ECOHYDROLOGICAL RESPONSE TO PEATLAND DRAINAGE AND WILDFIRE

Abstract

<p>Disturbed peatlands may undergo a dramatic alteration in ecohydrological conditions, potentially limiting the recolonisation of peat-forming species like <em>Sphagnum</em>. A poor fen was experimentally drained in 1984, both the drained and undrained portion of the peatland burned in 2001, providing an unique opportunity to examine the ecohydrological response to ‘double disturbance’.</p> <p>The undrained site<em> </em>was characterized by a healthy recovery of<em> </em>peatland microform <em>Sphagnum</em> species, low soil water pressure (Ψ), high volumetric soil moisture (θ) content and high and stable water table position. However, the drained site showed no recolonization of <em>Sphagnum</em> with <em>Brome</em> grasses representing the dominant surface cover nine years post-wildfire.</p> <p>While the study period was generally wet and as such Ψ did not exceed thresholds limiting <em>Sphagnum</em> growth (≥ -100 mb) during the study period, a series of ecohydrological influences were found to be operating, limiting <em>Sphagnum</em> recolonisation at the drained site. The physical peat structure following drainage and wildfire has been considerably altered, changing the moisture retention and water storage properties of the peat, largely through substantive increases in bulk density (ρ_b). Moreover, specific yield (<em>Sy</em>) has also decreased the drained peat having become more humified, increasing unstable water table fluctuations. As such, this has lowered the resilience to drought. Only smaller decreases in θ are required to reach Ψ ≥ -100 mb at the drained and impose ecophysiological stress on <em>Sphagnum</em> growth. Dense canopy cover (<em>Betula</em> and <em>Sali</em>x) has limited available radiation at the surface to recolonisation, shading out the surface, further limiting <em>Sphagnum</em> recolonisation.</p>