PlantCommunities 512

In this aerial photograph different plant communities are easy to distinguish. There is an obvious break between the forested dunes and the salt marsh because of the abrupt change in environmental conditions. On the left side of the photograph, riparian forest can be recognized by the deciduous trees. On the outer dunes are dune mat (upland areas) and herbaceous or forested swales (in depressions).

Plants and Plant Communities

Humboldt Bay National Wildlife Refuge is home to about 220 species of native plants. The high plant diversity is a result of the range of different habitats found on the refuge in its estuarine, dune and wetland ecosystems. In addition to these ‘vascular’ plant species, there are hundreds of species of lichen, mosses, algae and fungi (the latter are actually classified separately from both the animal and plant kingdoms). The plants found on the refuge include many with unique adaptations for their habitats. Some examples of adaptations to the dune environment include succulence to store water or reflective leaf hairs to reduce water loss; the ability to grow new shoots as plants are buried; and stolons or rhizomes (horizontally growing stems at the surface or below-ground) to expand into nutrient-deficient areas of open sand. Salt marsh plants are able to survive life in saline and low-oxygen conditions by sequestering salt in specialized cells, or by transporting oxygen from leaves to submerged roots.
Plants organize themselves into groups of co-occurring species called communities. Communities are structured by environmental gradients. An example is the juxtaposition of salt marsh, brackish marsh and freshwater marsh along a salinity gradient. In addition to interacting with their environment, plants interact with each other in ways that bring them together (mutualisms) or keep them apart (competition). Over time, plants can modify their own habitat, eventually causing a turnover of species known as succession. On dunes this process occurs as specially adapted “pioneer” plants colonize open sand, slowly building up organic matter in the soil until later successional species can establish. 
Another term for plant communities is vegetation type. Don’t confuse “vegetation” with “vegetative!” The word vegetative is only used to describe non-sexual parts of a plant (for example, “vegetative reproduction.” Vegetation is classified by ecologists at different levels of a hierarchy. At higher levels, the “physiognomy,” or structure, of the dominant plants are used to distinguish classes such as forest, shrubland, or grassland. At the lowest levels, species composition is used as the basis of classification.  Capturing the full extent of vegetation diversity requires the lowest levels of classification, the Alliance and Association. Identifying and describing these vegetation types is a quantitative science and has not been completed in many places.  Over most of the refuge, we have carried out vegetation sampling and completed the complex analysis needed to describe both native and “semi-natural” vegetation types at the Alliance and Association level. You can download a copy of the vascular plant list, which provides information on the conservation status and habitat preference for each species, along with its designation as a native, exotic, or invasive species.