Environmental Drivers of Water Use for Caatinga Woody Plant Species: Combining Remote Sensing Phenology and Sap Flow Measurements

• Published in: Remote sensing (Basel, Switzerland) Vol. 13; no. 1; p. 75
• Main Authors: Paloschi, Rennan A., Ramos, Desirée Marques, Ventura, Dione J., Souza, Rodolfo, Souza, Eduardo, Morellato, Leonor Patrícia Cerdeira, Nóbrega, Rodolfo L. B., Coutinho, Ítalo Antônio Cotta, Verhoef, Anne, Körting, Thales Sehn, Borma, Laura De Simone
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.01.2021
• Subjects: Air monitoring; Air temperature; automation; caatinga; cameras; Cavitation; Density; Digital cameras; Digital imaging; Dry forests; Dry season; Environmental monitoring; evolution; Flow measurement; Flowers & plants; image analysis; Measurement techniques; MODIS; Moisture content; monitoring; Net radiation; normalized difference vegetation index; Normalized difference vegetative index; phenocams; Phenology; Physiology; plant available water; Plant species; plant water availability; Precipitation; rain; Rainfall; Remote monitoring; Remote sensing; sap flow; Satellite imagery; Saturated soils; Seasons; Senescence; Sensors; Sentinel-2; Soil moisture; Soil profiles; Soil properties; Soil temperature; Soil water; South America; Species; Spectroradiometers; Time series; Transpiration; tree phenology; Vapor pressure; vapor pressure deficit; Vegetation; Vegetation index; Water availability; Water use; Wood; wood density; Woody plants; South America
• DOI: 10.3390/rs13010075
• ISSN: 2072-4292

We investigated the water use of Caatinga vegetation, the largest seasonally dry forest in South America. We identified and analysed the environmental phenological drivers in woody species and their relationship with transpiration. To monitor the phenological evolution, we used remote sensing indices at different spatial and temporal scales: normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), and green chromatic coordinate (GCC). To represent the phenology, we used the GCC extracted from in-situ automated digital camera images; indices calculated based on sensors included NDVI, SAVI and GCC from Sentinel-2A and B satellites images, and NDVI products MYD13Q1 and MOD13Q1 from a moderate-resolution imaging spectroradiometer (MODIS). Environmental drivers included continuously monitored rainfall, air temperature, soil moisture, net radiation, and vapour pressure deficit. To monitor soil water status and vegetation water use, we installed soil moisture sensors along three soil profiles and sap flow sensors for five plant species. Our study demonstrated that the near-surface GCC data played an important role in permitting individual monitoring of species, whereas the species’ sap flow data correlated better with NDVI, SAVI, and GCC than with species’ near-surface GCC. The wood density appeared to affect the transpiration cessation times in the dry season, given that species with the lowest wood density reach negligible values of transpiration earlier in the season than those with high woody density. Our results show that soil water availability was the main limiting factor for transpiration during more than 80% of the year, and that both the phenological response and water use are directly related to water availability when relative saturation of the soil profile fell below 0.25.