plots, showed that survival and growth of trees decreased with increased browsing severity. Severe browsing had less serious effects on large trees than on small ones. In response to browsing, new shoots were produced from large overwintering buds in larch and birch but, in pine, shoots were normally produced from dormant buds, which required a growing season in which to develop before vigorous growth was possible. Where browsing pressure was high, the deciduous species generally survived longer than pine because they were not subjected to severe winter damage and they probably suffered less interruption to their photosynthetic activity as a result of their more rapid response to browsing. Tree browsing records and observations in study plots confirmed that numerous mammals and birds browsed pine. Most species, however, had relatively little effect on woodland development. Densities of rabbits and mice were very low, and pine material was probably only a minor constituent in the diet of mountain hares and red grouse. Browsing by jred and roe deer could not be distinguished consistently, but the satisfactory development of natural regeneration in exclosures, where red deer were largely excluded but roe were common, suggests that roe densities of up to approximately 1*24 acres are too low to exert a serious effect on woodland development. Sheep commonly browsed pine in winter, but most animals were nonnally taken off the hill from November to May. Browsing on young regeneration by capercaillie was apparently restricted to pine of .4-30 inches high, which were few where capercaillie were numerous. Disbudding by black grouse was widespread but, in these areas, their browsing never affected tree survival and rarely prevented the addition of some increment during the year of damage. Browsing by red deer had the most serious effects on the survival and development of pine. Browsing had relatively little effect on tree development where red deer densities were approximately 1*150 acres in winter (Cambus O'May); but it caused mortalities in trees below 30 inches high and reduced growth in trees below 60 inches, in areas where winter densities approximated to 1:60 acres (Bush Lawsie). Densities of It10 acres (Meall Alvie) totally prevented the development of woodland. A comparison of tree browsing incidence with indices of red deer abundance in study plots, and a detailed examination of the conditions under which these trees were browsed, showed that whilst intensity of pine browsing is related to deer density, the two are not directly proportional to each other. The relationship is modified by environmental factors of climate and the habitat, notably the choice and availability of tree material and of the alternative vegetation which comprises the deer*a diet. Observations on feeding, rumen content analyses and comparisons of browsing intensity on trees of different origin and appearance showed that red deer browsed certain species of vegetation, and trees of certain sizes and condition, selectively. Habitats which contained large quantities of preferred vegetation and low quantities of acceptable tree material, therefore, suffered less pine browsing proportional to their use by deer than habitats in which these conditions were reversed. Deer abundance was invariably a significant factor in the amount of tree browsing which a habitat sustained, however, because increased browsing intensity removed more preferred vegetation and acceptable tree material and forced the deer to browse more heavily on less acceptable trees. Tree mortality from trampling had little effect on woodland development because damage was confined to very small trees in areas where regeneration was profuse. Relatively few trees were affected by antler damage, but these injuries could be locally significant where tree densities are low. On grouse moors, regular heather burning was principally responsible for the absence of natural woodland. Tree mortality from insects and fungi was negligible. Deaths from climatic agencies, notably drought and frost lift, were fairly few and were largely confined to very small trees. Snowbreak might have locally serious effects on the development of larger trees in winters of exceptional snowfall.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:459478 |
| Date | January 1967 |
| Creators | Holloway, Colin W. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=218136 |
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