JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. In Sweden, moose (Alces alces) feed to a large extent on birches (Betula pendula and B. pubescens). This study examined responses ofjuvenile birches to moose browsing and the responses of moose to browsed trees. Following browsing, the birches produced larger shoots with larger and more chlorophyll-rich leaves than did unbrowsed birches. Shoots on browsed trees had a longer growing season and contained less Ca, Mg, and crude fat than did shoots on unbrowsed trees. After browsing, some resting buds and buds on some of the short shoots developed into long shoots, a response that was more frequent in an open habitat than in a shaded one. The birches thus showed substantial compensatory growth following browsing by moose. Most of the potential buds were not transformed into long shoots, even though more growth was allocated to each individual shoot. For moose this meant that at moderate browsing pressures (1) the production of shoot biomass was maintained, (2) the available forage increased because the shoot growth was kept at lower positions, and (3) browsing was facilitated by the larger shoot size, but (4) the contents of Ca, Mg, and crude fat in the shoots decreased. Of the two similar birch species, moose preferred B. pendula to B. pubescens. This supports the hypothesis that plants with slow growth rates (B. pubescens) are less preferred by browsers than plants with high growth rates (B. pendula). Further, we found no support for the occurrence of induced defense in juvenile trees; those that had been browsed during the previous winter were more palatable than previously unbrowsed trees.

No abstract

Large herbivores affect the morphology and productivity of their food plants, which in turn affects food availability and foraging efficiency. These effects can occur directly, through tissue removal, or indirectly through additions of nutrients in dung and urine. Although influences of herbivores on plant communities are well established for grazers, less is known about the effects of browsers. We studied how tree morphology (number of shoots, shoot mass, and mean yearly height increase) and production of winter browse of Scots pine (Pinus sylvestris) and birch (Betula pubescens and B. pendula) responded to simulated moose herbivory in Swedish boreal forests. We simulated browsing, defecation, and urination to represent effects of four levels of moose density in each of eight exclosures. To be able to study the whole range of moose impact and obtain better mean estimates from the ecosystem perspective, the eight exclosures were placed along a forest productivity gradient. Treatments were applied for three consecutive years. For both birch and pine, the mean average number of shoots per tree and the mean yearly height increase decreased with increasing biomass removal. Mass of individual shoots increased for birch, but not for pine. The mean yearly production of winter browse (per m 2 ) was significantly reduced by biomass removal. The responses of birch followed a threshold model predicting no effect up to a low to moderate level of biomass removal, and thereafter a linear decrease, although the model describing constant linear decrease not could be ruled out (model selection based on Akaike Information Criterion). The response of pine followed a threshold model. We concluded that winter browse might be in shortage at high browsing pressure over extended time, but most woody plants eaten by moose should sustain browsing pressure at moose densities common in many areas in Sweden.

No abstract