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Accounting for clonality in comparative plant demography – growth or reproduction?

Janovský, Zdeněk, Herben, Tomáš, Klimešová, Jitka
Folia geobotanica 2017 v.52 no.3-4 pp. 433-442
branching, databases, demography, developmental stages, flora, herbaceous plants, longevity, models, ontogeny, reproduction
Clonal growth occurs in a high proportion of herbaceous plant species, but it is difficult to deal with in demographic transition matrix models. It is primarily a growth process, but in many cases gives rise to new individuals from the viewpoint of plant demography. In the present contribution, we review how clonality is treated in existing demographic studies of clonal species from the Central European flora. We based our analyses on publicly accessible data in the COMPADRE and CLO-PLA databases and compiling from these information on plant matrix population models (hereafter MPMs) and clonal traits. Out of the 55 species × study combinations of species with known clonality, ca 30% neglect clonality. Another 30% treat clonal growth as growth of mother ramet and only the remaining 40% address clonality as a separate reproductive pathway. However, but only about half of these studies (12; 22% of total) reported a separable submatrix of clonal transitions necessary for comparative analyses. Here we show that failure to report clonal transitions separately leads to a serious bias in estimation of many demographic characteristics derived from MPMs, such as generation time. Shoot ontogeny (namely shoot lifespan and its branching architecture) largely determined whether clonality was neglected, treated as growth or treated as reproduction. Additionally, species with long runners were under-represented in demographic studies relative to their proportion in the Central European clonal flora. To conclude, we discuss how to construct MPMs for species with varying degree of ramet integration. We recommend that demographic analyses should focus on ramets – the smallest unit capable of living through all life-cycle stages of the species – as a sampling and study unit of plant populations.