Anti-browsing effects of birch bark extract on fallow deer

Abstract

A major problem within forest industry is unwanted browsing on seedlings from mammalian herbivores. The aim of this study was to evaluate the effects of birch bark extracts as repellents towards fallow deer. Birch bark was extracted in a conventional way with ethanol as solvent at ambient temperature and with a new method, liquid CO2 extraction. An analysis of the ethanol-extracted birch bark showed that it contained large amounts of terpenoids, of which the most abundant was betulin. In seven different treatment trials, we used 15 individually handled fallow deer. To investigate the binary taste preferences, birch bark extract was added to food and presented in two bowls in typical two-choice tests. We found that the amount of a food type consumed during a trial and the number of shifts between food bowls were dependent on the amount of the birch extract the food contained. Concentrations of above 1 % by dry weight of birch extract acted as a repellent. In addition, such concentrations produced shorter feeding bouts by a greater willingness to change bowls. Therefore, our conclusion is that birch bark extract acts as a repellent towards fallow deer and is therefore likely to act as a repellent against other deer species. In addition, we show that birch bark extract produced by the new and more environmentally sustainable method employing liquid CO2 mixed with ethanol has the same repellent effect as the traditional ethanol extraction.