The infectious disease trap of animal agriculture.

Infectious diseases originating from animals (zoonotic diseases) have emerged following deforestation from agriculture. Agriculture can reduce its land use through intensification, i.e., improving resource use efficiency. However, intensive management often confines animals and their wastes, which also fosters disease emergence. Therefore, rising demand for animal-sourced foods creates a "trap" of zoonotic disease risks: extensive land use on one hand or intensive animal management on the other. Not all intensification poses disease risks; some methods avoid confinement and improve animal health. However, these "win-win" improvements alone cannot satisfy rising meat demand, particularly for chicken and pork. Intensive poultry and pig production entails greater antibiotic use, confinement, and animal populations than beef production. Shifting from beef to chicken consumption mitigates climate emissions, but this common strategy neglects zoonotic disease risks. Preventing zoonotic diseases requires international coordination to reduce the high demand for animal-sourced foods, improve forest conservation governance, and selectively intensify the lowest-producing ruminant animal systems without confinement.

The 'sustainability gap' of US broiler chicken production: trade-offs between welfare, land use and consumption.

In 2018, over nine billion chickens were slaughtered in the United States. As the demand for chickens increases, so too have concerns regarding the welfare of the chickens in these systems and the damage such practices cause to the surrounding ecosystems. To address welfare concerns, there is large-scale interest in raising chickens on pasture and switching to slower-growing, higher-welfare breeds as soon as 2024. We created a box model of US chicken demographics to characterize aggregate broiler chicken welfare and land-use consequences at the country scale for US shifts to slower-growing chickens, housing with outdoor access, and pasture management. The US produces roughly 20 million metric tons of chicken meat annually. Maintaining this level of consumption entirely with a slower-growing breed would require a 44.6%-86.8% larger population of chickens and a 19.2%-27.2% higher annual slaughter rate, relative to the current demographics of primarily 'Ross 308' chickens that are slaughtered at a rate of 9.25 billion per year. Generating this quantity of slower-growing breeds in conventional concentrated animal feeding operations (CAFO) would require 90 582-98 687 km2, an increase of 19.9-30.6% over the 75 577 km2 of land used for current production of Ross 308. Housing slower-growing breeds on pasture, the more individually welfare-friendly option, would require 108 642-121 019 km2, a 43.8-60.1% increase over current land use. Allowing slower-growing breeds occasional outdoor access is an intermediate approach that would require 90 691-98 811 km2, an increase of 20-30.7% of the current land use, a very minor increase of land relative to managing slower-growing breeds in CAFOs. In sum, without a drastic reduction in consumption, switching to alternative breeds will lead to a substantial increase in the number of individuals killed each year, an untenable increase in land use, and a possible decrease in aggregate chicken welfare at the country-level scale. Pasture-based management requires substantial additional land use. These results demonstrate constraints and trade-offs in animal welfare, environmental conservation and food animal consumption, while highlighting opportunities for policies to mitigate impacts in an integrated manner using a One Health approach.

Ecosystem heterogeneity and diversity mitigate Amazon forest resilience to frequent extreme droughts.

The impact of increases in drought frequency on the Amazon forest's composition, structure and functioning remain uncertain. We used a process- and individual-based ecosystem model (ED2) to quantify the forest's vulnerability to increased drought recurrence. We generated meteorologically realistic, drier-than-observed rainfall scenarios for two Amazon forest sites, Paracou (wetter) and Tapajós (drier), to evaluate the impacts of more frequent droughts on forest biomass, structure and composition. The wet site was insensitive to the tested scenarios, whereas at the dry site biomass declined when average rainfall reduction exceeded 15%, due to high mortality of large-sized evergreen trees. Biomass losses persisted when year-long drought recurrence was shorter than 2-7 yr, depending upon soil texture and leaf phenology. From the site-level scenario results, we developed regionally applicable metrics to quantify the Amazon forest's climatological proximity to rainfall regimes likely to cause biomass loss > 20% in 50 yr according to ED2 predictions. Nearly 25% (1.8 million km2 ) of the Amazon forests could experience frequent droughts and biomass loss if mean annual rainfall or interannual variability changed by 2σ. At least 10% of the high-emission climate projections (CMIP5/RCP8.5 models) predict critically dry regimes over 25% of the Amazon forest area by 2100.