An In Situ Method to Measure and Map Bark pH

Abstract

Bark pH is an essential parameter which partly governs the chemistry of the bark as well as its suitability as a microhabitat to a wide range of epiphytic organisms. Bark pH is known to vary with tree species, epiphytic cover, stemflow channelization, and anthropogenic influences. To date, reliable methods to quantify the spatial and temporal dimensions of bark pH have remained elusive. The aim of the present study was to develop and validate an in situ method to measure the surface pH of bark with high spatial resolution. Agar-agar panels, prepared with a pH indicator, were used to quantify and map the spatial variation of bark pH for cacao trees in Indonesia. Fine-scale changes of bark pH were clearly detectable and quantifiable with our bark pH mapping method. Bark pH was found to vary as a function of bark microrelief and the presence of epiphytes. The use of pH reference panels validated the bark pH measurements obtained from our method. The bark pH measurement method developed, described, and validated in this article is inexpensive and straightforward. It has the potential for wide adoption by scientists across disciplines who are interested in bark pH and its effect on life in the cortisphere. Unlike conventional methods to measure bark pH in deionized water or KCl extracts, our method is able to identify fine-scale spatial changes in bark pH that are relevant for the colonization of bark by organisms.