Forests (Tree crowns interlock to form closed canopies)

Forests are plant communities where trees grow in interlocking canopies. Forests provide an important resource for wildlife, recreation, climate moderation, rain water infiltration, and forest products. The diversity and complex structure of plant communities in forests provide a wide variety of niches for forest-dependent animal species to find food, seek shelter, avoid predation, and reproduce.

The dominant native forest ecosystems in St. Croix include subtropical dry forests and subtropical moist forests with various belnds of deciduous and evergreen trees growing in either two or three forest layers. Although several types of forest habitats can be recognized, they grade into one another and are generally difficult to delineate.

Virtually all of the primary tropical forest in St. Croix was cleared by the early twentieth century for the cultivation of sugarcane and other agricultural purposes. A large portion of these agricultural lands were abandoned as the Caribbean sugar industry declined and reverted back to secondary forest. These secondary forests now host a large number of tropical species introduced from throughout the world. “New forests” have become established over much of the island.

St. Croix's forest ecosystems periodically suffer hurricane damage, resulting in a dynamic mosaic of successional stages. In recent decades, the development of sprawling residential communities and commercial centers connected by paved road networks has caused considerable deforestation and degraded and fragmented the remaining forests. The adverse affects of deforestation to the environment included increased surface temperatures, increased soil erosion, and increased sedimentation and eutrophication of wetlands and inshore marine habitats. Deforestation and forest degradation and fragmentation also decrease their carrying capacity for wildlife populations, decrease genetic variability, increase genetic inbreeding, decrease effective wildlife population sizes, and increase risk of local exterminations. The introduction of exotic plants also threatens native vegetation, which is often crowded out, and can threaten native wildlife as well.

Forest habitats in St. Croix are further classified as:

• Moist Forests [Gallery moist forests, and Basin moist forests],
• Dry Forests [Semi-evergreen forests, Semi-deciduous forests, Drought-deciduous forests, and Gallery Semi-deciduous forests], and
• Woodlands [Evergreen woodland, Semi-deciduous woodland, Gallery semi-deciduous woodland, and drought-deciduous woodland].

See St. Croix Plants for more details.

Shrublands/Grasslands

Shrublands occur in dry locations at low elevations on all islands and offshore cays. These communities are at least 0.5 meters to 5 meters in height with 3 meter height typical. Shrubs are generally defined as multiple stemmed, bushy and interlocking in structure. Thorny shrubs and cactus species are common along with succulents in some locations. These vegetation types are quite difficult to distinguish between categories and vary in height, structure and species composition. Aspect, elevation and past land use history can have a profound effect. Due to severe environmental constraints of thin soils, strong winds and little moisture, vegetation height is limited. Land use history may impact many of these transitional communities where succession will create different cover types in the future

Gallery Shrubland - These cover types are found most commonly in small guts and ravines where additional catchment and soil moisture prevail. Many evergreen species are common to these locations and height of the vegetation is typically at the taller end of the spectrum. They may form very dense communities in these areas and may remain as a result of land use history, being transitional stages to other community types. Much of the gallery vegetation is protected by VI law.

Thicket/scrub - This deciduous formation is quite common on all three islands and cays. It is characterized by thorny scrub communities which generally form a very dense, closed cover community. The height of the vegetation averages approximately 3-4 meters with occasional emergent trees. These communities may have uniform height as mono-specific stands or structural variety as a mixture of two species. This community type may also exist in many locations as a transitional seral stage to taller woodland or dry forest types. Land use history has great influence in the distribution of this cover

Mixed Dry Shrubland - This vegetation cover is common to the drier parts of all three islands; east and south shores and low elevation locations. It may in some places extend as far up as 275 meters on south facing slopes. An extremely diverse community, Cacti and Agave are common though scattered, while vegetation height can range from 1-10 meters. The taller forms may consist of a canopy layer of larger individuals under slightly more moist conditions. The shorter forms are common to very exposed locations such as the east sides of headlands on the south shores.

Coastal Hedge - Shaped by wind shear and salt spray, these dense patch communities can be very low growing (less than 1 meter) or as tall as 3 meters. They are generally found on east, southeast or northeast coastal areas with exposure to prevailing winds. The limited species are generally wind and salt adapted. The formation may occur on the berms of beaches, seaward of salt ponds and flats or above rocky coasts or pavement. Hedge effect from wind is the prevailing structural architect for the environment as almost all of the species found here are capable of greater height in less hostile environments. The severe environment causes some plants to produce small, succulent leaves which are highly cutinized.

Herbaceous communities occur in areas of very low rainfall, along the coast or in areas which have been subject to disturbance by human activities associated with agriculture and grazing of livestock. Many herbaceous communities may have a small percentage of shrub species and broad-leaved evergreen and semi-deciduous trees as a component. These ecosystems are dominated by grasses and maintained by grazing and fire and are generally located on nearly flat or moderate slopes.

Pasture - These are primarily grasslands with a very low (less than 10%) incidence of shrub and tree species occurring as part of the community. These can generally be classified as planted and cultivated areas subject to maintenance by grazing and fire.

Pasture mixed scrub - Grassland dominated communities with greater than 10 - 25% thorn/scrub vegetation. This community type results when grazing and fire maintenance have been discontinued and successional changes occur within the community.

Mixed Dry Grassland - Grassland dominated communities with greater than 25% shrub, tree and herbaceous species usually formed by selective grazing of livestock that shun spiny and/or poisonous plants.

Coastal Grassland - Extremes of wind, salt spray and low moisture sometimes combine to form communities of grasses adapted to these harsh conditions.

Wetlands

Wetlands can be seasonally, tidally, semipermanently or permanently flooded vegetation communities. They are found near the coast in areas that are periodically or permanently flooded with salt water, or where freshwater collects from rainstorms. Wetland types vary greatly, from tall mangrove forests to open salt ponds or flats.

Mangrove Forest - Mangrove forests dominated by Red Mangrove, Rhizophora mangle, and other mangrove species exhibiting a closed tree canopy.

Mangrove Woodland - Similar to the above with a less dense association where the tree canopy is not closed. This woodland type lies at the shoreward extreme of the tidally flooded areas and may be dominated by Avicennia germinans, Laguncularia racemosa and Conocarpus erectus.

Mangrove Shrubland - Nontidal shrublands or scrub mangrove thickets dominated by Rhizophora mangle. Occurs in more stressed sites than mangrove forests and has shorter individuals (less than 5 meters and usually only one-half to two meters tall) and often sparser as well.

Fringing Mangrove - Shoreline and salt pond vegetation which is semi-permanently and tidally flooded. These areas are quite common to all islands.

Mixed Swamp - Semi-permanently and tidally flooded communities composed of a mixture of mangrove and wetland tree and shrub species.

Salt Flat - Coastal pond areas, sand and mud flats behind barrier beaches.

Salt Pond - Semi-permanently flooded coastal ponds.

Fresh pond - Permanent catchment and drainage areas of fresh water.

Reefs

The shallow coastal systems surronding St. Croix are bursting with biological diversity that is responsible for enormous marine productivity. Coral reefs are highly diverse and complex ecosystems made up of millions of tiny coral polyps that buil the reef structures. Most of the coral reefs around St. Croix are shallow fringing reefs that parallel the Island's coastline. These reefs support more than 40 coral species.

Coral reefs support small island fisheries, protect the shoreline from erosion, creat and nourish sandy beaches, and are one of the most valuable natural resources of St. Croix.

Fringing, bank, barrier and linear coral reefs are found around Buck Island, Turner Hole, Jack and Isaac's Bays, and Lang Bank on St. Croix. These large reefs are hardened substrates of mounded areas formed by the deposition of calcium carbonate by reef-building corals and other organisms.

Patch reefs & patch reef aggregates are found in Teague Bay, Ha' Penny Bay and Great Pond Bay. A patch reef is a small reef isolated from shore and other reef systems. Patch reefs are an island of biological complexity in the middle of flat sandy, grassy or hard bottom.

Colonized hard pavement is located at the mouth of Salt River, around Sandy Point and along the south shore of St. Croix. Hard pavement is any flat, hard, carbonate sea bottom that has a low percentage of live coral cover.

Gorgonian dominated pavement can be found in Buck Island's fore reef. These hard pavement habitats have abundant gorgonian [soft coral] cover and generally occur in areas with high current.

Colonized bedrock is found at the mouth of Salt River, and in Annaly and Butler Bays on St. Croix. This habitat is mostly exposed and eroded bedrock that underlies the adjacent island coastline. In these havitats, macroalgae and hard and soft corals are thick enough to obscure the bedrock underneath.

Marine Plant Communities

More than 600 species of Caribbean reef plants grow within St. Croix's marine plant communities and coral reefs. Marine plants are extremely important to reef ecology and reef-building. Caribbean reef plants, sea grasses and algae form the basis of the marine food chain. They produce oxygen through photosynthesis for other marine organisms. They need sunlight to grow, so are usually found in fairly shallow areas [up to approximately 100 feet deep].

Seagrass Beds are composed primarily of turtle grass, Thalassia testudinum, and manatee grass, Syringodium filiforme, and have some of the highest productivity rates of all ecosystems. Seagrasses are flowering plants whose leaves are usually covered with algae or sediment. Seagrasses have extensive root systems that are well-anchored by runners. They provide nutrients, sustain fisheries, create foraging grounds for endangered species and enhance biological diversity. They serve as important grazing areas for Green Turtles, Chelonia mydas. Seagrass beds can be found in Chenay Bay, Teague Bay, Great Pond Bay, and Ha'Penny Bay in St. Croix.

Algal Plains are found on the sea bottom along St. Croix's South shore at depths greater than 65 feet. Green algae are the most common types of algae found. They are clacareous and add large amounts of calcium carbonate to reefs. The algae grow in single-celled bubble, blade, brush and fan-shaped forms. Some common algaes include Lettuce Leaf Algae (Halimeda spp.), Green Grape Algae (Caulerpa spp.), and Bristle Brush Algae (Penicillus spp.).

Algal Ridges can be found on rocky coastlines and offshore rock habitats along St. Croix's South shore. Many reef crests exposed to high wave energy are cemented by species of calcareous red algae that form the algal ridge. Algal ridges are mostly made up of coralling algae (Lithophyllum congestum and some Porolithon pachydermum).

*Information presented has been excerpted from the 2005 Island Peak to Coral Reef: Field Guide to the Plant and Marine Communities of the Virgin Islands.