The Botanic Garden Seed List- A Curse to Plant Conservation?

Mark Richardson, 1994

Throughout the world the disastrous impact of introduced species has been felt, with the rabbit and prickly pear providing graphic examples. In 1925, the latter covered 25 million hectares of Australia and was expanding at 100 ha/hour (Leigh et al., 1984).

Most of such noxious species were introduced with good or at least innocent intent. Many early introductions into Australia were made under the patronage of organizations such as the Acclimatisation Societies, which were keen to see the introduction of exotic plants and animals into new localities as familiar food plants, ornamentals and game.

In addition to, and often in association with, groups such as Acclimatisation Societies, botanic gardens have been intimately involved in the distribution of plant species around the world. An important and long-standing means of dispersal has been the botanic gardens seed list or Index Seminum.

A botanic gardens seed list is a list of plant species of which a botanic garden has seed for distribution, available free of charge to other members of the botanic garden community. The lists vary from just a few tens of species to many hundreds. The seed itself may have been collected in the wild or from plants growing in botanic gardens. It is the intention of the Index Seminum system to make the distribution of seed between organisations as simple as possible. It merely requires the organisation submitting an order to list the corresponding catalogue numbers or in some cases circling those numbers on an order card accompanying the seed list. As a result it has been very successful, and seed exchange is an important function of many of the world's botanic gardens. Seed not only goes to other botanic gardens but also to other research groups and organisations such as city councils.

In the past, restrictions on the movement of seed has largely been limited or non-existent. Careful selection of species for the preparation of seed lists to avoid weed problems also appears to be virtually non-existent. Many of Australia's declared noxious weeds, or other plants known to be serious weeds, regularly appear in seed lists from many parts of the world. These include plants such as Hypericum perforatum, Lantana camara, Ligustrum lucidum, Cytisus scoparius, Ulex europaeus and Vinca major. McClintock (1987) also records the last three species among the aggressively invading exotics occurring in California.

The actual size of the weed problem is perhaps best appreciated in terms of money. In Australia alone, it is estimated that weed infestations cost around $3 billion annually in weed control and production losses (Humphries, pers. comm.)

Even individual species are having dramatic effects. Prickly Acacia (Acacia nilotica), introduced to Australia from the Middle East in the 1880s as a shade and fodder tree, now occurs on about 7 million hectares and is dense over 1.5 million hectares. It is causing not only significant reductions in agricultural production but is also serious depletion of natural grasslands. No long-term control methods have yet been found (Anon, 1991). Rubber Vine (Cryptostegia grandiflora) was introduced into Queensland from Madagascar as an ornamental in the 1870s and is now widespread through central and northern Queensland. By 1989 about 350,000 kmý of Queensland had some infestation by the Rubber Vine. It is already costing the cattle industry about $10 million annually and is destroying large areas of Queensland's riparian vegetation. As with Prickly Acacia, no long-term control method has yet been found (Anon, 1991).

Examples such as Prickly Acacia and Rubber Vine are not uncommon and, as further species become naturalised, those with invasive properties become obvious. Ross (1976) calculated that 5-6 species per annum have naturalised in Victoria over the past century. Such species not only include those coming from outside Australia but also a number from within the country. Several species of Australian Acacia introduced into areas outside their natural occurrence have already become serious weeds.

Many of the species that have naturalised as weeds are ornamentals and a significant proportion are available on botanic gardens seed lists.

Plants are by their very nature more easily distributed than animals. Once introduced into a new area they may be spread by a number of natural agents such as animals and wind. As a display in a botanic garden or park there is also the opportunity for visitors to "collect" and further distribute propagules. Materials arriving via the botanic gardens seed list system may, on occasions, provide the starting point.

It is not advocated that the movement of seed between countries should be totally stopped. However, weeds are a major threat to many other plants and to plant communities, and any efforts to at least stop the problem getting worse must be employed. The abandonment of the botanic gardens seed list system as it currently exists would greatly assist.

Such a proposal poses an important question for many of the world's botanic gardens. If seed is not being held as part of an ongoing seed exchange program, then what is the purpose of the seed store?

The seed store at the Australian National Botanic Gardens is maintained primarily to hold propagation material for the living collections and conservation projects. Its secondary role is to provide seed for other organisations on request. This latter role has been recently examined in the light of the arguments presented in this paper.

As noted earlier, it is not proposed to cease providing seed. However, it has been decided that requests will be considered more carefully. Warnings concerning potential invasiveness of introduced plants will be included with all seed and plant shipments. In extreme cases, requests for species reputed to be weeds in certain environments will be refused if the request is not justified.

While botanic gardens are only one of the many ways in which weeds have been spread throughout the world and while there are other issues (such as stricter quarantine controls) that need resolution, it is important that the botanic garden community sets an example. There are already many organizations that are aware of the environmental problems caused by weeds and they require support. The botanic garden community cannot on the one hand claim to be at the forefront of plant conservation and on the other continue to support a practice that may spell the destruction of millions of hectares of natural or semi-natural vegetation.

It is always easy to be clever in hindsight. We should take advantage of this fact, and greatly modify our seed distribution practices before we contribute yet further to weed problems. In the light of what we know, it would be irresponsible for us to do otherwise.

Reference to this paper:

Richardson, M. 1994. The botanic garden seed list - a curse to plant conservation?

Bot. Gardens Conservation News 2(3): 21-22.