Ecosystems and Ecoregions
It’s not really fair to blame our ancestors for their lack of ecological awareness. At the time the plains were settled, “ecology” as we know it had not yet been invented. Instead, the science of the day was focused on fixing life to a pin, labeled and safely dead, with the species laid out in straight rows and separate compartments. (This passion for “still life” was given concrete expression in the natural-history collections of nineteenth-century museums, those great mausoleums filled with pressed plants, dried skins, stuffed birds, and mounted insects—among them, many thousands of specimens from North American grasslands.) The conception of life as a tumultuous interaction between organisms and the world around them was of no great interest to a science that was largely content to follow in the footsteps of Linnaeus, collecting things and classifying them.
But on the fringes of science, new ideas had begun to stir. In 1866, for example, an eccentric German physician-turned-philosopher named Ernst Haeckel cobbled together two Greek roots—oikos, meaning “household,” and olgie, or “study of”—to describe a radical new approach to life science, ecology. Drawing his inspiration from Charles Darwin’s still-recent discovery that organisms are shaped by the environments in which they evolve, Haeckel described his new endeavor as the study of natural selection in action. It was, he said, “the investigation of the total relations of the animal both to its inorganic and organic environment,” including its relationships, whether “friendly” or competitive, direct or indirect, with all the other organisms in its surroundings. The essence of life, he hinted, lay not in a static array of species in a collector’s cabinet but in this wonderfully tangled web of interconnections.
By late summer, big bluestem—the characteristic grass of tall grasslands— often waves above the wild flowers, like the goldenrod seen here, and reaches into the lower branches of bur oaks and other trees.
This was a heady idea, more poetry than science, and for a long time, no one could figure out how to develop it any further. In the end, it took a pioneering biologist from Nebraska by the name of Frederic Clements to ground the new field in observation and hands-on evidence. With the native vegetation under assault all around him, Clements focused his attention on the ability of the wild prairie to recover after it had been burned over, plowed up, dried out, or otherwise disrupted. In a study published in 1916, he concluded that the prairie was a self-healing system in which, given the chance, groups of plants grew back in an orderly sequence, each wave creating the conditions required by the next, until the vegetation reached a stable configuration, or “climax.” Based on his observations, Clements proposed that not only the Great Plains grasslands but the entire living world was sustained by these self-organized, internally motivated processes of renewal.
Clements’s prairie-inspired theory of “community succession” made a stir in the intellectual capitals of the world. And it was there, in London, England, that his intuitions were eventually brought to a new stage of development. The concept of the “ecosystem”—the idea that the Earth operates as a series of self-organized complexes in which all components (both living and nonliving) are linked—was first advanced by British ecologist Arthur Tansley in 1935, in a self-conscious attempt to marry the study of nature with advances in math and systems theory. Suddenly, the young-and-still-somewhat-woolly-headed science of ecology, which had heretofore made do with hazy notions of “relationships” and “community,” could gird itself in the vocabulary of the physical sciences. Instead of a bewildering clutter of sensations, the living world had become a “complex, adaptive, open, nonlinear system,” complete with “feedbacks” and thermodynamic “fluxes.”
Yet for all this new exactitude (which has served the science well), the idea of the ecosystem has proven reassuringly resistant to precise definition. As Tansley himself acknowledged, “the systems we isolate mentally are not only included as parts of larger ones, but they also overlap, interlock and interact with one another.” The task of charting these overlapping and fluid realities— of acknowledging the differences between particular localities without denying their interconnectedness—remains a major preoccupation of ecologists. It is a challenge that, over the last thirty years, has inspired a continent-wide spree of “ecological land classification” and mapping. At its heart, this is an attempt to see beyond the human impacts of the last few centuries and uncover the enduring components of the environment (climate, soils, landforms, vegetation, and so on) that make one part of the continent biologically different from the next. Although we cannot go back in time and view the wild prairie in full bloom, we can attempt to identify and assess the factors that, over the long term, made them what they are or, at least, what they once were.
Ecological mapping began in the 1960s and 1970s as a relatively straightforward attempt to examine the relationship between natural vegetation and climate. Nowadays, however, with satellites to assist with mapping and computers to do the grunt work, the possibilities have spiraled. Instead of being limited to single variables, researchers can now consider the interplay among dozens of different ecological components all at once, factoring in everything from climate to geology, hydrology, physiography, soil chemistry, vegetation, species diversity, and where relevant, human effects on the environment. Yet even at this high pitch of sophistication, scientists have not been able to pin the living world neatly to the wall, sure that they have mapped its subtleties once and for all.
Rough fescue
Over the last decade, the ecological regions of the Great Plains have been mapped in different ways by different agencies, whether in broad strokes as part of continentwide research or more minutely, state by state and province by province. One result of this effort is a set of maps created under the joint authorship of the World Wildlife Fund Canada and its counterpart in the United States, the wwf–U.S. Seen through the lens of these organizations, the Great Plains grasslands come into focus as a mosaic of fifteen eco-regions. The Aspen Parklands ecoregion, for example, lies across the midriff of the Prairie provinces (Alberta, Saskatchewan, and Manitoba) and provides an interface between the boreal forest and the open plains. Rising in the north as a closed poplar woodland with occasional stands of spruce, it gradually unfolds into a rolling grassland dotted with aspen groves and dominated by various spear-grasses, wheatgrasses, and most notably, fescues.
Because of the predominance of fescues in the Aspen Parklands, the region is sometimes known as a fescue grassland. The same term is also applied, for the same reason, to the community of plants found in the Foothills Grasslands. Located on the undulating slopes at the foot of the Rocky Mountains, this ecoregion is dominated by rough fescue, together with lesser quantities of June grass, speargrass, wheatgrass, and various flowers and shrubs.
East of the foothills and south of the Aspen Parklands lie two ecoregions with subtly different characteristics. The Northern Mixed Grasslands takes its name both from its northerly location and from its characteristic mixed— which is to say, mixed-height—cover of grasses. Here, the sparse, tufted vegetation of the foothills gives way to a groundcover of ankle-high grasses, notably blue grama, intermixed with an overarching canopy of knee-high stands, including various spear- and wheatgrasses. As this mixed grassland flows southward, the canopy of taller, midheight grasses gradually thins out, and the overall height of the vegetation diminishes. This transition from mixed-to short-grass prairie continues to the south in the Northwestern Short/Mixed Grasslands ecoregion.
Subtle variations in soil, precipitation, drainage, and growing season determine which species of plants thrive in different regions of the Great Plains. The mixed grasslands of southern Saskatchewan, for
