Page 334 - Environment: The Science Behind the Stories

other forest products are now made using certified sustain- Carrying capacity:
able practices. In this way, consumer choice is influencing the Population size
ways forests are managed. Slow in the absence
growth of harvesting
Forest management is one type
of resource management Population size Fastest Managers harvest

Debates over how to manage forest resources reflect broader growth at this population
size to obtain
questions about how to manage natural resources in general. maximum
Resources such as fossil fuels and many minerals are non- sustained yield
renewable, whereas resources such as the sun’s energy are Slow
perpetually renewable (pp. 21–22). Between these extremes growth
lie resources that are renewable if they are not exploited too
rapidly. These include timber, as well as soils, fresh water, Time
rangeland, wildlife, and fisheries.
Resource management describes our use of strategies FIGURE 12.9 Maximum sustainable yield maximizes the
to manage and regulate the harvest of renewable resources. amount of resource harvested while sustaining the harvest
Sustainable resource management involves harvesting these in perpetuity. For a wildlife population or fisheries stock that grows
resources in ways that do not deplete them. Resource manag- according to logistic growth, managers aim to keep the population
at half the carrying capacity, because populations grow fastest at
ers are guided by research in the natural sciences, as well as intermediate sizes.
by social, political, and economic factors.
Resource managers help conserve soil resources with
farming practices that fight erosion (pp. 244–246); safeguard In forestry, maximum sustainable yield argues for cut-
the supply and quality of surface water and groundwater ting trees shortly after they go through their fastest stage of
(pp. 423–434); encourage low-impact grazing to manage growth. Because trees often grow most quickly at intermedi-
rangeland sustainably (p. 250); and protect fisheries and wild- ate ages, trees are generally cut long before they have grown
life from overharvesting (p. 303). as large as they would in the absence of harvesting. This prac-
tice maximizes timber production over time, but it also alters
Resource managers follow several forest ecology and eliminates habitat for species that depend
strategies on mature trees.
A key question in managing resources is whether to focus Ecosystem-based management Because of these
strictly on the resource of interest or to look more broadly dilemmas, more and more managers today espouse ecosystem-
at the environmental system of which it is a part. Taking a based management, which aims to minimize impact on the
broader view often helps avoid degrading the system and ecosystems and ecological processes that provide the resource.
thereby helps sustain the resource in the long term. Many certified sustainable forestry plans protect certain for-
ested areas, restore ecologically important habitats, and con-
Maximum sustainable yield A guiding principle in sider patterns at the landscape level (pp. 131–133), allowing
resource management has been maximum sustainable yield. timber harvesting while preserving the functional integrity of
Its aim is to achieve the maximum amount of resource extrac- the forest ecosystem. This means fostering the area’s ecologi-
tion without depleting the resource from one harvest to the cal processes, including succession (pp. 103, 106), in which
next. Recall the logistic growth curve (see Figure 3.17, p. 87), the forest community naturally changes over time.
which reflects how limiting factors slow exponential popula- It can be challenging, however, to determine how best to CHAPTER 12 • FOREST S, FOREST MAN A GEMENT, AND PR O TECTED AREAS
tion growth and then cap it at a carrying capacity. The logistic implement this type of management. Ecosystems are com-
curve indicates that a population grows most quickly when plex, and our understanding of how they operate is limited.
it is at an intermediate size—specifically, at one-half of car- Thus, ecosystem-based management has come to mean differ-
rying capacity. A fisheries manager aiming for maximum ent things to different people.
sustainable yield will therefore prefer to keep fish populations
at intermediate levels so that they rebound quickly after each Adaptive management Some management actions
harvest. Doing so should result in the greatest amount of fish will succeed, and some will fail. A wise manager will try new
harvested over time while sustaining the population indefi- approaches if old ones are not effective. Adaptive management
nitely (FIGURE 12.9). involves systematically testing different approaches and aim-
This management approach, however, keeps the fish pop- ing to improve methods through time. For managers, it entails
ulation at only half its carrying capacity—well below the size monitoring the results of one’s practices and adjusting them
it would attain in the absence of fishing. Reducing a popula- as needed, based on what is learned. Adaptive management
tion in this way will likely affect other species and alter the is intended as a true fusion of science and management,
food web dynamics of the community. From an ecological because it explicitly tests hypotheses about how best to man-
point of view, management for maximum sustainable yield age resources. This process can be time-consuming and com-
may set in motion significant ecological changes. plicated but highly effective. 333

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