Stand Dynamics Influence Masting/Radial Growth Relationships in Pinus palustris Mill

Longleaf pine (Pinus palustris) regeneration is dependent on above-average masting (i.e., cone crop) years that occur over 5- to 7-yr cycles. Not understood, however, is how annual cone mast influences radial growth for longleaf pine. Here, we collected tree-ring data from one site in South Carolina and two sites in North Carolina to examine: (a) the relationship between longleaf pine mast and radial growth; (b) how timber thinning at one site affected this relationship; and (c) how previous October to current April Palmer drought severity index (PDSI) affects mast. We used dendroecological techniques to assemble three radial growth chronologies and compared annual radial growth to annual mast. We found the strongest negative correlation when mast was lagged 1 year from radial growth (i.e., mast of Year X with radial growth of Year X - 1), but current-year mast and growth were not significantly correlated. Mast/radial growth relationships were only detectible when radial growth indices less than 0.95, suggesting that trees reallocated resources from radial growth to mast production. Thinning improved annual mast yield, yet neutralized the negative relationship between mast and radial growth. Mast correlated with PDSI in the unthinned site, but not in the thinned site, suggesting that stand dynamics in the thinned site may have overridden climate/mast relationships. These findings reveal the utility of detecting endogenous factors in radial growth for longleaf pine and the benefits of reducing stand density for improving mast.