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 , 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 : 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 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 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, and Systematics 34:487‐515. This was an excellent and thought‐provoking paper that decries the conflation of habitat fragmentation with habitat loss. The author intimates that, in studying habitat loss, researchers use fragmentation metrics that do not control for habitat loss. This is problematic because fragmentation may indicate habitat loss, a change in spatial configuration, or an increase in isolation, but the specific effect on any one of those processes may be positive or negative. The term ‘fragmentation’ seemed to be becoming a catch‐all term for negative human‐landscape interactions, but habitat loss has larger and more consistently negative impacts on biodiversity and does habitat fragmentation.

Fischer, J. and D.B. Lindenmayer. 2007. Landscape modification and habitat fragmentation: a synthesis. Global Ecology and Biogeography 16:265‐280. I primarily used this paper for the sections it contains on edge effects and connectivity. More broadly, this was a review paper that drew insight from a broad range of primary literature on landscape pattern and process. Edge effects are not necessarily universally negative, although that is often how they are portrayed, and have varying penetration depths into core area depending on the process in question and the patch‐matrix contrast. The authors noted that connectivity is a somewhat loosely applied term with several definitions and provided their own delineation (habitat, landscape, and ecological connectivities). The first refers to species‐specific connectedness among patches, the second to human perceptions of connections of native vegetation based on calculated metrics, and the third to cross‐scale ecological processes and flows. The authors describe the human‐centric as the simplest to understand and the most easily converted to conservation plans.

Fischer, J., D.B. Lindenmayer, and A.D. Manning. 2006. Biodiversity, ecosystem function, and resilience: ten guiding principles for commodity production landscapes. Frontiers in Ecology and the Environment 4:80–86. This paper introduces the problem that the supply of land devoted to maintaining biodiversity is not keeping pace with the demand. The authors’ proposition, maintaining biodiversity in production landscapes, seeks to be many things to many people as a way of combining economic profit and conservation. The authors provide ten strategies to guide the design of production landscapes that protect biodiversity, chief amongst them increasing core area size and connectivity between patches. They feature landscape pattern and process as guiding principles in creating an economically and ecologically feasible landscape. Their self‐criticism mirrors my thoughts, that the generality of their framework precludes “a prescriptive list of management actions”, but their work is cited elsewhere in articles that put flesh on the bones of their framework.

Hodgson, J.A., C.D. Thomas, B.A. Wintle, and A. Moilanen. 2009. Climate change, connectivity and conservation decision making: back to basics. Journal of Applied Ecology 46:964‐969. This was a fun title. The “back to basics” part almost sounds like the authors were exasperated with landscape ecologists. The paper did not adopt that tone, but did take issue with the focus on connectivity. I found it a useful paper to clarify my thinking on enumerating and ranking conservation priorities. The authors discussed the uncertainty involved with determining connectivity, given its many overlapping definitions and the difficulty in measuring functional connectivity. They conclude that the link between connectivity and population size is more complicated than that between patch area and population size. Their Table 1 I found especially useful, with its ideas to keep, develop, and discard. They recommend prioritizing areas with high endemism and large patches and recommend future research into functional connectivity.

Kingsland, S. 2002a. Designing nature reserves: adapting ecology to real‐world problems. Endeavour 26:9‐14. Kingsland, S. 2002b. Creating a science of nature : perspectives from history. Environmental Modeling and Assessment 7:61‐69. These are two papers that are so closely intertwined that I am combining their summaries. Together, they provide a good overview of the historical development of the single large or several small (SLOSS) debate that began in the 1970s and its foundation in island biogeography theory and morphed into one of ‘operations research’, or how to turn methodological and philosophical debates on ecological theories into conservation action plans in the real world. Since the shift in the debate, which parallels the development of landscape ecology as a discipline, the author notes that reserve design planning has become more consistent. There was also a thought‐provoking passage on the risks of making policy recommendations at an early stage of academic debate, since it may leave policy‐makers making decisions based on divided expert opinion. The closing line of the ‘a’ paper “[Clarifying conservation goals] might not guarantee that the goals of the scientists would be fully achieved, for compromise is part of the process, but it could help to ensure scientists a place at the table when these decisions were being made” summarizes the lesson from these papers.

Kupfer, JA. 2012. Landscape ecology and biogeography: rethinking landscape metrics in a post‐ FRAGSTATS landscape. Progress in Physical Geography 36:400‐420. This article touches on a point of contention that arose when I read about FRAGSTATS for the first time. It seems like a black box that spat out inappropriate or inconsequential numbers that specialist and non‐ specialist stakeholders alike could mistake for management insight. This article calls for more “functional approaches” to measuring landscapes that incorporate more landscape function. I hope that its calls are heeded and I can’t help but wonder if some of the inconsistency in measuring fragmentation described by Fahrig is the result of the phenomenon described here by Kupfer.

Martensen, A.C., R.G. Pimentel, and J.P. Metzger. 2008. Relative effects of fragment size and connectivity on bird community in the Atlantic Rain Forest: Implications for conservation. Biological Conservation 181:2184‐2192. I found this an interesting paper because I like those that inquire about the relative impacts of this versus that. The authors are among the first that I have found who compare the effects of fragment size and connectivity. Interestingly, because it contradicts the literature, they found that connectivity played a larger role than did fragment size in determining . They sampled a range of fragment sizes and examined avian species abundance. They conclude that a well‐connected network of smaller patches is more important than a single large patch because the amount of habitat area is larger. While this is at first glance inherently intriguing, I suspect conservation action plans based on it may be unstable. If connectivity is lost or degraded, perhaps by a natural disaster or a change in human attitude, then populations may not survive. I remain curious how much their results depend on the sample fragments they chose and how generally applicable are their conclusions to other taxa and locations.

Ribeiro, M.C., J.P. Metzger, A.C. Martensen, F.J. Ponzoni, and MM Hirota. 2009. The Brazilian Atlantic Forest: how much is left, and how is the remaining forest distributed? Implications for management. Biological Conservation 142:1141‐1153. This was an excellent paper that incorporated many of the issues I discuss above. It was fairly influential in the development of this paper. The authors used functional landscape metrics in estimating the amount and distribution of forest fragments landscape in the Atlantic Forest in Brazil. They found more remaining forest than they expected but noted that the fragments were relatively small patches. They discuss reducing edge effects and recommended prioritizing large, mature forests. They also mention the importance of implementing conservation plans that functionally link smaller patches to larger ones. Tjørve, E. 2010. How to resolve the SLOSS debate: Lessons from species‐diversity models. Journal of Theoretical Biology 264:604‐612. The SLOSS debate is alive and well! Though I note is contained in the Journal of Theoretical Biology, which in my experience publishes mathematically intensive works. The author presents species‐area relationships as a way to generate testable hypotheses about the SLOSS debate. The model explicitly ignores patch shape and connectivity in order to make the model tractable. It seems that a model that combines the approach taken in this paper with graph‐ or circuit‐theory might go a long way towards resolving the SLOSS debate. This is easier said than done, as it might take a good modeler a year or more to find results.

Uezu, A., J.P. Metzger, and J.M.E. Vielliard. 2005. Effects of structural and functional connectivity and patch size on the abundance of seven Atlantic Forest bird species. Biological Conservation 123:507‐ 519. The authors present an interesting study that incorporates many of the ideas I discuss here. They examined the same Atlantic Forest in Brazil that Metzger and Martensen have built their research programs around. They studied a range of patch sizes at a range of isolation distances and with varying structural and functional connectivity. They found that some species were more positively affected by patch size than by connectivity and vice versa. This species‐specificity complicates the already‐complex planning factors that must be considered during reserve design. The results presented here increase my curiosity about the generality of Uezu’s and Martensen’s conclusions since they stem from the same study system.

Vandermeer, J. and I. Perfecto. 2007. The agricultural matrix and a future paradigm for conservation. 21:274‐277. The authors focus on land‐use policies affecting and the land‐use policies affecting the agroecosystem matrix that connects the remaining fragmented natural vegetation patches. They explore two scenarios, during and after habitat conversion, and the management remedies and paths that can be enacted. While are being converted, structural economic changes can reduce the demand for agricultural land that can reverse deforestation. Once patches are isolated, connecting them becomes the priority. This paper provided a different angle for my thinking. I enjoyed its focus on the types of reasonable management plans under different scenarios.

Other works cited

Tambosi LR, AC Martensen, MC Ribeiro, and JP Metzger. 2014. A framework to optimize restoration

efforts based on habitat amount and landscape connectivity. Restoration Ecology 22:169‐177.

I found this paper but I believe its authors are sufficiently represented that their views are readily synthesized from their works cited above and those of the other authors. There are three steps in the framework: Determine the present state and attributes of the landscape, identify the species distribution among patches, and target the areas that will provide the greatest benefit to ecosystem function.