Changes in forest understory associated with Juniperus encroachment in Oklahoma, USA

Abstract

Question: Does understory vegetation cover and richness decline along a gradient of increasing Juniperus virginiana midstory canopy cover and is that decline best correlated with litter accumulation? Location: Cross Timbers Forest in Payne County, OK, USA. Methods: We measured vegetation in forest gaps as well as forest areas without J. virginiana, at the inner and outer edge of J. virginiana canopies and near J. virginiana trunks (200 plots) and compared vegetation differences among location to light, litter, soil and microclimate variables. Results: Species richness (11 spp m À 2 to 6 spp m À 2 ) and summer vegetation cover (53.3% to 12.7%) declined with proximity to trunks. Regression indicated that richness declines (R 2 5 0.08) and cover (R 2 5 0.18) were best correlated with J. virginiana litter accumulation. Partial canonical correspondence analysis (pCCA) revealed two strong canonical axes, one related to litter/light and another to cover of Quercus spp. versus J. virginiana. Tree seedlings and woody vines dominated near J. virginiana. Forbs, graminoids and Quercus spp. seedlings were more common in areas without J. virginiana. Conclusions: Increasing J. virginiana and consequent litter additions alter understory biomass and composition and, through inhibiting Quercus spp. recruitment, may lead to changes in overstory composition. Decreases in herbaceous litter, which historically contributed to fuel accumulation, may have positive feedback effects on midstory encroachment by reducing the potential for prescribed burning.

Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors in theCentralGreatPlains ofNorthAmerica

“…; Van Els et al . ). With time, this disruption of fuel continuity decreases fire transmission (Abades, Gaxiola & Marquet 2014; this issue), creating a positive feedback between J. virginiana and fire suppression.…”

“…With long‐term fire suppression, J. virginiana can also over‐top and replace shrubs, as shown in long‐term vegetation surveys and the inability of shrubs seedlings to regenerate under older J. virginiana canopies (Myster , Van Els et al . ). Thus, while the fires typical of grasslands and shrublands might prohibit tree establishment, exposing mature woodland trees to fires should have little effect.…”

Involvement of invasive eastern red cedar (Juniperus virginiana) in the expansion ofAmblyomma americanumin Oklahoma

“…Since the early 1940s, eastern red cedar ( Juniperus virginiana ) has been increasingly invading prairies and mixed woodlands in the Great Plains region (Engle et al , Meneguzzo and Liknes ). Used as windbreaks and shelterbelts across the Great Plains, this plant has rapidly expanded into historic prairies (Engle et al ), traditional oak and hickory forests, (Van Els et al ), and urban areas (Coppedge et al ), dramatically altering the soil and water composition (Pierce and Reich ) as well as bird and mammal fauna (Coppedge et al , Horncastle et al ). One of the major invasion zones for eastern red cedar has been in the southern Great Plains in Oklahoma (Bidwell et al ).…”

Long-term streamflow relations with riparian gallery forest expansion into tallgrass prairie in the Southern Great Plains, USA

“…For instance, at Konza Prairie (3487 ha) in the Flint Hills of Kansas, GIS analysis of historical aerial photographs uncovered an increase in riparian gallery forest from 157 ha in 1939 to 241 ha in 1985 (Knight et al, 1994). Eastern redcedar (Juniperus virginiana) encroachment into Great Plains rangelands (Linneman and Palmer, 2006;Coppedge et al, 2007;Crawford and Hoagland, 2009;Van Els et al, 2010;Wine et al, 2011) has been more widely documented than riparian gallery expansion. Similar to riparian gallery expansion, eastern redcedar encroachment is attributed to reduced fire frequency (Arend, 1950).…”