The cover image for our new issue shows an ancient bristlecone pine in the White Mountains of California. Author and photographer, Connie Millar shares her insight into this unique landscape, her stunning cover image and her related research paper “Symbiotic interactions above treeline of long‐lived pines: Mycorrhizal advantage of limber pine (Pinus flexilis) over Great Basin bristlecone pine (Pinus longaeva) at the seedling stage” by Shemesh, Boaz, Millar & Bruns.
Travelers crossing the American Great Basin experience a vast, seemingly empty landscape of dun-colored basins that ascend seamlessly into distant mountain ranges. Up close, this magical landscape is a mountaineer’s—and mountain scientist’s—paradise. Over 650 mountain ranges occur in this hydrographically defined region where all water drains internally, extending from the Sierra Nevada to the west to the Uinta Mountains to the east. Summits of those and 35 other ranges, reach >3050m — pushing peaks and alpine plateaus into the endlessly changing skyscape. Overall the Great Basin experiences a semi-arid climate with varying influences from the Pacific Ocean, Gulf waters, and continental circulation. The White Mountains, lying along eastern California, exemplify many superlatives of the Great Basin. From the highpoint at White Mountain Peak (4344 m) summit plateaus > 3700 m extend north and south, paralleling a fault-defined eastern escarpment that drops 3075 m to the basins below. Endemic flora and fauna find niches defined by the sharp changes in substrate, carbonate to granitic to volcanic, and from Precambrian to recent in age.
Forest ecologists have long revered the White Mountains for the occurrence of long-lived Great Basin bristlecone pines (GBBP; Pinus longaeva), which grow on its slopes. With a range limited to the highest California, Utah, and Nevada Great Basin mountains, GBBP has long been the focal species for the science of dendrochronology. Here are living pines, more than 4800 years old such as the Methuselah tree near the lower elevation border. GBBPs also attain great diameters, such as the Patriarch growing near treeline (3470m) with 11m girth. Preservation of pine wood in the cold, arid climate has allowed tree-ring chronologies to be developed that extend to the late Pleistocene. Reading growth patterns like bar codes, tree-ring scientists have reconstructed Holocene climate history, providing key evidence of anthropogenic warming to early IPCC reports.
I have been coming to the White Mountains for many years to study the responses of GBBP and its congener, limber pine (P. flexilis), to both historic and contemporary climates. One of the mysteries of GBBP is the remarkable capacity of individual trees to persist through millennia of historic climate variability. What does that portend for the future of the species under contemporary changes? While pine forests of both species form nearly continuous forests around the range, in only a few places are seedling pines establishing above the 20th century treeline. In those highly localized areas, however, robust regeneration of young trees dots the seemingly barren landscape. What enables regeneration in those places and not elsewhere? Why are these areas of regeneration dominated by young limber pines despite that mature GBBPs constitute the treeline forests? Could mycorrhizal fungi offer a clue? I recently teamed up with two forest microbial biologists, Tom Bruns (UC Berkeley) and Hagai Shemesh (Tel-Hai College), to try and answer this very question. Read what we discovered in our article: Symbiotic interactions above treeline of long‐lived pines: Mycorrhizal advantage of limber pine (Pinus flexilis) over Great Basin bristlecone pine (Pinus longaeva) at the seedling stage.
Connie Millar Pacific Southwest Research Station, USDA Forest Service, USA