| Florida scrub | |
|---|---|
 | |
 | |
| Ecology | |
| Realm | Nearctic |
| Biome | Temperate coniferous forest |
| Borders | Southeastern conifer forests |
| Bird species | 173[1][dead link] |
| Mammal species | 43[1][dead link] |
| Geography | |
| Area | 3,900 km2 (1,500 sq mi) |
| Country | United States (Florida) |
| Climate type | Humid subtropical (Cfa) |
| Conservation | |
| Conservation status | Critical/endangered[3] |
| Global 200 | No[4] |
| Habitat loss | Lake Wales Ridge: 85% Peninsula coasts: 90%[2] |
| Protected | 34.94%[1][dead link] |
Florida scrub is aforestecoregion found throughoutFlorida in the United States. It is found on coastal and inlandsand ridges and is characterized by an evergreenxeromorphic plant community dominated byshrubs and dwarfoaks. Because the low-nutrient sandy soils do not retain moisture, the ecosystem is effectively anarid one.Wildfires infrequently occur in the Florida scrub. Most of the annual rainfall (about 135 cm or 53 in) falls in summer.
The ecosystem is endangered by residential, commercial and agricultural development. The largest remaining block lies in and around theOcala National Forest.Lake Wales Ridge National Wildlife Refuge also holds a high proportion of remaining scrub habitat, while theArchbold Biological Station nearLake Placid contains about 20 km2 (7.7 sq mi) of scrub habitat and sponsors biological research on it.
Florida scrub is a community ofxeromorphic species living on poor, well-drained soil, including some combination ofsand pines,evergreen scrub oaks,Florida rosemary,rusty lyonia, andgallberry.[5] Depending on conditions, scrubs may be dominated bysaw palmetto, rusty lyonia, and gallberry; by Florida rosemary; by sand pines; or by some combination of evergreen oaks, includingsandhill oak,sand live oak,Chapman oak, andmyrtle oak.[6] Independently of the number of sand pines present in a scrub, theshrub layer is consistently dominated by myrtle oak, sandhill oak, saw palmetto, sand live oak, Chapman oak, rusty lyonia and Florida rosemary. Thescrub palmetto may also be present in scrubs on the Florida peninsula. While the shrub layer is usually dominated by oaks of varying density, some scrubs have a shrub layer consisting almost entirely of rosemary.[7]Herbert John Webber noted that the sand pine is the most noticeable plant in large and moderate sized scrubs, but stated that the scrub oaks are probably more important in maintaining the scrub community.[8]
Florida scrub is usually intimately associated with thelongleaf pine sandhill or high pine ecoregion.[9] High pinelands typically consist oflongleaf pines,wiregrass, and other grasses, often with clumps or individual trees of deciduous oaks, such asturkey oak, present.[10]
The term "scrub" may also cover plant communities in Florida called "sand pine scrub", "oak scrub", "rosemary scrub", "slash pine scrub", and "coastal scrub".[11] Intermediate between scrub and associated habitats are "scrubby flatwoods" and "scrubby high pine".[12] Some sub-types of Florida scrub are found outside of Florida. Myers notes that the "evergreen scrub forest" and "dune oak scrub" reported in southeasternGeorgia cannot be distinguished from the oak and rosemary scrubs of Florida.[13]
The Florida scrub is probably descended from thesclerophyllous Madro-Tertiary Geoflora.[a] The geoflora spread along the Gulf of Mexico coast, and was widespread in Florida during the latePleistocene. Near the end of the Pleistocene widespread rosemary scrubs in Florida were replaced byoak savannas, and then by sand pine scrubs. The range of scrubs in Florida contracted over the last 7,000 years as Florida's climate became more moist.[13]
Florida scrub was probably first recognized as a distinct community byCharles Vignoles in 1823, although several naturalists working in the middle of the 19th century still did not do so. Scrub is usually intimately associated with the high pine ecoregion. While the two communities occur on the same poor soil (consisting almost completely of silica sand), they comprise completely different species, and the transition from one community to the other historically (prior to human intervention to suppress wildfire) was abrupt.[15]Marjorie Kinnan Rawlings described the edge of the Big Scrub as "a vast wall, keeping out the timid and the alien."[16]
Webber states that at the end of the 19th century a naturalfirebreak separated scrubs from high pine land. The grasses and other herbaceous plants of high pine land diminished near the boundary with scrub, and did not quite extend to the brush layer of a scrub. The near absence of plants in the transition zone meant that any grass fire that did reach the zone did not have enough intensity to ignite the evergreen plants of the shrub layer of a scrub. Webber observed that in 1935 the natural firebreaks seemed to be weakening, which he attributed to the encroachment of human civilization on the areas where scrubs are found.[17]
Fire in Florida scrub is infrequent but intense, characterized as "catastrophic" or "stand-replacing". Any sand pines in a scrub are killed by such fires, while shrubs burn down to the ground. Fire causes sand pine cones to open and release their seeds to replace the stand. Most shrubs regrow from their roots, while rosemary regrows from seed.[18] As previously noted, the Florida scrub and longleaf pine sandhill (high pine) communities are closely associated, growing on the same types of soil and under very similar conditions. Both communities are shaped by periodic fires, and the frequency and intensity of fires may prevent one community from replacing the other. Longleaf pine sandhill communities experience frequent (typically one to ten year intervals), low-intensity fires that primarily burn grass and otherunderstory plants. Those low-intensity fires do not usually invade neighboring scrub communities. When fires have been suppressed in sandhill communities, sand pines and oaks that are typical of scrub begin invading sandhill. Scrub communities typically experience fires at 15 to 100 year intervals. Fires that occur more frequently than 15 years in scrub can prevent regrowth of sand pines and shrubs (oaks, rosemary, etc.), opening the area to invasion by plants of the sandhill community.[19] Scrubby flatwoods usually burn at 5 to 20 year intervals. Long-term suppression of fire in scrubby flatwoods allows them to develop intoxeric hammocks.[20]
Unlike in longleaf pine sandhills, the ground litter in scrub has a highheat of combustion, and it is not easy for fire to start or move into scrub. Fires may spread into scrub under extreme conditions, such as high wind, low humidity, and low fuel moisture. As a result of the resistance of scrub to fire, scrubs often serve as barriers to the spread of fire.[21]
Most fires in scrub result from the spread of a fire from an adjacent plant community. Scrubs that border less flammable ecosystems are somewhat protected from the spread of fire. On theLake Wales Ridge, scrubs often border or are surrounded by swamps, lakes, streams orbayheads. Along the coasts, scrubs are bordered by the Atlantic Ocean or Gulf of Mexico, and often by inlets, rivers, and swamps. TheBig Scrub of the Ocala National Forest lies between theSt. Johns andOklawaha rivers.[22]
The frequency of fire in scrub depends, in part, on the productivity of the soil. Sites with very poor soil tend to support rosemary scrubs (sometimes called "rosemary balds"), which rarely burn. The death of older rosemary bushes leaves open spots where new rosemary seedlings or sand pine seedlings may start growing. On sites with more productive soil, scrubs persist only if fires occur frequently enough (every 15 to 100 years). If a scrub burns more often than every 15 years, sand pines cannot reseed and the scrub becomes oak-dominated, or converts to high pine. If a scrub goes much longer than 100 years without burning, it begins to develop into axeric woodland.[23]
Damage from tropical cyclones may be more important than fire in maintaining the scrubs on the panhandle coast. As most of the sand pines of the panhandle produce open cones, seeds are released every year and not just after a fire, and the pines in a scrub vary in age, unlike the uniform age of the pines in a given peninsular scrub.[24]
Webber noted that fire in scrubs burns scrub oaks to the ground and kills other plants, including pines. Recovery of a scrub occurs because the scrub oaks have extensive root systems which survive a fire, and which quickly sprout new growth. He observed that in an area of scrub that had burned two years earlier, almost the entire area was covered by a thick 2 to 3 feet (0.61 to 0.91 m) high growth of scrub oaks. Many seedlings of sand pines (6 to 8 inches (150 to 200 mm) high), and of other plants typical of the scrub community, were growing under the oak canopy. The crowded conditions of the early stage of recovery leads to the death (thinning out) of many individual plants, and after a few years the typical scrub community is established.[25]
Rosemary scrubs regenerate after a fire from seeds that have accumulated in the soil. If rosemary scrubs burn less than ten years after a previous fire, it is unlikely that there will be sufficient rosemary seeds available to repopulate the community, and the scrub may be invaded by oaks.[20]
The soils in Florida scrub areentisols, recently developed soils withouthorizons, classified asquartzipsamments. They consist almost entirely of sand, with little to no silt, clay, or organic matter. They are very well-drained, and among the least fertile soils in Florida. The soils range in color from pure white to brown, grey or yellow. Thelitter on the ground in scrubs producesorganic acids which bleach color from sand grains, so that the darkness of soil color to a large degree correlates inversely with the length of time scrub vegetation has been growing on the soil.[11]
About 40 plant species, at least 40 arthropod species, and several vertebrate species are endemic to Florida scrub.[26] As of 1990, 13 endemic plant species were listed by the U.S. as endangered or threatened, and 22 were so listed by the state of Florida.[7]
Plants that are endemic to scrub and "scrubby" communities in Florida[b] and that are listed asendangered by theUnited States Fish and Wildlife Service (USFWS) include:Asimina tetramera (four-petal pawpaw),Chionanthus pygmaeus (pygmy fringetree),Cladonia perforata (Florida perforate cladonia, Florida perforate reindeer lichen),Conradina brevifolia (short-leaved false rosemary),Conradina etonia (Etonia rosemary),Crotalaria avonensis (Avon Park rattlebox, Avon Park harebells, Avon Park rabbit-bells),Dicerandra christmanii (Garrett's mint, yellow scrub balm, Lake Wales balm),Dicerandra cornutissima (longspurred mint, longspurred balm, Robin's mint)Dicerandra frutescens (scrub mint or scrub balm),Dicerandra immaculata (Lakela's mint, Olga's mint, spotless balm),Eryngium cuneifolium (wedgeleaf eryngo, wedge-leaved button-snakeroot, snakeroot),Hypericum cumulicola (Highlands scrub hypericum, Highlands scrub St. John's wort),Liatris ohlingerae (Florida blazing star, Florida gayfeather, scrub blazing star,sandtorch),Lupinus aridorum (scrub lupine),Nolina brittoniana (Britton's beargrass),Senega lewtonii (syn.Polygala lewtonii) (Lewton's polygala, Lewton's milkwort),Polygonum basiramia (syn.Polygonella basiramia) (wireweed, hairy wireweed, purple wireweed, Florida jointweed),Polygonum dentoceras (syn.Polygonella myriophylla) (sandlace, woody wireweed, Small's jointweed),Prunus geniculata (scrub plum),Warea carteri (Carter's pineland cress, Carter's mustard), andPseudoziziphus celata (syn.Ziziphus celata) (Florida jujube, Florida ziziphus).[27][28]
Plants that are endemic to scrub and "scrubby" communities in Florida[b] and that are listed asthreatened by the USFWC include:Bonamia grandiflora (Florida lady's nightcap, Florida bonamia, scrub morning glory),Clitoria fragrans (pigeon wings, sweet-scented pigeon wings),Eriogonum longifolium var.gnaphalifolium (syn.Eriogonum floridanum) (scrub buckwheat), andParonychia chartacea (papery Whitlow-wort, paper nailwort).[27]
Plants that are endemic to scrub and "scrubby" communities in Florida[b] and that are listed as endangered by the State of Florida (but not by the USFWC) include:Bonamia grandiflora (Florida lady's nightcap, Florida bonamia, scrub morning glory),Asclepias curtissii (Curtiss's milkweed),Chamaesyce cumulicola (coastal dune sandmat, sand dune spurge),Clinopodium ashei (syn.Calamintha ashei) (Ashe's savory, Ashe's calamint),Chrysopsis gossypina cruiseana (Cruise's golden aster),Chrysopsis floridana (Florida golden aster),Chrysopsis godfreyi (Godfrey's golden aster),Chrysopsis highlandsensis ((Highlands golden aster),Clitoria fragrans (pigeon wings, sweet-scented pigeon wings),Dicerandra thinicola (Titusville mint),Eriogonum longifolium var.gnaphalifolium (syn.Eriogonum floridanum) (scrub buckwheat),Euphorbia rosescens (scrub spurge),Lechea divaricata (spreading pinweed),Lechea lakelae (Lakela's pinweed),Paronychia chartacea (papery Whitlow-wort, paper nailwort),Rhynchospora megaplumosa (Manatee beaksedge), andSchizachyrium niveum (scrub bluestem).[28]
Plants that are endemic to scrub and "scrubby" communities in Florida[b] and that are listed as threatened by the State of Florida (but not by the USFWS) include:Conradina grandiflora (largeflower false rosemary, large-flowered rosemary),Garberia heterophylla (garberia, Garber's scrub starts),Lechea cernua (nodding pinweed), andPolygonum smallianum (syn.Polygonella macrophylla) (largeleaf jointweed).[28]
Other plants that are endemic to scrub and "scrubby" communities in Florida include:Carya floridana (scrub hickory)Euphorbia c.f.floridana (greater Florida spurge),Garberia heterophylla (garberia, Garber's scrub starts),Crocanthemum nashii (syn.Helianthemum nashii) (Florida scrub frostweed),Persea borbonia humilis (syn.Persea humilis) (silk bay),Pinus clausa (sand pine, Florida spruce pine, scrub pine),Quercus inopina (sandhill oak),Cartrema floridanum (syn.Osmanthus megacarpus) (scrub wild olive),Sabal etonia (scrub palmetto), andSisyrinchium xerophyllum (jeweled blue-eyed grass, Florida blue-eyed grass).([27]
Vertebrates endemic to Florida scrub and related habitats include theFlorida scrub jay (Aphelocoma coerulescens), theFlorida mouse (Podomys floridanus),sand skink (Neoseps reynoldsi),Florida scrub lizard (Sceloporus woodi), Florida worm lizard (Rhineura floridana), bluetail mole skink (Plestiodon egregius lividus), peninsula mole skink (Plestiodon egregius onocrepis),short-tailed snake (Lampropeltis extenuata), Florida scarlet snake (Cemophora coccinea coccinea), andFlorida crowned snake (Tantilla relicta).[29]
Arthropods known to be endemic to Florida scrub include:
TheFlorida scrub millipedes are three species endemic to Florida,Floridobolus floydi,F. orini, andF. penneri.F. penneri, the oldest described species, has been found only in scrubs on theLake Wales Ridge inPolk andHighlands counties.F. orini has been found only in the Big Scrub in Ocala National Forest inMarion County, andF. floydi only in scrubs on the southern part of the Brooksville Ridge inCitrus,Hernando, andPasco counties.[30]
Latrodectus bishopi, the red widow spider, has been found in scrubs on the southern Lake Worth Ridge and in scrubs on theAtlantic Coastal Ridge, but may have a wider distribution. Its webs are commonly found on the leafs of scrub palmettos.Zelotes ocala has been found only in scrubs on the Marion Uplands inAlachua, Marion andPutnam counties, and on the southern Lake Wales Ridge in Highlands County.Zelotes florodes has been found only on the Lake Wales Ridge in Polk and Highlands counties.Geolycosa xera, Mccrone's burrowing wolf spider, has two subspecies:G. xera xera has been found on the Marion Uplands inLake,Orange,Seminole, andVolusia counties and on the Lake Wales Ridge, whileG. xera archboldi has been found only on the southern part of the Lake Wales Ridge.[31]
The wolf spiderSchizocosa ceratiola (commonly calledLycosa ceratiola in scientific literature) has been found on the Mount Dora Ridge in Lake County, on Atlantic Coastal Ridge inMartin andPalm Beach counties, and on the Lake Wales Ridge in Highlands County. Another wolf spider,Hogna pseudoceratiola (often calledLycosa pseudoceratiola in scientific literature) has been found on the Atlantic Coastal Ridge inMiami-Dade, Palm Beach, Martin, andIndian River counties.Hogna ericeticola, the rosemary wolf spider, has been found in rosemary scrubs on the Marion Uplands in Putnam County.Sosippus placidus, theLake Placid funnel wolf spider, has been found on the southern Lake Wales Ridge in Highlands County.[32]
Arenivaga floridensis, the Florida sand cockroach, has been found in coastal scrub inPinellas County, on the Lakeland Ridge in Polk County, and on the Lake Wales Ridge in Polk and Highlands County.Schistocerca ceratiola, the rosemary bird grasshopper, has been found in Florida scrubs on the Orlando Ridge in Orange County, the Mount Dora Ridge in Lake and Orange counties, on the Atlantic Coastal Ridge in Martin county, and on the southern Lake Wales Ridge in Highlands County.Melanoplus indicifer, the east coast scrub grasshopper, has been found only on the Atlantic Coastal Ridge in Palm Beach County.[32]Melanoplus forcipatus, the broad cercus scrub grasshopper, is primarily found in Florida scrub, but also occurs in pine sandhill communities. It has been found on the Mount Dora and Orlando ridges in Orange County and the southern Lake Wales Ridge in Highlands County.Melanoplus tequestae, the tequesta scrub grasshopper, has been found on the Orlando Ridge in Orange and Seminole counties, on the Mount Dora Ridge in Orange County, and on the southern Lake Wales Ridge in Highlands County. The bird louseBrueelia deficiens is found in Florida only on the Florida scrub jay, and so is endemic to the same locations as the scrub jay.B. deficiens has also been reported as occurring on othercorvids in the western United States and Canada.[33][34]
Cicindela highlandensis, the Highlands tiger beetle, has been found only on the southern Lake Wales Ridge. Another tiger beetle,C. scabrosa, has been found on the Crescent City Ridge in Putnam County, the Atlantic Coastal Ridge in Broward County, and the Lake Wales Ridge in Highlands County.[33] The scarab beetlesSerica frosti andAnomala eximia have been found only at theArchbold Biological Station in Highlands County. The June beetlePhyllophaga elizoria has been found on the Atlantic Coastal Ridge in Indian River County and the Lake Wales Ridge in Highlands County. Other scarab beetles of thePhyllophaga genus includeP. elongata, found on the Lake Wales Ridge in Polk and Highlands counties, and in Hillsborough, Lake, Levy, and Marion counties; andP. panorpa andP. okeechobeea, found on the Lake Wales Ridge. Theflower chaferTrigonopeltastes floridanus has been found on the Lake Wales Ridge in Highlands County, the Orlando Ridge in Orange County, the Atlantic Coastal Ridge in Indian River County, the Mount Dora Ridge in Marion County, and the Northern Highlands in Alachua County. The earth-boring scarab beetleMycotrupes pedester has been found inCharlotte,DeSoto, andLee counties.Peltotrupes youngi, Young's deep digger scarab, has been found on the Mount Dora Ridge in Marion and Putnum counties.[35]
At least twodung beetles are endemic to the Florida scrub:Onthophagus aciculatulus has been found only at the Archbold Biological Station, andAtaenius saramari has been found on the Mount Dora Ridge and Sumter Uplands in Marion County, on the Atlantic Coastal Ridge in Martin andSt. Lucie counties, nearSt. Cloud, and on the Lake Wales Ridge in Highlands County. An undescribed dung beetle of thePsammodius genus has been found at the Archbold Biological Station.Aethecerinus hornii has been found in Lee County and on the Lake Wales Ridge in Highlands County. ThefireflyPleotomodes needhami has been found only at the Archbold Biological Station. The fireflyLucidota luteicollis has been found on the Lake Wales Ridge in Highlands and Polk counties, the Mount Dora Ridge in Marion County, and the Brooksville Ridge in Levy County.[36]
The waspDasymutilla archboldi has been found on the Lake Wales Ridge in Highlands and Polk counties.Photomorphus archboldi, the nocturnal scrubvelvet ant, has been found on the Lake Wales Ridge in Highlands County, and the Sumter Upland and the Mount Dora Ridge in Marion County. The antDorymyrmex elegans has been found on the Lake Wales Ridge in Highlands County.[37] The antDorymyrmex flavopectus has been found on the Lake Wales Ridge in Highlands County and the Mount Dora Ridge in Lake and Marion counties. The antOdontomachus clarus has been found on the Lake Wales Ridge in Highlands and Polk counties.O. clarus has also been reported from Mexico and the southwestern U.S. The beeDialictus placidensis has been found nearLake Placid and nearOneco.[38]
Nemomydas melanopogon, aMydas fly, has been found on the Mount Dora Ridge in Lake County, the Crescent City Ridge in Putnam County, and the Lake Wales Ridge in Highlands and Pol counties. Another Mydas fly,Nemomydas lara, has been found on the Mount Dora Ridge in Lake and Marion counties and the Orlando Ridge in Orange County. The fleaPolygenis floridanus is found only on theFlorida mouse, which is endemic to Florida scrub. Thegeometer mothNemouria outina has been found on the Lake Wales Ridge in Highlands County, the Brooksville Ridge in Hernando County, and the Orlando Ridge in Orange County.
Florida scrubs are found in three distinct areas in Florida: on a series of ridges running along the center of the peninsula (inland peninsula), along both coasts of the peninsula, and thepanhandle coast. Historically, the largest areas of scrub in Florida were in the Big Scrub (also known as the Etonia scrub), which is about 40 miles (64 km) long and 15 to 20 miles (24 to 32 km) wide, in and about theOcala National Forest, and a mosaic of patches of scrub along theLake Wales Ridge. High pine habitat occurs as islands in a sea of scrub in the Big Scrub, but in the rest of Florida scrub habitat occurs as islands as small as 50 feet (15 m) in diameter in an expanse of high pinelands.[39][40]
Florida peninsula inland scrub is the plant community for which this ecoregion is named. Clumps ofsand pines (Pinus clausa) constitute thecanopy.[41] Common plant species includesand live oak (Quercus geminata),myrtle oak (Q. myrtifolia),sandhill oak (Q. inopina),Chapman oak (Q. chapmanii),Florida rosemary (Ceratiola ericoides),[3]scrub palmetto (Sabal etonia),saw palmetto (Serenoa repens),garberia (Garberia heterophylla),fetterbush lyonia (Lyonia lucida),rusty staggerbush (L. ferruginea),cup lichens (Cladonia spp.),[42]scrub holly (Ilex opaca var.arenicola),American olive (Osmanthus americanus var.megacarpus),flag-pawpaw (Asimina obovata),silk bay (Persea humilis),Adam's needle (Yucca filamentosa), andeastern prickly pear (Opuntia humifusa).[43] As of 1990, about 70% of the scrub on the Lake Wales Ridge had been lost to citrus groves and housing developments.[44]
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Scrub communities on the peninsula coasts are found on dune systems associated with the Pamlico and Silver Bluffterraces of thePleistocene period.[c] Peninsular coastal scrubs are found on the east (Atlantic) coast of Florida as far north asSt. Johns County, and were formerly found as far south as northernBroward County, although the southernmost scrubs on the east coast have been lost to urban development. On the west (Gulf) coast, scrubs are found as far north as near theCedar Keys,[d] and were formerly found as far south asMarco Island, but the scrubs on that island have also been lost to urban development.[47] Extensive loss of scrub habitat has occurred throughout Florida. By one estimate, almost 70% of the scrub habitat in northernBrevard County was lost between 1943 and 1991.[48]
Mulvania observes that the scrubs on the coasts, and particularly those on the east coast, appear to be more recent in origin than scrubs of the interior. The soils on which coastal scrubs are found appear to be recently formed, containing a large proportion of shells, while shells have disappeared from the older soils on which interior scrubs grow. Mulvania also notes that the vegetation of coastal scrubs is less uniform than that of interior scrubs.[49]
Scrub communities on the panhandle coast are also found on Pamlico and Silver Bluff dune systems, as well as onrecent dune systems along the barrier islands of the panhandle from theOchlockonee River toGulf State Park in southernAlabama.[50] The easternmost scrubs of the panhandle coast, just west of the Ochlockonee River, are 200 km from the westernmost scrubs of the peninsula, near Cedar Key. The sand pines of the Florida peninsula and of the panhandle coast differ enough to be classified into two varieties orraces,Pinus clausa var.clausa (Ocala), on the peninsula, andPinus clausa var.immuginata (Choctawhatchee), along the panhandle coast. While most panhandle sand pines (var.immuginata) havenon-serotinious, or open, cones, most of the peninsular sand pines (var.clausa) have serotinous, or closed, cones.[51] The scrub palmetto, which may be present in scrubs on the Florida peninsula, does not occur in panhandle coastal scrubs.[7]
Various authors classify Florida scrub into several phases or types, including coastal scrub, oak scrub, oak-hickory scrub, oak-palmetto scrub, rosemary scrub or bald, sand pine scrub, and scrubby flatwoods.[52][48][53]
Coastal scrub is a habitat on barrier islands where oaks, in particular, a coastal form ofsouthern live oak, are dominant, and including saw palmetto,wax myrtle,tough buckthorn,rapanea, andFlorida privet.[54]
Oak scrub is a habitat dominated by a shrub layer of evergreen scrub oaks, but without a tree canopy. It may also include saw palmetto, rosemary, shrub hickory, and rusty lyonia shrubs.[55]
Oak-hickory scrubs are dominated by oaks andscrub hickorys, with a scattering of sand pines and slash pines.[56]
Scrubs without a pine tree canopy may fall on a gradient, with such scrubs on drier soil dominated by oaks, and on wetter soils dominated by saw palmetto. Oak-saw palmetto scrubs are intermediate on that gradient.[57] They are dominated by scrub oaks, saw palmetto, and several plants in theEricaceae family, includingrusty staggerbush,poor grub,feterbush lyonia, andtarflower.[58]
Rosemary scrubs or balds occur in the driest, and least often burned, portions of scrubs,[59] and are often found on the crest of a hill surrounded by other phases of Florida scrub or other xeric upland habitats. They usually have fewer species present than do scrubs dominated by sand pines or oaks. The exclusion of fire from scrub areas has allowed other species to encroach on rosemary balds so that they have become oak scrubs and, eventually,xeric oak hammocks.[60] The dominant species in rosemary scrubs are Florida rosemary and sand pine.[61]
Scrubs with a scattered to dense canopy of sand pines are known as "sand pine scrubs". Sand pine scrubs have a shrub layer consisting either of evergreen oaks, saw palmetto, rusty lyonia, and other species, often including rosemary, or one dominated by rosemary.[58] The World Wildlife Federation formerly classified "sand pine scrub" as atemperate coniferous forest ecoregion.[62]
Scrubby flatwoods has been defined as scrubs without a sand pine canopy that are dominated by saw palmettos, evergreen oaks, rusty lyonia, or Florida rosemary.[57] Scrubby flatwoods are anecotone, intermediate between sand pine scrubs andflatwoods, sitting higher and with better drainage than flatwoods, but lower and with poorer drainage than sand pine scrubs. The[63] Scrubby flatwoods have more scrub oaks in the shrub layer, and less coverage in the herb layer than flatwoods have.[64] Scrubby flatwoods occur widely in Florida, but are more common in the southern part of the peninsula, where they are subject to a subtropical climate. Associations resembling scrubby flatwoods occur along the Gulf coast into Alabama and Mississippi, and into Georgia and South Carolina on the Atlantic coast.[65]
Trees in scrubby flatwoods may includeSouth Florida slash pine, sand pine, and longleaf pine. The shrub layer includes scrub oaks, and saw palmetto. The scrub palmetto is also a common component of scrubby flatwoods in central Florida. Ground cover includes wiregrass andforbs,lichens, andspike moss. Scrubby flatwoods from which fire is excluded are eventually invaded by sand pine and associated scrub shrubs.[63]
Scrubby high pine habitats have both scrub-adapted species, which do not tolerate frequent fires, and high pine adapted species that depend on frequent fires. Fires in such communities occur at variable intervals, and both types of species can persist, but the communities are unstable. A higher frequency of fires can turn such communities into high pine habitats, while a lower frequency of fires can turn them into xeric hammocks.[12]