The Roles of Fire and Water As Major Determinants of Habitat Types in SW FL

In many parts of Florida fire is considered to be the major factor that determines the types of habitats that county, state and federal land managers hope to maintain. While there is some truth to this notion, what many fail to acknowledge is that fire dominated habitats are not the natural climax forest and that other factors, such as water, can be equally important in many contexts. My reason for bringing this up is to describe a situation in Myakka State Park along High Fox Rd/Trail where the FNPS had a nature walk on March 8, 2024. It illustrates very well the strong interaction of water with fire in determining the community structure of “dry prairies” and adjacent habitats. Perhaps the very name of dry prairie is part of the problem in understanding what prevents saw palmettos from dominating dry prairies. “Dry” is a misnomer since it is likely that historically these areas were under shallow water for some months. The dogmatic view is that a diminished fire regime within the past century is responsible. I believe that diminished amounts of surface and ground water are also very important.

As you enter the forest at High Fox Rd you will note that the woodland is primarily a secondary climax type- mainly live and laurel oaks, red maples, and cabbage palms with some very large slash pines. The mature pines tell us that when they were saplings, the area was open with lots of sunlight since young slash pines are relatively shade intolerant. It is also clear that the area is fairly wet since some laurel oaks (more tolerant to water than live oaks) have basal buttresses (the better to support the tree in wet ground which reduces underground roots), and “lichen lines” at 2-3 feet showing where seasonally high water levels lie.

As we walk through the climax forest we pass a recent burn and enter the dry prairie with interspersed wetlands. Some areas of the prairie have sparse palmettos and others have a greater density. We then enter an oak “flow way” or strand and follow this down hill to Clay Gully Creek. Parts of this strand are wetter than others based on elevation and in the lowest areas some large laurel oaks have been blown down most likely by the hurricane of September, 2022. The higher water tables in these areas have truncated the roots providing a less stable base for these heavy trees. A decided recent change in oak species present in this flow way is a loss of mature live oaks being replaced by laurel oaks. This may be occurring due to an increased surface flow killing the live oaks which are being replaced gradually by laurel oaks which are more resistant to higher levels of ground water. The elevated lichen lines illustrate such high but likely transient water levels. I cannot be sure but think this effect may be due to increased runoff from higher ground in the prairies. The scouring of a key seasonal pathway for water flow from the large prairie watershed above indicates the high and temporary nature of this flow.

It is also noticeable that In the bottom of the valley Clay Gully Creek flows with very dark clear waters down to the Myakka River. There are no sand banks along the creek. There are flotsam debris accumulations several feet up in the streamside willows, which lack any adventitious roots. The blackwater is an indicator of very low nutrient levels in the predominantly sandy watershed resulting in the production of tannins by the plants to reduce insect herbivory.

Lacking a time machine we can examine historic aerial photographs to gain some information on the vegetation within the last 83 years. For example look at the aerial from 1940. It shows an open “dry prairie” with few small bushes (likely palmettos), dark circular wetlands lacking much surface vegetation, and very distinct sand banks along the creek due to seasonally high water flows. In comparison look at the aerial from 1948. Already the prairies have more bushes (likely mainly palmettos), the circular wetlands show lighter colored vegetation due probably to lower water levels, trees are invading the prairies from the edges, and the creek has few or no sand banks due to a great reduction in seasonal flow. The lack of adventitious roots on creek side willows indicates that current high water flows (indicated by flotsam) are more temporary and of lesser magnitude than in 1940. Remember that palmetto is strictly an UPLAND species that is used to delineate the upper edges of wetlands. Then you will understand that palmettos in 1940 were thus limited from invading wetlands. These wetlands are being severely reduced by 1948, due to channelization and redirection of water flows and groundwater pumping. Consider how Flatford Swamp nearby on the Myakka River has been so flooded by pumping of water out of farm fields that the trees have died. So my hypothesis is that a combination of less fire (and at the incorrect time of year- winter instead of normal summer burns) and less water have resulted in an environment where palmettos thrive in dry prairies. The significant loss of groundwater and seasonal decrease in quantity and timing of surface water flow have made a major contribution to the difficulty of controlling palmettos in dry prairies.

Some flowers we encountered during this early March walk were interesting. In particular we found a rarely seen bush snowbell, Styrax, along the entry road in the secondary climax forest. Carolina jessamine vines were in full bloom. Blue flag iris were just starting to bloom in the edges of shallow wetlands. Paw paw flowers were present on mostly leafless shrubs. Pop ash leaves were just emerging on plants along the creek. We also encountered a bright “dog vomit” slime mold on the damp organic matter suitable for its saprophytic habits.

A dragonfly that was common along the pathways was the Carolina saddlebags. Not so wild turkeys are a common sight along the roadways of the park where they have become fairly used to people.

The overwhelming feeling you have while walking in this area of High Fox Rd is a remarkable quiet and separation from the hectic pace and noise of civilization ! But if you feel like exercising your brain in reconstructing what this area looked like 83 years ago when the 1940 aerial was taken, it is remarkable how much things have changed. The genesis of this change apparently started between 1940 and 1948. Consider my hypothesis that it is not only a change in the fire regime but a major shift in the amount and timing/duration of surface and ground waters that have disrupted the ecology of the dry prairies and other plant communities in the area.

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