Climate change effects are already apparent in some Southwestern US forests and are expected to intensify in the coming decades, via direct (temperature, precipitation) and indirect (fire, pests, pathogens) stressors. We grouped Southwestern forests into ten major types to assess their climate exposure by 2070 using two global climate models (GCMs) and two emission scenarios representing wetter or drier conditions and current or lowered emission levels. We estimate future climate exposure over forests covering 370,144 km² as the location and proportion of each type projected to experience climate conditions that fall outside 99% of those they currently occupy. By late century, 27–77% is climatically exposed under wetter or drier current emission levels, while lowered emission levels produce 10–50% exposure, respectively. This difference points to the benefits of reducing emissions from the RCP8.5 to the RCP4.5 track, with regard to forest retention. Exposed areas common to all four climate futures include central Arizona and the western slope of the Sierra Nevada. Vulnerability assessments also comprise sensitivity and adaptive capacity, which we scored subjectively by forest type according to the number of key stressors they are sensitive to and the resilience conferred by life history traits of their dominant tree species. Under the 2070 RCP8.5 emissions, four forest types are critically and six are highly vulnerable under the hotter GCM; and eight are highly and two moderately vulnerable under the wetter GCM. We discuss forest management adaptation strategies and the barriers to and co-benefits of such plans.

The impacts of different emission levels and climate change conditions to landscape‐scale natural vegetation could have large repercussions for ecosystem services and environmental health. We forecast the risk‐reduction benefits to natural landscapes of lowering business‐as‐usual greenhouse gas emissions by comparing the extent and spatial patterns of climate exposure to dominant vegetation under current emissions trajectories (Representative Concentration Pathway, RCP8.5) and envisioned Paris Accord target emissions (RCP4.5). This comparison allows us to assess the ecosystem value of reaching targets to keep global temperature warming under 2°C. Using 350,719 km² of natural lands in California, USA, and the mapped extents of 30 vegetation types, we identify each type's current bioclimatic envelope by the frequency with which it occupies current climate conditions. We then map the trajectory of each pixel's climate under the four climate futures to quantify areas expected to fall within, become marginal to (outside a 95% probability contour), or move beyond their current climate conditions by the end of the 21st century. In California, these four future climates represent temperature increases of 1.9–4.5°C and a −24.8 to +22.9% change in annual precipitation by 2100. From 158,481 to 196,493 km² (45–56%) of California's natural vegetation is predicted to become highly climatically stressed under current emission levels (RCP8.5) under the drier and wetter global climate models, respectively. Vegetation in three California ecoregions critical to human welfare, southwestern CA, the Great Valley, and the Sierra Nevada Mountains, becomes >50% impacted, including 68% of the lands around Los Angeles and San Diego. However, reducing emissions to RCP4.5 levels reduces statewide climate exposure risk by 86,382–99,726 km². These projections are conservative baseline estimates because they do not account for amplified drought‐related mortality, fires, and beetle outbreaks that have been observed during the current five‐year drought. However, these results point to the landscape benefits of emission reductions.

Core Ideas: Field crop diversity in the US peaked between 1940 and 1960. Current levels of field crop diversity are similar to what they were in 1900. Field crop diversity in the Midwest has been very low throughout the past 142 years. Describing spatiotemporal patterns of agricultural biodiversity may be an important step toward better understanding its effect on agroecosystem services. We describe species‐level field crop diversity at the national and state level for the United States, using annual survey data for a 142‐yr period. National‐level field crop diversity was very low around 1870 and peaked around 1960, after which time it began to decline. Many states had their highest levels of diversity between 1940 and 1960, but trends varied strongly among states. In 1900, the states with highest diversity were in the Northeast, but in 2012 the highest diversity was found in California, North Dakota, and the southeastern states. Diversity in the central US Corn Belt was very low throughout the 142‐yr period studied. These results show that changes in diversity do not necessarily follow a simple continuous decline when moving from “traditional” to “industrial” agriculture.

Natural resource managers need information about the risks associated with climate change to provide guidance on where to implement various management practices on natural lands. The spatial variation of projected impacts within a vegetation type can be used to target climate‐adaptive management actions because different locations will be exposed to different levels of climatic stress. Vegetation refugia are areas that retain non‐stressful climate conditions under future climates. Consensus vegetation refugia – areas retaining suitable climates under both wetter and drier future projections – represent only 14.6% of California's natural vegetation. One state and one federal government agency have incorporated vegetation refugia maps into conservation planning for 522 vertebrate species and for post‐wildfire reforestation. Monitoring how vegetation responds to management actions at sites within vegetation refugia can improve the conservation of plants subjected to a changing climate.

Understanding the effects of climate change is one of the most challenging goals for biodiversity conservation. The forests of Andalusia, in Southern Spain, are part of an important Mediterranean Basin biodiversity hotspot. However, great changes in climate are expected to occur in this region, and there is an increasing need to assess the vulnerability of its vegetation. We assess the vulnerability of twelve forest types in the region that are included in the European Directive 92/43/EEC as Habitats of Community Interest (HCI). HCI are natural habitat types which are in danger, have a small natural range, or present an outstanding example of a biogeographical regions in the European Union. We assessed vulnerability by analyzing the climate exposure level of each forest type under two global climate models (MRI-CGCM3, which predicts warmer and wetter conditions, and MIROC-ESM which predicts hotter and drier conditions), two emission scenarios (RCP4.5, a representative concentration pathway that predicts stable emissions of CO₂, and RCP8.5, that predicts the highest CO₂ emissions) by the mid- and end-century time periods. The vulnerability analysis also includes the sensitivity and adaptive capacity of the dominant tree species which compose each forest type. An overall vulnerability score was calculated for each forest type, model, scenario and time period. High-elevation forest types and those with high moisture requirements were more vulnerable to climate change, while forest types dominated by more thermophilic species were less vulnerable and more resilient. The worst climate impacts were predicted in the MIROC-ESM model and RCP8.5 scenario by the end of the century (2070-2100), while the least climatic stress was obtained in the MRI-CGCM3 model and RCP4.5 scenario by the mid-century (2040-2070), which still shows high potential stress for most forest types. By the end of the century, the climate exposure of the entire forest domain will range between 32 % in the least stressful situation (MRI-CGCM3 and RCP4.5), and 98 % in the most climatically stressful situation (MIROC-ESM and RCP8.5). However, the effects of climate change will be perceptible by the mid-century, with most of the HCI forest types suffering climate stress. The "Andalusian oak forest" and the "Corylus wet forest" types were the most vulnerable to climate change, while the "Mediterranean pine forest", the "Olea and Ceratonia forests" and the "oak forests" were the least vulnerable. This assessment identifies the vulnerable forest types to climate change in the south of the Iberian Peninsula, and provides context for natural resource managers in making decisions about how to adapt forests to the impacts of climate change.