Forest and Rangeland Soils of the United States Under Changing Conditions: A Comprehensive Science Synthesis

306 Pages·2020·19.536 MB·English

by  Richard V. Pouyat, Deborah S. Page-Dumroese, Toral Patel-Weynand, Linda H. Geiser

Richard V. Pouyat
Deborah S. Page-Dumroese
Toral Patel-Weynand
Linda H. Geiser
Editors
Forest and
Rangeland Soils
of the United States
Under Changing
Conditions
A Comprehensive Science Synthesis
Forest and Rangeland Soils of the United States
Under Changing Conditions
Richard V. Pouyat • Deborah S. Page-Dumroese
Toral Patel-Weynand • Linda H. Geiser
Editors
Forest and Rangeland Soils
of the United States Under
Changing Conditions
A Comprehensive Science Synthesis
Editors
Richard V. Pouyat Deborah S. Page-Dumroese
Northern Research Station Rocky Mountain Research Station
USDA Forest Service USDA Forest Service
Newark, DE, USA Moscow, ID, USA
Toral Patel-Weynand Linda H. Geiser
Washington Office Washington Office
USDA Forest Service USDA Forest Service
Washington, DC, USA Washington, DC, USA
ISBN 978-3-030-45215-5 ISBN 978-3-030-45216-2 (eBook)
https://doi.org/10.1007/978-3-030-45216-2
© The Editor(s) (if applicable) and The Author(s) 2020. This book is an open access publication.
Open Access This book is licensed under the terms of the Creative Commons Attribution 4.0 International License
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The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed
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Cover illustration: The soil around Lake Cleveland on the Sawtooth National Forest is formed in alluvium, colluvium,
and residuum from a variety of sedimentary and metasedimentary rocks, dominantly quartzite. (Photo credit: USDA
Forest Service)
This Springer imprint is published by the registered company Springer Nature Switzerland AG.
The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland
English Equivalents
When you know Multiply by To find
Millimeters (mm) 0.0394 Inches
Centimeters (cm) 0.394 Inches
Meters (m) 3.28 Feet
Kilometers (km) 0.621 Miles
Hectares (ha) 2.47 Acres
Square meters 10.76 Square feet
(m2)
Square kilometers 0.386 Square miles
(km2)
Kilograms (kg) 2.205 Pounds
Megagrams (Mg) 1 Tons
Petagrams (Pg) 1,102,311,311 Tons
Teragrams (Tg) 1,102,311.31 Tons
Degrees Celsius 1.8 °C + 32 Degrees Fahrenheit
(°C)
v
Executive Summary
Overview and Purpose
Soils have life-giving and life-sustaining capabilities that directly or indirectly support all liv-
ing organisms. Humanity’s well-being and health are tied directly to the health of soils.
Worldwide, soil processes contribute to an abundant supply of water, food, and fiber while also
tempering a warming climate. More than 40% of global terrestrial carbon (C) is stored in the
soils of forests, grasslands, and shrublands (Jackson et al. 2017). Forest and rangeland soils of
the United States make a disproportionately large contribution to such ecosystem services
compared to their geographic extent. Although forests and rangelands occupy only about one-
third of the land area in the United States, they supply 80% of the surface freshwater (Sedell
et al. 2000) and sequester 75% of the total C to a depth of 30 m stored in the nation (Liu et al.
2013). Ecosystem alterations associated with land-use change and other pressures may impair
the ability of soils to fulfill their foundational role.
Today, a number of disturbances compound the vulnerability of forest and rangeland soils
across the United States. Of greatest concern are various environmental changes, continued
overgrazing, catastrophic wildfire, and invasive plant and animal species. Effects on soil health
(soil functions mediated by living organisms) are expected to be more severe when two or
more of these disturbances or stressors interact with each other. Changes in the climate are
likely to magnify or accelerate all of these impacts on forest and rangeland soils. However,
great uncertainty surrounds predictions of climate-induced impacts because overall effects will
depend on the magnitude of temperature and precipitation changes and the frequency of
extreme events.
The purpose of this report is to synthesize leading-edge science and management informa-
tion about forest and rangeland soils of the United States, offer ways to better understand
changing conditions and their impacts on soils, and explore directions that positively affect the
future of forest and rangeland soil health. Other assessments provide similar information for
agricultural soils, so agricultural soils are not included in this report. This report outlines soil
processes and identifies the research needed to manage forest and rangeland soils in the United
States. Chapter 1 provides an overview of the state of forest and rangeland soils research in the
nation, including multidecadal studies. Chapters 2, 3, 4 and 5 summarize various human-
caused and natural impacts and their effects on soil C, hydrology, biogeochemistry, and bio-
logical diversity. Chapters 6 and 7 consider the effects of changing conditions on forest soils in
wetland and urban settings, respectively. Impacts include:
• Climatic variability and change. Shifts in precipitation patterns, temperature increases and
variability, and increases in atmospheric carbon dioxide (CO ) concentrations affect plant
2
productivity, flooding, nutrient cycling, and biological populations. Changes in climate,
coupled with an increase in the frequency and severity of extreme weather events, have had,
and will continue to have, direct and cascading indirect effects on soil formation and associ-
ated productivity rates, as well as physical, chemical, and biological processes.
• Severe wildfires. Regardless of origin, wildfires are becoming larger, more frequent, more
intense, and are lasting longer. Severe wildland fires impact the C and nitrogen (N) in soils,
vii
viii Executive Summary
alter the environment for various communities, and can change the trajectory of forest com-
position. Fire may also form hydrophobic (water repellent) layers in soil. These layers,
coupled with loss of vegetation, can lead to accelerated erosion and nutrient leaching.
• Invasive species, pests, and diseases. The introduction of a wide range of invasive species,
from microbes, macrofauna, and macroflora, has important impacts on soil processes which
are exacerbated by climatic changes. Furthermore, the ranges of some invasive insects and
pathogens are expanding. Invasive species contribute to tree stress, and lead to decline and
mortality, decline of biodiversity, and soil changes in organic matter composition and nutri-
ents. Similar to landscapes after wildland fires, problematic species can create soil condi-
tions that enhance flash flooding, soil erosion, and sediment loading.
• Pollution. Air and water pollutants can dramatically affect soil characteristics and species
composition. Acid deposition can cause nutrient leaching, while other pollutants such as
some hydrocarbon compounds and various trace metals can cause other chemical changes
in soils. Despite environmental policies designed to limit the release of pollutants, some
continue to impact forest and range soils. Soil recovery from the impacts of these pollutants
can take many decades.
• Non-urban land uses can potentially have an impact on forest and range soils. Compaction
is considered one of the most critical issues on forest and rangeland soils because it can
severely alter the movement and storage of air, water, and nutrients in the soil. These
changes can slow tree growth and negatively affect microbial populations. In addition, min-
ing has disturbed millions of hectares of forest and grasslands in the United States.
• Urban land use and change. Direct urban-induced effects that can impact soils include the
introduction of built structures, landfills, stormwater facilities, impervious surfaces, and
lawn management. Urban land use and change may also affect soils through indirect pro-
cesses such as the urban heat island effect, emissions of various pollutants, and the spread
of non-native species.
Chapter 8 considers approaches to maintaining or restoring forest and rangeland soil health
in the face of these varied impacts. Chapter 9 discusses mapping, monitoring, and data sharing
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 educa-
tional soils-centered programs are tabulated in appendix B). Chapter 10 highlights opportuni-
ties for deepening our understanding of soils and for sustaining long-term ecosystem health
(appendix C summarizes research needs). Nine summaries (appendix A) offer a more detailed
regional look at forest and rangeland soils in the United States and its affiliates.
Key Messages
Key Benefits of Forest and Rangeland Soils
Carbon and Water
Soil organic carbon (SOC) is a key indicator and dynamic component of soil health. The func-
tioning of a healthy ecosystem depends on the quality and quantity of SOC. For example, a
high proportion of SOC in forest and rangeland soils results in greater water and nutrient reten-
tion, which in turn helps to buffer soil against drought and pollution effects. With climate fac-
tors being approximately equal, most SOC in the United States is in forests, wetlands, and
rangelands that are not intensively managed. Very small changes to SOC can have profound
effects on atmospheric CO levels at a national or global scale. This sensitivity underscores the
2
importance of gaining knowledge about the magnitude and extent of disturbance impacts on
SOC. Some of the factors that directly affect SOC are climate change, overgrazing, overhar-
vesting, invasive species, use of fertilizers, and catastrophic wildfire. Management can proac-
tively help to limit the negative effects of these factors by managing fuel loads, fostering
reforestation, controlling invasive weeds, and preventing further unnecessary site
disturbances.
The scientific community is developing and beginning to adopt a new paradigm for under-
standing and predicting long-term accumulation of SOC. The new paradigm focuses on the
complex relationships between microorganisms and minerals in the soil instead of the charac-
teristics of the SOC itself. This analytical framework may allow for more accurate prediction
of SOC than previous models and quantifies factors that are easier to measure than SOC
molecular properties.
Soil organic carbon is also a key component of soil organic matter, which holds soil parti-
cles together through adhesion and also promotes fungi to form and stabilize soil aggregates.
Soil organic matter helps to reduce erosion and facilitates plant uptake of nutrients and water.
The loss of soil water holding capacity due to loss of SOC can result in catastrophic erosion,
as has been the case with many wildfires in the western United States. Soil organic material
also plays a key role in purifying drinking water and detoxifying pollutants in the soil. In fact,
clean water from United States forested watersheds supplies approximately two-thirds of the
drinking water for towns and cities.
Tree canopies usually prevent 2–30% of water from reaching the ground but also serve a
regulating function in allowing the water to infiltrate into soils at a rate that prevents massive
runoff events. The soil and its inherent characteristics affect how water moves on the surface
and in the subsurface through infiltration and percolation. This in turn affects the quantity and
quality of water from forests and rangelands. It is estimated that approximately 25% of pre-
cipitation is stored in soils and watersheds of forests. Less is known about rangelands due to
wide swinging precipitation patterns (e.g., monsoons).
Many hydrologic models continue working towards fully capturing the dynamics of soil.
Most models rely on climate and topography, but a growing body of research points to soil
layering and its relationship with bedrock as strong influences on how water is redistributed
across the landscape. Recent advances in data science, computing infrastructure, data avail-
ix
x Key Messages
ability, and new monitoring tools, create the opportunity to develop new frameworks for
modeling that lead to an integrated understanding of water dynamics and biogeochemical
cycles. The interaction of soil and water needs better quantification as current models continue
working to improve on prediction of this interaction at watershed scales. However, the paired
catchment studies of the twentieth century continue to provide a solid foundation for studying
more recent hydrologic and soil changes.
Biodiversity and Indicators of Soil Health
Soils and their components result in complex ecosystems with multifaceted webs of flora,
fauna, and other organisms that respond dynamically to external influences. Many of these
organisms, especially bacteria and archaea, fungi, nematodes, and insects, are largely unde-
scribed. Each gram of soil is estimated to contain 1 × 109 microorganisms and about 4000
species. Organisms that live in the soil also respond to myriad properties including textures and
structures. These soil dwellers vary greatly in their size, function, mobility, and response to
disturbances and environmental stress. The functional redundancy in soil is thought to increase
its resistance and resilience (Turbé et al. 2010). Research on soil response to lesser distur-
bances suggests that short-term impacts can persist in soil for up to 5 years before soil condi-
tions and communities return to the previous state. It is still unclear the impact that more
intense disturbances (e.g., wildfire, invasive plants and animals, and climate change) and the
resulting changes have on soil organisms over a longer period of time.
Biogeochemistry
Biogeochemistry, an area of study that emerged in the late twentieth century, explores how
physical, chemical, biological, and geological processes interact and affect the natural environ-
ment. Soils have a prominent role in biogeochemical cycles in forests and rangelands. They are
the major reservoir for plant nutrients as decomposition transforms organic matter into a con-
tinual supply of nutrients. While many ecosystem-level losses occur in forests and rangelands
through multiple pathways, the biogeochemical cycles of forests have been found to be gener-
ally effective in maintaining pools of many essential nutrients such as N, phosphorus, sulfur,
boron, and potassium.
Soil in Wetland and Urban Landscapes
Wetland and hydric soils are distinguished from “upland” or forested areas by their properties,
composition, and biogeochemistry. Wetlands are subject to long periods of anoxia, or lack of
oxygen, while upland soils are almost always oxic. Many wetlands are generally characterized
by anaerobic processes, and the vegetation that grows in wetlands is specifically adapted to this
environment. Wetlands also contribute to a wide variety of highly valued ecosystem services,
such as water supply and quality, C sequestration, wildlife habitat, and recreational opportuni-
ties. For example, wetland soils can store and sequester C at much higher rates than upland
areas.
Wetlands receive inputs from uplands through the soil by hydrologic forces. They discharge
outputs to groundwater and adjacent waterways and uplands. Prior to discharging outputs that
flow directly into streams and other bodies of water, wetlands absorb many pollutants includ-
ing pesticides and fertilizers, heavy metals, hydrocarbons, and road salts. Wetlands can also be
negatively impacted by pollutants that flow into them. Several regulatory control measures
have resulted in declines in pollutants such as mercury and sulfur, but other kinds of distur-
Key Messages xi
bances continue to be a threat to wetlands. Higher temperatures, changes in precipitation, and
an altering of species composition will all significantly affect wetland ecosystem processes.
Wetlands have not always been valued, and nearly 53% have been converted to other uses.
These wetlands were drained and used for other functions, particularly agriculture, until the
mid-1900s. Today, the primary threat to wetlands is urbanization (US EPA 2016).
By 2010 in the United States, almost 250 million people—about 81% of the total popula-
tion—lived in urban areas (US Census 2010). The global population is projected to exceed 11
billion before the end of the twenty-first century with an estimated 70% living in urban areas
(United Nations 2015). The relatively rapid expansion of urban populations in the United
States and worldwide suggests the increasing importance of “urban soils.”
Urban soil conditions vary based on the severity of disturbance and environmental changes
that typically occur in our cities and towns. These impacts vary from soils associated with
remnant forests or grasslands embedded in urban areas to drastically disturbed soils associated
with human-created landfills; surfaces sealed with asphalt, concrete, or other impervious sur-
faces; and altered physical conditions such as those associated with residential yards.
Despite these impacts, urban soils can provide many ecosystem services and support an
array of microorganisms and invertebrates. Some native and nonnative species survive and
thrive in the face of urban environmental changes. Others are affected through various avenues
such as management practices (e.g., irrigation, which supports particular biota) and landscap-
ing practices (e.g., composting and mulching, removal of woody and leaf debris). Similarly,
the use of green infrastructure such as green roofs and rain gardens provides habitats for many
soil organisms.
Management of urban ecosystems requires a holistic approach that takes into account the
many, and sometimes competing, services that the ecosystem can provide. These ecosystem
services include C sequestration, improved water quality, food production, recreation, stable
substrates for structures and underground utilities, and stormwater retention. The importance
of services provided by urban ecosystems is magnified because of their close proximity to
people.
In the United States, the classification and survey of soils in urban landscapes have advanced
tremendously in the last 20 years. For example, modern soil surveys have been conducted in
New York, NY; Chicago, IL; Los Angeles, CA; and Detroit, MI. These surveys have provided
detailed information on physical, chemical, and mineralogical properties of human-altered and
human-transported soils. The greater number of soil properties and the level of detail enable
more reliable interpretations for stormwater management, revegetation and restoration efforts,
urban agriculture, and resource inventories.
Degradation of Soil Health
Soils have finite qualities and take thousands of years to develop but can lose their ability to
contribute ecosystem services in a fraction of that time due to human-induced and natural
disturbances. Identifying key disturbances and understanding their effects are critical to devel-
oping sound management responses to sustain and restore soils. Key disturbances that impact
soils include climate change, severe wildland fire, invasive species and pests, and pollution
related to nonurban land uses and urban land uses.
Management
Management actions may cause soils to lose, retain, or improve their capacity to sustain life,
maintain balance in hydrologic and nutrient cycling, and provide other ecosystem functions
(Heneghan et al. 2008). Nutrient cycling is also susceptible to human-caused disturbances.
Active management manipulates aboveground and belowground nutrient cycles to achieve