The Irish Rare and Threatened Plant Seed Bank, and its Use in the Conservation of Irish Biodiversity
Volume 2 Number 5 - August 1995
James Martin, Steve Waldren and Aileen O'Sullivan
The Irish Red Data Book of Vascular Plants (Curtis & McGough, 1978) drew attention to the fact that Ireland has 159 species, 0.7% of the total flora, that are rare or threatened in some way.
In 1994 a collaborative project between Trinity College Botanic Garden, the Irish National Botanic Garden, the state Wildlife Service and the Irish Genetic Resources Conservation Trust was initiated to conserve rare and threatened Irish plant species, through the establishment of a seed bank at Trinity College Botanic Garden. The collaboration between the state, a non-governmental organisation, and an academic institute is a recognition of the fact that if the flora of Ireland is to be properly conserved all these different bodies must take a coordinated approach. The aims of the project were to collect the seeds of rare and threatened Irish plants, and then store these seeds in the seed bank.
At the western extremity of Europe, Ireland has a depauperate but interesting flora. It includes a number of species which are restricted to the extreme west of Europe, amphi-atlantic species which are rare or absent elsewhere in Europe (e.g. Hypericum canadense), and especially interesting populations of various species growing at the limit of their natural distribution, including arctic/alpine species and Mediterranean species occasionally growing in close proximity. This biogeographical interest of the Irish flora makes it important to conserve the genetic diversity of Irish plant populations.
Why Establish an ex situ Collection of Irish Plants?
The aim of the conservation strategy is to try to ensure that the species are conserved in situ; however in Ireland, as with many countries, it is increasingly difficult to achieve this aim with pressure on land for agriculture, industry and leisure activities. A complementary conservation strategy appears to be the best approach, with an ex situ collection of a species being established to ensure against absolute extinction if wild populations are destroyed.
What must be considered when establishing an ex situ collection ?
The primary biological aim when considering ex situ conservation is that such a collection must represent the maximum genetic variation from the in situ population sampled, otherwise the value of the collection for conservation purposes may be negligible. There are three ways that ex situ conservation could be achieved, a field gene bank, an in vitro gene bank, and a seed bank. As most Irish plant species have orthodox seeds, the most effective method is through a seed bank, as it is the most costeffective way of storing a large amount of genetic variation over long period.
Collection of Seed for the Seed Bank
Having identified a species requiring ex situ conservation, there are various questions that need to be answered if the majority of the genetic variance of the species is going to be conserved. These questions are:
- How many populations should be represented ex situ?
- Which populations should be represented?
- Number of individuals to be sampled from each population?
- How should the individuals be sampled?
- How many seeds should be collected from each population?
To answer the first four of these questions the Irish seed bank is following the guidelines published by the Center for Plant Conservation (1991). Between three and five of the populations representing a species are sampled from as diverse habitats and geographical ranges as possible, and 10-50 individuals are sampled per population, using a random stratified sampling system. To answer the fifth question, current minimum viable population theory (Shaffer, 1987; Menges, 1991) is being followed, and therefore the seed bank aims to collect a minimum of 1,000 seeds per population. To ensure that the seed sampled from a population is not genetically biased, similar numbers of seed are collected from each individual. When sampling small populations it is not always possible to collect 1,000 seeds, in this case only one fifth of the seed available on the day of collection is sampled, so that the small population continues to sustain itself in situ. Also ecogeographic data is recorded for each population, such as what was collected and when, it's geographical location, etc. A database will then be used to geographically locate rare Irish plant species, and also to give vital ecological data on the species.
Storage of the Seed
The aim of all the processes that are carried out on the seed after it has been collected is to keep viability as high as possible, so that the seed can be stored for long periods without regeneration. The protocol that is followed in the Irish seed bank is based largely on the work of Ellis et al. (1985a &1985b) which involves the cleaning, counting, drying, viability testing, and storage of seed.
Before storage, the collections are partitioned to 'active' and 'base' collections. The base collection will usually be duplicated, with one duplicate being stored in the Irish seed bank, and the other being stored outside Ireland as an extra insurance. The active collection will be used in 3 ways:
- Seed distribution to bonafide users
- Research at the Irish seed bank
- Source material for reintroduction experiments
An ex situ collection, such as the Irish rare and threatened plant seed bank should be used to contribute to in situ conservation activities using seed from the ex situ collections for reintroduction experiments. The experiments will involve reintroduction of species that are not currently effectively conserved in situ to sites where they have been recorded previously.
Two species that could benefit from reintroduction are meadow saffron (Colchicum autumnale L.) and cotton weed (Otanthus maritimus (L.) Hoffmann & Link;). Meadow saffron was once locally common in the Nore river valley in south-east Ireland, but is currently only found at two sites, due to its native habitat being destroyed by agricultural practices and drainage (Curtis & McGough, 1988). Cotton weed is in a similarly perilous position found only at two adjacent sites. These two Irish sites represent the northern limit of the species' range. If they could be reintroduced into some of the original sites their chance of survival in situ may be increased. The protocol that will be used to investigate reintroduction is based on the one used by Bowles et al. (1993) and can be divided into six stages.
- Establishment of a viable ex situ collection of the seed
- Detailed study of the species ecology
- A habitat study of possible sites for reintroduction
- Selection of a suitable site for reintroduction
- Reintroduction of seedlings
- Monitoring of the reintroduced plants
The results of the reintroduction experiments will provide the Irish seed bank with information on the conservation and ecology of rare Irish plants, and on the viability of reintroduction as a technique to conserve Ireland's biodiversity.
James Martin, Steve Waldren and Aileen O'Sullivan
Trinity College Botanic Garden
Palmerston Park, Dartry
Dublin 6, Ireland