PARENT SESSION
Contributed Oral Session 12: Arid Lands: Plant Response to Precipitation
Monday, August 8, 8:00 AM - 11:25 AM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal
Long-term monitoring of semi-arid annual plant community dynamics in relation to annual rainfall.
Boeken, Bertrand*,1, 1 Blaustein Institute for Desert Research, Midreshet Ben-Gurion, Israel
ABSTRACT- In semi-arid ecosystems the variation of primary production, density and species richness of the vegetation is assumed to depend on annual fluctuations in rainfall. This assumption was tested from a 12-year dataset (1993-2002) of annual plant communities in a semi-arid shrubland of the northern Negev desert of Israel. I counted all individual annual plants in 24 repeatedly monitored 1-m2 samples in soil disturbances (20 cm deep pits and 20 cm high soil mounds constructed in 1992) and equal-sized areas of undisturbed soil surface. In a second set of 24 samples we removed the vegetation above- and below-ground, and weighed dry mass per species. Mean biomass, plant density and species density did not show the expected strong positive correlation with rainfall of the same year (R2<0.30), nor of the previous one, or any combination of the two. Differentiating the species by incidence, the changes in biomass, plant density and species density were the net result of the divergent population behavior of 4 groups of species: 1) high-incidence, dominant grasses, 2) high-incidence, dominant forbs, 3) medium-incidence, subordinate herbs, and 4) low-incidence herbs. The dominant grasses tended to decrease little during low-rainfall years, but decreased the year after; the dominant forbs decreased at low rainfall but responded positively to higher rainfall in the following year. The subordinate species decreased, and many of the low-incidence species disappeared during low-rainfall years, while both tended to increase when the dominants decreased. The divergent responses to rainfall are associated with 1) seed dormancy, which is absent in the grasses but present in most forbs, and 2) release of (pre-emptive) competitive interactions in the case of the subordinate and minor species, when the dominants were reduced.
Key words: climatic variation, primary production, semi-arid shrubland, species richness