Natural Processes
Natural processes are interactions among plants, animals, and the environment that help create and shape natural communities.
Some natural processes can seem disruptive, such as fire or flooding. But even these powerful instruments can do incredible good for natural communities, the way a loud trumpet can add to an exquisite symphony arrangement. (But see Stewardship and Ecological Threats at Harpers Ferry NHP to learn what can happen when these ecological processes are interrupted or intensified.)
Explore this page:
- What Are Natural Processes?
- Examples of Natural Processes at Harpers Ferry NHP
- When Natural Processes Are Interrupted
What Are Natural Processes?
Natural processes (also known as ecological processes) are interactions among plants, animals, and the environment that occur naturally (without purposeful intervention by people). They are just as critical to the identity of natural communities as are the plants and animals that make up the communities. They also help maintain the health of natural communities.
Ecobit: Natural Processes as Pathways for Nutrients and Energy
Examples of Natural Processes at Harpers Ferry NHP
Let’s look more closely at a few natural processes that are particularly important for understanding the natural communities we see at Harpers Ferry NHP today. These are just a tiny fraction of all the natural processes busy at work, noticed or unnoticed, shaping natural communities.
Fire
Fire is a natural disturbance that can help maintain drier hilltop communities, such as Harpers Ferry NHP’s Chestnut Oak Forest and Dry Chestnut Oak - Northern Red Oak / Heath Forest by weeding out diseased vegetation as well as plant species that won’t survive fire over the long term.
Ecobit: Fire—Rising From the Ashes
In these hilltop natural communities, the predominance of species that respond well to fire indicates that repeated fires were likely an important natural disturbance here historically. Lightning strikes often start fires. Once started, fire tends to move upslope in dry areas and run along ridgelines.1
Floods
Flooding is a natural disturbance that is important for maintaining the Rich Floodplain Forest. This community’s species, such as American sycamore and box-elder, thrive through frequent flooding that might kill a dry-adapted chestnut oak.
Ecobit: Floods—Rich but Hard to Live With
Canopy Gap Regeneration
A gap in the forest canopy admits sunlight beneficial to young oak saplings.
Photographer: Tom Paradis, courtesy of CUE, NPS. Inset (white oak) – Erin Lunsford Jones.An important natural disturbance in forests is the creation of gaps in the canopy when large trees fall due to diseases or storms. Seedlings and saplings on the forest floor take advantage of the newly available sunlight to grow and join the canopy.
Ecobit: Canopy Gaps—Room to Grow
Herbivory
Herbivory is the consumption of plants by animals (including insects). It's an important part of what keeps plant populations at Harpers Ferry NHP from exploding! What would the park look like if every single seed produced there grew up to be a full-sized plant?
Ecobit: Herbivory—A Balanced Diet
Erosion and Sediment Transport
In Harpers Ferry NHP, erosion and sedimentation are most evident in the natural communities that grow in silt, sand, and rocks right along the shores and in the channels of the Potomac and Shenandoah rivers. These accumulations of sediments are called depositional bars because they are deposited by rivers. Floods or high water can change these bars overnight—either eating away at them or depositing a new load of sediment. Needless to say, this creates challenges for plants. You’re not likely to see large trees in this environment, because floods usually wash saplings away before they can mature. American water-willow, a low flowering plant that flourishes on depositional bars covered with running water, holds fast with a dense mat of roots woven under and around the rocks.
Sediments move around in other parts of the park as well. Sediments and soil creep or slide downslope over time, leading to thinner soils on steep slopes and thicker soils on flatter or concave landforms.
Ecobit: Erosion and Sediment Transport—Earth in Motion
Processes Affecting Soils
Many natural processes in Harpers Ferry NHP interact to determine soil characteristics, such as depth, moisture content, composition, and texture. These characteristics, in turn, determine where different natural communities can be found.
Ecobit: Soil Processes—Creating a Place to Take Root
Soil moisture is an obvious factor in determining what plants can grow where. On ridgetops and upper slopes in Harpers Ferry NHP, exposure to sun and wind create dry soils. These support the Chestnut Oak Forest and Dry Chestnut Oak - Northern Red Oak / Heath Forest.
The Rich Cove / Mesic Slope Forest, on the other hand, grows in soil that is mesic—not too wet, not too dry. Mesic soils tend to be found in areas protected from extremes in climate, such as lower slopes and rolling uplands. Another community, the Rich Cove Forest, also occurs on mesic soils.
In the lowest elevations of the park, along the Potomac and Shenandoah rivers, you’ll find natural communities growing in soils that can be quite wet, with the moisture being supplied by floods. There are many communities in Harpers Ferry NHP that thrive in saturated soil, including the Silver Maple Floodplain Forest and the Rich Floodplain Forest.
The depth of soil varies across the park as well. Neither the Sweet Birch - Chestnut Oak Talus Woodland nor the Subcalcareous Cliff & Rock Outcrop have much soil at all. Plants grow in crevices between rock pieces (talus) or cracks in rock outcrops, where their roots can find a bit of soil and moisture. The Rich Cove Forest on the other hand, has deep soil that’s accumulated in concave slopes. These soils are relatively rich compared to most other soils in the park, with good amounts of calcium and magnesium.
The Water Cycle
Harpers Ferry NHP’s rivers, tributaries, and groundwater are all part of the water cycle, which plays a central role in the park’s natural communities.
Natural communities on depositional bars or floodplains depend on a steady source of water from the rivers. Less water moves through the high and dry Chestnut Oak - Virginia Pine Woodland and Basic Woodland, and that water comes in the form of precipitation rather than flooding or groundwater.
Groundwater that seeps out of hillsides in coves or low on slopes may lend extra moisture and nutrients to communities such as the Rich Cove Forest, or the Limestone Oak - Hickory Forest.
Ecobit: The Water Cycle—What Goes Around, Comes Around
Forest Succession
Prior to the formation of the park, much of the land in Harpers Ferry NHP was logged for farming, homes and businesses, factories and canals, charcoal manufacture, and for Civil War fortifications and sightlines.
Some of the land is being maintained in a historical state. Other land has been allowed to revert to forest. Many of these forests look like they have always been there, but their composition tells us that they have grown up on sites that were formerly cleared. These are called successional forests.
Successional forests contain clues that can indicate whether the area was logged or whether it experienced more extreme disruption, such as plowing or earth-moving.
Ecobit: Forest Succession—Clues to the Past
Learn about Harper Ferry NHP’s successional forests.
When Natural Processes Are Interrupted
Harpers Ferry NHP deals with stewardship challenges related to several of these natural processes. See Stewardship and Ecological Threats at Harpers Ferry NHP.
- Fire suppression has the unintended consequence of allowing species that are not adapted to fire to move into natural communities that do well at handling fire—such as the Chestnut Oak Forest.
- Development in the region increases the amount of stormwater runoff and water pollution in the rivers. It decreases the amount of groundwater that gets replenished during rain events.
- Population explosions of white-tailed deer and non-native insects such as hemlock woolly adelgid and emerald ash borer can impair the ability of a forest to sustain itself. Read about these threats, in Population Dynamics and Non-Native Invasive Insects.
- Extreme summer or winter storms can create extensive holes in forests (rather than limited canopy gaps). These can end up being back-filled by unwelcome plants. Read about it in Non-Native Invasive Plants.