Water and Land Resource Centre, Addis Ababa University, P.O. Box 3880, Addis Ababa, Ethiopia.
CSIR Smart Places Cluster, 11 Jan Cilliers Street, Stellenbosch, 7599, South Africa.
Sci Rep. 2021 Jan 29;11(1):2688. doi: 10.1038/s41598-021-81776-6.
Dense impenetrable thickets of invasive trees and shrubs compete with other water users and thus disrupt ecosystem functioning and services. This study assessed water use by the evergreen Prosopis juliflora, one of the dominant invasive tree species in semi-arid and arid ecosystems in the tropical regions of Eastern Africa. The objectives of the study were to (1) analyze the seasonal water use patterns of P. juliflora in various locations in Afar Region, Ethiopia, (2) up-scale the water use from individual tree transpiration and stand evapotranspiration (ET) to the entire invaded area, and 3) estimate the monetary value of water lost due to the invasion. The sap flow rates of individual P. juliflora trees were measured using the heat ratio method while stand ET was quantified using the eddy covariance method. Transpiration by individual trees ranged from 1-36 L/day, with an average of 7 L of water per tree per day. The daily average transpiration of a Prosopis tree was about 3.4 (± 0.5) mm and the daily average ET of a dense Prosopis stand was about 3.7 (± 1.6) mm. Using a fractional cover map of P. juliflora (over an area of 1.18 million ha), water use of P. juliflora in Afar Region was estimated to be approximately 3.1-3.3 billion m/yr. This volume of water would be sufficient to irrigate about 460,000 ha of cotton or 330,000 ha of sugar cane, the main crops in the area, which would generate an estimated net benefit of approximately US$ 320 million and US$ 470 million per growing season from cotton and sugarcane, respectively. Hence, P. juliflora invasion in the Afar Region has serious impacts on water availability and on the provision of other ecosystem services and ultimately on rural livelihoods.
密集而难以穿透的入侵树种和灌木与其他用水户竞争，从而破坏生态系统功能和服务。本研究评估了常绿银叶相思（Prosopis juliflora）的水分利用情况，它是东非热带地区半干旱和干旱生态系统中主要的入侵树种之一。研究的目的是：(1)分析埃塞俄比亚阿法尔地区不同地点的银叶相思季节性水分利用模式，(2)将个体树木蒸腾和林分蒸散（ET）的水分利用从个体扩展到整个入侵区域，以及 3)估计因入侵而损失的水的货币价值。个体银叶相思树的液流速率使用热比法测量，而林分 ET 使用涡度协方差法量化。个体树木的蒸腾量范围为 1-36 L/天，平均每天每棵树耗水 7 L。一棵银叶相思树的日平均蒸腾量约为 3.4（±0.5）mm，茂密的银叶相思树林分的日平均 ET 约为 3.7（±1.6）mm。利用银叶相思树的盖度图（覆盖面积为 118 万公顷），估算阿法尔地区银叶相思树的耗水量约为 31-33 亿立方米/年。这些水量足以灌溉约 46 万公顷的棉花或 33 万公顷的甘蔗，这是该地区的主要作物，从棉花和甘蔗中，每个生长季分别产生约 3.2 亿美元和 4.7 亿美元的估计净收益。因此，阿法尔地区的银叶相思树入侵对水资源供应以及其他生态系统服务的提供产生了严重影响，并最终影响到农村生计。
