Feeding behaviour of red deer ( Cervus elaphus) on sitka spruce ( Picea sitchensis): the role of carbon-nutrient balance

• Published in: Forest ecology and management 1996-11, Vol.88 (1), p.121-129
• Main Authors: Iason, G.R., Duncan, A.J., Hartley, S.E., Staines, B.W.
• Format: Article
• Language: English
• Subjects: BROWSING; Carbon-nutrient balance; CERVUS ELAPHUS; FEEDING PREFERENCES; FISIOLOGIA DE LA NUTRICION; Foraging; NUTRITION PHYSIOLOGY; PATURAGE AERIEN; PHYSIOLOGIE DE LA NUTRITION; PICEA SITCHENSIS; PREFERENCE ALIMENTAIRE; PREFERENCIAS ALIMENTARIAS; RAMONEO; Red deer; Sitka spruce
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/S0378-1127(96)03817-0

This study aimed to establish the relevance of the carbon: nutrient balance hypothesis (CNB) to the browsing behaviour of red deer on Sitka spruce. The responses of Sitka spruce saplings to the four factorial combinations of neutral shade/no shade and high/low fertilizer application were examined. The effects of the resultant chemical and growth responses of the trees on feeding behaviour by red deer hinds were then experimentally tested. As predicted by CNB, high soil nutrient levels increased a range of growth characteristics and total nitrogen concentrations of shoots whilst the levels of condensed tannins, and fibre components were reduced. These growth effects were depressed by the simultaneous application of shade. In contrast, there were no treatment effects on leaf monoterpene content. In 36 trials, hinds were offered 16 saplings deriving from combinations of two of the four treatments. All six combinations of pairs of treatments were tested on each of six hinds. Larger trees or those with more lateral branches were more likely to be browsed by deer, were browsed for longer and suffered greater offtake than smaller or less bushy trees. Contrary to expectation, addition of the shade and fertilizer treatment into the regression model did not explain any additional variation in the probability of attack, offtake from trees or time spent at trees. In a further experiment to test the effects of the volatile monoterpenes on feeding behaviour, greater tree size was again associated with higher probability of attack while chemical parameters had no effect. However, those trees with greater leaf monoterpene concentrations suffered less offtake by deer when browsed, suggesting that these compounds only affect feeding behaviour after the tree was attacked. The hinds' prior assessment of trees as a food patch appeared to be limited to morphological assessment. Although several chemical constituents of Sitka spruce responded to shade and fertilizer according to the CNB predictions, no effect of these treatments on deer feeding behaviour was detected. In contrast, monoterpenes did not obey CNB predictions but had a negative effect on foraging behaviour. Whilst CNB may be able to predict some aspects of trees' secondary chemistry, these responses may not necessarily influence herbivores' browsing behaviour.