EFFECTS OF MARCESCENT LEAVES ON WINTER BROWSING BY LARGE HERBIVORES IN NORTHERN TEMPERATE DECIDUOUS FORESTS

Abstract

Presence of marcescent leaves during winter is a common phenomenon in northern-temperate deciduous forests across the Holarctic, but the ecological significance of marcescence on woody vegetation has received little attention. Especially, implications for browsing by cervids during winter have not been determined. Therefore, I conducted a feeding trial using free-roaming red deer (Cernus elaphus), fallow deer (Dama dama), and sika deer (Cervus nippon) to evaluate effects of marcescent leaves on herbivory of European beech (Fagus sylvatica), hornbeam (Carpinus betulus), and common oak  (Quercus robur) during winter. The feeding trial was conducted in Jægersborg Dyrehave, Denmark, during February 1992. Forty small-diameter (< 6 mm) branches of each tree species with < 2 years of growth and marcescent leaves present were divided into 2 groups. One group had their leaves removed (treatment) and the other group had the leaves retained (control). Branches were labeled, weighed, and randomly placed in a grid (0.5 x 0.5 m apart) in the field. After 7 days, branches were counted and weighed to determine amount of browse removed. In addition, 12 branches of each species were collected for biomass and chemical analyses. Stems and leaves were analyzed separately for crude protein, neutral-detergent fiver, acid-detergent fiber, lignin, and cellulose. Both beech and hornbeam were browsed significantly more by weight and by number of branches when the leaves were removed. Oak branches were browsed the same regardless of leaf presence. Biomass or marcescent leaves of beech and hornbeam were a significantly greater proportion of the overall branch biomass compared with oak. Chemical analyses showed that stems of hornbeam and beech, when compared with their marcescent leaves has a higher lignin content. Leaves compared with stems of common oak had a higher protein and lower lignin content compared with other species. These results indicate that marcescent leaves greatly reduced the nutritive value of winter browse, which was reflected in the lower browse preference for their leaves. Therefore, marcescent leaves may be viewed as an anti-herbivore mechanism.