Mast-seeding, or the synchronous and episodic production of seed crops, is hypothesized to be influenced by a combination of resource availability and discrete weather cues. As global climate continues to change, the conditions that initiate these events may become increasingly erratic and the resources necessary to produce large cone crops may become increasingly scarce, particularly in semi-arid systems that frequently experience chronic water stress. Yet these effects are unlikely to be uniform across a given region: the direction and magnitude of climatically driven changes in reproductive behavior may vary due to local physiographic conditions and long term patterns of productivity. This research leverages a novel, historic (15 year) dataset to quantify patterns of seed production across the latitudinal distribution of a semi-arid, mast seeding conifer- pinyon pine (Pinus edulis). We develop a quantitative model to describe the spatiotemporal patterns of mast seeding at 28 sites in Colorado and New Mexico as a function of local weather patterns and landscape-scale gradients of water deficit. Using this model, we investigated how local weather patterns interact with physiographic water deficits to affect seed production, and how these relationships exert controls over mast seed events in P. edulis.
Results/Conclusions
Cone production in P. edulis was strongly and negatively affected by the vapor pressure deficit (VPD) during periods of seed cone meiosis in the late summer and fertilization in the following spring. These relationships were strongly influenced by landscape level gradients of climatic water deficit and monsoonal precipitation, driving highly variable patterns of cone production across the latitudinal range of this species. We hypothesize that water stress during critical periods of seed cone meiosis and fertilization disrupts physiological processes critical to cone production, resulting in poor quality or entirely absent seed cone ovules and pollen production. Furthermore, access to a consistent source of late summer moisture strongly mediates this relationship and influences patterns of cone production across the landscape. These results suggest that mast seeding is largely an induction-limited phenomenon in P. edulis, and demonstrate the sensitivity of these processes to site level water deficits. Climatic disruptions of mast seed events in semi-arid conifers may significantly affect woodland regenerative and structural dynamics, as well as the wildlife populations that are dependent upon mast seed crops.