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The Big Sur ecoregion in coastal California is a botanically and ecologically diverse area that has recently experienced substantial mortality of oak (Quercus spp.) and tanoak (Lithocarpus densiflorus) trees due to the emerging forest disease sudden oak death, caused by the invasive pathogen Phytophthora ramorum. In response to the urgent need to examine environmental impacts and create management response strategies, we quantified the impact of P. ramorum invasion on tree mortality across the Big Sur ecoregion using high-resolution aircraft imagery and field data. Using the imagery, we mapped all detectable oak and tanoak trees possibly killed by P. ramorum infection within redwoodtanoak forests and mixed oak woodlands. To validate and improve our remote assessment, we quantified the number, size, and infection status of host trees in 77 field plots (0.25 ha). The field data showed that our remote assessment underestimated mortality due to the occurrence of dead trees in the forest understory. For each forest type, we developed regression models that adjusted our remote assessments of tree mortality in relation to field observations of mortality and local habitat variables. The models significantly improved remote assessment of oak mortality, but relationships were stronger for mixed oak woodlands (r 2 = 0.77) than redwoodtanoak forests (r 2 = 0.66). Using the field data, we also modeled the amount of dead tree basal area (m 2 ) in relation to the density of mapped dead trees in mixed oak woodlands (r 2 = 0.73) and redwoodtanoak forests (r 2 = 0.54). Application of the regression models in a GIS estimated 235,678 standing dead trees in 2005 and 12,650 m 2 of tree basal area removed from the ecoregion, with 63% of mortality occurring in redwood-tanoak forests and 37% in mixed oak woodlands. Integration of the remote assessment with population estimates of host abundance, obtained from an independent network of 175 field plots (0.05 ha each), indicated similar prevalence of mortality in redwood-tanoak forests (20.0%) and mixed oak woodlands (20.5%) at this time. This is the first study to quantify a realistic number of dead trees impacted by P. ramorum over a defined ecological region. Ecosystem impacts of such widespread mortality will likely be significant.
h i g h l i g h t s• We explored urbanization scenarios based on hypothetical land use policies.• We used a unique modeling method to represent conservation planning strategies.• No single strategy was best for achieving all conservation goals.• Effective planning requires assessment of tradeoffs between differing priorities.
a b s t r a c tLand that is of great value for conservation can also be highly suitable for human use, resulting in competition between urban development and the protection of natural resources. To assess the effectiveness of proposed regional land conservation strategies in the context of rapid urbanization, we measured the impacts of simulated development patterns on two distinct conservation goals: protecting priority natural resources and limiting landscape fragmentation. Using a stochastic, patch-based land change model (FUTURES) we projected urbanization in the North Carolina Piedmont according to status quo trends and several conservation-planning strategies, including constraints on the spatial distribution of development, encouraging infill, and increasing development density. This approach allows simulation of population-driven land consumption without excluding the possibility of development, even in areas of high conservation value. We found that if current trends continue, new development will consume 11% of priority resource lands, 21% of forested land, and 14% of farmlands regionally by 2032. We also found that no single conservation strategy was optimal for achieving both conservation goals. For example, strategies that excluded development from priority areas caused increased fragmentation of forests and farmlands, while infill strategies increased loss of priority resources proximal to urban areas. Exploration of these land change scenarios not only confirmed that a failure to act is likely to result in irreconcilable losses to a conservation network, but that all conservation plans are not equivalent in effect, highlighting the importance of analyzing tradeoffs between alternative conservation planning approaches.
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