Human activities affect peatland biodiversity in different ways and via various pathways. Biodiversity may be totally lost when the peatland entirely disappears as a result of overbuilding, inundation or peat extraction; or it may be modified only very slightly due to hunting, berry-picking or recreation. Changes can be quick and sudden or slow and creeping and even initially invisible. Human impacts on peatland biodiversity may be evaluated via changes in the three main peatland components that are central for all key peatland functions and processes: water, peat and plants. Anthropogenic changes in hydrology, geochemistry or vegetation may directly and indirectly lead to shifts in peatland biodiversity. Often minor changes in site conditions result in drastic changes in biodiversity. Even slight drainage makes peatlands more vulnerable to peat fires with dramatic impacts to biodiversity. Peatland biodiversity may be affected by interventions in the water balance of the entire peatland, of part of the peatland, and of the peatland's catchment area or surroundings. Water plays a central role for peatland biodiversity because peat contains about 95% of water by volume. Hence, any drainage leads to loss of soil volume and thus to subsidence. Hydrological and thus ecological conditions on a raised bog’s surface are largely determined by the local surface slope and the distance to the internal water divide, often referred to as the flow path length. With increasing flow path length, the surface slope becomes less critical and vice versa (Van der Schaaf 2002, Van der Schaaf and Streefkerk 2002, 2003).

Drainage of the bog margin may result in subsidence, increasing the slope of the bog dome. This then leads to increased runoff and lower water levels that may affect the vegetation in the entire peatland. Drainage of mire margins not only destroys the specific local vegetation, but also facilitates access to people, animals and plants, which may further impact the biodiversity of the rest of the peatland.

Drainage both in and in the surroundings of raised bogs may cause damage to the bog by subsidence. A first and immediate effect of internal bog drainage, usually by shallow open drains, is a drastic shortening of flow paths, loss of water from the upper peat and subsequent subsidence. Because the newly formed drainage base subsides at a speed that is only slightly less than the subsidence speed of the surface itself, the subsidence may continue for a long time.

Human activities in the peatland surroundings raise risks for peatland as well. In South Africa peatlands are in peril in areas where groundwater resources are exploited. Droughts have resulted in huge pressures on already water-stressed catchments and associated mires. The karst peatlands in the western part of South Africa are affected most. One of these peatlands, Bodibe, is permanently on fire.

Changes in peatland ecosystems can affect the biodiversity of surrounding areas. Often peatland drainage leads to lower groundwater levels in adjacent areas. This is especially the case with fens that are in contact with groundwater in the underlying mineral soil. Hydrological changes in bogs tend to have smaller effects as they usually have an almost impervious layer at their bottom and are much more isolated in this respect. Other examples include desertification in mountainous areas of Central Asia, Africa, and South America following the degradation of highland peatlands, and Arctic permafrost melting after vehicles damaged the thin peat layer, leading to feedbacks affecting biodiversity over a much wider area than that covered by peat. Mire growth and associated water level rises may lead to paludification of adjacent areas, as was already noted by Linnaeus (1749).

Loss of peatland habitats, their change and fragmentation, could lead to dramatic changes of species and intraspecific biodiversity. Human-induced changes in peatland habitats are often irreversible and accompanied by loss of natural species diversity. Habitat loss furthermore contributes to fragmentation where surviving populations are no longer able to exchange genes or recolonise an area. Roads and ditches cause fragmentation, as do peat extraction, drainage, overgrazing, fires, and floods. Whereas in theory fragmentation (isolation) may stimulate genetic diversity between populations, diversity within populations will strongly decrease through genetic drift and inbreeding (Young et al. 1996).

Peatland species are often closely connected to each other. Human induced loss of one species can lead to further impacts on others. Connections between species are often very tight in peatlands. The loss or change in characters of one species can lead to the loss of species dependent upon it, and to shifts in ecological webs, with far reaching consequences.

The long-term use of peatlands leads to fundamental changes in landscape, ecosystem and habitat diversity, as well in diversity between and within species. Peatland ecosystems that have been transformed in this way can support high and specific biodiversity, but they lose their natural sustainability and require continued human management. Cultural landscapes need sustained human management. Peatlands that were surficially drained and mowed for centuries now display large, specific species diversity, and need permanent mowing to avoid settlement of shrubs and trees and subsequent habitat changes. Peatlands on terraces in the Alps have formed biodiversity specific to today’s conditions due to long-term pasturing. The hay-meadows in East-Central Europe (Polessje, Biebrza river valley in Poland, Berezina in Belarus) demand permanent hand mowing for maintenance. In some cases, traditional peatland use is needed to support biodiversity that has been long-established by people, as well as to maintain the sustainability of indigenous and local human communities and their natural resources.