We are often asked why we remove trees and scrub from lowland raised bogs. The work can be costly, hard-work and seemingly never ending. And after all the target species for removal are often native species such as birch and Scots pine. So what's the problem??
The reason is all to do with water. Acidic peat bogs only form in areas of high rainfall (which is why Scotland is perfect for them!). They need a regular supply of rain to keep them topped up otherwise the upper layers of peat begin to dry out. Drying is harmful to the natural vegetation layer that depends on water-logged conditions and leads to exposure of dry peat to the elements. Erosion of the peat can then occur harming the overall integrity of the bog and leading to further drying. A vicious cycle of damage has now begun.
Scrub growth is a threat in some circumstances, particularly on lowland bogs as almost all of these are small and have been damaged by reclamation and drainage for agriculture. They are therefore less resilient and even small changes can have lasting effects. Scrub threatens lowland bogs by:
- intercepting and absorbing rainfall which normally would fall directly on the bog
- shading out important bog vegetation in particular sphagnum mosses which are the drivers of peat formation
- enriching the bog with nutrients from leaf and brash litter
- creating root 'plates' that form dry hummocks above the natural bog surface - combined with nutrient enrichment from leaf litter these hummocks often become little islands that are ripe for other non-traditional bog species to gain a foothold
Excessive scrub growth can also affect the biodiversity of a small lowland bog. For instance the Large Heath butterfly is dependent on abundant Hare's-tail cottongrass which is it's larval foodplant. The above photo shows birch scrub encroaching into suitable Large Heath habitat. And whilst the butterfly can survive well in that situation it isn't many years before the birch will start to shade out the cottongrass (and the Large Heath too) as shown in the photo below.
Simply cutting a birch tree down to a stump will results in further multi-stemmed growth from the same plant which is then harder to remove. So the methods our Bog Squad volunteers use are designed to remove roots where needed to reduce regrowth and thereby reduce the need for further scrub clearance in future years. To achieve this we employ a variety of tools that include:
- folding pruning saws that enable us to cut into the peat to get at roots
- mini-mattocks that help lever and cut stubborn scrub
- tree-poppers which lever up entire small trees