Accumulator, Transporter, Substrate, and Reactor: Multidimensional Perspectives and Approaches to the Study of Bark

Alexandra G Ponette-González

doi:10.3389/ffgc.2021.716557

Abstract

Woody ecosystems have a relatively thin but aerially extensive and dynamic layer of bark that, like leaves, regulates material exchange at the interface of air, water, and biota. Through interception, retention, and leaching of materials and interactions with epiphytic communities, bark alters the chemistry and composition of water draining over its surface during precipitation. This mini-review explores different perspectives and approaches to the study of bark and what they reveal about the myriad ways bark surfaces influence the quality of sub-canopy precipitation. Observational studies conducted over the past five decades in the fields of environmental science, ecohydrology, epiphyte ecology, and microbiology demonstrate that bark is an accumulator, transporter, substrate, and reactor. Bark passively accumulates materials from the atmosphere, water, and canopies, and also serves as an active transport surface, exchanging materials laterally and longitudinally. In addition, bark substrates influence epiphyte diversity, composition, and distribution, which, in turn, affect material cycling. Bark surfaces are dynamic over time, changing in response to disturbances (e.g., insect outbreaks, aging, and tree death)—how such changes influence the chemical and elemental composition of throughfall and stemflow merits further study. Moving forward, integration of diverse perspectives and approaches is needed to elucidate the influence of bark surfaces on solute and particulate transport and cycling within woody ecosystems.

Highlights

The outer bark of tree branches and stems constitutes a critical interface between the atmosphere, water, and vegetation that has important implications for the cycling of materials in woody plant-dominated ecosystems
In temperate forests, water adsorbed from the atmosphere during dry periods can constitute 10–30% of maximum bark water storage capacity, with values exceeding 60% at humid forest sites (Ilek et al, 2016, 2021). These findings suggest that bark surfaces with lower hygroscopicity will retain more water during storms, increasing water residence time and opportunities for canopy exchange on bark
Intraspecific changes in bark properties and associated nutrient gradients that occur with tree age represent an additional, though less well studied, control on epiphyte communities

Summary

Introduction

The outer bark of tree branches and stems (i.e., phellem or rhytidome) constitutes a critical interface between the atmosphere, water, and vegetation that has important implications for the cycling of materials in woody plant-dominated ecosystems. Bark exhibits a diverse array of physical and chemical properties that affect the chemistry and composition of waters draining over its surface (Oka et al, 2021). Porous, hygroscopic (absorb and retain water), and sorptive (Supplementary Figure 1), characteristics that influence deposition, leaching, and retention and interactions with epiphytes.

Results

Conclusion