Lacking Water, Trees Turn to Carbon Dioxide

Towering over the trees of the Yatir Forest on the southern slopes of Mount Hebron is a green metallic building. Passersby may mistake it for just another weather forecast station, but in fact, the research conducted there could help combat desertification around the world. The research station, operated by the Weizmann Institute of Science in Rehovot, is the only facility in the Middle East capable of measuring greenhouse gases.

The station at Yatir was set up six years ago, as part of the FluxNet worldwide network established by scientists to investigate carbon dioxide absorption by plants. Professor Dan Yakir, who operates the station, says that the Yatir forest station is unique because it alone is situated in a semi-arid climate.

And indeed, the data that he and his students have collected seems to be quite unusual: Apparently, the trees at Yatir forest grow just as fast as other trees growing in regions with twice the precipitation. A closer inspection revealed that the trees were compensating for the lack of water by making use of carbon dioxide.

These findings may create a new perspective on planting forests in arid regions, Yakir explains. Such forests could be planted to help curb desertification and reduce carbon dioxide levels in the atmosphere, which could help to prevent global warming. However, Yakir adds that the practical conclusions stemming from the findings are inconclusive.

For example, Yatir says, planting forests in arid areas would take up large quantities of water, which could otherwise be used for other needs.

Helping Yakir at the station are Naama Raz-Yassif, 37, and Leon Peters, 25, who belong to a team of five other graduate students. Raz-Yassif and Peters arrive once a week at the station to gather the data, clean the equipment (which includes more than 80 measuring devices) and provide maintenance.

On their weekly visit to the station yesterday, Leon installed a device to analyze isotopes in evaporated water. Each member of Yakir research team hails from a different field of study. Raz-Yassif, for example, conducts research into water. On her visit to the station yesterday she recovered a device that measures the rate of water evaporation from the soil.

Other FluxNet stations around the globe are also dedicated to understanding the role that forests have in the emission and absorption of carbon dioxide. That is because forests as a whole consume 25 percent of all carbon dioxide, a gas which has a profound effect on global warming. As in other FluxNet stations, the facility at Yatir examines all relevant climatic and geologic factors, such as salinity, wind and temperature.

Yatir forest was not selected at random. The area was chosen specifically for the scarce rainfall that it receives - less than 300 millimeters per year. "This level of precipitation is atypical of forests, including those being examined elsewhere in the world," Yakir explains. Moreover, the trees at Yatir forest are not natives. They were planted there in the 1960s.