Trade-off of ecosystem productivity and water use related to afforestation in southcentral USA under climate change

• Published in: The Science of the total environment Vol. 915; p. 170255
• Main Authors: Zhang, Tian, Yang, Jia, Winrich, Abigail, Will, Rodney E., Zou, Chris B.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10.03.2024
• Subjects: Climate transition zone; RCP45 and RCP85; Southern Great Plains; SWAT; Tree cover increase; SWAT; Climate transition zone; Tree cover increase; RCP45 and RCP85; Southern Great Plains
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.170255

The increase of tree canopy cover due to woody plant encroachment and tree plantations modifies both carbon and water dynamics. The tradeoffs between ecosystem net primary productivity (NPP) and water use with increasing tree cover in different climate conditions, particularly under future climate scenarios, are not well understood. Within the climate transition zone of the southern Great Plains, USA, we used the Soil and Water Assessment Tool+ (SWAT+) to investigate the combined impacts of increasing tree cover and climate change on carbon and water dynamics in three watersheds representing semiarid, subhumid, and humid climates. Model simulations incorporated two land use modifications (Baseline: existing tree cover; Forest +: increasing evergreen tree cover), in conjunction with two climate change projections (the RCP45 and the RCP85), spanning two time periods (historic: 1991–2020; future: 2070–2099). With climate change, the subhumid and humid watersheds exhibited a greater increase in evapotranspiration (ET) and a corresponding reduction in runoff compared to the semi-arid watershed, while the semi-arid and subhumid watersheds encountered pronounced losses in water availability for streams (>200 mm/year) due to increasing tree cover and climate change. With every 1 % increase in tree cover, both NPP and water use efficiency were projected to increase in all three watersheds under both climate change scenarios, with the subhumid watershed demonstrating the largest increases (>0.16 Mg/ha/year and 170 %, respectively). Increasing tree cover within grasslands, either through woody plant expansion or afforestation, boosts ecosystem NPP, particularly in subhumid regions. Nevertheless, this comes with a notable decrease in water resources, a concern made worse by future climate change. While afforestation offers the potential for greater NPP, it also brings heightened water scarcity concerns, highlighting the importance of tailoring carbon sequestration strategies within specific regions to mitigate unintended repercussions on water availability. [Display omitted] •SWAT+ was used to simulate afforestation impact on productivity and water use.•Increasing tree cover boosts carbon sequestration and water use efficiency.•Extensive tree cover reduces water yield, particularly in warmer, drier climates.•The development of afforestation policy should consider both carbon and water.