The ecohydrological functioning of forested peatlands: Simulating the effects of tree
shading on moss evaporation and species composition.
N. Kettridge1, D. K. Thompson2 & J. M. Waddington3
1
School of Geography, Earth and Environmental Science, University of Birmingham,
Birmingham, UK, B15 2TT
Phone: +44 121 4143575 Email: n.kettridge@bham.ac.uk
2
Northern Forestry Centre, 5320 122 Street Northwest, Edmonton, Alberta, T6H 3S5
Phone: 780 435 7257 Email: Daniel.thompson@NRCan-RNCan.gc.ca
3
School of Geography and Earth Sciences, McMaster University, Hamilton, ON, L8S 4L8
Phone: 905 525 9140 ext. 23217 Email: jmw@mcmaster.ca
Forested peatlands provide an important global carbon pool and an essential regulator of regional
water dynamics. Although trees increase water losses via transpiration, it has been suggested
that trees actually act as a water conserving agent within the peatland landscape, reducing the
available energy for moss evaporation. Hydrological disturbance associated with land-use
change and changing climate conditions has the potential to increase tree growth, modifying the
density, size and spatial arrangement of trees, providing a negative ecohydrological feedback
response to drying. To determine the magnitude of this feedback response, spatial variations in
short and long-wave radiation, turbulent energy fluxes and peat temperatures are simulated
through peatlands with real and idealized tree densities and distributions. For a random
distribution of trees, an increase in tree density from 0.0 to 3.5 trees per m2 decreased average
evaporation by 30% associated with a reduction in available energy. Increased tree densities also
induced autogenic succession from Sphagnum moss to feather moss associated with reduced
light availability at the peat surface. Feather moss has a higher surface resistance than Sphagnum
and the species transition further reduced evaporation rates by a total of 72%. Potential tree
distributions were simulated using a simple statistical model. The magnitude of this negative
ecohydrological feedback response is regulated by the spatial arrangement of trees. An
improved understanding of the spatial organisation of tree growth in response to drying is
necessary to accurately determine the magnitude of this feedback response.
Oral presentation
Session 1: Hydrology on the edge; research at the interface between hydrology and ecology