29. Forestry

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1. Scope

1.1 General
1.2 Subsectors

1.2.1 Biological production/Planning
1.2.2 Establishment of a stand
1.2.3 Stand utilisation
1.2.4 Harvesting techniques

2. Environmental impacts and protective measures

2.1 Sector-typical influences on the environment
2.2 Sector-typical protective strategies

3. Notes on the analysis and evaluation of environmental impacts

4. Interaction with other sectors

4.1 Complementarity
4.2 Social environment

5. Summary assessment of environmental relevance

6. References

Annex: Glossary of selected terms


1. Scope

1.1 General

Forestry is generally defined as utilisation of forests to satisfy human needs. Characteristic features of forestry are the extremely long production periods extending over several decades and, in the case of timber production, the fact that the product is identical with the production input. Production of commercial timber and the use of return on investment as a success criterion for forest owners, generally state authorities (cf. REPETTO), are unsuitable for integrated problem solutions in view of the socio-economic conditions.

Probably the most important aspects of forestry activities today are protection of species and biotopes and preservation of the human habitat. In virtually no other sector are the "limits of growth" demonstrated as clearly as by the global destruction of the forests. The impacts of this process are no longer confined to specific regions, but are interlinked on a global scale, as forests - along with the oceans - represent the most important terrestrial bioregulators of global cycling systems and the Earth's climate.

The tropical forest is particularly badly affected, with around 20 million hectares being clear-cut or degraded each year (cf. ENQUETE). Tropical moist forests cover only around 6% of the land on Earth, yet they provide a living environment for over half of all species of fauna and flora and for millions of people.

Although the worldwide destruction of the forests has a wide variety of forms, causes and consequences, it can nevertheless be ascribed above all to exploitation and conversion of forest resources to satisfy short-term economic and personal interests. This form of activity eventually leads to the degradation and loss of human habitats.

This situation imposes new demands in terms of executing agency, project size and site. Holistic approaches which also include the sectors immediately related to forestry (CARILLO et al.) are therefore essential.

1.2 Subsectors

The forestry sector differs from every other sector of an economy by virtue of its production period and the fact that it produces both tangible goods and intangible benefits. It thus calls for special forms of biological production. Four subsectors are involved: planning, formation and utilisation of forest stands, and harvesting. Attention will be drawn where necessary to the special features of tropical forest management.

1.2.1 Biological production/Planning

Biological production in the forestry sector is controlled through the various methods of forest management, agroforestry and product harvesting. The purpose of these methods is to achieve, by controlling site production potential, the management goals laid down during planning; such goals may involve production, conservation or a combination of the two.

Planning, establishment of a stand and utilisation are classed as subsectors of biological production.

All forestry planning is based on inventories (e.g. ZOEHRER), which provide the framework for forest management over a period of ten years in most cases. Apart from static elements such as timber stock, dynamic and structural elements such as increment and horizontal and vertical species and diameter distribution must also be recorded, particularly in tropical moist forests, otherwise the sustainability of yield regulation cannot be guaranteed.

In addition to measurement of quantitative stand parameters, multifunctional forest management also calls for comprehensive site mapping (e.g. DENGLER, MAYER, WENGER) which ascertains geoecological factors for each stand individually.

The combination of continuous forest inventories, site mapping and specification of planning targets is known as forest management planning, the details of which are laid down in forest management plans. The management and recording unit is the compartment. The division of a forest into compartments should reflect the topographical and hydrological differences between stands. Simple geometrical shapes are appropriate only in exceptional cases for lowland plantations. In heterogeneous tropical moist forests, division can be extended to water catchment areas (sub-catchments).

The individual management goals are laid down separately for each compartment on the basis of forest management planning and economic analyses. Apart from the traditional economic indicators such as internal rate of return, cost-effectiveness analyses (cf. FÄHSER, WENGER) can be used to assess the relative advantages of alternative management goals.

The function and structure of forest resources vary depending on the intensity with which they are utilised and the geoecological zone in question (MUELLER-HOHENSTEIN). The management concepts must be geared to the characteristic features of each type of resource, e.g. high and low forests, savannahs, mangroves and agroforestry systems or resources for gathering. The site-specific limiting factors - namely forest area, water, nutrients and light - restrict the scope for optimising forestry operations from the management viewpoint.

The different types of resource are closely interrelated and can complement one another in functional terms. These interrelationships necessitate integrated, interlinked planning. Storeyed, species-rich high forests of primary or secondary origin are best able to fulfil the necessary protective and utility functions over time and area. Commercial-timber plantations can alleviate demographic pressure on natural forests if the local population are involved in plantation management.

1.2.2 Establishment of a stand

Forests are regenerated by artificial or natural means at the end of their rotation periods or if they become overmature.

· Planting

Artificial forms of the establishment of a stand comprise conventional afforestation on open sites (EVANS, GOOR), planting under shelterwood to fill gaps in naturally regenerated stands or improvement measures in over-used forests (LAMPRECHT). The form of soil preparation and the planting technique depend on species, soil fertility, water balance and land condition. Brushwood and felled-area flora can be placed in windrows or burned unless this appears inadvisable on account of nutrient losses and soil erosion.

Planting techniques range from hole planting in clearings and deep soils through cuvette planting ("micro catchments") on slight slopes in arid regions to terracing on steep slopes in high mountain regions. For crusted laterite soils, complete turning of the soil is usual.

Irrespective of the technique used, artificial regeneration produces forests having a simple structure and largely open cycling systems. The tree species selected are generally vigorously growing, competitive pioneer species. The number of species and the degree to which they are mixed remain low for reasons of manageability. The biotic and abiotic risks to such plantations become greater as aridity increases (shortage of water, fire) and as soil fertility decreases, particularly on geologically old substrates in the inner humid tropics. The relatively small range of species on marginal sites is a result of natural factors.

Measures to protect stands against fire, storms, water stress, nutrient deficiencies and disease are frequently necessary (see FRANZ, for example, with regard to biological pest control). Controlled burning of organic surface layers (known as "prescribed burning") is a special plantation-management practice employed in arid regions to remove highly inflammable organic layers (BROWN, GOLDAMMER). Use of this method is restricted by the demands of soil and water conservation.

The planting stock needed for artificial afforestation is produced in nurseries, which usually concentrate on generative raising of planting stock from seed. Vegetative forms of plant production, such as propagation by cuttings, tissue cultures or seed production in seed plantations, are often capital-intensive and usually have to be carried out on a central basis by agencies possessing the necessary expertise (e.g. KRUESSMANN). It must be ensured that the consequences of genetic impoverishment can be overcome by means of an appropriate silvicultural strategy. Consumption and use of the inputs commonly required by nurseries (land, seed, fertiliser, substrate, water, pesticides, means of transport) depend on the specifications of the forest management plans (management goal type planning) and the propagation method employed. The high substrate consumption involved in production of pot or container plants calls for careful logistical planning.

Natural-forest programmes could involve small or temporary nurseries in the vicinity of the stand, as the provenances and varieties necessary to achieve the related management goals can best be produced on a decentralised basis. Regional afforestation programmes can be supplied by large central nurseries.

· Natural regeneration

Growth dynamics, phenology and adherence to the given spatial arrangement constitute criteria for selection of natural regeneration techniques (ASSMANN, GOLLEY, DENGLER, LEIBUNGUT, MAYER, WEIDELT, WHITEMORE). A general distinction is made between methods for clear-felling high forests, involving shelterwood and strip techniques, and the selection method for storeyed, species-rich stands. Special demands in terms of species protection and soil conservation arise in connection with conversion systems in tropical moist forests (LAMPRECHT) and management of high-altitude forests (MAYER).

Characteristic of all methods are a specific sequence and number of individual fellings over a long period, with care taken to preserve the dominated stand. During the regeneration process, the soil usually remains almost totally covered. Working of the soil is generally confined to preparing the germination bed with implements such as cultivators or harrows. Prescribed burning may become necessary for regeneration of pyrophytes (cf. section on planting).

Irrespective of the method used, the outcome will ideally be stands which, both horizontally and vertically, are more or less heterogeneous, species-rich and multi-storeyed, and which have closed natural cycling systems. Such stands are highly resistant to injurious factors and there is thus little need for protective measures and artificial raising of plants.

1.2.3 Stand utilisation

In generalised terms, distinctions can be made between the following forms of utilisation:

- conventional forest management for production of timber and to realise protective functions (e.g. DENGLER, LAMPRECHT, MAYER)
- agroforestry for integrated production of agricultural and forestry products (e.g. ICRAF)
- gathering, generally in connection with non-timber products (e.g. DE BEER).

Irrespective of the form of utilisation, it is essential to control the relevant economic (e.g. McNEELY) and demographic conditions in order to prevent over-utilisation. A key role is played by forest tending, without which it is impossible to utilise the wide range of opportunities offered by multiple-use forestry.

· Forest management

Distinctions are generally made between three types of forestry operation (e.g. DENGLER, MAYER):

- high forest created by means of natural or artificial regeneration, incorporating clear-felling (age-class) forest and all-aged (selection) forest
- middle forest originating from coppices and planting
- low forest originating from coppices

Low and middle forests are generally clear-cut in short rotation cycles. They are highly suited to production of fuelwood and other small dimensions for supplying local markets, provided that care is taken to implement the necessary protective measures such as regulation of forest grazing, terracing or cultivation of site-appropriate provenances. Management criteria are based on economic and technical data such as diameter and timber stock.

In high-forest management a distinction is made between final felling during stand regeneration and intermediate felling during forest tending. Long rotation periods and periodic tending measures make high forests suitable for achieving multifunctional goals such as production of high-grade timber and ensuring of welfare functions.

The purpose of forest tending is to raise stable stands by controlling the stages of stand development (e.g. MAYER). The management criteria relate to aspects of silviculture and forest yield science, such as basal area, number of trees, species and diameter distribution, or target diameter. Irrespective of the stage concerned, control of the limiting factor represented by light is a characteristic element of forest tending (e.g. BAUMGARTNER in MAYER).

In generalised terms, a distinction can be made between young growth tending, or pre-commercial thinning, and commercial thinning. Both chemical and mechanical methods are used, the latter being performed manually or with the aid of machines. Chemical methods are feasible only if non-persistent agents can be applied on a targeted basis. Systematic methods such as row thinning are commonly employed on monotypic plantations; only in favourable locations are they unlikely to give rise to problems (soil erosion).

Selective methods, known as selection thinning (e.g. MAYER) or timber stand improvement (WEIDELT, WENGER, WÖLL), are the most effective in terms of yield and from the ecological viewpoint. A characteristic feature of such methods is regulation of the growing space of trees preselected for harvesting through removal of competing adjacent trees. In all-aged forests, growing-space regulation, intermediate felling, final felling and regeneration can be combined, whereas in artificially formed plantations this is possible only if at least two tree species have coordinated degrees of shade tolerance.

Tropical moist forests have special requirements where timber production is concerned (e.g. LAMPRECHT; WEIDELT; WHITEMORE 1984).Selective methods are in most cases particularly suitable for such forests in view of the diversity of species, the horizontal mosaic structure, the vertical layering, the nutrient balance (see Section 3) and the phase-controlled growth dynamics. In simplified terms, it is possible to distinguish four cyclically linked development stages (WHITEMORE, 1978): terminal stage - gap/group stage - build-up stage - maturity/climax stage. Forest regeneration and timber harvesting must be geared to these growth dynamics.

In principle, even timber harvesting in primary forests containing irregularly fruiting tree species with uneven diameter distribution is justifiable if only dying individual trees in the main stand are removed using highly mobile harvesting methods (see 1.2.4) after fruiting ("mortality pre-emption", SEYDACK 1990). In stands consisting of tree species with even diameter distribution, located on fertile and erosion-resistant sites, the trees can be removed in groups. Less selective methods are possible where stand conditions are homogeneous, as is the case for example in many natural tropical coniferous forests. However, harvesting of hitherto unutilised tree species (lesser-known species) is acceptable only if the nutrient balance (see Section 3) remains in equilibrium and the reproductive biology of the species concerned is known.

Management of special forms of tropical forest vegetation, such as gallery forests, savannahs and mangroves, cannot be treated within the scope of this environmental brief (cf. CHAPMAN, GOLLEY et al. 1978).

· Agroforestry

It is above all in the humid tropics that increasing population pressure is blurring the dividing line between agriculture and forestry. In areas on the fringes of intact forests, combining agricultural and forestry operations is often the only way of meeting the population's food and wood requirements. Agroforestry operations exhibit a higher degree of ecological stability than purely agricultural ones and in many places are the only means of permitting permanent cultivation (e.g. JORDAN).

Although there are no universally valid definitions, distinctions can be made for practical purposes between agroforestry, silvopastoral and agrosilvopastoral systems.

The degree to which agricultural and forestry elements are integrated in terms of time and area (e.g. ICRAF) depends on the available know-how, the availability of water, the soil fertility and the market. In marginal areas remote from markets it is generally possible to realise only simple forms of agroforestry, such as slash-and-burn agriculture (also known as shifting cultivation) or pasture farming in savannahs (PRATT).

· Gathering

In many geologically old, tropical moist forests, gathering of non-timber products, known as "minor produce", is often the only possible form of sustainable use. This is particularly true of Central Amazonian sites highly deficient in nutrients, where intensive forms of roundwood production result in a negative nutrient balance. In many parts of South-East Asia, for example, the production value of the minor produce far exceeds that of timber production (DE BEER). As tropical forests yield an immense number of non-timber products, it is impossible to cover all the region-specific aspects of this area within the scope of this environmental brief.

1.2.4 Harvesting techniques

Forests and trees yield numerous products important to man: commercial timber, pharmaceutical products, spices, resins, rattan, foods and tanning agents. Each of these products requires a tailor-made harvesting method (CAPREZ, STAAF, DE BEER).

· Timber

Of all activities in the forestry sector, timber harvesting requires the greatest input of capital and is most likely to cause damage. The strained nutrient balance means that timber harvesting is often impossible in tropical moist forests located on geologically old substrates. Planning and execution of timber harvesting must therefore be based on both economic and ecological criteria. The paramount aim of all timber harvesting measures is to minimise damage to the soil and stand. The following criteria must be taken into consideration in selecting the method to be used:
- management goal (rights of use, protective forest, commercial forest)
- stand density (number of trees, structure, nutrient dynamics)
- type of felling (intermediate felling, final felling, timber assortments)
- topography and soil (skidding distance, soil erosion)
- infrastructure (accessibility, construction costs)

From the operational viewpoint, actual felling of the trees is considered separately from hauling of the felled trunks. While mobile harvesting machines are generally used in non-tropical regions, felling of trees in the tropics is performed manually with the aid of an axe, handsaw or power saw. The degree of success is largely determined by the training and remuneration of the forest workers and by the way in which work at the felling site is organised. Resource-conserving methods of timber harvesting include the following features:
- marking of stand before felling (inventory)
- directional felling
- conversion of shortwood at the felling site before hauling

In roundwood handling, distinctions are made in organisational terms between skidding or hauling within the stand and (long-distance) timber transportation (road, rail, waterway), in technical terms between manual, animal-powered and mechanical techniques, and in method-related terms between whole-tree methods and roundwood methods. The damage done to the stand increases in proportion to engine power, intensity of utilisation, slope inclination, degree of accessibility, trunk length and the amount of ground skidding involved. Inappropriate hauling methods can cause soil compaction, rill erosion along wheel tracks, destruction of forest soil flora and the dominated stand, and butt and root damage to the rest of the stand. The most important hauling methods are given below in generalised terms, listed in order of the potential degree of damage that may result from them:

- Ground-based methods

· skidding hoists for clear-cutting, final felling, moderate or long skidding distances, suitable anywhere from lowland to high mountain regions
· wheeled and tracked forest tractors for clear-cutting, final and intermediate felling, short to moderate skidding distances, hilly terrain
· animals (horses, oxen, water buffalo etc.) for intermediate felling, smallwood, short distances, lowland regions

- Gravity methods

· manual floating for intermediate and final felling, short distances, in high mountain regions
· log chutes (wooden or earthen chutes), generally for final felling, long distances, high mountain regions

- Airborne methods

· travelling winches for intermediate and final felling in high mountain regions
· cable cranes for universal use
· helicopters for transportation of high-grade timber

In view of the mosaic structure of tropical moist forests, timber harvesting in such regions is liable to cause damage to resources unless the methods used take account of the conditions of single-tree harvesting in groups by way of mobility, off-ground hauling and a low-density road network (HODGSON). Homogeneous forms of stand in lowland regions allow less complicated methods to be used. Full-tree or whole-tree methods are suitable only for nutrient-rich lowland sites that are resistant to erosion.

After felling and hauling, timber is stored for a short time in the forest by the side of the road until it is removed by the purchaser. It is thus not usually necessary to protect timber stored in this way. In exceptional circumstances, for example after natural disasters, it may be essential to store large quantities of timber for lengthy periods in specially created log dumps. Steps must then be taken to limit the amount of land required and the use of pesticides and to dispose of bark shavings.

Appropriate options are to be selected on the basis of time studies, forest damage analyses and economic criteria. In addition to conventional economic assessment tools such as cost-benefit analyses, cost-effectiveness analyses (e.g. WENGER) should also be employed. Such analyses must relate to the entire rotation period (production period), rather than being confined to individual operations.

Timber harvesting can have indirect effects of environmental relevance in that it opens up forest areas in a manner permitting their subsequent use. Apart from selection of environmentally sound timber harvesting methods, an efficient forest administration capable of carrying out surveillance of forest use is essential to minimise damage to the stands.

· Non-timber products

As non-timber products encompass such a broad range, the effects of harvesting them cannot be described in detail here. It is essential to draw upon available local know-how in this connection.

A distinction must be made between products harvested for the harvester's own use and those harvested for marketing, as there is generally no danger of over-use where products are intended merely to meet subsistence needs. Special precautions must be taken in harvesting tree products such as resin, bark or climbing plants (e.g. rattan), as the function of the trees as means of production or support can be permanently impaired. Harvesting of "non-tree products" such as fruit or game requires less in the way of specific management if the products in question are not to be marketed.


2. Environmental impacts and protective measures

2.1 Sector-typical influences on the environment

In terms of area, forests constitute the Earth's most important terrestrial ecosystems. Since the "invention" of arable farming around 10,000 years ago, they have been continuously fragmented and degraded and today cover less than a third of the Earth's inhabitable land surface, extending over an area of around 42 million km2 (STARKE). As forests can perform their protective functions only where they cover a large area, man's living environment in certain regions is in jeopardy. Four protective functions will be discussed here:

· Climate regulation

Together with the oceans, the Earth's forests constitute a biological climate regulator. By means of their high evapotranspiration, they generate a large proportion of the precipitation themselves in some places. Evaporation of this water absorbs up to three quarters of the radiation energy, particularly in the tropics, and thereby prevents excessive warming of the atmosphere. Large quantities of the greenhouse gas CO2 are fixed as well. These two climate-regulating functions can be most efficiently controlled by means of near-natural, long-lived types of forest containing abundant stocks and covering large areas. By virtue of their more favourable assimilation/respiration ratio, many temperate forest formations, such as the coastal forests in the north-west of the USA, store up to three times as much CO2 as tropical rainforests (STARKE, 1991).

· Protection of genetic resources

Although tropical moist forests cover only a fraction of the Earth's surface (6%), they contain around 90% of all apes, at least 80% of all insects, at least two thirds of all plant species and roughly 40% of all species of birds of prey. As the majority of these species can exist only in near-natural forms of forest extending over large areas, monotypic artificial forests covering small areas are unsuitable for protecting species and genetic resources.

· Soil conservation

Storeyed high forests are the most efficient biological means of soil conservation. Soil erosion and soil formation under such stands are balanced and in line with the geoecological norm. The simpler stand structures found in dry forests or grass savannahs mean that such regions differ less markedly from artificial forests. The same applies to alternative forms of forest in lowland regions. Under humid tropical conditions and in high mountain regions, the erosion rates in artificial forests may far exceed the natural soil loss rate (MORGAN).

· Protection of human habitats

Rapid deforestation is constricting the human habitat, particularly in tropical moist forests, while at the same time destroying jobs. Tax concessions for large-scale projects (timber exploitation, mining, cattle rearing) can accelerate this process locally and displace the labour-intensive methods involved in traditional resource utilisation. It is thus above all in natural-forest and agroforestry projects that training and upgrading can play an important part in raising decision-makers' awareness of the relevant issues.

2.2 Sector-typical protective strategies

Forests perform vital protective functions, but at the same time require protection themselves in their function as biotopes housing a variety of plant and animal communities. However, effective protection of forests is possible only if the state, industry and the local population all have an interest in their long-term preservation. The ways in which forests are used must therefore ensure protection of forest resources and sustainable generation of added value, besides being acceptable to all interest groups involved. From the hygiene viewpoint, for example, the clearance of African savannahs infested with the tsetse fly is highly beneficial. For Iko bushmen and other game hunters, however, it means the destruction of their living environment, while for hydrologists it means flooding in low-lying areas and for nature conservationists it represents the destruction of biotopes.

Depending on site conditions, a protective strategy in the forestry sector will include components such as the following:

- Political/economic instruments

· regulating forest utilisation by interlinking protective, buffer, exploitation and settlement areas
· ensuring the generation of added value through utilisation of forests by means of diversification in the producer region and reinvestment of profits, e.g. in forest-tending programmes
· participative planning, implementation and monitoring of forest utilisation concepts
· moratorium on timber exploitation in primary forests located in tropical and temperate zones
· market-oriented incentives such as input and output taxes or subsidies for substitutes (e.g. use of cable cranes instead of bulldozers in timber harvesting)

- Technical/ecological instruments

· reducing wood consumption through improvements in wood processing
· function- and needs-oriented forest management by means of silvicultural planning on a single-stand basis
· simulation of natural growth dynamics and forest tending through long rest periods and natural-regeneration periods

An implementation-oriented discussion of the above elements can be found in the reference literature (cf. BMZ, ENQUETE).

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