Harris County’s Historic Ecosystems

By John Carey, Park Naturalist

A visit to Harris County’s natural areas often reveals forests thick with vines, underbrush, and bushes. If it weren’t for trails, most hikers couldn’t travel more than a few yards.

These forests weren’t always so dense.

More than a century ago, Spanish explorers could ride horses for miles through our natural areas and prairies. Nearly 70% of the Harris County area was open grasslands and prairies in 1491. The impenetrable thickets that blanket the region’s forests today result from our attempts to quash a natural phenomenon: wildfire.

In the past, wildfires affected area forests once every five to seven years and the expansive coastal prairies every three to four years. Fires cleared out shrubby understory plants, allowing sunlight to reach the forest floor, spurring a resurgence of diverse new vegetation below. These forests featured lush, open understories interspersed by a few large, mature trees. In this environment, lush prairies of native wildflowers and grasses thrived.

Unfortunately, invasive species like Chinese tallow tree, Japanese climbing fern, grass carp, European starlings, and others have taken over our natural areas. The reason invasive plant and animal species are so harmful is that they reproduce rapidly and have few or no natural predators. Whether plant or animal, an overpopulation of anything that out-competes native organisms is detrimental.

Overdevelopment and habitat fragmentation also threaten our natural areas. When we build concrete jungles or grassy agricultural fields, we create ecologically barren zones that rob native plants and animals of valuable resources.

Habitat fragmentation happens when highways, power lines, or any other human-made barriers divide the land, cutting animals off from resources. Many species like the iconic American bison and mountain lion require large unbroken expanses of pristine habitat to roam. Even preserves with acres of quality habitat can be useless to some animals if they don’t have enough space to complete their life cycle.

There is hope, though. Jones Park continues to restore the land to its original ecosystem, and every day we see that vision move closer to reality. The Spring Creek Greenway stretches farther and farther each year, creating a lush, green bastion of Houston’s historic wilderness.