News and ResourcesFrom Field to Forest - February 5, 2017
From Field to Forest
A disused farm field, an abandoned golf course, a deserted back or side yard; nature has a way of reclaiming areas abandoned by humans, turning old fields, farms and other plots of land back into forests and scrubland.
When an abandoned field remains unused by humans for an extended period of time it starts to undergo natural succession. Natural succession is the change in the species structure, both flora and fauna, of an ecological community over time. Succession is a slow process and can take years, decades, and even millennia to happen, but it is constantly changing the face of our planet. Succession can turn marshes to fields, fields to forests, forests back to fields and much more. One form of succession seen frequently on the Eastern Shore is old field succession.
When a field is abandoned, it represents a new habitat for plant and animal species to colonize. Depending on the size and location of the field, it can be a great habitat for flora and fauna however there are many natural stressors. Due to the lack of trees, there are few shaded areas and no windbreakers to stop prevailing winds, which puts stress on the exposed plants and causes higher evaporation rates, amongst other things. That being said, the plants that can survive the constant sunlight and wind have plenty of light and nutrients available to grow.
This demanding environment is first colonized by a group of species called pioneer species. Pioneer species usually have long-lived seeds that can stay dormant for years in the soil, as well as having long-range dispersal. Pioneer species also utilize resources rapidly, allowing for quick growth and reproduction. Many pioneer species are what we would call weeds, such as ragweed, crabgrass, and foxtail. As the pioneer species die, dead plant material accumulates on the soil and retains moisture in the soil, changing the local environment.
This first stage of succession by pioneer species consists of a relatively few species of herbs, most of which are annuals. Species diversity at this point is relatively low, and most of the plants are herbaceous. This community lacks vertical structural complexity and provides only a few types of habitats for animal species.
After around three to ten years, perennial grasses and herbs, like goldenrod, gradually replace the pioneer species. The perennial herbs outcompete the pioneer species, which are unable to germinate and grow under the shaded perennial cover. As perennial grasses and herbs replace the pioneer species, species diversity increases, but most of the plants are still herbaceous and there is not much vertical structural diversity.
After about ten years shrubs begin to take over. Early in this stage the field will be a mixture of perennial grasses and small shrubs, like sumacs, bayberry, spicebush, and multiflora rose. As the shrubs grow they shade the ground and many of the shade-intolerant perennial grasses and herbs die off, turning the field into a nearly uninterrupted growth of tall shrubs. Vines such as poison ivy, Virginia creeper, and Japanese honey suckle may also be present. As the shrubs begin to grow, both vertical structural complexity and species diversity increase as the mixture of shrubs and herbaceous plants create diverse habitat and food sources for animals.
Eventually shade-tolerant tree seedlings begin to sprout among the shrubs. As the seedlings grow, the field will become a mixture of shrubs and young trees, and will begin to resemble a typical forest. As the trees begin to reach their maximum size, they shade out the shrubs beneath, killing off shade-intolerant shrub species. As the forest matures, other shade-tolerant shrubs will grow beneath the canopy; maple leaf viburnum and flowering dogwood are common examples.
In the final stage of succession, the mature forest, species diversity and vertical structural complexity reach their peak. Forest structure is distinctly layered into the uppermost canopy, the sub-canopy, a shrub layer, an herbaceous plant layer and a litter layer. The plant species that make up the layers beneath the canopy are shade-tolerant species, since most of the sunlight is blocked by the canopy. The diversity of habitats available is greatest in a mature forest due to the number of different species and vertical forest layers.
Succession is a continuous process and does not always proceed in neat stages. It is possible to find annuals like ragweed and perennial grasses growing near each other or notice that different parts of the same old field appear to be at different stages of succession.
Disturbances, like fire or a fallen tree, can change what stages of succession the field or forest is in. A fire may not destroy all the vegetation in an area, but it may create an opening that allows pioneer species to successfully reproduce, maintaining the site at an earlier stage of succession. Succession will also occur in gaps in the canopy from fallen trees; when a tree falls, it creates an opening in the canopy so more sunlight makes its way to the layers below, allowing other shade-intolerant species to grow.
Natural succession is a never-ending cycle that is constantly changing the face of our planet. The more we learn about natural succession, the more we understand about our local environments and the crucial roles each successional stage plays in the health of our ecosystem.
Jackson is the former Education Coordinator for the Maryland Coastal Bays Program and current graduate student at Clemson University.
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