Stefan Bengtson NRS 534 April 29, 2015 Cores Or

Stefan Bengtson NRS 534 April 29, 2015 Cores or connections? Managing landscapes by pattern and design Human land use change is a major driving force behind the loss of biodiversity, raising the importance of effective conservation actions. Debate remains, however, over the nature of those conservation actions, although guiding frameworks have been proposed (Fischer et al. 2006, Vandermeer and Perfecto 2007, Tambosi et al. 2014). These frameworks often reference core areas and connectivity. But is one more important than another? The literature on cores and connectivity as conservation and management aims revolves around four fundamental concepts in landscape ecology: core area, connectivity, fragmentation, and edge effects. Core area represents the amount of a patch that remains relatively free of human disturbance. This represents the best‐quality habitat for many native species. Connectivity and fragmentation are related concepts: where fragmentation subdivides a patch and may prevent or reduce inter‐patch material and energy flows, connectivity provides the means to maintain those flows (Fischer and Lindenmayer 2007). Edge effects represent the often‐sharp gradient between a patch and its surrounding matrix that tend to reduce the amount of core area within a patch (Fischer and Lindenmayer 2007). Disentangling these patterns and their effect on biodiversity was a challenge, though I take some comfort that I was not alone in my struggle (Fahrig 2003, Ewers and Didham 2006). Fahrig (2003) commented on the frequent conflation in the literature of habitat fragmentation with habitat loss and discussed the ways in which researchers should control for habitat size when examining the effect of fragmentation on biodiversity. Even with proper controls there are multiple confounding landscape patterns affecting biodiversity (Ewers and Didham 2006). Generally, however, increasing average patch size and shape complexity increases diversity while isolation decreases it. The complexity of biodiversity response stems from the variable response of patch spatial configuration to changes in patch size (Fahrig 2003). This may be a reason for the trend away from structural landscape metrics towards those that better reflect ecosystem function, though these are not faultless (Kupfer 2012). The few papers that have properly examined core area and connectivity by accounting for habitat area appear to fall on a spectrum in the debate between a single large and several small reserves (SLOSS; Kinglsand 2002a,b). Martensen et al. (2008) are at one end – they favor good connectivity. The idea behind this is that with good connectivity, landscape flows are so facilitated that distant, typically smaller, patches become one larger patch. Connectivity can be lost, however, by natural disasters or changes in public conservation goals and is species‐specific (Fischer and Lindenmayer 2007). Habitat fragmentation and the consequent increase in patch perimeter raise the likelihood of edge effects. Edge effects can render even well connected but small patches inhospitable (Fischer and Lindenmayer 2007). The strategy from the opposite end of the spectrum, of a single large isolated patch, is obviously insufficient for any conservation goal, given the nature of the rescue effect (Uezu et al. 2005). While Martensen et al. (2008) may ultimately be correct, I suspect that their results may be based on the samples they examined. For example, Uezu et al. (2005), who share authors with Martensen et al. (2009), found that some species are more affected by patch size and others by increased connectivity. It seems that some combination of core area habitat connected to others by connections of reasonable quality is the right way forward for designing conservation reserves and production landscapes. Such a plan was put forward by Ribeiro et al. (2009) which prioritized conserving large, mature forest stands and connecting them to smaller isolated stands. Where precisely the balance should lie in any particular scenario will, no doubt, be the seed of future research and the answer will probably be “it’s context dependent” as so much of nature is and management plans must be. Any plan will need to incorporate the present state of a landscape and incorporate stakeholder input to determine future goals. This seems especially important in designing production reserves which have been touted as a suitable compromise among diverse stakeholder groups (Fischer et al. 2006, Vandermeer and Perfecto 2007, Brockerhoff et al. 2008). As climate change becomes an increasing concern, it seems like reasonable foresight to design conservation plans with the goal of connecting patches that species can use as stepping‐stones towards more extreme and presumably more habitable patches. Hodgson et al. (2009) warned, however, that devoting too many resources to connectivity‐based management schemes may divert conservation funds from less‐uncertain projects involving habitat area and quality. They suggest ideas to keep, modify, and abandon in pursuit of conservation goals. Connectivity is one of them, which makes sense given its multi‐faceted definition. I think that the synthesis and recommendations of Fischer and Lindenmayer (2007) represent progress on that front. It is also important to prioritize biodiversity hotspots for patch expansion and connection regardless of size (Hodgson et al. 2009, Ribeiro et al. 2009). My opinion leans towards the larger patch and core area end of the SLOSS debate, other factors being equal, because the species/area curve has been well supported since its development although its precise details remain contentious (Tjørve 2010). This is not to ignore connectivity as a conservation consideration; the importance of the rescue effect and dispersal pathways in perpetuating species viability cannot be so lightly dismissed. The two are thoroughly complementary and any conservation plan worth its salt will incorporate both of them with equal weight at multiple scales of biological and legislative organization. Encouraging the help of land‐owners, loggers, and farmers will be a delicate balancing act that needs to walk a fine line between encouraging and directing compliance with connectivity and core‐area goals. To be certain, corridors improve connectivity. Because, however, there are many processes that affect connectivity such as patch‐matrix contrast, matrix quality, and isolation (Ewers and Didham 2006), there are many possible management avenues that managers can pursue to improve connectivity. Core area is different because of how few things impact it. Shape complexity and patch size both directly influence core area, but not much else does. This limits the available conservation choices that can be incorporated into a management plan. The difference between them is a question of scale. Focusing on plans that preferentially favor connectivity seem to accept fragmentation as an inevitability and may not always incorporate the influence of edge effects (but see Ribeiro et al. 2009). Connecting isolated patches is necessary to ensure the rescue effect. Yet problems arise for the manager who follows a plan that focuses too much on connection at the expense of patch size. Edge effects further reduce populations because on top of the limited habitat available to them. If the pendulum swings too far in the other direction managers lose the contingency option that corridors provide. As I’ve shown, either extreme in the SLOSS debate seems at best a solution for the short term as both have severe limitations in the long term. I am left to conclude that a balance between the two should be the most effective, subject to contextual limitations, considerations, and preferences. A conservation plan needs patches large enough to provide enough quality habitat away from edge effects and sufficient connection that species can migrate into and out of the patch with relative ease. BIBLIOGRAPHY Brockerhoff E.G., H. Jactel, J.A. Parrotta, C.P. Quine, and J. Sayer. 2008. Plantation forests and biodiversity: oxymoron or opportunity? Biodiversity and Conservation 17:925‐951. This paper provides a conceptual model that describes in some detail the form of agriculture over a gradient of production intensity from conservation forests to intensive agriculture. It is clear from the design of the main figure that the authors support a production landscape that incorporates conservation aims. The focal ecosystem here is forests so I would curious to see how well the framework put forth in this paper applies to grassland, aquatic, or coastal ecosystems. It is good that the authors provide multiple entries along a range of middle values on the production‐conservation spectrum and discuss stakeholder involvement. Ewers, R.M. and R.K. Didham. 2006. Confounding factors in the detection of species responses to habitat fragmentation. Biological Reviews 81:117‐142. This was an excellent and in‐depth overview of the nuances of habitat fragmentation. It covers a broad range of topics relating to species’ susceptibility to fragmentation and how various processes impact different patterns of landscape diversity. I found especially useful their figure 1 as a tidy summary of community responses to fragmentation. The complexity of incorporating fragment area, edge distance, shape complexity, isolation, and matrix contrast into one predictive model is daunting and remains an open problem in landscape ecology. Fahrig, L. 2003. Effects of habitat fragmentation on biodiversity. Annual Review of Ecology, Evolution,

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