Complete Enclosure of Stunted Trees to Study Greenhouse Gas Fluxes in Birch-Invaded Peatland

Ombrotrophic, naturally open peatlands are increasingly susceptible to invasion by scrub and trees due to human disturbance, N deposition and climate change. There is limited research on the effect these trees have on ecosystem functions and their removal can be costly, making decisions over best management practice challenging. The adverse growing conditions associated with many of these peatlands can result in stunted tree growth meaning that complete enclosure of a tree remains a practical possibility. In this study we aim to quantify the CH₄ and CO₂ fluxes from whole trees growing on a disturbed peatland and assess their significance relative to the fluxes between the vegetated peat surface and atmosphere. We also aim to identify if the establishment of trees impacts CH₄ and CO₂ fluxes from the vegetated peat surface, as compared to adjacent uninvaded peatland.

We have developed a removable chamber capable of enclosing whole trees of up to 3 metres high, making it suitable for use on juvenile or stunted trees. Being able to enclose an entire tree removes potential errors caused by estimating whole tree fluxes by upscaling measurements from a subsample of tree surfaces. The chamber is constructed with a transparent membrane and removable cover so that light and dark measurements can be taken. We use the chamber to take CH₄ and CO₂ flux measurements on a site with approximately 20-year-old silver birch trees (Betula pendula) of an average height of 2-3 metres. Flux measurements have been taken from the trees and ground collars at different times of year. We have also studied diurnal variation.

Our initial results have shown that the trees on our site are emitters of CH₄, although this emission is small in comparison to that produced by the rest of the habitat. The vegetated peat surface in the wooded area had lower CH₄ emission but reduced CO₂ uptake as compared to the open area. The diurnal study on one tree indicates that methane emissions increase at night. A further diurnal study is planned to explore this further. This study extends the limit on the size of vegetation that can be sampled by a manually operated flux chamber.