Fall weather often brings strong winds in the southwestern Yukon and it is no surprise that some trees get blown over. A research project near Haines Junction has given a first estimate of the actual number of trees that get blown over around Yukon clearcuts.

Scott Gilbert, who teaches Renewable Resources Management at Yukon College, has been tracking the effects of logging in the Marshall Creek area for several years. This area was logged in the winter of 1994-95 and replanted with seedlings in 1996. Together with students from the College and from St. Elias Community School, he began looking at how well spruce seedlings were surviving in the cutblocks.

As they tramped around the 60 hectare area, they noticed many green trees had been blown over by the wind. Some windfall is normal around new openings in a forest as the remaining trees are exposed to more wind. A good understanding of local conditions can help foresters design cutblocks to reduce the effects of wind on the remaining trees.

Gilbert decided that he and his students had a golden opportunity to gather information on windfall that could help with forestry management in the future. "We had two interests," says Gilbert. "How many trees had been blown over and what are the impacts of these windfalls on spruce bark beetles and snowshoe hares?"

In the summer of 1998, Gilbert and two students walked around the entire perimeter of the seven cutblocks. Among other things, they measured the size of the wind-thrown trees and their orientation to the prevailing winds.

They also measured windthrown trees in the small "islands" or tree patches left in the cutblock after logging. These trees are left standing to provide habitat for wildlife, but Gilbert noticed that many of the trees had been blown down by wind.

They found that most of the trees had been blown over by winds coming from the west. Gilbert says his study shows there is a need to take wind into account when designing cutblocks in the Kluane area. He estimates that trees are not sheltered from the effect of the prevailing winds until they are at least 30 metres away from the edge of the forest.

"If we are moving towards a forestry system where more patches are left in the cutblocks, you have to ask what good they are doing and why you are leaving them. It turned out that the size of the leave patches at Marshall Creek were all too small to resist the effects of the wind," he says.

"Smaller cutblocks that do not catch as much wind might be something to look at. The amount of windfall also could be reduced by orienting the faces of the cutblocks to minimize exposure to the prevailing wind."

Single trees have little chance of surviving on their own. Of the 76 solitary trees left standing in the Marshall Creek area, 50 had been blown over by the wind. The shallow roots on white spruce provide poor anchors for these tall trees, and they blow over more easily than aspen.

Wind-thrown trees provide prime breeding habitat for spruce bark beetles. Forest Resources at DIAND (Department of Indian Affairs and Northern Development) tries to control this problem by cutting up the wind-thrown spruce found around the perimeter of the cutblock. When the shorter logs are placed upright, they dry out more quickly and discourage spruce bark beetles from breeding successfully.

But this work took place in 1996, and Gilbert's study found that trees keep blowing down long after the logging has stopped.

Gilbert also found that the total volume of windfall was three times higher than had estimated. DIAND officials did not have local data to use for calculating windfall, so they adopted an approach used in British Columbia. They estimated the amount of windfall as a percentage of the total volume of timber harvested. This estimate for Marshall Creek is about 67 cubic metres while Gilbert's measurements of windfall spruce add up to 185 cubic metres.

Throughout this study, Gilbert has been tracking how much snowshoe hares browse on the planted spruce seedlings in winter, and estimates that about 20 percent of the seedlings are nibbled upon to some degree. He and his students noticed that snowshoe hares were congregating around the freshly downed trees, and they looked at whether the hares were also browsing more heavily on replanted seedlings close to the downed trees.

"We know that in winter hares will collect at windfall spruce in large numbers to feed on the green branches. Since hares were coming to use these windfall spruce as a buffet, we wanted to know if they then turned to the nearby planted seedlings for dessert?"

He found that the downed trees were the main attraction, and the hares were not browsing more heavily on the nearby seedlings. "That was pretty interesting," he says. "We did not know which way it would go."

Gilbert feels their study points to the need for more baseline data for forestry management. "The point is that logging is new to the Yukon, and it is interesting to see what is happening," he says. "There is a need for both baseline studies and field experiments. These forest systems are complicated and sometimes there are surprises."

For more information on this project, contact the Northern Research Institute at 668-8828.