Maximum Sustained Yield Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Maximum Sustained Yield (MSY) is a central concept used in the management of renewable, biological resources, most prominently in forestry and wild fisheries. It is based on the deceptively simple notion that harvesting pressure should be limited or controlled such that aggregate harvestsusually calculated on an annual basis-equal the rate of growth in the exploited population, and that in particular, harvest volume equilibrates with the maximum possible growth rate of the resource. This maximum in biological resources (again in theory) corresponds to the “culmination age,” the point in the life cycle of individual members of the commercially exploited species when annual growth is maximized. Mathematically, this corresponds to the maximum marginal and average rates of growth calculated over the life span of the species. By harvesting all individuals in the target population at the point when their growth rate (not their actual size) is maximized, the aggregate harvest will correspond to the maximum sustainable yield over time.

Note, however, that this does not necessarily mean management for maximum economic profit. In fact, these are unlikely to coincide, and the MSY is a strictly biomass maximum, not an economic one. The notion also implies that management for the MSY should result in the “production” of regulated populations, be they trees or fish, such that no individuals exceed the age of culmination. In this respect, despite the apparently desirable connotation of “sustainable” here, management for the MSY based on idealized and simple mathematical equations between maximum growth and maximum harvest can result in dramatic and often unforeseen ecological effects.

Forestry

In forestry, this idea derives mainly from the German Normalbaum, literally “normal tree” or “normal forest,” and more generally, from the development of scientific forestry in Europe during the 19th century (although with some antecedents in Asian forest management). A normal forest has been defined as “an ideally constituted forest with such volumes of trees of various ages so distributed and growing in such a way that they produce equal annual volumes of produce that can be removed continually without detrimental impacts to future production.” The implementation of this idea in industrial forestry, wherein each tree is harvested at its culmination age, typically entails rationalizing forests by rotating harvesting pressure across a collection of discrete stands of commercially desirable trees, with each stand homogenous by age (if not species) and with different stands representing different age cohorts. As each stand reaches its culmination age, it is harvested. Subsequently, harvesting pressure moves to adjacent stands, while the harvested stand is allowed to grow back. The geography of implementing this principle requires not only shifting harvesting pressure from one stand to another, but also a total area often called a “working circle” can be derived from a given maximum harvest volume and known rates of growth per unit area.

Historically, adoption of MSY forestry arose in the context of increasingly science-based forest management, which was typically state-centered or coordinated and reflected and reinforced the conversion of “wild” (i.e., unmanaged by industry or science) forests into managed ones. Largely a 19th century development in Europe, the formalization of sustained yield policy in North American forestry is a product in certain respects of Progressive era championing of rationalized, state-led, and science-based resource management based on utilitarian principles, but oriented (a la Gifford Pinchot) to efficiency, order, legibility, and the production of “the greatest good for the greatest number” (again, in contrast with profit maximization).

The institutionalization of MSY forestry in the United States and Canada took place largely between 1937 and 1945. This timing followed important conceptual developments, including the work of E.J. Hanzlik who developed a formula for the “orderly” conversion of old-growth forests to normal forests based on the liquidation of accumulated, large volume and “overmature” stands, attended by harvesting rates that would, in the shorter term, exceed long-run sustainable levels. Initial adoption of the MSY as official forest policy on public lands in both the United States and Canada was precipitated not only by zealous Progressives such as Pinchot, but also by industry figures such as David T. Mason interested in conferring some predictability on harvest rates, and by more widely held social concerns with stabilizing and underwriting the future economic development of forest dependent communities with predictable, secure, and sustainable harvest volumes. This has largely failed because of the naive equation of stable timber harvests with stable capitalist industrial employment and income.

Fisheries

In fisheries, the adoption of MSY as orthodoxy is largely a post-World War II phenomenon. It followed the decline and collapse of numerous fisheries, and a concomitant shift from the perception of fisheries (particularly ocean fish stocks) as inexhaustible to recognition that the failure of many fisheries was tied to overharvesting, and regulation needed to rein in fishing effort.

Institutionalization of MSY in fisheries regulation was advanced by development of the Ricker model of stock and recruitment in the mid-1950s, which specified the culmination age given known species-specific dynamics of birth, growth, and mortality. However, unlike trees, fish move around and interact with other fish, including schooling with fish of the same species across multiple age and size cohorts. Moreover, some fish reproduce late in life, potentially after reaching their culmination age. Thus, successful MSY regulation in fisheries has had to target not only the amount of effort, but also the type of gear used (e.g., net mesh size) so as not to catch fish younger than their culmination age (with fish size used as a proxy), and in addition, models of MSY fisheries management have also had to account for the so-called recruitment problem, ensuring that harvesting pressure on reproductive age adults is controlled to allow sufficient recruitment of juveniles into the next generation.

MSY Regulation

Difficulties in fisheries management point more generally to some of the problems with MSY regulations. Neo-classical economists have been quick to point out that the MSY does not correspond to profit maximization of a fishery or in forestry except by chance, and thus is likely to dissipate rents. From this perspective, the emphasis is on privatization and market-led exploitation, a direction of reform that has garnered considerable momentum, particularly in fisheries, propelled not least by the ascendance of neoliberalism. This is despite the uncomfortable reality that, under the right conditions, economically “optimal” behavior for utility maximizing individual fishers may well be to drive fish to extinction.

There are other problems with MSY, too numerous to fully elaborate here. One is that the MSY approach to regulation tends to rely on idealized representations of abstract and single species population dynamics that can disguise how little is known about the basic biology of exploited species, including how they will actually respond to harvesting pressure. In forestry, unknown rates of soil depletion, responses to chemical fertilizers and herbicides, and to commercial thinning and pruning among forests whose history of regulated, commercial exploitation may still be only one or two generations (of trees) old all confound the ability to accurately predict future yields. As a result, “errors” have been introduced in MSY timber estimates based on persistently excessive optimism.

Similar problems have plagued fisheries science. In general, regulating wild fisheries for MSY or otherwise has proven extremely difficult largely because of commercial pressures to cheat, because of incomplete or uneven regulation of fishing territories (e.g., between domestic and international waters), because of the ecological effects of habitat destruction and by-catch, and because fisheries ecology has often been poorly understood. To some extent, these problems with MSY could be ameliorated with more precautionary models that emphasize unpredictable or nonlinear fluctuations in environmental conditions and population dynamics, and that set harvest limits below critical population thresholds.

But focus on single species in MSY regulation has also often failed to account for interactions of the commercially exploited species with their biotic and abiotic environment, not to mention with social behaviors and institutions. Simple population models and metrics, at least in their initial instantiations, tended to discursively erase other species and elements of ecosystems, helping to produce the abstraction, individuation, and ultimately alienation from ecological (and sometimes socio-ecological) context necessary for commodification. Yet this has proven problematic when other, ostensibly nondesirable elements of the ecosystems in question turned out to be important, even from a narrow instrumental standpoint, as well as from broader biodiversity conservation perspective.

It also becomes problematic when social sensibilities change. Increasing conflict over logging in old-growth forests of western North America, for instance, signifies the declining political legitimacy of MSY regulation, as the ecological impacts of forest simplification have become evident, and as these impacts have been politicized by changing sensibilities about forests. This points to the naive or non-existent account of political economic context captured by simple MSY prescriptions for sustainable harvesting.

Responses to the shortcomings of the first generation of MSY regulation are myriad. They include not only the aforementioned emphasis on privatization and marketization, but also efforts to devolve governance and to involve resource user groups more directly in regulation, countering the generally top-down manner in which sustained yield has been implemented (and generally referred to under the rubric of community natural resource management). Alternatives also include efforts to regulate whole ecosystems in the form of ecosystem management, and to explore more adaptive forms of ecological management.

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