Designing seed banks for in situ conservation purposes: more species or better quality?
Volume 12 Number 2 - January 2015
Philippe Bardin and Stéphane Buord
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The Fédération des Conservatoires botaniques nationaux (FCBN) re-groups eleven Conservatoires botaniques nationaux (CBN) in a network of more than three hundred employees, seven conservatory gardens and nine seed banks dedicated to the conservation of wild species in France, including the overseas territories. With forty years of field expertise on species distribution, conservationists of this network are now able to identify species on the brink of extinction, and to undertake a combined approach between ex situ and in situ practices to address this potential loss of biodiversity.
From the seed bank to the field: a case study in the CBN of Brest
The seed bank of the CBN, Brest contains 1,165 threatened plant taxa categorized by IUCN as EW (Extinct in the Wild), CR (CRitically Endangered), EN (ENdangered) and VU (VUlnerable). These species mostly originate from the Mediterranean basin and oceanic islands around the world, notably Canary, Mascarene and Juan Fernandez Archipelagos. Seeds are preserved in freezers at -18°C. Dedicated to the world’s endangered flora, this seed bank is among the world’s largest according to the number of species it harbours. Created in 1975, the CBN of Brest was indeed a pioneer in this field, committed since the beginning to the ex situ conservation of the world’s threatened species.
The frozen seed collection is not an achievement in itself, but an essential tool for conservation actions, specifically in situ reintroduction or population reinforcement. For 40 years, a number of actions have been carried out from this collection of taxa to be restored in natura.
Among these species, Normania triphylla, an endemic species of Solanaceae from Madeira is noteworthy. The Normania genus is represented only by two species: Normania nava, an extinct endemic from Tenerife, Canary Islands, and Normania triphylla from Madeira, believed to be extinct since the last century until the botanist M. Nobrega found a few survivors in the Laurisilva in 1994. This extremely rare species suffers from strong competition of invading plants which overwhelm the few open areas of this subtropical forest. Twenty four seeds were handed to the CBN of Brest, who started an ex situ conservation programme, followed by in situ reintroduction, with the support of a private company.
The production of Normania plants began in July 2007 from a batch of a hundred seeds kept in the CBN freezers. In the spring of 2008, the number of adult plants for seed production and cuttings passed one hundred. Between 2007 and 2010, 80,000 Normania triphylla seeds where harvested in Brest’s greenhouses, 30,000 of which were sent to Madeira. Those were sown in cultivated areas, around 19 foresters’ houses within the Laurisilva, as well as in experimental sites in the wild. The aim of these forest nurseries was to obtain small cultivated populations in the mountains, in order to have a sustainable supply of accessible resources which could be progressively returned to the wild, in sites most favorable for the species establishment.
In 2010, reintroduction actions were carried out in the most favorable sites, in partnership with the Rui Viera de Funchal Botanical Garden, Madeira National Park and local schools. The success of the reintroduction of a species extinct in the wild requires some time and monitoring is underway. Nevertheless in 2013, new populations of Normania have been confirmed within and surrounding the testing sites.
This experiment highlights the importance of setting up in situ nurseries close to suitable habitats of the threatened species, partially due to the uncertainty of seeds maintaining high germination capabilities over a long time period during the banking process, and the risk of unwanted selection when species are cultivated in glasshouses and botanical gardens (Fridlander et al., 2000).
The need to resort to seed banking to protect wild species in the field is controversial, as this approach highlights. Amongst other issues, it does not address the continuing disappearance of wild species due to the many changes and misuses of their habitats. Furthermore, evidence indicates that climate change will disrupt distribution patterns for species, with consequent changes to the composition of plant and animal communities (Parmesan et al., 2002). However, as shown for Normania triphylla, genetic resources that have previously been seed banked are important to save species locally threatened with extinction, on condition that the habitat is still suitable to host the species. We do however advise considering the following point in order to successfully undertake reinforcement or reintroduction programmes in the future.
Can we trust admixtured populations to solve genetic issues?
Using allochthonous genetic resources to save local species has always provoked a strong debate. Under the precautionary principle, scientific authorities and public policies advocate only the use of local genetic material or express unambiguously this preference by highlighting the risks of using non-local genetic materials. In the same way, land managers and local communities are reluctant to host genetic resources different from those that are locally threatened, mainly because they consider that the population used to bring ‘new blood’ to the threatened population is a population of a distinct taxon (Maurice et al., 2013).
However, in some cases, the level of genetic diversity among the threatened population is extremely low and the high risks of failure strongly promote the introduction of new genetic material into the depreciated populations (Bottin et al., 2007).
The reintroduction of the large-flowered sandwort in the Fontainebleau forest (Arenaria grandiflora L.), recently led by the CBN of the Paris Basin and the CESCO team of the National Museum of Natural History located in Paris, is an innovative approach to test the benefits of mixing plants of different origins in order to restore a threatened population of this mountain species in the lowlands. In 1999, genetic investigations gave evidences of inbreeding or fixation of deleterious alleles by drift in the remnant Fontainebleau population. Thus, it was proposed to save this severely declining species in the lowlands by not using local genetic resources with low fitness and inability to adapt but instead promoting an increased level of genetic diversity in the population to be reintroduced. A ten- year experiment in mixing populations started in 2001 in the Fontainebleau forest. It was conducted in several 100 m² enclosures, sufficiently distant from the native population to avoid any cross pollination and seed dispersal that may have interfered. The experimental populations were composed of native individuals and individuals of the nearest lowland population, in the Loire Valley.
Ten years later, this experience has provided evidence that admixture has occurred in a positive way, with more vigorous individuals that exhibit a large number of flowers in the enclosures. Finally, in 2011, the species was reintroduced into the native population. The whole experiment is still being monitored to assess both the model in the enclosures and the reintroduction trial of the native population.
Taking forward Target 8 of the GSPC.
According to the Target 8 of the Global Strategy for Plant Conservation (GSPC), by the end of 2020, “at least 75% of the threatened plant species are in ex situ collections, preferably in the country of origin, and at least 20% are available for recovery and restoration programs” , with a priority given to critically endangered species.
The CBN are currently and massively involved in the completion of Red Lists at a regional scale. These are important due to the distribution patterns of species over the whole French territory, and have hugely improved, mainly over the past two decades. These Red Lists provide a basis for a new strategy for seed banking and it is now possible to assess the implementation of this GSPC target with a high level of accuracy.
For example, the Red List of the Ile-de-France region (Auvert et al., 2011) highlighted four hundred critically endangered species that conservationists must take care of, through ex situ and in situ conservation programs.
According to this review, one can consider that seed banking of seed from one location of those four hundred species is sufficient. However, the Arenaria grandiflora experiment clearly supports the idea that saving a species which is locally threatened with extinction will also need, in some cases, non-local genotypes. Because it is now possible to investigate genetic diversity rapidly and at affordable costs, seed banks must adapt and offer seed from different origins for species to be reintroduced or reinforced in the wild. People in charge of conservation programs should however take care of the ecological features of the habitats in which the seeds or cuttings are collected, to avoid any kind of outbreeding depression when this material is translocated into the population threatened with extinction. It is also important to investigate the genetic structure of the sampled population, for example when the founder effect leads to a patchy distribution of genetic diversity (Machon et al., 2003).
It is highly probable that a dilemma will soon emerge, in the context of limited resources dedicated to seed collecting, between banking seed from several locations of a regionally critically endangered species or focusing only on single locations, but for all threatened species. If the priority is given to seed banking all threatened species, any subsequent reinforcement or a reintroduction programmes need to clearly understand the threats on the population in the wild and if the population on the verge of extinction is genetically depreciated. Then seed banking from several locations is an alternative pathway to consider.
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