There are four ecosystem processes that are fundamental to all terrestrial ecosystems:
1. The Water Cycle
2. The Mineral Cycle
3. Plant and Animal Succession
4. Energy Flow
A report by the U.S. National Research Council on rangeland health suggests that evaluating and monitoring these processes is the best approach to proper ecosystem management . Here is a brief review of each process.
The Water Cycle
Precipitation which falls on the soil surface may infiltrate and enter the soil profile as water. Some will be stored and some will continue to percolate until it becomes part of the ground water. Some stored water will evaporate and re-enter the atmosphere as vapour and some will be taken up by plants and transpired or stored in plant tissues. Precipitation which does not enter the soil system may be evaporated from the surfaces of plants, rock, litter, and other materials. Or it may run off the site as surface flow. This constant process of precipitation, transpiration, evaporation, and surface and ground water flow is called the water cycle. The effectiveness of the water cycle and its overall functioning are directly influenced by land management practices.
The Mineral Cycle
The mineral cycle may also be referred to as the nutrient cycle. Nutrients follow cyclical patterns as they are used and re-used by all living organisms. Most nutrients are cycled through decomposer organisms in the soil system, but some including nitrogen, are atmospherically involved. Organic materials, such as plant litter, dung and urine, and decaying animals that are deposited on the soil surface are decomposed and reincorporated into the soil by living organisms. Physical processes such as oxidation, photo-decomposition, mechanical breakage, fire, and actions of wind and water are non-biological facets of the mineral cycle. The manner and rate at which nutrients are cycled play a critical role in rangeland health and are directly influenced by land management practices.
Plant and Animal Succession
The process of change is the only constant in all ecosystems. Populations of plants and animals change continually in response to all sorts of environmental pressures. Among these are climate and weather, grazing and other herbivory, disturbance by fire, farming, hunting, and logging, as well as hundreds of other factors. This process of continual change is termed succession. There appears to be an almost universal tendency for plant and animal communities to develop toward states of greater complexity and diversity. These states are sometimes referred to as climax, steady states, or potential natural communities (PNC). As resource managers, we have learned to manipulate succession through a variety of means, sometimes successfully. And sometimes not. We have many tools at our disposal which may be used to advance, arrest, or reverse succession. They are discussed in some detail in Chapter 4.
All of us have solar-powered hearts. The energy that keeps us moving and breathing comes from the sun via photosynthesis and the process of energy flow. Energy is not cycled and must be continually supplied to the earth by the sun. Energy can also be stored in a variety of forms, including fossil fuels such as coal and oil. Regardless, the flow of energy is one way - from the sun to the earth - and back to outer space as radiation. This flow of energy in our ecosystems is sometimes referred to as the carbon cycle because carbon is involved in all energy storage and transfer. Some of the solar energy captured by green plants is transferred to the animals which eat them. Some is used by the plants themselves for their own life functions. Energy is again transferred to animals which eat the herbivores. Decomposer organisms which break down the remains of plants and animals utilize the last remaining energy as they carry out their work. Energy that is not incorporated into tissues is expended as heat through the activities of organisms so that eventually there is no net energy remaining. Energy is never destroyed, only transformed.
Energy flow is closely related to the other ecosystem processes - water cycling, mineral cycling, and succession. It in fact drives these activities and makes them possible. As humans we are in the business of constantly attempting to manage energy flow, sometimes successfully, and sometimes not! When we harvest hay with machinery or harvest forage with livestock, we are in the midst of the energy flow process. Energy flow is a critical process on rangelands and is directly influenced by land management practices.
Remember: "The closer an ecosystem is managed to allow for natural ecological processes to function, the more successful that management strategy will be." (Elmore and Kauffman 1994)