Subdivision for conservation?

Highlights

• We demonstrate that subdivision, decoupled from development, can benefit conservation.

• Subdivision enabled strategic acquisition of lots that meet one or more objectives.

• Conservation outcomes improved despite planning units being socioeconomically defined.

• Subdivision achieved ecological goals while maintaining social and economic relevance.

Abstract

Creative and strategic approaches are needed to achieve conservation goals in contemporary landscapes. Protected area expansion competes with multiple demands for land and needs to accommodate the socio-economic realities of landscapes to be effective. Smaller planning units can improve targeted acquisitions for protected areas, but ‘subdivision’ used in conservation planning has typically followed ecological patterns. Instead, we suggest that subdividing based on anthropogenic land-development patterns could improve strategic achievement of conservation goals by producing smaller planning units that are also socio-economically relevant. We simulated this approach to subdivision in a New England, USA landscape and evaluated the outcomes for three conservation planning scenarios – protect riparian corridors, protect rare habitats, and protect representative habitats – in the original and subdivided property delineations. For each scenario-delineation combination, we identified protected land expansion solutions that optimized a priority objective within a budget or achieved a conservation target at minimum cost. We used a multi-objective optimization algorithm to identify solutions to navigate tradeoffs between ecological, social, and economic objectives. In our study area, subdivision allowed us to optimize ecological outcomes within a budget and achieve conservation targets at reduced cost. While subdivision solutions were not able to simultaneously improve outcomes for all objectives, they were often able to reduce individual and aggregate outcomes compared to solutions in the originally delineated landscape. Subdivision could be a useful tool for improving implementation of conservation goals because it results in smaller planning units that are able to spatially represent conservation objectives more exactly while remaining socio-economically relevant.

Introduction

Conservation planning increasingly needs to operate in human-transformed landscapes and in regions under development pressure (Barr et al., 2016, Bekessy et al., 2012, Moilanen et al., 2005, Pressey et al., 2007). Land conversion to residential or commercial uses is possibly the single greatest human threat to terrestrial biodiversity because it is almost always an irreversible transformation of land use (Bettigole, Donovan, Manning, Austin, & Long, 2014). Subdivision is a common precursor to land conversion because it transforms a single parcel into multiple, smaller parcels or lots for the purpose of future sale or building development (U.S. Department of Commerce, 1928). Subdivision may lead to habitat loss, habitat fragmentation, and increased human development (Best, 2002, Kilgore et al., 2013), which threatens biodiversity and makes the management of landscape-level processes more challenging (Shifley et al., 2014). However, it is development, not the redrawing of property boundaries that threatens biodiversity. Although subdivision is viewed as anathema to conservation, we suggest that subdivision, decoupled from development, could actually benefit biodiversity.

The term ‘subdivision’ for conservation planning has generally referred to any process that results in smaller planning units. Not surprisingly, conservation planning has primarily delineated planning units based on ecological boundaries such as watersheds (Noss, Carroll, Vance-Borland, & Wuerthner, 2002), ecoregions (Abell et al., 2008, Fernandes et al., 2005, Wilson et al., 2007), land cover types (Polasky et al., 2008, Pressey and Logan, 1998), land uses (Pouzols et al., 2014), or species distributions (Moilanen et al., 2005). Smaller planning units based on ecological attributes improves targeted acquisition for conservation because the new units are more precise in matching the spatial configurations of ecological features (Adams et al., 2011, Pressey and Logan, 1995, Pressey and Logan, 1998). Planners achieve greater ecological outcomes per unit area, which results in a higher return on investment and lower economic tradeoffs. Alternatively, uniform grids or tessellations comprised of squares (Chan, Shaw, Cameron, Underwood, & Daily, 2006), hexagons (Csuti et al., 1997, Mills et al., 2010), or triangles (White, Kimerling, & Overton, 1992) provide a systematic and unbiased way to delineate planning units. The drawback to ecological, uniform grid, or other tessellation approaches is that the resulting planning units lack social or economic anchoring and may result in plans that are difficult to implement. Most terrestrial systems have long histories of legislative and legal delineations that are anything but uniform in size or ecological composition.

It is unclear if smaller planning units are beneficial when the landscape is subdivided based on socio-economic factors rather than ecological ones. In this context, landscapes are subdivided based on anthropogenic land-development patterns, which we will refer to as subdivision. There is evidence that subdivision has been used effectively for navigating competing land-use interests and implementing land protection at local spatial levels. Land trust practitioners and land conservation organizations use creative subdivision strategies to achieve their land protection goals, albeit without calling it subdivision. For example, conservation organizations may sell a portion of a property for “conservation-minded” residential development to pay for the protection of the rest of the property (“purchase-protect-resale”; Hardy, Fitzsimons, Bekessy, & Gordon, 2018b). Alternatively, conservation organizations could retain partial (easement) or full (acquisition) land interest on the portion(s) of the property with conservation value but use proceeds from the residential lot sales to repeat the process on other properties (“revolving fund”; Hardy, Fitzsimons, Bekessy, & Gordon, 2018a). While these approaches have been implemented on a parcel-by-parcel basis, a systematic subdivision approach based on socio-economic factors could offer opportunities to improve outcomes for conservation goals as well as strategically navigate socio-economic tradeoffs (Knight et al., 2006, Mair et al., 2018, Paloniemi et al., 2018).

We investigated the potential of using subdivision to define planning units in a New England, USA watershed that was a mix of protected, natural, and residentially developed lands. We compared the quantitative and spatial outcomes of protected area solutions in both the original and subdivided property delineations. First, we assessed how attributes of the planning units (i.e., parcels) changed with subdivision delineation. Second, we explored how subdivision influenced our ability to achieve conservation planning goals. We explored how protected areas could be established for three common conservation planning scenarios: (1) protect riparian corridors; (2) protect priority habitats; and (3) protect representative habitats such that the ratio of habitats in the protected lands estate reflects the surrounding landscape. For each planning scenario, we identified a solution that fully achieved each scenario’s priority objective and a solution that maximized the priority objective within a budgetary constraint. To identify solutions, we used a multi-objective optimization algorithm that considered social and economic objectives jointly with ecological objectives. Finally, we investigated how systematic subdivision influenced our ability to navigate tradeoffs with competing objectives.