Non-Destructive Biomass Estimation in Mediterranean Alpha Steppes: Improving Traditional Methods for Measuring Dry and Green Fractions by Combining Proximal Remote Sensing Tools

The Mediterranean region is experiencing a stronger warming effect than other regions, which has generated a cascade of negative impacts on productivity, biodiversity, and stability of the ecosystem. To monitor ecosystem status and dynamics, aboveground biomass (AGB) is a good indicator, being a surrogate of many ecosystem functions and services and one of the main terrestrial carbon pools. Thus, accurate methodologies for AGB estimation are needed. This has been traditionally done by performing direct field measurements. However, field-based methods, such as biomass harvesting, are destructive, expensive, and time consuming and only provide punctual information, not being appropriate for large scale applications. Here, we propose a new non-destructive methodology for monitoring the spatiotemporal dynamics of AGB and green biomass (GB) of M. tenacissima L. plants by combining structural information obtained from terrestrial laser scanner (TLS) point clouds and spectral information. Our results demonstrate that the three volume measurement methods derived from the TLS point clouds tested (3D convex hull, voxel, and raster surface models) improved the results obtained by traditional field-based measurements. (Adjust-R2 = 0.86–0.84 and RMSE = 927.3–960.2 g for AGB in OLS regressions and Adjust-R2 = 0.93 and RMSE = 376.6–385.1 g for AGB in gradient boosting regression). Among the approaches, the voxel model at 5 cm of spatial resolution provided the best results; however, differences with the 3D convex hull and raster surface-based models were very small. We also found that by combining TLS AGB estimations with spectral information, green and dry biomass fraction can be accurately measured (Adjust-R2 = 0.65–0.56 and RMSE = 149.96–166.87 g in OLS regressions and Adjust-R2 = 0.96–0.97 and RMSE = 46.1–49.8 g in gradient boosting regression), which is critical in heterogeneous Mediterranean ecosystems in which AGB largely varies in response to climatic fluctuations. Thus, our results represent important progress for the measurement of M. tenacissima L. biomass and dynamics, providing a promising tool for calibration and validation of further studies aimed at developing new methodologies for AGB estimation at ecosystem regional scales

Holocene Chronostratigraphy of Dune Fields in Southern Utah: Geomorphic Record of Past Aridity in the Central Colorado Plateau

The southwestern United States is characterized by dry climate, and droughts are common. The region is currently in an extreme drought that began in 2000 CE and has lasted longer than any previous drought in at least 500 years. Models predict greater future climate extremes under human-caused climate change. Understanding of the natural range of climate variability is important to put these changes in context. Sedimentary archives of past sand dune activity can help extend the available instrumental observations (last century) and tree-ring records (last millennium). Sand dunes are landforms that are sensitive to aridity and decreased vegetation cover. They can reactivate and migrate downwind during periods of aridity leaving behind a sediment record of past dune field activity. Research goals were to reconstruct past dune activity the Kanab and San Rafael dune fields in southern Utah. This was accomplished by mapping the dune forms and sampling for age control and sediment character. Modern wind data were compared to the orientation of the older dune forms to determine if wind directions have changed. The Kanab dune field, in southwestern Utah, was found to have been active five times over the last 10,000 yr. The data indicate 1000 yr-long periods of activity separated by similar duration periods of stability. The San Rafael dune field, in east central Utah contained records of seven episodes of eolian activity from late Pleistocene (~17,000 years ago) to the present. Dunes are active today in this dune field with thinner dune deposits and sparser vegetation suggesting greater wind erosion than in the Kanab dune field. Comparing records between the two dune fields indicates three time periods when they were both actively migrating, suggesting regional aridity ~9,500-7,500, 2000-1500 and 1000-500 years ago. Expanding this comparison to existing sand dune records across the Colorado Plateau suggests at least these three periods, and as many as five periods of regional aridity, may have occurred in the last 10,000 years. Wind and geochemical data indicate similar wind and source sediments have been active over the history of the dune fields

Forest and Rangeland Soils of the United States Under Changing Conditions

This open access book synthesizes leading-edge science and management information about forest and rangeland soils of the United States. It offers ways to better understand changing conditions and their impacts on soils, and explores directions that positively affect the future of forest and rangeland soil health. This book outlines soil processes and identifies the research needed to manage forest and rangeland soils in the United States. Chapters give an overview of the state of forest and rangeland soils research in the Nation, including multi-decadal programs (chapter 1), then summarizes various human-caused and natural impacts and their effects on soil carbon, hydrology, biogeochemistry, and biological diversity (chapters 2–5). Other chapters look at the effects of changing conditions on forest soils in wetland and urban settings (chapters 6–7). Impacts include: climate change, severe wildfires, invasive species, pests and diseases, pollution, and land use change. Chapter 8 considers approaches to maintaining or regaining forest and rangeland soil health in the face of these varied impacts. Mapping, monitoring, and data sharing are discussed in chapter 9 as ways to leverage scientific and human resources to address soil health at scales from the landscape to the individual parcel (monitoring networks, data sharing Web sites, and educational soils-centered programs are tabulated in appendix B). Chapter 10 highlights opportunities for deepening our understanding of soils and for sustaining long-term ecosystem health and appendix C summarizes research needs. Nine regional summaries (appendix A) offer a more detailed look at forest and rangeland soils in the United States and its Affiliates