The Oak-Hickory Ecosystem thrives in areas with proper soil, sunlight, and moisture
What is a Healthy Oak-Hickory Ecosystem?
A healthy oak-hickory ecosystem has oak woodlands spread across southern Indiana on sites with the proper soil, sunlight, and moisture. Gaps in the tree canopy allows filtered sunlight to reach the forest floor. The landscape-scale forests have a diverse mixture of oak, hickory, and other tree species that typically appear in an oak forest. Oak and hickory trees should be found in the upper canopy, and oak and hickory saplings should also be seen at eye level. These forests include a diverse understory of grasses, flowers, and shrubs. This diversity provides habitat for birds and other wildlife. Healthy, thriving forests sequester carbon, and provide clean water, healthy soil, and clean air.
Ecology and History of Oak Ecosystems
Oak-hickory woodlands typically have open canopies; if you look up, you see that 30% to 80% of the sky is covered by the tree tops. Gaps between the tree tops that allow light in, a sparse midstory, and rich plant and animal communities are common in oak-hickory woodlands. They were maintained for thousands of years by Native American burning. Natural disturbance events such as wind and ice storms, tornadoes, and damage caused by massive flocks of Passenger Pigeons also maintained the open canopy nature of the woodlands.
Oak Ecosystem Ecology
Gaps in the canopies allows sunlight to reach the forest floor, resulting in a rich ground layer of grasses, flowers, and shrubs. Mast (acorns) produced by oaks and hickory nuts are a valuable source of wildlife food. These conditions support many woodland and early-successional plant and animal species.
Upland oak species evolved to thrive on harsh sites: dry ridgetops and south- and west-facing slopes that receive many hours of direct sunlight daily. Oaks also have many traits that make them highly tolerant of fire such as thick bark, dense wood, and extensive root systems.
Oak Trees Need Sunlight Regenerate and Thrive
Fire helps oak-hickory stands thrive by reducing competition from other trees. This maintains the open stand structure that allows sunlight to reach the ground.
Oak seedlings require proper amounts of sunlight to grow into the midstory and upper forest canopy. Oak seedlings that remain in dark, shaded understories for several years will not grow well, and ultimately die.
Oak seedlings can resprout after their top is killed from above-ground disturbance, primarily due to stored energy reserves in their well-developed root systems. The regular use of fire by Native Americans allowed fire-adapted species such as oaks to flourish prior to European settlement. As European settlers began to populate eastern North America, they continued to utilize fire to clear crop fields. The regular disturbance to the oak forests helped to maintain them across the landscape. The disturbance that maintained the ecosystem, however, began to decline in the early 1900s.
Threats to the Oak-Hickory Ecosystem
Lack of Disturbance
Policies established in the early 1900s have curbed the use of fire for the past century. This, combined with fewer natural disturbance events, reduces the number of oaks and hickories that are sprouting and growing. As oak and hickory trees mature and die, they are replaced by shade-tolerant and fire-sensitive species such as the maple and beech that are currently found in lower canopy levels in the forest. As beech and maple mature and move into the upper canopies, their branching and leaf structure do not allow sunlight to penetrate to the forest floor. The young oak and hickory trees are no longer receiving the sunlight they need to thrive.
Forest Fragmentation and Loss to Development
Forests are becoming more and more fragmented. Large tracts of forests are being divided and sold, so there are now many owners of the forests across southern Indiana. Some of these forests are converted to homes, and some near urban areas are developed, or converted to roads. Because intact forest tracts are no longer connected across the landscape, there are fewer opportunities for landscape-scale oak-hickory woodlands. Further, wildlife is unable to safely move throughout the fragmented forests, making them vulnerable to predators.
Non-Native Invasive Species
Non-native, invasive species also pose a threat to Oak-Hickory Ecosystems. Invasive plants, which often escape from landscaping, compete for sunlight and water resources in a forest. Non-native plants tend to grow quickly, green up earlier in the spring, and stay green later in the fall, which makes them dominate our natural areas and crowd out the native species. Removing non-native, invasive plants is expensive and time-consuming but needs to be done to preserve our Oak-Hickory Ecosystems.
Pathogens and non-native insects also threaten Indiana woodlands. Oak shot hole leaf miner (an insect), anthracnose and oak wilt, caused by fungus infestations, and over-mature forest stands result in defoliation and possibly mortality in the forest. And when there is a combination of stressors, such as a drought in addition to insect or pathogen infestations, this accelerates the decline of oaks in our woodlands.
Our Vision for the Future
A key component of the LSSI strategy for restoring and maintaining functional oak-hickory ecosystems in southern Indiana is working with our partners in focal areas called Forest Stewardship Collaboratives (FSC). Working together, we can manage large, intact blocks of forest and woodland. No single landowner, public or private, can accomplish this goal on their own; it will take the collaboration of public, private, and non-governmental organization (NGO) landowners to make a true large-scale, long-term difference. Also, the LSSI Indiana partnership cannot effectively address the decline of oak-hickory woodlands across all of southern Indiana. Therefore, the 13 Forest Stewardship Collaboratives were designated in which voluntary, cross-boundary, landscape-scale collaborative management efforts will take place.