The 2012–2015 drought has left California with severely reduced snowpack, soil moisture, ground water, and reservoir stocks, but the impact of this estimated millennial-scale event on forest health ...is unknown. We used airborne laser-guided spectroscopy and satellite-based models to assess losses in canopy water content of California’s forests between 2011 and 2015. Approximately 10.6 million ha of forest containing up to 888 million large trees experienced measurable loss in canopy water content during this drought period. Severe canopy water losses of greater than 30% occurred over 1 million ha, affecting up to 58 million large trees. Our measurements exclude forests affected by fire between 2011 and 2015. If drought conditions continue or reoccur, even with temporary reprieves such as El Niño, we predict substantial future forest change.
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Using remotely sensed imagery to identify biophysical components across landscapes is an important avenue of investigation for ecologists studying ecosystem dynamics. With high-resolution remotely ...sensed imagery, algorithmic utilization of image context is crucial for accurate identification of biophysical components at large scales. In recent years, convolutional neural networks (CNNs) have become ubiquitous in image processing, and are rapidly becoming more common in ecology. Because the quantity of high-resolution remotely sensed imagery continues to rise, CNNs are increasingly essential tools for large-scale ecosystem analysis. We discuss here the conceptual advantages of CNNs, demonstrate how they can be used by ecologists through distinct examples of their application, and provide a walkthrough of how to use them for ecological applications.
CNNs enable ecologists to identify biophysical components in high-resolution remotely sensed imagery by leveraging spatial context, and are particularly effective when ecological components have distinct shapes.
CNNs can be used for both object detection, where key components are identified throughout an image, and semantic segmentation, where each pixel is classified individually.
CNN accuracy is similar to human-level classification accuracy, but is consistent and fast, enabling rapid application over very large areas and/or through time.
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Spatial information on forest functional composition is needed to inform management and conservation efforts, yet this information is lacking, particularly in tropical regions. Canopy foliar traits ...underpin the functional biodiversity of forests, and have been shown to be remotely measurable using airborne 350–2510 nm imaging spectrometers. We used newly acquired imaging spectroscopy data constrained with concurrent light detection and ranging (LiDAR) measurements from the Carnegie Airborne Observatory (CAO), and field measurements, to test the performance of the Spectranomics approach for foliar trait retrieval. The method was previously developed in Neotropical forests, and was tested here in the humid tropical forests of Malaysian Borneo. Multiple foliar chemical traits, as well as leaf mass per area (LMA), were estimated with demonstrable precision and accuracy. The results were similar to those observed for Neotropical forests, suggesting a more general use of the Spectranomics approach for mapping canopy traits in tropical forests. Future mapping studies using this approach can advance scientific investigations and applications based on imaging spectroscopy.
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The carbon gain in restored logged forest
There is currently great interest in the capacity of global forest to store carbon and hence contribute to the mitigation of climate change in the coming ...decades. In a study of Southeast Asian tropical forest, Philipson
et al.
show that active restoration of logged forests generates higher rates of carbon accumulation than naturally regenerating forest. To estimate the economic feasibility of restoration treatments, they modeled the carbon price required to offset the cost of restoration, finding that the highest prices seen in recent years would be needed to approach those that could offset restoration costs. These results are important for tropical forest policy, establishing the importance of restoration for the carbon recovery potential of tropical forests.
Science
, this issue p.
838
Restoration of logged tropical forests will be incentivized by carbon prices, consistent with the 2016 Paris climate agreement.
More than half of all tropical forests are degraded by human impacts, leaving them threatened with conversion to agricultural plantations and risking substantial biodiversity and carbon losses. Restoration could accelerate recovery of aboveground carbon density (ACD), but adoption of restoration is constrained by cost and uncertainties over effectiveness. We report a long-term comparison of ACD recovery rates between naturally regenerating and actively restored logged tropical forests. Restoration enhanced decadal ACD recovery by more than 50%, from 2.9 to 4.4 megagrams per hectare per year. This magnitude of response, coupled with modal values of restoration costs globally, would require higher carbon prices to justify investment in restoration. However, carbon prices required to fulfill the 2016 Paris climate agreement $40 to $80 (USD) per tonne carbon dioxide equivalent would provide an economic justification for tropical forest restoration.
Humans pose a major threat to many species through land-use change in virtually every habitat. However, the extent of this threat is largely unknown for invertebrates due to challenges with ...investigating their distributions at large scales. This knowledge gap is particularly troublesome for soil macrofauna because of the critical roles many of these organisms perform as ecosystem engineers. We used a combination of high-resolution airborne Light Detection and Ranging and deep learning models to map the distribution of the ecologically important termite genus Macrotermes across a South African savanna land-use gradient, quantifying the effects of land-use change on patterns of mound densities, heights and spatial patterning. Despite significant anthropogenic alteration to landscapes, termite mounds persisted and shared a number of similarities to mounds in untransformed areas. Mean mound height was not substantially reduced in transformed landscapes, and over-dispersion of mounds at localized scales was conserved. However, mound densities were partially reduced, and height distributions in transformed areas differed to those in protected areas. Our findings suggest that mound-building termites persist even in areas of relatively high human disturbance, but also highlight important differences in termite distributions that could lead to reductions in ecosystem services provided by termites in human-modified landscapes. The persistence of at least half of mounds in human-modified landscapes could serve as starting points for savanna restoration.
Coral reef ecosystems are rapidly changing, and a persistent problem with monitoring changes in reef habitat complexity rests in the spatial resolution and repeatability of measurement techniques. We ...developed a new approach for high spatial resolution (<1 m) mapping of nearshore bathymetry and three-dimensional habitat complexity (rugosity) using airborne high-fidelity imaging spectroscopy. Using this new method, we mapped coral reef habitat throughout two bays to a maximum depth of 25 m and compared the results to the laser-based SHOALS bathymetry standard. We also compared the results derived from imaging spectroscopy to a more conventional 4-band multispectral dataset. The spectroscopic approach yielded consistent results on repeat flights, despite variability in viewing and solar geometries and sea state conditions. We found that the spectroscopy-based results were comparable to those derived from SHOALS, and they were a major improvement over the multispectral approach. Yet, spectroscopy provided much finer spatial information than that which is available with SHOALS, which is valuable for analyzing changes in benthic composition at the scale of individual coral colonies. Monitoring temporal changes in reef 3D complexity at high spatial resolution will provide an improved means to assess the impacts of climate change and coastal processes that affect reef complexity.
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•A framework for combined design and operations optimization of an ISCC is developed.•Physical and practical operational constraints are incorporated in the model.•Most ISCC designs are infeasible, ...but optimization reveals six viable configurations.•One configuration dominates all others with respect to NPV and CO2 emissions.•Tradeoffs between emissions and NPV are optimized for different economic settings.
Direct integration of solar thermal and natural gas systems can be achieved through integrated solar combined cycle (ISCC) power generation. In this work, optimal ISCC system design and hourly operations are determined simultaneously using computational optimization procedures. The full optimization problem is intractable, so a series of problem reductions are employed to explore the ISCC design space while ensuring that individual designs can operate feasibly for a wide range of operating conditions and under realistic constraints. We construct bi-objective Pareto fronts for two conflicting objectives: net present value (NPV) and average CO2 emissions intensity of power produced. A variety of ISCC designs are explored to find a superior configuration with physically feasible annual solar contribution (ASC) of up to 20%, a significant improvement over published designs. We then explore the sensitivity of the results to economic factors such as discount rate, power price, and capital cost. By examining the Pareto frontiers of each case, we quantify the economic cost of reduced CO2 emissions. The resulting ISCC-derived mitigation costs are found to be competitive with other CO2 mitigation technologies.
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Integrated solar combined cycles (ISCCs) need to be able to handle some of the most dynamic operating conditions of any power generation system in order to provide the flexibility of a natural gas ...combustion turbine while simultaneously utilizing variable incident solar irradiation. Yet to date, most work on ISCC design has focused on high-level treatments of system viability and potential impact, without thorough consideration of system operations. In this work, a computationally efficient ISCC model is constructed that includes detailed modeling of the heat recovery steam generator that links the natural gas and solar thermal systems. The model is validated against a model in the literature, and then used to perform computational optimization of the facility operations. Critically, a wide variety of practical system constraints are considered at each time step evaluated in order to ensure system feasibility under realistic conditions. It is shown that under different operating modes the ISCC design examined displays similar emission rates, yet significantly different profit ranges. A marked increase in the operating flexibility of the ISCC is observed when the outlet temperature of the solar heat transfer fluid is allowed to vary over the course of the day.
•An ISCC model that can run under a wide range of operating modes is developed.•Physical and practical operational constraints are incorporated in the model.•Variable heat transfer fluid outlet temperature enables operational flexibility.•Optimization results under different operating strategies are presented.•Profit and CO2 intensity vary depending on the operating mode employed.
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Hypoxia, a condition of low dissolved oxygen concentration, is a widespread problem in marine and freshwater ecosystems. To date, prevention and mitigation of hypoxia has centered on nutrient ...reduction to prevent eutrophication. However, nutrient reduction is often slow and sometimes insufficient to remedy hypoxia. We investigate the utility of a complementary strategy of pumping oxygenated surface water to depth, termed induced downwelling, as a technique to remedy hypoxia in the bottom water of marine and freshwater ecosystems. We introduce simple energy-based models and apply them to depth profiles in hypoxic estuaries, lakes, and freshwater reservoirs. Our models indicate that induced downwelling may be ~3 to 102 times more efficient than bubbling air, and 104 to 106 times more efficient than fountain aerators, at oxygenating hypoxic bottom waters. A proof-of-concept downwelling field experiment highlighted potential advantages and shortcomings. We estimate that regional-scale downwelling for continual hypoxia avoidance would require 0.4 to 4 megawatts per cubic kilometer of water (depending on local conditions), or 50 to 500 US dollars per hour per cubic kilometer of water (assuming 125 USD MWh−1 of electricity). Many potential side effects of downwelling are discussed, each of which would need to be explored and assessed before implementation. Downwelling does not replace nutrient management strategies, but under some circumstances may provide an efficient means to augment these strategies.
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•Downwelling may be up to 102 times more efficient than aeration at adding oxygen to hypoxic water bodies•A field experiment showed some success at localized hypoxia mitigation and areas for improvement•0.4 to 4 MW per cubic kilometer of water, or 50 to 500 US dollars per cubic kilometer per hour, could avert regional hypoxia•Capital costs, operating costs, and potential side effects may decrease the value of downwelling
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Forest carbon stocks in rapidly developing tropical regions are highly heterogeneous, which challenges efforts to develop spatially-explicit conservation actions. In addition to field-based ...biodiversity information, mapping of carbon stocks can greatly accelerate the identification, protection and recovery of forests deemed to be of high conservation value (HCV). We combined airborne Light Detection and Ranging (LiDAR) with satellite imaging and other geospatial data to map forest aboveground carbon density at 30m (0.09ha) resolution throughout the Malaysian state of Sabah on the island of Borneo. We used the mapping results to assess how carbon stocks vary spatially based on forest use, deforestation, regrowth, and current forest protections. We found that unlogged, intact forests contain aboveground carbon densities averaging over 200MgCha−1, with peaks of 500MgCha−1. Critically, more than 40% of the highest carbon stock forests were discovered outside of areas designated for maximum protection. Previously logged forests have suppressed, but still high, carbon densities of 60–140MgCha−1. Our mapped distributions of forest carbon stock suggest that the state of Sabah could double its total aboveground carbon storage if previously logged forests are allowed to recover in the future. Our results guide ongoing efforts to identify HCV forests and to determine new areas for forest protection in Borneo.
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