Narrow strips of vegetation, commonly referred to as leave strips, are often left along streams in order to protect them from the impacts of forest harvesting. However, the argument is often expressed that leaving exposed trees standing along streams is impractical and unwise because they will blow down.
A study of streamside leave strips of varying ages and vegetational compositions on Vancouver Island has shown that considerable blowdown has occurred on a number of streams in widely separated localities. However there are also leave strips on a number of widely separated streams that have stood exposed to the wind for several years with little or no blowdown. It is not true to state that all leave strips have blown down and it appears that, under the right set of environmental conditions, leave strips along streams will be reasonably windfirm.
The blowdown that has occurred is the result of the interaction of a number of natural factors including location of the stream, local topography, climate, aspect and slope, soil depth and texture, tree species and rooting characteristics, and stream characteristics occurring simultaneously.
Several factors serve as indicators of a high likelihood of blowdown. These include the presence of such topographical features as knolls, ridges or narrow valleys which funnel winds, the presence of skunk cabbage or standing water, or any indication of shallow tree rooting. Western hemlock and amabilis fir appear more likely to blowdown than Douglas-fir or western red-cedar.
Each of the factors influencing blowdown or windfirmness is presented in detail in Land Management Report number 3, entitled "Factors Contributing to Blowdown in Streamside Leave Strips on Vancouver Island", prepared by Keith Moore of the Research Division, Ministry of Forests. The report examines the effects, both beneficial and detrimental, that blowdown may have on a stream and suggests a method for assessing a proposed leave strip area and evaluating the likelihood of blowdown.
Copies of this report are available from the Information Division, Ministry of Forests, Legislative Buildings, Victoria, B.C. V8V 1X5.
[Abstract contains full text of memo.]
BC Forest Service - Research Division. 1978. Factors contributing to blowdown in streamside leave strips on Vancouver Island. British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Research Memo (FLNRORD). RM27
Topic: FLNRORD Research Program
Keywords: FLNRORD, Research Memo, British Columbia
To copy the URL of a document, Right Click on the document title, select "Copy Shortcut/Copy Link", then paste as needed. Only documents available to the public have this feature enabled.