Effects of rainfall and solar radiation on cone production in slash pine

A correlation between the number of conelets produced in a slash pine seed orchard and climatic conditions was tested using a SAS(Statistical Analysis System) program. Grafted, 11-year-old slash pine trees were classified into three groups according to their inherent flowering potential. Flowering data(number of female conelets produced in early spring) from 40 trees for a consecutive 8-year period(1960~1967) were used to correlate with monthly rainfall and solar radiation of the year preceding flowering. Rainfall and solar radiation in a month or a period of 2 to 4 months, separately or in combination of the two were fitted into linear simple and multiple regression and stepwise regression. In simple regression, October rainfall showed the highest R² of 0.26, and May solar radiation the second highest 0.25(both negatively correlated). In multiple regression, May rainfall combined with May solar radiation showed a negative correlation with R² of 0. 35. When May through June rainfall was combined with solar radiation of the same period, it showed R² of 0.32. In stepwise regression, solar radiation in May was the single variable to fit best for cone production. Rainfall and solar radiation if combined showed negative correlation in all 6 models tested, suggesting that cloudy and dry season in late spring(May and June) favored abundant cone production in slash pine.