人造針葉林與天然闊葉林鳥類群聚之比較

Abstract

為瞭解將天然闊葉林改種成人造針葉林對鳥類歧異度的影響，自民國八十三年三月到七月及八十四年三到四月於北插天山與東眼山進行天然闊葉林與人造柳杉林的繁殖鳥類群聚比較。鳥類調查採用穿越線法，並分析三十項環境因數與鳥類群聚之關係。 研究期間共記錄到三十五種繁殖鳥類，這三十五種鳥均曾出現於天然闊葉林，總計有1548隻次；柳杉林中則出現過十八種鳥，共計1332隻次。天然闊葉林中不同鳥種間的相對數量差距較小，柳杉林的鳥類數量則集中於少數幾個優勢種。天然闊葉林之鳥種歧異度或豐富度均遠高於人造柳杉林，且鳥種歧異度與樹種枝葉歧異度有顯著相關，顯示天然闊葉林中由於有多樣的樹種，所能提供給鳥的資源種類可能遠高於柳杉人造林。 影響研究區內鳥類分佈的主要環境因數為海拔與底層植被密度。底層鳥類密度與底層植被的枝葉密度有正相關，但中上層植被也可能會影響底層植被的疏密而間接影響底層鳥類的分佈。在海拔相近的樣區間，闊葉樹與針葉樹的枝葉量比例成為影響鳥類分佈的主要因數。在柳杉林中的中上層食蟲鳥類之種類和數量可能會因闊葉樹形成的塊集提供了相當數量的資源而增加。 在天然林之中、上層，鳥類生物量的垂直高度分佈與枝葉密度的分佈之正相關顯示出鳥類對樹種的利用較平均；而在柳杉林之中、上層，鳥類的生物量分佈與棲枝利用比率則顯示出鳥類較偏向使用中層的闊葉樹。研究期間所見超過五隻次的鳥共有二十種，其中十八種依其覓食行為共可分為五個生態同功群，這五個同功群在天然林及柳杉林中均存在，但在天然林中屬於同一個同功群的鳥種之相對數量多較平均，而柳杉林內之同功群成員間數量差異常常頗大。

To understand the effect of exotic conifer plantation on breeding bird communities, the comparison of breeding bird communities between conifer plantation and natural boardleaf forest was conducted in Mt. Bay-chia-ten-shan and Mt. Don-yan-shan between March-July 1994 and March-April 1995. I conducted bird censuses using the line-transect method. In both forests, 30 environmental variables were measured to investigate the relationship between habitat features and bird communities. In the boardleaf forest, 1548 individuals of 35 breeding bird species were recorded but only 18 species, 1332 individuals, were found in the conifer plantation. The evenness, richness and species diversity of bird community was higher in the boardleaf forest than in the conifer plantation. The significant positive correlation between bird species diversity and plant species-foliage volume diversity suggests that the complex plant species diversity in the boardleaf forest provided more diverse resources for birds than did the conifer plantation. The most important environmental factors that influenced the birds' distribution were altitude and the density of understory foliage. The density of understory birds and understory foliage were positively correlated. The mid- and upperstory foliage may affect the density of understory birds through affecting the density of understory foliage. In plots with similar altitudes, the primary environmental factor that determined birds' distribution was the ratio of boardleaf to conifer foliage. Patches of boardleaf tree in the conifer plantation could have contributed to the species richness and abundance of mid- and upperstory insectivorous birds. In the natural boardleaf forest, the relationship between height distribution of the biomass of mid- and upperstory birds and the height distribution of the foliage implies that birds utilized all tree species and all heights proportional to their availability. In the conifer plantation, the biomass distribution of mid- and upperstory birds and the perch utilization ratio of boardleaf to conifer trees implies that birds preferred boardleaf to conifer trees. The 18 species of birds with sufficient foraging data were classified into five feeding guilds. The five guilds were all found in both forests; however, the relative density of different species in each guild were more even for the boardleaf forest than the one in the conifer plantation.