Environmental observation networks, such as AmeriFlux, are foundational for monitoring ecosystem response to climate change, management practices, and natural disturbances; however, their effectiveness depends on their representativeness for the regions or continents. We proposed an empirical, time series approach to quantify the similarity of ecosystem fluxes across AmeriFlux sites. We extracted the diel and seasonal characteristics (i.e., amplitudes, phases) from carbon dioxide, water vapor, energy, and momentum fluxes, which reflect the effects of climate, plant phenology, and ecophysiology on the observations, and explored the potential aggregations of AmeriFlux sites through hierarchical clustering. While net radiation and temperature showed latitudinal clustering as expected, flux variables revealed a more uneven clustering with many small (number of sites < 5), unique groups and a few large (> 100) to intermediate (15-70) groups, highlighting the significant ecological regulations of ecosystem fluxes. Many identified unique groups were from under-sampled ecoregions and biome types of the International Geosphere-Biosphere Programme (IGBP), with distinct flux dynamics compared to the rest of the network. At the finer spatial scale, local topography, disturbance, management, edaphic, and hydrological regimes further enlarge the difference in flux dynamics within the groups. Nonetheless, our clustering approach is a data-driven method to interpret the AmeriFlux network, informing future cross-site syntheses, upscaling, and model-data benchmarking research. Finally, we highlighted the unique and underrepresented sites in the AmeriFlux network, which were found mainly in Hawaii and Latin America, mountains, and at under-sampled IGBP types (e.g., urban, open water), motivating the incorporation of new/unregistered sites from these groups.

Climate change has increased forest fire extent in temperate and boreal North America. Here, we quantified the contribution of anthropogenic climate change to human mortality and economic burden from exposure to wildfire particulate matter at the county and state level across the contiguous US (2006 to 2020) by integrating climate projections, climate-wildfire models, wildfire smoke models, and emission and health impact modeling. Climate change contributed to approximately 15,000 wildfire particulate matter deaths over 15 years with interannual variability ranging from 130 (95% confidence interval: 64, 190) to 5100 (95% confidence interval: 2500, 7500) deaths and a cumulative economic burden of $160 billion. Approximately 34% of the additional deaths attributable to climate change occurred in 2020, costing $58 billion. The economic burden was highest in California, Oregon, and Washington. We suggest that absent abrupt changes in climate trajectories, land management, and population, the indirect impacts of climate change on human-health through wildfire smoke will escalate.

As the climate warms, extended drought and heat events in the United States are driving an increase in acres burned and homes lost to wildfire. The most devastating wildfires happen when dry winds carry embers long distances, start spot fires and ignite homes. Burning homes then become the fuel that ignites other nearby homes, causing mass conflagrations. Today wildfire is largely approached as a problem that can be controlled through vegetation treatments and firefighting, but that strategy has not stopped the loss of homes and even entire communities. However, new observational and analytical tools have given firefighters, governments, and the public a better understanding of wildfire and how to prepare for it. By redefining the wildfire problem as a home ignition problem, communities can survive even extreme fires and can safely reintroduce fire to the land.

Abstract The interdependent crises of climate change and biodiversity losses require strategic policies to protect, manage, and restore essential ecosystems. Here, we evaluate the relative importance of US national forests (NFs) for protection and conservation as natural climate and biodiversity solutions. We compared landscape integrity (degree of modification by humans), habitat for three keystone species, forest carbon density, accumulation, and total biomass carbon stocks across 154 NFs in the United States. Southern Alaska's Tongass and Chugach NFs hold disproportionally large amounts of high landscape integrity area among all NFs with 25.3% and 5.6% (total 30.9%) of all high (≥9.6) landscape integrity found on NF lands. The Tongass and Chugach store approximately 33% and 3% of all biomass carbon stocks that occur in NFs with high landscape integrity. These two NFs together account for about 49%, 37%, and 18% of all bald eagle, brown bear, and gray wolf habitat found on NF lands. Gray wolf habitat extent was 4% of the total or less on remaining NFs. The Tongass and Chugach were historically wetter and cooler among NFs, and are projected to experience much larger increases in precipitation and much lower increases in maximum temperatures over the coming century. Combined with relatively low recent occurrence of wildfire, this makes permanence more likely. The Tongass and Chugach forests, along with the Pacific Northwest's high carbon density forests should be a high priority for protection and conservation to meet climate and biodiversity goals given their landscape‐scale scarcity and high value.

Economic modelling of the global carbon cost of harvesting wood from forests shows a much higher annual cost than that estimated by other models, highlighting a major opportunity for reducing emissions by limiting wood harvests.

Abstract Protecting the climate system requires urgently reducing carbon emissions to the atmosphere and increasing cumulative carbon stocks in natural systems. Recent studies confirm that large trees accumulate and store a disproportionate share of aboveground forest carbon. In the temperate forests of the western United States, a century of intensive logging drastically reduced large‐trees and older forest, but some large trees remain. However, recent changes to large tree management policy on National Forest lands east of the Cascade Mountains crest in Oregon and southeastern Washington allows increased harvesting of large‐diameter trees (≥53 cm or 21 inches) that account for just 3% of all stems, but hold 42% of total aboveground carbon. In this article, we describe synergies with protecting large trees for climate mitigation, biodiversity, and forest resilience goals to shift species composition, reduce fuel loads and stem density, and adapt to climatically driven increases in fire activity in eastern Oregon.

Previous studies have reported cross‐site relationships between stem diameter at breast height (DBH) and whole‐tree transpiration ( Q t ) across a variety of species and locations. These relationships enable us to estimate canopy transpiration rates using DBH data from forest inventory networks worldwide. However, transpiration responses to environmental conditions such as soil moisture often depend on tree species and age, suggesting that the DBH– Q t relationship varies with soil moisture conditions. In the present study, we collated Q t of 41 ponderosa pine ( Pinus ponderosa Dougl. ex P. Laws.) trees in young (23‐year‐old), mature (90‐year‐old) and old‐growth (250‐year‐old) forests using the sap flow technique. Sap flux density considering the radial decline ( u ) was three times higher in young trees than mature and old‐growth trees under wet soil conditions. The largest declines in u were observed in young trees and then mature trees when soil moisture condition changed from wet to dry. Decreases in u were smaller for old‐growth trees than for young and mature trees. The DBH– Q t relationship differed with soil moisture conditions, showing a strong linear correlation under wet condition across all four age groups but a non‐linear correlation under dry condition. u was overestimated by up to 50%, particularly in the young trees when neglecting differences in the response of u to soil water deficit among different ages. These results suggest that differences in u and its responses to soil water deficit among stand ages should be considered when applying the DBH– Q t relationship for other tree species.

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Both global and US data show associations between COVID-19 death rates and overweight or obesity, which are also risk factors for several other outcomes. Evidence suggests that among the strategies to reduce overweight and obesity are the simple actions of increasing fruit and vegetable consumption and physical activity. Potential benefits include saving thousands of lives and billions of dollars in a future pandemic and reduced risk of other chronic conditions. Once transmission of COVID-19 expanded beyond Asia, the role of cardiometabolic risk factors and especially overweight and obesity, became clear. With early data coming from China where Target Health Data LLC, Suffield, CT, USA Corresponding Author: Mary Adams, On Target Health Data LLC, Suffield, CT 06093, USA. Email: madams.ontargethealthdata@gmail.com Knowing Well, Being Well 385

Climate change impacts are accelerating and there is an urgent need to address this global issue. Tackling climate change in an effective and socially just manner needs to involve mitigation strategies that address the underlying causes of climate change, but also adaptation strategies that help us prepare for current and future impacts. Historically, mitigation and adaptation strategies have been treated separately, but there is now growing awareness of important synergies between them. We highlight these synergies across six key areas where humans need to make transformative changes in order to reduce the impacts of climate change, including energy, pollutants, nature, food, population and the economy. In doing so, we show the enormous potential for civil society, government, world leaders and the private sector to take advantage of the fact that mitigation strategies can also provide adaptation opportunities to lessen humanity’s suffering as we navigate the uncertainties of the climate crisis.

This paper provides a review and comparison of strategies to increase forest carbon, and reduce species losses for climate change mitigation and adaptation in the United States. It compares forest management strategies and actions that are taking place or being proposed to reduce wildfire risk and to increase carbon storage with recent research findings. International agreements state that safeguarding biodiversity and ecosystems is fundamental to climate resilience with respect to climate change impacts on them, and their roles in adaptation and mitigation. The recent Intergovernmental Panel on Climate Change report on impacts, mitigation, and adaptation found, and member countries agreed, that maintaining the resilience of biodiversity and ecosystem services at a global scale is “fundamental” for climate mitigation and adaptation, and requires “effective and equitable conservation of approximately 30 to 50% of Earth’s land, freshwater and ocean areas, including current near-natural ecosystems.” Our key message is that many of the current and proposed forest management actions in the United States are not consistent with climate goals, and that preserving 30 to 50% of lands for their carbon, biodiversity and water is feasible, effective, and necessary for achieving them.

Mounting evidence indicates dryland ecosystems play an important role in driving the interannual variability and trend of the terrestrial carbon sink. Nevertheless, our understanding of the seasonal dynamics of dryland ecosystem carbon uptake through photosynthesis [gross primary productivity (GPP)] remains relatively limited due in part to the limited availability of long-term data and unique challenges associated with satellite remote sensing across dryland ecosystems. Here, we comprehensively evaluated longstanding and emerging satellite vegetation proxies in their ability to capture seasonal dryland GPP dynamics. Specifically, we evaluated: 1) reflectance-based proxies normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), near infrared reflectance index (NIRv), and kernel NDVI (kNDVI) from the MODerate resolution Imaging Spectroradiometer (MODIS); and 2) newly available physiologically-based proxy solar-induced chlorophyll fluorescence (SIF) from the TROPOspheric Monitoring Instrument (TROPOMI). As a performance benchmark, we used GPP estimates from a robust network of 21 western United States eddy covariance tower sites that span representative gradients in dryland ecosystem climate and functional composition. We found that NIRv and SIF were the best performing GPP proxies and captured complementary aspects of seasonal GPP dynamics across dryland ecosystem types. NIRv offered better performance than the other proxies across relatively low-productivity, sparsely non-evergreen vegetated sites (R2 = 0.59 +/- 0.13); whereas SIF best captured seasonal dynamics across relatively high-productivity sites, including evergreen-dominated sites (R2 = 0.74 +/- 0.07). Notably, across grass-dominated sites, all reflectance-based proxies (NDVI, SAVI, NIRv and kNDVI) showed significant seasonal bias (hysteresis) that strengthened with the total fraction of woody vegetation cover, likely due to seasonal patterns in woody vegetation reflectance that are unrelated to or decoupled from GPP. Future efforts to fully integrate the complementary strengths of NIRv and SIF could significantly improve our understanding and representation of dryland GPP dynamics in satellite-based models.

After taking office, President Biden signed an executive order announcing his America the Beautiful plan to conserve 30% of US land and water by 2030. He challenged Americans to collaboratively “conserve, connect, and restore the lands, waters, and wildlife upon which we all depend” at a national scale (US Departments 2021, p. 9). Here, we take a major step in advancing President Biden's plan by envisioning a bold and science-based rewilding of publicly owned federal lands (hereafter, federal lands) in the American West. Beyond concerns for human survival and flourishing, a principled commitment to the natural world and a sense of moral urgency underpins the motivation for our proposal. In general, rewilding aims to reestablish vital ecological processes that can involve removing troublesome nonnative species and restoring key native species. Our rewilding call is grounded in ecological science and is necessary regardless of changing political winds. Our objective is to follow up on President Biden's vision to conserve, connect, and restore by identifying a large reserve network in the American West suitable for rewilding two keystone species, the gray wolf (Canis lupus) and the North American beaver (Castor canadensis). We focus first on the gray wolf, a wide-ranging species requiring extensive areas of habitat. Gray wolves were largely eradicated from the American West following Euro-American colonization and manifest conquest of the West. Through measures afforded by the US Endangered Species Act, in the midto late 1990s, gray wolves were reintroduced to portions of the northern Rocky Mountains and Mexican gray wolves (Canis lupus baileyi) to portions of New Mexico and Arizona. Nevertheless, the wolf 's current range in the 11 Western states is approximately 14% of its historical range (figure 1a). Once likely numbering in the tens of thousands, there may be as few as approximately 3500 wolves in the American West today (supplemental table S1). As an apex predator, wolves can trigger strong ecological effects on prey and plants across a variety of landscapes of western North America (Beschta and Ripple 2009). Beaver restoration forms a second key feature of our rewilding proposal. Beaver populations had once been robust across the American West but were decimated by an estimated 90% to 98% in the wake of settler colonialism and are now extirpated from many streams (Butler and Malanson 2005). By felling trees and shrubs and building dams, beavers enrich fish habitat, increase water and sediment retention, maintain water flows during drought, provide wet fire breaks, improve water quality, initiate recovery of incised channels, increase carbon sequestration, and generally enhance habitat for many riparian plant and animal species (Castro et al. 2015). Beaver restoration is a cost-effective means of repairing degraded riparian areas. Although riparian areas occupy less than 2% of the landscape, they provide habitat for up to 70% of wildlife species (Poff et al. 2012).

Creating strategic forest reserves is essential for stemming the loss of biodiversity and contributing to climate mitigation and adaptation. Meeting preservation targets of 30% protection by 2030, and 50% by 2050 would lead to greater protection of animal taxa and tree species habitat, carbon stocks and accumulation, and forests that are important sources of drinking water. Here, we develop a regional framework to specifically identify at a fine resolution (30 m) high priority forestlands for preservation in Oregon, USA. We include a resilience metric that represents connectivity and topographic diversity, and identify areas within each ecoregion that are ranked high priority for carbon, biodiversity, resilience and drinking water. Oregon has less than 10% of its forestlands protected at the highest levels, yet its temperate forests are among those with the highest carbon densities in the world. Reserves for surface drinking water sources and forest habitat for birds, mammals, amphibians, and reptiles could increase to 50–70% protection at the highest levels by 2050. Protected aboveground biomass carbon could triple to 635 teragrams of carbon by 2050. The ownership of the high preservation priority lands for carbon and biodiversity is primarily federal (67% by 2050) followed by private (28% by 2050), with much less in the other ownerships. Forest reserves could be established on federal lands through executive action, regulation and rule-making, while private landowners could be incentivized to store more carbon, limit harvest in certain areas and transfer ownership to land trusts. Protecting mature and old forests on federal lands fulfills an urgent need for protection and provides a low-cost way to simultaneously meet national and international goals. This study provides a flexible, dynamic framework for identifying areas that are high priority to protect for climate mitigation and adaptation at regional and sub-regional scales.

Evergreen conifer forests are the most prevalent land cover type in North America. Seasonal changes in the color of evergreen forest canopies have been documented with near-surface remote sensing, but the physiological mechanisms underlying these changes, and the implications for photosynthetic uptake, have not been fully elucidated. Here, we integrate on-the-ground phenological observations, leaf-level physiological measurements, near surface hyperspectral remote sensing and digital camera imagery, tower-based CO2 flux measurements, and a predictive model to simulate seasonal canopy color dynamics. We show that seasonal changes in canopy color occur independently of new leaf production, but track changes in chlorophyll fluorescence, the photochemical reflectance index, and leaf pigmentation. We demonstrate that at winter-dormant sites, seasonal changes in canopy color can be used to predict the onset of canopy-level photosynthesis in spring, and its cessation in autumn. Finally, we parameterize a simple temperature-based model to predict the seasonal cycle of canopy greenness, and we show that the model successfully simulates interannual variation in the timing of changes in canopy color. These results provide mechanistic insight into the factors driving seasonal changes in evergreen canopy color and provide opportunities to monitor and model seasonal variation in photosynthetic activity using color-based vegetation indices.