Species richness is not an indicator for the success of habitat restoration
Roy van Grunsven, Wageningen University
14 August 2015
In this paper the authors show that rewetting of a drained peatland results in an increase in both the number of individuals and species of dragonflies. Three years after the restoration they find ten species of dragonflies in the restored peatlands, comparable to pristine peatlands and much more than the 2 or 3 species in drained bogs. They claim that the restoration was thus successful. However, looking at species numbers as a measure for the success of habitat restoration can be misleading.
As stated in the background the goal of restoration of degraded ecosystems is to prevent the loss of biodiversity and the restoration of the original structure and function of the ecosystem. This would mean that the restoration should benefit the species that are threatened by the loss of the habitat under study, i.e. the stenotopic species that depend on this habitat type. A mere increase in the alpha diversity is not sufficient to label the restoration as a success if this is caused by an increase of eurytopic species. For example, fertilisation of a drained peatland will lead to a strong increase in the number of vascular plant species, but this can clearly not be considered successful habitat restoration.
When we look at the stenotopic dragonfly species that are restricted (Somatochlora arctica and S. alpestris) or largely restricted (Coenagrion johansonii and Aeshna subarctica) to peatlands (Karjalainen 2010, Wildermuth Martens 2014) the image is less positive. Somatochlora arctica did occur on 4 sites before restoration but was not found after restoration. The number of S. alpestris is too low to draw any conclusion (one individual in a drained and one in a restored peatland). Coenagrion johansonii has only been found in the pristine sites and not in drained or restored sites. Of A. subarctica only one larva was found, the same number as in the drained sites and much less than in the pristine sites. Thus the stenotopic species, which should be the aim of peatland restoration, do not (or not yet) benefit from the rewetting.
The conclusion that there is an increase in abundance and species richness after the restoration is correct, but this is a result of the colonisation of the newly created habitat by more eurytopic species. Therefore this does not demonstrate that the restoration of the original structure and function of the ecosystems has been achieved, the goal as stated by the authors. Furthermore, the restoration does not improve the conservation status of peatland dragonflies, as the species depending on this habitat type do not benefit while the species that do benefit are more common (Karjalainen, 2010).
When the hydrological conditions are restored the vegetation structure can recover and the stenotopic species will recolonise these areas given enough time. Only then can we conclude that the habitat restoration was a success for dragonflies. Claiming that the restoration was a success, simply because the number of dragonflies and dragonfly species increased, may lead to the false conclusion that the restoration of peatlands is quick and easy.
Karjalainen S. The dragonflies of Finland (revised edition). Helsinki: Tammi; 2010
Wildermuth H, Martens A. Taschenlexikon der Libellen Europas Alle Arten von den Azoren bis zum Ural im Porträt. Wiebelsheim: Quelle & Meyer Verlag; 2014
Competing interests
The author declares that he has no competing interests.
Species richness is not an indicator for the success of habitat restoration
14 August 2015
In this paper the authors show that rewetting of a drained peatland results in an increase in both the number of individuals and species of dragonflies. Three years after the restoration they find ten species of dragonflies in the restored peatlands, comparable to pristine peatlands and much more than the 2 or 3 species in drained bogs. They claim that the restoration was thus successful. However, looking at species numbers as a measure for the success of habitat restoration can be misleading.
As stated in the background the goal of restoration of degraded ecosystems is to prevent the loss of biodiversity and the restoration of the original structure and function of the ecosystem. This would mean that the restoration should benefit the species that are threatened by the loss of the habitat under study, i.e. the stenotopic species that depend on this habitat type. A mere increase in the alpha diversity is not sufficient to label the restoration as a success if this is caused by an increase of eurytopic species. For example, fertilisation of a drained peatland will lead to a strong increase in the number of vascular plant species, but this can clearly not be considered successful habitat restoration.
When we look at the stenotopic dragonfly species that are restricted (Somatochlora arctica and S. alpestris) or largely restricted (Coenagrion johansonii and Aeshna subarctica) to peatlands (Karjalainen 2010, Wildermuth Martens 2014) the image is less positive. Somatochlora arctica did occur on 4 sites before restoration but was not found after restoration. The number of S. alpestris is too low to draw any conclusion (one individual in a drained and one in a restored peatland). Coenagrion johansonii has only been found in the pristine sites and not in drained or restored sites. Of A. subarctica only one larva was found, the same number as in the drained sites and much less than in the pristine sites. Thus the stenotopic species, which should be the aim of peatland restoration, do not (or not yet) benefit from the rewetting.
The conclusion that there is an increase in abundance and species richness after the restoration is correct, but this is a result of the colonisation of the newly created habitat by more eurytopic species. Therefore this does not demonstrate that the restoration of the original structure and function of the ecosystems has been achieved, the goal as stated by the authors. Furthermore, the restoration does not improve the conservation status of peatland dragonflies, as the species depending on this habitat type do not benefit while the species that do benefit are more common (Karjalainen, 2010).
When the hydrological conditions are restored the vegetation structure can recover and the stenotopic species will recolonise these areas given enough time. Only then can we conclude that the habitat restoration was a success for dragonflies. Claiming that the restoration was a success, simply because the number of dragonflies and dragonfly species increased, may lead to the false conclusion that the restoration of peatlands is quick and easy.
Karjalainen S. The dragonflies of Finland (revised edition). Helsinki: Tammi; 2010
Wildermuth H, Martens A. Taschenlexikon der Libellen Europas Alle Arten von den Azoren bis zum Ural im Porträt. Wiebelsheim: Quelle & Meyer Verlag; 2014
Competing interests
The author declares that he has no competing interests.