1589 Highway 11 West
P.O. Box 746
Hearst, Ontario, Canada
P0L 1N0
Tel.: (705) 362-4464
F
ax: (705) 362-7057
E-mail: hfmi@hearstforest.com

   

Surficial Geology, Site Types and Climate

 

Geology, Soils and Sites

Topography and surficial geology in the Forest is the result or outcome of several glaciations. The majority of the area has very little topographical relief, having been overridden and depressed by glacial ice and then buried beneath lacustrine deposits of glacial lake Barlow-Ojibway. However, in the south and southwest portions of the Forest and along the northeast boundary, a mixture of glacial and lacustrine deposits and pre-Cambrian bedrock exposure causes topography to vary from gently rolling to very hilly.

The Forest is divided into two main regions of soil classification. The difference between the regions is primarily the influence of glaciations:

  • The north and central portions of the Forest are part of the Great Clay Belt, with soils generally consisting of clays through silt clays to clay loams, having been deposited as glacial-lacustrine sediments, and
  • The southern, southwest and northeast portions of the Forest which have soils varying from clays to loams to sands, resulting from a wide range of types of glacial deposition.

Interspersed throughout the regions described above are areas of organic soils and poor drainages. The extent of these areas varies, ranging from insignificant to expanses large enough to influence operational planning in forest management. Organic soils occur in large expanses on the Great Clay Belt but are limited in extent elsewhere.

Beyond the northern boundary of the Forest are the poorly drained, deep organic soils of the James Bay Lowlands. The conditions favouring the development of these organic soils are a result of glaciations. The northern boundary of the Forest follows the approximate beginning of the extensive Lowlands. Growth of forest cover in the Lowlands is not consistent and predominantly follows drainage ways.

Site Types and Management Implications

The Hearst Forest falls within Hill’s Site Region 3E. The majority of the forest is within Hills Site District 3E2 with portions of the northern section within Site Districts 3E1 and 3E3.

A classification of predominant vegetation and soil types was completed in 1983. These soil site relationships were then organized into Ecosite Types. The Ecosite Types serve as a guide for harvest, renewal and tending operations. The site types were described in detail in the Field Guide to Forest Ecosystems of Northeastern Ontario: Second Edition (Taylor et al. 2000). The original guide and others were expanded into Book III: Ecological and Management Interpretations for Northeast Site Types of the Silviculture Guide to Managing for Black Spruce, Jack Pine and Aspen on Boreal Forest Ecosystems in Ontario (OMNR, 1997).

The predominant tree species on the Hearst Forest is black spruce (Picea mariana Mill. B.S.P.). Sixty-seven percent of the landbase is composed of Forest Units in which black spruce is a major component.

The better-drained more productive lowland transitional and upland sites, where the Spruce Pine (SP1) and Spruce Fir (SF1) Forest Units are found, make up 30 percent of the landbase. These Forest Units are often site class (SC) 1 or better sites and are commonly found in Ecosites 5, 6, 8, 9, 11, 12 and 13. On these sites, black spruce may be found with white spruce, jack pine (Pinus banksiana Lamb.), balsam fir (Abies balsamea (L.) Mill) and trembling aspen (Populus tremulodies Michx.).

In many instances on the clay belt section of the Hearst Forest, black spruce is found on lowland areas in pure stands and in association with cedar and tamarack. These lowland sites are characterized by moderately deep to deep i.e. 20-40 centimetres to more than 40 centimetres organic soil over clay, in Ecosites 9, 11, 12 and 13. The productivity of these areas varies from low, SC 3 in the Spruce Site Class 3 (SB3) Forest Unit to moderate, SC 2 in the Spruce 1 (SB1) Forest Unit. These lowland sites are located on poorly drained, toe slopes, bottoms of valleys and adjacent to waterways with strong seepage flow. The most poorly drained Forest Units are SB3 and SB1 which make up 34 percent of the landbase.

Black spruce is a dominant species within the Lowland Conifer (LC1) Forest Unit. LC1 is a very wet but well drained Forest Unit with strong groundwater seepage often supporting cedar (Thuja occidentalis L.), tamarack (Larix laricina (Du Roi) K. Kock) and white spruce (Picea glauca (Moench) A. Voss). The Ecosites making up LC1 are 8, 9, 11, 12 and 13. The LC1 Forest Unit makes up 2.9 percent of the Hearst Forest landbase.

The abundance of lowland sites generally constrains forest operations in the LC1, SB1 and SB3 Forest Units to winter months when the ground is frozen. This is because lowland sites have a low bearing strength and are easily disturbed by heavy equipment in non-frost seasons. Occasionally, portions of these lowland Forest Units occur on dryer ground and can be operated in non-frost periods with high-floatation equipment. When considering regeneration, the organic nature of these lowland sites turns into a silvicultural advantage. Natural regeneration can be accomplished effectively and inexpensively because the understory and sphagnum moss seedbed remain relatively undisturbed during the winter operations. Removal of the mature trees exposes the understory to light and releases any regeneration from competition. It also provides seeds with an opportunity to germinate, thus providing the stock for the future forest.

Approximately 25 percent of the land base occurs on mineral soils on upland sites associated with mixedwood stands consisting of jack pine, black and white spruce, trembling aspen, balsam poplar (Populus balsamifera L.), white birch (Betula papyrifera Marsh.) and balsam fir. The dominant Ecosite types are 3 and 6. The soils present are fine loam to sandy clay with less than 20 centimetres of organic material. With one exception, these soils generally have high bearing strength and are valued as summer harvesting areas.

A consideration for silviculture on uplands in the Hearst Forest is choosing the appropriate site preparation method. On the majority of the forest the generally fine, heavy, mineral soils encountered are prone to frost heaving, severe drying and nutrient loss occurs when the organic layers are exposed, even in very small areas. On these soils, site preparation is usually carried out on frozen ground with the objective of aligning slash and reducing duff thickness, while avoiding exposure of mineral soil. Bulldozer mounted shearblades have proven extremely effective at achieving the desired results. In areas where sands are found, summer site preparation using bulldozer mounted angle blades or trenching with disc trenchers are very effective in achieving the desired results.

The hardwood dominated stands consisting of 75 percent intolerant hardwood or greater make up 5.5 percent of the land base. The most common Ecosites they occupy are 7 and 10 with poor (SC 3), to high (SC 1) productivity. The soils that support these stands tend to be deep, dry to fresh; coarse loamy to fine clayey soils with generally less than 20 centimetres of organic material over the mineral soil. Operations on these sites are similar to Mixedwood uplands; except for Ecosite 10 which can only be operated in drier summer conditions, these soils generally have high bearing strength and are valued as summer harvesting areas.

Approximately 3 percent of the land base consists of stands that are dominated by jack pine on mineral soils. The dominate Ecosites they occupy are 2, 3 and 4. The soils present are coarse to fine loamy mineral soils and in some cases are very shallow e.g. Waxatike area. These sites are operable in the summer.

Climate

The climate of the Hearst Forest is classified as “modified continental”, exhibiting the temperature extremes of a continental type climate with increased rainfall and often-cool summer temperatures due to the influences of the Great Lakes to the south and Hudson Bay to the north. The mean annual temperature for the climatic region is 1.1 degrees Celsius with a mean annual minimum temperature of -40 degrees Celsius. The mean daily maximum and minimum temperatures for January are -11.7 degrees Celsius and -24 degrees Celsius respectively. The mean daily maximum and minimum temperatures for July are 23.9 degrees Celsius and 10.6 degrees Celsius respectively. There is an annual average of 92 frost-free days within the Hearst Forest (OMNR, 1983).

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