Academic journal article The American Midland Naturalist

Differential Consumption of Eastern Red Cedar (Juniperus Virginiana) by Avian and Mammalian Guilds: Implications for Tree Invasion

Academic journal article The American Midland Naturalist

Differential Consumption of Eastern Red Cedar (Juniperus Virginiana) by Avian and Mammalian Guilds: Implications for Tree Invasion

Article excerpt

ABSTRACT.-

Increased abundance and distribution of eastern redcedar (Juniperus virginianus), a native species in the Great Plains, has been associated with changes in ecosystem functioning and landscape cover. Knowledge of the main consumers and dispersal agents of eastern red cedar cones is essential to understanding the invasive spread of the species. We examined animal removal of cedar cones in three habitats (tallgrass prairie, eastern red cedar and woodland-prairie margins) in the Cross Timbers ecoregion using three exclosure treatments during autumn and winter. Exclosure treatments excluded study trees from ungulates, from terrestrial rodents and ungulates or from neither (control). Loss of cones from branches varied by a habitat-time interaction, but was not affected by exclosure type. Loss of cones from containers located under experimental trees varied by a habitat-treatment-time interaction. In December and January, cone consumption from containers in no-exclosure treatments was highest in margins, followed by tallgrass prairie and eastern red cedar habitats. We conclude birds consumed the majority of cones from branches and small-and medium-sized mammals consumed cones on the ground. Both birds and mammals likely contribute to the spread of eastern red cedar but at different scales. Limiting invasion of eastern red cedar in forests may require early detection and selective removal of pioneer seedlings in cross timbers and other habitats that attract a high diversity or density of frugivores.

INTRODUCTION

Eastern red cedar (Juniperus virginiana) has colonized native vegetation at exponential rates in Oklahoma due to fire suppression (Engle et al., 1996) and is rapidly converting remnant native grassland habitats in other areas of the Great Plains of the United States (Gehring and Bragg, 1992; Coppedge et al., 2001; Hoch et al., 2002). Invasion by eastern red cedar impacts ecological and human health by homogenizing diversity, reducing wildlife habitat quality, increasing fire risk, altering hydrology and nutrient cycling and producing highly allergenic pollen (Engle et al., 1996; Norris et al., 2001). Fire was a process that historically limited the spread of eastern red cedar, a fire-intolerant species that reproduces solely by seed in contrast to most woody plants of the Great Plains that reproduce vegetatively and can resprout after fire (Briggs et al., 2002). In the absence of fire, eastern red cedar spreads rapidly across the landscape (Bragg and Hulbert, 1976), mostly from animal-driven dispersal of the ripened, fruit-like cones. Eastern red cedar is dioecious, with female cones developing into a blue, berry-like or drupe-like structure (Gleason and Cronquist, 1963).

Junipers (Juniperus spp.), in general, are adapted for dispersal by frugivorous vertebrates, especially birds and mammals by virtue of their fleshy, fruit-like cones (Chambers et al., 1999). At least 71 species forage on eastern red cedar (Van Dersal, 1988) and seed dispersal apparently depends heavily upon birds and small mammals (Phillips, 1910; Livingston, 1972). Birds are considered the most efficient and quantitatively important group of vertebrates for dispersing seeds of eastern red cedar, with cedar waxwings (Bombycilla cedrorum), robins (Turdus migratorius) and mockingbirds (Mimus polyglottus) being the most common dispersal agents (Phillips, 1910; Holthuijzen and Sharik, 1985). Eastern red cedar seeds passed unharmed through the digestive tract of yellow-rumped warblers (Dendroica coronta) and cedar waxwings and showed a 1.5-3.5-fold greater germination rate than manually depulped seeds (Holthuijzen and Sharik, 1985).

The role of mammals in red cedar dispersal is less well-known, although a variety of mammal species has been identified as dispersal agents for other junipers (Chambers et al., 1999). Red cedar cones and seeds have been found in feces of raccoons (Procyton lotor), foxes (Vulpes spp.), bobcats (Lynx rufus) and small mammals (Phillips, 1910). …

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