California mixed conifer-hardwood forests are tolerant of summer drought and even longer-term drought conditions. Oaks, in particular, are extremely resilient trees. They have persisted since the mid-Cretaceous, with life forms ranging from shrubs to large trees, from evergreen to deciduous. They have two distinct, but critical adaptations to drought that make this “mesic” taxon adaptable to dry hot environments. First, they form both arbuscular and ectotrophic mycorrhizae, with a high diversity of fungi that independently evolved many times. This means that a single tree forms mycorrhizal symbioses with partners adapting to different conditions and accessing many different resources. Several tree species have deep roots including both oaks and some pines. This allows access to water resources deep in the groundwater, and with hyphae that extend into the granite matrix. Thus, water can be accessed even during drought periods when surface soils are extremely dry. Fine roots and mycorrhizal hyphae persist utilizing hydraulically lifted water, and can even take up nutrients during these extremely dry conditions. These mycorrhizal hyphae remain viable during drought periods allowing them to rapidly utilize surface precipitation from summer monsoonal events. Both EM and AM mycorrhizal form networks that link mature trees. Seedlings can tap into these networks to access hydraulically-lifted water during the dry season, and access nutrients mineralized during both the dry and wet seasons by the network.
These characteristics could be used to re-design urban uses of oaks increasing seedling establishment, carbon sequestration, and reducing heat islands.
Michael Allen received a BS degree in Biology from Southwestern College (1974) in Kansas, and a MS (1977) and PhD (1980) from the University of Wyoming in Botany. He was a postdoc at the University of Nebraska, a Research Assistant Professor at Utah State University, and a faculty member at San Diego State University. He moved to the University of California-Riverside in 1998 as the Director of the Center for Conservation Biology. Originally serving as the Chair of Plant Pathology and Microbiology (2004-2012), he is now Chair of Biology.
Allen was a program officer at NSF from 1993-1995, for Conservation and Restoration Biology, Ecosystems, and the Long-Term Ecological Research programs.
His research focuses on mycorrhizae in conservation and in restoration of disturbed lands. He has published about 225 refereed papers in this area. He has worked to facilitate regional Habitat Conservation Plans for which he received the American Planning Association, Inland Empire Section, Distinguished Leadership-Academic Award for 2003. He was elected a AAAS Fellow in 2005 and received the Chevron Conservation Award in 1999. Allen was the Chair of the Soil Ecology Section for the Ecological Society of America 2011-2013, and is currently the President of the International Mycorrhizal Society for 2013-2015.