The ecological implications of rubber‐based agroforestry: Insect conservation and invasion control. Issue 8 (10th May 2020) - Lee, Roger Ho
Abstract: Protected areas are increasingly threatened by biological invasions, especially in tropical Asia where extensive areas of natural habitats have been converted to monoculture plantations. Such disturbance provides a gateway for exotic species invasions, highlighting an urgent need for cross‐boundary solutions to mitigate invasion impacts. Agroforests, with multi‐storied trees and crops resembling the complex structure of natural forest, are known to promote native species compared to monoculture plantations. Yet, our knowledge on their roles in controlling exotic species is limited to plant invaders, with effects on animal invaders still unknown. Given that protected areas are increasingly threatened by invaders from surrounding plantations, with a majority of them represented by insects, it is important to evaluate the effect of agroforestry practice, and mechanisms of associated management to control invasions. By using both taxonomic and functional trait‐based approaches, we studied leaf litter ant communities in 12 rubber monoculture (mono‐rubber), 9 rubber plantation with understory crops (agro‐rubber), 16 secondary and 12 old‐growth secondary forest plots in and around protected areas in Hainan, China. Sampled ants were further classified into groups based on their invasive potential (tramp vs. non‐tramp) to determine the ecological values of agro‐rubber. We found that despite mono‐rubber and agro‐rubber presenting similar species richness, the latter (a) supports species composition and functional diversity more similar to secondary forests and (b) reduces tramp ant species occurrence, a novel management incentive. Nonetheless, agro‐rubber is not comparable to secondary forest in terms of non‐tramp ant species composition. Synthesis and applications. Against the increasing threat of biological invasions, preserving natural forests in human‐dominated landscapes is crucial. Increasing the area of agro‐rubber at the periphery of protected areas as a proactive mitigation can, however, be perceived as an additional measure to reduce invasive species' establishment and spread across the landscape. Plantation‐based agroforestry has emerged as a potential management avenue and incentive for transforming monoculture plantations into a less 'harmful' alternative. Abstract : Against the increasing threat of biological invasions, preserving natural forests in human‐dominated landscapes is crucial. Increasing the area of agro‐rubber at the periphery of protected areas as a proactive mitigation can, however, be perceived as an additional measure to reduce invasive species' establishment and spread across the landscape. Plantation‐based agroforestry has emerged as a potential management avenue and incentive for transforming monoculture plantations into a less 'harmful' alternative. 摘要: 因農業需求增加 保護區周邊的自然棲息地亦被開墾成種植單一樹種的人工林 情況於東南亞地區尤其顯著。這些生境上的改變增加了保護區被外來物種入侵的風險。為降低有關風險 人工林的運作模式應從生態角度上去作出考慮及優化。 與種植單一樹種的人工林相比 以林下套種模式運作的人工林由多層作物組成 仿傚天然林的生境結構 有利本地物種的使用。然而 林下套種技術能控制外來植物的入侵 但其於控制入侵性動物上的成效仍有待研究。鑑於入侵性動物（大部份是昆蟲）對保護區的威脅日趨嚴重 我們有需要評估林下套種技術於控制入侵性昆蟲上的成效。 我們在中國海南的保護區周邊及區內範圍分別採集了12個橡膠單作人工林樣地（常規組）﹑9個橡膠林下套種人工林樣地（套種組）及16個次生林和12個成熟次生林的地棲螞蟻群落。我們根據入侵潛力 把螞蟻品種分成具入侵性（Tramp ）和 非具入侵性（Non‐tramp）種 再就其群落的組成和功能性狀（Functional trait）作出分析來比較各組的生態價值和抗入侵的能力。 我們發現 儘管常規組和套種組表現出相似的地棲螞蟻品種豐度 但後者的螞蟻物種組成和功能多樣性狀與次生林更為相似 並且減少了具入侵性（Tramp ）種的出現率；但就非具入侵性（Non‐tramp）種的物種組成 套種組還不能與次生林相比。 合成與應用: 面對日益嚴重的生物入侵威脅 保存保護區周邊的天然森林至關重要。然而 增加保護區周邊的套種組面積亦可作為一項緩解入侵威脅的措施 減少入侵物種的建立和擴散。以林下套種模式取代單作人工林可是一種相對'危害較小'的替代方案 值得我們關注。