Reproductive ecology of Pinus nigra in an invasive population: individual- and population-level variation in seed production and timing of seed release
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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.
KeywordsCone production Individual variation Pinus nigra Seed abscission Linear mixed-effects models Negative binomial distribution Seed traps
Thanks to Scion for providing lab space in Christchurch and equipment, with a special thanks to Alan Leckie for favours too numerous to mention. Also thanks to Landcare Research in Lincoln for providing randomised sampling plots. Thanks to Gordon Baker for sharing his knowledge of pines in New Zealand.
This study was funded by the Australian Research Council (DP0771387) and an Australian Research Fellowship to YMB. KC was supported by funds from these grants. PC was funded through an Australian Research Council-OCE Postdoctoral Fellowship. SC was funded by an Australian Research Council-linkage scholarship. NL was funded by Scion.
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