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- About Natural Processes
- Natural Processes: An Interconnected Web
- Some Natural Processes in More Detail
About Natural Processes
Looking at a list of natural processes, it may be hard to tell what they all have in common. The answer is two-fold: they are all processes or interactions rather than things, and they all involve moving nutrients and/or energy from one place to another.
Examples of natural processes:
- energy flow and nutrient cycles (photosynthesis, food webs, decomposition webs)
- sediment transport and soil formation
- the water cycle
- reproduction/regeneration mechanisms
- natural disturbances (fires, floods, storms)
- plant/animal interactions (facilitation, competition, pollination, herbivory, and seed dispersal)
- climate and microclimate
Let’s look at a few examples of natural processes to see how they create pathways to move nutrients or energy.
Bedrock contains elements that plants use for growth, but how do these nutrients get out of the bedrock and into the plants? Natural processes such as rain, groundwater movement, freeze-thaw cycles, and the action of plants, animals, and microorganisms break the bedrock into smaller and smaller pieces until the elements are available in the soil for plants to take up with their roots.
The process of photosynthesis moves carbon from the atmosphere (as carbon dioxide gas) into plant tissues (as solid carbon).
The process of pollination moves pollen from flower to flower using energy supplied by insects or other animals. The animal gets nutrients from the plant, and the plant gets help reproducing itself.
While all natural processes move nutrients and/or energy, the time scale and the magnitude of the processes vary enormously. Some operate at the scale of an individual plant, such as photosynthesis or pollination. Others affect multiple members of the community at once, such as a forest fire or the availability of groundwater. Some natural processes occur quickly, such as a flood, while others can take hundreds of years or longer, such as soil formation.
Natural processes ultimately influence where different plants and animals are able to thrive. Because of their role in forming habitat, natural processes are critical in creating and shaping natural communities.
Natural Processes: An Interconnected Web
Natural processes form a complex web, such that virtually none of them operates in isolation from others.
For example, many different natural processes—from weathering to decomposition—work together across many time scales to form topsoil. Changes in one process can influence another: a change in climate can create a change in the rate of weathering of the bedrock, which can create a change in the shape of the landscape, which can create a change in whether soil accumulates or washes away.
Because natural processes are interconnected, disrupting one process can have unexpected consequences on other processes, and may eventually change patterns of vegetation or even lead to the conversion of one natural community to another. Since each natural community has a different role to play in the environment (including functioning as habitat to different animals), the loss of any natural community represents some loss of function.
Some Natural Processes in More Detail
To illustrate the importance of natural processes in shaping our natural world, let’s look more closely at a few that seem particularly important for understanding the patterns in vegetation. Note that some of these occur every day while others are infrequent. Some are ongoing while others are temporary. Fire and flood are examples of temporary processes that can have profound effects. These are called natural disturbances. Other examples are ice storms and insect infestations.
Fire: Rising from the Ashes
When fire sweeps through natural areas, it moves nutrients from branches and other plant or animal matter into nutrient-rich ashes, poised to fertilize the plants that remain.
Fire is destructive to some natural communities but it helps maintain those that contain fire-adapted plant species. Some fire-adapted species, such as chestnut oak, have thick bark to help them survive small to moderate fires. Others, such as mountain laurel, contain oils that encourage quick and complete burning—but are able to quickly re-sprout from the roots after fire has swept through.
Some plant species actually require fire. In the Atlantic Coastal Plain, many pitch pine cones are serotinous, which means they stay tightly closed unless the heat of fire opens them; only then do they drop their enclosed seed onto the freshly groomed (burned!), sunlit forest floor.1
Floods: Rich But Hard to Live With
Flooding is another natural process that can be destructive to some communities, but beneficial to others. Natural communities on floodplains benefit from the rich soil, full of nutrients brought in by floods. But not all plants can tolerate repeated inundation, soil saturation, and flood damage.
Green ash flourishes in a flood-prone environment. It has incredibly wide-spreading roots2 that enable it to maintain a hold in this environment. Small plants that thrive in floodplain soils must be either extremely well-rooted or able to grow fast enough to mature and produce seed between floods in which they are often flattened, buried by debris, or swept away.
When floodwaters rise higher than usual, they can damage or destroy plants in natural communities that don’t typically experience flooding.
Canopy Gaps: Making Room to Grow
These small-scale canopy gaps can help maintain natural communities, by allowing new trees to become part of the canopy. But when large sections of forest are leveled by severe storms or landslides, the forest’s character will be radically reshaped, at least in the near term, if not permanently. This is especially true if non-native invasive plants are nearby, ready to encroach into newly opened spaces.
Herbivory: A Balanced Diet
Herbivory is an important natural process in most if not all plant communities. Plants can survive the loss of some proportion of their leaves and stems, and tree populations produce enough seedlings to successfully regenerate even if many of those seedlings end up being eaten by animals.
However, the introduction of non-native animals, or an overpopulation of native herbivores, can have devastating effects.
Non-native invasive insects, such as the gypsy moth, can repeatedly defoliate large areas of forest and weaken mature trees so that they are more susceptible to disease. An overabundance of white-tailed deer can decimate shrubs and drastically reduce the number of tree seedlings and saplings, to the point where the ability of a forest to regenerate itself is compromised.
Studies suggest that deer prefer many species of oak over American beech, red maple, and blackgum, trees common in the mid-Atlantic states. As a result, excessive herbivory by deer could alter the structure and composition of forests both now and in the future. If nearly all of the oak seedlings are eaten by deer, then other common tree species will be able to take full advantage of gaps in the forest canopy as they open up. A decline in oak would decrease the amount of acorns—a wildlife staple, high in energizing fats and carbohydrates—and probably shift wildlife dependence onto other available food sources such as beechnuts.
Erosion and Sediment Transport: Earth in Motion
The natural processes of erosion and sedimentation are most evident in the floodplains and floodways of streams.
Streams erode sediment from the steep, concave bluffs on the outsides of stream bends, and deposit it downstream. Some sediments are deposited as point bars on the insides of stream bends, while others are deposited on other surfaces of the floodway and floodplain.
These processes happen every day, but they happen on a larger scale during and after floods. As stream waters overflow their banks, they replenish the floodplain with sediments from upstream.
Over the course of years, a stream can meander through its floodplain, acting as an agent of natural disturbance. Stream channels are continuously changing through these natural processes.
On a smaller scale, erosion and sedimentation processes occur everywhere, including hillslopes. When rainwater washes over a steep or convex upper slope, it erodes sediments and carries them downslope to deposit them in flatter or more concave areas, like toeslopes.
Gravity and weather can work together on slopes to transport larger amounts of material downslope. This movement can happen quickly in avalanches or mudslides, or slowly, when frost-heaving and gravity cause soil and rocks to move gradually downslope.
Soil Processes: Creating a Place to Take Root
Natural processes that influence the texture, depth, composition, and moisture content of soil play a pivotal role in determining the locations of natural communities upon the landscape.
Exposure to weather, which is often a function of topography, helps determine moisture content, nutrient levels, and thickness. Soils on hilltops and upper slopes are often relatively dry because they are exposed to more sun and wind than soils in protected ravines. Furthermore, rainwater rushes off hilltops quickly, eroding soil and leaching away nutrients.
Even apart from rainwater, gravity and weather work together to transport material downhill through landslides, frost-heaving, and soil creep, all of which affect soil thickness. Upper slopes are areas of erosion, often resulting in shallow, droughty soils, whereas lower slopes or ravines are areas of soil accumulation, helping to build deep soils in concave areas along and at the base of a slope. Soils in these low, concave areas may be moister because rainwater has more time to soak in, and because they may be closer to streams and groundwater seeps.
In general, the nutrient composition of soil is largely determined by the mineral content of the underlying bedrock or sediments. However, downslope movement can bring rocks and soil from upslope that differ in composition from the underlying bedrock.
Read more about soil formation in Physical Setting.
The Water Cycle: What Goes Around, Comes Around
Water shapes natural communities in both obvious and indirect ways.
Of course plants and animals need to consume water to grow and survive. But water also erodes and transports sediments, and plays a crucial role in chemical reactions necessary to create soils and to change them over time.
Water processes occur on all scales. Molecular-scale processes determine whether an individual soil particle is dry or moist (whether it holds water). Large-scale geologic processes determine how much groundwater is available for a community relying on groundwater seepage, or how frequently a particular area is flooded. Planet-wide processes shape huge storms over ocean waters that can spiral onto land bringing rain or creating severe natural disturbances.
Of course, not all rain flows directly to that river or one of the streams feeding into it. If it did, plants would wither, animals living in the uplands would be thirsty, and there would be disastrous flash flooding in the valleys every time it rained. Rather, some of the water evaporates, and some of it soaks into the ground immediately, or after pooling.
Water in the ground slowly percolates down, filling pores between sediments or cracks in bedrock, until it reaches an impermeable layer. Above the impermeable layer some amount of sediment or bedrock is saturated with groundwater. The top of this layer is called the water table.
The water table can rise or fall in response to long-term drought or rainy seasons, but in general it is some distance below our feet. However, the water table does intersect with the surface in some places, and where it does, you’ll see a spring, a swamp, or a stream that’s running despite a lack of recent rain.
Groundwater can return to the surface in other ways as well. Humans pump it out in wells. Plants suck it up with their roots, then return it to the atmosphere through transpiration (giving off water vapor through leaves). Some large trees such as oaks are capable of pumping 200 gallons of water out of the ground on a hot day! (Ever notice land in a low area getting a bit swampy after cutting down a big tree there?)
When water processes are disrupted within a watershed, there can be profound consequences, both above ground (such as increased stormwater runoff) and underground (contaminated groundwater, or diminished groundwater). See Water and Land Use under Stewardship and Ecological Threats.
Forest Succession: Clues to the Past
Land that has been previously disturbed by logging or farming has often returned to a semi-natural state, full of large trees. However, clues in the composition of these forests tell us that they are the result of successional processes—processes that influence the reestablishment of vegetation on a site that was formerly cleared or heavily disturbed.
Where a forest was logged with minimal ground disturbance, a blend of various trees, including many of the original hardwood species, may quickly return from stump sprouts or from saplings that were left behind. Non-woody vegetation on the forest floor may recover as well. Trees within a formerly logged forest may vary somewhat in age, especially if the forest was only selectively logged.
Telltale signs of a formerly logged forest include old stumps or multi-trunked trees (multiple sprouts regrown from a single stump). You may also find fairly deep holes in the ground left by rotted stumps, sometimes outlined at the surface by neighboring tree roots that once encircled the old trunk.
By contrast, where intensive fire, plowing, or earth moving has removed not only trees, but also stumps and seed banks (seeds in the soil ready to germinate), an entirely new forest is created.
The new forest is populated by pioneer species whose seeds germinate quickly when they reach bare mineral soil. These tree seedlings quickly spread their large, juvenile leaves to the sun, casting shade that reduces the ability of some other plants to germinate or thrive on the forest floor.
In the Mid-Atlantic, these forests tend to regrow as even-aged stands of pine and/or tuliptree (or sweetgum in the Coastal Plain). Little by little, as mature trees die, an even-aged successional forest of this type may eventually give way to an uneven-aged suite of trees, shrubs, and herbaceous plants typical of a natural community found in the same environment. This process can take centuries.
- 1. , “Pinus rigida. In: Fire effects information system”, 2007. [Online]. Available: http://www.fs.fed.us/database/feis/plants/tree/pinrig/introductory.html.
- 2. , “Trees of New England: a Natural History, page 67”, Guilford, CT: The Globe Pequot Press, 2005.