Contrasting sap flow characteristics between pioneer and late-successional tree species in secondary tropical montane forests of Eastern Himalaya, India

Abstract
The interactive role of life-history traits and environmental forcing on plant-water relations is crucial for understanding species response to climate change but remains poorly understood in secondary tropical montane forests (TMFs). Comparing contrasting life-history traits (pioneer vs late-successional species) in a biodiverse Eastern Himalayan secondary TMF, we investigated sap flow responses in co-occurring pioneer species, Symplocos racemosa (n=5) and Eurya acuminata (n=5), and late-successional species, Castanopsis hystrix (n=3), using modified Granier’s Thermal Dissipation probes. The fast-growing pioneers S. racemosa and E. acuminata) had 2.1- and 1.6-times higher sap flux density than the late-successional C. hystrix, respectively, and exhibited characteristics of long-lived pioneer species. Significant radial and azimuthal variability in sap flow (V) between species was observed and attributed to life history traits and the canopy’s access to sunlight...., Sap flux was measured using custom-built Granier's thermal dissipation probes. Microclimate observations were used to understand the drivers of stand transpiration. Air temperature (°C), relative humidity (Rh, %), wind speed (U, m s-1), and incoming short-wave radiation (Rs, kW m-2) were recorded using an automatic weather station (AWS) (Vantage-pro Davis Net, USA). On-site Precipitation (P, mm hr-1) was recorded using an automated tipping-bucket rain gauge. Additionally, long-term trend analysis was done using daily precipitation (PIMD, mm d-1) extracted from the 0.25⁰ gridded precipitation product by the Indian Meteorological Department (IMD) for the pixel containing the sap flow site (Pai et al., 2014). In-canopy air temperature and relative humidity were recorded using microsensors (iButton hygrochrons, Maxim Int., USA). Forest reference evapotranspiration (EF, mm hr-1) was computed based on FAO’s Penman-Monteith method using meteorological data from the installed AWS and the crop c..., The dataset contains some missing values marked as \"NA\".
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