Effects of Time Lag in Establishment of Deer-proof Fences on Recovery of Floor Vegetation and Regeneration of Tall Trees in a Beech Forest Diminished by Sika Deer Browsing in the Tanzawa Mountains of Central Japan

27 Mar Effects of Time Lag in Establishment of Deer-proof Fences on Recovery of Floor Vegetation and Regeneration of Tall Trees in a Beech Forest Diminished by Sika Deer Browsing in the Tanzawa Mountains of Central Japan

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Abstract

ニホンジカの採食圧で1980年代後半からスズタケが退行したブナ林において, 同一斜面上で1997年と2002年に隣接して設置された植生保護柵 (以下, 1997柵, 2002柵) 内で, スズタケの回復と高木性樹種の更新のしやすさを, 柵を設置して7年後のデータから考察した。スズタケの稈高は1997柵内と2002柵内の両方で56∼75 cmであり同程度であった。スズタケの被度は1997柵内では経年的に増加する傾向を示したが, 2002柵内では増加しなかった。相対優占度でみると1997柵内ではスズタケと高木, 低木が18∼35%で競合したのに対して, 2002 柵内では低木が82%を占めていた。スズタケ稈高よりも高い更新木の密度は両柵ともに1,250本/haであった。以上のことから, スズタケの回復を目的として柵を設置するなら, 退行しはじめた段階で設置することが望ましいと考えた。一方, 樹木の更新にとっては柵を早期に設置する必要はないと結論づけた。どの樹種が林冠の後継樹となるかは引き続き追跡調査が必要である。

English Abstract

Recovery of dwarf bamboo (Sasamorpha borealis) and regeneration of tree species were investigated inside and outside two deer-proof fences in a beech forest diminished by sika deer. One fence was installed in 1997 (1997F) and the other was installed next to it in 2002 (2002F). The time lag in installing the deer-proof fences was evaluated from the data 7 years after the installation of the fences. The height of the S. borealis protected by 1997F was equal to that protected by 2002F. Coverage of S. borealis inside 1997F grew wider with progress of time, but that inside 2002F did not increase. Floor vegetation inside 1997F consisted of S. borealis (21%), trees (18%), and shrubs (35%) in relative domi nce, while that inside 2002F consisted solely of shrubs (82%). The density of regenerated trees higher than S. borealis was 1,250/ha in both 1997F and 2002F. These findings demonstrated that the early establishment of deer-proof fences e bles the best possible recovery of S. borealis. In contrast, our evaluation suggested that early establishment of deer-proof fences is not necessary for the regeneration of tall trees. Further monitoring is required to predict the future regeneration of trees.