Soil Rehabilitation Guidebook

[Soil Rehabilitation Guidebook Table of Contents]


Revegetation strategies to restore ecosystem function

Revegetation is a fundamental part of all rehabilitation projects. The type of revegetation techniques used depend largely on the rehabilitation objectives, which may include:

Determining desired characteristics of vegetative cover

Revegetation of some kind is an essential part of every rehabilitation process. Bare soil will erode, recompact (if it has been recently tilled), lose soil structure, lose nutrients and undergo invasion by weed species. A wide variety of approaches to revegetation is possible. Traditional approaches have usually involved seeding a mixture of agronomic grasses and legumes with erosion control as the primary objective. Modern rehabilitation projects have more demanding objectives, however, such as re-establishing a commercial forest. Sometimes, techniques required for one objective (such as developing complete ground cover to prevent erosion) may conflict with others (establishing a free growing crop of trees).

The guidelines below, and the discussion of various revegetation strategies that follow, show how different techniques might be used to achieve a variety of rehabilitation objectives.

Grass and legume seeding

Native plants, domesticated native plants and introduced agronomic species are all useful for rehabilitation.

Seeding of agronomic grass and legume species is an established technique for erosion control in British Columbia (Carr 1980, 1985). There is a very large selection of species to choose from, and seed mixes can be easily tailored to achieve particular effects.

Grass and legume seeding can also be used to meet many other revegetation objectives such as restoring soil structure, enhancing site nutrient status, hastening green-up and producing forage.

Native and domesticated grasses and legumes can be used in the same situations and applications as agronomic varieties, and in many cases, they will be better suited for use on a particular area. Many native plants may be well adapted to conditions of low nutrient status, and they likely reduce potential adverse effects on biodiversity that may arise from seeding introduced plant cultivars in forest and range ecosystems.

Choosing the proper species for a particular situation requires that the characteristics of the species be matched with the site conditions and rehabilitation objectives. Attributes such as root form, reproductive system, growth form, timing, and adaptability all affect the suitability of plants for a particular site and objective.

Advantages of seeding grass and legumes for rehabilitation

Disadvantages of seeding grasses and legumes for rehabilitation

Planting shrubs

Revegetation with native shrubs can be a valuable rehabilitation tool, particularly in highly sensitive areas such as recreation areas, alpine tundra and grasslands. Native shrubs have not received a great deal of attention for rehabilitation of forest lands in the past, but the infrastructure necessary to allow routine use of shrubs has been rapidly developing in recent years. Commercial seed-pickers are available to collect material from anywhere in British Columbia and several nurseries currently grow native species in a variety of container stock types.

Various methods can be used to establish native shrubs. Container stock can be hardy and, although it may be browsed in some areas, it can be planted in areas where seed retention and survival are problems. Many species such as alder, rose, soopolallie and juniper may be planted by direct seeding if a source of seed can be found. As well, several species can be established as rooted cuttings and willow can be established as unrooted cuttings of stems but mortality rates are high. Species such as saskatoon and wolf willow can be easily established as cuttings from roots.

Advantages of planting shrubs for rehabilitation

Disadvantages of planting shrubs for rehabilitation

Planting hardwood trees

Much of the previous discussion on native shrubs applies to hardwood trees as well. Hardwood planting is gaining more acceptance in British Columbia as markets expand for the common species. Investigation into mixed planting has indicated that, in certain situations, these techniques may confer some growth and performance advantages to the conifer component of a mixed planting.

Advantages of planting hardwood trees for rehabilitation

Disadvantages of planting hardwood trees for rehabilitation

Planting conifers

Planting conifers for rehabilitation requires more flexibility and perhaps more stringent planting practices than would be used in planting most cutover areas. For example, consider planting at higher than maximum stocking densities where soil conservation or risk of increased seedling mortality are issues; in rutted areas, take more care to select good microsites for planting; consider larger than normal stock where the need for more robust seedlings is indicated, and species requirements may change as a result of disturbance.

Advantages of planting conifers for rehabilitation

Disadvantages of planting conifers for rehabilitation

Bioengineering techniques

Bioengineering in rehabilitation refers to the use of living plants to create structures, usually to control erosion or stabilize slopes. Bioengineering techniques involve the very intensive use of relatively large pieces of living material. The living material is used in such quantity that it helps provide slope stability even before it begins to grow. As the living material grows, the benefits of revegetation and slope stabilization are achieved in one action.

Bioengineering can be used to stabilize existing slopes or to help reshape slopes to more stable forms. Small terraces, for example, can be created to trap sediments and dissipate the energy of running water. Bioengineering techniques may be useful where:

The major categories of bioengineering techniques include (from Beese et al. 1994):

For help in applying these techniques, consult an expert in bioengineering.

Advantages of bioengineering techniques for rehabilitation

Disadvantages of bioengineering techniques for rehabilitation

Cattle grazing and rehabilitation

In some situations, cattle grazing may interfere with the prescribed goals of establishing conifer seedlings and maintaining vigorous vegetation cover. Agronomic seed mixes are often very palatable and may attract cattle to the rehabilitated area, resulting in trampling damage to planted tree seedlings. Vigorous vegetation cover is required to rebuild soil structure. High rates of vegetation removal by cattle may seriously reduce the effectiveness of this treatment. It is therefore important on blocks with grazing to consider how best to manage cattle.

Cattle management is carried out within the broad strategies established under a range use plan for the range agreement holder, usually a local rancher. Changes in cattle management and the range use plan require the cooperation of the rancher and consultation with local agrologists. Rehabilitation plans must include provisions to ensure that the accumulated effect of cattle damage does not reduce conifer stocking to less than acceptable levels.

To prevent cattle from congregating on rehabilitated areas, consider such practices as: