Background/Question/Methods
Very few study systems offer the ability to examine the detailed population and community-level dynamics of long-lived species on time-scales relevant to their life history, or to probe the climatic controls on population behavior over more than a few decades. The Bristlecone pines (Pinus longaeva) of the White Mountain Range are not only the longest-living (non-clonal) species on record, but deceased individuals and relict wood can remain intact for millennia in their cold and dry high elevation environment.   To better understand the forces promoting both individual and population longevity in these trees, I used dendrochronological analyses to reconstruct the spatial and temporal history of a high-altitude Bristlecone population with a relict wood record spanning 7000 years.  To better understand the effect of the early-life stages on population dynamics, I estimated individual fecundity for three consecutive years and conducted extensive field surveys to locate and date new seedlings.   Additionally, I used several experimental approaches to identify the major determinants of germination success and the most significant causes of mortality for very young seedlings.
Results/Conclusions
The population reconstruction was completed using over a thousand living and dead trees.  Over many millennia, the major source of mortality has been individual lightning strikes.  The frequency of these strikes is positively correlated with recruitment success and also varies consistently with some large-scale climatic trends.    Field surveys for new seedlings has revealed that over the last 50 years, seedling recruitment has been extremely episodic, with major successful events occurring only during years in which the summers were both unseasonably cool and wet (e.g., the early 1980’s).  Experimental placement of both seeds and seedlings has demonstrated that fewer than 1 in a million seeds will successfully germinate in average years, yet juvenile survival can be remarkably high for a long-lived tree-species.  Estimates of individual tree fecundity suggest that less than 10% of the trees produce over 85% of the annual seeds.  These disparate data sets have been used to estimate population-wide vital rates and to parameterize stage-based demographic models.   The models show a remarkable increase in population growth rate, concurrent with climatic warming, and indicate that population dynamics are driven largely by rare episodes of successful germination.