Reproductive ecology of Pinus nigra in an invasive population: individual- and population-level variation in seed production and timing of seed release

The details of fecundity, such as its distribution and timing, can have important consequences for forest dynamics. We detail two aspects of the reproductive ecology of an exotic population of Pinus nigra in New Zealand. We compare our findings with those reported for P. nigra in southern France and Britain. We describe variation in fecundity, both within the population and through time, and relate seed release to climatic conditions. On average, trees entered reproduction earlier than reported in European studies. Although the mean number of cones per tree varied through time, the distribution of cone production among trees was consistently best described using a negative binomial or mixed gamma-exponential distribution. Both distributions are right skewed and trees maintained fecundity hierarchies over time, suggesting that some trees in the population have much higher lifetime reproduction than others. We found that trees released significantly more seeds when conditions were dry and windy, potentially increasing the proportion of seeds that disperse long distances. Right-skewed fecundity distributions have the potential to slow spread rates, while preferentially releasing seeds in dry windy conditions is likely to increase spread rates. The net effect of these processes is an open question.