Exploring novel dendrometers: an IoT application for simultaneous and in situ monitoring of tree stem growth increment.

Field measurements have historically been the main source for data acquisition on individual trees, although rapid development of novel approaches such as terrestrial LiDAR and even mobile phone applications are steadily becoming more efficient and cost effective. Dendrometers, however, typically remain as the most practical method to measure and detect temporal changes in stem girth. A key feature of any tree measurement is indeed its girth and a myriad of dendrometry tools exist for such measurements. Electronic point dendrometers for example, are widely utilised to monitor stem incremental growth, differing in measurement instrumentation and precision where large scale deployment is often constrained by cost and expertise. We explore two cost effective novel electronic dendrometers developed and adapted in house, embedded in the novel IoT platform the ‘Treetalker’ facilitating autonomous real time measurements of stem radial and circumference growth. The first uses infrared optics and the second uses a linear magnetic encoder. We will present design features, calibration procedures and sensitivity analysis. Initial results suggest that the infrared proximity sensor could not detect clear diurnal patterns of stem water interactions, however, patterns at weekly and seasonal scales are well represented. Furthermore, we observed that sensor signal stability is dependent on sensor shielding in addition to variations in target surface features e.g. bark surface properties. For the linear magnetic encoder, we observed initial coherent responses to seasonal stem growth activation, however mechanical design limitations result in a significant underestimation of stem circumference growth. Improvements in sensor design have potential as signalled by initial results. Finally, mass deployable autonomous IoT dendrometers could offer a frontier in forest science as they represent a cost-effective viable option for individual tree mass monitoring, thus contributing to established methods for assessing forest ecosystem function through space and time.