Tuesday, October 26, 2010
Harvesting of Spruce Tops is Harming Bogs
Harvesting of Spruce Tops is Harming Bogs
by Norm Aaseng, plant ecologist, Minnesota County Biological Survey. This is a summary of his talk at the Nov. 5, 2009, MNNPS meeting.
Decorative tree harvesting is the cutting of the top two to four feet of stunted (six- to 15-foot) black spruce trees. These spruce tops are shipped to garden stores and other outlets where they are sold as decorations during the winter holiday season. In the mid-1990s, the harvesting of spruce tops in Minnesota began to expand, and today an estimated one-half million to one million tree tops are harvested per year. Surveys indicate that there is a market for three times that number of spruce tops. Harvesting occurs primarily on state and county lands in northwest Aitkin, southwest St. Louis, northwest Carlton, and southwest Itasca counties from mid-September to mid-December. This activity provides income to local harvesters from lands that typically do not generate any revenue.
Although black spruce trees are found in a variety of peatland and upland native plant community classes, almost all decorative tops come from the Northern Spruce Bogs (APn80 in the DNR’s Field Guide to the Native Plant Communities of Minnesota). The Northern Spruce Bog is the most nutrient poor as well as the most acidic native plant community occurring in Minnesota. These conditions create a very inhospitable environment in which only 25 vascular plant species are adapted to survive. Typical species found in bogs include carnivorous plants, such as pitcher plant (Sarracenia purpurea), ericaceous shrubs, such as bog rosemary (Andromeda glaucophylla) and bog laurel (Kalmia polifolia), and graminoids such as cotton grasses
(Eriophorum spissum) and bog wiregrass sedge (Carex oligosperma). Hummocks of sphagnum moss cover the ground surface. The severe conditions are responsible for the stunted size and shape of black spruce trees desired by harvesters.
As tree-top harvesting operations increased in size, environmental impacts from harvesting became apparent. DNR Forestry assembled a field team to determine the impacts of tree-top harvesting and the factors contributing to the damage. The team found that the cutting of the spruce tops did not appear to have a significant impact. Tree tops were reported to grow back and be harvested in 10 - 20 years.
However, very significant impacts occurred from rutting on all-terrain vehicles (ATV) access trails. Initial passes by ATVs create a trail by compressing the sphagnum peat, but repeated traversing of trails, especially with heavy vehicles, resulted in cutting through the live root mat that occurs in the upper six inches of the peat. Once this mat is cut, the weight-bearing capacity of the peat is severely reduced, resulting in increasing size and depth of pools with every pass of an ATV. The deeper the ruts are, the longer it takes the vegetation to recover. If damage is significant, there can be a conversion of vegetation to marsh or even exotic plant species. Water tracks and laggs (shrubby wet moats occurring between the interface of peatland and upland) were found to be particularly susceptible to damage from ATVs. The creation of deep pools and the elimination of existing vegetation easily occurred along the ATV trails in these areas.
To minimize these impacts, the DNR instituted regulations that limited the depth and length of rutting allowed on trails as well as imposing restrictions on the access of harvest areas through laggs and water tracks.
Despite the regulations, some impacts continued to occur, primarily through “rogue” or inexperienced harvesters. Because public auction requires that the sale of tree tops go to the highest bidder regardless of competence of the harvesters, the DNR no longer offers this option for decorative harvesting. Instead, private sales are negotiated with proven operators that possess the appropriate equipment, such as low pressure-tired vehicles. Because these private sales are much smaller in size than public auctions, the DNR sales are now limited to a total of 200,000 tree tops per year. With increasing demand for spruce tops it may be that operations will be shifting to lands that are less regulated.
Harvesting of spruce