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Essential Ecological Attributes of Ecosystems

Digest: 
The overall structure of Great Lakes Inform follows an organizing framework of Essential Ecological Attributes. This article provides an overview of this framework and how it facilitates consistency in presenting content, ease of learning, and a comparative understanding among major ecosystem types.

 

Collage of Essential Ecological Attributes

 

Importance of Ecological Condition

Now more than ever, as good stewards of the environment, all sectors of society need better information on the condition of our ecosystems.

We depend on ecosystems for many reasons. Rivers and lakes provide us with food and water. Forests generate construction materials, filter pollutants from air and water and play an important role in storing atmospheric carbon. Wetlands purify water supplies, mitigate flood damage and sustain an incredible diversity of life. We also derive aesthetic, spiritual and recreational value from rivers, wetlands and forests among many other ecosystems. Because of our reliance on ecosystems for our well-being, we as a society are growing more concerned with the ecological condition or ‘health’ of the ecosystems on which we all depend, especially as ecological change becomes more pronounced.

However, ecosystems are complex and not many people, even ecological scientists, fully comprehend what it means for an ecosystem to be in good condition. Because of this complexity, many ecological studies and projects address small-scale questions that are easier to answer. Yet, to address landscape scale conservation issues meaningfully and to balance resource use with sustainable livelihoods, we need to know more about the ecological integrity of entire ecosystems, not just parts of ecosystems, like a branch of a river or a patch of a wetland. To improve our knowledge, conservationists are seeking more information about all the parts of an ecosystem and how they interact over longer time scales and larger spatial extents.

Symbols are often used to make learning easier. And the U.S. EPA (EPA) Science Advisory Board (SAB) produced a simple and logical framework consisting of symbols for comparing the ecological conditions of any terrestrial or aquatic ecosystem to what scientists would consider desired conditions. The framework is based on six essential ecological attributes (EEAs) that when considered together reflect the overall health of an ecosystem. It is a scientific approach requiring a commitment to learning new concepts and advancing our understanding of the world, but with better information about the condition of ecosystems, resource managers and decision makers will be able to make better decisions about resource use. This comprehensive framework also highlights the current state of conservation, in which we have a good understanding of the concepts and theory about how different ecosystems work, but we lack adequate data on the actual current status of ecosystems.

 

Essential Ecological Attributes Framework in Great Lakes Inform

The essential ecological attributes framework is used as an organizing structure in all six modules of Great Lakes Inform. Through this basic organizing framework, Great Lakes Inform will advance information delivery, ease of learning and a comparative understanding of Great Lakes ecosystems.

Essential Ecological Attributes framework

The six EEAs, including biotic condition; landscape condition; chemical and physical condition; energy and material production cycles and flows; hydrology and geomorphology and natural disturbance regimes, are the basis for understanding complex ecosystems. They are the symbols that can make learning about the complexities of an ecosystem, like a whole watershed or an entire Great Lake, easier.  And because they can paint a comprehensive picture of the overall health of almost any ecosystem, they are used to organize and deliver Great Lakes knowledge and information in Great Lakes Inform.

One area of Great Lakes Inform where this structure underlies the organization of content is the Knowledge Network. All ecological articles in the Knowledge Network module are structured using the EEA framework. The EEAs form the architecture for conveying information about ecological condition in a consistent and comprehensive way. Understanding Great Lakes ecosystems in their entirety through this simple framework will promote land and water management activities that account for all important parts of an ecosystem across different spatial and temporal scales. The EEA framework also makes searching for content in Great Lakes Inform more efficient. There are several categories of search filters in Great Lakes Inform, used to find data, tools and information. The category of search filters called “Major Ecological Attributes” includes filters for searching content related to ecosystem patterns and processes that encompass all six EEAs. Indexing knowledge, data and information resources using the EEA framework creates a consistent filing system for organizing and sharing ecological information across ecosystems and issues. It also creates an opportunity to learn about ecosystems by encouraging a broader perspective of landscape conservation and a comparative approach to understanding the diverse habitats that comprise the whole Great Lakes ecosystem.

In general, the EEA framework offers conservationists of all types, whether a private landowner or a conservation agency, with a simplified way of evaluating the ecological condition of an ecosystem, and it is also a great tool for educating the public about ecosystems and their value.

 

Breakdown of Essential Ecological Attributes

The essential ecological attributes divide up the universe of ecological information into a logical framework of ecological patterns and processes.

The EEAs are a checklist for evaluating the health of an ecosystem.  Six EEAs comprise the core ecological attributes that are necessary for accurately and comprehensively evaluating the condition of a terrestrial or aquatic ecosystem. The six EEAs include biotic condition; landscape condition; chemical and physical condition; energy and material production, cycles and flows; hydrology and geomorphology; and natural disturbance regimes. These EEAs can be further categorized based on whether they are an ecological “pattern” or “process.” The EEAs for ecological patterns include biotic condition, landscape condition, and chemical and physical condition. The EEAs for ecological processes include energy and material production, cycles and flows; hydrology and geomorphology; and natural disturbance regimes. In comparison with a game of chess, ecological processes are like the rules of the game and the moves made by each player, and ecological patterns are like the various arrangements of chess pieces after a game begins. Ecological processes create and maintain patterns of habitat and ecological structure. The patterns in turn influence other ecological processes. For example, the process of erosion and sedimentation creates patterns in the shape of riverine channels and instream habitat conditions. The shape of a channel then influences ecological processes, such as energy and material flows by controlling the movement and interaction of materials and organisms.

The flow of water constantly changes habitat patterns in a river

Biotic Condition

Biotic condition indicates the biological health of an ecosystem at multiple levels.

As the name suggests, biotic condition refers to the biological elements of an ecosystem, but not just regarding what organisms occur in a habitat. Biotic condition also includes how plants and animals interact and form ecological communities and ecosystems. In more technical terms, the biotic condition addresses the structural and compositional aspects of biota at different levels of ecological organization. For the purpose of the EEA framework, there are three scales for assessing biotic condition: ecosystem and community; species and populations; and organism condition.

An ecological community is a group of species within an area that are connected through ecological processes, environmental features or gradients, and form a distinctive, cohesive unit. Understanding the structure and composition of an ecological community tells us about the type of ecosystem, how it may have changed over time, and what these changes might mean for important ecological processes like material and energy production, nutrient cycling, water transport, and others.  The composition of species living together in a habitat is a basic metric of an ecological community.

Species and populations can be important indicators of biological health, but can be challenging to monitor from a practical standpoint. It’s important to know what types of plants and animals comprise a community, how they interact, which become dominant or are outcompeted, and how populations of different species change in relation to resource and food chain dynamics.  However, instead of trying to monitor every species in a patch of prairie or a wetland slough – there can be hundreds of species in a single habitat – ecologists target a subset of species referred to as “focal species,” which have overlapping habitat needs with many other species and can be used as a proxy for the health of a whole ecological community.

In some cases, the health of individual organisms may indicate other ecological conditions that affect populations or communities. For example, the condition of foliage on trees in a pine forest can reveal patterns in soil, light or air that affect the health of leaves. One of the main indicators of nutrient deficiency in a forest is the discoloration or abnormal growth in leaves and branches.1 In aquatic systems, visual symptoms on fish and other organisms can also be a sign that larger problems are underway. For example, viral hemorrhagic septicemia (VHS) is a type of virus that has been introduced to the Great Lakes and infected important fishes like northern pike, walleye, yellow perch, Chinook salmon, lake white fish and many others.2 The most obvious sign of an invasion of this invasive species virus is hemorrhaging, bulging eyes and unusual behavior in fish.

Whether looking at a community of a dozen different fishes, changes in population numbers over time, or the signs of disease or stress in individual organisms, the biotic condition shows directly how “healthy” an ecosystem is by the status of life that a set of resources can support. Biotic condition can also reflect how well larger ecosystem patterns and processes provide the necessary conditions for biological health.

The veery (Catharus fuscescens) is a focal species for habitat restoration and protection in the Great Lakes region.

Landscape Condition

Landscape condition describes ecosystem health at the broadest level.

A landscape is defined as an area composed of multiple interconnected ecosystems or habitat “patches.” The condition of these relatively uniform habitat patches may reflect that of both biotic (living) and abiotic (nonliving) features. More recently, ecologists have recognized that ecosystem patterns and processes often operate at larger scales and over greater time periods than previously known. Even where larger scale patterns and processes have been recognized, the resources and planning for studying and managing from a landscape context have been limited. Therefore, natural resource managers need more data showing how landscape patterns influence ecological processes at a variety of scales for all types of ecosystems.

The landscape condition of an ecosystem can be measured by patch extent, landscape composition, and landscape pattern/structure.

Patch extent is the overall area of a habitat type within a landscape. One reason landscape condition is of interest to natural resource managers is that reduced habitat area is correlated with reduced biodiversity, i.e., the number and variety of species. Also, many species require a certain area of suitable habitat in order to maintain viable populations.

Landscape composition refers to the number, diversity and proportions of different habitat types within a landscape setting. Dominant habitats in a landscape have significant influence on the prevailing species and communities that live there, and may reveal patterns in other environmental conditions, such as the abundance and availability of water and the quality of soil. Furthermore, the dominance of certain landscape patches, including agricultural land, urban development, and industrial corridors, can have a meaningful impact on the availability and quality of habitat for natural communities.

Landscape patterns and structures are the spatial arrangements of habitats within a landscape. These spatial relationships determine resource dynamics and thus biological assemblages and ecosystem functions. For example, the density of wetland habitat patches can be important for the reproductive success of amphibians, which have restricted mobility.3

Large-scale landscape patterns can influence the availability and quality of natural habitat

Chemical and Physical Condition

The chemical and physical condition of an ecosystem is a basic indicator of habitat quality and is often used as a first measure of ecological condition. Aside from the importance of chemical and physical conditions for aquatic and terrestrial ecosystems, these indicators are also commonly used to monitor water and soil quality for public health.

The chemical and physical conditions of an ecosystem are critical to ecological patterns and processes. The relative abundance of light, moisture, sediment and pollutants, among other factors, are all important drivers of habitat conditions and can define an ecosystem or signify habitat degradation. Chemical and physical characteristics can result from thousands of years of geologic events, such as volcanic eruptions, earthquakes and glacial epochs. They can also reflect patterns in land, air and water from human activities, including land use change, industrial pollution, agricultural runoff, and carbon emissions from burning fossil fuel. Because of the obvious importance of chemical and physical parameters on natural communities, resource professionals often collect data on soil, air and water conditions first. In, fact, more data is collected on chemical and physical metrics than any other ecological attributes, in part because they are often required for reporting to meet pollution permits under federal, state/provincial and local regulations. Accordingly, many mandates are based on public health concerns rather than ecological issues. In general, an ecosystem and the life within are adapted to a historical range of chemical and physical conditions, beyond which biota and ecological processes are altered.

Chemical parameters: 

Many chemical parameters are important to ecosystems and the wildlife that inhabit them, from basic nutrients, to the presence of foreign pollutants, to minute concentrations of trace chemicals that occur naturally in very low abundance.  

Nutrients are required by all autotrophic organisms (organisms that produce their own food). Monitoring the concentrations of nutrients in an ecosystem is important, because some nutrients, such as phosphorus, nitrogen and potassium can limit plant growth if their abundance is too low. When a nutrient or other environmental factor, such as light or moisture, restricts ecosystem or biological functions, it is called a limiting factor. Conversely, nutrients can cause harmful side-effects when introduced into the environment via fertilizers for crop production or sewage discharges during high flow storm events.  Eutrophication is a common negative effect of unnaturally high nutrients in aquatic ecosystems, where excessive nutrients from runoff lead to a rapid increase in the production of algae, followed by reductions in dissolved oxygen and sharp declines in aquatic life as oxygen in the water is used up by microbes breaking down decaying algae.4

Trace inorganic and organic chemicals (trace elements) are common to all ecosystems and many are necessary for basic plant nutrition. For example, iron, boron, magnesium and calcium are all essential to plant growth, but these micronutrients are almost always abundant enough that deficiencies are rarely a problem. Some trace chemicals, however, are a concern even in very low concentrations. Trace metals, including lead, mercury and cadmium, are common pollutants that typically enter ecosystems through atmospheric deposition or industrial effluents and are hazardous to wildlife and people.  Mercury, for example, can cause health effects in fish-eating wildlife, such as birds and mammals, at concentrations as low as 0.27 parts per million (ppm).5 That’s equivalent to 1 minute in over 7 years! Other trace chemicals, including organic compounds found in pesticides, herbicides, fertilizers, and industrial solvents can also be toxic at low levels. Although many toxic chemicals including mercury, lead, polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) are banned in the U.S. from industrial, commercial and agricultural use, these chemicals persist in the environment for many years and accumulate in organisms as they move up the food chain. Therefore, legacy toxic pollutants introduced to water and soil decades ago are still causing harm to wildlife and putting people at risk to health problems from food and water supplies.

Other chemical indicators, including pH, salinity, dissolved oxygen and total organic matter, among others, are often less obvious indicators than nutrients and contaminants, but these are just as important for understanding how ecosystems function and how they are changed by human and non-human influences. For example, conservation scientists often track dissolved oxygen, which aquatic life require for “breathing” underwater. Although dissolved oxygen is replenished by waves and natural mixing between air and water, lakes and ponds can be deprived of oxygen when excessive nutrients from surrounding land uses cause algal blooms and eutrophication. In the Great Lakes region, Lake Erie is especially known for its seasonal eutrophication and “dead zones,” where life cannot persist because of insufficient dissolved oxygen.6

Physical parameters:

Sometimes both chemical and physical conditions will provide the most useful information about an ecosystem. These parameters are intended to complement other physical attributes of an ecosystem, such as habitat diversity and the structural composition of habitat patches. Examples of physical parameters include measures of local and regional climate, especially air temperature and precipitation; water temperature; physical slope; and soil density. Physical parameters can help scientists and land managers understand important ecological functions and processes like the rate of photosynthesis in a forest, prairie or wetland; the groupings of fishes into different temperature regimes; and the effects of unusual climate trends on human developments and ecosystems.

Toxic pollution, like mercury and volitile organic chemicals, from industrial processes can lead to long-term habitat impairment

Energy and Material Production, Cycles and Flows

In any ecosystem, energy and material production, cycles and flows are central to maintaining ecosystem processes and functions that sustain life, and thus biodiversity.

Though difficult to measure in some systems, the metabolic functions of an ecosystem, which involve energy flow, elemental cycling (nutrients and minerals), and the production, consumption and decomposition of organic matter, can be a good indicator of how well all the working parts of an ecosystem are functioning. For example, a forest that produces a lot of biomass (trees), likely has the right balance of productive soils, adequate water and organisms to recycle nutrients back into the earth. Similarly, a river with good connectivity among its segments and branches may cycle nutrients more efficiently and provide better access for migrating fish than one that is blocked by poorly designed dams or that is flooded with sediments from mismanaged farmlands.

Ecosystem productivity, or the ability to capture sunlight and convert it to energy, is a fundamental ecological attribute. Energy flows through an ecosystem in a continuous balance of production, consumption and decomposition of plants and animals. The efficiency of this balance is what determines the ability of an ecosystem to consistently produce a certain level of biological material, which could be plankton in a lake, trees in a forest or fish in a river. Therefore, not only is the flow of energy in an ecosystem important for the “health” of an ecosystem, maintaining organisms and populations of species and supporting productive food chains, it’s also the key to promoting sustainable fisheries, timberlands and agricultural lands.

Like energy flows, material flows are fundamental to ecosystem functions. But instead of entering food chains from the photosynthesis of plants and moving up through the food web and ultimately released as heat, material flows cycle within habitats. Material cycles are the biogeochemical cycles that move organic matter and inorganic nutrients through an ecosystem. Plants and animals borrow this material by producing leafy vegetation (in the case of plants) and consuming plants and animals (in the case of animals, and some plants that consume insects). Then when they die, excrete waste, or become the source of energy and “building material” for other organisms, that material is recycled and used by other organisms. Material is also cycled through physical pathways in an environment.  For example, streams move large quantities of sediment, nutrients and biomass just by the natural force of gravity. All this material is captured and transferred to other streams, floodplains and deltas, where new life can use it. In this continuous and ever-changing display of life cycles, material and energy flows are intimately linked.Nearshore areas of the Great Lakes can be highly productive, because of significant energy and material exchanges between terrestrial and aquatic habitat.

Hydrology and Geomorphology

The hydrology and geomorphology of an ecosystem show the important interplay between water and landforms. They define rivers, lakes, wetlands and groundwater systems, and they influence terrestrial habitats like forests, prairies and beaches.

Hydrology and geomorphology reveal the complex relationship between water and land. The hydrology of a system describes how surface and groundwater flow over and through a landscape. Geomorphology refers to the landforms, channel structures, soils and sediments of a landscape. Combined, the hydrology and geomorphology of an ecosystem determine physical and chemical conditions, shape landscape features and influence natural disturbance regimes, all of which affect the distributions and interactions of plants and animals.

We can determine the condition of an ecosystem’s hydrology and geomorphology by measuring water flow, dynamic structural features and patterns in sediment and other material transport.

Water flow can describe either the dynamics of surface water or groundwater. The flow of water over, under or through a landscape determines when a river or stream is bankfull (meaning the flow of water is high enough to spill over into the floodplain), when a wetland is inundated and for how long, and how fast a groundwater aquifer can recharge its water supply after being pumped for human consumption. All of these effects of water flow are important factors that shape resource conditions and affect life that has evolved to particular patterns in the flow of water. The flow of water also affects the flow of nutrients, salts, contaminants and sediments and therefore is directly linked with the chemical and physical condition of an ecosystem.

Dynamic structural features such as riverbeds and banks are determined by water flow and sediment movement. Appropriately, measures relating to dynamic structural characteristics indicate the integrity of water flow and sediment movement, as well as habitat diversity and quality. Dynamic structural features could also describe the development and destruction of terrestrial habitat, like beaches and dunes, which undergo continuous change from the effect of wind and waves. Terrestrial landforms, including ridges, ravines, mountains, moraines and others are also dynamic structural features, changes in which can have an impact on the health of biological communities. For example, an eroding ridge in a forest can influence the distribution and spread of natural disturbance regimes like fire, flooding, and disease.

Sediment and material transport is the means by which dynamic structural features in an ecosystem take form and change. Wind, rain, flooding and geologic activity can mobilize and transfer sediments and other materials from one part of a system to another, with the effect of changing the physical environment and natural resource conditions. For example, river systems “mature” from headwater streams into networks of larger and larger segments as the flow of water erodes and deposits sediment downstream, morphing the shape and direction of the channel along the way. The slope and underlying substrate of the channel also determine the ability of the river to erode and deposit sediment, which emphasizes the binding relationship between land and water.7  In addition to changing the structure of a river channel, sediment in the water column directly effects aquatic life. Native species have adapted to particular sediment regimes, some with high sediment and some with low sediment. Deviations from historic patterns in sedimentation can be a key indicator of ecosystem stress.

Large rivers like the Mississippi can dramatically change the shape of the land, but we also change the shape of rivers to manage shipping and protect property, which has consequences for river habitat

Natural Disturbance Regimes

Natural disturbances are the driving forces of change in any ecosystem. As such, it is not surprising that understanding the dynamics and measuring the patterns that result from these ecological processes are essential for sustainable resource management and effective conservation.

Natural disturbance regimes alter resource conditions and exert strong forces on the structural, functional and biological diversity in an ecosystem. In a way, natural disturbance regimes are like the blind watchmakers of ecosystems, who create and destroy habitat over and over, halting the production and diversity of life in the midst of a raging fire or a hundred-year flood, only to set new trajectories for ecological development. Common examples of natural disturbances include wildfires; floods; drought; wind and ice storms; insect outbreaks; microbial or disease epidemics; nonnative species invasion; volcanic eruptions; earthquakes; and avalanches. Ecosystems can have many, or just a few disturbance regimes that play dominant roles in shaping resource conditions, and some disturbance regimes interact, creating more complex patterns of change. Ecologists can monitor the frequency, intensity, extent and duration of any natural disturbance to characterize its disturbance regime and to get a better understanding of all other ecological conditions.

Natural disturbances like forest fires can destroy habitat, but the cyclical patterns of a disturbance regime help maintain healthy ecosystems

Putting the Essential Ecological Attribute Framework to Work

Together, the six essential ecological attributes—Landscape Condition; Biotic Condition; Chemical and Physical Parameters; Energy and Material Production, Cycles and Flows; Hydrology and Geomorphology; and Natural Disturbance Regimes—provide a comprehensive view of ecosystem health.

At some point, each of us has probably thought about and considered every one of the six EEAs that comprise the main patterns and processes of almost any ecosystem, at least individually.  Imagine sitting on a riverbank and watching the rush of water tumble over the rocks of the riverbed. Maybe a few waterbugs skid across the surface, or maybe you’re fishing for trout. You’re probably aware of the obvious presence or absence of vegetation and life in and around the stream. But would you consider the water quality, the concentration of nutrients and chemical pollutants? How about the flow of water, and where it’s coming from? Would you consider how efficiently the stream cycles energy and material, or what surrounding land uses might impact the flow of water or the introduction of sediment and contaminants? Thinking in terms of all of the EEAs in a single setting can open a world of possibilities for learning about ecosystems and solving ecological problems. That is why Great Lakes Inform uses the EEA framework as part of its core structure to help natural resource professionals develop and deliver nearly comprehensive data, knowledge and information about the Great Lakes. It’s an approach that will support education and outreach, help fill knowledge gaps in the profession, and increase effectiveness in conservation planning and action. This framework makes it easy to divide up ecological knowledge in a logical way that can be stored and then easily recalled and applied to almost any ecosystem type. The EEA framework also makes it easier to discuss ecological conditions in context of human activities and conservation strategies. Using a common set of ecological categories, we will increase our capacity to restore and protect valued habitats and ecosystem services.

The EEA framework offers opportunities to think about ecosystems comprehensively and holistically