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Tuesday 5 September 2017

Deep Roots: Foundations of Forestry in American Landscape Architecture

Published in Scenario 04: Building the Urban Forest
Spring 2014


Author
by Roxi Thoren

“The more you think about the services of the forest, the more you understand them, the more essential they appear. It is true indeed that the forest, rightly handled – given the chance – is, next to the earth itself, the most useful servant of man.”
– Gifford Pinchot [1]

For a brief period at the turn of the last century, landscape architecture and forestry occupied the same physical and conceptual space — the design of landscapes and the management of natural resources were inextricable. The work of Frederick Law Olmsted and Gifford Pinchot at Biltmore Estate in North Carolina in the 1890s represents the beginning of American forestry and a model of professional collaboration, as the founding figures of two professions used the design and management of the estate to test the viability of scientific land and resource management.
Olmsted, the preeminent American landscape architect at the close of the 19th century, proposed scientific forestry for much of the prestigious commission, and he hired Gifford Pinchot to implement his forest management plan on Biltmore’s eroded, wasted hillsides. Pinchot would go on to become the first chief of the United States Forest Service and governor of Pennsylvania, but at the time, he was a young man freshly trained in Europe in the scientific practice of forest management. Together, they created an expansive laboratory for land reclamation and land management. Their collaboration represented shared ideals and thinking about land and landscape, and their Biltmore work continues to inform both the practice and the discourse of forestry today.
Over the intervening century, the fields of landscape architecture and forestry have moved apart, following internal imperatives. Yet today, as both professions are re-examining forests, especially in urban contexts, there is an opportunity to recover the early collaboration of landscape architects and foresters and to integrate the two practices.
Biltmore House & Gardens
Biltmore house and the gardens: From north (right) to south (left): the esplanade, the water garden, the ramble, and barely visible below the slope, the productive garden, providing vegetables and flowers. A pine plantation is visible behind the productive garden. The gardens were intended to be a ”small park” and a “small pleasure ground and garden” – a clearing in the woods. (Images courtesy of the Frederick Law Olmsted National Historic Site, collaged by author)

The Biltmore Estate

In 1888, George Washington Vanderbilt II began to assemble 6,000 acres of hilly land along the French Broad River, near Asheville, North Carolina, intending to create a French-style chateau surrounded by formal gardens and large parklands beyond. Vanderbilt intended Biltmore to be a true estate — self-supported by agriculture, timber, and other productive landscapes — and he hired Olmsted for the commission. At sixty-seven, Olmsted was the nation’s foremost landscape designer, and had significant experience in park and garden design as well as in scientific forestry and farming. At Biltmore, Olmsted found an exhausted landscape, severely degraded from previous uses, and he proposed forestry as a means of ecological restoration, material and economic productivity, recreation, and education. Olmsted advised his client,
“The soil seems to be generally poor. The woods are miserable, all the good trees having again and again been culled out and only runts left. The topography is most unsuitable for anything that can properly be called park scenery….Such land in Europe would be made a forest; partly, if it belonged to a gentleman of large means, as a preserve for game, mainly with a view to crops of timber. That would be a suitable and dignified business for you to engage in; it would, in the long run, be probably a fair investment of capital and it would be of great value to the country to have a thoroughly well organized and systematically conducted attempt in forestry made on a large scale. My advice would be to make a small park into which to look from your house; make a small pleasure ground and garden, farm your river bottom chiefly to keep and fatten live stock with a view to manure; and make the rest a forest, improving the existing woods and planting the old fields” [2].

The soils had been depleted from logging, fires to clear land, farming, and pasturing animals. Much of the steep land had eroded, and soils had washed away [3]. Olmsted proposed forestry to stabilize the land, improve the soils, provide profit for his client, and also provide a model of experimental forestry for the nation.
Biltmore Estate, Asheville, NC
Plan of the Biltmore Estate in 1896: The house and gardens are middle right, and a 300-acre nursery is on the right (north) bank of the Swannanoa River (the smaller river on the north edge of the property). The majority of the property, then approximately 8,000 acres, was given to forestry. (Image courtesy of the Frederick Law Olmsted National Historic Site)

Scientific Land Management

Throughout his career, Olmsted proposed landscape architecture as an ameliorative practice to improve the productivity of sites. He began his career as a scientific farmer, and proposed scientific forestry in California in the 1860’s. In the emerging profession of landscape architecture, Olmsted saw a need for rigorous scientific inquiry to ground the wise management of landscapes.
Biltmore was not Olmsted’s first forest commission, nor his first proposal for scientific land management. Rather, it was a chance to realize ideas that he began developing in Central Park, his first landscape design. In 1876, Olmsted wrote to the president of the Central Park Commission to propose that the park operate as a form of forestry laboratory. The first trees had been planted there eighteen years earlier, and Olmsted proposed recovering the weather conditions, maintenance regimes, and tree health for that period, and tracking that data into the future, saying that “it will be regarded as a matter of some national interest that such a record should be made and hereafter presented and continued. The Central Park would then form a Museum of Arboriculture arranged and catalogued suitably for profitable study” [4]. However, the park board did not act on Olmsted’s recommendation, and it would require private, not public lands for Olmsted to enact his vision of a national forestry laboratory.
In 1880, Olmsted designed Moraine Farm in Beverly, Massachusetts as a 275-acre scientific farm with a 75-acre experimental forest, both intended to advance an American mode of productivity. Over 60,000 larch, pine, spruce, and birch were planted as an experimental forest, determining which trees produced the best timber yields on degraded New England soils [5].
Private landownership meant that he could implement long-term projects, and design by cutting trees as well as planting. By 1889, about the time he began work on Biltmore, Olmsted had become so frustrated with his inability to effect scientific forestry in his large park projects that he wrote, with J. B. Harrison, Observations on the Treatment of Public Plantations, More Especially Related to the Use of the Axe, a pamphlet intended to educate the public on the necessity of thinning and removing trees.
The same year, in his report to Vanderbilt, Olmsted wrote, “as the undertaking now to be entered upon at Biltmore will be the first of the kind in the country to be carried on methodically, upon an extensive scale, it is even more desirable than it would otherwise be that it should, from the first, be directed systematically and with clearly defined purposes, and that instructive records of it be kept” [6]. Having witnessed visitors to Central Park attempt to “wrest the axe from the hand of the woodsman” in planned campaigns of thinning the thickly planted woods, planning a scientific forest on private lands must have seemed a rare opportunity to Olmsted [7]Biltmore Productive Pines
Productive Pines:  In 1892, the property encompassed approximately 7,000 acres. The light green shows pine plantations from the winter of 1889/90 (86 acres), dark green shows plantations from winter 1890/91 (169 acres). These plantations occurred before Pinchot was hired, and concentrated as they are in the viewshed of the house, they seem to be both ameliorative (for the soil) as well as aesthetic, creating the sense of a clearing in the woods. (Images courtesy of the Frederick Law Olmsted National Historic Site, collaged by author) 
Gifford Pinchot, the man Olmsted selected to oversee forestry at Biltmore, was at the time a young and inexperienced forester; the first (and at the time only) U.S.-born, trained forester; an ambitious twenty-six year old with a national vision for forest productivity and conservation. Pinchot saw a lax attitude in the United States towards natural resources, and he championed the nascent conservation movement, calling for governmental protection, on the European model, of natural resources from corporate abuse.
By 1890, Pinchot had studied forestry for a year at the École Nationale Forestière, in Nancy, France, and had spent months observing the forestry works in the Sihlwald forest in Zurich and on a tour of German forests led by one of the world’s preeminent foresters, Dietrich Brandis. His observations of the Sihlwald and on European forest policy had been published in Garden and Forest; although young, he was one of the nation’s leading experts on forestry [8].
Pinchot’s father James was a friend of Frederick Law Olmsted. Both were members of the same social clubs and professional associations, and they shared an interest in forestry [9]. Knowing of the work at Biltmore, James encouraged Gifford to apply to Olmsted for the position of forest manager; Gifford familiarized himself with the property, and approached Olmsted with preliminary suggestions for the land. In December 1891, Pinchot was hired to oversee the forest at Biltmore.
Biltmore Openwood
Forestry at Biltmore included both selective thinning of extant forests and planting in open fields. Here, young trees have been thinned for an open wood. (Image courtesy of the Frederick Law Olmsted National Historic Site)

The Biltmore Forest Proposal

Pinchot intended a steady yield of timber from the forest. At the time, wood was needed for heating, for industrial furnaces, for fence, wagon, and building construction, for road and railroad construction, and for naval shipbuilding. American forests were being rapidly consumed for construction, for fuel, for development, for agriculture. Pinchot had toured forests in thirty-three states, and seen what he later described as the “absolute devastation” of most logging practices, which reflected the common perception of forests as having a single use — timber — and extracted the greatest one-time value from them, without considering either the time required to get the forests to their then-current state, nor made any provisions for their future growth [10].
America needed forests that could produce dependable, sustainable yields of timber. Pinchot also saw the need for synthetic forestry that expanded beyond simple timber benefits. His approach was grounded in resource conservation, and took nature as its guide. This was perhaps learned from Brandis, whose mid-nineteenth-century forestry has been called “proto-ecological,” as he understood the forest as an environment, with links between species and disturbance events [11]. Pinchot used this ecological approach in his own work; he saw a healthy forest as one with a broad distribution of tree ages, with trees close enough together that they would encourage straight growth, but far enough apart that they could be felled. Pinchot’s improvements and harvesting techniques were inspired by nature. Group cuts mimicked blowdowns, a natural form of clearing in the wood that encouraged young trees to sprout. Linear cuts mimicked tornadoes, but were limited in length to protect the forest, and typically ran east-west to minimize drying the forest floor.
At Biltmore, Pinchot sought to prove that logging and forest management were not incompatible, and that productive forestry could be profitable. His three goals for the Biltmore forests were to generate profit; be self-sustaining; and improve the health of the forest. He proposed a phased plan, first improving the existing forests by thinning poor stands, promoting natural regeneration and fencing out livestock that grazed on young trees, along with extensive planting. The first, poor-quality harvests would occur over six years, with an eventual 150-year harvest cycle that used a hybrid of two traditional forestry practices — high-forest harvest and selective harvest.
In high-forest harvest, land was divided into sections equal in number to the number of years for mature harvest. Each section contained even-aged trees, and the sections were sequentially harvested and replanted, with harvest returning to the first section after the prescribed number of years. In selective harvest, the entire forest was logged annually, felling only those trees of sufficient maturity. The latter method was more difficult, in terms of ground covered annually, selecting trees to fell, and preserving the remaining trees, but it resulted in an ecologically healthy, mixed-age forest. Biltmore’s hybrid method harvested 1/5 of the property over five years, creating a 25-year harvest cycle, in a high-forest rotation. But as in a selective harvest, only trees over 130 years of age were harvested, all others left to continue growing [12]. Pinchot published the physical and economic results of the first years’ work in a pamphlet distributed at the Chicago Columbian Exposition, a report that Garden and Forest called “a most important step in the progress of American civilization” [13].
Pinchot proved that the forest could be simultaneously materially, economically, and ecologically productive. In addition, Olmsted and Pinchot envisioned several other innovations: an arboretum, a nursery, and the nation’s first, albeit short-lived, school of forestry at Biltmore, which was implemented by Pinchot’s successor at Biltmore, Carl Schenck. The arboretum was to display both ornamental and forestry trees, while the nursery provided trees and shrubs not only to Biltmore itself, but to landscape projects around the country. (In a planting plan where the entry road alone contained over 5,000 rhododendrons, an on-site nursery made a great deal of sense.) The nine-mile-long linear arboretum was to be planted along one of the roads, with trees “classified and arranged for study,” to be “an Experiment Station and Museum of living trees” [14]. While the arboretum never reached Olmsted’s vision, the 300-acre nursery was one of the top nurseries in the country, and in fact the world, for twenty years [15].Biltmore Pine Plantation
A pine plantation along one of the hillsides will grow in to create a frame for the new carriage road. (Image courtesy of the Frederick Law Olmsted National Historic Site)

The National Conservation Conversation

Although a private estate, Biltmore reflected Olmsted’s conservation ethic, a polemic that spanned his career from his early work on Central Park, through his campaigning for a national park system, and in his park designs for natural monuments such as Yellowstone and Niagara Falls. In the same 1876 letter to the Central Park Commission president that had outlined a Central Park forest laboratory, Olmsted had written that “the conservation of Woods and Forests…will soon be [a subject] of great national concern….Our sources of supply for all productions of the forest are rapidly shrinking, while the demand for them on the whole is prodigiously increasing” [16]. He went on to describe the benefits of forestry on deforested lands, and to explain the difficulty of scientific observation of forestry, due to the long time span of trees.
Olmsted believed that extraordinary lands should be preserved as public lands in support of a Jeffersonian ideal of a physically and politically healthy citizenry. State and national parks, Olmsted felt, should be reserves against the “false taste, the caprice or the requirements of some industrial speculation of their holders” that could result from the privatization of lands in the westward expansion [17].
Like Olmsted, Pinchot saw the management and use of the nation’s landscapes and natural resources as an issue of social justice. “The conservation issue is a moral issue, and the heart of it is this: For whose benefit shall our natural resources be conserved – for the benefit of us all, or for the use and profit of the few,” he asked young, politically ambitious men in 1910, before encouraging them to enter politics as a way to effect a more socially just natural resource policy [18]. Pinchot’s utilitarian philosophy, in which he sought “the greatest good of the greatest number in the long-run,” addressed the social ills resulting from industrialization. His was a modern forestry: scientific, functional, efficient.
Where most Americans saw a conflict between forest conservation and timber extraction, Olmsted and Pinchot saw the two as coexisting — healthy forests could produce useful timber. Like Olmsted’s scientific farming, Pinchot’s forestry was based in an understanding of edaphic and biotic ecological systems, and sought to optimize production of a crop or service through interventions into the processes of these systems.
To manage or to protect? This disagreement between preservation and conservation spanned Pinchot’s life and continues today. While on the National Forest Commission, Pinchot clashed with botanist Dr. Charles S. Sargent, director of the Arnold Arboretum, and founder of the influential weekly publication Garden and Forest [19].  Sargent believed that the national forests should be preserved as wilderness; Pinchot believed they should be managed productively for multiple services and functions. Pinchot’s diary entry on the dispute reads, “Sargent opposed to all real forest work, and utterly without a plan or capacity to decide on plans submitted. Meeting a distinct fizzle” [20]. This dispute continued in the famous disagreements between Pinchot and John Muir, and indeed continues today in discussions of the desired future condition of a forest and what cultural uses we want or need therein.
Olmsted’s firm agreed with Pinchot. Olmsted’s partner, Charles Eliot, wrote in Garden and Forest in 1897 about the need to manage forests, not simply protect and preserve them. Speaking against the “all too prevalent feeling that nothing can justify the felling of a tree,” Eliot wrote, “unless this superstition can be put to rout, we may as well attempt no parks or reservations, for if the axe cannot be kept going, Nature will soon reduce the scenery of such domains to a monotony of closely crowded, spindling tree trunks” [21]. Clearly, the Olmsted firm believed, as Pinchot did, that for forests to provide a social and cultural benefit, they must be managed, not merely protected.
Biltmore Forest School
Along with timber and nursery stock, the forests at Biltmore produced knowledge. Here, Biltmore Forest School students establish a plantation along Coxe Ridge [Left], and measure logs and estimate yields [Right]. (Images courtesy National Forests of North Carolina Historic Photographs, D.H. Ramsey Library, Special Collections, University of North Carolina at Asheville)

“How Shall the Use of the Axe be Guided?”

The Olmsted firm instilled their work, and that of the larger profession of landscape architecture, with the new understanding of forestry processes tested at Biltmore. Olmsted had told his son, Frederick Law Olmsted, Jr. (Rick), that “Your school for nearly all wisdom in trees and plants and planting is at Biltmore” [22]. When, in 1895, Rick became a partner in the Olmsted firm, he brought to the firm extensive knowledge from his education at Biltmore: horticultural and nursery knowledge, forest composition and management, and the financial aspects of the nursery trade and forestry. As the most influential landscape architecture practice in the United States in the first half of the twentieth century, the Olmsted firm’s approach to forestry filtered out to the larger profession of landscape architecture even as it influenced their own design of urban park systems, university campuses, and civic monuments.
Yet even as scientific forestry infused the Olmsted practice, the two professions began to distance themselves and stake out their disciplinary turf. A debate played out in the pages of Garden and Forest. In 1897, Charles Eliot asked the question, “how shall the use of the axe be guided?” An earlier editorial had proposed that public parks require expert knowledge and maintenance of trees and forest, often through thinning, and that Americans “object on general principles and on all occasions to cutting down a tree;” forests in parks throughout America were severely neglected and their trees in very poor heath as a result [23]. Eliot conceded that foresters — “experts,” — must be “engaged at least as teachers of technical methods,” but argued that the work of foresters needed to done within the framework of a designer’s long-term vision, staking public parks as the domain of the designer. “But how shall the experts themselves be guided?” Elliot asked. “Shall they be permitted to reduce the groves and woods of our public domains to collections of specimen trees, or to the monotony of the typical German forests, as, by the way, they surely will do if they are not controlled?…Engineers who direct the building of park roads are expected to conform their work to the requirements of the adopted general plan. Woodmen, foresters and planters should be similarly controlled by the requirements of the same plan” [24].
Similarly, and in the same venue, Pinchot sought to define his field as a distinct profession. In 1895, he wrote polemically:
“Forestry deals exclusively with forests — a fact which will bear a good deal more publicity than has been accorded to it hitherto. It is connected with arboriculture and landscape art only from the fact that it employs to a certain extent the same raw material, if I may use such a figure, but applies it to a wholly different purpose. That the subjects overlap at certain points is therefore true, but so do carpentry and the manufacture of wood-pulp paper, yet there is no confusion between them. That wise forest-management secures the natural beauty of a region devoted to it is a fortunate accident, but none the less an accident, pure and simple. The purpose of forestry is in a totally different sphere” [25].

With the dawn of the twentieth century and the first mature stirrings of modernism, professions began to differentiate themselves and to lose the “disposition to ready and cordial cooperation between these branch professions … desirable for the public interests” that Olmsted Sr. had called for a decade earlier [26].
Biltmore's Three Natures
 The ramble, walled garden, and esplanade and water garden represent three natures: wild, productive, and perfected. They are a treatise on the nature of nature, carved out of the woods. To create the sense of a clearing in the woods, the forests around the house and gardens had to be re-established through plantations. (Images courtesy of the Frederick Law Olmsted National Historic Site, collaged by author)

“Ready and cordial cooperation”

For a few brief years, at the end of Olmsted’s career and the beginning of Pinchot’s, landscape architects and foresters spoke the same language, worked the same problems. Olmsted was, in Pinchot’s words, “one of the men of the century,” [27] a great pre-professional, synthetic designer who knew no professional boundaries and whose projects hybridized aesthetics, infrastructure, ecology, social justice, and economic productivity. Pinchot, one of the giants of his generation, carving out a new profession in America, was an early champion of the modernist value of elegant efficiency. Biltmore occupies a key temporal moment, situated at the emergence of a mature modernism.
Olmsted’s Romantic ethic and aesthetic informed his definition of and attitude towards nature. And his generation valued broad, synthetic knowledge. Farmer, journalist, landscape architect, sanitation secretary — Olmsted practiced across a range of fields. Yet he regretted his lack of deep, scientific training. He appreciated his son’s work for the U.S. Coast and Geodetic Survey as a way to learn “topographical common sense,” and urged his study at Biltmore as a way to “establish the names of plants in your memory and attach ideas, figures, pictures to these names….No one here [at the Olmsted firm’s Brookline office] has done half enough of this” [28].
Pinchot, meanwhile, fully embraced this optimistic, modernist faith in scientific knowledge, and advocated for specialized training and professionalization. Olmsted and Pinchot were both seminal figures in the professionalization of their fields, and by the end of Pinchot’s career, one’s practice was rapidly becoming one’s profession, with associated training, and increasingly, examination and licensure. This undoubtedly led to more rigorous, deep practice, in all environmental design and stewardship fields. But it also distanced fields from one another, and Pinchot’s modernist, utilitarian praxis has led to forests “like well-managed orchards” [29]. Biltmore suggests ways to recover some of the deep roots of “ready and cordial cooperation,” and perhaps suggests the urban forest — complex, enmeshed in social and cultural processes, and long neglected by foresters and conservationists alike — as the site for deeper cross-disciplinary engagement and collaboration.
One of the lessons of Biltmore concerns time. Forests — as crops, as a collection of species, as habitats and systems — have time frames well beyond that of a human life. At H.J. Andrews Experimental Research Forest, in Oregon, researchers are nearing the fourth decade of a 200-year-long log decomposition experiment. Because of the duration of forest systems, we still do not understand, fully, scientifically, something so seemingly simple as decomposition. How can we act in a system whose fundamental processes we do not understand?
At Biltmore, the Olmsted firm designed for at least a century, and designed with what ecologist John Magnuson calls “the invisible present” of growth, succession, and decay, as well as the invisible present of modernity and professionalization [30]. Pinchot managed the Biltmore forests for timber yields, which may not be our primary desire for most urban forests. But his choreography of the forest across space and time, accounting for trees, water, animals, and people as actors, provides lessons for today’s designer. The invisible present includes agents of change: climate change and invasive plants and insects that stress or eliminate some tree species; animal browsing or human maintenance that eliminates entire next generations of seedlings; cultural desires that limit the robustness of the forest.
A second set of lessons from Biltmore relates to collaboration between fields, and design for multiplicity. Olmsted wanted the Biltmore forests to produce nursery stock, pleasure, economic return, improved soil, and education. Pinchot described various ways that a forest could be useful: environmental protection of water and soil; material production of timber, nuts, habitat; monetary production as an investment. Both saw the forest producing professional knowledge and political agency. Olmsted and Pinchot pushed each other to imagine more. To see a forest as only ecological, only aesthetic, only economic limits our capacity for invention, while collaboration between fields expands our sense of possibility.
Biltmore Before & After
Before: The woods at Biltmore when Vanderbilt purchased them were generally of poor quality, requiring thinning and replanting [Left].
After: Forestry prescriptions such as “coppice under standards” were used to generate sustainable yields of timber from the property. A mature white pine forest on the estate [Right]. (Images courtesy National Forests of North Carolina Historic Photographs, D.H. Ramsey Library, Special Collections, University of North Carolina at Asheville)
And a third lesson of Biltmore is to recognize what Elizabeth Meyer calls “sites of invention.” Olmsted and Pinchot saw the devastation of extant forests, and they fought to set aside large tracts of land and to establish methods for managing those tracts. The threatened site of extant forests fostered the invention of the conservation movement and national forests. Today we find ourselves in a different context, with new challenges and opportunities. We have already had our national conversation about those large forests, and they have been placed, appropriately, under the long-term care of foresters, not landscape architects. We are still trying to truly understand urban forests, and here is where we need to apply our understanding of both cultural and ecosystem values, of both urban and forest composition, structure and function, of recreation and arboriculture, in a synthetic and interdisciplinary way. The urban forest is a contemporary site of invention, and it is here that professional collaboration may hold the most promise. At Biltmore, the two men dealt with a degraded, eroded, depleted landscape. While rural in setting, it had challenges common to an urban site, and forestry offered them an ameliorative, productive practice. We may find the same to hold in the urban forest.
Both landscape design and forest design are simultaneously hopeful and futile acts. They deny the lie of the master plan, with designs that set processes in motion. They envision a future condition that will likely never be, but set the stage for a new design in the next generation.
Many cities are currently inventorying their urban forests, a critical first step to a forest management plan. Foresters, planners, and designers are repeating in cities what Pinchot did at Biltmore: quantifying the benefits of the forest, and providing a baseline against which to measure improvements or failures. Concurrent with these metrics, we need a national conversation on how and why we value the forest. In Pinchot’s era, the forests in the United States were open for development, and very much under threat. Pinchot and Theodore Roosevelt set aside over 160,000,000 acres of national forests, a staggering public trust of beauty, habitat, and ecosystems services. What is the public trust we will leave for the future?


Roxi ThorenRoxi Thoren is an associate professor in the departments of architecture and landscape architecture at the University of Oregon. Prior to joining the UO, she practiced architecture and landscape architecture in Boston, Charlottesville, and Philadelphia. She is the author of Landscapes of Change, to be released in fall 2014, in which she examines innovative landscape architectural strategies that respond to new social and physical contexts. Professor Thoren is the Director of the UO’s Fuller Center for Productive Landscapes, which investigates the integration of productivity in landscape architecture design, including most recently a series of projects around forestry.

Notes
[1] Gifford Pinchot, Breaking New Ground (Washington, D.C.: Island Press, 1972), 32.
[2] Frederick Law Olmsted to Frederick J. Kingsbury, January 20, 1891, Frederick Law Olmsted Papers, Manuscript Division, Library of Congress, Washington, D.C.
[3] Bill Alexander, “Biltmore Estate’s Forestry Legacy,” Forest Landowner, January / February, 2011.
[4] Frederick Law Olmsted to Henry G. Stebbins, February 1, 1876, in The Papers of Frederick Law Olmsted, Vol. VII: Parks, Politics, and Patronage, 1874-1882, ed. Charles E. Beveridge et al. (Baltimore: The Johns Hopkins University Press, 2007), 175-6.
[5] “A Modern Massachusetts Farm,” Garden and Forest, March 30, 1892, 145-6.
[6] “Project of Operations for Improving the Forest of Biltmore,” no date, Biltmore Estate Archives, Asheville, NC.
[7] Frederick Law Olmsted and J. B. Harrison, “Observations on the Treatment of Public Plantations, More Especially Related to the Use of the Axe,” in Forty Years of Landscape Architecture: Central Park, eds. Frederick Law Olmsted, Jr. and Theodora Kimball, (Cambridge: MIT Press, 1973), 362-75.
[8] For Pinchot’s essays on the Sihlwald, see Garden and Forest vol 3, issues 127-129; for European forest policy, see vol. 4, issues 150-152.
[9] Nancy P. Pittman, in “James Wallace Pinchot (1831-1908): One Man’s Evolution toward Conservation in the Nineteenth Century” (Yale F&ES Centennial News. Fall 1999, 5) describes James Pinchot and Olmsted’s membership in the exclusive Century Association. Olmsted and James Pinchot’s friendship is described in the USDA’s  Historic Structures Report: Grey Towers (United States Department of Agriculture, Forest Service. FS-327, 2) and in Laura Roper, FLO: A Biography of Frederick Law Olmsted (Baltimore: Johns Hopkins University Press, 1973), 418-19.
[10] Gifford Pinchot, journal entry August 11, 1937, in The Conservation Diaries of Gifford Pinchot, ed. Harold K. Steen (Washington, DC: Island Press, 2001), 174.
[11] Dan Handel, “Into the Woods,” Cabinet, 48 (2012/13).
[12] Standard forestry practices are from US Department of Agriculture, Bureau of Forestry, A Primer of Forestry. Part II: Practical Forestry, by Gifford Pinchot, Bulletin 24, part 2, (Washington, DC: Government Printing Office, 1905). Biltmore forestry practices are from Gifford Pinchot, Biltmore Forest: An Account of its Treatment, and the Results of the First Year’s Work, Chicago: Lakeside Press, 1893.
[13] “Mr. Vanderbilt’s Forest,” Garden and Forest, February 21, 1894, 71.
[14] Frederick Law Olmsted, “George W. Vanderbilt’s Nursery,” Garden and Forest, December 30, 1891, 615.
[15] Charles E. Beveridge, “’The First Great Private Work of Our Profession in the Country’ Frederick Law Olmsted, Senior, at Biltmore,” National Association for Olmsted Parks Workbook, 5, no. 3 (1995), and Bill Alexander, The Biltmore Nursery: A Botanical Legacy, (Charleston, SC: History Press, 2007), 11.
[16] Frederick Law Olmsted to Henry G. Stebbins, 1 February 1876, in The Papers of Frederick Law Olmsted, Vol. VII: Parks, Politics, and Patronage, 1874-1882, ed. Charles E. Beveridge et al. (Baltimore: The Johns Hopkins University Press, 2007), 175-6.
[17] Frederick Law Olmsted, “Preliminary Report upon the Yosemite and Big Tree Grove” in The Papers of Frederick Law Olmsted, Vol. V: The California Frontier, 1863-1865, ed. Victoria Post Ranney et al. (Baltimore: The Johns Hopkins University Press, 1990), 488-518
[18] Gifford Pinchot, address to the Roosevelt Club of St. Paul, Minnesota, June 11, 1910.
[19] M. Nelson McGeary, Gifford Pinchot: Forester – Politician (Princeton, NJ: Princeton University Press, 1960), 39.
[20] Gifford Pinchot, journal entry May 16, 1896, in The Conservation Diaries of Gifford Pinchot, ed. Harold K. Steen (Washington, DC: Island Press, 2001), 72.
[21] Charles Eliot, “Trees in Public Parks,” Garden and Forest, January 27, 1897, 37.
[22] Susan L. Klaus, “’A Better School Could Scarcely be Found’ Frederick Law Olmsted, Junior, at Biltmore,” in The Olmsteds at Biltmore: Frederick Law Olmsted, Senior, eds. Charles E. Beveridge and Susan L. Klaus, (Bethesda, Md: National Association for Olmsted Parks, 1995).
[23] “Trees in Public Parks,” Garden and Forest, Dec. 23, 1896, 511.
[24] Charles Eliot, “Trees in Public Parks,” Garden and Forest, January 27, 1897, 37.
[25] Gifford Pinchot, “The Need of Forest Schools in America,” Garden and Forest, July 24, 1895, 298.
[26] Frederick Law Olmsted, “Paper on the Back Bay Problem and Its Solution,” in The Papers of Frederick Law Olmsted: Supplementary Series Vol. 1 Writings on Public Parks, Parkways, and Park Systems, eds. Charles E. Beveridge and Carolyn F. Hoffman (Baltimore: Johns Hopkins University Press, 1997), 437-460.
[27] Pinchot, Breaking New Ground, 48.
[28] Charles E. Beveridge, “’The First Great Private Work of Our Profession in the Country’ Frederick Law Olmsted, Senior, at Biltmore,” National Association for Olmsted Parks Workbook, 5, no. 3 (1995)
[29] Alan G. McQuillan, “Cabbages and Kings: The Ethics and Aesthetics of New Forestry,” Environmental Values 2 (1993): 205.
[30] John J. Magnuson, “Long-Term Ecological Research and the Invisible Present,“ BioScience, 40, no. 7, (1990): 495.
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How Many Trees Are Enough? Tree Death and the Urban Canopy

Published in Scenario 04: Building the Urban Forest
Spring 2014


Author
by Lara A. Roman

Introduction

Massive city tree planting campaigns have invigorated the urban forestry movement, and engaged politicians, planners, and the public in urban greening. Million tree initiatives have been launched in Los Angeles, CA; Denver, CO; New York City, NY; Philadelphia, PA, and other cities. Sacramento, CA even has a five million tree program. These planting campaigns – and urban forestry programs in general – are justified by models that estimate and monetize the environmental and socioeconomic benefits of trees [1,2]. These ecosystem services, defined as “the benefits that humans derive from nature,” play a major role in urban natural resource management [3,4].
However, realizing the ecosystem services associated with planting depends on tree survival. Despite the major focus on city tree planting over the past few decades, Nowak and Greenfield found that overall canopy cover levels in major US cities have been declining [5]. As these authors noted, “it is apparent that tree planting and natural regeneration are insufficient to offset the current losses.” With major new planting campaigns, how many of those trees will survive for decades, reaching a mature size at which their environmental and socioeconomic benefits are greatest? How many trees are enough – that is, how many need to be planted to make a lasting impact, and meet a city’s canopy cover goals? What are the implications of future tree death for managing the urban forest, in terms of cycles of tree removal and replacement? Answering these most basic questions in urban forest planning requires information about tree mortality and growth rates.
Sacramento's Tree Canopy
Figure 1. The urban forest canopy of Sacramento, CA in the spring. Image courtesy of the Sacramento Tree Foundation.
Unfortunately, long-term studies are sorely lacking for city trees. While cities rely on urban forest assessments, such as inventories and canopy cover analysis, to guide management, planning, and policy [6], long-term monitoring and associated mortality data are key missing pieces. Projected losses for the million tree campaigns demonstrate the importance of mortality data for estimating environmental benefits. The mortality rate patterns embedded within tree population projections for New York City [7] are based on a single study of maple street trees from Syracuse, NY [8], and survival scenarios for Los Angeles [9] do not cite any particular field studies. These and other authors have noted that mortality rates are a major source of uncertainty in predicting urban forest change over time. In the study about Los Angeles’ million tree program, a low mortality scenario projected that 17% of planted trees would be dead after 35 years, and a high mortality scenario projected 56% mortality.
These huge differences in mortality assumptions led to a large range in anticipated benefits: $1.95 billion to $1.33 billion in ecosystem services for the low and high mortality predictions, respectively. While mortality field data in Los Angeles has not yet been reported, we can compare the Los Angeles predictions to observations with MillionTreesNYC and the Sacramento Shade Tree program (Figure 1). For street trees in New York City, eight to nine years after planting, 26.2% were dead [10]. For a yard tree give-away program in Sacramento, five years after planting, 29.1% had died, on top of 15.1% that were never planted by residents [11] (Figure 2). For these yard and street tree examples, over a quarter of the trees planted died within the first five to nine years, and furthermore, for the tree give-away, some trees never made it into the ground. The Los Angeles low mortality scenario therefore appears overly optimistic.
While researchers have noted the importance of understanding mortality and generating long-term data, local practitioners have already started tracking the trees that they plant and manage [13]. Yet these practitioner-led efforts are somewhat isolated, and rarely documented in publications [14]. Journalists and bloggers have begun asking questions about tree survival in the massive planting campaigns as well, with article titles such as “A million trees? Only if we can keep them around” [15]. Given the call for monitoring the success of urban tree planting programs from the public, urban forest professionals, and researchers, the timing is ripe to finally embark on a nationally coordinated monitoring network. Towards this end, a new collaborative endeavor is underway to develop standardized tree monitoring protocols. By generating data that can be compared across cities and programs, we will enhance our ability to understand tree mortality rates and causes [16]. This kind of data can feed both academic and applied interests, from studying the biophysical and socioeconomic drivers of urban tree mortality, to recording tree survival as an indicator of local program success. While it will take years for us to produce the long-term data sets we seek, we can strive in the meantime to promote a common understanding of the role tree death plays in urban forest management.
In this essay, I discuss street tree mortality in terms of demographic concepts, and advocate for the application of these approaches in urban forest planning. Demography – the statistical study of populations – is used to analyze mortality trends and project future changes in systems ranging from human societies to endangered wildlife communities and natural forests. The same concepts and calculations used by actuaries (to determine risk of death for life insurance) and conservation biologists (to assess species extinction risk) can be used to study tree death in cities. While street trees do not encompass the entire urban forest, they are a major focus of tree planting and management operations, and are often the first line of public engagement with tree planting and stewardship. As we produce more long-term data in the years ahead, we will be able to compare different site types within the urban forest, such as streets, yards, and parks, and tailor population projections to the varied management regimes and species palettes within the urban forest landscape.
Roman_YardSurvival-Sacramento
Figure 2. Yard tree survival in Sacramento County, CA from a tree give-away program: a tree that survived [left]; a vacant, foreclosed property where trees were never planted [right]. In this study, some trees were lost due to failure to plant, in addition to post-planting mortality [12]. Images © Lara Roman.

Street tree lifespans

A common notion heard among arborists and urban planners is that street trees live, on average, for seven years. This figure comes from a 25-year-old article stating that suburban trees have an average lifespan of 32 years, and street trees seven years [17]. A similar study published a few years later reported that downtown trees have an average lifespan of 13 years [18]. These numbers were based on a questionnaire sent to urban foresters across the US, asking the local experts to estimate the typical tree lifespans in their cities. However, the questionnaire-based figures should be replaced with field data for a more accurate representation of urban tree longevity. In the decades since those articles were published, several more studies have reported primary field data on street tree death, offering the opportunity to combine results. Based on my analysis of 11 previous studies, the typical street tree mean life expectancy is 19-28 years, and the annual mortality rate is 3.5-5.1% [19]. This is far longer than the seven or 13-year figures previously reported. In fact, if the mean life expectancy was truly seven years, annual mortality would be 13.3%, far higher than the rates reported in published studies. While the mortality scenarios in ecosystem services projection models might be overly optimistic, the seven-year lifespan idea appears to be overly pessimistic. For purposes of natural resources planning and ecosystem services models, we need realistic expectations based on observations, rather than overly optimistic or pessimistic speculations.
Additionally, mean life expectancy may not be the best metric for communicating about urban tree longevity and death. As the average lifespan across all individuals, the mean life expectancy becomes very high when just a few individuals reach old age. A term with more practical application to managers is the population half-life: the time by which half of the planted trees can be expected to die. With the typical street tree mortality rates of 3.5-5.1% mentioned above, the population half-life is 13-20 years [20] (Figure 3). In other words, for every 100 street trees that get planted, only 50 will make it to 13-20 years [21]. These field data on urban tree mortality suggest that as the number of trees originally planted die over time, community foresters have to keep replacing trees, year after year, to have any chance of increasing population counts and canopy cover.
Roman_Survivorship Curves
Figure 3. Survivorship curves with population half-life: Survivorship curves for street trees when annual mortality is constant at 5.1 or 3.5%, as estimated from a meta-analysis of previous studies, adapted from Roman and Scatena (2011) [22]. These curves depict exponential decay in cumulative survivorship. The population half-life is the time at which half the population has died (survivorship = 50%). Note that survivorship curves are often drawn in the demographic literature with log-transformation, but that this graph is not log-transformed for ease of interpretation.

Tracking population fluxes

To understand changes in urban forests over time, we need more than mortality data. Like any population, urban forests change through inputs and outputs to the system. In human and animal populations, those fluxes are birth, death, immigration, and emigration. In the urban forest, we have losses from mortality and removal, and inputs from planting and natural regeneration of seedlings. In the heavily managed street tree environment, natural regeneration is negligible, so the main source of new trees is planting [23]. This makes tree-lined streets more akin to an orchard: a cultivated landscape, stewarded by humans, and grown for human benefit.
Roman_StreetTrees-Oakland
Figure 4. Street trees in the West Oakland neighborhood of Oakland, CA: a street lined with magnolia trees [left]; a dead young tree [right]. Images © Lara Roman.
An example of the fluxes in a street tree population comes from five years of annual monitoring in Oakland, CA [24]. The goal of this study was to understand net change in street tree population counts, in relation to annual planting and mortality (Figure 4). The West Oakland neighborhood has been the focus of recent planting efforts by both the City of Oakland and a local non-profit, Urban Releaf. These planting programs seek to provide socioeconomic benefits and address environmental injustices in an underserved community. There was an initial neighborhood street tree inventory in 2006, followed by an annual census for tree mortality, removals, and new plantings. We observed an overall population increase during the five-year study period: 995 live street trees in 2006, and 1166 in 2011, for an increase of 17%. The annual mortality rate was 3.7%, which is within the range of typical street tree mortality rates from the literature review discussed earlier. So far, so good: the mortality rates are within the “normal” range and the population is on the rise. However, mortality of small, young trees was a serious problem that prevented the population from growing even faster.
Approximately half of the 2006 trees were small, with trunks 3 inches in diameter or less. Annual mortality in that smallest size class was 5.6%, about four times the rate for all the other size classes (Figure 5). In other words, most of the tree losses came from recently planted, small trees. The planting campaigns in this neighborhood were barely out-pacing young tree deaths, and could have had a larger impact if young tree survival were enhanced. These findings support an older arboriculture study, which suggested that young street tree death drives population cycles, and the need for replacement planting [25]. The West Oakland data also supports the concept of an establishment phase for urban trees – the first few years after planting during which trees are more likely to die, [26, 27] Extra vigilance during the establishment phase, in terms of maintenance and stewardship, might have the most payoff for ensuring planting survival, and thus achieving larger canopy objectives.
Size-class Mortality Curves copy
Figure 5. Size-class mortality curve for West Oakland street trees. Total n = 940. Adapted from Roman et al. (in press) [28].

Changing the conversation

The street tree studies discussed above are examples of demographic analysis applied to urban forests, illustrating the insights gained from a population ecology perspective. Assessments of urban tree mortality and monitoring data have implications for urban forest planners and designers. We need both more long-term data and appropriate analytical frameworks to understand the role of tree mortality in urban forest management. In order to reap the benefits of urban tree planting programs, the trees have to survive, thrive, and grow, within the context of an existing urban forest population of varying ages. Planting a few hundred trees, or even a million, does not automatically translate into an increase in the overall tree population over the long-term. To increase population levels, the survival and planting rates have to out-weigh losses from tree death and removal, including both old and young individuals. While this essay focused on street trees, the same underlying implications apply to trees in parks and residential lawns: many planted trees may not last to provide the ecosystem services that motivate planting campaigns [29]. This is a sobering thought, but an important one to bring to the surface in conversations between community foresters, policy-makers, landscape architects, planners, and researchers. Developing realistic projections about long-term urban forest population levels, canopy cover, and ecosystem services requires field data about mortality trends.
Let us shift the emphasis in urban forestry away from counting sheer numbers of trees planted, and towards touting exemplary records of tree survival. Rather than asking, “How many trees are enough?” I propose that the question be re-framed in a more nuanced manner: “To achieve a particular canopy cover goal, how many trees need to be planted every year?” Tackling this question involves knowledge about not only planting levels and mortality rates, but also natural seedling regeneration rates and urban-specific tree growth rates under varying site conditions. Managing towards a canopy cover goal necessitates consideration of urban tree population cycles: planting, growth, removal, and replacement.
Practitioners interested in making educated guesses about how their tree planting efforts compare to mortality losses can use new population projection tools under development by the Forest Service and OpenTreeMap [30]. However, even these tools are subject to great uncertainty in scenario-building, due to the lack of long-term monitoring data to produce reliable survival assumptions. Collaboration between researchers, arborists, urban forest managers, planners, and designers will be essential to produce longitudinal urban tree data [31], analyze that data with appropriate tools, and connect research results to practice. As both researchers and practitioners move forward and produce new data on tree mortality, growth and longevity, we can improve the tools available for urban forest managers to plan ahead, embedding their planting campaigns within the population dynamics of cultivated city landscapes.

Acknowledgements

I am grateful to many urban forest practitioners whose dedication to planting trees and studying mortality have inspired my research, especially colleagues at the Sacramento Tree Foundation, Urban Releaf, Canopy, Friends of the Urban Forest, NYC Parks & Recreation, and Pennsylvania Horticultural Society. I also thank M. Piana, N. Pevzner, D. Nowak, L. Mozingo, K. Podolak, S. Low, and G. Silvera Seamens for their thoughtful comments on this manuscript, and J. Battles, J. McBride, and the late F. Scatena for many conversations about ecological and demographic approaches to urban tree mortality that shaped my research.


Roman_144Lara A. Roman is a Research Ecologist with the USDA Forest Service, Philadelphia Field Station. Her current research uses analytical tools from demography and epidemiology to understand urban tree mortality rates and processes. She received a PhD in Environmental Science, Policy and Management at UC Berkeley, where she studied tree death in Sacramento and Oakland, CA. Lara serves as Secretary of the Urban Tree Growth & Longevity Working Group, and is leading the effort to develop standardized protocols for urban tree monitoring in partnership with researchers and community foresters across the US. Her studies take a participatory research approach, collaborating with non-profits and municipal arborists for study design and implementation. Lara also holds a Bachelors in Biology and Masters of Environmental Studies from the University of Pennsylvania.

Notes

[1] Georgia Silvera Seamans, “Mainstreaming the environmental benefits of street trees,” Urban Forestry & Urban Greening 12no. 1 (2013): 2–11.
[2] Robert F. Young, “Mainstreaming urban ecosystem services: A national survey of municipal foresters,” Urban Ecosystems 16no. 4 (2013): 703-722.
[3] TEEB – The Economics of Ecosystems and Biodiversity, “TEEB manual for cities: Ecosystem services in urban management,” (United Nations Environment Program, 2011), accessed at www.teebweb.org.
[4] Diane E. Pataki, et al., “Coupling biogeochemical cycles in urban environments: Ecosystem services, green solutions, and misconceptions,” Frontiers in Ecology and the Environment 9, no. 1 (2011): 27-36.
[5] David J. Nowak and Eric J. Greenfield, “Tree and impervious cover change in U.S. cities,” Urban Forestry & Urban Greening 11, no 1 (2012): 21-30.
[6] US Forest Service, Northern Research Station, “Urban tree canopy analysis helps urban planners with tree planting campaigns,” Northern Research Station Research Review 13 (2011). http://www.fs.fed.us/nrs/news/review/review-vol13.pdf.
[7] Arianna Morani, et al., “How to select the best tree planting locations to enhance air pollution removal in the MillionTreesNYC initiative,” Environmental Pollution 159, no. 5 (2011): 1040–7.
[8] David J. Nowak, “Silvics of an urban tree species: Norway maple (Acer platanoides L.).” (MS Thesis, State University of New York, College of Environmental Science & Forestry, 1986).
[9] E. Gregory McPherson, et al., Los Angeles 1-Million tree canopy cover assessment. USDA Forest Service, Pacific Southwest Research Station, GTR-207 (2008).
[10] Jacqueline W.T. Lu, et al., “Biological, social, and urban design factors affecting young street tree mortality in New York City,” Cities and the Environment 3 (2010).
[11] Lara A. Roman, “Urban tree mortality” (PhD Dissertation, University of California, Berkeley, 2013). This includes results of the Sacramento Shade Tree Program survival study, for which I tracked a cohort of yard trees for five years after distribution to residents. This program is funded by the local utility district and implemented by the Sacramento Tree Foundation.
[12] Ibid.
[13] Lara A. Roman et al., “Identifying common practices and challenges for local urban tree monitoring programs across the United States,” Arboriculture & Urban Forestry 39, no. 6 (2013): 292-299.
[14] Two notable exceptions are Lu et al. (2010) [10] and Steven Boyce, “It takes a stewardship village: Effect of volunteer tree stewardship on urban street tree mortality rates,” Cities and the Environment 3 (2010).
[15] Leda Marritz, “A million trees? Only if we can keep them around,” Next City, 1/18/2012, http://nextcity.org/daily/entry/a-million-trees-only-if-we-can-keep-them-around.
[16] “Urban Tree Growth & Longevity”, www.urbantreegrowth.org.
[17] Gary Moll, “The state of our urban forest,” American Forests 95 (1989): 61-64.
[18] Bob Skiera and Gary Moll, “The sad state of city trees,” American Forests (1992): 61-64.
[19] Lara A. Roman and Frederick N. Scatena, “Street tree survival rates: Meta-analysis of previous studies and application to a field survey in Philadelphia, PA, USA,” Urban Forestry & Urban Greening 10, no. 4 (2011): 269-274. This paper provides mathematical equations relating annual survival to long-term survivorship, mean life expectancy, and population half-life. These equations were adapted from classic demographic texts to street trees. With very low annual mortality rates, mean life expectancy would get absurdly high – hundreds or thousands of years – because of the asymptotic relationship between mean life expectancy and annual mortality.
[20] Ibid.
[21] The NYC street tree mortality study [10] found that over a quarter of trees had died 10 years after planting. This is also similar to the prediction from the survivorship curves in Figure 4. See [19] for a discussion of how to project the time at which 50% (or any other portion) of the planting cohort will be dead.
[22] Lara A. Roman and Frederick N. Scatena, “Street tree survival rates: Meta-analysis of previous studies and application to a field survey in Philadelphia, PA, USA,” Urban Forestry & Urban Greening 10, no. 4 (2011): 269-274.
[23] While seedling regeneration is likely negligible for street trees in most cities, regeneration is a major component of urban forest change in other land uses, such as remnant forest patches and private residential lands. Exotic invasives are an important contributor to natural regeneration. More details provided in David J. Nowak, “Contrasting natural regeneration and tree planting in fourteen North American cities,” Urban Forestry & Urban Greening 11, no. 4 (2012): 374-382.
[24] Lara A. Roman, John J. Battles and Joe R. McBride, “The balance of planting and mortality in a street tree population,” Urban Ecosystems (in press).
[25] Norman A. Richards, “Modeling survival and consequent replacement needs in a street tree population,” Journal of Arboriculture 5, no. 11 (1979): 251-255.
[26] Ibid.
[27] Randall H. Miller and Robert W. Miller, “Planting survival of selected street tree taxa,” Journal of Arboriculture 17, no. 7 (1991): 185-191.
[28] Lara A. Roman, John J. Battles and Joe R. McBride, “The balance of planting and mortality in a street tree population,” Urban Ecosystems (in press).
[29] While street tree survival studies are more abundant than other segments of the urban forest, the limited data available for other site types also suggests relatively high mortality. In the Sacramento Shade Tree Program, observed mortality was higher than program expectations for energy-saving benefits (Roman 2013) [11].
[30] i-Tree Forecast is in beta testing (David Nowak, personal communication with the author, www.itreetools.org), as is the population projection feature of OpenTreeMap (Deborah Boyer, personal communication with the author, https://opentreemap.org).
[31] Longitudinal data are repeated observations on the same individuals over time. Studies of health and mortality outcomes in epidemiology and demography use longitudinal data. Some long-term forest ecology data sets are longitudinal (e.g., repeated census of tagged trees on research plots), but in urban forestry, studies tracking the same individual trees have only recently begun.

Header image of Sacramento byNicole J. Huber
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