Velocity of the falling dispersal units in Zelkova abelicea: remarkable evolutionary conservation within the relict tree genus

Abstract

PREMISE Seed dispersal is extremely important for the recovery and restoration of forest communities. Relict tree genus Zelkova possesses a unique dispersal mechanism: mature fruits fall with the entire twig, and the dried leaves that are still attached function as a drag‐enhancing appendage, carrying the fruits away from the parent tree. This singular adaptation has never been investigated in Z. abelicea. METHODS Drop tests with dispersal units and individual fruits of Z. abelicea were performed in controlled conditions to measure their dispersal velocity and to define their flight mode. RESULTS Zelkova abelicea uses both slowly falling dispersal units with chaotic motion, as well as fast falling individual fruits using a straight path. The falling velocity of Z. abelicea dispersal units is 1.53 m s‐1, which is virtually identical to that of the East Asiatic Z. serrata (1.51 m s‐1). In contrast, the falling velocity of individual fruits was 2.74 m s‐1 (Z. serrata: 5.36 m s‐1). CONCLUSIONS Members of the genus Zelkova, growing today in distant regions, show remarkable evolutionary conservation of the velocity and flight mechanics of their dispersal units. This is surprising because the Mediterranean and East Asiatic Zelkova species have been separated at least 15–20 mya. Zelkova abelicea, although growing in the Mediterranean with completely different forest structure and composition, still uses the same dispersal mechanism. The dispersal capacity of the genus Zelkova is less efficient than that of other wind dispersed trees, and it presumably evolved for short‐distance ecological spread and not for long‐distance biogeographical dispersal.

From glacial refugia to hydrological microrefugia: Factors and processes driving the persistence of the climate relict tree Zelkova sicula

“…3.2 Ma), which turned into even greater dryness during the glacial periods, from 2.3 Ma onwards (Suc et al, 2018). Such a contrasting climate, along with the presence of east-west oriented physiographic barriers (e.g., the Pyrenees, the Alps and the Mediterranean Sea) and restricted dispersal effectiveness (Certini et al, 2020;Svenning & Skov, 2007) remarkably limited the migration and recolonization chances for Zelkova species and were responsible for their stepwise massive extinction at higher latitudes (Magri et al, 2017;Suc et al, 2018). Rather common in Central Europe at the Mio-Pliocene boundary up to Late Pliocene (e.g., Kvaček (Magri et al, 2017).…”

“…As stated by Dobrowski (2010), to assess the climatic basis for microrefugia two factors must be carefully evaluated: suggest that the Sicilian climate relict could be represented now by "rear edge" populations (Hampe & Petit, 2005). They supposedly have been left behind during the northward species range shift following the Last Glacial Maximum (Hampe & Jump, 2011), owed to low dispersal ability (Certini et al, 2020) in face of long-distance recolonization or topographic/geographic barriers.…”

“Phoenix in Flight”: an unique fruit morphology ensures wind dispersal of seeds of the phoenix tree (Firmiana simplex (L.) W. Wight)

“…Winged diaspores that use spinning have strong positive correlations between the descent velocity and wing loading, similar to diaspores with other flight methods [ 6 , 7 , 16 ]. However, these winged diaspores require a complex aerodynamic mechanism to slow the seeds as they fall.…”

Predicting the effect of climate change on the geographic range of the Mediterranean relict tree Liquidambar orientalis Mill

“…However, it is noteworthy that the distribution range of the oriental sweetgum remained confined to the Anatolian refugium. The lack of return of the oriental sweetgum to Europe has been attributed to geological barriers and constraints on both natural and human‐mediated seed distribution for other relict trees such as P. fraxinifolia and Zelkova abelicea , as discussed by Certini et al (2020) and Song et al (2021), respectively. Recently, there has been a significant disruption of appropriate habitats of the species through human activities.…”