最新衛星資料研究顯示，位居世界第二大熱帶雨林的非洲剛果雨林，在過去十年間已經消失大半。
科學家用衛星測量方法量測雨林的「綠度」，做為森林健康的指標之一。而新研究顯示，剛果地區2000年開始的長期大旱已影響森林的面積，而且在研究測量的13年間情況越來越嚴重。
紐約州立大學奧爾巴尼分校航太與環境科學系副教授周黎明博士帶領的研究團隊，以多個獨立衛星感應器測量乾旱對剛果雨林的長期效應，研究結果於23日發表在《自然》期刊。
每年4到6月是剛果雨林的第一個雨季和成長期。研究團隊分析這段期間剛果盆地森林覆蓋完好的區域，發現綠度有逐漸降低的趨勢，顯示森林正在緩慢適應長期的乾旱。
「了解雨林的改變很重要，因為多數的氣候模型預測，21世紀更乾熱且嚴重缺水的氣候，會增加熱帶雨林的生存壓力。」周黎明說。
周黎明的研究團隊表示，如果乾旱趨勢持續，很可能改變剛果雨林的組成和結構，影響其生物多樣性和吸收二氧化碳溫室氣體的能力。
與亞馬遜雨林間歇性乾旱造成的大規模樹木死亡相比，剛果雨林的反應和緩許多。森林褐化和水源減少的趨勢相符，包括雨水、地下水、表土含水和植物中的水份。
研究共同作者、美國太空總署加州帕薩迪納噴射推進實驗室的科學家Sassan Saatchi說，「剛果盆地森林能適應中等的氣候變遷程度，因為過去幾百年間剛果森林也曾處在乾燥氣候中。然而，近來氣候變遷造成的氣候異常和大西洋暖化，已引起熱帶地區嚴重乾旱，嚴重影響森林成長。」
剛果雨林跨越赤道，遍佈6個國家，覆蓋700,000平方英哩（1,800,000平方公里），佔全球僅存雨林的1/4。
剛果雨林中棲息著450種哺乳動物，包括森林象、霍加狓和倭猩猩，大猩猩的三個亞種，山地大猩猩、低地大猩猩和東部低地大猩猩都在這裡出現。此外還有300種爬蟲類、200種兩棲類、超過1000種鳥類和超過11000種植物物種。
Africa’s Congo rainforest, the second-largest tropical rainforest in the world, has lost its much greenness over the past decade, a new analysis of satellite data shows.
The study demonstrates that a persistent drought in the Congo region since 2000 has affected the greenness of an increasing amount of forest area and that the browning trend has intensified over the 13 years of the study.
Scientists use the satellite-derived measurements of forest “greenness” as one indicator of a forest’s health.
Published Wednesday in the journal “Nature,” the research uses several independent satellite sensors to measure the effects of long-term drought on the Congo rainforest.
The research team was led by Dr. Liming Zhou, associate professor of atmospheric and environmental sciences with University at Albany, State University of New York.
“It’s important to understand these changes because most climate models predict tropical forests may be under stress due to increasing severe water shortages in a warmer and drier 21st century climate,” said Zhou.
Straddling the equator and covering 700,000 square miles (1,800,000 km2) in six countries, the Congo rainforest contains a quarter of the world’s remaining tropical forest.
This rainforest is inhabited by some 450 species of mammals, including forest elephants, okapi, bonobos, and all three subspecies of gorillas – the mountain gorilla, lowland gorilla, and the eastern lowland gorilla.
There are 300 reptile species, 200 amphibians, over 1,000 species of birds and more than 11,000 different plant species.
Zhou and his team say if the drying trend continues it might alter the composition and structure of the Congo rainforest, affecting its biodiversity and ability to absorb the greenhouse gas carbon dioxide.
Zhou and his team analyzed intact, forested regions in the Congo basin each year during the months of April, May and June – the first of the area’s two peak rainy and growing seasons.
The study found a gradually decreasing trend in Congo rainforest greenness, or “browning,” suggesting a slow adjustment to the long-term drying trend.
This is in contrast to the more immediate response seen in the Amazon, such as large-scale tree mortality, brought about by more episodic drought events.
The browning of the forest canopy is consistent with observed decreases in the amount of water available to plants, whether that is in the form of rainfall, water stored in the ground, water in near-surface soils, or water within the vegetation.
“Forests of the Congo basin are known to be resilient to moderate climate change because they have been exposed to dry conditions in the past few hundred years. However, the recent climate anomalies as a result of climate change and warming of the Atlantic Ocean have created severe droughts in the tropics, causing major impacts on forests.”said co-author Sassan Saatchi of NASA’s Jet Propulsion Laboratory in Pasadena, California.
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