b. Vegetation Zones . It is helpful to group dune plants into broad 

 categories based on their place in the dune complex. The majority of 

 coastal dune systems in the United States fit into a division of three 

 vegetation zones similar to that by Davis (1957) : (1) the pioneer zone, 

 (2) the scrub or intermediate zone, and (3) the forest zone (Fig. 13). 

 The zones are arranged in order of increasing distance from the sea and 

 in order of increasing age. 



The location, extent, and nature of these zones vary widely depending 

 on a number of factors such as coastal topography, climate, nature and 

 rate of erosion and deposition, and sea level changes. The pioneer zone 

 is sometimes lacking due to recent severe storms or to persistent long- 

 term beach recession. Forest cover will not develop on many low, narrow 

 barrier islands and on dry coasts such as those in southern California 

 and southern Texas. However, in extreme cases of erosion and beach 

 recession, both the pioneer and intermediate zones may be lost leaving 

 the forest zone next to the beach. Also, on very high coasts (where 

 salt spray is confined near the surf zone) forests may develop close 

 to the sea. This also occurs around the Great Lakes where salt spray 

 is absent. 



(1) Pioneer Zone . This is the area of recent or continuing sand 

 movement that usually occurs on the upper beach and foredunes. It is wide 

 on prograding beaches, less on stable sites, and narrow to nonexistent on 

 receding coasts. Vegetation in a typical pioneer zone is limited to a few 

 species of grasses, sedges, and forbs that can withstand salt spray, sand- 

 blast, sand burial, flooding, drought, as well as wide temperature fluctu- 

 ations and low nutrient supply. New barrier dunes develop in this zone 

 and the pioneer plants are usually used to build new dunes or to stabilize 

 bare dunes. This report is focused primarily on the pioneer plants. 



(2) Scrub or Intermediate Zone . This is a highly variable, ill- 

 defined area lying immediately behind the more active pioneer zone. It 

 consists of secondary dune ridges and swales, flats, deflation plains, 

 and occasionally includes the back slopes of large foredunes. Plants 



in this zone include, in addition to the pioneer species, forbs, shrubs, 

 and in some cases, stunted trees. The area receives little fresh sand 

 and nutrient levels are usually low. This results in a scrubby, starved 

 appearance of the vegetation. Growth and vigor, particularly of the 

 remaining pioneer species, is substantially lower than in the active 

 zone but the intermediate zone plants are adapted to these conditions 

 and are valuable as stabilizers. Some intermediate species are planted 

 for ornamental purposes and as wind breaks. In nature, the plants tend 

 to invade and gradually replace the pioneers as soon as an area becomes 

 sufficiently stable and oceanic influence is sufficiently reduced. This 

 is why these plants are not usually planted in the pioneer zone. 



This zone is normally considered a progression in the ecological 

 succession toward the stable climax forest, away from the highly change- 

 able, unstable state of the pioneer zone. Sand movement decreases or 

 ceases completely. The area is populated by a wider variety of plants 



26 



