Phenology, developmental patterns and growth cycles for multiple seed crops in Pinus elliottii Engelm. and P. clausa (Engelm.) Vasey

Abstract

Pines are known to produce one seed crop each year and mature about 20 months after pollination. The entire life cycle may take two to three years. Recent observations, however, show that a greater number of crops may develop annually and that cone development may be faster. In Pinellas County, Florida, Pinus clausa and P. elliottii now have three seed crops annually, and consequently, more seeds during the year. Also, there is no dormant phase from pollination time to seed maturity in the primary (most abundant) crop of these species. The reason for this change in reproductive strategy is thought to be as a response to climatic changes, in particular, CO2 levels. Pines seem to be reacting to increases of available atmospheric CO2 that fluctuate seasonally. The gas may act as a biochemical switch for developmental stages and be a mechanism for controlling cone growth. Furthermore, there are definite phenological shifts forward in the primary seed crops of P. clausa (about 105 days) and P. elliottii (about 150 days) that present more opportunity for their hybridization. Pines are known to show sensitivity to their environment, and therefore, are climatic indicators of changes that are probably occurring in other economically valuable plants.