Reframing landscape fragmentation’s effects on ecosystem services

Mitchell, M. G. E. et al. 2015. Trends in Ecology and Evolution,  Vol. 30, No. 4, pp. 190-198.
Landscape structure and fragmentation have important effects on ecosystem services, with a common assumption being that fragmentation reduces service provision. This is based on fragmentation’s expected effects on ecosystem service supply, but ignores how fragmentation influences the flow of services to people. Here we develop a new conceptual framework that explicitly considers the links between landscape fragmentation, the supply of services, and the flow of services to people. We argue that fragmentation’s effects on ecosystem service flow can be positive or negative, and use our framework to construct testable hypotheses about the effects of fragmentation on final ecosystem service provision. Empirical efforts to apply and test this framework are critical to improving landscape management for multiple ecosystem services.

One effect of human building activities that our blog has not yet discussed much is the fragmentation of our landscape. What used to be more or less uninterrupted habitat is now fragmented by the infrastructure we utilize to travel, mainly roads. Finding areas that are not interrupted by roads is increasingly difficult. For example, a few years ago I spent a little time at the Tiputini Biodiversity Station, a tropical research station in Ecuador. It is so remote that I could only reach it by boat, using the Tiputini River as a natural conduit. Recent oil exploration, however, has brought roads for oil wells dangerously close to the station. This will inevitably be the end of one of the remaining almost pristine pieces of rainforest.

We tend to think that fragmentation by roads has mostly negative effects: for example it often disrupts animal migratory paths and leads to population isolation or mass mortality of migratory species as they try to cross a road. I was part of a study investigating strategies to mitigate amphibian mortality on roads in which our team protected thousands of toads and frogs and provided them with an alternative habitat (see Schlupp & Podloucky, cited below). But are the consequences of fragmentation in fact always negative? Could roads or other man-made paths also be positive?

That possibility arises when we think about ecosystem engineering and ecosystem services, which have been important themes on this blog (see, for example, Kiza Gates’ post on the classic article, “Organisms as Ecosystem Engineers”). In that light one could argue that the fragmentation humans create is a form of ecosystem engineering. Consider how you get to your favorite tract of beautiful landscape: likely some road is involved.

That brings me to Mitchell et al.’s recent review paper in TREE. Mitchell and his team study the combined effects of fragmentation and ecosystem engineering, and reach a few surprising conclusions. They bring social sciences into play and borrow language from economics: supply, demand, and flow. And they use this thinking to analyze the effects of fragmentation on one of the recipients of ecosystem services: humans. They argue against the concern that, by interfering in ecological processes, fragmentation will inevitably reduce the supply of ecosystem services–i.e. that fragmentation is an example of how human use of the environment can be self-defeating. They point out that fragmentation can increase the flow of ecosystem services to society. With a more nuanced understanding of the effects of fragmentation, they argue, the human interaction with the landscape can be planned better, with the goal of maintaining a flow of ecosystem services over time.

This paper presents a line of thinking I don’t always agree with. But it is very interesting. Their approach is very human-centered: in their argument, the benefits of ecosystem services are always in the human domain (see their Figure 1). This does not leave much room for the undisturbed nature I value. But like all good scientists the authors call for more research–and with this I have to agree.

Schlupp, I. & Podloucky, R. 1994. Changes in breeding site fidelity: A combined study of conservation and behaviour in the common toad, Bufo bufo. Biological Conservation: Vol. 69, No. 3, pp. 285-291. As a measure to mitigate mortality during migration, we created a new habitat for toads to direct them away from a nearby road. Though it was expected toads would reject the new habitat they did not. Overall, however, habitat fragmentation due to the road had rather negative consequences.

5 thoughts on “Reframing landscape fragmentation’s effects on ecosystem services

  1. This follows another recent article which points out that the pollinator producing benefit of forests can only flow to agriculture if we fragment forests by converting portions of them to farms. The benefit increases as the fragmentation increases (up to a point). It is far from clear that ecosystem services has been or could become an effective an effective frame for conserving ecosystems and species.

  2. Very interesting and open to different ethical/political interpretations. I like the idea that humans need to figure out ways to coexist with healthy ecosystems that support an abundance of other species, including those that provide us with “services.” I am less fond of the idea that fragmenting currently un-fragmented ecosystems is desirable because it increases their value as service providers.

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