Change in Extent of Meadows and Shrub Fields in the Central Western Cascade Range, Oregon∗

∗This research was supported by USDA Forest Service, Pacific Northwest Research Station; Oregon State University; the Long-Term Ecological Research program at the H. J. Andrews Experimental Forest supported in part by the National Science Foundation; and Senshu University, Japan. We thank J. Jones for help with statistical analysis and ecological considerations, and C. Halpern, J. Jones, J. Rice, and P. Weisberg for helpful comments on earlier drafts.

Abstract

We examined change in areal extent of mountain meadows and fields of deciduous shrubs and conifer saplings in the central western Cascade Range of Oregon, based on analysis of aerial photographs taken in 1946 and 2000. These nonforest vegetation patches are distinctive habitats in dominantly forested landscapes, such as the Cascades, and change in extent of these habitats is of interest to scientists and land managers. We mapped and dated even-aged forest stands of probable postfire origin around the nonforest patches, using tree-ring analysis and interpretation of aerial photographs. We used these and archival data to interpret possible influences of past wildfire and sheep grazing on the extent of nonforest patches. The total area of nonforest vegetation patches decreased from 5.5 percent of the study area in 1946 to 2.5 percent in 2000. Significantly more cases of contracted patches were observed for mesic and xeric meadows which have adjacent forest established after wildfire in the approximately 150 years preceding 1946. A higher proportion of mesic (47 percent, n = 47) than xeric (17 percent, n= 115) meadows contracted between 1946 and 2000. Broad-leaved shrub fields were unchanged, probably because of topo-edaphic controls, dense cover of shrubs, and snow effects; but all fields of conifer saplings underwent succession to forest. We observed no strong influences of sheep grazing on the extent of meadows.

Examinamos el cambio en la extensión del área de praderas de montaña y campos de matorrales deciduos asi como de árboles jóvenes de coníferas en la región medio occidental de la Cordillera de las Cascadas en Oregón, basándonos en el análisis de fotografías aéreas que se tomaron entre 1946 y 2000. Estas áreas de vegetación no forestal son hábitats diferentes en paisajes dominantemente forestales, como las Cascadas, y el cambio en la extensión de estos hábitats es de interés para los científicos y administradores de tierras. Mapeamos y fechamos rodales de edad uniforme que probablemente se originaron después de un incendio alrededor de zonas no forestales, usando el análisis de los anillos de crecimiento y la interpretación de fotografías aéreas. Usamos estos datos y material de archivo para interpretar las posibles influencias de incendios forestales pasados y el pastoreo ovino en la extensión de las zonas no forestales. El área total de las zonas de vegetación no forestal disminuyó en la zona de estudio del 5.5 por ciento en 1946 al 2.5 por ciento en 2000. Se observaron significativamente más casos de zonas reducidas en las praderas mésicas y xéricas con bosques adyacentes establecidos después de un incendio forestal aproximadamente 150 años antes de 1946. Una mayor proporción de praderas mésicas (47 por ciento, n= 47) que xéricas (17 por ciento, n= 115) disminuyeron en área entre 1946 y 2000. Los campos de arbustos de hoja ancha permanecieron inalterados, probablemente debido a controles topo-edáficos, la densa cubierta de los arbustos y los efectos de la nieve; pero todos los árboles jóvenes de coníferas experimentaron una sucesión a bosques. No observamos influencias fuertes del pastoreo ovino en la extensión de las praderas.

Key Words:

• Cascade Range
• forest fire
• landscape scale
• meadow contraction
• sheep grazing

关键词:

• 卡斯卡德草原
• 森林大火
• 景观尺度
• 草甸收缩
• 绵羊放牧

Palabras clave:

• Cordillera de las Cascadas
• incendio forestal
• escala del paisaje
• contracción de praderas
• pastoreo ovino

SADAO TAKAOKA is a Professor in the Department of Geography at Senshu University, Higashimita, Tama-ku, Kawasaki-shi, Kanagawa 214–8580, Japan. E-mail: [email protected]. His research interests include disturbance ecology and vegetation dynamics in mountainous regions.

FREDERICK J. SWANSON is a Research Geologist with the USDA Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis OR 97331. E-mail: [email protected]. His research interests include effects of physical disturbance processes, both natural and human, on forest and stream ecosystems in mountain landscapes.

Notes

∗This research was supported by USDA Forest Service, Pacific Northwest Research Station; Oregon State University; the Long-Term Ecological Research program at the H. J. Andrews Experimental Forest supported in part by the National Science Foundation; and Senshu University, Japan. We thank J. Jones for help with statistical analysis and ecological considerations, and C. Halpern, J. Jones, J. Rice, and P. Weisberg for helpful comments on earlier drafts.