The case for tree species selection

Forest Research has been involved in several studies regarding the restoration and revegetation of closed landfill sites. Observations of tree growth and health have led to the development of general guidance on the suitability of different tree species based on the site’s soil characteristics, its exposure and levels of air pollution.

The case for tree species selection

Tree species selection should form one of the final decision-making processes in land reclamation, with choice governed by a proper assessment of the ability of the newly restored site to support plant growth, and an evaluation of the limiting factors which will hinder the flexibility of choice and expectation. Unfortunately, it is often the case that tree species are chosen early in the restoration process with little regard to site and soil constraints.

Even if restored well, landfill sites often suffer from comparative exposure, drought and infertility. Badly restored, compaction and waterlogging can also compromise tree growth. Species choice is therefore crucial and it is vital that only species are chosen that have a proven ability to tolerate relatively harsh conditions.

Species suitability

Our research has shown that some tree species, notably those like alder, poplar and willow that tolerate waterlogged soil conditions, may be more able to penetrate cracks that exist in the underlying landfill clay cap.  Unless there is an adequate soil cover over an unprotected clay cap, these species may pose a small risk to cap integrity and should not be planted.

The tables below give guidance on species suitability. In general, so-called ‘pioneer’ tree species should be chosen over more demanding ‘climax’ species.

Broadleaved species suitability for different site types
++ Very suitable, + Suitable, – Not suitable

Conifer species suitability for different site types
++ Very suitable, + Suitable, – Not suitable