While riparian areas are recognized as having great importance disproportionate to the area they occupy in landscapes, there is little information available concerning the role of fire in and around these areas before the implementation of fire suppression. As a result, a great deal of uncertainty exists about the long-term role of fire in the dynamics of riparian environments. Although the Klamath Mountains of northern California and southwestern Oregon receive ample annual precipitation to grow beautiful forests, there is a pronounced annual drought. This annual drought guarantees that, even in years much wetter than average, the conditions for fire to easily spread once ignited are achieved in the dry season. Recognizing the dominant features of this Mediterranean climate and the fact that fire history studies show that fires were frequent in most vegetation types, it is logical to assume that, historically, fires regularly affected many riparian areas.
Natural resource managers are having to try to balance what is thought to be best for riparian areas with the reality of the fire regime driven by the Mediterranean climate. How often and in what seasons should prescribed fire be used in riparian areas (if at all)? Should fuels treatments differ along ephemeral, intermittent, and permanent water courses or should they all be treated the same? How to provide for natural variation and sustain biodiversity? Indeed, much hand wringing and teeth gnashing has occurred in this regard due to little data to suggest what the nature of fire's influence on riparian areas has been.
Several recent fire history studies conducted in the Klamath Mountains are beginning to shed some light on the long-term nature of fire in regard to riparian areas. One study was a preliminary investigation to develop fire histories specifically from riparian reserves along permanent water courses and compare them to neighboring uplands (Skinner in press). Two other studies involved intensive spatial sampling of 4,000-7,000 acre landscapes to look at the spatial and temporal dynamics of the fire regime (Taylor and Skinner 1998; in progress). In each case, we developed fire history from fire scars found in stumps and standing trees.
The first study cited above (Skinner in press) covers the period of 1525 to 1933. Here, the median fire return intervals (FRIs) for five riparian reserve sites were approximately double the FRIs from nearby upland forest sites, while the ranges of FRIs were very similar. These preliminary data suggest that FRIs in riparian reserves may have been more variable than in adjacent uplands and tend to be longer. The study proposes that riparian areas may have enhanced the spatial and temporal diversity of landscapes by acting as occasional barriers to many low- and moderate-severity fires.
The second study mentioned above (Taylor and Skinner 1998) was conducted on Thompson Ridge in the Seiad Late Successional Reserve adjacent to the Applegate AMA. Here, we analyzed tree species composition, structure (diameter, age), and fire scars from 75 upland plots distributed across approximately 4,000 acres. We found that fires burned with similar frequencies (median FRIs of 12-19 years) throughout the landscape. The average fire size from 1627 to 1987 was approximately 900 acres with 16 fires having burned more than a third of the study area. Patterns of past fire severity, inferred from age-classes and patch size patterns, indicate that upper slopes, ridgetops, and south- and west-facing slopes experienced more severe fires than lower slopes or east- and north-facing slopes. Implications are that lower slopes and north and east aspects are more likely than other topographic positions to sustain or promote long-term, late-successional conditions. The significance for riparian areas is that upper reaches of stream courses, especially where there is no permanent water, are likely to have burned more severely than lower reaches within the local topography. The lower reach riparian areas would be similar to east and north-facing uplands, while the upper reach riparian areas would probably be more like that of south and west-facing slopes.
The third study is a work in progress. Thus, what is reported here is preliminary information and subject to revision before final publication. This study took place in the Rusch and Judd Creek watersheds between Hayfork and Hyampom in the Hayfork Adaptive Management Area (AMA). Here data were collected from 130 plots distributed across approximately 7,000 acres and covers the period of 1650 to 1930. Analogous to Thompson Ridge, FRIs were found to be similar throughout the study area regardless of dominant vegetation. A preliminary assessment of fire sizes also appears to be similar to Thompson Ridge. This study was different from the Thompson Ridge study in that here there were many permanent water courses dissecting the area. Base on the prehistoric fire patterns, many of the fires appear to have been bounded by either riparian areas with permanent water or by ridgetops. That these patterns emerge from the data suggests that fuel conditions were quite different than today. Fuel quantities would have to have been considerably lower than today for these landscape features to have contained many of the fires. Although there seems to have been fires in most years, most of these were less than 1000 acres in size, setting up a mosaic of burns that were self-limiting over time apparently due to limited fuel accumulation in any one spot. The limited fuel accumulations were likely the result of frequent fires burning in the mosaic pattern. However, there were several fires each century that appear to have burned almost the entire study area, as fires were forced by apparently severe conditions through even recently burned areas. These widespread fires appear to have been associated with extremely dry conditions probably not unlike 1924 in this century.
These studies suggest that historical fires regularly affected riparian areas. Yet, fires appear to have affected riparian areas of perennial streams less frequently than in the adjacent uplands. Nonetheless, in the upper reaches of watersheds where riparian reserves are associated with intermittent streams, fires appear to have burned with frequency similar to the surrounding uplands. These preliminary results, the ecological importance of riparian areas, and the uncertainty associated with attempting to develop long-term plans for riparian reserves point to the need for more intensive landscape level fire history studies. Such studies would help to clarify the long-term influence of fire on pattern and structure at the landscape scale. They would provide important information for understanding the long-term influence of fires on landscape components including riparian areas.
Developing successful, long-term management plans for riparian reserves in California and southwestern Oregon is likely to be problematic without a serious consideration of the physical and biological potential for fire and its ecological function in those environments. -
You can reach Carl at: nskinner_psw@fs.fed.us
Skinner, Carl N. (in press). Fire history in riparian reserves of the Klamath Mountains. In: Proceedings - Fire in California Ecosystems: Integrating Ecology, Prevention, and Management. (Eds: Cooper, Sandra; Sugihara, Neil) International Association of Wildland Fire, WA
Taylor, Alan H.; Skinner, Carl N. (1998). Fire regimes and landscape dynamics in a late-successional reserve in the Klamath Mountains, California, USA. Forest Ecology and Management 111: 285-301.
Taylor, Alan H.; Skinner, Carl N. (in progress). Fire regimes and landscape dynamics in the Hayfork Adaptive Management Area, Klamath Mountains, California, USA. 2
