Urban Edge Effects on Soil Conditions, Stand Structure, and Understory Composition in a Coast Redwood Forest

Abstract

Forests in the wildland-urban interface (WUI) can experience edge effects caused byhuman activities, such as timber harvest and urban development, altering vegetation composition and structure. Both the WUI and resulting edge effects are well studied in general; however, the influences of the urban edge on coast redwood forests specifically are not well understood. I analyzed soil properties, stand structure, and understory composition in a coast redwood preserve in the Santa Cruz Mountains, California using twenty 300 m transects established across an anthropogenic edge and twenty transects within a forest interior control. Spearman’s rank correlations indicated that several variables exhibited positive correlations with distance from the edge, including soil pH and moisture, duff depth, canopy cover, an abundance of Sequoia sempervirens and Notholithocarpus densiflorus, tree diversity, and the abundance of coast redwood understory species. In contrast, soil temperature and the abundance of Quercus wislizenii exhibited negative correlations. Mann-Whitney U and chi-square tests of independence indicated some differences between edge and control treatments with regard to soil conditions, stand structure, and species composition; however, these findings were confounded by unavoidable physiographic and anthropogenic differences between the treatments. The results of this study support previous research in other forest types and provide evidence that urban edges can impact stand structure and understory composition within coast redwood forests.