A global action plan for the conservation of threatened Zelkova species
June 2013 - BGCI, the Natural History Museum Fribourg and the Botanic Garden of the University of Fribourg, Switzerland, have published a global action plan for the conservation of the six extant species of Zelkova, a relict genus that dates back to the Tertiary era (~65-2.5 million years BP). Developed over a period of three years, this collaborative and interdisciplinary project has generated a wide range of research findings that inform integrated action for the protection of the species of Zelkova and the habitats in which they occur, including ex and in situ conservation status assessments, studies of phylogeny and phylogeography, as well as analyses of population genetics and structure.
Found in disjunct regions in Eurasia (Sicily: Zelkova sicula; Crete: Z. abelicea; Caucasus: Z. carpinifolia) and East Asia (China, Japan, Korean Peninsula: Z. serrata; China: Z. schneideriana and Z. sinica), and having outlived changing environmental conditions over an enormous geological time span, this genus serves as a model taxon to study and interpret past and recent biogeographical and evolutionary processes that affect species distribution and differentiation. A better understanding of these linkages will also contribute to informing future biodiversity management approaches in a climate of rapid global change. With very restricted distributional ranges and few remaining populations in the wild, all six Zelkova species occur in distinct habitats and altitudinal zones that in turn shape plant habit, ecological features and reproductive mechanisms.
In and ex situ conservation status assessments
In situ conservation status assessments (Red listing)
Detailed conservation status assessments according to the IUCN Red List categories and criteria have been undertaken to date for the southwest Eurasian species:
Discovered in 1991 in the Iblei mountains in eastern Sicily, Italy, with a second population found in 2009 in relative proximity to the former, Z. sicula is one of the rarest and most endangered trees worldwide. While bovine grazing exerts a significant pressure on this species that occurs in thermophilous, evergreen and semi-deciduous oak wood communities, extreme climatic fluctuations and drought in recent years, have accelerated the process of degradation in both populations. Unlike the other members in the genus which are all diploid, Z. sicula is triploid and exhibits pollen anomalies; this may explain why to date only sterile fruits and vegetative propagation have been observed in this species.
Endemic to Crete, Greece, Z. abelicea represents one of the main biological treasures of this island. Found in supra- and oro-Mediterranean mountain forests, the four ranges – Levka Ori, Psiloritis, Dhikti and Thripti – host some some 40-50 stands of Z. abelicea of considerable diversity between and within the populations. Ovine and caprine grazing, soil erosion, as well as water stress and fire represent major threat factors. The species has been logged since ancient times for its valuable timber.
Occurring in lowland as well as mountain forests across the Caucasus, including two main population centres in the east (Hyrcania) and the west (Colchis), Z. carpinifolia has the widest distributional range (some 100 populations) of the three Eurasian species. Molecular studies revealed a significant genetic differentiation between the two main groups which is indicative of the many million years gone by since these populations fragmented into their current distribution. By and large, in all regions where the species occurs, overgrazing, expanding mass tourism and related infrastructure development in areas of scenic beauty, are major drivers of change. Although numerous natural reserves and parks have been created in Georgia, Azerbaijan and Iran, containing important forest stands with Z. carpinifolia, the pressure on these habitats is steadily rising.
Z. serrata, Z. schneideriana and Z. sinica
With all three species in the East Asiatic group generally occurring in temperate to subtropical forest communities, Z. serrata exhibits the largest geographical distribution ranging from Japan to the Korean Peninsula and China, while Z. schneideriana and Z. sinica are found only in China. Rapid habitat transformation and logging represent major threats. Detailed conservation status assessments of all three species have not been undertaken to date, but are part of Phase II (2013-2015) of Project Zelkova.
Global Ex situ Survey
In 2010, a worldwide survey was carried out to gauge the status of Zelkova species in living ex situ collections, including a presence-absence analysis, an assessment of the extent and average size of collections, as well as of plant provenance and genetic representativeness.
By and large, the majority of botanic institutions with Zelkova collections are not found in locations of their origin, but in central and northern Europe and North America, in countries with a long-standing horticultural tradition. Of the 275 Zelkova records (collections) gathererd from 146 institutions in 27 countries, almost 50% of all Zelkova ex situ collections are in the United States, United Kingdom and Germany. Other countries with significant collections include China, France, Belgium and Australia. Except for the East Asiatic species Z. sinica, serrata and schneideriana that are worldwide best represented in some 25 Chinese collections, the Mediterranean Z. sicula and Z. abelicea as well as the Transcaucasian Z. carpinifolia species are found to a very limited degree in the countries of the species’ natural distribution. Zelkova species with the widest distributional range (Z. serrata and Z. carpinifolia) are also the most common ones represented in ex situ collections, whereas, as can be expected, the most threatened species (Z. sicula, Z. abelicea and Z. sinica) are least in cultivation.
Worldwide distribution of Zelkova spp. collections and extent of collections in-country
Generally, collections are small, in 90% of the records they either hold one individual or two to 10 trees at most. In addition, the majority of ex situ collections is not well documented. Not only is the origin of the plant material unknown, but often also their taxonomic status and/or cultivation history in the given institution. These collections are therefore inappropriate for scientific study and unsuitable for practical conservation, especially for restoration programmes.
A mere 20% of the plants grown in ex situ collections is of known wild provenance. While ex situ collections of Z. carpinifolia represent to some extent the in situ variability of its two distinct, phylogeographic western and eastern lineages (some 15 haplotypes identified to date) with 10 botanic gardens hosting trees from both groups (representing 11 haplotypes), the complex genetic diversity of Z. abelicea is not reflected in collections with only two out of at least 36 haplotypes found in botanic gardens. As far as Z. sicula is concerned, all five existing collections are based on plant material gathered from the population discovered 1991.
Read BGCI's report 'Global Survey of Ex situ Zelkova Collections' (10 pages)
Phylogeny and phylogeography
Chloroplast and nuclear DNA analyses confirm the fragmented geographic distribution with a southwest Eurasian cluster containing Z. sicula, Z. abelicea and Z. carpinifolia, and an East Asiatic group with Z. serrata, Z. schneideriana and Z. sinica. However, genetic similarities of Z. carpinifolia and Z. schneideriana suggest that close linkages of these species existed during an earlier geological period that later became disconnected as a result of environmental changes. The differentiation into an East Asiatic and southwest Eurasian group is likely to have occurred during the Tertiary’s Middle Miocene (18-12 million years BP). This division might have come about as a result of growing aridity in Central Asia that acted as a barrier against reunification.
Schematic phylogeny of the genus Zelkova
Z. abelicea is the genetically most diverse species in the southwest Eurasian group, with each mountain massif where the plant occurs representing a separate genetic unit. Two main groups have been identified in Z. carpinifolia, an eastern (Hyrcanian) and western (Colchis) clade. Genetically impoverished, Z. sicula is likely to be of hybrid origin, with the parents of this taxon suggested to be close to Z. abelicea and Z. carpinifolia ancestral species. Further genetic analyses in the East Asiatic group are needed based on large-scale collection of plant samples from natural populations, to clarify the phylogenetic and phylogeographic position of the species.
The Zelkova global action plan concludes with a number of specific recommendations for priority action pertaining to further survey work, in and ex situ conservation, regional and international research partnerships and networking, and enhanced public outreach.
Click on the cover image to download the action plan (3.75Mb)
Relict species from ancient times not only function as storehouses of information of the Earth’s transformation over millions of years but also deliver a diverse range of ecosystem services. Although ultimately a matter of societal choice, their conservation may therefore present a vital element in the development of future ecosystem management approaches, especially in a time of unprecedented, rapid global change.
Read more about BGCI's work to save threatened trees: Global Trees Campaign.
Read about the exhibition Encounters with an ancient natural heritage - Green Treasures of Azerbaijan
The Botanic Garden of the University of Fribourg and the Natural History Museum in Fribourg have created a website for Project Zelkova, with with more information about Zelkova projects.