0796-B4
Jane Okalebo 1
Tropical forests play a vital function in life systems. Forests are a source of food, shelter and medicine. They are a home to millions of species of which about half are not yet known to science. Forests protect soils from erosion and regulate water quality and flow. Forests are carbon sinks that stabilize climate by locking up a vast amount of carbon dioxide that would otherwise be released to the atmosphere and contribute to climate warming.
This paper highlights some ecological effects of logging, which include damage to the forest structure, composition, richness of species and abundance. Frugivores, herbivores, insectivores and man are directly or indirectly affected by logging practices. Regeneration of the forests to their earlier form is a big challenge due to effects of large logging gaps and opportunistic species. These problems constitute the negative impacts of logging and pose a major challenge to foresters today.
Emphasis is placed on the need for more information from a wider interdisciplinary approach to fill in gaps in knowledge on the ecology of the forests and the interdependence of birds, primates, trees, insects, soil biota and other species on each other. This should be heeded very urgently before massive losses are accrued in the biodiversity of our tropical forests and their valuable functions are impeded.
In order to limit and/or eradicate unsustainable tropical forest logging; efforts should be directed at: improving food production on existing croplands; encouragement of plantation forestry; participation of international, regional and government bodies in sustainable forest management. There is also an urgent need of educating and raising awareness amongst forestry users and beneficiaries of forests on the potentially negative impacts of logging.
Sustainable logging of tropical forests does not exist in practice and the application of science often has had adverse side effects in the process of converting tropical forests into production forests (Bowles et al, 1998). De Almeida and Uhl, (1995) found that management systems "are frequently not sustainable from an ecological standpoint". Furthermore, Fearnside (1997) comments, "Sustainable management of tropical forests has long been illusory, often serving as a smoke-screen for destruction". Rodan et al. (1992) lament that mahogany is currently logged from natural forests unsustainably. Rice et al, (1999) are of the opinion that the bulk of tropical rain forests are unsuitable for large-scale logging.
In many jurisdictions, law enforcement has proven incapable of implementing forestry legislation or curbing illegal trade of commercial timber species in many tropical countries (Uhl et al, 1997; Fearnside, 1997). International organizations like International Tropical Timber Organization, ITTO, do not have the authority to control the illegal trade of timber or to enforce policies on sustainable harvesting protocol (Rodan et al, 1992). The Rainforest Foundation criticized the Forest Stewardship Council for misleading consumers that the FSC's labeled timber and timber products originate from environmentally-friendly and sustainably managed resources (Counsel and Loraas, 2002).
In that regard, Conservation International (Rice et al, 1999) and other NGOs, advocate that natural forests should be protected in order to conserve their genetic resources because sustainable forestry management is not economically feasible for logging companies and communities (Rice et al., 1999). Harvest intensities (m3/ha), need to be high enough to cover transportation, labour and machinery costs in order to yield a profit when operating under Reduced Impact Logging, RIL, (Rice et al., 1999) relative to Conventional Logging, CL. Pearce et al., (2003) state that "Empirical studies tend to confirm the conclusion of [Rice et al. (1997)] that although sustainable timber management sometimes provides reasonable rates of return, conventional timber harvesting is generally more profitable" which creates a significant obstacle to Sustainable Forest Management, SFM. High harvest intensity results in significant damage to the forest and adverse regeneration problems (Struhsaker, 1997; Rice et al., 1999; Verissimo et al., 1992).
To date, CITES (Convention on International Trade in Endangered Species) has failed to monitor and protect commercial timber species and lacks the full commitment of countries and their governments to conserve these species (Rodan et al, 1992; Bowles et al, 1998). Monetary constraints, corruption and political problems as reported in the journals and the media (Browder, 1986, ITTO, 1988; Plowden and Kusuda, 1989; Lutzenberger, 1992 cited in Rodan et al, 1992), have resulted in an uncontrolled logging industry. The evidence highlighted in this paper, points us to the fact that SFM has failed in the tropics and there is now an urgent need to conserve the meager fragments of the tropical forests (Bowles et al, 1998; Rice et al, 1999).
Tropical forests are increasingly impacted by both RIL and CL (Verissimo et al, 1992; Fearnside, 1997; Uhl et al, 1997). Often the commercial species targeted are hard woods like mahogany (Swietenia macrophylla King) (Fearnside, 1997). The profits realized from high value species can be as high as $900 per hectare (Verissimo et al, 1992) and US$ 700 per m3 for rough lumber in Europe and North America (Fearnside, 1997). Tectona grandis, a slow-growing species, is highly valued for it sawn timber and veneer wood of high quality (Lamprecht, 1990).
Fearnside (1997) notes that the selective logging of mahogany is less damaging to the forest than the more intensive logging and agricultural uses that follow. For every high value tree that is harvested about 27 trees greater than or equal to 10cm dbh (diameter at breast height) are damaged (Verissimo et al, 1992). Johns et al, (1996) report that about 16 trees of more than 16 cm dbh were damaged in studies conducted in the Amazon Basin. In the process, the species distribution, species richness and diversity is often restructured and affected depending of the logging intensity, road construction, transportation technique, treatments or other interventions that follow (Dykstra and Heinrich, 1996). For example, the composition and structure of a forest 90 km of Manaus, Brazil, was altered when commercial species formed a population of 15% more than that of the control or natural forest when silivicultural practices were conducted (Magnusson et al, 1999). These alterations may influence dependent species within the forest ecosystem thereby affecting the functional processes of the forest (Dale, 2001).
Often, loggers have to clear considerable volumes of vegetation to construct roads for transporting the logs. Verissimo et al, (1992) estimate that 40m of logging road and 600m2 of canopy are cleared with each tree harvested. Furthermore, ecological and social problems for indigenous peoples follow along the roads in the logger's wake (Fearnside, 1997; Kammesheidt, 2001). It is reported that loggers irresponsibly left a highly damaged residual stand in the western Venezuelan plain forests after logging operations (Kammesheidt et al, 2001) which in turn reduces recovery and regeneration capability of the stand.
Evidence suggests that both selective and conventional logging alters the composition and structure of natural forests. Tree species composition and forest understory growth was significantly altered an Amazon forests (Thiollay, 1997). Chapman and Chapman (1997) who worked in Kibale National Park discovered that the sapling density was reduced due to high logging intensities which resulted in a delayed vegetation recovery and a reduced tree species diversity measured 25 years after high intensity logging (Struhsaker, 1997). Consequently, lack of tree regeneration has a potentially large impact on soil erosion rate and water quality in streams and rivers. Moreover, without trees to secure them, nutrients are lost through leaching due to the heavy rainfall characteristic of tropical areas.
As a result, lack of tree regeneration similar to that of unlogged natural forest, diminishes the sustainability of logging of natural forests (Struhsaker, 1997). The inability to regenerate the forests to their former state changes the species composition and structure of tropical forest changes after logging (de Almedia and Uhl, 1995, Thiollay, 1997; Chapman and Chapman, 1997; Pelissier et al., 1998; Hall, 2000).
The dense evergreen forests of the Western Ghats in India (Pelissier et al., 1998) have undergone medium-term modification that in the long-term is not sustainable due to lack of tree regeneration. Gullison et al., (1996) discovered that only 7 - 9 % of the gaps created by logging contained natural regeneration and opportunistic species had colonized most gaps in Bolivia. Under such condtions, the species distribution, species richness and diversity is often restructured and affected which makes logging unsustainable.
Gullison et al. (1996) and Fearnside (1997), note that mahogany has delayed reproductivity. The fecundity of mahogany rises gradually with dbh size and peaks at 130 cm with one tree of this size, producing approximately 33,000 seeds (Gullison et al., 1996, cited in Veríssimo and Grogan, 1998). Consequently, harvesting of high quality trees based on minimum dbh may result in a loss of genetically superior regeneration material. Hall (2000) noted that in the Central African Republic, there was lack of regeneration of the Entandrophragma spp. due to sensitivity to light, nutrients and moisture in logged gaps. Additionally, fungal, rodent and insect damage, affected regeneration of this species (Hall, 2000).
Trees provide shelter, food, and shade to different animals and plants (Smith, 1992). Woodpeckers are sensitive to logging and deforestation (Styring and Ickes, 2001) as they are dependant on large trees for nesting and standing dead trees for forage. Their species abundance and richness was significantly reduced in a lowland dipterocarp forest in Malaysia due to logging operations and forest management practices that omitted the need for old growth (Styring and Ickes, 2001).
When the composition of a forest and its structure are altered, the distribution and abundance of food for frugivores is also impacted. The repercussion to this decline in frugivore species may affect the regeneration of tree species that are animal-dispersed. Cordiero and Howe (2001) observed that forest fragmentation has led to a decrease in frugivore species in Usambara mountain forests in Tanzania. The reduction and loss of these fruvigore species has resulted in a threefold count reduction in the number of recruitment seedlings and juveniles of 31 animal-dispersed tree species in forest fragments of less than 9 hectares compared to those forest fragments greater than 30 hectares in size (Cordiero and Howe, 2001).
In an Amazonian forest, a dynamic spatial pattern in habitats provides the majority of fruit resource on a seasonal basis to the community of frugivores (Wallace et al., 2002). At different times of the year, certain habitats provided key resources that sustained communities of frugivores. In 1989, ITTO recommended the urgent need to include phenological information (studies of fruiting, seed development in relation to climatic conditions), in order to ensure sustainability. Unfortunately, data is lacking (Wallace et al., 2002) on the impacts of logging on tree- or fruit-dependent species in tropical forests which would emphasis the need for caution while conducting logging operations.
The competing utilization of montane bamboo (Arundinaria alpina) by man's logging activities and mountain gorillas resulted in unsustainable logging in Uganda (Mosango, 2000). The rich and complex, Bwindi Impenetrable forest and Mgahinga Gorillas National Parks of southwestern Uganda, are home to the endangered mountain gorillas and chimpanzees (Frank, 2002). The communities, who live close to these national resources, utilize the bamboo for construction and for weaving trays and constructing granaries yet the Bamboo shoots form an important part of the diet of the gorillas.
Similarly, elephants in the Kibale forest tend to concentrate their activities in logged areas due to the new aggressive herb community (Chapman and Chapman, 1997). This shows that the shift in distribution of one species has repercussions on vegetation and other animal and plant species (Struhsaker,1997). The destruction of young saplings trampled by large herds of elephants concentrated in one area, reduces the chances of natural regeneration (Chapman and Chapman, 1997).
Thiollay (1997), conducted research in northeastern Amazonia and noted that the overall bird species richness and abundance were depressed by 27 - 34% in the logged areas compared to primary forest. Additionally, the study showed noted that the mature forest understorey species especially the terrestrial ones and mixed flocks of insectivores also decreased by 37 - 98% in abundance.
(Brown et al., 2001) from studies conducted in Asia-Pacific, consider that the banning of logging is may act in slowing or stopping destructive logging practices. However, the same studies concluded that ineffective implementation of banning logging, "often contributed to further deforestation and degradation through the lack of enforcement and control, and through the inadvertent creation of perverse incentives and impacts" (Brown et al., 2001). Banning of logging needs to be adapted selectively and employed in combination with other complementary policy mechanisms to promote SFM (Brown et al., 2001).
Another option that is considered as the way forward towards achieving SFM is the use of Reduced Impact Logging (Dykstra and Heinrich, 1996; Brown et al., 2001). FAO continually conducts case studies on improved harvesting and engineering in timber operations in a bid to protect ecosystems in the forest and encourage SFM. An example of this is in the utilization of elephants in low impact logging operations in Sri Lanka relative to highly mechanized operations which may have detrimental effects to the environment (Jayasekera and Atapattu, 1995).
Timber certification systems internationally may act to offer incentives to promote SFM (Pearce, 2003). An acknowledgement of the vital carbon sequestration capacity and biodiversity conservation roles of tropical forests should act as an incentive and compete favourably against conventional timber harvesting (Pearce, 2003). Should new carbon markets emerge (Pearce 2003) in the Clean Development Mechanism, CDM, under the Kyoto Protocol, developing countries will be able to benefit and be supported to work towards SFM.
For tropical forests to be well managed sustainably for our children and grandchildren, capacity building (Temu and Kowero, 2000) and long-term research need to be undertaken to fill existing the gaps of knowledge in all various disciplines of forest ecology. An integrated research approach should be undertaken involving soil scientists, ecologists, zoologists, botanists, climatologists, hydrologists, microbiologists, and anthropologists, amongst others. There is an urgent need for inventories of existing fauna and flora and seasonal keystone habitats. The dependence and interaction of plant and animal species needs to be appreciated within ecosystems in tropical forests. In order to limit and/or eradicate unsustainable tropical forest logging; efforts should be directed at: improving food production on existing croplands; encouragement of plantation forestry; participation of international, regional and government bodies in Sustainable Forest Management, SFM. There is also an urgent need of educating and raising awareness amongst forestry users and beneficiaries of forests on potentially negative impacts of logging.
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1 Faculty of Forestry, 33 Willcocks Street, University of Toronto, Toronto, Ontario, Canada, M5S 3B3. [email protected]