Ariel E. Lugo
Introduction
The forestry profession should benefit from current world trends because they provide strong justification for forest management. Examples of world trends that justify increased attention to forest management are:
Foresters will be the white knights of the 21st century because they have to resolve the dilemma of having to attain increasing yields and services from a shrinking natural resource base. Unfortunately, the search of solutions to the problems of forest land management often bypasses forestry. In most tropical countries, and even in the United States, sectors of society other than forestry are taking over the job of developing and implementing resource use policies. Foresters are being replaced by a variety of other disciplines from academia, the private sector, and government. The forestry profession is wrongfully associated with those who exploit timber at the expense of other forest values. The profession needs to react to the changes taking place in the world today by articulating with greater vigor and elegance the relevance of forest management to modern society.
We are in a period of transition and learning that requires greater attention to research and science excellence. This in itself is a challenge, because the scientific community finds itself in the same situation facing the forestry profession. In addition, scientists must deal with the difficulty that lay people have in understanding science. Lay people also do not relate to the scientific method, the long-term lag between research and application, and the apparent irrelevancy of much of the basic science that underpins resource management and technological applications. The challenge facing forest management and forestry research at the turn of the new millennium is doubly difficult. Both have to show relevancy in a complicated world situation where success requires the reduction of the time gap between research and application. Long rotation times in forestry compound the problem. However, the need to articulate the value of science to an increasingly incredulous public is not to be done at the expense of the quality of science. Similarly, the need to articulate the relevancy of forest management is not to be done at the expense of excellence in land management.
Ecosystem Management
To effectively address the changing world situation, forestry must embrace ecosystem management and effectively articulate what ecosystem management is, and what it is not (cf. Ecosystem management: will it work? Journal of Forestry 92(8): 1994, Stanley 1995). Part of the difficulty in doing this is the lack of a unified understanding of ecological terminology and the paradigms that constitute ecosystem management. Even the term ecosystem is defined differently by different people (discussed below). Moreover, there is still a debate about the relevancy of ecology to environmental management (cf. Shrader-Frechette and McCoy 1994).
Ecosystem management is different from other forest management approaches in the scope and profundity of analysis done before interventions on the ground. Under ecosystem management, ground interventions continue to involve the same techniques used traditionally in forestry by its many disciplines. However, comprehensive analysis determines what techniques to use, where and when to use them, the suitable mix of technological tools, and the intensity of applications. Such analysis is at the core of what ecosystem management is.
I defined ecosystem management as "using holistic analysis to [guide the management of] lands and water for products, services, and conservation of biodiversity" (Lugo 1994). This definition has several features that deserve explanation. First, the definition recognizes that the holistic aspect of ecosystem management occurs at the analysis or planning stage. The actual management actions can be quite specific in their application, as already stated. Second, the definition includes both land and water as the targets of management as is now done in watershed forestry. The atmospheric system is explicitly excluded from the analysis. The reason is that we do not intervene directly with the atmosphere. Cloud seeding is an exception. Humans alter the atmosphere with pollution but mitigate these actions by modifying emissions or through the management of terrestrial or aquatic systems.
Third, the definition states that the purpose of ecosystem management is the acquisition of products and services while conserving biodiversity. Products and services are part of the objective of management because people of all social strata and cultural origin will always demand them. The reason we manage is to satisfy legitimate human needs. The conservation of biodiversity is the ecological constraint on the extraction of products and services. This constraint ensures the sustainability of management actions. However, by conserving biodiversity I do not mean maximizing complexity nor do I exclude simplification of stands to achieve maximum net productivity. Intensive management activities have a place in ecosystem management and fit in time and space without causing irreversible changes in biodiversity.
Holistic Analysis:
What Does it Encompass?
Holistic analysis of ecosystems depends on evolving ecological paradigms (Table 1). Individually, some of these paradigms are not new, but when combined, they lead to a management style that is different from traditional approaches. Some of these paradigms are still developing and lack full acceptance by ecologists or resource managers. As a result, we are in a period of transition where old, new, and evolving paradigms are competing for attention. Such a situation can lead to great innovation but it can also lead to confusion, paralysis, temporary dead ends, and even to retrogressive actions. It is thus important to recognize and understand the changes in ecological theory that are driving the change in paradigms of forest management.
This ambivalence is certain to be frustrating to forest managers used to empirical approaches that appear to accomplish their objectives. While we must not change proven management styles for the sake of change, we must recognize that the changing social and ecological context under which forestry operates is demanding the changes that ecosystem management addresses. For this reason we must operate under an adaptive management mode in which we do things, monitor the results, learn lessons from experience, and adapt to the new conditions through planning and reiteration. This allows room for innovation without sacrifying ongoing activities.
Odum (1971, 1983, 1989), Odum and Odum (1987), Savoy (1988), Holling et al. (1995), and Botkin (1990) discuss holistic approaches to ecosystem management. Holistic approaches are those that move outward in the hierarchy of functional complexity and turnover time (Figure 1a). They seek understanding of natural phenomena from an "outside" perspective. Holism seeks to understand how forces originating at higher and lower levels of a hierarchy drive a given level of biotic organization. Reductionism moves inward in the hierarchy of functional complexity. It seeks understanding of natural phenomena from an "inside" perspective. Reductionism seeks to understand how internal forces drive biotic organization. The dictum of systems science that a system is more then the sum of its parts is a summary of holism. The corresponding dictum for reductionism is that a system is the sum of its parts.
Holism and reductionism are both needed to gain a comprehensive understanding of how the world function. However, ecosystem management has to be holistic because its focus is the ecosystem. Ecosystem management addresses ecosystem components by manipulating the systems to which they belong rather than the ecosystem component individually.
The Term Ecosystem
The common use of the term `ecosystem' is a barrier to the implementation of ecosystem management. Some people view ecosystems as physical entities, i.e. plant or animal communities. Others view ecosystems as something more complex than a community, i.e. the community plus its physical environment. Still others use the term to refer to any sector of the biota, i.e. a city, a forest, or a lawn. In 1935, Tansley introduced the idea of the `ecosystem' as a functional unit with arbitrary physical boundaries (McIntosh 1985, Odum 1971). Francis C. Evans (1956) argued that the ecosystem was a basic unit of ecology and made the following comments about what the term meant:
"In its fundamental aspects, an ecosystem involves the circulation, transformation, and accumulation of energy and matter through the medium of living things and their activities."
As defined, ecosystems lack predetermined boundaries. Its spatial and temporal boundaries are arbitrary. One can make any portion of the Earth an ecosystem, from a drop of water to a continent or an ocean. In fact, the Earth is an ecosystem (spaceship Earth). There are all possible combinations of ecosystem sizes between these extremes. For this reason, I do not include the `ecosystem' in the biological hierarchy of Figure 1a.
The ecosystem encompasses the full spectrum of biotic systems beyond the population level. Once anybody identifies the artificial boundaries of a particular ecosystem, it is possible to refer to that ecosystem as if it had spatial and temporal limits. Examples would be: the temperate forest ecosystem or the Harvard Forest ecosystem. Such a system can be studied or managed with certain precautions. The main precaution is the monitoring of all the inputs and outputs across the boundaries of the system. This facilitates understanding the function of the ecosystem. Examples of fluxes across boundaries would be populations of organisms, propagules, water, nutrients, gases, etc.
The difference between the formal definition and the common use of a fundamental idea such as `ecosystem', illustrates the significance of the problems caused by the changing paradigms in ecology and forestry. If there is misuse or misunderstanding of paradigms, management solutions will not be effective because there will be misdirection in the applications and the response of ecosystems. The change in ecological paradigms requires those interested in ecosystem management to think of ecosystem functions and to understand the relation between function and the physical boundary of the biotic system.
The subject under discussion raises a number of scientific challenges. These include: (1) the determination of the various scales of complexity at which biotic functions occur, (2) the identification of the properties and functions of different levels of complexity, (3) the interlinking between different hierarchical levels, and (4) their relevance to management actions. Here, I briefly review four areas of research that illustrate some of the changes in paradigms taking place in ecology and their importance to the success of ecosystem management.
Figure 1. (a) A hierarchy of biotic organization along scales of functional complexity and time. The size of the circles and their location along the time and functional complexity scales are arbitrary. (b) The relationship between biotic hierarchies and other hierarchies commonly used for management or planning purposes (cf. Table 2). Ecosystem classification, study, and management should be organized around the biotic hierarchies to target ecosystem management actions to the units of function. Care is needed when using size or other types of hierarchies that are not based on biotic units of organization.
Size and Function in Hierarchies
We know the biosphere functions as a living system within clear planetary limits. We also recognize functional entities at the individual organism and population levels of complexity. Most of the research effort in ecology concerns these two levels of biotic organization. Beyond these obvious examples, we lack understanding of how to define other living hierarchies of the world, how they function, and how to manage them. Successful ecosystem management requires understanding of all scales in the hierarchy of biotic function.
Better understanding of the hierarchies of time and space contributes to more successful environmental management (Beyers and Odum 1993, Magnuson 1990, Morrison et al. 1982, Odum 1983, Swanson and Sparks 1990). However, hierarchies of time and space can be different from hierarchies of biotic function. An example is watersheds, which are well-defined hydrologic systems that function and are managed as units. However, watersheds can be of any size, from less than a hectare to continental scale. Watersheds are not biologically homogeneous as they can contain a diverse array of different biological units, i.e., different plant associations in different climatic life zones or with different edaphic conditions. In short, watersheds can be hydrological or size units but are not biotic units of organization.
| ECS Level | Typical size | Map scale | ECS group | Used for |
| Subregion | Two or more states | 1:4 million | ||
| Province | Multistate - thousands of square miles | 1:2 million - 1:4 million | Upper levels | National planning |
| Section | Thousand of square miles | 1:1 million - 1:5 million | ||
| Subsection | Hundreds of square miles | 1:120,000 - 1:500,000 | ||
| Landtype Association | 1 to 10's of square miles | 1:32,000 - 1:250,000 | Intermediate levels | Forest planning |
| Ecological Landtype | 1/10 to 1 square miles | 1:15,840 - 1:60,000 | ||
| Landtype Phase | 6 to 64 acres | 1: 7,500 - 1:15,840 | Lower levels | Project planning |
| Site | A point usually less than 6 acres | Less than 1:6,000 |
Figure 1a illustrates the idea of time and functional complexity hierarchies applied to biotic units of organization. Each level of organization has a unique position in the hierarchy, and has a unique function. Moreover, each level of complexity has functional continuity with the level below and the level above the hierarchy. Each level of organization requires specific management actions. These hierarchical organizations have order, control, and homeostasis (Beyers and Odum 1993, Odum 1983).
However, there is a potential pitfall in the identification of hierarchies for ecosystem management. Planners, managers, and scientists use a variety of hierarchical classifications to address issues of land management (cf. Table 2). These classifications are usually defined by preconceived size units. Figure 1b shows that hierarchies based on biotic organization do not coincide with those based on arbitrary size units. The advantage of hierarchies based on size is that they conform to the realities of political or managerial boundaries of property. However, defining hierarchies by size criteria presents a problem to ecosystem management because the units of management may not have biotic or ecological meaning. The problem is that different scales of biotic function or organization are mixed together in a management unit. Such a mixture can lead to less than optimal management results because each level of biotic organization has its unique characteristics and management responses to specific treatments. Mixing different biotic scales into a single size category can result in contradictory responses to treatments.
Ideally, the units of ecological classification and management should closely approach the units of biotic organization. The reason is that the focus of ecosystem management is usually the biotic system, i.e., trees, animals, microbes, forests, etc. Management interventions should be more effective if they closely meet with biotic phenomena. The scientific challenge is the identification and understanding of biological hierarchies beyond the population level and up to the global level.
Disturbances
After the identification of the proper hierarchy, another scientific challenge is understanding hierarchical response to disturbance. A disturbance is a perturbation to any state variable or flux of an ecosystem by any force external to the ecosystem. Disturbances drain or transfer mass and energy from one sector of the ecosystem to another. A disturbance is a stressor sensu Lugo (1978), but the term underscores the periodic occurrence of the stressing effect. Disturbances can be natural such as hurricanes, fires, and insect or disease outbreaks; or anthropogenic, such as arson, logging, artificial flooding, or drainage.
A difference between natural and anthropogenic disturbances is that most natural disturbances have a periodicity, which over time, allows for a genetic (evolutionary) response from the biota. Human-induced disturbances can occur at any time (they are truly unpredictable) and without apparent periodicity. However, some human-induced disturbances can become chronic and/or develop periodicity that allows for genetic and community responses. Examples are mowing and grazing, which select for weeds of certain sizes and flowering phenologies, as well as certain densities of species and species composition (Grime 1973, Harper 1977).
While anthropogenic disturbances are not natural phenomena, this does not mean that they are always pejorative. In fact, management is a planned disturbance. Well-planned human disturbances can have positive effects on the ecosystem while satisfying human needs. An example could be using fire to restore desired forest types.
All types of disturbances have five components that are relevant to
assessing ecosystem effects. These components are: (1) severity, (2) frequency
of occurrence, (3) duration, (4) spatial scale, and (5) point(s) of
interaction with the ecosystem. Ecological research is just beginning to
focus on these aspects of disturbance. The diversity of forests in need
of management attention is the focus of this research (cf. Pickett and
White 1985a and b, Lugo et al. 1996). The availability of new technologies
for conducting forest research and the formation of research teams with
long-term goals will greatly accelerate this task. The pay-off of this
research is to allow scientists to assess with precision ecosystem resiliency
and suitability to human use. The silviculture literature already provides
a head start in this goal
(cf. Smith 1962).
Exotic Species
The change in species composition taking place in the world today is not a chaotic process. Instead, it is a directed process responding to fundamental changes in the conditions of the planet. Age-old ecological constraints such as time, energetics, biotic factors, growth conditions, opportunity, etc. are at play regulating which species is successful and which one is not in specific locations (Hengeveld 1989). Human activity is causing environmental change to which organisms respond through adaptation, evolution, or formation of new groupings of species and communities (Egler 1942).
The product of human activity is a heterogeneous set of habitats and environmental conditions, some new to particular regions. It is likely that today the world is more biologically diverse than before human activity became so prevalent, even if endemic species have gone extinct in the process. Prance (1990) estimated the extinction of 5,050 plant taxa since 1700 AD. Clearly the number of plant species has declined since 1700 although we do not know how many new species evolved in the last 300 years. However, the richness of the combinations of species that colonize and develop in the new habitats created by humans has increased (cf. Burgess and Sharpe 1981). More habitats, greater environmental heterogeneity, and a greater mix of species from all over the world, contribute to the formation of new communities of species. These new communities have their own intrinsic characteristics, ecological functions and services, and evolutionary potential. This translates into greater diversity of biotic interactions.
However, the scenario that I just described as positive, is considered negative by those who favor a situation where exotic species are excluded from the landscape (Temple 1990). Ecological practice as well as conservation biology finds itself at an important cross road concerning exotic species. Are they to be extirpated or do they have a role to play? (cf. Temple 1990, Coblentz 1991, Lugo 1990 and 1992).
We must maintain an open mind and analyze the issue of exotic species introductions and management as an intrinsic and continuous process in a world where our species is the main driver of change. It is in our power to take actions to mitigate the negatives of our activities and to enhance the positives. The following are actions that may help: (1) learning to manage and control environmental change, (2) rolling with the punch when conditions are obviously beyond our control, (3) avoiding prejudging species by successional stage or ecological function, (4) improving our capacity to manage biotic resources, (5) concentrating human activity to allow more space for native ecosystems, (6) encouraging environmental heterogeneity as a mechanism to maximize biodiversity. One thing is clear, the world will continue to change and become less familiar to those that walked it or wrote about it centuries ago. The scientific challenge is to understand the threshold of change of ecosystems so that managers have clear guidelines on the tolerance to species invasions and environmental change of individual ecosystems.
New Forest Ecosystems
In the Caribbean island of Jamaica, over half of the forest types identified in satellite images, are new forests reflecting human effects on these ecosystems (Grossman et al. ND). These effects include the introduction of species, changes in forest composition, or site degradation. On a global scale, the area of converted tropical forest lands is now larger than the area of mature tropical forests (FAO 1993). These examples highlight the need for ecologists and foresters to address the issue of new forest ecosystems, which are products of human activity and will soon be the predominant forest resource of the world. Many of these `new forests' are secondary forests in transitional stages of succession that lead to mature native forests. Others may be in arrested succession and in need of treatment to achieve optimal productivity and mature states. Still others may themselves be mature steady state forests adapted to the new environmental conditions created by human activity (cf. Moravcík 1994). I call them new forest ecosystems because their species composition is the result of human activity as are their site conditions. Without human intervention, these forests would not exist.
Regardless of their state or condition, these new forest ecosystems serve a dual purpose. First, they are a challenge to forest managers because in the future we may have to rely on them for products and services. Second, they represent an example to follow as a new strategy for dealing with all aspects of global change. This strategy is to proactively design management strategies that create new forest ecosystems for specific purposes in particular sites that are incapable of supporting native forests. Both purposes present scientific challenges because ecological research has traditionally focused on mature native forests and ignored exotic and human impacted forests. This is an area of research where traditional forest management has considerable practical experience. Empirical forestry experience will be useful and essential in the planing and advancement of ecological research to expand the scope of understanding and potential for human intervention in forest ecosystems.
Conclusion
The four topics discussed above underscore the challenges facing ecologists and the state of change that typifies the ecological field. Unfortunately, the new paradigms of ecology are not clearly established even though they are critical to the successful implementation of ecosystem management in a social and environmental context that itself is rapidly changing. Whether ecosystem management is successful or not determines what role, if any, forestry will play in the upcoming millennium. Scientists, managers, and the public will have to maintain effective communication and continuous sharing of information and experience to make ecosystem management work. Above all, the management of the worlds' forests requires the best ecological knowledge available.
Acknowledgements
I thank C. Domínguez, W. Edwards, M. Rivera, F.H. Wadsworth, and C. Yocum for their help in the preparation of this manuscript. The work was done in cooperation with the University of Puerto Rico.
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