Succession
Succession, broadly defined, is the progressive shift in floristic composition of ecological communities over time. In the context of bog turtle habitat, succession occurs as the gradual shift from herbaceous (typically graminoid) communities to those that are woody-dominant, i.e. sedge meadow ---> hardwood swamp. Bog turtle habitat was once classified as “early-successional,” following the premise that it represents the youngest phase of an inexorable progression of discrete floristic communities that culminate in a “climax” forest. Today, ecologists concur that changes in vegetation overtime conform less to a linear, predetermined process; but rather, the occurrence and/or abundance of a species or community is mediated by a variety of ecological and environmental factors. Take for instance rich fens, which are calcareous, sedge wetlands favored by bog turtles in the northern portions of its range. The calcium, which is carried into the wetland by groundwater flowing through carbonate bedrock or till, immobilizes phosphorous and thus limits the fertility of the soil. Other than calcicolous shrubs like shrubby cinquefoil (Dasiphora fruticosa), woody plants are sparse or occur as stunted, gnarled forms in rich calcareous fens. Left unadulterated, rich fens can remain ecologically stable for thousands of years; however, even minor hydrological impacts (e.g., reduced groundwater recharge) or nutrient enrichment (e.g., farm run-off) can tip the balance of nutrient availability, favoring woody plants and facilitating a rapid successional shift in floristic structure.
Throughout the range of the bog turtle, woody succession is a persistent and pervasive threat, precipitated (and oftentimes accelerated) by cultural eutrophication, urbanization, and anthropogenic impacts. Techniques for staving off woody succession are relatively straightforward and highly effective. Over the past two decades, hundreds of acres of woody-encroached bog turtle habitat under NRCS easements and other federal/state programs have been cut, chemically-treated, and grazed, conveying enormous benefits to bog turtles. Nevertheless, in most efforts, the underlying factors driving woody succession are either overlooked or are too complex to be remedied, necessitating a vigilant, long-term commitment to the control of woody vegetation.
In the absence of anthropogenic disturbance, bog turtle habitats generally have a natural resilience to rapid woody succession conferred by perennially high water tables and, in calcareous regions, soil chemistry. Improving wetland water quality through treating or redirecting run-off, protecting groundwater recharge areas to maintain water tables, reversing hydrological modifications (e.g. ditches, tile drains, livestock ponds), and promoting sustainable agricultural and urban land use practices can dramatically improve and/or restore this resilience and provide greater long-term habitat stability for bog turtles. - Jason Tesauro, March 2020
