Geology topics

James D. McIver

Publications and source records attributed to James D. McIver.

5 recordsLinked to original sources

USGS2022

Piñon and juniper tree removal increases available soil water, driving understory response in a sage-steppe ecosystem

Over the past century, piñon and juniper trees have encroached into sagebrush steppe lands of the interior United States, and managers have for many years removed trees to stimulate the favored understory. While consistent understory response to tree removal in these semiarid lands suggests that trees outcompete other plants for water, no studies have linked increased soil water to understory response after tree removal. We tested the hypothesis that tree removal at six sagebrush steppe sites increased soil water, leading to increased understory plant cover. Using a structural equation model, we found that before tree removal, trees suppressed shrubs (standardized coefficient [SC] = −0.87), perennial deep-rooted (SC = −0.50) and shallow-rooted bunchgrasses (SC = −0.36), but had no influence on cheatgrass. The model explained between 2% (cheatgrass) and 40% (shrubs) of pretreatment cover variation. Measurement of the same plots six years post-treatment showed that most cover variation was due directly to plant growth, with standardized coefficients between 0.51 (perennial shallow-rooted grasses) and 0.72 (cheatgrass). Competition between cheatgrass and perennial deep-rooted grasses was evident, with perennials having twice the influence on cheatgrass than vice-versa (SC = −0.24 vs. −0.11). Spring soil water (wet-degree days) increased significantly after tree removal, measured as cumulative over 6 years (SC = 0.30), and in the early Spring of year six (SC = 0.16). Treatment-induced increase of cumulative Spring wet degree-days explained variation in shrub cover at year 6 (SC = 0.12) and the increase of early Spring wet degree-days at year 6 led to increases in perennial deep-rooted grasses (SC = 0.24) and cheatgrass (SC = 0.23). We detected no influence of Spring wet degree-days on perennial shallow-rooted grasses. The post-treatment model explained between 34% (shallow-rooted perennial grasses) and 69% (deep-rooted perennial grasses) of variation in understory cover. Most variation was explained by re-measurement of the same populations, followed by treatment effects mediated through increased soil water availability, soil factors, and direct effects of the treatment itself. In conclusion, our model is consistent with the a priori hypothesis that additional wet degree-days due to tree removal is a significant mechanism behind observed increases in understory cover.

California, Idaho, Nevada, Oregon, Utah↗

USGS2017

Restoration handbook for sagebrush steppe ecosystems with emphasis on greater sage-grouse habitat—Part 3. Site level restoration decisions

Sagebrush steppe ecosystems in the United States currently (2016) occur on only about one-half of their historical land area because of changes in land use, urban growth, and degradation of land, including invasions of non-native plants. The existence of many animal species depends on the existence of sagebrush steppe habitat. The greater sage-grouse ( Centrocercus urophasianus ) depends on large landscapes of intact habitat of sagebrush and perennial grasses for their existence. In addition, other sagebrush-obligate animals have similar requirements and restoration of landscapes for greater sage-grouse also will benefit these animals. Once sagebrush lands are degraded, they may require restoration actions to make those lands viable habitat for supporting sagebrush-obligate animals, livestock, and wild horses, and to provide ecosystem services for humans now and for future generations. When a decision is made on where restoration treatments should be applied, there are a number of site-specific decisions managers face before selecting the appropriate type of restoration. This site-level decision tool for restoration of sagebrush steppe ecosystems is organized in nine steps. Step 1 describes the process of defining site-level restoration objectives. Step 2 describes the ecological site characteristics of the restoration site. This covers soil chemistry and texture, soil moisture and temperature regimes, and the vegetation communities the site is capable of supporting. Step 3 compares the current vegetation to the plant communities associated with the site State and Transition models. Step 4 takes the manager through the process of current land uses and past disturbances that may influence restoration success. Step 5 is a brief discussion of how weather before and after treatments may impact restoration success. Step 6 addresses restoration treatment types and their potential positive and negative impacts on the ecosystem and on habitats, especially for greater sage-grouse. We discuss when passive restoration options may be sufficient and when active restoration may be necessary to achieve restoration objectives. Step 7 addresses decisions regarding post-restoration livestock grazing management. Step 8 addresses monitoring of the restoration; we discuss important aspects associated with implementation monitoring as well as effectiveness monitoring. Step 9 takes the information learned from monitoring to determine how restoration actions in the future might be adapted to improve restoration success.

Circular↗

USGS2015

Restoration handbook for sagebrush steppe ecosystems with emphasis on greater sage-grouse habitat—Part 2. Landscape level restoration decisions

Sagebrush steppe ecosystems in the United States currently (2015) occur on only about one-half of their historical land area because of changes in land use, urban growth, and degradation of land, including invasions of non-native plants. The existence of many animal species depends on the existence of sagebrush steppe habitat. The greater sage-grouse ( Centrocercus urophasianus ) is a landscape-dependent bird that requires intact habitat and combinations of sagebrush and perennial grasses to exist. In addition, other sagebrush-obligate animals also have similar requirements and restoration of landscapes for greater sage-grouse also will benefit these animals. Once sagebrush lands are degraded, they may require restoration actions to make those lands viable habitat for supporting sagebrush-obligate animals. Land managers do not have resources to restore all locations because of the extent of the restoration need and because some land uses are not likely to change, therefore, restoration decisions made at the landscape to regional scale may improve the effectiveness of restoration to achieve landscape and local restoration objectives. We present a landscape restoration decision tool intended to assist decision makers in determining landscape objectives, to identify and prioritize landscape areas where sites for priority restoration projects might be located, and to aid in ultimately selecting restoration sites guided by criteria used to define the landscape objectives. The landscape restoration decision tool is structured in five sections that should be addressed sequentially. Each section has a primary question or statement followed by related questions and statements to assist the user in addressing the primary question or statement. This handbook will guide decision makers through the important process steps of identifying appropriate questions, gathering appropriate data, developing landscape objectives, and prioritizing landscape patches where potential sites for restoration projects may be located. Once potential sites are selected, land managers can move to the site-specific decision tool to guide restoration decisions at the site level.

California, Idaho, Montana, Nevada, Oregon, Utah, ↗

USGS2015

Restoration handbook for sagebrush steppe ecosystems with emphasis on greater sage-grouse habitat—Part 1. Concepts for understanding and applying restoration

Sagebrush steppe ecosystems in the United States currently occur on only about one-half of their historical land area because of changes in land use, urban growth, and degradation of land, including invasions of non-native plants. The existence of many animal species depends on the existence of sagebrush steppe habitat. The greater sage-grouse ( Centrocercus urophasianus ) is a landscape-dependent bird that requires intact habitat and combinations of sagebrush and perennial grasses to exist. In addition, other sagebrush-obligate animals also have similar requirements and restoration of landscapes for greater sage-grouse also will benefit these animals. Once sagebrush lands are degraded, they may require restoration actions to make those lands viable habitat for supporting sagebrushobligate animals. This restoration handbook is the first in a three-part series on restoration of sagebrush ecosystems. In Part 1, we discuss concepts surrounding landscape and restoration ecology of sagebrush ecosystems and greater sage-grouse that habitat managers and restoration practitioners need to know to make informed decisions regarding where and how to restore specific areas. We will describe the plant dynamics of sagebrush steppe ecosystems and their responses to major disturbances, fire, and defoliation. We will introduce the concepts of ecosystem resilience to disturbances and resistance to invasions of annual grasses within sagebrush steppe. An introduction to soils and ecological site information will provide insights into the specific plants that can be restored in a location. Soil temperature and moisture regimes are described as a tool for determining resilience and resistance and the potential for various restoration actions. Greater sage-grouse are considered landscape birds that require large areas of intact sagebrush steppe; therefore, we describe concepts of landscape ecology that aid our decisions regarding habitat restoration. We provide a brief overview of restoration techniques for sage-grouse habitat restoration. We conclude with a description of the critical nature of monitoring for adaptive management of sagebrush steppe restoration at landscape- and project-specific levels.

Arizona, California, Colorado, Idaho, Montana, Neb↗

USGS2012

Fuel treatment impacts on estimated wildfire carbon loss from forests in Montana, Oregon, California, and Arizona

Using forests to sequester carbon in response to anthropogenically induced climate change is being considered across the globe. A recent U.S. executive order mandated that all federal agencies account for sequestration and emissions of greenhouse gases, highlighting the importance of understanding how forest carbon stocks are influenced by wildfire. This paper reports the effects of the most common forest fuel reduction treatments on carbon pools composed of live and dead biomass as well as potential wildfire emissions from six different sites in four western U.S. states. Additionally, we predict the median forest product life spans and uses of materials removed during mechanical treatments. Carbon loss from modeled wildfire-induced tree mortality was lowest in the mechanical plus prescribed fire treatments, followed by the prescribed fire-only treatments. Wildfire emissions varied from 10–80 Mg/ha and were lowest in the prescribed fire and mechanical followed by prescribed fire treatments at most sites. Mean biomass removals per site ranged from approximately 30–60 dry Mg/ha; the median lives of products in first use varied considerably (from <10 to >50 years). Our research suggests most of the benefits of increased fire resistance can be achieved with relatively small reductions in current carbon stocks. Retaining or growing larger trees also reduced the vulnerability of carbon loss from wildfire. In addition, modeled vulnerabilities to carbon losses and median forest product life spans varied considerably across our study sites, which could be used to help prioritize treatment implementation.

California, Oregon, Montana, Arizona↗