Climate controls biodiversity

Heat and water decide on plant biodiversity

World map of plant biodiversity. © Nees Institute of the University of Bonn
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The more heat and water there is, the greater the biodiversity: this is the rule of thumb for the result of a study that has now appeared in the journal Proceedings of the National Academy of Sciences (PNAS). An international team of scientists has for the first time linked the worldwide biodiversity of plants with local climatic and environmental factors.


Botanists know about 300, 000 plant species today. Humanity depends directly on them: they provide food, clothing, medicine, regulate the climate and the water balance. But plants are not evenly distributed over the earth: in the whole Federal Republic there are just 2, 700 different species; In the lowland rainforest of Borneo, on the other hand, it is almost four times as much.

Holger Kreft from the Nees Institute for Biodiversity of Plants at the University of Bonn and his US colleague Walter Jetz from the University of California at San Diego have for the first time related these differences to geographical and climatic factors. More than 1, 000 different regions worldwide were included in the study.

Rainfall, temperature, topography as well as historical influences crystallized as essential for the biodiversity. 70 percent of biodiversity differences can be explained by these factors alone. display

Availability of water is crucial

"The climate is particularly important here: in most regions, the availability of water is crucial for plant biodiversity, " explains Kreft. This insight is particularly important against the backdrop of the current climate debate: "Climate change is causing many regions in the world to become significantly drier - biodiversity could decline sharply here. This is especially true for tropical and subtropical areas, which are home to most of global biodiversity. "

Another factor in biodiversity is the available heat energy, measured as "potential evapotranspiration". Put simply, the higher the temperature, the higher the biodiversity. However, this statement only applies with one important restriction: "We find a positive correlation between temperature and biodiversity only below a certain average temperature, which is almost always undershot in the higher latitudes, " emphasizes Jetz.

Species numbers in unexplored areas can be estimated

"Unfortunately, we botanists are far from knowing the distribution of every single plant species on the globe. With the help of this model, we can estimate the species numbers in previously unexplored areas, "says the director of the Nees Institute Professor Wilhelm Barthlott. "Only by understanding today's biodiversity distribution can we make reliable predictions about future changes."

Rousing Cape region

Before R tsel, the researchers provided the relatively dry Cape region of South Africa. Today's climate does not seem to play the crucial role here. For many generations of botanists, the Cape region has been famous for its extraordinary biodiversity.

In the red areas biodiversity is mainly controlled by temperature, in the blue regions it mainly depends on the availability of water. Nees Institute of the University of Bonn

"We also find twice as many plants there as we would expect according to our model, " says Kreft. Biologists are still disagreeing about the reasons: The explanation approaches range from a particularly stable climate to the exact opposite, ie recurring climatic fluctuations. But perhaps it is simply the special situation of South Africa between a cold ocean current in the west and a warm one in the east. This leads to an extremely strong change of environmental conditions and thus to many different living conditions in a confined space.

(idw - University Bonn, 20.03.2007 - DLO)