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Drought-Prone Rangelands in a Warming World

Shafran-Nathan, R., Svoray, T. and Perevolotsky, A. 2013. Continuous droughts' effect on herbaceous vegetation cover and productivity in rangelands: results from close-range photography and spatial analysis. International Journal of Remote Sensing: 10.1080/01431161.2013.793864.
In a study published in the International Journal of Remote Sensing, Shafran-Nathan et al. (2013) write that "the expectation of regional or global climate changes introduces an urgent need to identify the responses of ecosystems to changes in climatic conditions," citing Grime et al. (2008), because, as they continue, "climate-change forecasts suggest that the frequency of droughts in our region [the northern Negev of Israel] will increase (Yosef et al., 2009)." And, therefore, they investigated the dynamics and persistence of productive patches of herbaceous vegetation during a two-year-long drought from two different perspectives: high-resolution vertical photography and onsite field work. Both years were quite dry, with 2007-2008 receiving 201 mm of rain compared to the long-term average of 298 mm, while 2008-2009 received only 135 mm, making it "the driest year in this region during the last 31 years." So just how bad did things get for the region's so-called "productive patches" of vegetation during these back-to-back moisture-starved years?

The three Israeli researchers report that the droughts "led to spatial convergence of the productive patch size," and that both "productive and less productive patches persisted while plant cover decreased with rainfall reduction." And "interestingly," as they put it, "production processes continued long after the last rainfall event ... for 45 days in 2007-2008 and for 66 days in 2008-2009, unlike two and a half weeks in regular years." In addition, they say that "even though there was almost no rainfall supplementation during the productive phase in either year, plant cover increased until the peak of the productive phase and then declined until senescence."

Another strategy that they felt was operative in maintaining rangeland productivity in drought-stressed years was the development of "a relatively stable seed bank that is accumulated over the years and may buffer the effect of drought," citing in this regard the work of Osem et al. (2004). Most important of all, they concluded that the various phenomena they documented made the ecosystems they studied "more resilient than expected," leading them to declare that rangelands may well "maintain productivity under more severe drought scenarios than those currently predicted in the climate change literature." And, it might be added, these ecosystems appear to be capable of doing so right now, even without the additional future help that will be provided by the aerial fertilization effect and the transpiration-reducing effect of the additional CO2 that will be released to the air in the years and decades to come via mankind's continued burning of coal, gas and oil, which should make things better still for Earth's rangelands for a long, long time to come.

Additional References
Grime, J.P., Fridley, J.D., Askew, A.P., Thompson, K., Hodgson, J.G. and Bennett, C.R. 2008. Long-term resistance to simulated climate change in an infertile grassland. Proceedings of the National Academy of Sciences 105: 10,028-10,032.

Osem, Y., Perevolotsky, A. and Kigel, J. 2004. Site productivity and plant size explain the response of annual species to grazing exclusion in a Mediterranean semi-arid rangeland. Journal of Ecology 92: 297-309.

Yosef, Y., Saarfoni, H. and Alpert, P. 2009. Trends in daily rainfall intensity over Israel 1950/1-2003/4. Open Atmospheric Science Journal 3: 196-203.

Archived 5 November 2013