Matthew T. Jarvis

An Automated Instrument for the Measurement of Bark Microrelief

Bark microrelief is of importance to the physiological ecology of forested ecosystems because it has been documented to influence the distribution of corticolous lichens, stemflow generation, and forest biogeochemical cycles. Hitherto no instrument existed to characterize the inherent variability of bark microrelief with high spatial resolution. Our newly designed prototype instrument consists of a hinged ring, laser rangefinder, and motor linked to a standard laptop. The prototype produces trunk cross sections at a 0.33° horizontal resolution and detects bark-ridge-to-furrow heights at < 1 resolution. The prototype was validated by comparing measurements of bark microrelief between the instrument and digital calipers. The mean absolute error of the prototype as a percentage of the measured average microrelief was 1.0%, with a mean absolute error of 0.83 mm. Our bark microrelief prototype instrument can supply critical requisite information of bark microstructure that can be used by researchers to interpret the distribution of lichens and bryophytes on tree surfaces, relate stemflow yield and chemistry to bark microrelief, and provide detailed measurements of the changes of bark microrelief with stem dehydration. In short, the prototype instrument can be used to gain a more holistic understanding of the physiological ecology of forest ecosystems.

Instrumental method for reducing error in compression-derived measurements of rainfall interception for individual trees

Abstract This technical note presents an instrumental method for the precise and timely installation of mechanical displacement sensors to investigate stem compression and relaxation associated with whole-tree rainwater loading and evaporation, respectively. We developed this procedure in response to the conclusions of Friesen et al. (2008), which called for the development of a precision mounting method for strain sensors on inherently-irregular trunk cross-sections so that rainfall interception, storage and evaporation may be distinguished from other strain-related phenomena. To supply precise sensor installation locations, high-resolution trunk profiles are generated using the LaserBarkTM automated tree measurement system. These scans are utilized to approximate the location of neutral bending axes. A routine then instructs a mobile rangefinder along the cross-section to optically indicate exact positioning for strain sensors over the bending axes. As imprecise sensor placement linearly increases error and diminishes signal-to-noise ratio, this automated installation routine is designed to remove significant distortions created by wind throw, off-centre loading within unevenly-distributed canopies, and human error that can lead to erroneous measurements of rainfall interception. Citation Van Stan, J. T. II, Jarvis, M. T., Levia, D. F. Jr & Friesen, J. (2011) Instrumental method for reducing error in compressionderived measurements of rainfall interception for individual trees. Hydrol. Sci. J. 56(6), 1061–1066.