COMMERCIAL HORTICULTURE  (FEBRUARY / MARCH 2010)

Last issue, Comm Hort published comments from retired nurseryman, Ken Davey, in which he said eco-sourcing was a far from perfect practice and its outcome unpredictable. His article has prompted two replies, which we publish here. 

Eco-sourced plants at the Forest Flora Nursery, Ngaruawahia.	Natural areas like this provide eco-sourced seeds

Communication, understanding, commitment 
— the essence of good eco-sourcing practice

—by Wayne Bennett, Forest Flora (seen here collecting Syzigium maire seed)

It is sometimes hard to come to terms with the fact that the little trees we propagate and nurture will one day grow up and become sexually active. 

This is not so much an issue in parks and gardens but there is a big movement to planting natural areas where the trees are not tended and their seedlings are allowed to compete with all the others for their space in the sun. 

This is where eco-sourcing has become important because, not only is the natural range of each species different but species vary genetically throughout their range. Where a species, ecotype or single gene is absent, it leaves space for another. This variety in living things is what we call biodiversity. It is the basis of what resilience there is in natural systems and it is being reduced drastically through all kinds of human activity.

After over 200 years taxonomists have still not completed cataloguing all our native plant species and we have only scratched the surface understanding the regional differences within species. 

When I went to school there were three species of kowhai; now eight are recognised. Recently two new species of dianella were described in our area. Had we propagated those species without matching their origins and destinations we would have run the risk of introducing a species outside its natural range and on the scale we are now working, the risk of compromising a species.

Here in the Waikato, those involved in restoring natural areas work together to ensure that eco-sourcing is done well. We define eco-sourcing as: “Propagation of native plants from a representative sample of the local wild population.”

We will continue to increase our understanding and refine what we mean by “local” and “representative” but the principle remains the same.

The Waikato landscape is ideally suited to intensive farming so little of the original native vegetation is left. What is left is in small isolated pockets, often unable to share seed and pollen with the wider population. The widespread replanting of native plants in natural areas can help this by providing “stepping stones” for pollen and seeds, but only if the same species and genes found in remnant natural areas are replanted in these projects.

My firm, Forest Flora, specialises in restoring natural areas. We collect seed from all the native plant populations we can assure ourselves are naturally occurring. Our aim is to restore to a site those ecosystems, species and genes which might reasonably be expected to disperse there if it were not for recent human disturbance. 

We also aim to propagate from all the remaining populations to ensure their survival. Of course we have to be pragmatic and although that is the ideal we are always dealing with a practical compromise.

A key component of eco-sourcing is record keeping. We collect seed from as many natural sites as we can, bearing in mind the projects we are involved in. We collect seed from as many individuals at each site as we can although sometimes this may only be one. Different lines of seed are kept separate and the source and number of “parent” plants is noted. 

When it comes time to planning a site we can then choose from the closest and most similar sources, whilst ensuring we have sufficient sources to avoid inbreeding.

Eco-sourcing isn’t always done well; most frequently insufficient care is taken to avoid propagating from planted or naturalised plants, but also sometimes seed is collected from only a few convenient specimens. 

Good eco-sourcing needs good communication between everyone involved and it really needs everyone to have some understanding of what is important and why. If eco-sourcing really is important on a project then the manager will have to ask some searching questions to assure themselves of what they are getting.

Eco-sourcing does require attention to detail, commitment and better understanding, however all kinds of businesses are working towards more sustainable activities and our customers reward us for that.

Eco-sourcing seed on Wellington’s South coast

Eco-sourcing – Right on! 

Rewi Elliot, New Zealand Plant Conservation Network

Eco-sourcing – sourcing local plants for local plantings – should be a consideration whenever moving plants around the country. The concept follows evidence that single species can vary genetically from one region to another. Eco-sourcing seems to be a kiwi term, but the concept is not. Overseas it is often known as local provenance or genetic provenance.

A variety of forms of a single gene can exist within a single species (these forms are known as alleles) meaning that the genes of a local species can differ from another population of the same species. That is to say, a population of a plant species from Northland may differ genetically from a population of the same species from Otago and a variety of plant traits may exist as a result.

New Zealand’s plant species are not uniform and the genetic diversity here should be valued. Proponents of eco-sourcing generally agree that the natural genetic variation found around New Zealand should be protected by avoiding mixing genetically distinct populations of the same species as much as is practicable and desirable. 

The success of invasive weed species shows that non-local genotypes can successfully out-compete local genotypes. We’re not always sure how the introduction of non-local plants will affect the genetic constitution of the same species occurring locally. Mixing a single species of differing genetic constitutions may result in a deleterious effect as they reproduce over successive generations. 

Eco-sourcing has become the norm for many planting projects to alleviate concerns about new plantings affecting existing local populations. In New Zealand it is most often associated with restoration or re-vegetation plantings, but is relevant to any planting endeavour. 

A common example of genetic variation within a single New Zealand species is in manuka, Leptospermum scoparium. Manuka is widespread in New Zealand and is tolerant of a wide range of environmental gradients. 

There appears to be a genetic basis in manuka tolerance to water logging (Cook et al, 1980) and frost (Greer and Robinson, 1995); to leaf size, plant form, and flowering phenology (Yin et al, 1984); and to differing essential oil chemotypes (Harris, 2002).

Honey made from manuka pollen (sold as manuka honey) contains antibacterial properties called the ‘unique manuka factor’ (UMF). The percentage of UMF in manuka honey varies as manuka growing in different parts of New Zealand yield different levels of UMF. Environmental gradients have limited effect on the variability of UMF, suggesting that the variation is genetically heritable (Stephens and Molan, 2008). 

How local is local varies from species to species and landscape to landscape. Genetic material is dispersed as far as pollen and seed is carried across New Zealand. This can be a considerable distance for some species – even as far as Australia! 

Movement of genetic material like this is termed gene flow, and the overall effect is to decrease the differences between populations. The potential for this gene flow diminishes as the distance between populations becomes greater, and varies between pollen and seed-dispersal mechanisms – such as birds or the wind. 

Following on from this it makes sense that the further apart populations become, the less likely they are to be influenced by gene flow and the more likely they are to begin to separate from the prevailing gene pool. This is termed genetic drift and is considered to be one of the factors that can result in the evolution of a new species over time. 

Eco-sourcing is an attempt to replicate the arrival of plant species that might naturally occur (via our seed collecting and planting). Sometimes it’s a far from perfect practice. Some species are difficult to propagate from, in remote sites we are at the mercy of what seed we find on the day of our visit, seed may fail at the propagation stage, and so on. Responsible practitioners endeavour to collect broadly from many individual plants. 

Our collective planting history is usually associated with beautification and ‘improvement’ of the landscape. Revegetation is definitely laced with amenity tendencies. Inevitably some species or individual plants are favoured over others. 

Vascular plants reign, others like mosses and lichens are almost never grown as a part of revegetation projects. Fungi that form important associations with many plants (mycorrhizal associations) are not commonly considered in potting mixes. Weeds may sometimes be inadvertently introduced, and disputes about ‘how local is local’ may arise.

There may be times when it is not desirable to source revegetation plants locally. Threatened species which have been reduced in some areas to very small remnant populations might benefit from the introduction of genetic material from elsewhere. Two small disjunct populations may fare better in the future if they are mixed. Sounds like too much mucking with nature? Well, sometimes we just have to salvage what remains.

Eco-sourcing is a consideration when moving plants around, not a hard and fast rule. It’s as successful as our knowledge allows. Don’t let this stop you from doing what you think is best. Do a bit of reading, have a few chats with others, and come to a conclusion about what you think is reasonable. 

Eco-sourcing is not about re-creating a frozen portion of time like a snapshot of natural history. It’s an attempt to protect biodiversity and kick start natural processes such as natural selection, seed dispersal, succession etc. It’s about moving forward, using the past as a reference point to get started.

So have a think about where you source plants or seed and ensure, where practicable and desirable, you’re sourcing local plants for local plantings of our unique vegetation – eco-source.

If you want to learn more about NZ’s native or exotic flora then visit the website of the New Zealand Plant Conservation Network www.nzpcn.org.nz and use the Network’s on-line forum if you want to ask questions about eco-sourcing or how to grow native plants.

References

Cook, J. M. et al. 1980. Responses of Leptospermum scoparium and L. ericoides 
(Myrtaceae) to water logging. New Zealand Journal of Botany. 18: 233-246.

Greer, D.H., Robinson, L.A. (1995). Temperature control of the development of frost 
hardiness in two populations of Leptospermum scoparium. Tree Physiology 
15: 399-404.

Harris, W. (2002). Variation of inherent seed capsule splitting in populations of 
Leptospermum scoparium (Myrtaceae) in New Zealand. New Zealand Journal of Botany 40: 405-417.

Stephens, J. and Molan, P. (2008). The explanation of why the level of UMF varies in 
manuka honey. The New Zealand Bee Keeper, March, pp 17-21.

Yin, R., Mark, A.F., Wilson, J.B. (1984). Aspects of the ecology of the indigenous 
shrub Leptospermum scoparium (Myrtaceae) in New Zealand. New Zealand Journal of Botany 22: 483–507.