Background
Problem or Question
Ecological education and the creation of an environmentally literate society has been identified as one of the most pressing needs for development in the 1990s. In higher education, undergraduate ecology and environmental science education is taught primarily through lecture, recitation or seminar. Where courses include a laboratory component much of the student experiences are through mensurative field observations or short-term manipulative experiments. This is in stark contrast to a large proportion of empirical ecological and environmental research which is based upon field-experiments and the scientific method. Further, there is an increasing reliance on long-term field experiments in the development and testing of modern ecological theory. Thus a dichotomy between teaching and research exists despite the long-held belief among educators that students learn through inquiry and the scientific method as practiced by practitioners of the discipline. We suggest that the incorporation of field experiments into the curricula will greatly benefit undergraduate students taking ecological and environmental science courses, especially pre- and in-service teachers, as they attain a better appreciation for how relevant research is undertaken.
Goals and Specific Objectives
We propose to introduce undergraduate students taking ecology and environmental science courses to the concept of long-term experimental field research through the establishment of a series of long-term experimental study plots.
Historical Perspective
1. The need for field experiments in the teaching of environmental sciences
The need to incorporate laboratory and field experiences in the teaching of the environmental sciences cannot by overemphasized. Numerous studies have attested to the educational value of such 'hands-on' learning (Dewey 1938; National Science Board Commission on Precollege Education in Mathematics 1983; Seago 1992). Indeed, the 'doing' of science is the very essence of the subject, and often draws students into the discipline. Teaching science through inquiry is especially centered around this approach (e.g., Schwab 1960; Seymour et al. 1974; Rice & Dunlap 1982; Collette & Chiappetta 1989). We argue that there is a need to incorporate a specific type of field experience, i.e., field experiments in the teaching of environmental science and ecology.
The time and logistic constraints associated with including lab and field work into the curriculum often means that these experiences are not fully developed. Laboratory experiments play a central role in exposing students to key concepts such as photosynthesis, respiration, and hormonal growth effects under controlled conditions. These conditions ensure that the effects of the concept in question can be readily demonstrated, providing appropriate advanced organizers are provided to facilitate understanding and learning (Ausubel 1963). Laboratory exercises, including controlled greenhouse experiments, are thus an integral part of the majority of lab-based science courses at all levels.
In the last two decades there has been an increased incorporation of environmental and ecological material into science curricula nationwide. For example, the curriculum supplements Project WILD and Project Learning Tree have involved the participation of over 30 million students (primarily at the Elementary level) worldwide (Berkowitz 1993). The American Association for the Advancement of Science has sponsored Project 2061 which includes ecological concepts regarded as critical for the teaching of science (AAAS 1993). The Ecological Society of America, as the principal United States professional organization for ecologists is undertaking several projects designed to promote ecology education (Berkowitz 1993). Recognition of the importance, relevance, and need for field-based experiences is implicit in these and other new curricula (Leal Filho 1993; Tilling 1993). Despite these programs, much needs to be done to improve ecology teaching at all educational levels. It has been estimated for example that only 20% of teachers include ecological concepts in their courses (NRC 1990). Kuechle (1995) recently observed that ecology is usually placed last in biology textbooks. Gibson (1996) showed that one of the most important ecological concepts, i.e., succession, is presented in an outmoded manner in undergraduate environmental textbooks.
Fieldwork and field-based experiences in ecology and the environmental sciences have been described as the 'Achilles heel' in the success of teaching the discipline (Tilling 1993). Back in 1951, the British ecologist Sir Arthur Tansley noted that a 'good ecologist' should 'above all ... have a practical experience of field work' (Tansley 1951). Lisowski & Disinger (1991) showed that students' understanding of ecological concepts were significantly improved following field-based instruction. Field settings are appropriate to present students with experiences that encourage them to abandon their ecological misconceptions (Munson 1994). For example, a misconception of ecosystem function is that varying the population of an organism will only affect the others that are directly connected through a food chain (Griffiths & Grant 1985). The less formal nature of the field setting may also alleviate lack of confidence and anxiousness that some freshman students' have in taking science courses (Gibson & Gibson 1993).
Field-based experiences in the environmental sciences are more likely than laboratory experiences to involve mensurative exercises where students, for example, are asked to compare the number and abundance of tree species in an upland versus lowland area of forest. Other examples of this approach include comparing water quality factors in polluted versus unpolluted streams, counting the number of aquatic invertebrate species at different places in a wetland area, etc. Zonation patterns of plants and animals on rocky shores or across sand dune or wetland transitions are frequently shown to students as examples of succession (e.g.,(Alexander 1991). However, this 'space-for-time' substitution (Pickett 1989) often involves questionable assumptions about the process and does not illustrate the dynamic nature of succession (Crothers & Lucas 1982). At best, these approaches are natural snapshot experiments (Diamond 1983; 1986) in which ecosystems that differ from one another in only one or two characteristics (e.g., polluted versus unpolluted) are compared. These experiences, like the laboratory experiences discussed above, are invaluable in the teaching of environmental sciences and are well integrated into environmental science curricula. Problems that educators face with this approach include the time and expense of transporting students to field sites.
There is far less emphasis in environmental science curricula in field experiments compared with laboratory experiments or field experiences. Field experiments involve the controlled manipulation of experimental treatments under the natural, but seasonally variable, climatic conditions of the environment (Pigott 1982).
Hairston (1990) has documented an increasing trend in the use of field experiments since his plea for ecological field experiments (1957) and Varley's presidential address to the British Ecological Society, also in 1957. Tilman (1989) surveyed published ecological research over a ten-year period and noted that field experiments were used in 25% of the studies. Experiments (both greenhouse and field) were used in 40.5% of 3,108 ecological articles surveyed by Stiling (1994). Clearly, field experiments are important to the practitioners and researchers in ecology and so it follows that the methodology should form an integral part of its teaching. Ebert-May et al. (1993) wrote, "Thus, the most critical aspect of ecology education is the learning of how ecologists come to 'know.' We envision no better way to do this than to 'do what ecologists do'." Similarly, the National Research Council (1990) observed, "... rather than have students memorize lists of every conceivable biotic and abiotic factor on the globe, how much better it would be to engage students in field observations!"
The advantages of incorporating a well-designed field experiment into an environmental-science curriculum include:
Experimental treatments are tightly controlled.
Statistical rigor and hence facility to analyze data in a meaningful manner.
An increasingly large and valuable data set accumulates as the experiment is operated over several seasons. Such long-term experiments can reveal many important environmental effects (see section 4, below).
Precise concepts can be illustrated (i.e., based on the treatments).
Students can learn a variety of data collection procedures.
Concepts that operate only over the long-term can be illustrated.
'Set-up' and 'take-down' for each lab is unnecessary.
Many student groups can use the same experiment providing the exercises are individually tailored for each group and academic level.
High degree of realism, far more so than in a greenhouse or laboratory.
Surprisingly, few such field experiments are incorporated into environmental science curricula (see section 1. 5. A 2. The Nettlecombe Grassland Experiment and other model field experiments). Laboratory manuals for ecology do not include field experiments of this nature (Philips 1964; Rolan 1973; Cox 1990; Rosenthal 1995). This is perhaps because of the time and financial commitment necessary to maintain an ongoing experiment. Certainly, field experiments are used by educators when they are available. For example, at Konza Prairie Research Natural Area in Manhattan, KS, an NSF-funded Long Term Ecological Research site, local schools and societies are invited to visit the site and are given site tours as part of an educational out-reach program.
In this proposal, we argue that field experiments can be an invaluable component of a environmental science curricula, especially when used by many students in several courses representing multiple academic levels (freshman to college seniors and graduate students). We propose to set up a long-term field experiment, patterned after a successful model system in England, the Nettlecombe Grassland Experiment. We plan to use the field experiment in the teaching of undergraduate through graduate students. Short-term experiments will be established within the long-term experimental plots. Students will be heavily involved in all aspects of the experiment including design, set up, maintenance, monitoring, data collection, analysis and report writing. These sort of student-originated and student-run ecology projects are valuable in fostering interest and enthusiasm for science (Fail 1991).
2. The Nettlecombe Experiment and other model field experiments
The Nettlecombe Experiment was set up in 1968 by Crothers & Lucas (1982) in a small pasture in England. A Latin square design (Potvin 1993) was used to establish four mowing treatments (mown weekly during growing season, mown annually in June, not mown, cleared to bare soil in 1968 and left unmown). Sixteen square plots of 9 m2 allowed four replicates of each treatment. From 1968 through 1990, student groups collected point quadrat cover data annually from the treatment plots as part of ecological investigations run by the English Field Studies Council (FSC) (Crothers & Lucas 1982; Crothers 1991). The FSC is an organization that runs week-long and weekend field courses for students of all academic levels. Over the 28 years through which the experiment was run, the different student groups have amassed a large data set that in addition to showing the effects of the four mowing treatments upon the grassland, shows the interaction with long-term climatic changes (Crothers 1991).
Educational processes and concepts provided by the Nettlecombe Experiment include:
Experimental design
Comparative methods of data collection
Data analysis
Methods of data presentation (Crothers 1981)
Grasslands ecology
Species identification
Succession
Effects of long-term climatic change (specifically drought)
The Nettlecombe experiment lends itself to several different teaching approaches. The traditional approach involves the teacher asking the biological question and showing the students how the design relates to and assists in addressing the question. A second approach is in the form, 'problem not given, method given, solution not given'. With this approach students are led to understand that there should be a logical relationship between the problem being investigated and the experimental approach used (Crothers & Lucas 1982). Advanced students can also be asked to provide appropriate designs for follow up experiments to test new hypotheses arising from the long-term data set (e.g., species A responds differently to drought than species B because of differences in water use efficiency].
The longest running ecological experiment in the world is the Park Grass Experiment at Rothamstead in Hertfordshire, England. The Park Grass Experiment was established in 1856 with the object of determining the effect of different fertilizer regimes on the yield of hay from permanent grassland. Seventeen plots were established in species-rich grassland of uniform botanical composition (Lawes et al. 1882). The plots were subdivided and supplemented during the course of the following 100 yr. Samples of hay taken on a semi-regular basis since 1862 revealed significant changes in the botanical composition of the plots according to the fertilizer regimes. Most importantly, there have been significant long-term changes in the composition of the plots despite the maintenance of the same fertilizer regimes (Silvertown 1980; Dodd et al. 1995). Trends in species patterns through the 100+ years of the experiment have been used to test theoretical models of resource competition and community structure (Tilman 1982), vegetation classification schemes (Dodd et al. 1994) and demonstrate ecological stability and succession over the long-term (Silvertown 1980; 1987).
The educational value of the Park Grass Experiment was summed up by M.J. Crawley;
" We use Park Grass for teaching in the most immediate way possible by taking the students to see it, just before it is cut in June. This is a tremendous experience for them because it really brings the statistics to life. It is the most visually impressive experiment that I know about. No one, having seen it, can ever doubt that 'Nutrients Matter' !!" (M.J. Crawley, Pers. Comm., 1995).
Ebert-May et al. (1993) have designated a wetland habitat near Flagstaff, Az as a student research site, specifically for teaching introductory ecology. The site is modeled after the nationwide network of NSF-Long Term Ecological Research sites. They noted the following advantages to using their own 'LTER' teaching site, 1) long-term data bases become available for student use, 2) large numbers of students become involved, 3) course field trip mileage costs have decreased, and 4) students have easy access to the site on their own.
3. Succession as a framework for teaching environmental science
Succession is the process and pattern of changes following a disturbance in communities through time at a site (Gibson 1996). It is an integral component of natural ecosystems and forms an important part of both traditional and modern theories of ecosystem structure; see recent reviews by Pickett & McDonnell (1989), Glenn-Lewin et al., (1992), and McCook (1994). Environmental perturbations, both natural (e.g., volcanic eruptions, earthquakes, lightening strike fires) and anthropogenic (e.g., release of pathogens and pollutants) can alter successional pathways or initiate primary or secondary succession. The colonization of plants and animals on the volcanic islands of Krakatau, Indonesia following the 1883 eruption provides a well known example of succession (Bush & Whittaker 1991). The replacement of American chestnut (Castanea dentata) by other tree species in the former oak-chestnut forests of the eastern US provides an example of succession following the anthropogenic introduction of a pathogen (chestnut blight - Cryphonectria parasitica) (Korstian & Stickel 1927).
The topic of succession was ranked second in a list of the 50 principal concepts in ecology by members of the British Ecological Society (Cherrett 1989). It was also ranked joint first, along with the concept of limiting factors, in the examination syllabus for high school science in Great Britain (Hale & Hardie 1993). In a survey of members of the Ecological Society of America, succession was considered less important and ranked as the 22nd of 29 concepts studies in ecological research (Stiling 1994). The topic is covered, nevertheless, in all undergraduate ecology and environmental science text books (Gibson 1996) and is an integral part of ecological curricula.
As a teaching tool, succession allows students to understand the changing nature of communities, as well as conceptualize the result of species interactions (Gibson 1996). It is also important to help students appreciation the long-term nature of many ecological phenomena, such as the response to disturbance. Thomas (1993) notes that an understanding of species immigration and extinction rates, for example, is important in understanding the effects of global ecological problems at the local level. The teaching of succession is usually through mensurative field observations of ecosystems at different stages of succession following a disturbance such as fire. Some teaching guides suggest the collection of data from, e.g., fields of different ages since abandonment (Rosenthal 1995). However, this approach has all the disadvantages of non-experimental field studies mentioned earlier (sections 1.2 & 1.5 A. 1.) and incorporates a high degree of pseuodoreplication (Hurlbert 1984).
The successional concept is clearly important, it is embodied in the Nettlecombe Grassland Experiment, and we use it as the basis for proposed field experiment.
Modes of Instruction and teaching methods
1. General approach
By taking more than one ecology-orientated course in SIUC's environmental studies program, students will become familiar with the long-term experiment on several occasions. Incorporation of the experiment into specific courses will reflect the goals and objectives of each course (see below, section 1.4 C). Nevertheless, because of the single semester duration of individual courses the long-term nature of the educational experience afforded to the student might be considered to be somewhat paradoxical. To address this problem a combination of 'pulse' and 'press' perturbation experiments are planned (Bender et al. 1984; Inchausti 1995). Pulse experiments are an instantaneous and one-time alteration of a system in which the reaction of the system is studied as it 'relaxes' back to its previous equilibrium (i.e. recovery following a single disturbance event). By contrast, a press experiment involves the sustained application of a treatment and the system is studied as it moves towards a new equilibrium. In these terms, the changes associated with secondary succession on an abandoned farm field (i.e. old-field) that is otherwise not further disturbed is a pulse experiment, whereas succession following repeated application of fertilizer to a pasture would be a press experiment. The repeated mowing treatments in the Nettlecombe Grassland Experiment and the continuous fertilizer applied to the Park Grass Experiments (section 1.5 A) are examples of press experiments. We propose to establish both a pulse and a press experiment.
The field experiments are designed within the framework of current research in succession. One of the most widely studied models of succession is the Intermediate Disturbance Hypothesis (IDH) (Connell 1978; Peet et al. 1983; Wilson 1994). This model makes two predictions; viz, that species richness will be highest in communities with moderate levels (frequencies) of disturbance (Fig 1), and at intermediate time spans following disturbance (Fig 2). In addition, the Initial Floristic Composition (IFC) model (Egler 1954), which states that nearly all species are present at the start of succession, predicts that richness should be highest immediately following disturbance (Fig 2). Collins et al. (1995) have recently shown that the two predictions of the IDH are independent and unrelated in Kansas tallgrass prairie subject to prescribed burning. They showed that rather than a maximum species richness at intermediate frequency of disturbance (fire), there was a monotonic decline during succession in support of the IFC. A second prediction of the IDH that species richness reached a maximum before declining with time since the last disturbance was supported. We plan to test the generality of these findings in an old-field (abandoned farm field) succession.
Old-field successions typically involve large shifts in plant species composition through time (Vankat & Carson 1991). This is in contrast to the more gradual shifting of dominance relationships following fire in tallgrass prairie (Gibson & Hulbert 1987) where Collins et al (1995) noted the decoupling of IDH predictions. Herbivory, which is at high levels from white-tailed deer at our study sites, will allow high levels of species richness (McNaughton 1983; Middleton in press). Because of these differences between the two types of system, we do not expect the two predictions of the IDH to be decoupled in the old fields that we plan to study.
We address these predictions in an upland and a lowland abandoned farm field following a major soil disturbance (disking). Mowing (zero, and once and twice per year) and fertilizer (zero, once, and annually) treatments will provide two simple gradients of disturbance frequency. These treatments also provide a combination of 'pulse' and 'press' perturbations (Bender et al. 1984; Inchausti 1995). Pulse experiments are an instantaneous and one-time alteration of a system in which the reaction of the system is studied as it 'relaxes' back to its previous equilibrium (i.e., recovery following a single disturbance event). By contrast, a press experiment involves the sustained application of a treatment and the system is studied as it moves towards a new equilibrium. In these terms, the changes associated with secondary succession in an old-field that is otherwise not further disturbed is a pulse experiment, whereas succession following repeated application of fertilizer or mowing is a press experiment. At each of two field sites (upland and lowland), we have two intensities of pulse treatments; disked control plots (unmowed, unfertilized) and disked plots fertilized only in year one (also unmown).