Challenge to define and quantify ecosystem collapse debt

Degradation and loss of ecosystems are of great global concern. It is likely that decline of ecosystems will continue and a debt of ecosystem loss exists, comprising of 1) direct and expectedly continued forcing by detrimental anthropogenic actions and 2) of indirect ongoing gradual change of defining characters set in motion by an initial perturbation. Both direct destructive actions and indirect gradual changes contribute to collapse, i.e. loss of defining characters of certain type of ecosystem. Classification and typology are central to any assessment of risk of ecosystem collapse. Following indirect gradual change, an ecosystem does not vanish, but it may lose its characters and fall beyond its definition. Resulting state after such change may present another known ecosystem type or a novel ecosystem type. The recognition between these alternative states can be based on identifying novelty, degree of deviance from existing ecosystem typology, e.g. using measures of dissimilarity of biotic communities. Ecosystem Collapse Debt (ECD) refers to the amount or proportion of certain ecosystem type that has not yet collapsed, but is predicted to collapse as a direct consequence of continued actions or as indirect response to prevailing or foreseeable future circumstances. This prediction needs to be based on known processes and mechanisms. Examples are presented of cases of peatland ecosystems. Intensive drainage and peat extraction activities, representing destructive exploitation, have caused tremendous loss of natural peatland ecosystems during recent past. However, the remaining untouched peatland areas are changing too, although more gradually, e.g. due to climate change or hydrological alterations of catchments. Such changes may contribute to ECD of peatlands even if most destructive utilization had ceased. In Finland, approximately 15 % of boreal aapa mire area (patterned fens) has been lost during recent past (ca. 50 yr) due to direct effect of drainage of these peatlands, representing a relatively low level of disturbance among different peatland types. However, it is estimated that approximately 40 % of the remaining aapa mires occur in situations, where their hydrology is disturbed by drainage of surrounding areas. From case studies we know that such changes can lead to collapse within few decades, as defined by major vegetation changes readily observed from remote sensing proxies. If all disturbed aapa mires are changing beyond our definition of aapa mires, the ECD in this case may amount up to about 150 000 ha or about one third of the remaining area of this ecosystem type in Finland. Furthermore, it is likely that climate change will have impact on this northern ecosystem and contribute to build up ECD. This is a rough calculation of limited precision and conditional to many details, including the definition of the ecosystem. However, it should work to exemplify how ECD works to communicate the extent of ecosystem degradation.peerReviewe