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Oconee Mafic Communities

Oconee Mafic Communities

Approximate size: 7,404 acres
Old-growth known: 0 acres

Felsic rocks high in silicon, such as granite-gneiss, dominate the geology of the Oconee National Forest (ONF). However, mafic rocks high in iron and magnesium, such as gabbro, underlie a significant fraction of the ONF. They weather into nutrient rich and relatively high pH soils that support a distinct suite of plant species. These areas often stand out as islands of hardwood forests in a sea of pines. Many of the showiest spring wildflower reach their greatest abundance on mafic soils, including spring beauty, trilliums, and atamasco lily.

Different combinations of bedrock, topography, and weathering result in at least three distinct mafic communities: mafic knobs, bottomlands, and Monticello glades. Small rocky mafic knobs or outcrops of one to several acres are shaded by not only calcium-demanding species such as Shumard oak and southern shagbark hickory, but also drysite and fire-adapted species such as blackjack oak and post oak. Burgess Mountain in Putnam County is a particularly large, topographically distinct example of a mafic knob.

Extensive mafic bottomlands and adjacent slopes are also found on the ONF along Rock Creek in Putnam County, portions of the Ocmulgee River in Jasper County, and steep slopes along Lake Oconee in Greene County. In these stands, Shumard oak and slippery elm mix with more typical bottomland species such as sweetgum and sugarberry.

Monticello Glades south of Monticello include “globally imperiled” upland gabbro depression forests. Resting on impermeable hardpans formed by mafic Iredell soils, the Glades are paradoxically upland wetlands. Their perched water tables support a mix of bottomland species such as willow oak, dwarf palmetto, supplejack, and the rare Oglethorpe oak.

Some mafic soils are very fertile, which has led to them being disproportionately in private ownership and in agriculture. Of the fraction on the ONF, only a small portion are currently in management categories that recognize their uniqueness and need for special management consideration. Yet nearly all the populations of rare plant species known from the ONF occur on mafic soils. A thorough botanical survey of the ONF is sorely needed to effectively manage and protect its diversity. For example, a very large population of the federally endangered relict trillium was found only by accident within the last decade.

Help us protect this 16,000-acre oasis of waterfalls, old-growth, rare species, panoramic views, and world-class trails.

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