Abstract: As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.

Abstract: We determined reference hydro-climatic and land use/cover sensitivities of stormwater runoff and quality in the Miami River Basin of Florida by developing a dynamic rainfall-runoff model with the EPA Storm Water Management Model. Potential storm runoff in the complex coastal-urban basin exhibited high and notably different seasonal sensitivities to rainfall; with stronger responses in the drier early winter and wetter late summer months. Basin runoff and pollutant loads showed moderate sensitivities to the hydrologic and land cover parameters; imperviousness and roughness exhibited more dominant influence than slope. Sensitivity to potential changes in land use patterns was relatively low. The changes in runoff and pollutants under simultaneous hydro-climatic or climate-land use perturbations were notably different than the summations of their individual contributions. The quantified sensitivities can be useful for appropriate management of stormwater quantity and quality in complex urban basins under a changing climate, land use/cover, and hydrology around the world.

Abstract: Plant roots are reported to enhance the aeration of soil by creating secondary macropores which improve the diffusion of oxygen into soil as well as the supply of methane to bacteria. Therefore, methane oxidation can be improved considerably by the soil structuring processes of vegetation, along with the increase of organic biomass in the soil associated with plant roots. This study consisted of using a numerical model that combines flow of water and heat with gas transport and oxidation in soils, to simulate methane emission and oxidation through simulated vegetated and non-vegetated landfill covers under different climatic conditions. Different simulations were performed using different methane loading flux (5–200 g m−2 d−1) as the bottom boundary. The lowest modeled surface emissions were always obtained with vegetated soil covers for all simulated climates. The largest differences in simulated surface emissions between the vegetated and non-vegetated scenarios occur during the growing season. Higher average yearly percent oxidation was obtained in simulations with vegetated soil covers as compared to non-vegetated scenario. The modeled effects of vegetation on methane surface emissions and percent oxidation were attributed to two separate mechanisms: (1) increase in methane oxidation associated with the change of the physical properties of the upper vegetative layer and (2) increase in organic matter associated with vegetated soil layers. Finally, correlations between percent oxidation and methane loading into simulated vegetated and non-vegetated covers were proposed to allow decision makers to compare vegetated versus non-vegetated soil landfill covers. These results were obtained using a modeling study with several simplifying assumptions that do not capture the complexities of vegetated soils under field conditions.

Abstract: Conservation goals are ideally set after a thorough understanding of potential threats; however, predicting future spatial patterns of threats, such as disturbance, remains challenging. Here, we develop a novel extension of network fortification-interdiction models (NFIM) that deals with uncertainty in future spatial patterns of disturbance by optimally selecting sites that will best mitigate a worst-case scenario for a given magnitude of disturbance. This approach uses information on between-patch movement probabilities and patch-specific survival, which can be estimated from mark-recapture data, to optimize life expectancy. Optimization occurs in three interrelated stages: protection, followed by disturbance and then assessment. We applied the modelling approach to two mark-recapture data sets: roseate terns Sterna dougallii in the north-eastern United States and the Everglade snail kite Rostrhamus sociabilis plumbeus in Florida. We contrasted the results to a more conventional approach of protecting sites that maximize connectivity (by minimizing the distances among protected sites) and a bi-objective model that maximizes connectivity and the number of individuals under protection. Protecting sites that best mitigate future worst-case disturbance scenarios consistently resulted in higher predicted life expectancies than protecting patches that minimize dispersal distance. Predicted life expectancy was similar between NFIM and the bi-objective model for the small roseate tern network, yet the NFIM predicted higher life expectancy than any of the scenarios in the bi-objective model in the snail kite network.Synthesis and applications. This application of interdiction models prescribed a combination of patches for protection that results in the least possible decrease in life expectancy. Our analyses of the snail kite and roseate tern networks suggest that managing to protect these prescribed patches by the network fortification -interdiction models (i.e. protecting against the worst-case disturbance scenario) is more beneficial than managing patches that minimize dispersal distance or maximize the number of individuals under protection if the conservation goal is to ensure the long-term persistence of a species. This application of interdiction models prescribed a combination of patches for protection that results in the least possible decrease in life expectancy. Our analyses of the snail kite and roseate tern networks suggest that managing to protect these prescribed patches by the network fortification -interdiction models (i.e. protecting against the worst-case disturbance scenario) is more beneficial than managing patches that minimize dispersal distance or maximize the number of individuals under protection if the conservation goal is to ensure the long-term persistence of a species.

Abstract: In West Africa’s highly weathered soils, plant-available soil-P levels determine sorghum performance and yield to a far greater extent than projected variability in climate. Despite local landrace varieties having excellent adaptation to the environment and a relatively stable yield, sorghum grain yield remains quite low, averaging less than 1 t ha−1. Low P availability in West African soils has significant effects on crop development and growth with potential grain yield losses of more than 50%. Use of mechanistic models, which integrate physiological processes, could assist with understanding the differences in P-uptake among varieties and guide effective P management. Yet only few crop models include a soil-plant P model for simulating crop yield response to P management. A generic soil-plant P module was developed for crop models in the Cropping System Model (CSM) of the Decision Support System for Agrotechnology Transfer (DSSAT) but the module was adapted and tested only on two crops, groundnut and maize. The aim of the study was to adapt the soil-plant P module for sorghum and perform initial testing on highly weathered soils in West Africa. Data used in adapting and testing the soil-plant P model for sorghum consisted of in-season P concentrations and dry weights of stems, leaves and grain from four sorghum varieties covering a range of maturities and photoperiod sensitivities and grown in high-P and P-deficient soils at ICRISAT-Mali. Results showed that the coupled CERES-Sorghum − P module reasonably reproduced the vegetative and grain yield reductions experienced in the field experiments with an average RMSE of 1561 and 909 kg ha−1 under high P conditions and 1168 and 466 kg ha−1 under low P conditions, respectively. The simulations are in most cases within the observation error. We also confirmed that contrasting variety types differ in their P-uptake dynamics relative to above-ground growth change over time, and hence respond differently to available P.

Abstract: The targeting of spawning aggregations is one of the most significant pressures facing coral reef ecosystems. The use of seasonal closures has been advanced for protecting aggregating fisheries for which managers have limited information on the location and timing of their reproductive events; however, few studies have examined the performance of these types of closures. This study assesses the perceptions of 150 fishers regarding the performance of seasonal closures in the Commonwealth of Puerto Rico. Our results show that most fishers perceived that seasonal closures are effective fishery management measures. Across the six seasonal closures examined, fishers reported that these closures protected spawning aggregations and, to a lesser degree, increased fish abundance. These measures, however, did not always improve fishers' livelihoods nor result in their support for the seasonal closures. The loss of resource and market access during periods of high consumer demand and overlapping seasonal closures were the main causes of financial distress.

Abstract: Tea is the second most consumed beverage worldwide, and the production of tea is of economic importance in over 50 countries. As a woody perennial, tea plants are cultivated in production systems for numerous decades and thus experience the multiple decadal effects of climate change including influences on tea yields and quality. Changes in tea yields and quality can have notable impacts on the livelihoods of laborers and farmers as well as on regional economies more broadly. This chapter provides an overview on the effects of global climate change on tea production. We start with a review on global climate change trends that highlight robust multi-decadal warming and changes in extreme weather events that have increased. This review on climate change trends is followed with a synopsis of the major effects of climate change on agriculture broadly as well as on tea plants more specifically. We provide a review on tea ecophysiology and thresholds followed by a synthesis on the key abiotic and biotic stressors associated with climate change that impact tea plants including carbon dioxide concentrations, temperature, rainfall, humidity, solar radiation, wind, soil conditions and microorganisms, pests, and pathogens. This chapter ends with a discussion on socioeconomic implications of climate change in major tea-producing areas globally in order to highlight the need to better understand tea physiology in the context of climate change. Overall, the scientific literature and news reports highlight that climate change is already impacting tea systems and that expected climate changes can increase the likelihood of severe and irreversible impacts for tea production and associated livelihoods. Evidence-based adaptation and mitigation strategies through a community-based approach are called for toward a more sustainable tea sector.

Abstract: Global change stressors such as drought and plant invasion can affect ecosystem structure and function via mediation of resource availability and plant competition outcomes. Yet, it remains uncertain how native plants respond to drought stress that co-occurs with potentially novel resource conditions created by a nonnative invader. Further, there is likely to be temporal variation in competition outcomes between native and nonnative plant species depending on which resources are most limiting at a given time. Interacting stressors coupled with temporal variation make it difficult to predict how global change will impact native plant communities. To address this knowledge gap, we conducted a 5-yr factorial field experiment to quantify how simulated drought, plant invasion (by cogongrass, Imperata cylindrica), and these stressors combined, affected resource availability (soil moisture and light) and competition dynamics between the invader and native longleaf pine (Pinus palustris), a foundation species in southeast U.S. forests. Drought and invasion mediated the survival and performance of pine seedlings in temporally dynamic and unexpected ways. Drought and invasion alone each significantly reduced pine seedling survival. However, when the stressors occurred together, the invader offset drought stress for pine seedlings by maintaining high levels of soil moisture, humidity, and shade compared to uninvaded vegetation. This facilitative effect was pronounced for 2 yr, yet shifted to strong competitive exclusion as the invasion progressed and the limiting resource switched from soil moisture to light. After 3 yr, pine tree survival was low except for pines growing with uninvaded vegetation under ambient precipitation conditions. After 5 yr, pines experiencing a single stressor were taller and had greater height to diameter ratios than pines under no stress or both stressors. This outcome revealed a filtering effect where poorly performing trees were culled under stressful conditions, especially when pines were growing with the invader. Together, these results demonstrate that although drought and invasion suppressed a foundation tree species, the invader temporarily moderated stressful drought conditions, and at least some trees were able to survive despite increasingly strong competition. Such unpredictable effects of interacting global change stressors on native plant species highlight the need for additional long-term studies.