The Mournes contain one of the best-developed areas of heathland in Europe. The vegetation of Dwarf Shrub heaths or heathland is dominated by a variety of different species of heather and other related small shrubs. A variety of different heathland types have developed under the influence of such factors as climate, altitude and soil conditions. Lowland heath tends to occur on acidic granite rocks, over which a layer of shallow peat has developed.
Leaching of soil nutrients and peat formation tend to increase with altitude, reflecting the rise in rainfall. In the uplands two distinctive communities are distinguished by the relative wetness of the soil, Wet heath and Dry heath. The dry heath of the Mourne Mountains is one of the best examples in the UK of this vegetation type. On the highest mountains dwarf shrub heath grades into Montane Heath which contains some plants more normally found in the Artic, such as Dwarf Willow and starry saxifrage
Lowland Heaths have declined as a result of agriculture reclamation, while in the upland grazing, especially by sheep, has become intensification, replacing heather with grass such as the unpalatable mat grass.
Bogs are found where peat has accumulated to form a deep layer and cover most of our uplands. Bogs are made of 95-98% water, most of which comes directly from rainfall, which is very poor in the nutrients that plants need to grow. As a result relatively few species live in bogs but the plants and animals that do occur there tend to be very specialised. One of the most important groups of species associated with bogs are the Sphagnum mosses. These play a crucial role in both peat formation and water retention.
There are two main types of bog – raised bog, which occurs in natural depressions in the lowlands, and blanket bog, which is one of the main vegetation types in the uplands.
Raised bogs are so called because they form a shallowly domed profile of deep peat. This can maintain its own water levels, which are thus raised above the surrounding groundwater table. Lackan Bog is a good example of a lowland raised bog and has been designated an A.S.S.I.
Blanket bogs have experienced heavy grazing, as the uplands have become more intensively used for agricultural production. This favours grazing tolerant species at the expense of others and can lead to erosion of the peat as the vegetation cover is removed. Most bogs have been cut for peat resulting in the loss of more sensitive species.