Artificial shade shelters mitigate harsh microclimate conditions and enhance growth in tropical tree seedlings planted in degraded land

Abstract

We evaluate the efficacy of artificial shade shelters in promoting seedling growth and ecophysiological traits in degraded tropical forest land. Seedlings of Dyera costulata were planted in an open control plot and two open-top shade shelters (2 and 3m in height). Leaf traits, including nitrogen content, the ratio of variable to maximum fluorescence (Fv/Fm), and chlorophyll content (SPAD value) were assessed in the nursery prior to planting, and again at 2, 7, 12, and 16 months after planting. Seedling height, diameter, biomass, and leaf number were also assessed. Shade shelters reduced light intensity to approximately 70% and maximum temperature by up to 3.1°C. Minimum daily air humidity was up to 12% higher in the shelters relative to the open control. Seedling growth was better under both shelters relative to the open control, but particularly for the 2m shelter. Seedlings planted in the open lost roughly half their leaves immediately after planting due to environmental stress, whereas leaves were retained by seedlings under the shelters. A decrease in the Fv/Fm ratio was observed in the open control both 2 and 7 months after planting, indicating photoinhibition. The maximum photosynthetic rate decreased in all conditions immediately after planting, but seedlings under the shelters recovered faster, especially in the 2m shelter. Decreases in leaf number and photosynthetic capability in the initial stages following planting may limit seedling growth in open conditions. The improved growth and ecophysiological parameters under the shelters persisted for up to 16 months after planting, indicating that shelters may be valuable tools for reforestation and rehabilitation in degraded tropical forests.