Geology topics

Wen Zhang

Publications and source records attributed to Wen Zhang.

3 recordsLinked to original sources

USGS2026

Tropical and subtropical drylands dominate the interannual variability in global net terrestrial carbon flux irrespective of different global ecosystem classifications or geographic scales

Global terrestrial ecosystems exhibit substantial interannual variability (IAV) in net carbon (C) flux. Determining the biogeographic origin of this variability is essential for the understanding and forecasting of global C cycling and carbon-climate feedbacks. Currently, most studies identify either global drylands or moist tropical forests as the dominant source of IAV. Considering this, we investigated whether the use of three different global ecosystem classifications of drylands and moist tropical forests, as well as two alternative geographical scales, could alter which ecosystem is the dominant contributor to terrestrial net C flux IAV. Using the simulation results of 18 dynamic global vegetation models from the TRENDY v11 model intercomparison, we calculated the absolute and area-weighted contributions of net C flux IAV for: individual 0.5° grid cells, global ecosystem classifications, and ecoregions (intermediate scale between grid cells and global ecosystems). For all three of the global ecosystem classification schemes, we found the drylands IAV contributions of 41%, 32%, and 37% were significantly greater than the associated IAV contributions of 20%, 19%, and 24% from the moist tropical forests ( p < 0.001). However, the moist tropical forests had a higher IAV contribution per unit area across all three classification schemes (∼3% versus ∼1%–2% ( p < 0.001)). At the ecoregion scale, this switch between drylands and moist tropical forests was absent; as seven of the ten highest absolute and nine of the ten highest area-weighted contributing ecoregions were drylands. Specifically, we found tropical and subtropical grasslands, savannas, and shrublands to be particularly substantial contributors to global terrestrial net C flux IAV, with the Cerrado’s absolute IAV contribution of 3.52% exceeding all but one of the other 763 global ecoregions IAV contributions (all p < 0.05). Our findings demonstrate that drylands persist as the dominant contributor to global terrestrial net C flux IAV, irrespective of different global ecosystem classifications or geographic scales.

Environmental Research: Climate↗

USGS2024

A global view of remote sensing of rangelands: Evolution, applications, future pathways

The application of digital remote sensing to rangelands is as long as the history of digital remote sensing itself. Before the launch of the Earth Resources Technology Satellite (ERTS) – later renamed Landsat, scientists were evaluating the use of multispectral aerial imagery to map soils and range vegetation (Yost and Wenderoth 1969). During the late 1960’s, the promise of ERTS, designed to drastically improve our ability to update maps and study earth resources, particularly in developing countries, was eagerly anticipated by a number of government agencies (Carter 1969). With the ERTS launch on July 23, 1972, a flurry of research activity aimed at the application of this new data source to map earth resources began. Practitioners who pioneered the use of satellite based digital remote sensing found the new data source a significant value for rangeland assessments (e.g., Rouse et al., 1973, Rouse et al., 1974, Bauer 1976). This early work established many of the basic techniques still in use today to assess and monitor global rangelands. The following sub-sections discuss the evolution of remote sensing data, methods, and approaches in various decades.

Book chapter↗

USGS2024

Adaptation and Response in Drylands (ARID): Community insights for scoping a NASA terrestrial ecology field campaign in drylands

Dryland ecosystems cover 40% of our planet's land surface, support billions of people, and are responding rapidly to climate and land use change. These expansive systems also dominate core aspects of Earth's climate, storing and exchanging vast amounts of water, carbon, and energy with the atmosphere. Despite their indispensable ecosystem services and high vulnerability to change, drylands are one of the least understood ecosystem types, partly due to challenges studying their heterogeneous landscapes and misconceptions that drylands are unproductive “wastelands.” Consequently, inadequate understanding of dryland processes has resulted in poor model representation and forecasting capacity, hindering decision making for these at-risk ecosystems. NASA satellite resources are increasingly available at the higher resolutions needed to enhance understanding of drylands' heterogeneous spatiotemporal dynamics. NASA's Terrestrial Ecology Program solicited proposals for scoping a multi-year field campaign, of which Adaptation and Response in Drylands (ARID) was one of two scoping studies selected. A primary goal of the scoping study is to gather input from the scientific and data end-user communities on dryland research gaps and data user needs. Here, we provide an overview of the ARID team's community engagement and how it has guided development of our framework. This includes an ARID kickoff meeting with over 300 participants held in October 2023 at the University of Arizona to gather input from data end-users and scientists. We also summarize insights gained from hundreds of follow-up activities, including from a tribal-engagement focused workshop in New Mexico, conference town halls, intensive roundtables, and international engagements.

Earth's Future↗