Sustainable forestry

2007 Schools Wikipedia Selection. Related subjects: Environment

Sustainable forestry is a forest management concept. The basic tenet of sustainable forestry is that the amount of goods and services yielded from a forest should be at a level the forest is capable of producing without degradation of the soil, watershed features or seed source for the future. It differs from Sustained Yield Forestry and Sustainable forest management according to the sets of forest goods and services that we attempt to "sustain".

Sustainable forestry includes, clean water,wildlife, recreation natural cover and forest where seed trees are left for natural regeneration. The sensitive ecosystems are not all about the tall trees but rather the whole mosaic of forest entities. The potential natural vegetation, annual growth and the basal area, combined with the amount of trees per stand to develop a management plan for area sizes from a stand to an ownership through the entire forest, as well as considering the landscape and position of the forest within it are considered.

Boreal forests

In boreal forest and other forests, clear cutting and intensive silviculture have been blamed for biodiversity problems. Many environmentalists believe that clearcutting is not sustainable, while single tree management is. Many foresters assume that in boreal situations clear cutting imitates natural forest fire and other dynamics in important ways. Recent research has suggested that large-scale fires did not occur very frequently and that the end result of fire or other natural dynamics are not comparable with the end result of clear cutting. However, considering that boreal forests have low biodiversity to begin with, these claims may be unsubstantiated.

Clearcutting and other types of even-aged forest management are used as silvicultural tools to promote growth of shade-intolerant species and are used in some forest types in order to promote regeneration. Levels of spatial patchiness (horizontal structural diversity) at the expense of variety of canopy layers (vertical structural diversity), both necessary for many wildlife species, are increased with some level of even-aged management. Selection system, or uneven-aged forest management, has low levels of horizontal structural diversity with a high level of vertical structural diversity. Thus it seems that both types of management should be considered at the landscape level.

Old Growth Forests

If sustainable forestry is an experiment, reserves are the control of that experiment. By comparing a management regime to a close to natural setting, we can better devise schemes for optimal growth. Aside from being a good standard to compare our commercial forests to, old growth forests are a good seed source. The two-hundred year old trees in old growth forests are not representative of all the trees two hundred years ago- they are actually the most resilient trees of their time. The old trees are the trees that made it, while others did not- those trees are more disease resistant, fire resistant and fit than any other.

High grading

One ecological advantage of clearcutting is that it avoids the risk of selection cutting and single tree management. When harvesting individual trees from a stand, some jurisdictions consider it sustainable practice to cut the tallest, fastest growing and generally best trees. This ' high grading' leaves the dwarfed, non preferred trees to make up the gene pool of the forest. The result is a short, poor growing forest, especially when there is a lack of an outside seed source. High grading has long been discredited in some jurisdictions, such as Canada, where any recent examples would be rare.

Fire suppression

Fire and insect infestations are the dominant natural disturbances in the Taiga and is an important disturbance mechanism in many other forest types, including temperate, sub-alpine and chaparral forests. Large, stand-replacing fires, particularly in the boreal forest, determine the age distribution and spatial age mosaic of the forested landscape.

In North America, the belief that fire suppression has substantially reduced the average annual area burned is widely held by resource managers and is often thought to be self-evident. Direct empirical evidence however is essentially limited to just two studies by Stocks (1991) and Ward and Tithecott (1993), that use Ontario government fire records to make comparisons of average annual area burned between areas with and without aggressive fire suppression policies. Numerous subsequent studies have presented the same information, often in a different format (Martell 1994, Martell 1996, Weber & Stocks 1998, Li 2000, Ward & Mawdsley 2000). The proponents of these studies argue that areas without aggressive fire suppression policies have larger average fire sizes and greater average annual area burned and a longer interval between fires and that this is evidence of the effect of fire suppression.

However, the idea that fire suppression can effectively reduce the average annual area burned is the focus of a vocal debate in the scientific literature. In particular, several recent papers have argued against this idea (Miyanishi & Johnson 2001, Miyanishi et al. 2002, Bridge et al 2005). These papers claim that statistically rigorous techniques for estimating the average annual area burned, called the fire cycle, do not show changes in the fire cycle associated with fire suppression and that the evidence used to support the effect of fire suppression is biased and has been presented in a way that is flawed. Note that none of these papers criticize fire management agencies for being anything less than completely committed to their mandate. Nor do they suggest that fire personnel are not well trained, efficiently deployed or well managed. Instead, these papers simply suggest that despite the resources employed, fire management agencies are simply unable to effectively reduce the average annual are burned.

The impact that effective fire suppression may have on the average annual area burned is important for many reasons, but in particular, its impact is key to the current paradigm of sustainable forest management in many jurisdictions. One of the core aspects of SFM in many jurisdictions is the use of wood supply models to determine sustainable harvest levels. This determination of sustainable harvest levels often assumes that fire suppression has been effective at reducing the average annual area burned. Thus, if current assumptions about the effect of fire suppression are wrong, the impact on SFM could be substantial.

One area where it is largely accepted that fire suppression has altered the “natural” fire regime is the Pinus ponderosa ecosystems in the interior West of the United States, where a historical regime of frequent surface fires had maintained open-canopy conditions. With the arrival of European settlers, the frequency of surface fires decreased, changing both the accumulation and arrangement of fine fuel. Growth of an intermediate-height ladder of vegetation and the increased bulk density of canopy fuel allowed surface fires to burn into the crown, thus creating a crown-fire regime (Fuli et al. 1997, Shinnerman & Baker 1997).

Harvest

Harvest of trees can deplete nutrients in forest with poor soil. This is particularly true with whole tree harvest as many nutrients are held in the tops and branchs. Harvest often doesn't allow for different successional stages. Forests have different stages of height, age and species diversity, and different animals depend on each. Some harvest techniques eliminate one or more stage of forest development, reducing the value of the wildlife in the forest, and reducing the health of the trees overall.

There are six different kinds of tree harvesting:

Selective cutting, Shelterwood Cutting, Seed-Tree Cutting, Clear-Cutting, Strip Cutting,

Fragmentation

Urban sprawl and other construction can fragment forests. This creates edge habitat, habitat not protected by other trees and exposed to an urban environment. If the same area of forest is spread over different fragments, than there will be more edge than if all of that area were in one lump. If that same area is in a narrow line, then all of the forest becomes the degraded edge with little or no middle. Edge trees are not protected from storm wind, and are more easily consumed by deer. The wildlife living along the edge will suffer predation by racoons or may simply leave because the species will not live that close to humans. There is also the problem of dispersal between fragments. If a part of a contiguous stand of trees is damaged, it can be repopulated by the existing trees around it. However if that stand happened to be a part of a fragment with no dispersal from the rest of the fragmented area, it would take human intervention to maintain the stands. Wildlife species with poor dispersal would suffer in this situation also, even including some birds that will very rarely fly over highways.

Solutions

Using untouched reserves as a model, we can try to recreate those forest conditions. Selection cutting is a practice which mimics some natural disturbances like a tree falling down. Clearcutting mimics other natural disturbances such as intense forest fires. If we can mimic natural conditions, trees have been evolving to grow well under those conditions far longer than under modern forestry conditions, and our mimicry will yield better trees. Selection cutting can be based on gap sizes and woody debris found in our natural reserves. Sustainable forestry also involves re-introducing fire to forests. This has the added benefit of bringing back a variety of wildlife species. And there are also harvest practices that can allow all successional stages of a forest to exist.

Dispersal corridors are lines of habitat that go between fragments so that beneficial wildlife can travel at a regualar rate between forests. This helps lichens and poor dispersing plants and animals to survive in between forest fragments. However, this does not reduce edge effects or help protect trees from the wind. It can help the trees cross pollinate and expand their gene pool, however.