Data from: Will trees or grasses profit from changing rainfall regimes in savannas?

• Increasing rainfall variability is widely expected under future climate change scenar- ios. How will savanna trees and grasses be affected by growing season dry spells and altered seasonality and how tightly coupled are tree-grass phenologies with rainfall? • We measured tree and grass responses to growing season dry spells and dry season rainfall. We also tested if the phenologies of 17 deciduous woody species and the Soil Adjusted Vegetation Index of grasses were related to rainfall between 2019 and 2023. • Tree and grass growth was significantly reduced during growing season dry spells. Tree growth was strongly related to growing season soil water potentials and limited to the wet season. Grasses can rapidly recover after growing season dry spells and grass evapotranspiration was significantly related to soil water potentials in both the wet and dry seasons. Tree leaf flushing commenced before the rainfall onset date with little subsequent leaf flushing. Grasses grew when moisture became available regardless of season. • Our findings suggest that increased dry spell length and frequency in the growing season may slow down tree growth in some savannas, which together with longer growing seasons may allow grasses an advantage over C3 plants that are advantaged by rising CO2 levels.

• 未来气候变化情景下，降水变异性加剧已是学界普遍预期。生长季干旱期、季节节律改变将对稀树草原（savanna）的木本植物与草本植被产生何种影响？木本-草本植物的物候与降水的耦合紧密程度又将如何？
• 本研究测定了木本与草本植被对生长季干旱期及旱季降水的响应；同时验证了2019-2023年间，17种落叶木本物种的物候特征与草本植被的土壤调整植被指数（Soil Adjusted Vegetation Index）是否与降水存在关联。
• 生长季干旱期会显著抑制木本与草本植物的生长。木本植物的生长与生长季土壤水势密切相关，且仅局限于湿季；草本植被在经历生长季干旱期后可快速恢复，其蒸散发速率在湿季与旱季均与土壤水势显著相关。木本植物的展叶始期早于雨季起始日期，后续展叶量极少；而草本植被则会在水分可获得时即刻生长，不受季节限制。
• 本研究结果表明，生长季干旱期时长与频次的增加，或会减缓部分稀树草原中木本植物的生长；结合更长的生长季，这一效应或将使草本植被相较于因CO₂浓度升高而获益的C3植物更具竞争优势。