Environment Impact of Logging Operation_Alberta

Timber harvesting can have long-term effects on your farm and the surrounding landscape; the subsequent land use may have even greater impacts. These impacts relate to runoff, gully erosion, in-field erosion, streams, watertables, wildlife habitat, aesthetics and economics. The nature and extent of the impacts will depend on the logging practices, subsequent land use and landscape characteristics.

Runoff and Gully Erosion

Gully erosion and other runoff related problems such as flooding can occur when surface runoff from rainfall or snowmelt becomes extreme. By clearing forested land, you may increase the risk of runoff problems for you and your neighbours.

On forested land, the potential for such problems is low. The trees intercept rain and dissipate rainfall energy, reducing the volume and energy of rain reaching the forest floor. Water on the forest floor moves within the litter cover layer which slows water movement. This allows more water to infiltrate the soil, leaving less water to contribute to surface runoff.

On cleared land, however, watersheds of only a few hundred acres can generate sufficient runoff to wash out culverts or flood low lying land and to form gullies too large to repair with farm equipment.

Farm watersheds, because of their small size, can respond more quickly to runoff events than large, regional watersheds. Even local showers can produce rapid runoff, so the risk of gully erosion and flooding can be high. In addition, as more small watersheds within a regional watershed are cleared, the whole regional watershed becomes more sensitive to runoff. This increases the potential for flooding, erosion, sedimentation and water quality degradation throughout the area.

Logging on a farm watershed needs careful planning and management to reduce these negative effects. If a cleared forest is regenerated promptly, the impact on the watershed can be minimized.

In-Field Water Erosion

In-field water erosion refers to soil removal by raindrops hitting the ground and runoff flowing as sheet flow or in small rills. Characteristics that increase the risk of in-field erosion include:
• steep slopes or long, uninterrupted slopes;
• sandy or silty soils;
• soils without a protective vegetative cover;
• reduced infiltration resulting from low permeability at or near the soil surface (due to soil crusting, frozen soil, fine textured soil, shallow soil or other characteristics); and
• soils low in organic matter.
Forested areas in Alberta typically have Gray Luvisol (Gray Wooded) soils which have many of these characteristics. Most forested landscapes in the settled part of Alberta are gently to moderately sloping and have minimal risk of erosion unless converted to cultivated land.

The litter and tree residue remaining immediately after logging usually protect the soil from in-field erosion, unless logging practices result in excessive surface disturbance. Land developed to pasture is also reasonably well protected if the pasture is properly managed to maintain good ground cover. On cultivated land, however, slopes greater than 5 per cent are susceptible to in-field erosion. Long slopes (greater than 800 m (2,600 ft) in length) are susceptible to erosion at slopes as low as 2 per cent.

Wind Erosion

Depending on the subsequent land use, logging can also increase the risk of soil erosion by wind. Conditions promoting wind erosion include:
• sparse or absent vegetative cover,
• dry, loose and finely aggregated soil,
• smooth soil surface,
• large fields, and
• high velocity winds.
Vegetative cover, including crop residue, is particularly important in reducing wind erosion. It anchors the soil, increases surface roughness, reduces wind speed, conserves soil moisture and adds organic matter which helps bind the soil particles into aggregates. Clearing and cultivating land removes the vegetative cover for part or all of the year. Large, open fields are especially erosion prone because long, unobstructed distances allow the wind's velocity to increase.

Streams

Tree roots help stabilize stream banks, and tree shade helps reduce algae growth in streams in some cases. Streamside vegetation also traps sediments before they reach the stream and absorbs nitrates from groundwater. Clearing trees removes these benefits.

Stream banks can also be damaged by equipment or livestock trampling, resulting in reduced water quality and increased sedimentation. In extreme cases, stream banks may be destroyed, and the diverted stream flow can cause flooding and sedimentation in new locations.

Trees left standing after selective harvesting are susceptible to windthrow. Excessive windthrow next to streams can reduce bank stability and increase sedimentation.

Watertables

Trees act as living pumps that draw moisture out of the soil and release it into the atmosphere. At the same time, tree shade and shelter may prevent excessive evaporation from dry sites. Depending on topography, soil and availability of water, clearing trees can have one or more of the following effects on watertables and associated site conditions:
• waterlogged soils that are difficult to reforest or crop,
• reduced soil moisture and drying of existing wetlands,
• fluctuating watertables causing increased soil salinity or changes in soil pH, or
• problems with water quantity or quality in existing dugouts, springs or wells.
Wildlife

Wildlife need food, water, shelter and cover to hide in. Adequate wildlife habitat must contain all these components. Although clearing may benefit some species, generally forested land provides habitat for more species than pasture land, and pasture land provides habitat for more species than cultivated land.

Aesthetics

Removing forest cover changes the aesthetics of the local landscape. In some areas, public opinion may result in pressure to modify timber harvesting practices to reduce the visual effect.

Economics

Logging and any subsequent land development can have significant economic consequences. You will need to carefully estimate the costs and benefits to decide if timber harvesting is the best economic choice for you. For example:
• The merchantable value of timber varies greatly from site to site. What is the value of the timber at your site?
• Costs for slash disposal and reclamation or development of agricultural land can be large; they may be higher than the value of the harvested trees.
• Removing tree cover removes the environmental benefits associated with trees. This can have economic impacts. For instance, crop yields on open fields are typically less than those on sheltered fields. As well, unsheltered farmsteads have greater heating costs, and unsheltered livestock operations have greater feed and bedding costs.
• Clearing may affect the real estate value of your property. Are wooded areas worth more than cleared land? Are they likely to be worth more in the future?
• Estimate the investment of time and capital for the various land use options you are considering. Weigh these against the returns to decide if the proposed activities will help meet your goals.
• Much debris remains after logging, even with the good logging methods shown in the photo. Removing this debris can be costly