Israeli ecosystems appear too tough for climate change

Climate change may not pose a serious risk to plants in parts of Israel in the coming decades, according to an ecological study based on years of induced drought. The conclusion — the plants are tougher than the changes — runs counter to the current scientific consensus.

Semi-arid and Mediterranean ecosystems are thought to be among the most vulnerable to climate change, but in the study, conducted by an international team of scientists, a nine-year climate change rainfall simulation had almost no effect on two such ecosystems in Israel.

The scientists, who say they were as surprised as anyone by their findings, reason that plants in Israel and in the rest of the Eastern Mediterranean region may have been girded against climate change by millennia of exposure to drought and climatic variability — possibly dating back to the seven-year famine that Joseph foresaw in the Bible.

Published this month in the journal Nature Communications, the study offers some hope that Israel and other parts of the world will hold up better than expected against global warming and other human-wrought changes to Earth’s climate.

Prof. Marcelo Sternberg, a plant ecologist at Tel Aviv University, who led the study. (photo credit: Courtesy)

“Based on our study, the current hypothesis that all semi-arid regions will react strongly to climate change needs to be revised,” said Prof. Marcelo Sternberg, a plant ecologist at Tel Aviv University, who led the study.

Though the study is the longest climate change experiment conducted to date in the Middle East, it only roughly approximated the effects of climate change. Given the complexity of natural ecosystems, the scientists say their findings cannot be extended more than a few decades into the future.

Breaking the model

The Eastern Mediterranean, which rings the Mediterranean Sea from Greece clockwise to Egypt, is a region where climatologists agree on the likely extent of climate change. They say rainfall will decrease as much as 30 percent, and temperatures and extreme weather conditions will increase. As a result, water resources are expected to be depleted, damaging the diverse plant life that forms the foundation of the region’s ecosystem.

That prediction is based mostly on bioclimatic models that assume plants can survive only under their current conditions. To see how plants would actually react to predicted climate change, the scientists subjected two natural sites in Israel to drought. One site was in was in the northern Negev near Beersheba, a semi-arid ecosystem, and the other was in the Judean Hills near Jerusalem, a Mediterranean ecosystem.

The scientists say drought can serve as a proxy for climate change, because it is expected to be the dominant element in the region.

Between 2001 and 2010, the scientists reduced rainfall at the sites by 30 percent by erecting shelters. Once a year, they measured the growth of plant life at the sites. The scientists focused on annual plants, which have a one-year life cycle, because they make up 70-90% of the species in the region and almost single-handedly support the rest of the food chain.

Contrary to bioclimatic models and the scientists expectations, over the nine-year drought, the plant biomass, species diversity, and composition of the plants remained more or less constant. Just as in areas not subjected to drought, the plants looked the same in 2010 as they did in 2001, the baseline year for the study.

Predictions based on this are tricky. “It would be not serious for me to say that we know exactly what is going to happen, because in nature, interactions are very important, and interactions are not additive,” said Sternberg. “It’s not that one plus one gives you two. It can give you three or four, because there are so many positive and negative feedbacks around the issue of the water cycle. It’s very hard to predict.”

What doesn’t kill you

Plant life at the study sites appeared to survive the drought by adapting, rather than by migrating to more hospitable areas, as bioclimatic models assume. Israeli plants likely evolved this resilience through to regular exposure to drought over thousands of years in the Eastern Mediterranean. To this day, droughts often slash average annual rainfall in the region by more than the 20-30 percent expected from climate change.

“In retrospect, it was naive to think that a little drought would be enough to affect plants that evolved under these kinds of conditions,” said Sternberg.

It is possible that the world’s other Mediterranean and semi-arid ecosystems have adapted in a similar way, the scientists say.

Though the scientists used sites in Israel’s other climate ecosystems — mesic Mediterranean and arid — for comparison, they did not subject them to drought. As result, they cannot yet predict how Israel as a whole could be affected by climate change.

The study was part of the GLOWA Jordan River project, a multidisciplinary collaboration between Israeli, Palestinian, Jordanian, and German scientists, with funding from the German government. The project ended in 2011, and Sternberg is looking for collaborators and funding to keep monitoring the research sites. Each year of the experiment, he says, provides more powerful evidence about the impact of climate change in the region than did the year before.