MANAGEMENT OF PROTECTED AREAS
The theory of island biogeography predicts that, in areas of less than 10,000 km2, there will be gradual loss of species. Most protected areas (PA's) are much smaller than 10,000 km2 and, to prevent loss of biodiversity, ACTIVE MANAGEMENT of such areas is necessary. Furthermore outside influences will always affect PA's (e.g. poachers entering the park to kill animals etc.) and unless such factors are controlled, the PA will gradually deteriorate. The amount of management effort required in a PA increases as the size of the PA decreases. Management of PA's can be broadly divided into three categories: i) HABITAT management, ii) PLANT/ANIMAL POPULATION management and iii) PEOPLE management.
HABITAT MANAGEMENT
The objectives of habitat management should be:
i) to optimize the habitat for species which are particularly vulnerable to extirpation (e.g. large vertebrates, species dependent on short-lived early successional habitats, carnivores etc.) i.e. to anticipate faunal/floral collapse and prevent it and/or
ii) to maintain or maximize biodiversity in the PA.
Habitat management usually involves manipulating the rate or direction of SUCCESSION. Succession is the natural process by which ecosystems change over time. It is a predictable series of ecosystems replacing each other over time; an orderly process of change of species composition brought about by interactions between organisms and their local environment. A SERAL STAGE is a temporary ecosystem in a successional series. A CLIMAX ecosystem is the final stable ecosystem in a successional series.
Management of habitats usually involves one of the following:
i) preventing a climax ecosystem from becoming disturbed and reverting to an earlier seral stage e.g. protecting primary forest from logging or fire;
ii) deliberately disturbing climax ecosystems to create earlier seral stages or preventing the progress of succession early seral stages, to conserve species, which live only in such ecosystems e.g. preventing a mountain bog from drying out and developing into a forest, and
iii) accelerating succession by manipulating disturbed, early, seral stages towards the climax ecosystem e.g. planting tree seedlings to accelerate forest succession.
Protecting climax ecosystems
Climax, stable ecosystems are often high in biodiversity and support many species unable to cope with the rapidly changing conditions present in early successional habitats. On the other hand some climax ecosystems can become dominated by few species, since very long periods of stability allow competitive exclusion to occur. In small PA's, protection of species-rich, climax ecosystems is essential to prevent gradual loss of species. Most disturbances to climax ecosystems are man-made e.g. logging, construction of dams and roads, tourist development etc. These will be dealt with under management of people in PA's. Natural disturbances (e.g. landslides, floods, some fires etc.) are not normally a problem in very large PA's, since animals can find refuge in unaffected areas of habitat. However, they can cause problems in small PA's, if they threaten a significantly large percentage of any particular climax ecosystem. The problem with natural disturbances is that they are unpredictable in time and place and therefore very difficult to prevent. A common strategy is to allow disturbance to occur and then take steps to accelerate succession back towards the climax ecosystem as quickly as possible.
Conserving early successional ecosystems
Some organisms have evolved to live only in early successional ecosystems. Such ecosystems are usually very short-lived, tending to develop into later successional stages, so organisms dependent upon them usually have strong dispersal ability, enabling them to find new patches of disturbed, early-successional ecosystems, as their original habitat develops into later successional stages.
In large PA's, new areas of early successional ecosystems will occur naturally and frequently throughout the area. However small PA's (i.e. those smaller than the MINIMUM DYNAMIC AREA) often do not support all the natural processes that create all successional stages. Therefore, to maximize biodiversity and prevent extirpation of species dependent on early successional stages, it is sometimes necessary to create such areas (by artificially disturbing climax ecosystems) or prevent succession from progressing within early successional ecosystems, to conserve them until other areas of such habitat are created naturally elsewhere.
For example, wetlands (e.g. bogs, marshes etc.) are rather rare habitats in tropical countries. No new wetlands are being created by natural processes, since streams and rivers are now controlled by dams etc. Many are under threat of drainage for agricultural development. Many rare species are specialized to live in wetlands and occur nowhere else. If a wetland is left alone, organic matter accumulates and eventually the wetland dries out and gradually becomes grassland and then a forest. A wetland may need to be dredged to maintain areas of open water.
In some forested PA's, areas of open grassland (sometimes created by Man) or savannah provide grazing for large herbivores and an opportunity for tourists to view large mammals. Such opportunities are rare in tropical forests. Left alone, such areas may gradually convert back into forest. A savannah may be maintained by fire, grazing by domestic animals, hand cutting or applying herbicides to trees saplings.
Many organisms require more than one habitat to complete their life cycles and it is therefore necessary that both climax and early successional ecosystems are maintained or created within protected areas. For example the Euglossa spp. bees are the sole pollinators of many species of epiphytic orchids in primary forest in the neotropics (they are therefore termed MOBILE LINKS), but the bees also need secondary forest where they feed on nectar produced by secondary forest plant species and gather resin for nest building from secondary forest trees. So indirectly the epiphytic orchids, which grow in primary forest, also need secondary forest nearby, for without the Euglossa spp. bees, the orchids cannot reproduce.
Assisted or Accelerated Natural Regeneration (ANR)
Some PA's have suffered heavily from destruction of climax ecosystems and in such degraded areas, it is necessary to recreate the original habitat. The most common kind of habitat restoration is reforestation. In PA's, the aim of reforestation should be to re-create the original forest ecosystem as closely as possible, not to plant fast-growing commercial tree species. With time, forest will re-establish itself by the natural process of succession. However, several factors might limit the rate of succession or prevent it completely e.g. frequent fire, browsing by large herbivores (especially domestic cattle), soil erosion, a change in the micro-climate or a lack of seed supply. Therefore the objective of forest restoration should be to accelerate the natural processes of succession, but before reforestation is attempted, survey work is essential to determine:
1) Is succession slower than some "desirable rate”?
2) What are the main factors limiting the rate of succession?
3) How can such factors be counteracted to accelerate succession?
The "desirable rate" of succession will depend on how important the area is for watershed protection, tourism or wildlife conservation. Survey work should determine tree seedling density, species richness and growth rate in the degraded area. Surveys of the nearest available area of undisturbed forest (of similar altitude, aspect etc.) should also be undertaken to discover the normal species richness of the forest. This helps to establish the aims of the forest restoration project and to identify those species which are locally available but are not able to re-establish themselves in the degraded area. Surveys of tree seedlings are particularly difficult because tree seedlings often have very different leaves to the adult trees.
"Natural" experiments can be used to identify the factors which might be limiting the rate of succession. For example if fire is suspected, compare seedling density and species richness in burnt and non-burnt areas. Such experiments are not really scientific, because they lack adequate controls and the conditions before burning occurred are not known, but they are the best method available. It would be unethical to deliberately burn forest within a PA to do a proper controlled experiment.
If fire is the problem, fire breaks need to be cut, fire lookout towers built and manned and a forest fire control unit established.
If domestic cattle are a problem and they must be removed from a PA, villagers must be provided with an alternative supply of food for their cattle. They might be encouraged to keep their cattle at home and to cut fodder (avoiding young trees) and transport it to the cattle. This would have the advantage of reducing competition between young trees and herbs. In some cases, cattle actually help forest regeneration. They may disperse seeds in their dung. Trampling provides micro-habitats where seedlings can become established. Do research to prove that cattle are preventing forest regeneration before removing them.
When a forest is felled, the top soil is quickly washed away and many tree species are unable to establish seedlings in the underlying sub-soil. Under such circumstances, soil organic matter content needs to be increased to accelerate natural regeneration or before a tree planting program. Soil organic matter can be increased by growing a cover crop or green mulch. If possible, look for a local species of legume for this purpose and establish a seed production nursery. Re-introduction of soil invertebrates, especially earthworms can also improve soil structure.
Deforestation also causes a dramatic change in