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Kathryn MartellPatterns of Riparian Disturbance in Alberta's Boreal
Mixedwood Forest: Beavers, Roads, and Buffers

Effects of Beavers

Beaver foraging can extensively restructure stream corridors, increasing the width and diversity of non-forest riparian vegetation.

Around the dams I studied, beaver felling removed most or all deciduous trees within 30 - 40 m of the pond edge. This creates wide patches of meadow and shrubs along streams. Beaver dams show up clearly on aerial photographs so I also examined a 50-year time sequence of air photos at each site. In 1951, almost no dams were present and the creeks were very narrow and almost indistinguishable from the surrounding forest. In the 1970's, beaver dams start to appear and by the late 1990's, the streams have long chains of dams. These ponds increase the number and diversity of wetlands throughout the whole area. Beavers also create meadows and areas of young forest when the dams are abandoned and the ponds drain.

The majority of aspen within 35 metres of the streams were felled by beavers Culverts are often plugged by beavers A one-year-old beaver stump
The majority of aspen within 35 metres
of the streams were felled by beavers
Culverts are often
plugged by beavers
A one-year-old beaver stump

These findings highlight the importance of beavers along streams in northern Alberta. Current logging rules require companies to leave uncut 'buffer strips' along streams to protect aquatic habitats from negative impacts. At the ponds I studied, beavers are removing 90% of trees within 35 m of the water - management planning for aquatic habitats should therefore consider this impact and account for beaver activities.

Comparing road crossings and beaver dams

Throughout the study area, beavers and roads interact: beavers take advantage of road crossings and create ponds by plugging the culverts, instead of building dams (very clever! beavers aren't fools). Due to this interaction, it was impossible to separate the effects of road crossings themselves.

On the whole, road crossings and beaver dams seemed to have similar effects on riparian vegetation, raising water levels upstream. Vegetation zones were much more variable at beaver dams, implying that road crossings may be more permanent sites of flow interruption than beaver dams.


This project received funding and logistic support from Alberta Pacific Forestry Ltd., the Sustainable Forest Management Network, and the Adaptive Management Experiment Team. Thanks also to Scott Boorman, Kristen Ostermann, Carla Mellott, and Kaia the Dogg for help and fun in the field, and to NSERC, Ralph Steinhauer Award, Alberta Ingenuity, Walter H. Johns scholarship and the Department of Renewable Resources for financial support.

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