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81.
/ Many of the aquatic and terrestrial ecosystems of the Pacific Northwest United States have been simplified and degraded in part through past land-management activities. Recent listings of fishes under the Endangered Species Act and major new initiatives for the restoration of forest health have precipitated contentious debate among managers and conservation interests in the region. Because aggressive management activities proposed for forest restoration may directly affect watershed processes and functions, the goals of aquatic and terrestrial conservation and restoration are generally viewed as in conflict. The inextricable links in ecological processes and functions, however, suggest the two perspectives should really represent elements of the same problem; that of conserving and restoring more functional landscapes. We used recent information on the status and distribution of forest and fish communities to classify river subbasins across the region and explore the potential conflict and opportunity for a more integrated view of management. Our classification indicated that there are often common trends in terrestrial and aquatic communities that highlight areas of potential convergence in management goals. Regions where patterns diverge may emphasize the need for particular care and investment in detailed risk analyses. Our spatially explicit classification of subbasin conditions provides a mechanism for progress in three areas that we think is necessary for a more integrated approach to management: (1) communication among disciplines; (2) effective prioritization of limited conservation and restoration resources; and (3) a framework for experimentation and demonstration of commitment and untested restoration techniques. 相似文献
82.
Disturbance and recovery of large floodplain rivers 总被引:7,自引:0,他引:7
Richard E. Sparks Peter B. Bayley Steven L. Kohler Lewis L. Osborne 《Environmental management》1990,14(5):699-709
Disturbance in a river-floodplain system is defined as an unpredictable event that disrupts structure or function at the ecosystem,
community, or population level. Disturbance can result in species replacements or losses, or shifts of ecosystems from one
persistent condition to another. A disturbance can be a discrete event or a graded change in a controlling factor that eventually
exceeds a critical threshold.
The annual flood is the major driving variable that facilitates lateral exchanges of nutrients, organic matter, and organisms.
The annual flood is not normally considered a disturbance unless its timing or magnitude is “atypical.” The record flood of
1973 had little effect on the biota at a long-term study site on the Mississippi River, but the absence of a flood during
the 1976–1977 Midwestern drought caused short- and long-term changes. Body burdens of contaminants increased temporarily in
key species, because of increased concentration resulting from reduced dilution. Reduced runoff and sediment input improved
light penetration and increased the depth at which aquatic macrophytes could grow. Developing plant beds exerted a high degree
of biotic control and were able to persist, despite the resumption of normal floods and turbidity in subsequent years.
In contrast to the discrete event that disturbed the Mississippi River, a major confluent, the Illinois River, has been degraded
by a gradual increase in sediment input and sediment resuspension. From 1958 to 1961 formerly productive backwaters and lakes
along a 320-km reach of the Illinois River changed from clear, vegetated areas to turbid, barren basins. The change to a system
largely controlled by abiotic factors was rapid and the degraded condition persists.
Traditional approaches to experimental design are poorly suited for detecting control mechanisms and for determining the critical
thresholds in large river-floodplains. Large river-floodplain systems cannot be manipulated or sampled as easily as small
streams, and greater use should be made of man-made or natural disturbances and environmental restoration as opportunistic
experiments to measure thresholds and monitor the recovery process.
Coauthors are listed in alphabetical order. 相似文献
83.
This article summarizes the views of aquatic scientists who gathered to assess the ability of stream ecosystem theory to predict
recovery from disturbance. Two views of disturbance were evident: a discrete removal of organisms vs an unusual deviation
from normal. These were perceived as applying to different scales and/or objectives. Long-term information is required from
both points of view to define recovery. Recovery also may be defined in different ways, but it is clear that recovery has
both spatial and temporal components, and includes both physical and biological processes. Consensus was very strong that
a major role (and challenge) for theory lies in the understanding of spatial aspects, temporal scales, coupling of physics
and biology, and the interaction of these features in recovery processes. Some progress is evident in the articles of this
volume, but among the topics identified as critical for further theoretical contributions were: homogeneous vs heterogeneous
distribution of disturbance, local extent of disturbance relative to a regional context, critical vs noncritical patches (size
and location) of disturbance at different spatial scales and temporal frequencies, delineation of reversible and nonreversible
processes, and physical and biological constraints on the time frame for recovery. Such concepts need attention across different
types of lotic ecosystems. Thus, there was strong consensus that a national monitoring system of representative lotic ecosystems
within ecological regions be established. The purpose of this monitoring system would be to acquire long-term data on natural
variability, to establish viable indicators of spatial and temporal aspects of recovery, and to develop and test emerging
theoretical developments. 相似文献
84.
Recovery of lotic periphyton communities after disturbance 总被引:2,自引:0,他引:2
Periphyton communities represent potentially excellent candidates for assessing the recovery of lotic ecosystems after disturbance.
These communities are ubiquitous, relatively easy to sample and measure (in terms of total community biomass), have short
generation times, and may influence the recovery rates of higher trophic levels. The first section of this article analyzes
how site availability, species availability, and differential species performance influence periphyton successional dynamics.
This background information provides a foundation for understanding how periphytic organisms respond after a disturbance.
The second section of this article analyzes how periphyton communities respond to four different types of disturbance (flood
events, desiccation, organic nutrient enrichment, and toxic metal exposure). Although data are limited, it is concluded that
the fast growth rates and short generation times of periphytic organisms, coupled with their flexible life history strategies
and good dispersal ability, allow lotic periphyton communities to recover relatively quickly after a disturbance. In addition,
disturbance type and severity, local environmental conditions, and site-specific factors also will influence recovery rates.
Future research needs include a better understanding of: (1) what periphyton property(ies) would serve as the best index of
recovery; (2) whether or not the robustness of this index varies among different environments and different disturbances;
(3) interactions between autotrophs and heterotrophs within the periphyton mat, particularly with respect to nutrient cycling;
(4) competitive interactions among organisms; (5) functional redundancy of organisms; and (6) the influence of the riparian
zone and channel geomorphology on periphyton recovery rates. 相似文献
85.
Stuart G. Fisher 《Environmental management》1990,14(5):725-736
The concept of succession has a distinguished history in general ecology and has been applied to stream ecosystems with some
success. Succession in streams is largely secondary, follows initial floristics models, and occurs through a variety of mechanisms.
The process is moderately predictable but is highly influenced by “climatic” factors, particularly nutrient chemistry. In
desert streams, succession does not result in a climax state. While evidence is slim, succession may not be a significant
process in streams of certain types or in certain regions.
Successional theory is difficult to apply in spatially heterogeneous, hierarchically organized ecosystems. It also suffers
in being only one component of a better integrated concept, that of ecosystem stability, which deals more directly with disturbance
and ecosystem resistance in addition to resilience (which encompasses succession). Succession has so suffered from a half
century of confusion that a strong case can be made for abandoning the term, at least as it applies in streams, in favor of
the broader view provided by stability theory. 相似文献
86.
We present a narrative account of case studies of the recovery of flowing water systems from disturbance, focusing on the
investigators' conclusions about recovery time and the factors contributing to recovery. We restrict our attention to case
studies in which the recovery of some biological property of the system has been examined, excluding those that deal only
with physical or chemical properties. Although natural processes and rates of recovery are emphasized, studies of reclamation
or restoration of damaged ecosystems are included where they contribute to an understanding of recovery processes.
For the majority of studies examined, the systems recovered quite rapidly. The most commonly cited reasons for short recovery
times were: (1) life history characteristics that allowed rapid recolonization and repopulation of the affected areas, (2)
the availability and accessibility of unaffected up-stream and downstream areas and internal refugia to serve as sources of
organisms for repopulation, (3) the high flushing rates of lotic systems that allowed them to quickly dilute or replace polluted
waters, and (4) the fact that lotic systems are naturally subjected to a variety of disturbances and the biota have evolved
life history characteristics that favor flexibility or adaptability. In general, longer recovery times were observed in disturbances,
such as channelization, that resulted in alterations to physical conditions.
This review also indicates that much of our knowledge of recovery in lotic ecosystems is fragmented and uncoordinated. In
addition to establishing the bounds of recovery time, our review identifies some research gaps that need to be filled. 相似文献
87.
88.
89.
Jacky Girel 《Environmental management》1994,18(2):203-221
In France and the United States it has been shown that strong linkages exist between vegetation and alluvial landforms within homogeneous river stretches characterized by geomorphological processes, flood duration, flood magnitude, flood frequency, and sediment size. Furthermore, perturbations induced by man (such as embankments and damming) have been shown to have an effect on both succession and plant distribution patterns. Yet, in numerous cases it is not possible to find either the communities or the plants whose presence might be predicted by reference to the river section characteristics (such as straight, braided, anastomosed, or meandering channels) or by reference to perturbation effects well known in piedmont valleys (such as variations of the water-table depth, variations of magnitude, and frequency and duration of floods). Unexpected species, new communities, and even new successional sequences are often observed. The presence of new alluvial forms explains these differences. An “artificial” substratum generated by an old human perturbation (limited in the time) has been established in the past; consequently, the natural distribution patterns of water and matter flows have been disturbed. Archive research has enabled a classification of abandoned systems that were commonly used during the 16th, 17th, 18th, and 19th centuries on European floodplains. Several case studies were chosen in order to illustrate and explain the importance of stream corridor history. The example of the Isère River valley, downstream from Albertville, is chosen to highlight the heterogeneity of the vegetation mosaïc pattern outside the dikes. The historical reconstruction explains the role of the additional disturbances that cause deviation from the system evolution patterns. 相似文献
90.
Island biogeographic theory offers a powerful conceptual framework for understanding and managing insular diversity. The human
impact on insular environments is constantly growing, especially because of tourism. We performed a simulation study aimed
at improving the understanding of the role of disturbance in islands. We also built an individual-oriented computer model
of an archipelago subjected to chronic disturbance of varying degree. Results are discussed in the light of island biogeographic
theory. Relevant results show the importance of autoecological characteristics of the species considered, regarding the attainment
of equilibrium and the species-area relationship in both disturbed and undisturbed cases. The possibility of bias in the predictions
of the equilibrium model is pointed out. Fundamental criticisms concerning the ecological relevance of the equilibrium theory
are discussed. 相似文献