Reproductive Ecology of Pinus Nigra in an Invasive Population

Reproductive ecology of Pinus nigra in an invasive population: individual- and population-level variation in seed production and timing of seed release Shaun Coutts, Caplat, Cousins, Ledgard, Yvonne Buckley To cite this version: Shaun Coutts, Caplat, Cousins, Ledgard, Yvonne Buckley. Reproductive ecology of Pinus nigra in an invasive population: individual- and population-level variation in seed production and timing of seed release. Annals of Forest Science, Springer Nature (since 2011)/EDP Science (until 2010), 2012, 69 (4), pp.467-476. 10.1007/s13595-012-0184-5. hal-00930835 HAL Id: hal-00930835 https://hal.archives-ouvertes.fr/hal-00930835 Submitted on 1 Jan 2012 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Annals of Forest Science (2012) 69:467–476 DOI 10.1007/s13595-012-0184-5 ORIGINAL PAPER Reproductive ecology of Pinus nigra in an invasive population: individual- and population-level variation in seed production and timing of seed release Shaun R. Coutts & Paul Caplat & Katrina Cousins & Nick Ledgard & Yvonne M. Buckley Received: 3 October 2011 /Accepted: 18 January 2012 /Published online: 23 February 2012 # INRA / Springer-Verlag France 2012 Abstract & Conclusions Right-skewed fecundity distributions have & Context The details of fecundity, such as its distribution the potential to slow spread rates, while preferentially re- and timing, can have important consequences for forest leasing seeds in dry windy conditions is likely to increase dynamics. spread rates. The net effect of these processes is an open & Aims We detail two aspects of the reproductive ecology of question. an exotic population of Pinus nigra in New Zealand. We compare our findings with those reported for P. nigra in Keywords Cone production . Individual variation . Pinus southern France and Britain. nigra . Seed abscission . Linear mixed-effects models . & Methods We describe variation in fecundity, both within Negative binomial distribution . Seed traps the population and through time, and relate seed release to climatic conditions. & Results On average, trees entered reproduction earlier than 1 Introduction reported in European studies. Although the mean number of cones per tree varied through time, the distribution of cone The details of fecundity, such as its distribution within a production among trees was consistently best described population (Clark et al. 2001) and timing (Soons and using a negative binomial or mixed gamma-exponential Bullock 2008), can have important consequences for distribution. Both distributions are right skewed and trees population persistence and spread. For most forest species, maintained fecundity hierarchies over time, suggesting that these dynamics have been well described at stand or regional some trees in the population have much higher lifetime scale (Oliver and Larson 1996). Studying the variation of reproduction than others. We found that trees released fecundity in populations established outside of the species’ significantly more seeds when conditions were dry and windy, native range can give great insights into the species’ response potentially increasing the proportion of seeds that disperse in different environments (Dehlin et al. 2008). This is partic- long distances. ularly important considering many conifer species, including Mediterranean pines, are invading large parts of the world (Richardson and Rejmanek 2004). Further, the reproductive Handling Editor: Eric Rigolot ecology of Pinus species is an important predictor of their Contribution of co-authors Paul CAPLAT, field work and editing of invasiveness (Rejmánek and Richardson 1996). manuscript. Katrina COUSINS, field work, lab work and editing This study describes the reproductive ecology of an manuscript. Nick LEDGARD, information about Mt Barker history, invasive population of Pinus nigra at Mt Barker, New field work. Yvonne M. BUCKLEY, field work, statistical advice and Zealand. Pinus nigra is a masting species, with highly editing of manuscript. – : : : : productive mast years occurring once every 3 5yearsin S. R. Coutts (*) P. Caplat K. Cousins N. Ledgard British and French populations (Kerr 2000; Kerr et al. Y. M. Buckley 2008; Boulant et al. 2009). Differences in cone production School of Biological Sciences, University of Queensland, Building 8( Brisbane, QLD 4072, Australia between low and high coning years can be dramatic. In an e-mail: [email protected] invasive French population trees averaged 33 cones in low 468 S.R. Coutts et al. years and 757 cones in mast years (Boulant et al. 2009). would reduce the amount of seed available for long distance Although detailed studies of its reproductive ecology have dispersal, which has been shown to be important in been undertaken near its native range in Europe (Southern driving spread in the Mt Barker population of P. nigra France) and in Britain (Kerr 2000;Kerretal.2008), far (Buckley et al. 2005). less is known about the reproductive ecology of P. nigra in We undertook a detailed study of the timing and distri- its invasive range in the southern hemisphere. bution of fecundity in an invasive population of P. nigra at The distribution of fecundities within many plant popu- Mt Barker, New Zealand. We compare our results with those lations is often right skewed, with a few highly fecund from studies of P. nigra nearer it home range in Europe, to individuals producing most of the seed (Cook and Lyons see how its reproductive ecology changes between ranges. 1983; Scheiner 1987; Bullock 1989; Herrera 1991; Herrera We also discuss the implications of our results for popula- and Jovani 2010). Further, in perennial plants fecundity tion spread, a process which is of fundamental importance to hierarchies can persist through time, i.e. it is the same understanding and managing invasive plants (Caplat et al. individuals that are highly fecund each year (Herrera and 2012a; Richardson and Pysek 2006). Jovani 2010). This leads to a few individuals producing many more seeds over their lifetime than the majority of the population. These large variations in total lifetime 2 Method fecundity between individuals have the potential to substan- tially reduce spread rates (Clark et al. 2001). We first describe the study species and main study area In the genus Pinus, seeds are often released as cones dry (Mt Barker), and then describe field methods, outlining out (cones are xerochastic; Greene et al. 2008), thus changes how seeds and cones were counted and/or trapped and in relative humidity may play a role in seed release. The how meteorological data was collected. This is followed mechanism behind Pinus species cone response to lower with a description of the data analysis. We outline how humidity is well established (Dawson et al. 1997; Reyssat distributions were fit to cone production within the and Mahadevan 2009), and several cases have documented population and the distribution of seeds per cone. We dry conditions promoting seed abscission in conifer species. then describe the analysis of cone opening and seed In a British population of P. nigra, lower relative humidity release, and how seed release was related to relative increased seed release rates (Kerr et al. 2008), while seed humidity and windiness. All data analyses were carried release in a Mediterranean population of P. halepensis was out in the R statistical package, and unless otherwise stated strongly correlated with seasonal hot dry winds (Nathan et all functions used were part of the “base” or “stats” libraries al. 1999). Also, North American west coast populations of (R Core Development Team 2010). the spruce Picea sitchensis open their cones when drying air descends from nearby mountains (Harris 1969). 2.1 Study species The relationship between relative humidity and seed release may be especially important where strong winds The main subspecies of P. nigra presentatMtBarkeris are also dry. Then, if P. nigra does release more seeds P. nigra Arn. ssp. laricio (Buckley et al. 2005), but a when relative humidity is low, a disproportionate number minority of pine at Mt Barker also display characteristics of seeds may be released when wind speeds are higher, of subspecies nigra Arn. The genetic structure of the causing higher spread rates (Nathan and Ne'eman 2004). population has not yet been studied, and hereafter we This effect is potentially very important at our study site refer to all pines in the Mt Barker population as P. nigra. in New Zealand; the prevailing wind from the northwest Pinus nigra is a wind-dispersed species, with winged is warm, dry, and much stronger than winds from other seeds that have a low mass relative to other Pinus species directions (Caplat et al. 2012b). Wind itself may also (Rejmánek and Richardson 1996). Our dataset contained 15 play a role in seed release, both increasing evaporative trees at Mt Barker that did not produce cones in 2008 but loss and mechanically loosening seeds from cones did in 2009. From these trees, we calculate cone production (Greene et al. 2008). started at a median age of 16 years, with trees as young as Pinus nigra may disperse some seeds still inside its cones 13 and as old as 19 observed to produce cones for the first when it drops them at the end of each dispersal season. In a time. Pinus nigra produce one growth node per year and British population, Kerr et al. (2008) found 46% of seeds can be aged by counting nodes (Buckley et al. 2005). dispersed in this way. If this mode of dispersal occurs more generally, then assuming all seeds are released and enter the 2.2 Study area wind dispersal kernel may overestimate spread.

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