Florida Peninsula Inland Scrub

This system appears in many forms, but generally consists of xeromorphic shrub vegetation (mostly evergreen oak species) with or without an emergent overstory of Pinus clausa. The shrubs can be very thick in places, but usually there are open patches. Ground cover is always sparse, and bare soil patches are typically evident. It is found on a sequence of sand ridges and ancient dune fields which are oriented essentially north-south in the Florida Peninsula. The appearance, floristics, and boundary of Florida scrub may contrast dramatically with the "high pine" or sandhill vegetation which is often adjacent, although lack of fire can blur these boundaries.

This system is dominated by xeromorphic, evergreen shrub species with or without an emergent layer of Pinus clausa. The shrub layer composition is relatively constant, as is the abundance of individual species. Quercus myrtifolia, Quercus inopina, Serenoa repens, Quercus geminata, Quercus chapmanii, Lyonia ferruginea, and Ceratiola ericoides are the most important species. Myers (1990) indicates that much of the variability in Florida scrub is due to variation in fire-return interval, ranging from once every 10 to 100 years. Ground cover is always sparse but typically includes Licania michauxii, Rhynchospora megalocarpa, Andropogon floridanus, and a variety of lichens (Cladonia species). There are a number of endemic plant species which may occur in inland Florida scrubs, including at least 13 federally listed species; many of the rarest scrub species are found only in the Lake Wales region.

This system has long been noted for its unique and interesting vegetation by authors such as Vignoles (1823), Harper (1914), Mulvania (1931), Kurz (1942), and Laessle (1958, 1968). More recent treatments by Myers (1990) and Menges (1999) have provided the most comprehensive summaries of scrub available. According to Harper (1927), "the nearly pure white sand of the ground surface, when viewed from a short distance, gives the impression of a thin rift of wind-driven snow. The vegetation is mostly dwarfed, gnarled and crooked, and presents a tangled, scraggly aspect." The appearance, floristics, and boundary of Florida scrub contrast dramatically with the "high pine" or sandhill vegetation which is often adjacent (Laessle 1968), although lack of fire can blur these boundaries. Scrub generally consists of xeromorphic shrub vegetation, such as evergreen Ceratiola ericoides, Lyonia spp., Quercus spp., Sabal etonia, Sabal palmetto, and Serenoa repens, with or without an emergent overstory of Pinus clausa.

This system is restricted to a sequence of north/south-trending sand ridges, ancient dune fields, and former shorelines in the Florida peninsula. The largest inland scrub is found in two primary areas, essentially isolated from one another. The so called "Big Scrub" of the Ocala National Forest is the largest expanse of this system, with a somewhat smaller, more southerly area associated with the Lake Wales Ridge. According to Myers (1990), inland scrub occurs on Quartzipsamments which are excessively well-drained, nearly pure siliceous sands low in nutrients. Although all scrub soils are Entisols, there is considerable variation in soil color. This color variation appears to be related to the amount of leaching which has taken place, and appears to be related to the amount of time a site has been occupied by scrub vegetation. Excessive leaching, due to inferred long occupation by scrub vegetation, is believed to bleach upper soil horizons and develop pure white soils (such as the St. Lucie series), while moderate leaching, due to shorter occupation by scrub, contributes to less bleaching and consequently more yellow-colored soils (Paola and Orsino series).

Florida scrub is a pyrogenic system with floral and faunal components adapted to fire. Unlike most ecological systems of the Gulf and Atlantic coastal plains, this system is maintained by high-intensity, infrequent fires. Litter-fall rates are high, while turnover rates are low, contributing to fuel buildup (Lugo and Zucca 1983, Schmalzer and Hinkle 1996). However, scrub typically lacks fine-textured fuels necessary to ignite fires; most scrub fires ignite in other adjacent ecological systems. If fire spreads into scrub it is often under severe conditions of high wind, low humidity, and low fuel moisture. When fires occur in scrub they can be stand-replacing events. Pinus clausa, if present, is killed outright but may regenerate from seed released from serotinous cones. In parts of fires that burn completely, the shrub layer is typically killed back to ground layer but rapidly resprouts and returns to prefire levels of cover (Abrahamson 1984, Schmalzer and Hinkle 1992b). Other species such as Ceratiola ericoides may regenerate from seeds stored in soil (Johnson 1982). Eryngium cuneifolium and Dicerandra christmanii are narrowly endemic herb species which exhibit peaks in survival, recruitment, and density after fire (Menges 1999, Menges et al. 1999, Menges and Quintana-Ascencio 2004). Many scrub fires burn heterogeneously with resulting patches of unburned fuels. This gap dynamics can be significant (Weekley and Menges 2003), especially in the most xeric types like rosemary scrub (Menges 1994). In the sustained absence of fire, smaller shrubs and herbs may be lost as a consequence of increasing dominance of oak stems (Menges et al. 1993).

This system has likely persisted on fossil dunes since the Pleistocene (Laessle 1968), but remaining examples are merely remnants of an ecosystem once expansive in the late Pleistocene (Myers 1990). The stature and appearance of Florida scrub may be due primarily to nutrient-poor soils, to which many of the scrub species have adapted evergreen habits (Monk 1966). Drought stress is most likely during winter and early spring, but frequent fog during these periods may ameliorate such conditions (Menges 1994). Surprisingly, given the excessively well-drained soils, drought stress may not be an important ecological factor except to limit seedling establishment (Myers 1987, 1990).

Lack of fire is a big threat to Florida scrub ecosystems. Threats also include the loss of habitat to agriculture, commercial and residential development, and fragmentation of remaining Florida scrub habitat by roads and development (Weekley et al. 2008). These threats limit prescribed burning due to urban interface, safety and smoke management concerns. Since Florida scrub burns at high intensity, the use of prescribed fire on land which includes urban interface is especially difficult. Invasive exotic plant species are threats, but due to the very dry and low-nutrient coarse sand soils, invasive plant threats are less than in certain other habitats in Florida. Conversion to intensively managed pine plantations, citrus, and pasture has been a threat. By 1990, the scrubs of the Lake Wales Ridge were nearly gone (Myers 1990, Weekley et al. 2008). Scrub has been protected at numerous sites, but management with prescribed fire is difficult, so many are still threatened with lack of fire. The extensive scrub on Ocala National Forest is managed in blocks clearcut for pulpwood, in a manner which attempts to mimic the natural dynamics of a patch mosaic of disturbance (Myers 1990). Mechanical treatments (including logging, mowing and roller-chopping) and herbicides have been used to reduce woody vegetation in scrubs, but these should be used in conjunction with fire if possible. These methods may be useful to prepare sites for prescribed fire, which otherwise would not be possible due to very high fuel buildup (Menges and Gordon 2010).

This system is endemic to the Florida Peninsula. It is most common in two discrete islands or patches, the Big Scrub of Ocala and the Lake Wales Ridge, which is now highly fragmented and mostly lost to agriculture and development (Weekley et al. 2008).