by Daniel Weber, Ph.D
That’s the number you need to know. There are four parts to the environment, and four factors that influence and are influenced by the environment, and four operative dimensions of life. If we neglect these environmental concepts we will likely end up like planet number four-lifeless.
Pick your favorite ecosystem: secluded ponds deep forests mountain valleys, or harsh desert beauty. Each requires four, interrelated compartments to function properly:
1. Atmosphere that dictates the climate,
2. Water-upon which all life depends,
3. Soil that provides nutrients of life and
4. Organisms themselves.
The fundamental processes of each of the four, interrelated compartments are called “state factors” because they define the state of all other ecosystem processes. The four state factors are time, geography and geogology, climate, and biota.
Life occurs in a four-dimensional universe: height, width, length, and time. Given enough time, the physical environment of life can change. Daily weather changes form long-term patterns of climate. Mountains slowly rise and then erode into soil. Living matter decomposes and nourishes the soil. Yet, even short time frames are important as daily life cycles (such as the cyclical blooming and closing of flowers on the forest floor) are determined by the 24-hour rhythm of light and dark.
Geography and Geology
Time does not act in a vacuum. As time moves forward, other state factors change. Geography and geology are not constant and dramatically affect life’s patterns. For example: Walk through a valley and compare its two sides. If the valley has a north and south side, the north side will be wetter and cooler simply because it has less direct sunlight. Due to this difference in microclimate, even in the hills of Israel, the north-facing slope will have a more lush display of vegetation than the south-facing slope. In more temperate regions, snow will stay longer on the north-facing slopes, delaying the emergence of spring flowers but ensuring that the soil will be moister for a longer period. (Any guesses on what will happen with east- vs. west-facing slopes? Does any of this matter which hemisphere you are in?)
All mountains are made of rock, but rocks have different compositions and rates of weathering. As they erode, the remaining soil has very different qualities due to the parent rock material. Depending upon the minerals in the parent rock material, the soils produced during erosion will be able to support different types of plants because of the different acidity levels. For example, some plants are better suited to tolerate the toxicity created by copper. Therefore, mining companies seek those plants to identify sites for potential copper mines. Other rocks, such as limestone, are relatively soft and erode quickly to produce more alkaline soils. Granite, formed by volcanic activity, is hard and weathers slowly. Rock layers below the surface can affect the movement of groundwater, an essential element in the replenishing of lakes and streams.
Climate, the important third state factor, was demonstrated by the recent hurricanes. While the hurricane itself is a display of weather, the interlocking patterns in the atmosphere and ocean create long-term conditions that define a region’s climate. Over time, climates change-sometimes very quickly. There is evidence that the Sahara Desert was once a lush tropical garden and Antarctica was warmer and without the continent’s extensive ice sheets. Climatic change is determined by a variety of factors ranging from the internal workings of the sun, changing orbits and tilt of the Earth, ocean currents, and a recent development-human activity. Ecosystems will be patterned upon the climatic processes that determine water availability, rates of soil formation through erosion of rocks and decomposition of organic matter, lengths of growing seasons, and species abundance and distribution.
Plants and animals-or biota-are the fourth and last state factor to affect the patterns and processes of an ecosystem. Life itself affects life’s physical framework and the biological interactions among species. While the latter is more obvious (e.g., prey and their predators, social interactions) the way life affects the nonbiological world is a crucial and under appreciated feedback system in the environment. A well-known example is the earthworm’s ability to change the quality of soil. The worm’s burrowing activity loosens the soil and increases the ability of roots to obtain oxygen necessary for cellular respiration. By feeding upon the forest floor litter, worms increase the rate of decomposition and the formation of humus, the organic matter in soil that holds moisture and provides a source of nutrients.
The role of the American bison to maintain the prairies of the Great Plains is a more complex example. Before the advent of widespread agriculture, the region between the Rocky Mountains and the Mississippi River was a vast expanse of grasslands and prairie flowers. The topography influenced the local climate by limiting the rainfall so that only grassland ecology could be supported (due to the Rockies’ rain shadow effect). Equally important, and often overlooked, is the importance of bison grazing. Without the grazing, these grasslands may have eventually given way to a savannah ecosystem, a land of scattered shrubs and trees. Grazing prevented these shrubs and saplings from ever becoming dominant. Ecologists also talk about “keystone species,” or species whose role in a habitat is so crucial that they define and regulate the very structure of the biological community. For example: when sea stars (related to starfish) preyed upon mussels in a Washington (state) intertidal zone, it devastated kelp beds, which caused population crashes of crabs, fish, clams, and snails that lived in the kelp beds.
Functions and Services of Ecosystems
Ecosystems are more than a result of biological and physical events and consequences. The second major component related to ecosystem pattern and process is that ecosystems provide the local organisms four specific functions and services. For humans, the ecosystem provides products such as timber and other forest goods. A major function of ecosystems is the cycling of water, important gases, and nutrients. The flow of Earth’s oxygen and carbon dioxide are a function of the ecological “breathing,” which directly affects everyone’s air quality. This aspect, plus the fact that ecosystems store carbon in both living and dead material, is critical to evaluating the effects of human activity on global climate change. For example, before human interference, American Great Plains grassland ecologies were an important carbon sink. Most of the carbon, unlike the rainforests of the Amazon Basin, was located in the deep humic soils that resulted from thousands of years of decomposing grasses and prairie flowers. Thus, farming became highly successful in these states, although modern agriculture has sorely depleted those soils. A fine-tuned ecosystem also provides for the maintenance of a diverse flora and fauna and high quality stream and lake water. Changing ecosystem patterns and processes, by paving over large tracts of land in urban centers alters the functions of services of ecosystems.
Two other interrelated functions and services provided by ecosystems are the creation of landscape diversity and biology. Ecosystems are made up of many microhabitats that create a mosaic of landscape forms. This diversity presents opportunities for many species to survive. While ecosystems have different diversity levels, defined by ecologists as a mathematical intersection of abundance and distribution of species, a properly functioning system can maintain a range of species whose niche can vary from being a resource generalist to a specialist. For example: bears are considered resource generalists because they eat fruits and fish and therefore are very resilient to environmental changes. The Kirtland Warbler is a resource specialist because it only lives in one specific habitat found in Michigan and can be very vulnerable to minor changes in its home range. When humans decrease landscape diversity, biodiversity inevitably suffers.
Life, as we all know, can be rather random. A variety of natural events occur at irregular intervals and are called stochastic factors, the third component that affects ecosystem patterns and processes. Just ask anyone in the Caribbean or southeast United States about how these random factors have totally disrupted their lives in the last month! Extreme events, such as hurricanes, tornados, or droughts, can have profound effects on the biological and physical elements of an ecosystem. Geological events, such as earthquakes or volcanoes will also disrupt or change patterns of organization in nature to create new opportunities for life to develop. When the new island of Surtsey formed, by a volcanic eruption off the coast of Iceland nearly 40 years ago, an opportunity for new life was created. In fact, the island was closed to the public so scientists could follow the succession of life forms that colonized this new piece of real estate. Landslides in mountainous regions may block off a river and create a lake.
Rivers change course and leave remnants of the old river isolated into what are called “ox-bow lakes” due to their shape. River species may become locally extinct and are replaced by species that can survive in the stagnant pools left behind. Lightening-caused fires are common in many forest and prairie ecosystems. Many species of plants, such as Jack Pine, can only germinate in recently scorched areas. Fires are critical to removing accumulated brush and litter from forest floors; fire suppression only allows for higher levels of organic matter to accumulate so that when a fire does occur it is much more intense and causes much more damage. Lastly, biological events such as insect infestations can have profound effects on ecosystem patterns and processes. Furthermore, when large herbivores are freed from their natural predators and not controlled by other methods, large-scale changes in the abundance and distribution of native flora can occur. Such changes have been documented with deer in areas that have been freed of predation by wolves and hunters.
Ecosystem management and human activity represent the fourth and final component that affects ecosystem patterns and processes. It is the only external factor to the ecosystem itself and can be imposed from far distances. These human-directed processes can have positive or negative effects. Human-accelerated climate change, land use disturbances, pollution-creation activities, dredging of rivers, and introduction of invasive species certainly have consequences that profoundly disturb normal ecosystem function; however restoring wetlands, silviculture (the technical name for forestry practices) techniques that reduce forest disturbance, reintroduction of top carnivores, ecotourism, and organic farming are a few of the activities that actually have recreated balance and had a positive effects on ecosystems.
Maintaining life on this planet is a set of complex processes that still puzzle scientists. We understand the overall themes of ecological existence, but as we tinker with the fundamental mechanisms of ecosystem function, we recognize that we are still a long way from fully comprehending the majesty of nature.
Originally posted in “On Eagles’ Wings” November 28th 2004