Conservation reports and data

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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.

Available here

San Pedro River Wet/Dry Map Animation (October 2020)

Every June groups of volunteers walk the entire 170 mile length of the San Pedro River and record where it is wet and where it is dry during the hottest, driest time of the year. Twenty years’ worth of data on summertime surface flows in the San Pedro River within the San Pedro Riparian National Conservation Area (SPRNCA) are now available as an animation. Watch to see the changes in surface flow over time. These observations were recorded by citizen scientists through the Wet/Dry Mapping project- a collaboration between TNC and the Bureau of Land Management on this particular reach of the San Pedro River.  Follow this link to see what they found from 1999 to 2019 on the approximately 50 miles of the San Pedro River that flows through the SPRNCA.

Notes about the data and animation:

  1. Use the play, pause, and advance buttons at the bottom to view the animation.

  2. Use the plus or minus keys to zoom in on portions of the river.

  3. Survey dates varied from year to year, but have been standardized to June 29 for purposes of this animation.

  4. Although the animation time scale at the bottom indicates a one year date range, the data shown is actually the annual standardized June 29th survey date. To make the scale date appear as that one point in time, click on and drag one of the time markers on top of the other.

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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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Scope and Intensity of Land-Use Modification Across Arizona (October 2017)

GIS dataset that depicts intensity and spatial distribution of prior human modification on non-tribal Arizona lands. Based on inspection of 2010 aerial imagery and reference datasets, prior human modification estimated within one square mile hexagons in following categories: 0%, 1-5%, 5-25%, 25-50, and >50%. Dataset can be used to inform conservation and infrastructure planning.

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A Place for Human Modification and Intactness Data in Regional Mitigation (October 2017)

This report describes a human modification dataset for non-tribal lands in Arizona that can be used for conservation and infrastructure planning processes. The report describes methodology used to develop dataset, summarizes intensity and spatial distribution of prior human modification across the state, presents a case study for use in regional mitigation planning of an infrastructure project, and compares dataset to other models of landscape intactness. Dataset is available for download on this website.

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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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San Pedro River Wet-Dry Maps (October 2020)

The San Pedro River wet/dry mapping dataset is a community effort to track the river’s health by monitoring the persistence of surface water during the driest time of each year. It is created by recording the end points of every wet section of the San Pedro River during June each year. Maps depict the wet portion of the San Pedro River.

Enduring a decade of drought: Patterns and drivers of vegetation change in a semi-arid grassland (September 2016)

This study used a long-term dataset to examine the impacts of drought on grassland conditions at Las Cienegas National Conservation Area in southeastern Arizona from 2004-2014. Changes included declines in perennial grass basal cover with patchy mortality, leaf litter increases, shrub declines and increases in non-native grass, Lehmann’s Lovegrass (Eragrostis lehmanniana). Grassland cover declined by 25-50% in years with low precipitation from January-June. Given that global climate models predict steep declines in spring rainfall, grassland managers could improve grassland resilience by monitoring rainfall and associated mortality across multiple months, including non-traditional seasons, and by establishing contingency plans for various types of drought. The dataset was developed through a partnership between The Nature Conservancy and Bureau of Land Management with monitoring assistance from stakeholders.

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