Forest reports & data

Winter Inputs Buffer Streamflow Sensitivity to Snowpack Losses in the Salt River Watershed in the Lo (December 2020)

Recent streamflow declines in the Upper Colorado River Basin raise concerns about the sensitivity of water supply for 40 million people to rising temperatures. Yet, other studies in western US river basins present a paradox: streamflow has not consistently declined with warming and snow loss. A potential explanation for this lack of consistency is warming-induced production of winter runoff when potential evaporative losses are low. This mechanism is more likely in basins at lower elevations or latitudes with relatively warm winter temperatures and intermittent snowpacks. We test whether this accounts for streamflow patterns in the Salt River and its tributaries, which is a sub-basin in the Lower Colorado River Basin (LCRB). Despite significant warming from 1968–2011 and snow loss in many of the Salt basins, annual and seasonal streamflow did not decline. Between 25% and 50% of annual streamflow is generated in winter when runoff ratios are generally higher and potential evapotranspiration losses are one-third of potential losses in spring. Short term streamflow responses to winter inputs were larger and more efficient than spring and summer responses and their frequencies and magnitudes increased in 1968–2011 compared to 1929–1967. In total, 75% of the largest winter events were associated with atmospheric rivers, which can produce large cool-season streamflow peaks. We conclude that temperature-induced snow loss in this LCRB sub-basin was moderated by enhanced winter hydrological inputs and streamflow production.

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Landscape restoration minimizes tree growth vulnerability to 21st century drought in a dry forest (October 2020)

With hotter temperatures and less precipitation projected in the future, reducing tree density is a possible strategy to minimize the impacts of drought on forest growth. Many forest restoration programs are focused reducing tree density to minimize wildfire risks, but it is unknown how these efforts will impact drought vulnerability. In this study, we looked at how the Four Forest Restoration Initiative (4FRI) would alter landscape-scale patterns of forest growth and drought vulnerability throughout the 21st century. We found that hotter and drier conditions in the future could reduce tree growth, but the severity of drought and the magnitude of future growth declines was lessened by the thinning treatments. Compared to historical conditions, proportional tree growth by 2050 declines by ~40% if thinning continues at the status quo pace.  By comparison, proportional growth declines by only 20% if the 4FRI thinning treatments are fully implemented, and < 10% if stands are thinned even more intensively. These results indicate that forest restoration projects designed for other objectives can also have substantial benefits for minimizing future drought vulnerability in dry forests and provide additional incentive to accelerate the pace of restoration.

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Large-Scale Forest Restoration Stabilizes Carbon Under Climate Change in the Southwest U.S. (September 2019)

A century of fire suppression along with a warmer climate have increased the size, frequency and severity of wildfires, which has increased risk to communities, water supplies, wildlife, forest cover and carbon stocks. The Four Forest Restoration Initiative (4FRI), a collaboration between the U.S. Forest Service and stakeholders to accelerate forest thinning, was formed in response to the large fires. We examined the fate of forest carbon with different rates of forest thinning across 1 million acres of 4FRI in northern AZ by simulating carbon sequestration and emissions between 2010 and 2100 under four climate change scenarios and different rates of mechanical thinning followed by prescribed fire. We examined how forest thinning and prescribed fire will affect wildfire severity and forest growth under a changing climate. We found that accelerated forest thinning followed by prescribed fire resulted in a 9-16% increase in carbon, stabilizing forest carbon stocks for decades and buying considerable time to better understand the effects of climate change on forests. In the accelerated forest thinning scenarios, 70% of the gains in carbon were due to a decrease in wildfire severity and 30% were due to an increase in forest productivity. Fire-adapted forests comprise more than 40% of the total forest cover in the western U.S., the majority of those forests are at risk of catastrophic fire. This study suggests that accelerated forest thinning can sustain forest cover and mitigate greenhouse gas emissions by reducing catastrophic wildfire.

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Forest Management and Warming Effects on a Century of Salt River Streamflow (November 2017)

Recent studies suggest that climate change has altered the flow and provision of water from western US rivers to downstream cities and natural communities, but fewer studies have examined hydrological influences related to a century of fire suppression. This study evaluated the effects of changing forest and temperature conditions on 20th century flow patterns in the Salt River in central Arizona. Seasonal and annual flows declined by 8-29% in the first half of the century which coincided with a 10-fold increase in ponderosa pine forest densities. Based on a scientific review, there is strong evidence that changes in forest structure contributed to these flow declines. In the 2nd half of the century, warmer temperatures led to earlier timing of peak spring flows of almost 2 weeks but had negligible direct effects on flow magnitudes. These results suggest that forest change had effects on flow well before anthropogenic warming and that large-scale restoration projects hold some promise of recovering seasonal flows.

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Technology and Trees: Increasing trust and efficiencies in forest restoration (April 2016)

With over two million acres of Arizona’s forests vulnerable to catastrophic wildfire, we must change how we manage forests to reduce this risk. Accelerating the pace and scale of forest restoration treatments to meet this challenge requires new ways of doing business. Today’s forest management requires a collaborative approach between the Forest Service, wood product industries, and organizations like The Nature Conservancy to modernize rules and regulations; test, develop, and use new technology to work smarter and faster at less cost; and forge innovative partnerships that provide the support needed for this transformation. The Nature Conservancy is developing new technology that help harvesters, the Forest Service, and stakeholders meet today’s forest restoration goals. Using satellite and 3D imagery, geographic information systems, and electronic tablets, our efforts show promise in creating efficient, less-costly methods to digitally “mark” trees, prepare sites for treatments, harvest trees, and monitor effects of treatments.

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Accelerated Forest Thinning Improves Runoff in Salt-Verde watersheds (October 2014)

This article examines the influence of climate variability and accelerated forest thinning on runoff in ponderosa pine forests in the Salt and Verde River watersheds in central Arizona. The effects of thinning treatments were examined over 15-, 25-, and 35-year periods. Over the course of treatments, cumulative runoff on thinned forests was about 20% greater than un-thinned forests, regardless of whether forest thinning occurred in a dry or wet period. Runoff gains were temporary and modest when compared to total annual flows in Salt-Verde (≤3%). Nonetheless, additional runoff from thinning could help offset projected declines in snowpack due to warming, augment river flows on a seasonal basis, improve conditions for water dependent natural resources, as well as provide incidental benefits to downstream users.

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The First Five Years of the White Mountain Stewardship Project (August 2010)

The White Mountains Stewardship Project on the Apache-Sitgreaves National Forest in Arizona was designed to reduce the impacts of wildfires on communities, improve wildlife habitat, and help stimulate employment in the wood products industry. A multi-party monitoring board was convened to design a program for evaluating project effectiveness. This report summarizes results from five years of data on economic, social, administrative, and ecological indicators and provides recommendations for improving program effectiveness moving forward.

Historical Range of Variation for Potential Natural Vegetation Types of the Southwest (June 2007)

Descriptions of the Historical Range of Variation or Variability (HRV) characterize the change over time and space in the condition of the Southwest’s major vegetation types and the ecological processes that shape those types. HRVs enable land managers and the public to understand the drivers of change in our region’s major vegetation types.

Southwest Forest Assessment Project Peer Review Process (October 2006)

All of the reports and data sets developed for the Southwest Forest Assessment Project were subjected to external peer review to ensure conformance with the Forest Service’s Science Consistency Review Standards. This report includes a complete list of the resource professionals who reviewed the various components of this project.

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Ecosystem Diversity Reports for National Forests in Arizona and New Mexico (August 2006)

Ecosystem diversity reports were developed to support the Forest Service’s need for information on the species and ecosystems that occur on National Forests in Region 3. The reports contain data summaries and analyses of a variety of regional datasets. Each report is packaged with an introduction and chapters describing methods and data sources.

What is the Southwest Forest Assessment Project? (June 2006)

Brief overview describing a collaborative effort between The Nature Conservancy and U.S. Forest Service Region 3 in Arizona and New Mexico, a project designed to develop scientific information for forest plan revisions and to help in the restoration of ecosystems.

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Historical Fire Return Intervals for Arizona and New Mexico (May 2006)

Synthesizes the scientific literature on historical fire return intervals associated with the major vegetation systems across Arizona and New Mexico. Included is a crosswalk table for use with the Southwest Regional Gap Analysis Project’s land cover dataset and three ArcGIS layer (.lyr) files that enable the user to mimic the report graphics.

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U.S. Forest Service Region 3 Species Database (May 2006)

Provides an up-to-date, searchable excel database on the species that occur on Region 3 Forests in Arizona and New Mexico.

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