University of California, Davis, Davis, CA 95616, United States of America.
Macalester College, St Paul, MN 55105, United States of America.
Sci Total Environ. 2022 Dec 1;850:157908. doi: 10.1016/j.scitotenv.2022.157908. Epub 2022 Aug 6.
Millions of people depend on ecosystem services provided by Tropical Dry Forests (TDFs), yet their proximity to population centers, seasonally dry climate, and the ease at which they are converted to agriculture has left only 10 % of their original extent globally. As more TDFs become protected, basic information relating TDF age to subsurface water resources will help guide forest recovery. Severe deforestation and recent reforestation around Bahía de Caráquez, Ecuador produced a mosaic of different successional stages ideal for exploring relationships between TDF age, subsurface water availability and species-specific responses to seasonal drought. Over one year, we measured gravimetric water content, predawn and midday leaf water potential, and the stable isotope composition of xylem and source waters in two regenerating and one primary forest. Over the transition from wet to dry season, we discovered a sharper decrease in predawn water potential in younger successional forests than in the primary forest. Growing in degraded subsurface environments under increased competition, successional forest trees accessed deeper sources of moisture from unsaturated weathered bedrock and groundwater through the dry season; however, different species employed distinct water use strategies. Ceiba trichistandra maintained midday water potentials above -1.27 MPa through a drought avoidance strategy dependent on groundwater. Sideroxylon celastrinum tolerated drought by lowering predawn and midday water potential through the early dry season but took up greater proportions of saprolite moisture and groundwater as the dry season progressed. Contrastingly, Handroanthus chrysanthus maintained access to shallow soil and saprolite moisture by dropping midday water potential to -4.30 MPa, reflecting drought tolerance. Our results show that limited subsurface water resources in regenerating TDF's lead to species-specific adaptations reliant on deeper sources of moisture. The recovery of soil and saprolite hydrologic properties following disturbances is likely to exceed 100 years, highlighting the importance of forest conservation.
数百万人依赖热带干旱森林（TDF）提供的生态系统服务，但由于其靠近人口中心、季节性干旱气候以及易于转化为农业用地，目前全球仅剩下 10%的原始 TDF 面积。随着越来越多的 TDF 得到保护，与 TDF 年龄相关的基本信息与地下水资源相关联，将有助于指导森林恢复。厄瓜多尔卡拉克斯湾的严重森林砍伐和最近的重新造林导致了不同演替阶段的镶嵌模式，非常适合探索 TDF 年龄、地下水资源可用性以及物种对季节性干旱的特定响应之间的关系。在一年的时间里，我们测量了两个再生林和一个原始林的土壤重量含水量、晨始和中午叶片水势以及木质部和水源的稳定同位素组成。在从湿季到干季的转变过程中，我们发现年轻演替林的晨始水势下降幅度比原始林更为明显。在退化的地下环境中，与竞争加剧的情况下，演替林树木通过干季从非饱和风化基岩和地下水获取更深层次的水分；然而，不同的物种采用了不同的水分利用策略。Ceiba trichistandra 通过依赖地下水的干旱避免策略，将中午水势保持在-1.27 MPa 以上。Sideroxylon celastrinum 通过在早干季降低晨始和中午水势来耐受干旱，但随着干季的进行，它吸收了更多的风化层和地下水水分。相比之下，Handroanthus chrysanthus 通过将中午水势降至-4.30 MPa，反映出耐旱性，从而保持了对浅层土壤和风化层水分的获取。我们的研究结果表明，再生 TDF 中有限的地下水资源导致了对更深层次水分源的物种特异性适应。干扰后土壤和风化层水文特性的恢复可能需要超过 100 年的时间，这突显了森林保护的重要性。
