For many visitors, the abundance of trees on the Parkland Walk is part of its charm. Many also believe that this dense woodland is the answer to addressing climate change. However, as with many things, the answer is not that simple. Climate change has to be approached in partnership with addressing ecological decline. These are two separate issues but they are bound closely to each other.
Over the years, the Parkland Walk has gone from being a well-balanced mix of woodland and meadow to an arboreal monoculture where the ground cover is predominantly by ivy and bramble. The trees that dominate the nature reserve are ash and sycamore. Ash is currently being reduced in numbers by disease although it is not critically under threat. Sycamore is a highly successful non-native species that can spread very effectively and can prevent native trees from becoming established. It is also less beneficial to insects and birds than native species, for example, fruit-bearing trees and hedgerow plants. From the point of view of biodiversity, it’s essential that the woodland has a broad variety of species.
Ecosystems function at many different levels, from micro moths, insects, fungi and wildflowers to trees, small mammals and birds. Insects all need a broad range of flora to thrive. Bats, birds and small mammals also have specific and wide ranging habitat requirements. Some need hedges or shrub for nesting and protection, some birds like sparrow hawks, owls and kestrels, need open grasslands so they can stalk and catch their prey. Some trees, such as the English Oak can be a host to hundreds of species of insect whereas the highly successful and fast growing sycamore supports just over a dozen and therefore can have a negative impact on invertebrate variety and a broadly balanced ecosystem.
For these reasons, the Friends would support the removal of large numbers of trees in specific locations with the intention of providing areas of glade to encourage healthier ground cover but also to allow the planting of a broader range of native trees in order to revitalise invertebrate populations.
The Value of Different Tree Species for Invertebrates and Lichens
The table below shows the number of insects and epiphytic (growing on plants) lichens which have been recorded in association with common trees and shrubs in Britain. The figures in brackets include mite species as well as insects.
|Tree or Shrub||Associated Insect Species||Associated Lichen Species|
|Oak (pendunculate & sessile)||284 (423)||324|
|Willow species||266 (450)||160|
|Birch (silver & downey)||229 (334)||126|
|Poplar species (including aspen)||97||no data|
|Crab apple||93||no data|
|Field Maple||26 (51)||93|
|Sweet Chestnut*||5||no data|
|Horse Chestnut*||4||no data|
|Holm Oak*||2||no data|
*Non native species
The table above is a useful tool, although it does not begin to provide the whole picture of the value of different tree species for wildlife. It should by no means be assumed that because the table shows relatively few animal/lichen species associated with a particular tree species, that this species is therefore of little value for wildlife. More information about this table, it’s sources, context and further interpretation can be found on the countrysideinfo website.