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Restoring Prairies, Savannas, and Woodlands With Fire

Arkansas Natural Heritage Commission - Friday, October 04, 2019
by Theo Witsell

The specific effects of fire depend largely on the intensity and also the timing, or seasonality, of a particular burn. Stand replacement fires, intense fires that move through the tree canopy, can drastically alter ecosystems. In contrast, relatively “cool” (moderately intense) fires may creep through the understory with flames a few inches high, killing the aboveground portion of small shrubs and trees, and consuming leaf litter.

Plants that are actively growing at the time of a burn will be harmed or reduced, and plants that are dormant during the time of a burn generally benefit. Fires in the late summer, fall, or dormant season (winter) generally benefit spring and early summer (“cool season”) grasses and wildflowers. Fires in the spring, when early season plants are actively growing, do the opposite, reducing the number of these plants and favoring summer and fall (“warm season”) grasses and some wildflowers. Which kind of fire is desired depends on the management objectives at a particular site.

The results following a burn can be dramatic. Species that were uncommon before a burn can suddenly become common, and species that were not detected at all may suddenly appear, sometimes in great numbers. Before the fire, these species were likely present in the seedbank, or perhaps barely hanging on – such as a single small leaf getting just enough light to keep the plant alive, but not enough to flower and reproduce. Under the right conditions, this sort of response can be seen following a single burn, though these sorts of results may take several burns (in the proper season) to achieve.

Once fire is reintroduced to a forest or woodland, it allows more light to reach the ground, which is good for most plants. This, in turn, stimulates herbaceous plant growth, increasing the fuel for the next fire. This could cause the next fire to be more intense, allowing even more light to penetrate, stimulating even more herbaceous plant growth, and so on.

If fire is excluded for a long enough period (just a few years in some cases), the woody plants will again become dense, the herbaceous plants will decline, and low-intensity fuels (like leaf litter) will dominate. It should also be noted that when the trees and shrubs reach a certain density, fire alone would likely not be effective in restoring it to woodland or savanna conditions. For example, an Ozark glade that has been completely overgrown with cedars for decades will not support a fire hot enough to kill the cedars and begin the cycle of reopening the glade. In cases like this, a certain percentage of the cedars (or other trees) will have to be mechanically removed to allow the herbaceous fuels to build back up to a level where fire can work its magic. See Prairies, Glades, and Barrens: Rare Habitats for Rare Species and Restoring Shale Glades at Middle Fork Barrens.

Wildlife Benefits of Fire


The benefits of fire to the native wildlife can also be dramatic. A burned system has more herbaceous cover, which is good for many animal species. There are more flowering plants, so butterflies and other nectar feeding insects have more food, which means more insects for other wildlife to eat. With more flowers, there are more fruits and seeds, which feed wildlife dependent on those resources. Quail, and other grassland bird species (many of which are in decline), need these insects and seeds, as well as an open to shrubby habitat structure. Specialist insects (including many butterflies and moths) need specific grassland plants to survive and will benefit from larger numbers of host plants.

There are legitimate concerns that burning an entire isolated prairie or savanna remnant at one time will harm many insects and other animals. This can be avoided by leaving sizable portions of the area out of the burn unit in order to provide refuge for these animals, which will then recolonize the burned areas the following year, reaping the benefits of increased flowering, seed set, and plant vigor.

Photos:

Top - Prescribed burn at Downs Prairie Natural Area. 

Middle - Prairie gayfeather at Cherokee Prairie Natural Area.

Bottom - Pipevine swallowtail at Devil's Knob-Devil's Backbone Natural Area.



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