Selecting tree species for landfill regeneration

The case for tree species selection

Tree species selection is an important decision point in land regeneration that can directly impact the longterm success of the project. Choice should be governed by a proper assessment of the ability of the newly reclaimed site to support plant growth, and an evaluation of limiting factors to choice and expectation. Unfortunately, it is often the case that tree species are chosen early in the regeneration process with little regard to site and soil constraints.

Landfill sites are often very exposed and, even if reclaimed well, often suffer from drought and soil infertility. Compaction and waterlogging are common problems at badly restored sites, further compromising tree growth. Species choice is therefore crucial and it is vital that species are chosen that have a proven ability to tolerate the site conditions.

Species suitability

Our research has shown that some tree species, notably alders, poplars and willows, tolerate waterlogged soil conditions, but may also be more able to penetrate any cracks 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

Species

Heavy soils

Calcareous soils

Acidic soils

Exposure

Air pollution

Comments

Ash

-

++

-

-

-

More fertile sites only

Common alder

++

+

+

+

++

Nitrogen-fixing

Crack willow

++

++

-

-

+

 

Downy birch

+

+

+

++

++

Tolerates low fertility

English oak

+

+

+

+

+

More fertile sites only

False acacia

+

+

++

-

++

Nitrogen-fixing South only

Field maple

+

++

+

+

+

 

Goat willow

+

+

+

-

++

 

Grey alder

++

+

+

+

+

Nitrogen-fixing

Grey poplar

++

++

+

++

++

 

Hawthorn

+

+

+

++

+

Tolerates browsing

Italian alder

+

++

-

-

++

Nitrogen-fixing

Norway maple

+

++

-

++

+

 

Red alder

++

-

+

++

+

Nitrogen-fixing

Red oak

+

+

++

+

+

 

Rowan

+

+

+

++

+

 

Silver birch

-

-

++

++

++

Tolerates low fertility

Swedish whitebeam

++

+

+

+

+

 

Sycamore

+

++

+

++

++

 

Turkey oak

++

+

+

+

+

 

Whitebeam

+

++

++

+

+

 

White poplar

++

-

+

+

++

 

Wild cherry

-

+

-

-

+

More fertile sites only

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

Species

Heavy soils

Calcareous soils

Acidic soils

Exposure

Air pollution

Comments

Corsican pine

+

++

++

++

++

Below 250 m O.D.

European larch

+

-

+

+

-

 

Japanese larch

+

-

+

+

+

 

Scots pine

-

-

++

++

-