As noted in the previous section, the earth is a dynamic place. Change, not stasis, is the norm. Changes are not all human-induced, and they are all not negative. The concept of conservation is, therefore, philosophically and scientifically flawed. Conservation means to retain or keep as is. Assuming that we could maintain the environment at some level of "sustainability" or point in time, which we cannot, at which level or point would that be? Also, how do we account for so-called "natural" environmental changes? Take, for instance, the eruption of Mt. St. Helens. The eruption resulted in thousands of hectares of cropland being covered with ash. Initially this was an aesthetic and economic disaster to some people. Subsequent years proved otherwise. The ash soon became invisible as crops grew profusely, resulting in record high crop yields and hence profits [example].
Geographers have a long tradition of studying land use. However, there are no special instruments to measure land use that have not been covered already. Cadastral measurements are typically used with existing maps and aerial photographs. The greatest problems in land use description and analyses involve identification and classification. The bewildering variety of possible land uses necessitates devising a system of "grouping" in order that measurements may be taken. These broad categories can then be sub-divided further. A series of upper and lower case letters and Roman and Arabic numbers can be used for coding [example]. Also, land use factors can be "combined" with a classification of natural environmental factors [example]. Undoubtedly, because of the great variety of possible combinations, there exists no universal or standardized land use classification system.
Given that the world is dynamic, land use studies invariably provide only a glimpse of a landscape at a given point in time. One can conduct time-series or diachronic studies, but these take time and, therefore, are often infeasible. Also, they really only show a series of slices of time. Changes from one time period to another are typically inferred. Geographers have a habit (good or bad?) of inferring process from pattern. This is typically a function of the available data. For example, aerial photographs taken in 1985 might show corn growing in a field. An aerial photo taken of the same field in 1995 might show oranges. With only these data one can do no more than hypothesize how the change actually took place. Field work is needed, and two factors must be taken into consideration--the frequency/magnitude relationship, and scale.
Frequency/magnitude. Some changes occur slowly (small) and continuously, while others are massive and infrequent. Soil salinization and mass wasting are examples of each respectively. There are two levels of measurement. Incidental observation is the crudest. It involves events which were recorded because an observer just happened to be there or because it was regarded as an unusual happening. A classic example of a massive and infrequent event would be the person who fortuitously has a video recorder handy when a tornado hits. An example of understanding slow continuous changes involves the corn to orange case mentioned above. In 1999 I happened to see a field in Honduras that had coffee saplings planted between the rows of corn [example]. Clearly this was formerly a corn field that within a few years would be a coffee finca. As the bushes matured and the canopy cover increased, there would be less sunlight for the corn. A keen eye and special observation skills are certainly helpful for geographers when it comes to measuring such changes.
Controled observation is much more accurate than incidental observation. It is also more expensive and time-consuming, and requires greater training, but it involves fewer powers of observation. Typically sample plots or test areas are monitored closely over a lengthy period of time. One example of this might be a series of erosion pins used to quantify the amount and rate of soil loss. Another might be to study one locale over a period of years [example] [example], or to record business turn-overs along a particular street. James J. Parsons said in his presidental address to the Association of American Geographers several years ago: "It pays to keep going back to a region. New things can be observed."
Scale. Can we make measurements of change at one scale and from them infer rates of change at another? It would be convenient, for example, to measure timber harvesting in a few locations thought to be representative, then calculate deforestation rates, and finally compute regional, country or even continental rates of change. The prospect is appealing. Are the results justified? No. Rates of deforestation at the field scale will, when extended to the scale of the forest, grossly overestimate the total number of trees being removed. It needs to be remembered that deforestation is not permanent. Trees grow back. If a 10 ha plot is harvested each year, after 10 years 100 hectares will have been harvested, but only one or two of the plots will be without trees of some age. The other eight or nine will have trees, at least one plot will have reasonably mature trees.
Succession is a concept developed in plant ecology which emphasizes replacement, and is predicated on the notion that disturbance must first take place. Disturbance, of course, can be "natural." It is also predicated on the notion of equilibrium. Recall, the epistemological problem with conservation? However, the concept of succession can be applied with some degree of confidence to human activities. In large part, this is because people do "disturb" things.
Erosion was discussed in a previous section. Removal of vegetation can result in increased runoff and soil loss upslope and sedimentation downslope. Alluvium can also contain cultural artifacts that become deposited in various horizons as well. Analyses of these horizons can therefore tell us something about past conditions, their sequences, and events. A specialized field of study called geoarchaeology deals with exactly these types of analyses. For example, remnants of decrepit terraces on a slope and large sediment deposits downslope bear witness to human efforts to thwart erosion, efforts which eventually failed.
Water obviously plays a frequent roll in landscape evolution. In arid lands well are frequently dug to tap groundwater for various purposes, not the least of which is irrigation. Does extracting a non-visible resource such as ground water have visible impacts? Yes. First, when water is applied to the surface much evaporates leaving a layer of mineral salts which eventually affect crop production. Also, if drawn from a distant source, irrigation waters can raise local ground water levels exacerbating the problem. And, gullying can occur in those place where the water is extracted and the water table drops. Gullies are typically straighter, deeper, narrower, and more straight-sided than natural channels
There are several detailed techniques for measuring landscape change. One involves comparing rocks picked-up every two meters during zig-zag traverses of 100 meter stretchs of two streams. All other things being equal, the stream with the smaller sediments has experienced much greater disturbance.
For most of us, however, it is probably more important to hone our observational skills, and look for things that indicate landscape change (e.g., sediments, artifacts in horizons, salts on the surface, gullies). These need not always be of physical nature, but can be human as well. For example, old houses that have been converted into law offices say something about urban transformation. And, barbed wire used to enclose fields and attached to posts set previously by neighbors who enclosed their fields will indicate the direction of agricultural expansion [example] [example].
Created by William E. Doolittle. Last revised 27 June 2013, wed