Treehuggers: Wireless Sensor Networks for Automated Measurement and Reporting of Changes in Tree Diameter

Abstract:

Ground-based measurements of changes in tree diameter and subsequent calculation of carbon storage provide validation of indirect estimates of forest productivity from remote sensing platforms, and measurements made with high temporal resolution provide critical information about the responsiveness of tree growth to variations in important physical drivers (e.g. temperature and water availability). We have developed an environmentally robust instrument for automated measurement of expansion and contraction in tree diameter that can be deployed in remote locations (TreeHuggers; TH). TH uses a membrane potentiometer to measure changes in circumference with resolution ≤ 6 mm at user-selected intervals (≥ 1 min). Simultaneous measurement of temperature is used to correct for the thermal properties of the stainless steel band. Data are stored on micro SD cards and transmitted tree-to-tree to a base station. Preliminary measurement of beech trees shows the precise initiation of growth and the emergence of diel changes in stem diameter associated with sap flow. Because of their low cost and on-board data logging and communication packages, TH will greatly increase the capacity of the scientific community and private sectors to monitor tree growth and carbon storage. Possible applications include deploying TH in the footprint of eddy covariance sites to help interpret drivers affecting net ecosystem exchange and evapotranspiration. A large scale implementation of TH will contribute to our ability to forecast changes in the carbon sink strength of forests across environmental gradients and biotic disturbances, and they could prove useful in assessing changes in forest stocks as part of evaluating carbon offsets purchased by commercial entities.