Sarcopoterium spinosum: Revisiting shrub development and its relationship to space occupation with time

We describe and quantify the process of space occupation by the dwarf shrub, Sarcopoterium spinosum, in mesic and xeric Mediterranean environments. The shrubs were sampled in fifteen 2 m x 1 m plots in an arid Mediterranean site (Lahav, northern Negev, Israel) and in a 10-m² patch in a sub-humid Mediterranean site (Elkosh, Galilee). The results revealed three clear stages of development that follow the seedling stage (first year): "Sapling", "Young", and "Adult" stages, each of which contributes differently to the persistence of the individual shrub and its population in space and time. The timelines in the xeric and mesic sites were very similar, though development was more intense in the mesic site. The "Sapling" stage is characterized by rapid elongation of only a few stem axes during the first 5 years. The transition to the "Young" stage is marked by the onset of canopy expansion and the proliferation of stem axes, and during this stage clonal structures are formed, i.e., the connected ramets (stem-axes), the split proximate ramets, and the integrated ramets (layering branches with or without daughter shrubs). The "Adult" stage starts around the age of 15 years. Although only small fractions of the population survive to this age, this stage is highly viable and it is characterized by escapes from senescence, manifested in proliferation of clonal structures and canopy expansion. The minimum age for sexual reproduction observed in the field was 4 years, however, this reproduction mode varied greatly between environments and in the xeric environment, peaking was at the "Adult" stage, with 60% of this age class exhibiting sexual reproduction.