A quantitative succession model for nine montana forest communities

A quantitative succession model was developed both to meet resource management needs in Montana's Lewis and Clark National Forest and to develop a modeling methodology. It builds upon previous concepts and incudes three new features: quantitative prediction of all tree species and seedlings; quantitative predictions of important understory species; and successional pathways determined by fire intensity and scorch height. The method is described and demonstrated for selected Montana habitat (community) types. It is also available in managerial guidelines and has been programmed as a new module in theforplan simulator. Weaknesses of this and other models are discussed. Conclusions relate succession modeling to resource management needs.     

CHANNEL FORM AND STREAM ECOSYSTEM MODELS1

A system is proposed to classify running water habitats based on their channel form which can be considered in three different sedimentological settings: a cobble and boulder bed channel, a gravel bed channel, or a sand bed channel. Three physical factors (relief, lithology, and runoff) are selected as state factors that control all other interacting parameters associated with channel form. When these factors are integrated across the conterminous United States, seven distinct stream regions are evident, each representing a most probable succession of channel forms downstream from the headwaters to the mouth. Coupling these different channel profiles with typical biotic community structures usually associated with each of the channel types should result in considerable refinement of the applicability of the River Continuum Concept and other holistic ecosystem models by realizing the nonrandomness of the effects of geo-morphology on stream ecosystems. Thus, this regional perspective of streams should serve to make persons concerned with water resources more aware of the geographical considerations that affect their study areas.     

Predicting streamflow response to fire-induced landcover change: implications of parameter uncertainty in the MIKE SHE model

Fire is a primary agent of landcover transformation in California semi-arid shrubland watersheds, however few studies have examined the impacts of fire and post-fire succession on streamflow dynamics in these basins. While it may seem intuitive that larger fires will have a greater impact on streamflow response than smaller fires in these watersheds, the nature of these relationships has not been determined. The effects of fire size on seasonal and annual streamflow responses were investigated for a medium-sized basin in central California using a modified version of the MIKE SHE model which had been previously calibrated and tested for this watershed using the Generalized Likelihood Uncertainty Estimation methodology. Model simulations were made for two contrasting periods, wet and dry, in order to assess whether fire size effects varied with weather regime. Results indicated that seasonal and annual streamflow response increased nearly linearly with fire size in a given year under both regimes. Annual flow response was generally higher in wetter years for both weather regimes, however a clear trend was confounded by the effect of stand age. These results expand our understanding of the effects of fire size on hydrologic response in chaparral watersheds, but it is important to note that the majority of model predictions were largely indistinguishable from the predictive uncertainty associated with the calibrated model - a key finding that highlights the importance of analyzing hydrologic predictions for altered landcover conditions in the context of model uncertainty. Future work is needed to examine how alternative decisions (e.g., different likelihood measures) may influence GLUE-based MIKE SHE streamflow predictions following different size fires, and how the effect of fire size on streamflow varies with other factors such as fire location.     

WATERSHEDS AS THE BASIC ECOSYSTEM: THIS CONCEPTUAL FRAMEWORK PROVIDES A BASIS FOR A NATURAL CLASSIFICATION SYSTEM1

ABSTRACT: A scheme is outlined to classify watersheds as ecosystems, based on their natural attributes. Two physical factors of the environment, climate and geology, are selected as state factors. Climate is the master factor that supplies energy and water to all ecosystems; geologic structure supplies the materal from which the forces of climate carve landforms to establish ecosystems. At the next lower level, soil and vegetation interact in a succession of transactions to produce a mosaic of tesseras within each watershed. It is these interacting tesseras that moderate climate and store energy within the ecosystem that influences the embedded stream. At the bottom of the scale is the stream with its passive role and inability to interact with the higher factors of the ecosystem. Thus, we have a controlling force consisting of two elements (climate and geology), a reacting force (soil and vegetation) that responds by circular conditioning to controlling forces, and at the lowest level, the stream which responds to all factors of the living system within its watershed.     

Basic principles and ecological consequences of changing water regimes: riparian plant communities

Recent research has emphasized the importance of riparian ecosystems as centers of biodiversity and links between terrestrial and aquatic systems. Riparian ecosystems also belong among the environments that are most disturbed by humans and are in need of restoration to maintain biodiversity and ecological integrity. To facilitate the completion of this task, researchers have an important function to communicate their knowledge to policy-makers and managers. This article presents some fundamental qualities of riparian systems, articulated as three basic principles. The basic principles proposed are: (1) The flow regime determines the successional evolution of riparian plant communities and ecological processes. (2) The riparian corridor serves as a pathway for redistribution of organic and inorganic material that influences plant communities along rivers. (3) The riparian system is a transition zone between land and water ecosystems and is disproportionately plant species-rich when compared to surrounding ecosystems. Translating these principles into management directives requires more information about how much water a river needs and when and how, i.e., flow variables described by magnitude, frequency, timing, duration, and rate of change. It also requires information about how various groups of organisms are affected by habitat fragmentation, especially in terms of their dispersal. Finally, it requires information about how effects of hydrologic alterations vary between different types of riparian systems and with the location within the watershed.     

Conversion of temperate forests into heaths: Role of ecosystem disturbance and ericaceous plants

Fire and logging in nutrient-poor temperate forests with certain ericaceous understory plants may convert the forests into heaths. The process of disturbance-induced heath formation is documented by using examples ofCalluna in western Europe,Kalmia in Newfoundland, andGaultheria (salal) in coastal British Columbia. In a cool, temperate climate, rapid vegetative growth ofCalluna, Kalmia, and salal following disturbance results in increasing organic accumulation (paludification), nutrient sequestration, soil acidification, and allelochemicals. These are thought to be the main reasons to conifer regeneration failure in disturbed habitats. If continuation in forest is a land-use objective, then temperate forests with an ericaceous understory should not be logged unless effective silvicultural methods are devised to control the ericaceous plants and restore forest regeneration. Preharvest vegetation control may be considered as an option. Failure to control the understory plants may lead to a long-term vegetation shift, from forest to heathland, particularly in nutrient-poor sites. Successful methods of controllingKalmia andGaultheria, however, have yet to be developed. While theKalmia- andGaultheria- dominated heathlands are undesirable in Canada and the Pacific Northwest, a wide range ofCalluna heathlands of western Europe are being conserved as natural and seminatural vegetation.     

Recovery processes in lotic ecosystems: Limits of successional theory

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.     

Evaluation of fire as a management tool for controllingSchinus terebinthifolius as secondary successional growth on abandoned agricultural land

Schinus terebinthifolius, native to South America, has become an aggressive woody weed in southern Florida, displacing native vegetation as well as rapidly invading disturbed sites. Studies to evaluate the effectiveness of fire as a management option for controllingSchinus on abandoned farmland in Everglades National Park, known as the “Hole-in-the-Donut,” began in 1979. Study plots were established to monitor any change(s) in herbaceous cover and in numbers and size ofSchinus stems. Except in the control plot (which was not burned), each site was burned as often as fuel conditions permitted (usually once every one or two years), through 1985. Results indicated that both the number and density ofSchinus stems increased over the course of the study. While plots that burned showed a reduction in the rate ofSchinus invasion, invasion still progressed rapidly with or without the occurrence of fire. The increase inSchinus stem density from 1980 to 1985 was highly significant in all transects except one. Herbaceous cover showed no clear trends relative to burning.     

Simulating secondary succession of elk forage values in a managed forest landscape,western Washington

Modern timber management practices often influence forage production for elk (Cervus elaphus) on broad temporal and spatial scales in forested landscapes. We incorporated site-specific information on postharvesting forest succession and forage characteristics in a simulation model to evaluate past and future influences of forest management practices on forage values for elk in a commercially managed Douglas fir (Pseudotsuga menziesii, PSME)-western hemlock (Tsuga heterophylla, TSHE) forest in western Washington. We evaluated future effects of: (1) clear-cut logging 0, 20, and 40% of harvestable stands every five years; (2) thinning 20-year-old Douglas fir forests; and (3) reducing the harvesting cycle from 60 to 45 years. Reconstruction of historical patterns of vegetation succession indicated that forage values peaked in the 1960s and declined from the 1970s to the present, but recent values still were higher than may have existed in the unmanaged landscape in 1945. Increased forest harvesting rates had little short-term influence on forage trends because harvestable stands were scarce. Simulations of forest thinning also produced negligible benefits because thinning did not improve forage productivity appreciably at the stand level. Simulations of reduced harvesting cycles shortened the duration of declining forage values from approximately 30 to 15 years. We concluded that simulation models are useful tools for examining landscape responses of forage production to forest management strategies, but the options examined provided little potential for improving elk forages in the immediate future.     

Island biogeographical theory: Can it be used to predict lotic recovery rates?

Classic island biogeographic theory predicts that equilibrium will be reached when immigration and extinction rates are equal. These rates are modified by number of species in source area, number of intermediate islands, distance to recipient island, and size of intermediate islands. This general model has been variously modified and proposed to be a stochastic process with minimal competitive interaction or heavily deterministic. Predictive models of recovery (regardless of the end point chosen) have been based on the appropriateness of the MacArthur-Wilson models. Because disturbance frequency, severity, and intensity vary in their effect on community dynamics, we propose that disturbance levels should first be defined before evaluating the applicability of island biogeographical theory. Thus, we suggest a classification system of four disturbance levels based on recovery patterns by primary and secondary succession and faunal organization by primary (invasion of vacant areas) and secondary (remnant of previous community remains) processes. Level 1A disturbances completely destroy communities with no upstream or downstream sources of colonizers, while some component of near surface interstitial or hyporheic flora and fauna survive level 1B disturbances. Recovery has been reported to take from five years to longer than 25 years, when most invading colonists do not have an aerial form. Level 2 disturbances destroy the communities but leave upstream and downstream colonization sources (level 2A) and, sometimes, a hyporheic pool of colonizers (level 2B). Recovery studies have indicated primary succession and faunal structuring patterns (2A) with recovery times of 90–400 days or secondary succession and faunal structuring patterns (2B) with recovery times of 40–250 days. Level 3 disturbances result in reduction in species abundance and diversity along a stream reach; level 4 disturbances result in reduction of abundance and diversity in discrete patches. Both disturbance types lead to secondary succession and secondary faunal organization. Recovery rates can be quite rapid, varying from less than 10 days to 100 or more days. We suggest that island biogeographical models seem appropriate to recovery by secondary processes after level 3 and 4 disturbances, where competition may be an important organizing factor, while models of numerical abundance and resource tracking are probably of better use where community development is by primary succession (levels 1 and 2). Development of predictive recovery models requires research that addresses a number of fundamental questions. These include the role of hydrologic patterns on colonization dynamics, the role of nonaerial colonizers in recovery from level 1 disturbances, and assessment of the impact of changes in the order of invasion by colonizers of varying energetic efficiencies. Finally, we must be able to assemble these data and determine whether information that guides community organization at one level of disturbance can provide insights into colonization dynamics at other levels.     

Environmental logistics engineering: A new approach to industrial ecology

Industrial Ecology is, thus far, the most plausible model for realizing the ideal of sustainability. It dispels the notion that the flow of resources can continue along a one-way street from nature to mankind. Today, it is fairly well-understood that economies and ecosystems are structured and operate in strikingly similar ways. Healthy economies and healthy ecosystems depend on elemental diversity and unencumbered interchanges. Yet, maintaining and sustaining both healthy economies and healthy ecosystems continue to be viewed as disparate goals. How can this unfortunate mind-set be changed? The authors show how logistics engineering could be the best approach to implementing a two-part solution to this environmental business conundrum.     

Natural and Anthropogenic Methane Emission from Coastal Wetlands of South India

For the first time, the methane emissions from diverse coastal wetlands of South India have been measured. Annual emission rates varied widely, ranging from 3.10 mg/m²/hr (Bay of Bengal) to 21.56 mg/m²/hr (Adyar River), based on nature of the perturbance to each of the ecosystems studied. Distinct seasonality in methane emission was noticed in an unpolluted ecosystem (mangrove: 7.38 mg/m²/hr) and over a twofold increase was evident in the ecosystem that was disturbed by human activities (21.56 mg/m²/hr). The wide ranges in estimate suggest that methanogenesis occurs by both natural and anthropogenic activities in these coastal wetlands. Several physical and chemical factors such as salinity, sulfate, oxygen, and organic matter content influenced methanogenesis to a large degree in each of these ecosystems in addition to individual responses to human-induced stress. For example, there was a clear negative correlation between oxygen availability (0.99), sulfate (0.98), and salinity (0.98) with CH₄ emission in the Adyar river ecosystem. Although similar results were obtained for the other wetland ecosystems, CH₄ emission was largely influenced by tidal fluctuations, resulting in a concomitant increase in methanogenesis with high sulfate concentrations. This study demonstrates that coastal wetlands are potentially significant sources of atmospheric methane and could be a greater source if anthropogenic perturbations continue at the current rate. RID=" ID=" *Author to whom correspondence should be addressed.     

Denitrification potential in urban riparian zones

Denitrification, the anaerobic microbial conversion of nitrate (NO3-) to nitrogen (N) gases, is an important process contributing to the ability of riparian zones to function as "sinks" for NO3- in watersheds. There has been little analysis of riparian zones in urban watersheds despite concerns about high NO3- concentrations in many urban streams. Vegetation and soils in urban ecosystems are often highly disturbed, and few studies have examined microbial processes like denitrification in these ecosystems. In this study, we measured denitrification potential and a suite of related microbial parameters (microbial biomass carbon [C] and N content, potential net N mineralization and nitrification, soil inorganic N pools) in four rural and four urban riparian zones in the Baltimore, MD metropolitan area. Two of the riparian zones were forested and two had herbaceous vegetation in each land use context. There were few differences between urban and rural and herbaceous and forest riparian zones, but variability was much higher in urban than rural sites. There were strong positive relationships between soil moisture and organic matter content and denitrification potential. Given the importance of surface runoff in urban watersheds, the high denitrification potential of the surface soils that we observed suggests that if surface runoff can be channeled through areas with high denitrification potential (e.g., stormwater detention basins with wetland vegetation), these areas could function as important NO3- sinks in urban watersheds.     

Analysis and application of forest fuels data

Recent advances in fire modeling permit quantitative estimations of fire behavior from quantitative inputs that describe the fuel array and conditions, such as weather and site data, under which it will burn. This paper describes the collection, analysis, and stratification of flammable forest fuels data for coniferous forest ecosystems in Montana and then illustrates the resource management application of these data in three areas: the development of the fire behavior model, a determination of the model's sensitivity to input errors as reflected by fire behavior prediction errors, and the development of a fire hazard simulator (TAROT). A new integrated stand simulator, GANDALF, is highlighted.Conclusions center on the need to integrate fire management into the land management planning decision-making process.This work was supported by a USDI National Park Service contract to Gradient Modeling, Inc., a nonprofit research foundation devoted to ecologic research and resource management applications, and by cooperative aid agreements between Gradient Modeling, Inc. and the USDA Forest Service, Intermountain Forest and Range Experiment Station, Northern Forest Fire Laboratory (Fire in Multiple Use Management, R, D, and A Program).     

Use of created cattail (Typha) wetlands in mitigation strategies

In order to balance pressures for land-use development with protection of wetland resources, artificial wetlands have been constructed in an effort to replace lost ecosystems. Despite its regulatory appeal and prominent role in current mitigation strategies, it is unclear whether or not created systems actually compensate for lost wetland resources. Mitigation predictions that rely on artificial wetlands must be analyzed critically in terms of their efficacy. Destruction of wetlands due to burial by coal fly ash at a municipal landfill in Danvers, Massachusetts, USA, provided an opportunity to compare resulting growth of created cattail (Typha) marshes with natural wetland areas. Once the appropriate cattail species was identified for growth under disturbed landfill conditions, two types of artificial wetlands were constructed. The two systems differed in their hydrologic attributes: while one had a surface water flow characteristic of most cattail wetlands, the second system mimicked soil and water conditions found in naturally occurring floating cattail marshes. Comparison of plant growth measurements for two years from the artificial systems with published values for natural cattail marshes revealed similar structure and growth patterns. Experiments are now in progress to investigate the ability of created cattail marshes to remove and accumulate heavy metals from polluted landfill leachate. Research of the type reported here must be pursued aggressively in order to document the performance of artificial wetlands in terms of plant structure and wetland functions. Such research should allow us to start to evaluate whether artificial systems actually compensate for lost wetlands by performing similar functions and providing the concomitant public benefits.     

Predicting Sustained Fire Spread in Tasmanian Native Grasslands

Fire is widely used in conservation management of native grasslands. Burning is often carried out under conditions that are marginal for sustained fire spread, and therefore it would be useful to be able to predict fire sustainability. There is currently no model allowing such prediction in temperate grasslands. This study aims to identify the environmental variables that determine whether fires will sustain in native grasslands in Tasmania, Australia, and develop a model for predicting fire sustainability in this vegetation. Fuel characteristics and weather conditions were recorded for 111 test fires. Logistic regression modeling identified dead fuel moisture content, fuel load, and percentage dead fuel as predictors of fire sustainability. Classification tree modeling identified dead fuel moisture and fuel load threshold values for sustaining fires. There was also evidence indicating a percentage dead fuel threshold. The logistic regression model and a model combining the results of the classification tree and the percentage dead fuel threshold accurately predicted the outcomes of a small set of experimental fires. These models are likely to have utility in predicting fire sustainability in Tasmanian grasslands and are also likely to be applicable to similar grasslands elsewhere.     

Development and application of an ecosystem management approach for protected natural areas

Preservation of small natural areas is not in itself a sufficient measure to maintain the integrity of the ecosystems for which they were initially set aside. Intense pressure from recreational use is just one of the many human-caused stresses that may degrade natural areas. Therefore, land-use planning and management from an ecological perspective is necessary to assess, ensure, and in some cases increase, the ecological integrity of protected natural areas. An ecosystem management approach for small protected natural areas with high recreational use is presented, based on three interrelated components: an ecological evaluation procedure of ecosystems, the implementation of management interventions on ecosystems, and the development of a monitoring scheme of ecosystem components. The ecological evaluation procedure combines two concepts: the biotic value of vegetation and wildlife and the abiotic fragility of the soils. This combined evaluation process results in the creation of a sensitivity map that can be used as a management tool for planners and managers. Management interventions, the second component of the management approach, are derived from concepts of ecological succession. Intentional human interventions are used to maintain the ecological integrity of ecosystems or in some cases to restore degraded sites. For the third component, only the basic principles of the monitoring program will be discussed. A pilot project in one of the Montreal urban community protected areas is presented to illustrate aspects of the proposed ecosystem management approach.     

Simulation of vegetation dynamics and management strategies on south Texas, semi-arid rangeland

In this paper, we describe a model designed to simulate seasonal dynamics of warm and cool season grasses and forbs, as well as the dynamics of woody plant succession through five seral stages, in each of nine different plant communities on the Rob and Bessie Welder Wildlife Refuge. The Welder Wildlife Refuge (WWR) is located in the Gulf Coastal Prairies and Marshes ecoregion of Texas. The model utilizes and integrates data from a wide array of research projects that have occurred in south Texas and WWR. It is designed to investigate the effects of alternative livestock grazing programs and brush control practices, with particular emphasis on prescribed burning, the preferred treatment for brush on the WWR. We evaluated the model by simulating changes in the plant communities under historical (1974-2000) temperature, rainfall, livestock grazing rotation, and brush control regimes, and comparing simulation results to field data on herbaceous biomass and brush canopy cover collected on the WWR over the same period. We then used the model to simulate the effects of 13 alternative management schemes, under each of four weather regimes, over the next 25 years. We found that over the simulation period, years 1974-2000, the model does well in simulating the magnitude and seasonality of herbaceous biomass production and changes in percent brush canopy cover on the WWR. It also does well in simulating the effects of variations in cattle stocking rates, grazing rotation programs, and brush control regimes on plant communities, thus providing insight into the combined effects of temperature, precipitation, cattle stocking rates, grazing rotation programs, and brush control on the overall productivity and state of woody plant succession on the WWR. Simulation of alternative management schemes suggests that brush canopy removal differs little between summer and winter prescribed burn treatments when precipitation remains near the long-term average, but during periods of low precipitation canopy removal is greater under winter prescribed burning. The model provides a useful tool to assist refuge personnel with developing long-term brush management and livestock grazing strategies.     

Competing conservation goals, biodiversity or ecosystem services: element losses and species recruitment in a managed moorland-bracken model system

Conservation management in Europe is often geared towards restoring semi-natural ecosystems, where the objective is to reverse succession and re-establish early-successional communities, to comply with national and international conservation targets. At the same time, it is increasingly recognised that ecosystems provide services that contribute to other, possibly conflicting policy requirements. Few attempts have been made to define these conflicts. Here, we assess some potential conflicts using a Calluna vulgaris-dominated moorland invaded by bracken (Pteridium aquilinum) as a model system, where the current policy is to reverse this process and restore moorland. We examined impacts of bracken control treatments on services (stocks and losses of C and mineral nutrients), litter turnover and biodiversity within a designed experiment over 7 years. Bracken litter was >2000 g m(-2) in untreated plots, and treatments reduced this quantity, and its element content, to varying degrees. Cutting twice per year was the most successful treatment in reducing bracken litter and its element content, increasing litter turnover, and increasing both mass and diversity of non-bracken vegetation. Diversity was greatest where bracken litter had been reduced, but species composition was also influenced by light sheep grazing. There was a significant loss of some chemical elements from bracken that could not be accounted for in other pools, and hence potentially lost from the system. In absolute terms large amounts of C and N were lost, but when expressed as a percentage of the total amount in the system, Mg was potentially more important with losses of almost a third of the Mg in the surface soil-vegetation system. There is, therefore, a potential dilemma between controlling a mid-successional invasive species for conservation policy objectives, especially when that species has evolved to sequester nutrients, and the negative effect of increasing environmental costs in terms of carbon accounting required, the potential input of nutrients to aquatic systems, and long-term nutrient loss. There is, therefore, a need to balance conservation goals against potential damage to biogeochemical structure and function.