Indicators based on systems theory have high potentials to represent complex issues in a holistic manner, but they tend to be rather abstract and difficult to communicate.
Vigor, organization, and resilience (V-O-R model)
Measures of vigor, organization (or performance), and resilience are often used to assess ecosystem health. However, they are more easily described in theory than quantified in practice. Vigor is usually represented by activity, metabolism, or primary productivity. A study of the Great Lakes Basin (North America) showed the decline in the abundance of fish and infertility of agricultural soils within the basin as an example of reduced vigor. Organization represents the diversity and number of interactions between system components. An example, also from the Great Lakes, is the reduced morphological and functional diversity of fish associations that occurs under multiple stresses. Resilience is normally understood as a system's capacity to maintain structure and function in the presence of (external) stress. When resilience is exceeded, the system can shift to an alternate state. A prime example is the shift from benthic to pelagic dominated fish associations in the Laurentian Lower Great Lakes Basin. In this approach ecosystem health is closely related to the concepts of stress ecology where vigor, systems organization, resilience and the absence of signs of ecosystems distress are the main factors for the health of a system.
Further holistic indicators are the exergy index and the specific exergy index. Exergy is derived from thermodynamics and measure the energy fraction that can be transformed into mechanical work. In ecosystems, the captured exergy is used to build up biomass and structures during succession. Hence, exergy can be used as a measure of biomass, structure, energy, and information stored in the biomass. Therefore, more complex organisms and systems also have more built in exergy than simpler ones. Specific exergy is defined as exergy per biomass. Both exergy and specific exergy can be used as indicators for ecosystem health. Relations between the exergy values and other ecosystem health characteristics like diversity, structure, or resilience can be found. For example, specific exergy expresses the dominance of the higher organisms as they per unit of biomass carry more information (they have higher ^-values). A very eutrophic ecosystem has a very high exergy due to the high concentration of biomass, but the specific exergy is low as the biomass is dominated by algae with low ^-values. The combination of exergy index and the specific exergy index gives usually a more satisfactory description of ecosystem health than the exergy index alone, because it considers the diversity and the life conditions for higher organisms.
The holistic ecosystem health indicator (HEHI) was developed in 1999 in Costa Rica as an integrative indicator which might be an appropriate tool for assessing and evaluating health of managed ecosystems. The HEHI follows a hierarchical structure starting with three main branches: ecological, social, and interactive. Measures about the condition and trend of the ecosystems are organized within the ecological branch. Socioeconomic measures concerning the community dependent on the ecosystem or affected by management decisions are organized within the social branch. The interactive branch includes measures relating to land-use and management decisions that characterize the interactions between the human communities and the ecosystem. Furthermore, each branch is subdivided into categories or criteria.
The indicators belonging to the categories serve as measures for the performance of each category. If we for example take soil quality, this is a category within the ecological branch and it can be measured using indicators such as microbial biomass, water infiltration, compaction, etc. Each category is given a target or a benchmark, which is based on references available in scientific literature, policies, etc. For example, a water-quality indicator can have a target defined by legal limits specified by the administrative authority in charge, while a target for a productivity indicator may be defined by a combination of the capacity of the system and objectives set by stakeholders.
The National Resources Conservation Service (NRCS) of the US Department of Agriculture assigned an NRCS indicators action team in 1994 which developed an indicator selection model for the use of indicators in evaluations of ecosystem conditions.
The team identified framing questions for four different ecosystem aspects namely: ecosystem processes, recovery processes, landscape and community structure, and abiotic features. The framing questions represent a minimum set of diagnostic questions, which need to be answered when doing comprehensive evaluations of ecosystem conditions or health. The questions are asked at all scales of ecosystem evaluation:
System processes. The questions asked at 'system processes' are as follows:
1. Are precipitation and groundwater resources captured, stored, used and released in a safe and stable manner.?
2. Are kinds and flows of chemicals (minerals, nutrients, other) and energy in balance and optimized for plant and animal communities and biomass production requirements.
3. Are annual cash flows, technical assistance, and conservation incentives timely and adequate for desired community and land user incomes.
Recovery processes. The questions asked at 'recovery processes' are as follows:
1. Are soil, water, air, plant, and animal resources and biophysical processes in place and in a condition to allow timely and full recovery from stresses and disturbances and to meet management objectives?
2. Are social and economic systems available to allow land users and communities and the resources they manage to recover from environmental and socioeconomic stresses.
3. Are there human and animal resource health concerns associated with the management of present or planned enterprises.
Landscape and community structure. The questions asked at 'Landscape and community structure' are as follows:
1. Do landscape features and patterns facilitate use, protection and optimization of ecosystem processes.
2. Do commodity markets, investment capital and public programs encourage land uses, enterprises and resource management that are compatible with ecosystem processes.
3. Are decision-making processes available to communities and individuals to resolve conflicts regarding current and desired uses, management and protection of natural resources.
4. Does the social infrastructure (healthcare, education, multicultural recognition, etc.) support and promote the desired quality of life for the communities and individuals.
Abiotic features. The question asked at this scale is: Are current and planned land uses and desired future conditions suited to the abiotic conditions (e.g., stream temperature, flow velocities, riffle/pool ratios, riparian shading, climate, topography, soils, and geology).
Within the next step, for all ecosystem components (environmental, ecological, socioeconomic, cultural, or political factors), which are considered to be necessary elements of the respective system, appropriate indicators are listed. These indicators are the quantitative or qualitative tools in this model to assess the status, condition, or trend of a given ecosystem attribute or component. The underlying assumption for the use of such indicators is that relationships can be inferred between a relatively easily measured ecosystem attribute (i.e., litter distribution and amount) and the more difficult to measure ecosystem components or processes (i.e., energy flow and nutrient cycling).
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