Rainforests are among the most charismatic as well as the most endangered ecosystems of the world. Strangely, they occur in tropical but also temperate climates. The conditions they need remained poorly understood so-far.

Canopy height is not a continuum

This is remarkable according to Marten Scheffer who led the investigating team: “If you study the whole earth, it turns out that canopy height is not a continuum. Canopies of 25 meter high are surprisingly rare. Canopies are either lower, or you get the true gigantic rainforest canopies. There is little in between.”

Expansion of giant forests

The researchers show that the distribution of such giant trees is sharply limited to situations with a mean annual precipitation above a threshold of 1500 mm rainfall that is surprisingly universal across tropical and temperate climates. The total area with such precipitation levels is projected to increase by about four million km2 globally over the next decades with climate change.

“These results imply that strategic management could in principle facilitate the expansion of giant forests, securing critically endangered biodiversity as well as carbon storage in selected regions.” says Xu Chi, the specialist from Nanjing University who analyzed the data.

Implications

Marten Scheffer highlights the profound implications: “Authors ranging from Charles Darwin to John Steinbeck have described the deep spiritual impact that giant trees have on humans. We now know that these forests also harbor much of the critically endangered biodiversity and store vast amounts of carbon. The fact that the very wet regions are projected to increase across climate zones, allows us to give a cautious positive twist in times where bad news of climate effects prevails. Of course, this opportunity can only be materialized if we succeed in managing those precious ecosystems better globally.”