The Biological Flora of Coastal Dunes and Wetlands: Chamaecrista chamaecristoides (Colladon) I. & B.

Abstract

Chamaecrista chamaecristoides (Colladon) I. & B. is a tropical shrubby legume endemic to the Mexican coastal sand dunes of the Gulf of Mexico and to a lesser extent, of the Pacific coast. It grows mainly on mobile dunes, and it is the first colonizer. In this study we present information regarding the plant's geographical distribution, range of habitats, physiological ecology, population biology, reproduction, its role in geomorphology and interactions with other species. Ch. chamaecristoides is very tolerant to drought and low nutrient availability in the soil. Biomass accumulation and relative growth rates increase significantly when seedlings are covered by sand. The legume may be considered as a nurse plant that modifies environmental conditions and facilitates the successional process. Temperature fluctuations in the shade of adult plants decrease noticeably when compared with bare sand temperatures. Further, bacterial and mycorrhizal associations are abundant. All these characteristics probably play an important role in dune dynamics since late colonizers are only able to arrive after Ch. chamaecristoides has reached a rather high (2x2m) plant cover. The plant's hard coated seeds germinate gradually throughout the year, after seeds have been exposed to naturally occurring temperature fluctuations on the sand surface. Seedling mortality is very high during the first three months, and only 5% reach adult stage. Winter storms are a major cause of death, since drought and sand movement become drastic during these months (November to March). We found that seedling size plays an important role in survival and reproduction. Larger seedlings are the ones with higher survival rates and reproduce earlier. Ch. chamaecristoides plants decrease sand movement and hold the substrate together, promoting dune stabilization. This is important to humans, since mobile dunes continuously encroach nearby roads, cities and crop fields. There is no practical experience in dune stabilization with this species.