BIOLOGY Volume 1 - A Guide to General Biology - 2004

10. ORGANISMS AND THE ENVIRONMENT

10.9. Environmental Conservation

10.9.5. Sustainable Exploitation of Plant and Animal Resources

The issues surrounding deforestation (Section 10.8.3) and the African elephant (Section 10.9.3) demonstrate how the overexploitation of valuable biological resources, driven by ecological ignorance or sheer greed, leads to stock depletion, community degradation, and even species extinction. Conversely, resource utilization based on scientific principles yields steady long-term revenues, although sometimes at the expense of short-term gains. A prime example of this approach is The regulation of fisheries through an international quota system. Species and ecosystems with long recovery times, such as elephants and forests, require particularly careful resource management. Fortunately, the challenges of sustainable and efficient forestry have been a concern for humanity for decades.

Overfishing

The world's marine biota is suffering from chronic overfishing. Fig. 10.36 illustrates the trends in global marine fish catches from 1950 to 1993. Currently, nine of the world's 17 major fishing areas are experiencing sharp declines in stocks, and four are considered fully depleted. In 1992, the cod fishery off the coast of Newfoundland, Canada, was indefinitely suspended. In the North Sea, mackerel catches have dropped by more than half since the 1960s, while herring catches, suspended between 1977 and 1982, have never recovered to their former levels. The world's largest-scale anchovy fishery off the coast of Peru and Chile has completely collapsed.

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Fig. 10.36. Global catches of all fish species between 1950 and 1993 (F. Pearce New Scientist, 2016, 10th February 1996, p. 4.)

The ROOT cause of all these problems is overfishing. Clear signs of overfishing were already apparent in the 1960s; nevertheless, global marine fish catches increased by nearly 50% over the following decades. This was made possible by the advent of factory freezer trawlers—vessels equipped not only with refrigeration units but with complete Processing lines to handle the catch on board—as well as the regular shifting of fishing effort from one target species to another. In other words, as stocks of one fish species became depleted, the exploitation of another was intensified.

Heavy fishing leads to populations dominated by small, juvenile individuals that are inaccessible to traditional fishing gears. If left in the sea a little longer, these fish would quickly reach standard sizes, increasing total catch biomass, improving quality per unit of fishing effort, and, consequently, boosting profits. However, many fishers, eager to fulfill quotas and avoid even short-term drops in income, target juveniles that have not yet reached spawning age. As a result, the reproductive potential of populations is undermined, threatening a catastrophic decline in commercial fish numbers and even the disappearance of entire species from certain oceanic zones.

Fishing quotas are designed to conserve fish stocks. They are based on recommendations from population ecologists who, in turn, use complex simulation models that can theoretically predict the Abundance of specific fish species under various harvest rates. However, numerous challenges arise in this process, including the following:

1) the difficulty of obtaining reliable field data for modeling fish populations;

2) the difficulty of accounting for climate change;

3) the difficulty of persuading governments to follow scientific advice;

4) the difficulty of monitoring compliance with international agreements;

5) the difficulty of reconciling the needs of local traditional fishing communities with those of large-scale commercial fishing fleets under changing conditions.

Tropical Rainforests

The sustainable exploitation of certain ecosystems is exceptionally difficult due to their very nature. For instance, in the Amazon, high crop yields on cleared rainforest land can only be maintained for a very short time. Even with substantial outside investment and sound agricultural management, fields typically have to be abandoned after 10–15 years. Weeds, pests, crop diseases, and, most importantly, rapidly declining soil fertility make continued farming unprofitable. At the same time, mature rainforests rarely regenerate on abandoned lands. This is because agricultural use severely depletes soil nutrient levels and damages soil Structure. No forest seeds remain in the soil; those blown in from the surrounding jungle struggle to germinate in open areas, and seedlings find it hard to establish themselves (these species require the high humidity provided by a closed canopy). At best, secondary scrub forest develops, with a productivity lower than that of the primary forest. In principle, only primitive shifting cultivation is viable here. Intensive agriculture in this zone will never be sustainable. All attempts at such farming will result solely in the squandering of natural resources, specifically the replacement of primary rainforests—many species of which may simply vanish—with low-productivity secondary forests. Admittedly, scientific principles for the sustainable exploitation of tropical rainforests that promote economic and social development in rapidly growing local populations have not yet been developed, and this remains one of the most critical challenges facing the global community today.

Traditional Forestry Systems in Britain

For centuries, British woodlands served as vital sources of fuel and timber. Management systems were developed to ensure the continuous renewal of resources while preserving their productivity. The remnants of ancient oak woods reflect this long history and, in most cases, differ markedly from Britain's primeval forests. Today's semi-natural stands harbor many species that would vanish if traditional management of these communities were to cease.

Very few forests can be considered truly primeval, and even those have been partially altered by human activity. The majority of broadleaf woodlands are secondary, having developed on sites where the original forests were cleared. Woodlands existing prior to 1600 are classed as "ancient" and are now strictly protected. Such forests typically exhibit high species diversity, particularly among slow-growing long-lived organisms such as Lichens, yet even they bear signs of past human use.

The two most common management systems were wood-pasture (Fig. 10.37) and coppicing. Wood-pasture was widespread on relatively poor soils and involved a combination of grazing and timber harvesting. The presence of livestock hindered tree regeneration, but this problem was overcome through pollarding—cutting the main trunks above the browse line (around 2 m) to stimulate the growth of side branches, which were periodically harvested for various uses. Over the centuries, the most palatable understory species, such as hazel, disappeared and were replaced by browse-resistant species like holly and hawthorn. The future of such woodlands depends on regeneration, which requires a reduction in grazing pressure.

Fig. 10.37. Wood-pasture in the New Forest, Britain.

On relatively rich soils, low forest coppicing was the dominant practice. Understory species, typically hazel and ash, were coppiced at ground level every 15—20 years, depending on regrowth rates and the desired timber products. Large stems were used for construction, furniture making, and fencing, while thin branches served as sheep fodder, roofing material, wattle, lath for plaster, and basketry. Virtually everything was utilized, leaving almost no waste. Selected 'standard' trees were allowed to grow nearly to full maturity; these were felled less frequently and sawn into beams and planks. This management system created periodic surges of light that encouraged a rich herbaceous understory, which still retains a high diversity of plant species, including many that are rare and historically significant.

Although pristine primeval forests no longer exist in Britain, the preservation of ancient, traditionally managed woodlands helps safeguard the rich biota of its virtually vanished native communities.

Hedgerows

Hedgerows are widely regarded as a vital asset for conservation. Dating back to Anglo-Saxon times, they were originally established to demarcate land boundaries and enclose pastures. Over the centuries, their species diversity has steadily increased—on average, one new woody plant species was added for every 27 m of hedgerow length per century. As a result, ancient hedgerows serve as hotspots of biodiversity and, in some cases, act as the sole remaining refuges for plants typical of the area's original wildwoods.

Between 1950 and 1980, thousands of miles of hedgerows across lowland Britain were ripped out to enlarge fields for large-scale modern farm machinery. Farmers believed this practice would simultaneously eliminate reservoirs of weeds, agricultural pests, and plant pathogens. Yet hedgerows undeniably provide essential habitats for numerous predators of agricultural pests. Furthermore, by breaking the force of the wind, they shelter livestock and prevent soil erosion. They support a wealth of songbirds and game birds, alongside other woodland wildlife, not to mention insect pollinators. Hedgerows also function as ecological corridors, linking isolated patches of broadleaved woodland scattered across agricultural landscapes. This connectivity is particularly crucial for small mammals, such as dormice, which struggle to traverse open terrain. Such corridors are equally beneficial for plants with limited long-range dispersal capabilities.

In certain regions of Britain, farmers are now provided with financial grants to restore hedgerows. However, newly planted hedges, while effective as windbreaks, fall far short of the rich species diversity found in the ancient communities destroyed during the 1960s.