科研之友
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摘要
After the elimination of wolves (Canis lupis L) in the 1920s wood ripari in plant communities on the northern range of Yellowstone National Park (YNP) declined an estimated 50% After the reintroduction of wolves in 1995-1996 riparian willows (Salix spp) on YNP s northern range showed significant growth fin the first time since the 1920s However the p ice of willow recovery h is not been uniform Some communities have exceeded 400 cm while others are still at pre 1995 levels of <80 cm mean height We took intensive repeated mensurements of abiotic factors including soil and water table characteristics to determine whether these factors might be contributing to the varying pace of willow recovery Willows it all of our stud) sites were short (<250 cm max height) piror to 1995 and has e recovered to varying degrees since We contrasted till (>250 cm max height) willow sites where willows had escaped elk (Cervus elaphus L) browsing with short willow sites that could still be browsed Unlike studies that m inpulated willow height with fences and artificial dams we examined sites that had natural growth differernces in height since the reintroduction of wolves Tall willow sites had greater water availability more rapid net soil nitrogen mineralization greater snow depth lower soil respiration rates and cooler summer soil temperatures thin ne irk short willow sites Most of these differences were measured both in herbaceous ate is adjacent to the willow pitches and in the willow patches themselves suggesting that they were not effects of vu-sing willow height rumen but were instead preexisting site differences that may have contributed to increased plant productivity Our results agree with c idler studies in experimental plots which suggest that the varying pace of willow recovery has been influenced by abotic limiting factors that interact with top down reductions in willow browsing by elk
- 出版日期2010-10
