Nucleation and facilitation in salt pans in Mediterranean salt marshes

Arthrocnemum macrostachyum is a perennial species acting as a primary colonizer of salt pans in Mediterranean high salt marshes. Salicornia ramosissima, an annual, occurs in salt pans under Arthrocnemum canopies and in open areas. The aim of this study was to analyse, in wild populations and a transplant experiment, how S. ramosissima population dy- namics and growth are affected by A. macrostachyum. The environmental conditions within the patches of Arthrocnemum were less stressful than in the open areas, with lower radiation levels and salinity concentrations. In the inner areas of A. macrostachyum patches, density-dependent mortality proc- esses of S. ramosissima seedlings led to low densities of adult individuals with greater morphological development and re- productive success than in open areas. However, at the edges of Arthrocnemum patches facilitation of seedling survival favoured high densities. Environmental stress hindered devel- opment, decreased reproduction and premature death. These results are in agreement with the general theory of factors controlling vegetation distribution that biotic interactions domi- nate in low stress environments, while abiotic interactions dominate under harsher environmental conditions. A. macro- stachyum plays an essential role in the succession in these salt pans, facilitating seed production and stimulating nucleation processes in S. ramosissima.

[1]  S. R. Olsen,et al.  Estimation of available phosphorus in soils by extraction with sodium bicarbonate , 1954 .

[2]  Anthony J. Davy,et al.  Lower limits of Spartina densiflora and S. maritima in a Mediterranean salt marsh determined by different ecophysiological tolerances , 2000 .

[3]  M. Bertness,et al.  Competition and Facilitation in Marsh Plants , 1993, The American Naturalist.

[4]  A. J. Belsky,et al.  Influences of Trees on Savanna Productivity: Tests of Shade, Nutrients, and Tree-Grass Competition , 1994 .

[5]  I. Ungar,et al.  Growth and Survival of the Halophyte Salicornia Europaera L. Under Saline Field Conditions , 1981 .

[6]  P. Nobel,et al.  Effect of Nurse Plants on the Microhabitat and Growth of Cacti , 1989 .

[7]  M. Bertness,et al.  Cooperative and Competitive Interactions in the Recruitment of Marsh Elders , 1994 .

[8]  D. Srivastava,et al.  A POSITIVE FEEDBACK : HERBIVORY, PLANT GROWTH, SALINITY, AND THE DESERTIFICATION OF AN ARCTIC SALT-MARSH , 1996 .

[9]  M. Bertness,et al.  Structural interdependence : an ecological consequence of morphological responses to crowding in marsh plants , 1996 .

[10]  I. Ungar,et al.  THE DISTRIBUTION AND GROWTH OF SALICORNIA EUROPAEA ON AN INLAND SALT PAN , 1979 .

[11]  A. Ellison.  Density‐Dependent Dynamics of Salicornia Europaea Monocultures , 1987 .

[12]  Jonathan M. Levine,et al.  Nutrients, competition and plant zonation in a New England salt marsh , 1998 .

[13]  R. Jefferies,et al.  POPULATION BIOLOGY OF THE SALT MARSH ANNUAL SALICORNIA EUROPAEA agg. , 1981 .

[14]  R. Jefferies,et al.  Ecological Processes in Coastal Environments , 1979 .

[15]  R. Whittaker,et al.  The Saguaro: A Population in Relation to Environment. , 1963, Science.

[16]  J. Carlos.,et al.  Ecología de las marismas del Odiel , 1984 .

[17]  Marten Scheffer,et al.  The interplay of facilitation and competition in plant communities , 1997 .

[18]  Richard E. Miller,et al.  Life history variation and local adaptation within two populations of Bouteloua rigidiseta (Texas grama) , 1994 .

[19]  R. Callaway,et al.  FACILITATIVE AND INTERFERING EFFECTS OF ARTHROCNEMUM SUBTERMINALE ON WINTER ANNUALS , 1994 .

[20]  T. T. Veblen,et al.  Facilitation by nurse shrubs of resprouting behavior in a post-fire shrubland in northern Patagonia, Argentina , 1998 .

[21]  A. R. Tipton,et al.  Shrub emergence and seedling growth in microenvironments created by Prosopis glandulosa , 1996 .

[22]  J. Bakker,et al.  Nitrogen and phosphorus limitation in a coastal barrier salt marsh: the implications for vegetation succession , 1999 .

[23]  J. Chambers.  Pinus monophylla establishment in an expanding Pinus-Juniperus woodland: Environmental conditions, facilitation and interacting factors , 2001 .

[24]  J. Lepart,et al.  Shrub facilitation of Quercus humilis regeneration in succession on calcareous grasslands , 1999 .

[25]  M. E. Figueroa,et al.  Nucleation and facilitation in saltmarsh succession : interactions between Spartina maritima and Arthrocnemum perenne , 1994 .

[26]  Jordi Sardans,et al.  Plant competition in mediterranean‐type vegetation , 1999 .