Science > Turkey Lakes Harvesting Impacts Projet

Turkey Lakes Harvesting Impacts Projet

Project Description:

Tolerant hardwood forest, dominated by sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton), is typical of upland sites in the Algoma Section of the Great Lakes--St. Lawrence Forest Region. Undisturbed, stands develop as uneven age forest, often containing stems of substantial size and age. The area has long been home to hardwood lumber and veneer industries. Past high grading for good quality stems frequently left sites dominated by defective material. During recent years, interest has arisen in rehabilitating and sustainably managing such stands. Two basic management systems are in vogue with respect to tolerant hardwood management in Ontario. On more productive sites or where sufficient ‘acceptable growing stock' remains, the selection system (an uneven-aged silvicultural system in which trees are removed individually over a large area) prevails. On less-productive sites or where insufficient ‘acceptable growing stock' remains, the shelterwood system (an even-aged silvicultural system in which, in order to provide a source of seed and/or protection for regeneration, a crop is removed in two or more successive cuttings) is more common.

The Turkey Lakes Watershed, 10.5 km2 in area, is situated approximately 60 km north of Sault Ste. Marie, Ontario, and 13 km inland from Batchawana Bay on Lake Superior. It is occupied by a remnant of old-growth, generally mature-to-overmature, sugar maple-yellow birch forest. Unlike much of the area, the watershed is relatively undisturbed, save for a light partial cut for veneer-grade yellow birch over parts during the mid-1950s. Long the site of an interdisciplinary study of the impacts of long-range transport of air pollutants on aquatic and terrestrial, the watershed boasts exceptional baseline information on forest structure and function.

Consequently, in 1997, a harvesting impacts experiment was initiated. One set of objectives, primarily of concern to forest managers, is silvicultural and involves adapting the selection and shelterwood systems to the tolerant hardwood forests of the area. A second set of objectives, primarily of concern to forest research agencies involves impacts of forestry practices (thus the name ‘harvesting impacts project'). Some of these impacts are ‘on-site'. Soils of the region, for example, are shallow and the topography rugged. Surface erosion as a result of harvesting, as well as soil compaction and nutrient removal are potential impediments to sustained productivity. Also, productivity is lower than in similar forest types elsewhere and, as a result, resilience is lower and recovery from perturbation is slower. Maintaining a diversity of both plant and animal species on site are likewise objectives in this category. Finally, a third set of objectives focuses on off-site impacts, chiefly on water yield and quality including sedimentation and temperature change, and effects of these on aquatic life.

The core experiment of the Turkey Lakes Harvesting Impacts Project is a single-factor randomized block field trial in four blocks comparing alternative silvicultural systems, viz. shelterwood, selection and clear-felling, versus uncut control. Treated areas range in size from 4.6 to 66 ha. The shelterwood system, utilizes a two-coup uniform shelterwood, with deviation only to spare significant patches of established yellow-birch poles. The long-term objective is an even-aged high forest with an increased complement of high-quality yellow birch crop trees over current average ca. 10% of basal area as yellow birch. The prescription called for marking to reduce canopy coverage to 50% of original. Except where necessary for crown opening, all better quality dominant or co-dominant yellow birch (for seed production) and better quality sugar maple were marked for retention. White spruce and red oak were similarly marked. During July-September 1997, marked trees were harvested by feller buncher with on-site delimbing, cable yarding and skidding to roadside. Provided a well-established regeneration is present, the second felling coup will follow in ca. ten years (2007).

The selection system was applied in its single-tree variant. The current average basal area is ca. 27 m2/ha. Of this, only 6 m2/ha was considered ‘acceptable growing stock', with the remaining 21 m2/ha being ‘unacceptable growing stock'. Although the ‘acceptable growing stock' was below recommended guidelines for selection management, it resided primarily in pole and small sawlog size classes, which provided an opportunity to improve the growing conditions and develop an acceptable stand structure. The principal species, sugar maple, is ideally suited to selection management. A residual basal area of 18 m2/ha was targeted. However, markers were instructed to adjust their marking based upon species encountered, tree quality, and stand structure. Some group selection openings were made (maximum diameter of one tree height) where conditions favourable to yellow birch regeneration were encountered.

Clear Felling is not a recommended silvicultural treatment for managing tolerant hardwoods. This treatment was included, however, to allow for the examination of maximum impact in terms of nutrient loss, etc. in response to canopy removal and site disturbance. The treatment involved felling and removing all overstory trees > 20 cm DBH (with delimbing at the stump) and the felling of all trees > 10 cm DBH (additional felling of smaller stock was at the discretion of researchers interested in effects of this treatment). Finally, four compartments, one per block, were retained as untreated controls. A five-year remeasurement is scheduled for 2002.