Disturbance and Diversity

Patterns of natural disturbance are vital in understanding the distribution of species and habitats on the landscape. Numerous birds, invertebrates, and other species depend on habitats shaped and maintained by disturbance, including early successional habitats, floodplains, coastal systems, and fire-maintained systems. These periodic disturbances create habitat heterogeneity, promote species diversity, and alter plant species composition. Restoration of historic natural disturbance regimes that our native wildlife evolved with should be a high priority. However, research suggests that restoration of plant species diversity via these disturbance regimes may not be effective without concurrent reduction in herbivore browse levels (Nuttle et al. 2013, Thomas-Van Gundy et al. 2014). 

Fire 

The Mean Fire Return Interval (MFRI) layer of LANDFIRE quantifies the average period between fires under the presumed historical fire regime. Using this vegetation-based fire return interval model, much of Delaware falls within a fire return interval range of 36-100 years, with large areas of coastal marsh and maritime forest and shrubland falling within a short (0-5 year) interval (LANDFIRE 2016). Data from the Mid-Atlantic region on historic fire regimes based on dendrochronological studies indicates an even shorter historical fire regime, with estimates of fire frequency in oak-dominated forests in the region ranging from 7-30 years (Abrams 2000; Lorimer 2001). Cessation of major fire began after 1900 and brought a concurrent decrease in oak recruitment (Abrams 2000). 

DNREC’s Division of Fish and Wildlife has developed a prescribed fire program, working on both state wildlife area lands and the private lands of conservation partners, to restore habitat critical to the survival of multiple SGCN, including the Northern Bobwhite. The Delaware Forest Service operates a prescribed fire program to help landowners manage their lands. While many prescribed burns are still conducted on the Coastal Plain, fire as a grassland management tool has only recently returned to the Delaware Piedmont.  

Inland Flooding, Wind, and Ice 

Windthrow and other natural disturbance events that fell trees in forested areas are important for maintaining heterogeneity at a small to medium scale in forested habitats. Since Delaware’s forests are all relatively young, the rate of tree mortality due to senescence is low, and thus the role of disturbance events may be of even greater importance than in an older forest. 

Inland flooding events help to create early successional habitat in dynamic riparian systems, and flooding, along with ice scour, is important in maintaining key riparian microhabitats like cobble bars and shrub thickets. 

Beaver-created wetlands were an important source of disturbance on the landscape in pre-settlement times. Beaver dams created pools in low-gradient streams, generating habitat heterogeneity for fish and other aquatic organisms, at the same time creating emergent freshwater floodplain wetlands used by many species of wildlife. The North American Beaver (Castor canadensis) appeared extirpated from Delaware by the mid-1800s. It was reintroduced to the state in 1935 with the release of 1 pair in each county. Since then, additional animals have moved in from Maryland. By the mid-1980s, the beaver was beginning to come into conflict with humans, primarily because of road and field flooding and destruction of trees. In 1990, DNREC’s Division of Fish and Wildlife captured and relocated 28 beavers in Sussex and southern Kent Counties. A 1991 survey of beaver colonies found 126 statewide. There is an active program to trap and remove beavers from areas where they are causing conflicts. From 2015-2025, approximately 170 beaver per year were harvested statewide (DNREC 2025).  

Beaver-created wetlands were once a driving force of Delaware’s landscape

Coastal Flooding and Coastal Storms 

Hurricanes, nor’easters, and other coastal storm events are important in shaping Delaware’s wildlife habitats. Severe coastal weather has affected both coastal landforms and the position of the shoreline itself. In the last 10,000 years, the overall trend for the sandy coastline has been westward retreat. 

Hurricanes are more powerful than coastal storms, but the latter are more frequent in Delaware. While hurricane season generally runs from June through November, coastal storms can occur at any time of year, but are most common between fall and early spring. Storm surge, strong winds, and torrential rainfall associated with these storms can cause extensive flooding and coastal erosion.    

Related Topics:  draft