The Ecology of Unpredictability

Prologue: Three Projects

Landschaftspark Duisburg-Nord, Duisburg, Germany

Walking between walls of shrubby greenery, you see an opening ahead, and soon arrive at an elevated prospect. The weedy, dusty ground drops away sharply. Gardeners have trimmed the rowdy vegetation to provide a view over the slope toward rusting remains of tramways, furnaces, and bunkers belonging to the former Thyssen Ironworks. The concrete bunkers enclose a series of gardens, planted with shrubs and trees to create the Landschaftspark Duisburg-Nord. A canal divides the view. Around the edges of the bunkers, you see birch trees with white bark. The largest stand at the center of a thicket, with a hierarchy of saplings colonizing outward.

Tate Modern, London, England

You step onto the Millennium Bridge, heading south toward Bankside. Below flows the Thames. Restrained by flood-control embankments since the 19th century, the river no longer creates a liminal space — between city and water, between high water and low — to shelter riparian vegetation. But as you cross the bridge, a dense canopy of green appears against the bricks of the former Bankside Power Station, now Tate Modern. Turning to your left before descending the ramp to ground level, you find yourself standing almost within the canopy of a thicket of birch trees with white bark. The city seems to recede behind the leaves.

Jardin des Étangs Gobert, Versailles, France

After a day spent strolling the Gardens of Versailles — including circumnavigation of the Grand Canal by bicycle — you walk along Avenue de Sceaux, in the shade of a double row of mature plane trees. The street ends, but the axis continues through a plaza. Oaks line this walkway. In contrast to the tidy ranks of plane trees, the oaks are spaced unevenly, some closer to and some farther from the plaza’s edges. You climb a steep embankment, up two flights of stairs, and look down into a space ten feet below. It’s lushly occupied by birch trees with white bark. You catch a glimpse of lawn at the center of the thicket.

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At Duisburg-Nord in the early 1990s, Latz + Partner allowed existing birches to continue colonizing areas of disturbed and polluted soil around the abandoned metalworks, forming thickets. At Tate Modern in 2000, Kienast Vogt planted rectilinear blocks of birch, forming thickets. At Jardin des Étangs Gobert in 2010, Michel Desvigne edited the early successional vegetation already growing in what had been a reservoir, in order to shape and emphasize an extant birch thicket. Individual birch trees have long been used as accent specimens in designed landscapes. But until quite recently, the indiscriminate tangle of a thicket was not an accepted planting typology. As these projects attest, this element of landscape design has now fully arrived in public spaces. ¹

What are the design possibilities of functional and/versus representational ecologies? Can a birch thicket’s unruly tangle help us decide?

Birches clumped in thickets have historically been found not in gardens but at derelict sites, and in woodlands recently disturbed by fire or wind or logging. Why are designers now appreciating this form? What can the use of thickets tell us about the design possibilities of functional and/versus representational ecologies — landscapes in which plantings and their upkeep can be quantitatively measured as supporting wildlife habitat needs, conserving resources, minimizing labor costs, etc., versus designs that visually display or signal ideas of ecological responsiveness? These are issues in botany, economics, and aesthetics. They are also questions of public reception, historical context, and changing definitions of ecology as such. ²

Birch species, the genus Betula, run from glaciers. Prior to the most recent glacial maximum in the temperate latitudes of the Northern Hemisphere, which occurred some 25,000 to 35,000 years ago, birch trees retreated south. ³ Yet birches also chase glaciers. When the planet wobbled 20,000 years ago and those same sheets of ice began to crack and melt, depositing a parched, infertile soil of dust and sand and boulders, birches were among the first trees to return north. Spreading rapidly, and resilient in snow and wind, they thrive in a variety of climates and across a spectrum of soil types, where they assume a variety of forms, from mid-canopy trees that inhabit mixed mesophytic forests in eastern Asia and eastern North America, to dwarf shrubs that suck nutrients and water from between shelves of rock in alpine zones. As one of the earliest flowering trees to evolve, the genus has existed for 70 million years — plenty of time to diversify; to remain bound within a common ancestry and yet to be distinguished by characteristics forged through geological upheavals and climate fluctuations. ⁴

Considering subgenera — a level of taxonomic distinction between genera and species — is thus helpful when thinking about birches. And when discussing recent uses in landscape architecture, the subgenus Betula, or Betula Betula, is particularly important. ⁵ This subgenus contains species that have evolved within the past 10 million years, making them less genetically diverse than Betula as a whole. ⁶ Primary among their characteristics: these trees have white bark. ⁷ Amidst forests of oak, beech, and pine, Betula Betula is conspicuous enough that even people who typically ignore trees tend to notice them. The word “birch” is derived from the old English beorht, bright, and a birch trunk is a slash of light. ⁸ Betula Betula also produces abundant seeds at a young age, allowing it to aggressively colonize after a disturbance — mudslide, ice age, industrial toxicity. Toward bare soil that lacks nutrients, a million seeds fly. In disturbed terrain, Betula Betula is in the arboreal vanguard.

A birch trunk is a slash of light. Even people who typically ignore trees tend to notice them.

Compared to long-lived oaks, Betula Betula is patchy, ephemeral. Thickets explode from bare ground, but within 30 to 50 years, they will be moribund, overcome by the shade of species that are slower to mature. Even so, Betula Betula has assumed a circumpolar distribution in the northern hemisphere, restricted only in the steppes of Asia and North America, where the climate is too dry for any tree. Botanists traveling to eastern Asia in the 18th century saw birches with white trunks and assumed that they had identified a new species, not having realized that a single species, Betula pendula or silver birch, which ranges from England to Japan, had taken on a variety of traits across this colossal swath of territory. ⁹

The biogeography of this subgenus thus overlaps with an area of the planet that underwent intense industrialization in the 19th century and has since endured an equally jolting deindustrialization, leaving abandoned urban and peri-urban sites available to be recolonized. Betula Betula has obliged, springing up in thickets beside Interstate 90 in central Massachusetts, and proliferating along RER lines in suburban Paris. In the last several decades, birch thickets have infiltrated the designed environment too — although here they have had significant help from landscape architects. Designers, in turn, have been influenced by changing definitions of ecology as such.

The Rise of “Chaos”

As a branch of the biological sciences, ecology is typically understood as the objective observation of relationships among species. Yet, as the environmental historian Donald Worster has argued, the discipline should more accurately be seen as a reflection of cultural perception about that which we call nature. ¹⁰ The interrelation of species has not changed, but Western views about those relations have.

Biogeography of the subgenus Betula Betula overlaps with an area of the planet that has endured a jolting deindustrialization.

Ecological perspectives, derived from centuries of acculturated beliefs about the natural world, of course existed long before the term Oecologie was coined in 1866 by Ernst Haeckel. Early in the 20th century, when ecology emerged as a cohesive discipline in Europe and the U.S., idealist concepts dominated thinking in the field, primarily regarding ideal plant communities. The work of botanist Frederic L. Clements typifies this era, and in 1916 he proposed a deterministic model of plant succession. ¹¹ Clements wished to better understand why the vegetation on a given parcel of land looked the way it did, and how it might appear at later times. He assumed that such change was formulaic, and he proposed that he could analyze any plot and determine what type of vegetation would grow there in the future. He called this “dynamic ecology,” but despite his focus on dynamism, Clements assumed that vegetation progressed in predictable stages toward foreseeable climax communities, where species would exist in harmony with the climate, the larger environment, and each other. ¹²

This idea of steady, predictable succession toward coherence dominated ecological study until after World War II. ¹³ An ecology of order and structure translated into ideals that guided design professionals and the public’s reception of their projects, with the result that planting types remained what they had mostly been for a few centuries: allées, bosques, hedges, orchards, and romantic yet orderly clumps and specimen trees whose use descended from the English landscape garden. ¹⁴

Biologist Daniel Simberloff, writing in 1980 and examining paradigmatic shifts in the science of ecology from the mid-19th century onward, has identified what he calls “the overthrow of idealism,” arguing that the discipline began to shed its reliance on types and ideals, and to turn toward a probabilistic conception of the world. ¹⁵ Science at large — along with other areas of cultural production — began to explore the unharmonious, the unpredictable, even the unknowable. Simberloff considers the year 1859, with the publication of Darwin’s The Origin of Species, Wagner’s Tristan and Isolde, and Marx’s Critique of Political Economy, as a start-point for this change, and traces its implications through Einstein’s Special Theory of Relativity (1905), the second law of thermodynamics as articulated by Max Planck (1926), and Heisenberg’s Uncertainty Principle (1927). Worster notes that by the 1960s — a century after the turning point identified by Simberloff — ecologists were thinking “in terms of massive uncertainty, flexibility, and adjustability.” ¹⁶ An altered paradigm emerged, what Worster calls “a new ecology of chaos.” ¹⁷

A new aesthetic in landscape architecture emerged, a set of forms and styles that emphasize impermanence and chance.

The emergent ecology of unpredictability coincided with a rush of environmental worries taking hold in the postwar era. Since that time, these developments — from visions of order and stasis, to scientific descriptions of chaos, to popularizations of those disorderly or chaotic schema — have helped to create a new aesthetic of the ecological in landscape architecture, a set of forms and styles that emphasize impermanence and chance. ¹⁸ Disruption, transformation, instability: these have become culturally accepted ecological principles in the west, altering how designers talk about plants and how the public responds to plantings.

This alteration in cultural context has created space for the positive reception of birch thickets. As opposed to individually planted trees or groves, birch thickets appear scraggly and dense, masses of wily stems and wiry branches. Such visual qualities — especially in urban contexts — are effectively deployed by designers interested in highlighting the ecology of chaos. Other trees form thickets too, and could have played the role — certain species of alder, cherry, or plum, for instance. But Betula Betula is particularly effective because, even within tangled stands, their light bark reads as an intentional, graphic gesture, mediating between organic vicissitudes and the hardened built environment. ¹⁹

Designing Birch Thickets

Early succession vegetation, including birches, had colonized the 230-hectare site that became Landschaftspark Duisburg-Nord well before Latz + Partner won a competition to design the new landscape park. The firm proposed to allow and even encourage this inherited growth, at least in places. ²⁰ Peter Latz wished neither to idealize nor to banish the traces of heavy industry. Instead, he hoped to develop a “possible congruence” between the Thyssen ruins and freeform natural growth. ²¹ Both Elissa Rosenberg and Udo Weilacher have called Latz’s approach “archeological,” although their uses of this word largely suggest the material or spatial, relating to Latz’s physical manipulations of the site. ²² However, if Duisburg-Nord can be said to recognize archeological space, it should also be considered in terms of archeological time. Latz seems equally fascinated by the built remnants of the factory and by unregulated processes such as erosion, oxidation, and forest succession that had taken over since the metalworks was abandoned in 1985. In this way, he becomes not only a designer but an archeologist of change.

Latz uses the term “artefact” in describing his design philosophy, and he understands this as implying less a static object and more a locus or result of process. At Duisburg-Nord, blast furnace 5, the bunker complex, and the Piazza Metallica are all artefacts in this sense. Latz has argued against the birch tree as a symbol of bucolic or pastoral nature. ²³ But the birches that colonized Duisburg-Nord can be seen as artefacts in much the same way as the furnace or the bunker; if the seeds of these trees found their way here via transportation of raw materials for steel production, then they too can be understood as industrial residues. ²⁴ Whether growing individually along a path, in a single thicket inside a crumbling, slightly damp and sooty-smelling concrete structure, or in a complex of thickets across the monumental topography of spoil piles, birches exist here because of the disturbance caused by industry. ²⁵ The thickets that park-goers enjoy are hybrid processual entities, brought to the site, over time, by the industrial economy and the disturbances it caused, in interplay with the biogeography of Betula Betula, and with Latz himself.

The decision to allow self-seeded birches to remain and spread illustrates their aptness in low-input and low-maintenance landscapes.

Latz’s decision to allow the self-seeded birches to remain and to spread illustrates the aptness of birch thickets in low-input and low-maintenance landscapes — that is, in designs that are genuinely resilient in ecological terms. ²⁶ In some ways, the trees themselves design the thicket landscapes. ²⁷ At Duisburg-Nord, in particular, this tendency to proliferate, to reforest, and to then yield to other species fits scholars’ definitions of Fourth Nature — vegetation spontaneously rising on abandoned sites. ²⁸

In contrast to Duisburg-Nord, where Betula Betula had taken hold prior to the designer’s intervention, the site of the power plant that became Tate Modern had been cleared of early successional vegetation — including thickets of birch — before the designer arrived. ²⁹ Bankside saw a period of disuse between deindustrialization and the resurgence of residential and commercial development in the last decade of the 20th century. Moreover, while the Thames is restricted in this zone by flood-control walls, elsewhere along the river floods create disturbances that still allow birches to grow spontaneously. The landscape architecture firm Kienast Vogt drew on these precedents. ³⁰

Kienast Vogt’s thickets at Tate Modern are planted as orderly masses — rectilinear both vertically and on the ground plane — that define public landscape rooms between the museum and the riverbank. Descending the ramp from the Millennium Bridge, you pass between two of these rectangles. Each includes multiple birch species, their bark ranging from bronze to brilliant white, creating subtle variations in hue and light. The trees vary in diameter and are irregularly spaced, many just a few inches apart. ³¹ In this density and variety, the plantings evoke the idea of a birch thicket without trying to mimic the natural thickets that would be found in a truly neglected industrial lot. A birch thicket as a process in a wasteland becomes a Birch Thicket as an art object. Such thickets fit the concept of hypernature: they exaggerate and simplify the appearance of that which would occur without human attention. ³²

A birch thicket as a process in a wasteland becomes a Birch Thicket as an art object.

This visual or conceptual distillation of natural process is enhanced by the ways in which Vogt’s plantings are maintained. The thickets at Bankside are allowed to grow as they wish within the rectangular blocks, but gardeners trim the edges to maintain a roughly geometric structure. In a few instances, individual birches were planted to appear as if they had strayed into the adjacent lawn, hinting at an active thicket that might later colonize the entire area. From certain viewpoints, it still feels as if the place has been abandoned, as if the birches are growing randomly — but move a few feet further and the thicket’s linear massing is revealed again, reestablishing control. If the designing of ecology at Duisburg-Nord is based in actual ecological process, here at Tate Modern it’s a representation of ecology, evoking (but not recreating) an historical ecological process no longer active on the site.

Jardin des Étangs Gobert offers a third approach. Situated primarily inside a tank built by Thomas Gobert in the 17th century to provide water to the fountains of Versailles, the park is located at the terminus of Avenue de Sceaux, at a point where the geometry established by Le Nôtre syncs with the region’s natural topography as the line of Avenue de Sceaux encounters a hill, whose elevation was exploited to increase the volume and pressure of the fountains. Use of the water tank ceased relatively recently and it was drained and then colonized by a dense early successional forest — including a high percentage of Betula Betula. ³³ Because it was inside the tank, this growth was contained as a neat geometry.

Michel Desvigne is known for landscape designs that provide for visual massing and ecological function while remaining flexible enough to accommodate future adaptations — for instance, to allow for the construction of new buildings. ³⁴ At Jardin des Étangs Gobert, this model is reversed. Instead of plantings that will later be modified, Desvigne has modified and refined a birch thicket that had “planted” itself through seed dispersal and forest succession. ³⁵

The birch thicket creates an intimate, immersive atmosphere; visitors repose within sculpted disorder.

Unlike the stands at Duisburg-Nord and Tate Modern, the thicket at Jardin des Étangs Gobert has an accessible interior; Desvigne’s alteration of self-seeded growth involved carving a central clearing and cutting narrow pathways by which to reach it. On the lawn within the clearing, an irregular ring-shaped bench in white concrete, designed by Inessa Hansch, invites visitors to sit among the trees, chatting with friends while children run in circles.

There’s an important inversion at work here. Park visitors may of course look in toward the grass from the birch thicket, but the design clearly intends to position the viewer looking outward toward the trees from within the clearing. The thicket creates an intimate, immersive atmosphere, in which the white concrete of Hansch’s bench rhymes with the trees’ white bark. At the end of the perfect line drawn by Le Nôtre, visitors repose within sculpted disorder.

Birch Thickets and Representational Ecologies

These three projects demonstrate that, in limited forms at least, ecologies of chaos are increasingly accepted in the designed environment. But even ecologically sensitive design often remains wedded to views of nature as inherently balanced. ³⁶ As the ecologist Aaron M. Ellison has argued, the practice of ecology has not been entirely remade, despite a century of discourse that understands natural processes as open-ended.

Ellison published his argument in 2013, and perhaps this attachment to romantic notions of ecological order has shifted somewhat. Still, we should ask: to what degree can designed birch thickets truly help to alter popular conceptions of ecology and the natural world, to teach viewers to appreciate what looks unruly or accidental? Representational ecologies are easily critiqued as being just for show. Yet I think we are wrong to overlook the power of “merely” representational planting typologies. ³⁷ Birch thickets on designed sites have great potential as visual signifiers of often overlooked biological and ecological processes. Tree plantings in public spaces can persist for decades; they are durable, engaging forms that affect the meanings and values that visitors find and create.

At Duisburg-Nord, birch thickets have been given the space and time to spread, embracing the aleatory dynamics of seed dispersal. This makes Latz’s work the most literally ecological of the three projects discussed here, in that he embraces the real process of birch colonization, rather than planting birches in a pattern that recalls or symbolizes that process. Perhaps for this reason, however, the plantings in Germany are also the easiest to for park visitors to ignore. They look more or less like birch thickets growing on abandoned lots anywhere in the Northern Hemisphere. Elsewhere in the park, Latz attempted to draw a contrast between the spontaneous and the designed, using gridded tree plantings and geometric gardens. But in his approach to the birches, no mediated interaction — and hence no heightened awareness — is facilitated for park visitors.

The artificiality — the hypernature — of the thickets encourages visitors to experience ‘thicketness’ in a curated way.

In contrast, at Tate Modern, the birch thickets are purely representational, meaning that the patterning and density of their planting suggests seed dispersal and dense seedling growth without allowing those processes to play out. Yet Kienast Vogt has not evoked this ecology of spread in a shallow, greenwashing way. The artificiality — the hypernature — of the thickets encourages visitors to concentrate on their form, to experience “thicketness” in a curated way. There’s a link here to the riparian forests that probably did grow once along the Thames, a reminder that our built environment actively suppresses the ecological dynamics of a given site. This foregrounding of what used to be not only establishes contrasting forms, but refers to overlapping spatial histories, encouraging visitors to consider the ethical implications of what now exists.

The birch thicket at Jardin des Étangs Gobert falls somewhere in between. Birches existed on the site prior to its redesign, having spread as they wished. Yet, unlike Latz’s permissive strategy at Duisburg-Nord, Desvigne deliberately centers the dynamics of the thicket. Visitors could almost believe that the thicket had not been manipulated, yet Desvigne’s subtle editing, the carving of the lawn and bench, and the contrast between the thicket and the surrounding city undercut such naturalistic perceptions, soliciting active consideration of the thicket and why it’s there. Jardin des Étangs Gobert incorporates the environmentally sensitive use of existing trees, as at Duisburg-Nord, while heightening the thickets’ role as elements of a design, as at Tate Modern.

Essentially, representational plantings redraw baseline expectations. This might seem to be merely a question of how plantings “look.” But representational planting projects shift the cultural, political, and ethical context in which landscape designs are received by the public at large, and in so doing expand options for the implementation of genuinely functional plantings, i.e. those that involve less energy, less maintenance, and lower cost. An interest on the part of landscape architects in such sustainable approaches won’t be adequate over the long term; in order proliferate the use of chaotic-ecological design in public spaces, and to fund such projects on a much larger scale, more park-goers and taxpayers will need to understand and appreciate these kinds of landscapes. The curated, representational experiences described here — those that draw attention to unexpected form without being mimetic — can, somewhat paradoxically, help to intensify this public appetite.

Examples of next-generation “chaotic” design might entail planting thickets of saplings to reclaim brownfields or abandoned lots; permitting forest succession at suburban or urban sites in order to filter stormwater, or as part of restoration after hurricanes or floods; or seeding aggressive, patch-forming herbaceous plants and shrubs to address the unpredictable long-term dynamics of planned coastal retreat. Birch thickets and other representational plantings that help to reveal the ecology of chaos in action will not directly address the world’s ecological problems. But they can set the stage for planting strategies that will.