环艺设计外文翻译--绿色景观规划的基础设施(节选自书籍)

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本科外文翻译

绿色景观规划的基础设施

Green Infrastructure for Landscape Planning

学部（院）：建筑与艺术学院

专业：环境艺术设计

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完成日期：2015/4/10

Chapter Three

Ecosystem functions and health

Maintaining biological diversity

One of several goals of the following chapters is to show how to maintain or enhance biodiversity at the landscape and municipal level through the use of green infrastructure. Maintaining biodiversity is a challenge, since many species are negatively impacted by human activity or require large territories. In fact, some species require huge territories virtually undisturbed by humans in order to sustain viable populations (Figure 3.11). For example, grizzly bears occupy overlapping home ranges, but their density in the Yellowstone ecosystem is about one bear per 34 square miles.20 Other species are extremely sensitive to human presence and activity (Figure 3.12). For these species, a country residence in the forest can reduce the presence of these species for as much as 600 feet into the forest.21

Figure 3.12 The hermit thrush (Catharus guttatus) is a forest interior species and highly sensitive to human presence and activity. Its presence is reduced around country residences in the forest for as much as 600 feet.

In contrast, many species do adapt to the presence of people and the land-use changes they establish. Some species seem to adapt to fragmentation of their habitat. The scarlet tanager is an interior forest bird, but it seems to breed in forest fragments less than 25 acres (10 ha) in size when its preferred interior habitat is diminished.10 Some species, such as crows, are even considered completely urbanized and flourish in cities even to the point of becoming pests, as is the case with rats and cockroaches. Biological diversity within urban areas can be higher than it is within the surrounding, more natural, ecosystems. This is explained by the many exotic or invasive species that are encouraged or supported by human activities. Exotic plants, whose original habitats are distributed across the globe, usually dominate the ornamental landscape of urban centers and residential gardens. The biodiversity of native species is always much lower within urban and suburban environments. However, the variety of native species and the number of individuals supported in these environments can be maximized through careful urban planning and design, as discussed in the following chapters.

Invasive species

Non-indigenous species that become established within natural ecosystems threaten the healthy function of the system. Invasive species in the US, such as kudzu, zebra mussels, grass carp, starlings and nutria, have damaged ecosystem health.4 As for biodiversity assessment, there is no national mapping and monitoring of all invasive species and their impact, although for some areas and habitat types more information is available. The assessment of the aquatic ecosystems (soft-bottom estuaries) along the coast from northern California to Canada can serve as an indicator of the impact of invasive species. A study of this region measured the abundance of benthic (organisms living on the sediment or in sediment) invasive species. It revealed that the invasive species had a higher negative impact on the ecosystem than sedimentation or eutrophication, which are also anthropogenic in origin. About 15 percent of the monitored sites within this region contained a greater

number of invasive than native organisms. Another 20 percent of the monitored sites were moderately invaded by nonnative species.4

Ecosystem resilience

Ecosystems are subject to shocks from natural and man-made catastrophes. Some ecosystems are quite vulnerable to perturbation. Some, such as fireadapted communities, even invite certain kinds of dramatic change. Other ecosystems have a greater capacity to adsorb shocks while maintaining ecosystem functions, but recover slowly.5 This variability of vulnerability and resilience leads to a regional landscape of dynamic ecosystems. Thus regions are composed of disturbed, recovering and mature ecosystems that form a landscape mosaic. The biological diversity present in ecosystems before perturbations occur is related to their resilience. Each species extinction, whether local or global, represents a potential loss of ecosystem resilience. Extinction of a functional group of species can be a severe impact to ecosystem functions.

Resilience is the ability to return to the stable state after disturbance. If the disturbance is severe, it can cause the ecosystem to change states and represents long-term declines in species composition and ecosystem functions. Resilience can be expressed as a measure of the time it takes the ecosystem to return from the stressed state to the original condition, or expressed as the return of the network of species in the undisturbed system.

Climate influences ecosystem resilience, so climate change could increase or decrease recovery rates. At the local scale, resilience is reduced if infiltration, soil moisture and nutrient cycles diminish. Therefore, soils structurally resistant to change contribute to high resilience.22 Sustainable use and management of forest ecosystems requires protection of soils and preservation of seed sources and the rapid migration of seed into damaged landscapes. Since commercial forestry and damage associated with climate change, such as fires and insect infestations, have large impacts on expanses of forest, attention to the resilience of this ecosystem is urgent. Poorly resilient ecosystems that are damaged may require active management and restoration by humans (Figure 3.13), such as thinning stands, fuel load reduction, erosion prevention and re-vegetation. The resiliency of the ecosystems damaged by hurricanes has been studied. Publicly available

remote-sensing data (moderate resolution imaging spectroradiometer, MODIS) was used to monitor the recovery of the landscape after Hurricane Rita. Rita came ashore on 24 September 2005 and caused considerable damage to southwestern Louisiana towns, crops and natural ecosystems. This study established a baseline of gross primary biomass production derived from data collected between 2000 and 2005. Gross primary production was measured for several ecosystem types for the 12 months following Hurricane Rita and this was compared to the baseline. This study really traces the regeneration of the landscape, which is slightly different from resilience since only one ecosystem function is being measured. Nevertheless, the study demonstrated that ecosystem biomass recovery was surprisingly rapid for coastal wetlands and several other ecosystems. The exception was evergreen forests, which remained below the baseline for the entire year. The most resilient ecosystem was the shrub/scrub type. As during Hurricane Katrina, it was resistant to storm damage.23

Figure 3.13 A helicopter on a recently burned forest in Arizona drops a 900-pound bale of straw to control erosion and flooding. One ton of straw per acre was placed over 25,000 acres seeded with barley and other plants to help restore damage from the largest forest fire in the history of Arizona.

The Louisiana study also demonstrated links between the resilience of the ecosystems and recovery of human systems. Businesses linked to ecosystem services, such as fisheries, agriculture and forestry, were least resilient when tied to the least resilient ecosystem types. Conversely, the resilient wetlands and croplands were linked to higher business resilience.23

Indicators

The study above used an indicator of ecosystem health, assuming that other aspects would match the performance of the indicator. Ecosystem resilience is even more complex to demonstrate and monitor than ecosystem health. To simplify the process, reduce cost and communicate more clearly with citizens and decision makers, the use of ecosystem indicators simplifies data collection, assessment and communication. Many people are familiar with the concept of indicator species. The presence, abundance and distribution of the indicator species are used as proxies for the whole system. For example, the condition and number of plants of a native buckwheat species has been used in California as an indicator of sustainable human recreational use of a natural area because it is sensitive to trampling.