A perception amongst some natural resource management people that I deal with is that interventions to prevent degradation of environmental resources should occur at the highest relevant scale – for example, at the scale of the catchment for a water body. There are at least four reasons why this can be incorrect.

One of the big challenges in managing the environment is knowing how well the available management actions will perform – what difference will they really make? We usually have a lot of uncertainty about this, either because we generally lack knowledge of the relevant cause-and-effect relationships, or because there is a lot of spatial variability in the system, or both.

Even with good scientific knowledge available, variability can be a crucial factor, requiring a case-by-case assessment of each possible intervention. One of the factors that varies is scale. For one natural asset, degradation might be due to processes within or close to the asset itself, while for another apparently similar asset, degradation might be due to processes occurring at some distance away. For example, a wetland connected to a river could be degraded by nutrients washing off from nearby land, or by nutrients coming from a long way up river. We obviously need to understand the causes and sources of such damage in order to manage it well.

The importance of dealing appropriately with the scale of an environmental problem is well recognised, but I have noticed that there is sometimes some confusion about it. For example, “Integrated Catchment Management” is a great idea, if applied well. The basic idea is that you understand all the issues within the catchment for a waterway or water body, and bring together all those issues appropriately when deciding on management actions. That’s fine, but for some reason, some people involved in catchment management actions sometimes seem to jump from there to assuming that actions need to be taken at the whole-catchment scale – that integrated catchment management is synonymous with catchment-scale management. For example, if an area of land is threatened by rising saline groundwaters caused by recharge within its sub-catchment, and the area of the sub-catchment is say 50,000 ha, then the view would be that perennial vegetation (a land use that can help to prevent groundwater rise in the Australian context) needs to planted over a large portion of the 50,000 ha.

There are at least four reasons why this view can be incorrect:

1. It may be possible to target interventions within the relevant area. In the salinity example, there may be smaller areas that contribute most of the salinity, or there may be areas that should not be planted with perennials because this would reduce fresh surface water yield to the waterway. If targeting is physically possible, then it is likely to be beneficial in terms of the cost-effectiveness of interventions.

2. In some cases, the best responses to water management problems are engineering works, which, may be best located at the point of impact, or at some particular point up stream, rather than all over the catchment (depending on the nature of the engineering works). These works may or may not also need to be complemented by land-use changes in the catchment.

3. In some environments, works may generate a worthwhile localised response, even though they are located within a larger catchment. For example, this can be the case with management of saline groundwater in very flat landscapes. In such cases, the majority of groundwater rise can be caused by on-site recharge rather than lateral movement or pressure from further afield. Analyses in the wheatbelt of Western Australia have shown that in that environment, the priority area for any new perennial vegetation is likely to be on the valley floor (where the salinity would occur), not higher up in the catchment.

4. For some issues, the most appropriate response is adaptation to a changed environment, rather than fruitless attempts to prevent or repair damage. Such adaptation may occur at almost any scale, not just at the whole-catchment scale.

The misconception that interventions should be at the catchment scale sometimes feeds into the selection of very poor investment strategies, prompting untargeted “vegemite” style spreading of resources, too thinly to achieve any NRM outcomes.

David Pannell, The University of Western Australia