農地造林對鳥類群聚及其多樣性之影響

The Effects of Plantation on Farmland Upon Avian Community and its Diversity

為了彌補因移除森林而喪失的生物多樣性，新植人工林是作法之一，但目前對於在農地上造林對地區生物多樣性所產生的影響，所知有限、亟待了解。台灣花東縱谷地區原為闊葉林覆蓋，現在則大多為農業生產利用，而花蓮縣光復鄉原從事甘蔗生產的大農大富農場自2002年改植闊葉樹，迄今面積達1000 ha。為評估該造林是否已恢復闊葉林鳥類群聚及其多樣性，以及其對周邊農地鳥類群聚及多樣性的影響，本研究於2009年及2010年的4-6月及9-11月在大農大富地區之周邊農地、鄰近海岸山脈之闊葉次生林地及人工林地調查鳥類群聚。結果顯示農地與闊葉次生林地的鳥類群聚組成及主要物種不同，農地的鳥類群聚組成較不穩定且歧異度指數較低；人工林地與闊葉次生林地之鳥類群聚亦不相同，前者之種豐富度及歧異度指數較低；農地鄰近人工林地的鳥類群聚不同於周圍無造林農地，且前者歧異度指數較高。我們認為農地若恢復為闊葉林可穩定鳥類群聚結構並增加其多樣性，但目前尚年輕的人工造林並未恢復闊葉林的鳥類群聚與多樣性，應與人工造林之植被結構簡單及物種單純有關，不過人工造林在地景上仌有增進農地鳥類多樣性的作用。為豐富人工林地的鳥類多樣性，建議減少除草並加強營造其中下層植被，可能增加目前過少的灌木層鳥種。

Planted forests may help offset biodiversity loss from deforestation, but the impacts of converting crops to plantations on local biodiversity are poorly understood. The east rift valley of Taiwan was originally covered by broad-leaved forests. Nowadays, most of the lands in the valley have been converted for various agricultural needs. The Danongdafu farm in Guanfu Township, Hualien County, was built to grow sugarcane in the 1910's. Since 2002, no more sugar is produced and broad -leaved trees were replanted over 1000 hectare of lands in the valley. Base on the plantation, this study is an evaluation of (1) the effects of converting broad-leaved forests to crops on the avian community and its diversity, (2) the recovery of broad-leaved forest avian species and its diversity, and (3) the impacts to the avian community and its diversity on adjacently remnant croplands. In Danongdafu forest park and its neighboring farmland and secondary broad-leaved forest, we investigated the avian communities in four habitat types including farmlands, farmlands adjacent to plantations, plantations, and secondary broad-leaved forests in April-June and September-November during 2009-2010. We found different avian species compositions and typical species in farmlands and secondary forestlands. The avian species compositions in the farmlands were less stable and the diversity indices were lower compared to the secondary forestlands. Avian species compositions were different between plantations and secondary forests, and the former communities were less diverse than the latter. Farmlands adjacent to plantations had different avian species compositions from farmlands away from plantations, and the former had higher avian diversity indices than the latter. We conclude that avian species compositions will become stable and diverse after farmlands are converted to broad-leaved forests. Avian species and diversities in broad-leaved forests did not recover in the rather young man-made plantations due to their simple vegetation structures and low plant species diversities. On the other hand, plantations might enhance avian diversities in the adjacent farmlands on the landscape. It is suggested that one of the ways to increase bird diversity in the plantation is to increase avian species in the shrub layer of planted forests, decrease the weeding frequency and create vegetation in understory of the forests.