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Summary

Introduction

This chapter is organized as follows. The basic concepts are introduced in Section 8.2. Experimental results about intermittency in the inertial range, based on velocity measurements, are presented in Section 8.3. Exact results, independent of any phenomenology, are presented in Section 8.4. Two broad classes of phenomenological models of intermittency are then discussed. In the first class (Section 8.5), intermittency is studied via velocity increments. It comprises the β-model (Section 8.5.1), the bifractal model (Section 8.5.2) and the multifractal model (Sections 8.5.3 and 8.5.4). Implications of the multifractal model for the dissipation range and for the skewness and flatness of velocity derivatives are presented in Sections 8.5.5 and 8.5.6, respectively. In the second class (Section 8.6), intermittency is studied via the fluctuation of the dissipation; inertial-range quantities are related to such fluctuations by a bridging ansatz, originally introduced by Obukhov and Kolmogorov (Section 8.6.2). Random cascade models are presented in Section 8.6.3; their multifractal behavior is shown to be a direct consequence of the probabilistic theory of ‘large deviations’, which is presented in an elementary fashion in Section 8.6.4. The lognormal model and its shortcomings are discussed in Section 8.6.5. Shell models, a class of deterministic nonlinear models which can display intermittency, are presented in Section 8.7.

The order chosen here for the presentation of the entire material on the theory of intermittency is pedagogical, not historical. Most of the latter aspects are discussed in Section 8.8. Recent trends in intermittency research are presented in Section 8.9.

Summary

Rivers … are the natural highways of all nations, not only leveling the ground and removing obstacles from the path of the traveller, quenching his thirst and bearing him on their bosoms, but conducting him through the most interesting scenery, the most populous portions of the globe, and where the animal and vegetable kingdoms attain their greatest perfection.

Henry David Thoreau, A Week on the Concord and Merrimack Rivers, 1849

A stream or river corridor is a strip of vegetation that encloses a channel with flowing water. The corridor may only include the channel and its adjacent banks, or may be wide enough to include a floodplain, hillslopes, and adjacent strips of upland. The focus here is not on the stream or river, nor on the network qualities of a river system, nor on the whole drainage basin, though general aspects of these are included. Rather, the emphasis is on the vegetation corridor, its components, functioning, and dynamics. Riparian corridor or vegetation generally refers to the floodplain portion of a stream or river corridor, although the concept sometimes is considered synonymous with stream or river corridor.130

Landscape urologists, to use a medical analogy, can fill a bottle with stream or river water, analyze its contents, and tell much about the health of the landscape. Natural processes produce water that may be considered a control. Human activities, either directly in the corridor, or indirectly in the surrounding basin, alter the water in numerous telltale ways. A busy urologist, quietly filling bottles in many channels, can both locate and identify most human activities affecting the landscape.

River corridors are so important to people that every component of society has its hand in the corridor. Its water is extracted for irrigation and drinking supplies. Water flow is altered for flood control, transportation, and hydroelectric dams that generate power. Wastes are carried away in this sewer of society. Fish and fishermen duel in the water. Recreation and aesthetics are enhanced with corridors. Sediments and mineral nutrients are absorbed, and move down the corridor. Beaver, livestock, and other large mammals alter its anatomy. Biodiversity and many rare wetland species are protected here. Agriculture, forestry, roads, and buildings are often rampant in river corridors. Like all corridors, width and connectivity are keys to each of these societal roles.

Summary

These farms which I myself surveyed, these bounds which I have set up, appear dimly still as through a mist; but they have no chemistry to fix them … The world with which we are commonly acquainted leaves no trace, and it will have no anniversary.

Henry David Thoreau, Walking, 1862

Since the onset of agriculture, woody strips have spread to become the most conspicuous feature in many landscapes. Thus, the noted British ecologist, Charles Elton, observed (1958) that, ‘our own highly managed landscape is still interlaced with a wonderful network of hedgerows and roadside verges. These long winding strips of habitat by the road and land and field margins are the last really big remaining reserve we have’

Hedgerows were originally created to keep livestock in a field, or to exclude livestock or wild herbivores from a field. Woody strips were used to clearly delineate boundaries. And windbreaks provided protection against wind, as well as defense against marauding humans.

In contrast to trough corridors (chapter 5), woody strips have a canopy higher than the surroundings, and include windbreaks, hedgerows, and woodland corridors. Windbreaks or shelterbelts are planted to protect against wind. Hedgerows are narrow line corridors up to a few tree or shrub diameters in width that separate open areas. The term hedgerow is used in a generic sense to include examples produced by any mechanism, such as fencerows, planted hedges, and remnant lines of trees (see glossary in chapter 1 appendix). Woodland corridors are wider strips composed of natural vegetation. All wooded strips are of anthropogenic (human) origin, either directly planted or resulting from human activities on adjacent sides. Most are relatively straight, narrow, and costly to maintain. ‘Greenways’ that support recreation are included in this chapter, but ‘roadside natural strips’ are described in chapter 5, and stream and river corridors in chapter 7.

Woods may produce wood products, but other economic and ecological values normally are more important. Gifford Pinchot, America's pioneering forester, pointed this out in 1905: ‘Not only does [the forest] sustain and regulate the streams, moderate the winds, and beautify the land, but it also supplies wood’ Thus, windbreaks are planted to reduce soil erosion, catch and hold snow, provide soil moisture in steppe areas, protect crops from desiccation, protect livestock, and reduce home energy costs.

Summary

But when I consider that the nobler animals have been exterminated here - the cougar, panther, lynx, wolverine, wolf, bear, moose, deer, the beaver, the turkey, etc., etc. - I cannot but feel as if I lived in a tamed, and as it were, emasculated country … I listen to a concert in which so many parts are wanting … for instance, thinking that I have here the entire poem, and then, to my chagrin, I hear that it is but an imperfect copy that I possess and have read, that my ancestors have torn out many of the first leaves and grandest passages …

Henry David Thoreau, Journal, 1856

Robert Burns’ classic description of change as ‘Nature's mighty law; reminds us that whatever humans do, it is set within a changing land driven by natural processes. Furthermore, change, whether natural or human induced, is the norm. Short static or equilibrium phases are common within the broad dynamics. But persistent static phases are the exception, and they never persist indefinitely.

The preceding chapters have explored the structural patterns and functional flows of mosaics during a static phase. This was useful for explanation, but in this and the following chapters we focus explicitly on the changing landscape or region. This chapter examines change driven by natural processes or by mainly unplanned human activities. The subsequent two chapters focus on change where human planning is also important.

The subject of land transformation and fragmentation is significant to all human issues that involve land. Wise forestry, economics, biodiversity conservation, agriculture, landscape architecture, sociology, wildlife biology, soil science, and so forth explicitly recognize and deal with a dynamic land. These dynamics also characterize finer and broader scales, albeit at different rates, including succession within a patch1233,1029 and global climate change.1413,1158

Many of the ideas and syntheses in this chapter were developed jointly with George F. Peterken; indeed, he is almost a coauthor of chapter 12. No overall review of the subject of this chapter exists. However, individual topics are reviewed as follows: fragmentation225,683,1793,1536,39; spatial processes683,501,1742,661; and geometric modeling of mosaic sequences.518

Chapter 1 introduced the concepts of patch mosaic dynamics and landscape change.

Summary

In our most trivial walks, we are constantly, though unconsciously, steering like pilots by certain well-known beacons and headlands, and if we go beyond our usual course we still carry in our minds the bearing of some neighboring cape; and not till we are completely lost … do we begin to find ourselves, and realize where we are and the infinite extent of our relations.

Henry David Thoreau, Walden, 1854

Dragons have played a key role in history and now are nearly extinct. This keystone species (or guild of species) apparently had population centers at least in Ethiopia, northern Europe, and China.738 The large ugly scaly reptile-relatives generally lived in deep caves, lakes, or rivers, and foraged singly across landscapes, both on the ground and in the air. They were attracted to virgins in distress, and repelled by heroes with swords. Chinese dragons were frightened by iron, centipedes, wax, leaves of the lien tree (Melia), and other objects. Populations fluctuated, with sighting records in Europe higher during the Middle Ages, in the seventeenth century when classification treatises were published, and in the nineteenth century when Darwin's evolutionary theory suggested relationships with known dinosaurs, such as pterodactyls. With increased human population and technologies including satellite images, remote habitats have decreased and dragon populations crashed. Most recent sighting reports have been of Chinese dragons, in areas where the species has traditionally received generosity and respect. But alas, too little information is available on how dinosaurs and these mythological dragons used pattern in moving across a landscape or region, the subject of this chapter. Therefore we must learn from movements of today's less fearsome animals and plants.

The subject of species movement at this scale is critical in many arenas. Conserving biodiversity depends primarily on landscape and regional pattern. Forest regeneration in most regions depends on seed dispersal. Invasions of exotic species are inhibited or enhanced by landscape pattern. Plagues of insects or herds of herbivores attack crop fields one after another. And migratory fish move long distances through heterogeneous river systems.

This chapter, along with the preceding one, is about movement across mosaics. It assumes familiarity with concepts in chapters 2, 3, 5, 8 and 9. Indeed, chapter 8 considers the resistance to species movement by a landscape, and chapter 9 examines species movement in mountains.

Summary

Thus from generation to generation it goes bounding over lakes and woods and mountains … sailing … on various tacks until the wind lulls, to plant their race in new localities - who can tell how many miles away? … And for this end these silken streamers have been perfecting themselves all summer, snugly packed in this light chest, a perfect adaptation to this end - a prophecy not only of the fall, but of future springs.

Henry David Thoreau, The Dispersion of Seeds, 1862

Weather always seems to come from somewhere else. Storms, cold fronts, and dry air, produced by energy and water flows in adjacent or distant regions, keep rolling in. We, along with vegetation and animals, get frozen, broiled, desiccated and drenched. But the circulating air brings more than heat and water. Air-borne particles increase rain just downwind of most cities. Sulfur oxides and heavy metals from factories damage vegetation in a downwind plume. Dust from cultivated fields filters through the cracks of far-off houses.

Weather and climate also depend on the internal characteristics of a landscape. The arrangement of land uses and the contrasts between adjacent ecosystems in the landscape help create or sustain flows of energy, water, and air. In short, both flows from outside and pattern within determine the wind and water flows in mosaics.

The objective of this chapter is not to learn meteorology or global cycles, though bits of them are introduced. Rather, after eight chapters primarily exploring spatial pattern and its ecological significance, this is the leadoff chapter with principles focusing on flows, movements, and changes in the land mosaic.

The principles in this chapter are a key to spatial planning, management, and conservation, because of the extensive flows among local ecosystems in a land mosaic. Plans and management schemes must highlight not only adjacencies (chapter 9), but sources and sinks at varying distances. Upwind and upslope sources of heat, water, and pollutants are highly significant in, for example, suburban development, nature reserve protection, crop growth, and forest production. Downwind and downslope sinks at various distances also affect the ecological characteristics of an ecosystem or land use.

Summary

Virtually all the great questions of our time involve land. I rank the following near the top. Can we reduce the number of mushrooming megacities, environmental refugees, and regional wars? As human linkages to the land are severed, can we discover a way to rewrap humans and nature? Can biodiversity be protected? What is lost when civilization converts the soft curves of nature to the hard lines of geometry? Can we shift our attention from the local site or ecosystem to the whole landscape or region soon enough to reverse cascading degradation? Since space on the planet is finite and few will be global managers, is regional decision-making the key to global protection? Is there a way to accelerate sustainable thinking at the time scale of human generations. All wise answers have roots in landscape and regional ecology.

The perspective in this book is captured by adding the following two middle lines to words in a classical Chinese verse (At Heron Lodge, by Wang Chih-huan, Tang Dynasty, 618-906; Bynner & Kiang 1929).

Summary

In the cloistered tradition of scientific specialization, most ecologists think of the world narrowly, as a system of natural environments beleaguered by human activity. They live, as Aldo Leopold put it, in a world of wounds. They have reason to think this way. Today, less than 10% of the land surface remains in a mostly unchanged state, and only 4% has been set aside in natural reserves. In their own specialty, planners and landscape designers tend to stay in their larger and wholly different world. For them, the bulk of the land has been given over to humanity; and now, they say, people must redesign it to their liking.

Neither view, taken to exclusion of the other, is viable any longer. Ecologists increasingly recognize that they must extend their science to embrace artifactual environments. More reflective planners and landscape designers understand that they cannot afford to ignore organisms - the right organisms - needed to sustain a healthy, pleasing environment. A few scholars, of which Richard Forman is a notable example, have come to focus on the intellectually rich domain of overlap between the two fields. The result of their deliberate intermediacy is the new discipline of landscape ecology.

In Land Mosaics, Forman joyously embraces the human-altered environment and proposes that its living part can be improved by use of the best principles of environmental biology. He recognizes, as the book's title implies, that the real world consists of finely fragmented habitats. The pieces range from radically altered urban parks and gardens to remnant pockets of the original environment. Across periods as short as a few years, living species arrive, impinge, dominate, yield, and disappear in this kaleidoscope. The vast majority of the inhabitants we never see, because they are too small and obscure: creepy-crawlies, immense in diversity, from insects to fungi and bacteria. All together, they are as important as the towering trees and the birds on which our attention is ordinarily focused. The species that can survive in the habitat fragments come together to determine the health and beauty of the places in which we live.

Forman and other scientifically educated landscape ecologists address the question: ‘Given that humanity is now in charge of most of the land surface, and responsible for it, what designs of the terrestrial landscape are best for the rest of life, and therefore for us?'

Summary

There is something indescribably inspiriting and beautiful in the aspect of the forest skirting and occasionally jutting into the midst of new towns … Our lives need the relief of such a background, where the pine flourishes and the jay still screams.

Henry David Thoreau, A Week on the Concord and Merrimack Rivers, 1849

Artists and photographers use contrast to create stunning images. High contrast is attained by accentuating the difference between adjacent areas, and by sharpening the boundary. This chapter focuses on the myriad types of boundaries that separate ecosystems or land uses in a landscape (Fig. 3.1).

Of what use are these boundaries within a landscape? In wildlife management edges typically have an abundance of game and other animals that move along or across boundaries. In questions of biodiversity and land fragmentation, the ratio of edge to interior habitat is critical. In aesthetics, views are often dominated by edges. In forestry, edges are commonly characterized by crooked trunks and blowdowns. In agriculture, edges are often the source of pests, as well as predators controlling pests. In soil erosion control, boundaries cause wind speed changes and turbulence. In park and nature reserve management, boundaries may be barriers to human overuse. In detecting global climatic change, boundaries are often proposed as a sensitive indicator, the ‘canary in the mine'. And in sustainability issues, humans are edge species, but by carving up the land and increasing edges enormously, we eliminate the key values of large patches, thus degrading our landscapes.

Useful literature reviews are available for boundary ecology as a whole (Holland et al. 1991, Hansen & di Castri 1992), as well as for ecotones360,1769,403 and the edge effect as related to biodiversity and wildlife.1700,684,1941 Boundaries between land and water are analyzed in chapter 7.

The present chapter begins with the structure of boundaries, and the developmental mechanisms controlling them. Next, functions are presented, including the edge effect and movements and flows across boundaries. Width and curvilinearity are examined as major variables affecting both anatomy and flows. Finally we explore boundaries moving on the land.

TYPES AND ABRUPTNESS

Boundary types and theory

In chapter 1 we noted that introducing energy causes a system, such as a landscape, to become spatially heterogeneous in one of two ways.503

Summary

We have an account in the newspapers of every cow and calf that is run over, but not of the various wild creatures … It may be many generations before the partridges learn to give the cars a sufficiently wide berth.

Henry David Thoreau, Journal, 1858

Nature creates corridors in the form of streams, ridges, and animal trails. Humans create roads, powerlines, ditches, and walking trails. How do the two types differ? Nature's are curvy, until humans straighten them. Nature's are continuous until humans superimpose grids on them, and create gaps. Human corridors are generally narrow and costly to maintain.

Corridors, as strips that differ from their surroundings, permeate the land. Vegetation corridors contribute significantly to many goals of society, here lumped into six categories.491 First, corridors provide biodiversity protection, including key riparian habitats, rare and endangered species, wide-ranging species, and dispersal routes for recolonization following local extinction. Second, corridors enhance water resource management, such as flood control, control of sedimentation, reservoir capacity, clean water, sustainable fish populations, and fishing. Third, linear strips may enhance agroforestry production by acting as windbreaks for crops and livestock, controlling soil erosion, providing wood products, and preventing desertification. Fourth, recreation in corridors includes game management, wildlife conservation for nature enjoyment, and hiking, bicycling, boating, and skiing in suburban greenbelts. Fifth, community and cultural cohesion may be enhanced with greenbelts, which create neighborhood identity, provide wildlife corridors crossing roads that concurrently inhibit strip (ribbon) development along a road, and function as regional topographic barriers that enhance cultural diversity. Sixth, corridors provide dispersal routes for species

isolated in nature reserves, and coastal strips threatened by rising sea level in the event of climatic change.

Useful reviews of corridor attributes are given by Forman & Godron

(1986), Schreiber (1988), Brandie et al (1988), Bennett (1990a, 1991),

Saunders & Hobbs (1991), Forman (1991), Malanson (1993), and

Smith & Hellmund (1993). Reviews of specific topics include the corridor

as a conduit685,688,1228, the corridor as a filter174,1038,130, road and roadside

vegetation109,111,1492, and trails.968,1842

Windbreaks, hedgerows, and wooded strips are presented in chapter 6, and stream and river corridors in chapter 7. Corridors are also commonly interconnected to form networks, as explored in chapter 8.

This chapter begins with general patterns and principles that apply to virtually all corridors.

Summary

Only when the city, the hamlet, or the cottage is viewed from a distance does man's life seem in harmony with the universe … The sunlight on cities at a distance is a deceptive beauty, but foretells the final harmony of man with Nature.

Henry David Thoreau, Journal, 1841

Dreams of Utopia have sparked the establishment of communities in every century. Social, political, or religious fervor and commitment have created such communities, especially in rural landscapes. Yet rather few of these experiments have lasted a century. At the other extreme are civilizations and societies that have continued for centuries and even millennia (Fig. 14.1). In all cases success or failure depends both on human dimensions and the land.

Two central components of sustainability are thus introduced. The time frame is over human generations, and the key characteristic is a dynamic with equal emphasis on human and environmental dimensions. The preceding chapter on land planning and management elucidated principles based on this combination of land processes and human resource use. But the time scale was years (or up to a few decades), the normal framework for planning, design, conservation, management, and policy. The difference in time scale is the primary characteristic separating sustainability from normal year-to-year planning. For planning over human generations, if we are to learn from history, the most instructive history is of human-land interactions over two or more centuries.286

Most sustainability literature focuses on the globe.1414,286,1929,768 Only a few countries have begun seriously addressing the implications of sustainability.434,1002,1431,476,778 Although this chapter touches on the built environment, the idea of sustainable urban development is not directly addressed. However, agriculture, economics, forestry, fisheries, sociology, and more recently ecology have taken a particular interest in sustainability, often considering it within their own disciplines. Surprisingly, the role of spatial arrangement of land is commonly overlooked.. Little literature on sustainability exists at the landscape and regional scales.492 Yet these scales may be the most important for attaining sustainability.

This chapter assumes general familiarity with principles in most preceding

chapters; indeed many points will otherwise be unclear or counterintuitive.

The chapter begins with the basic concepts of sustainability.

It then focuses in detail on key sustainability attributes, organized by

time, space, humans, assays, and adaptability. Next, we learn from

human histories, and briefly revisit regional ecology.

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CHAPTER 8 - Intermittency

Summary

Part V - Changing Mosaics

Frontmatter

References and author index

7 - Stream and River Corridors

Summary

Part III - Corridors

4 - Patch Shape

6 - Windbreaks, Hedgerows, and Woodland Corridors

Summary

12 - Land transformation and fragmentation

Summary

11 - Species movement in mosaics

Summary

Part II - Patches

Part I - Landscapes and Regions

10 - Wind and Water Flows in Mosaics

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Preface

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Foreword page

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3 - Boundaries and Edges

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5 - Corridor Attributes, Roads, and Powerlines

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14 - Creating sustainable environments

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Part IV - Mosaics and Flows

Dedication

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