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The mountain pine beetle (MPB; Dendroctonus ponderosae) is native to western North America, attacks most trees of the genus Pinus, and periodically erupts in epidemics. The current epidemic of the MPB is an order of magnitude larger than any previously recorded, reaching trees at higher elevation and latitude than ever before. Here we show that after 2 decades of air-temperature increases in the Colorado Front Range, the MPB flight season begins more than 1 month earlier than and is approximately twice as long as the historically reported season. We also report, for the first time, that the life cycle in some broods has increased from one to two generations per year. Because MPBs do not diapause and their development is controlled by temperature, they are responding to climate change through faster development. The expansion of the MPB into previously inhospitable environments, combined with the measured ability to increase reproductive output in such locations, indicates that the MPB is tracking climate change, exacerbating the current epidemic.

Significance In drylands worldwide, where plant cover is sparse, large amounts of the ground surface are covered by specialized organisms that form biological soil crusts (biocrusts). Biocrusts fix carbon and nitrogen, stabilize soils, and influence hydrology. Extensive physical disturbance from livestock/human trampling and off-road vehicles is known to destroy biocrusts and alter ecosystem function. More recent work also indicates that climate change can affect biocrust communities. Contrary to our expectations, experimental climate change and physical disturbance had strikingly similar impacts on biocrust communities, with both promoting a shift to degraded, early successional states. These results herald ecological state transitions in drylands as temperatures rise, calling for management strategies that consider risks from both physical disturbances and climate change.

5 páginas.- 2 figuras.- 46 referencias.- Free Access in https://doi.org/10.1111/nph.15992 Global environmental changes such as climate and land-use change affect ecosystems worldwide, and this New Phytologist Virtual Issue brings together fundamental research questions and novel approaches associated with the study of biological soil crusts in the context of such shifts. In a changing world, organisms can display a limited set of responses that will determine their persistence over varied spatial and temporal scales. Specifically, organisms might tolerate the change – for example, via phenotypic plasticity – and remain present in local communities. Alternatively, organisms might shift or retract their range to match their historical niche, they may adapt to the directional selection pressures imposed by change, or they could be driven to local (and possibly global) extinction. Efforts to understand which of these responses particular plant species or assemblages will exhibit are necessary for predicting changes in ecosystem functioning and trophic interactions under global change scenarios, and for managing and supporting sustainable terrestrial ecosystems. Accordingly, the assessment of plant responses to global change has become a significant research focus. Despite this impressive effort, our understanding and combined work to measure the responses to global change for species and communities of nonvascular autotrophs, such as the cyanobacteria, lichens, and bryophytes that form biological soil crusts (Fig. 1), remain rare compared with the large focus on vascular plants (Fig. 2; Reed et al., 2016). Nevertheless, these nonvascular photosynthetic communities and their responses to change could have critical implications for determining ecosystem structure and function at the global-scale (Elbert et al., 2012; Ferrenberg et al., 2017; Rodriguez-Caballero et al., 2018). This article was also supported by the US Department of Energy Office of Science (DE-SC-0008168), the Strategic Environmental Research and Develoment Program (RC18-1322), and by the US Geological Survey Ecosystems Mission Area. MD-B acknowledges support from the Marie Sklodowska-Curie Actions of the Horizon 2020 Framework Program H2020-MSCA-IF-2016 under REA grant agreement no. 702057. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. Peer reviewed