WETLAND - A U.S. FISH AND WILDLIFE SERVICE SYSTEM USED FOR DETECTION OF WETLAND CHANGES W. E. Frayer, Dean and Professor School of Forestry and Wood Products Michigan Technological University Houghton, MI 49931 USA ABSTRACT: A network of 6195 sample units has been established throughout the lower 48 states and Alaska for the purpose of establishing baseline data and monitoring changes in wetlands. Each sample unit is four square miles in area and, for general usage, is classified with a minimum mapping unit of 0.1 acres. Impacts of large-scale, catastrophic events can be examined and quantified with the sample network. Samples in the lower 48 states have been routinely measured twice. In addition to large changes that were somewhat expected (conversion of wetlands to agriculture), unexpected changes of over a million acres were experienced during the last period between measurements. INTRODUCTION The United State Fish and Wildlife Service has major responsibility for the protection and proper management of migratory and endangered fish and wildlife and their habitats. Of particular concern are wetlands and associated deepwater habitats. Since 1974 the U.S. Fish and Wildlife Service, through its National Wetlands Inventory Project, has been conducting an inventory of the nation's wetlands. The purpose is to develop and disseminate comprehensive data concerning the characteristics and extent of wetlands. In addition to the all-encompassing, site-specific inventory of the nation's wetlands, timely information at the national level -- or for other large areas -- is often needed as a basis for policy decisions and legislation. This is potentially of an emergency nature, as might be the case if large expanses of forested wetlands were suddenly and permanently defoliated. For these reasons, a sampling network was established which allows for precise estimation of wetland changes. Two routine measurements have been made of the samples in the lower 48 states. Wetland gains and losses between the 1950's and 1970's were studied by Frayer et al. (1983). The second study of wetlands in the lower 48 states documented natural and human-induced wetland and deepwater habitat gains and losses between the 1970's and the 1980's (Frayer et al., 1991). The statistical design used in the national trend study can be used with intensified sampling to obtain reliable estimates for individual states or other selected geographical areas. This has been done for the Central Valley of California (Frayer et al., 1989), Florida (Frayer et al., 1991), and Alaska (Frayer et al., 1993). The Alaska study is the first for that state, and it provides the baseline data for future estimates of change. WETLAND CLASSIFICATION The definitions, classifications and categories of wetlands and deepwater habitats used are those described by Cowardin et al. (1989) and Anderson et al. (1976). In general terms, wetland is land where saturation with water is the dominant factor determining the nature of soil development and the types of plant and animal communities living in the soil and on its surface. Common terms used to describe various wetlands include marshes, swamps, bogs, small ponds, sloughs, potholes, river overflows, mud flats, and wet meadows. Deepwater habitats consist of certain permanently flooded lands. Common names used for deepwater habitats include bays, lakes, rivers, and reservoirs. The details of the classification system are beyond the scope of this paper. The kinds of wetlands and deepwater habitats studied and some common examples include: Wetlands -------- Marine intertidal (ocean beaches) Estuarine intertidal unconsolidated shore (mud flats) Estuarine intertidal aquatic beds Estuarine intertidal emergent (salt marshes) Estuarine intertidal forested and scrub/shrub (mangroves) Palustrine unconsolidated shore Palustrine open water (ponds) Palustrine aquatic beds Palustrine emergent (wet meadows) Palustrine forested (swamps) Palustrine scrub/shrub (bogs) Deepwater habitats ------------------ Estuarine subtidal (bays) Lacustrine (lakes and reservoirs) Riverine (rivers) Other surface area ------------------ Agriculture Urban Other More detailed discussions, exact definitions, and fuller descriptions are presented by Cowardin et al. (1979) and Anderson et al. (1976). SURVEY AND ANALYSIS PROCEDURE The sampling network was designed to provide the means of developing baseline data for estimates of change. We now have the network in place for all states except Hawaii. There are several ways in which the network can be used. Two examples are: (1) The samples can be measured at a current point in time and changes from an earlier measurement can be estimated. (2) The samples can be measured before and after a specific event, in order to estimate the changes caused by that event. This was essentially the case for the Mississippi Delta area during the first "routine" measurement of the lower 48 states. Aerial photo coverage was obtained before and after the devastating land clearing of bottomland hardwoods for agriculture. These uses of the network have been made with high-altitutde aerial photography which allows for minimum mapping units of 0.1 acres. For some events, the minimum mapping units might be larger and satellite data could be used. Other events might require the use of large-scale photography or ground examination. In any case, the same locations are in place and the user can choose the measurement methods. A stratified random sampling design is used, with the basic strata being formed by state boundaries. In the lower 48 states, these are further divided by the 35 physical subdivisions described by E. H. Hammond (1970). In Alaska, the 25 physical subdivisions described by Rieger et al. (1979) are used. In all coastal states, additional coastal strata are used to encompass most of the marine and estuarine categories. Special strata are also used in states bordering the Great Lakes to separate those bodies of water. This resulted in over 230 strata. Sample units are allocated to strata in proportion to expected amounts of wetlands and deepwater habitats as estimated by U.S. Fish and Wildlife personnel. The total number of sample units is 6195. Each sample unit is a four-square mile area, two miles on each side. The units are plotted on U.S. Geological Survey topographic maps. In general, aerial photographs are obtained for the samples for at least two points in time. The photography is then interpreted and annotated in accordance with the classification system described earlier and procedures developed by the U.S. Fish and Wildlife Service's National Wetlands Inventory Project. The results of the most recent classification are compared with earlier classification(s), and any changes are annotated. SELECTED RESULTS OF APPLICATIONS It was expected that large losses in wetlands had taken place in the 1950's and 1960's. The first trends study of the lower 48 states was used to estimate these changes. Although the results are not indicative of a catastrophe which happened overnight, the magnitude of the changes occurring in a 20-year period are still rather "sudden" in terms of natural resource trends. It was shown that 4.5 million acres of forested wetlands were lost in the Mississippi Flyway. Most of it was in the Mississippi Delta and was the result of conversion to agriculture. The national net loss in wetlands alone during the 20-year period was 11 million acres, an area as large as the combined states of Massachusetts, Connecticut and Rhode Island. Nearly all of the net loss was due to agriculture. Substantial amounts of coastal wetlands, especially in Florida, were converted to urban development. In all, 20 states showed significant wetland loss during the period. Documentation of these losses helped to pave the way for legislation and policy directives aimed at curbing wetland losses. A third measurement of the sample network in the lower 48 states was conducted to estimate losses from the 1970's to 1980's. It was found that losses had continued. In addition to the 20 states having significant losses in the previous period, another 11 states now showed significant losses. However, some of the losses were of a different nature. Over one million acres were converted from forested swamps to "other" uses during this recent period. Most of this is along the southeastern coast. Although the study did not define the specific cause, the author believes a large amount is due to forestry operations. A loss of another nature - and what came as a surprise - was a tremendous change in area of freshwater vegetated wetlands. Net changes from large to smaller vegetation were as follows: Palustrine forested to palustrine scrub/shrub (482.8 thousand acres) + palustrine forested to palustrine emergent (722.2 thousand acres) + palustrine scrub/shrub to palustrine emergent (68.6 thousand acres) = 1,273.6 thousand acres. This change of over 1.25 million acres in a nine-year period between 1974 and 1983 came as a surprise. What is the cause? It is not a sudden occurrence, but it is of such magnitude that it should be of concern. Could it be a long-term effect of road construction? That is, could subsurface water flows have been altered by roads or other human-induced causes such that effects are being noticed many years later? Perhaps. The data are available to determine where and maybe why these changes have happened and may still be happening. IN CONCLUSION The sampling network described has been used for studies of the wetlands and deepwater habitats of the lower 48 states and Alaska. The design involves careful measurement of a sample of the nation's surface area. In general, results are meaningful only at the national level or for broad areas. With intensification of samples, results can have adequate reliability to be useful at flyway or state levels. Continual monitoring of surface area use and changes in use is needed to provide the basis for wise decisions. This report is the result of one such method of monitoring initiated by the U.S. Fish and Wildlife Service. Monitoring can be a routine, scheduled procedure. When necessary, the network provides the basis to assess changes caused by catastrophic events. LITERATURE CITED Anderson, James R., Ernest E. Hardy, John T. Roach and Richard E. Witmer. 1976. A land use and cover classification system for use with remote sensor data. U.S. Geological Survey Prof. Paper 964. 22 p. Cowardin, L. M., V. Carter, F. C. Golet and E. T. LaRoe. 1979. Classification of wetlands and deepwater habitats of the United States. U.S. Fish & Wildl. Serv. 103 p. Frayer, W. E., T. J. Monahan, D. C. Bowden and F. A. Graybill. 1983. Status and trends of wetlands and deepwater habitats in the conterminous United States, 1950's to 1970's. Colo. State Univ. 32 p. Frayer, W. E., Dennis D. Peters and H. Ross Pywell. 1989. Wetlands of the California Central Valley: status and trends, 1939 to mid-1980's. U.S. Fish & Wildl. Serv. 28 p. Frayer, W. E. and John Hefner. 1991. Florida wetlands. U.S. Fish & Wildl. Serv. 32 p. Frayer, W. E. 1991. Status and trends of wetlands and deepwater habitats in the conterminous United States, 1970's to 1980's. Mich. Technological Univ. 32 p. Frayer, W. E., Jonathan V. Hall and Bill O. Wilen. 1993. Alaska wetlands. U.S. Fish & Wildl. Serv. 32 p. In press. Hammond, E. H. 1970. Physical subdivisions of the United States. In: National Atlas of the United States. U.S. Geological Survey. 417 p. Rieger, Samuel, Dale B. Schoephorster and Clarence E. Furbush. 1979. Exploratory soil survey of Alaska. U.S. Dept. of Agr., Soil Cons. Serv. 213 p.