Enquirer

Dear Micky,

I'm looking for anything about planting UK native trees to clean up a heavily contaminated site.

What techniques should one use, and what species have the best chances in an arid site heavy in sulfates and with underlying gas being produced.

Many thanks

John Roy

Dear Jon

There is quite alot of information about Phytoremediation on the site, have a look at these links :-

Dear Jon

There's been loads of work on using trees, going back 30 years or more. However, a lot of it was looking at which trees survived on these sites rather than bioremediated it!

But I would imagine the bioremediation angle is something that has now been looked at in more depth in recent years.

It is usually the pioneer species which survive best on contaminated sites:

• Willows (e.g. Salix caprea, Salix cinerea)
• Birch (Betula pendula + pubscens)
• Aspen (Populus tremula)

These are also native species which have fast rates of growth. Alder used to be a favourite as its N-fixing properties gave it advantages on sites with poor fertility, such as old coal slag heaps. Hawthorn (Crataegus monogyna) is another pioneer which I have seen colonising our own local disused refuse tip (where there was hardly any superficial capping but some heavy metal contamination).

It might be of value to consider tree and shrub seed collections from existing contaminated sites like this which have been naturally colonised by trees and shrubs, as the plants growing in these places must be pretty well adapted to difficult situations and may show some localised adaptation (possibly). THere are people who do such seed collections to contract.

Indeed it would be of some value to establish some specialised nurseries of native trees and shrubs that have colonised these types of sites, to provide a supply of planting material that may be better adapted than a lot of the imported material (trees and shrubs) that is mostly planted these days - ie native species but of foreign origin (which may be climatically maladapted apart from anything else).

I don't know how these species deal with contaminants but this must be documented somewhere? Do they store it in their tissues, or emit some toxic compounds in gaseous form, or are some contaminants not taken up at all?

The ability of trees to assist the development of soil and associated microbes will be an obvious and important aspect of using trees to ameliorate sites. Presumably a combination of tree planting plus the addition of microbes is something that has been looked at?

By the way am an ecologist with knowledge of native trees, but only limited and ancient knowledge of using trees on contaminated land. I am also interested in utilising the genetic diversity of native trees, shrubs and other native plants found in the UK, for biodiversity and ecological restoration. I head up an initiative called Flora locale, which aims to promote the use and propagation of native-origin plants. At the moment, the vast majority of trees and shrubs planted are not of UK native-origin.

Tony Bradshaw, ex. Liverpool University, is an expert in this area. Try looking at references by Bradshaw, A.D. There was a unit at Liverpool dedicated to the ecological aspects of contaminated land restoration - I presume that it still exists.