Masting or highly synchronous intermittent production of large seed crops is common among many perennial plant species and may be strongly influenced by climate. In previous studies conducted in the 1970s, masting in pinyon pine (Pinus edulis) populations of northwestern Oklahoma and New Mexico were negatively correlated with warm late summer temperatures. From the 1970s to the present, temperatures across this region have increased by ca. 1.3 º C. Following this, we predicted that increasing temperature across the region has led to declines in ovulate cone production and as such these populations may be potentially vulnerable to climate change. In this study, we used the previously collected pinyon pine (Pinus edulis) cone production data from 1969-1978 (1970s) and data from 2003 – 2012 (2000s) to understand how cone production has changed over the past 35 years. In both the 1970s and 2000s, cone production was quantified using the cone-abscission scar method at 9 sites across northwestern Oklahoma and New Mexico.
Results/Conclusions
There were significant declines (>25% at the majority of sites) in both the strength of masting events and overall cone production from the 1970s to the 2000s. However, sites varied drastically in the percent change in cone production (-1 to -64%) and also in the percent increase in growing season temperatures (2 to 12%). Notably, declines in seed cone production were greatest in areas with larger increases in growing season temperatures during the 3 years prior to masting events. These results suggest seed production may be an increasingly narrow bottleneck for pinyon pine regeneration with climate change. While our research was on pinyon pine, similar declines may be occurring in other tree species, especially other semi-arid pines. We recommend continued monitoring of tree species reproduction to better understand how widespread, both in geographic area and across taxa, these declines are.