Document: ORN-3-37-23

The recolonization of abandoned fields by the clonal shrub Sarcopoterium spinosum L. evidenced from archive aerial photos, wood rings and field observations.

REISMAN-BERMAN, O.* ¹, R.KADMON ² and M.SHACHAK ¹

Ben-Gurion University, Beer-Sheva, Israel. ¹
The Hebrew University of Jerusalem ²

Abstract:
Recolonization of abandoned fields (Northern Negev, Israel), by Sarcopoterium spinosum, an Eastern Mediterranean native clonal shrub, was studied via age analysis of shrub annual wood rings and corroborated by historic aerial photographs. The study objectives were: 1.) To quantitatively describe the spatio-temporal patterns of recolonization and invasion of S. spinosum and 2.) To relate the observed patterns to the shrub recruitment modes. (i.e sexually by seedling and vegetatively by ramets). The average and maximum age of individuals decreased with distance from source population, bordering the abandoned field. Aerial photos supported the age analysis results. The detected progress in invasion characterized by the change in shrub patch size density. Filling of gaps in an already occupied space occurred mainly by the growth of shrub patches and not by the formation of new ones. Patterns of shrub vegetative growth, as well as spatial patterns of seedlings recruitment observed in the field, supported spatial patterns detected from aerial photos. Seedlings recruitment occurred almost exclusively beneath shrub canopy. Seedling density was maximal at intermediate adult density, and adults density was negatively correlated with average age of individuals in the plot. Detailed demographic observations indicated that individuals younger than 5 yr. develop only one or two elongated axes, reaching 80% of shrub maximum height. Branching and canopy development commence subsequently. Rooting from root crown and the formation of subunits started within only 10% of the population at ages between 6 to 10 yr. Rooting from prostrate branches and the formation of distant ramets, occurred within 50% of the population at ages between 20 to 25 yr. Space occupation dynamics along invasion axis showed a clear evolvement from dispersed single shrubs to clusters consisting of vegetatively recruited individuals and individuals recruited from seeds. Cluster expansion was characterized by the growth of individual shrubs that facilitate seedling recruitment. However, mature individuals that develop a dense canopy and vegetative growth, limit seedling recruitment. Abandoned agricultural fields were demonstrated to be an excellent system to study spatial demographic processes that take place during recolonization of unoccupied space.

Keywords: Sarcopoterium spinosum, recolonization, clonal shrub, aerial photographs, annual rings

This abstract is being presented at: 10:30 AM in session:
PLANT DEMOGRAPHY