Climate Change: Defining Reference Conditions and Restoring Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 203

9
Climate Change: Defining Reference
Conditions and Restoring Freshwater
Ecosystems
Richard K. Johnson, Richard W. Battarbee, Helen Bennion,
Daniel Hering, Merel B. Soons and Jos T.A. Verhoeven
Introduction
Natural ecosystems, already under considerable stress from land-use change and
pollution, now face additional pressures from climate change (e.g. Mann et al .
1998), both directly and indirectly through interactions with other drivers. At the
same time, the world's biodiversity is also being reduced at an unprecedented
rate, which has recently manifested in a growing concern that when species are
lost, ecosystem services may also become impaired. Such concerns have resulted
in a growing interest in restoring both the biodiversity and functioning of
ecosystems to a more natural or reference state. Restoration usually entails
removing or mitigating the activities causing the degradation, but may also require
more active management such as physical reconstruction of freshwater ecosystems
(e.g. by re-meandering streams) or by altering internal habitat conditions (e.g. by
replacing large woody debris in streams, either directly, or indirectly by promoting
the growth of riparian forests).
To determine if restoration has been successful requires knowledge of the
condition that is expected to occur in the absence of human-induced stress.
Specifically, reference conditions are needed: (i) to understand how the current
condition differs from the ecological target/reference condition; (ii) to determine
what factors have been degraded and by how much; (iii) to identify the drivers of
the observed change; and (iv) to decide what steps are needed to restore the
ecosystem to the desired condition. Ideally, restoration studies, and indeed all studies
of disturbance and recovery, should be based on deviation from an undisturbed
condition (e.g. Downes et al . 2002). However, finding adequate controls at the
scales that are usually relevant for ecosystem studies, such as contemporary
landscapes/ecosystems where disturbances have not occurred, is often problematic.
Consequently, the most common approach is to establish the reference condition