Journal Article

Asynchronous Forest-stream Coupling in a Fire-prone Boreal Landscape: Insights from Woody Debris

élodie Bouchon, étinenne Boucher, Dominique Arsenneault

2007

Overview

1 We used dendrochronology to reconstruct the transfer of coarse woody debris across a forest-stream interface in a fire-prone boreal landscape. A sequence of regulating factors was considered from source to sink of in-stream woody debris (SWD), including fire history at the landscape scale, patterns of post-fire recovery of riparian forest and inputs of SWD at the scale of a stream reach and its associated floodplain, and burial of SWD at an excavated site. 2 Fires occurred repeatedly in the studied landscape (at least in 1708, 1733, 1791, 1811, c. 1838, c. 1850, 1882, 1941 and 1998), and were generally patchy on the floodplain because of the firebreak effect of the riparian corridor. Unburned forest remnants were regularly generated at the stream margin, thus permitting temporally continuous but spatially localized transfer of woody material across the forest-stream interface. These remaining forest patches also increased forest resilience by dispersing seeds and promoting conifer re-establishment in burned areas. 3 Because of higher severity compared with previous fires, the 1941 fire burned almost everywhere on the floodplain, creating only a few widely isolated unburned forest remnants. Consequently, following an abrupt post-fire increase, SWD inputs almost completely ceased. In addition, post-fire recovery of the riparian wood source is slow because of the spatially restricted seed source. 4 In this alluvial stream, wood burial is faster than decay and largely determines the residence time of SWD. Because the residence time is about 150 years, the current density of SWD is high and contrasts sharply with the very low tree density at the stream margin. Although this long residence time helps maintain stream integrity while the forest is recovering from the 1941 fire, it is unlikely that SWD inputs would resume extensively before burial of the current SWD pool. 5 Our research exemplifies the potentially complex impacts of disturbances on material transfer between a source and a sink ecosystem. We conclude that when certain components of ecosystems are coupled by unidirectional flow, those components will behave asynchronously if a disturbance impact at the source ecosystem does not propagate rapidly to the sink and the source and the sink recover at different rates.

• Publisher: British Ecological Society,Blackwell Publishing Ltd,Blackwell Science
• Subject: Alluvial rivers / Animal and plant ecology / Animal, plant and microbial ecology / Aquatic ecosystems / aquatic woody debris / Biological and medical sciences / Boreal forests / boreal landscape / coarse woody debris / Coniferous forests / conifers / Creeks & streams / Dendrochronology / Detritus / disturbance severity / Ecology / ecosystem coupling / ecosystem resilience / Ecosystems / fire break / Fires / Floodplains / Forest & brush fires / Forest ecology / Forest ecosystems / Forest fires / Forest regeneration / Forestry / Forests / forest–stream interface / Fundamental and applied biological sciences. Psychology / General aspects / General forest ecology / Generalities. Production, biomass. Quality of wood and forest products. General forest ecology / lateral flow / nonlinear ecosystem dynamics / Riparian ecology / riparian forest / Riparian forests / seeds / source–sink dynamics / Streams / trees / Vegetation-Environment Interactions and Ecosystem Dynamics / Wood