Science 7 December 2012: Vol. 338 no. 6112 pp. 1305-1306 DOI: 10.1126/science.1231070
[abstract] Large old trees are among the biggest organisms on Earth. They are keystone structures in forests, woodlands, savannas, agricultural landscapes, and urban areas, playing unique ecological roles not provided by younger, smaller trees. However, populations of large old trees are rapidly declining in many parts of the world, with serious implications for ecosystem integrity and biodiversity.
Majia here: Bobby's analysis of radiation-consuming fungi's role in killing vegetation is relevant reading http://optimalprediction.com/wp/radiation-eating-fungi-they-kill-trees-and-they-kill-people/
hat tip: Decline of the Empire