Encroachment Dynamics of Juniperus virginiana L. and Mesic Hardwood Species into Cross Timbers Forests of North-Central Oklahoma, USA

Abstract

Cross Timbers forests, typically dominated by Quercus stellata Wangenh. and Q. marilandica Muenchh., are the transition zone between eastern deciduous forest and prairie in the southern Great Plains. Fire exclusion beginning in the mid-1900s has led to increasing stand density and encroachment of fire-intolerant Juniperus virginiana L. and mesic hardwood. We measured current forest structure and tree ages of 25 stands (130 plots) in north-central Oklahoma to characterize the extent and dynamics of encroachment. The respective basal area and stand density of the overstory (diameter at breast height; dbh > 10 cm) were 19.0 m 2 ha −1 and 407 trees ha −1 with Q. stellata comprising 43% of basal area and 42% of stand density. Quercus marilandica represented only 3% of basal area and 4% of overstory density. Juniperus virginiana represented 7% of basal area and 14% of stand density while mesic hardwoods, e.g., Celtis spp., Ulmus spp., Carya spp., 33% of basal area and stand density. The sapling layer was dominated by mesic hardwoods (68%) and J. virginiana (25%) while the seedling layer was dominated by mesic hardwoods (74%). The majority of Quercus recruited into the overstory between 1910-1970, while recruitment of J. virginiana and mesic hardwoods began more recently (post 1950s). Growth rate, based on the relationship between age and dbh, was faster for mesic hardwoods than for J. virginiana and Q. stellata. These results indicate that removal of recurrent surface fire as a disturbance agent has significantly altered forest composition in the Cross Timbers region by allowing encroachment of J. virginiana and fire-intolerant, mesic hardwoods. This increases wildfire risk because J. virginiana is very flammable and will alter how these forests respond to future drought and other disturbance events.

Expansion of Eastern Redcedar (Juniperus virginiana L.) into the Deciduous Woodlands within the Forest–Prairie Ecotone of Kansas

“…Eastern redcedar encroachment into the deciduous woodlands as a percentage of existing deciduous woodlands for the three sites were 25%, 13%, and 18%, respectively. This observed ERC encroachment into deciduous woodlands within the forest-prairie ecotone of Kansas, is in parallel to what was reported for other forest types in this region, such as the Cross Timbers of north-central Oklahoma [39] and the glade-like forest types in mid-Missouri [40]. Table 6.…”

“…Thirty-year ERC change within the three study areas. what was reported for other forest types in this region, such as the Cross Timbers of north-central Oklahoma [39] and the glade-like forest types in mid-Missouri [40]. Total eastern redcedar (ERC) encroachment between 1986 to 2017 in the three study areas, broken down by conversion of deciduous forests and non-forest classes to ERC.…”

“…In addition to altering species composition and affecting associated ecosystem services, ERC encroachment increases the risk of wildfires [39,42]. Due to its structure, the highly flammable ERC trees can act as ladder fuels, increasing the risk of initiating a crown fire and converting it to a wildfire [18,39].…”

“…In addition to altering species composition and affecting associated ecosystem services, ERC encroachment increases the risk of wildfires [39,42]. Due to its structure, the highly flammable ERC trees can act as ladder fuels, increasing the risk of initiating a crown fire and converting it to a wildfire [18,39]. High flammability of ERC trees was visible during a controlled burn in Kansas [8], where some crowns of standing ERC trees (Figure 9a) and thinned trees lying on the ground (Figure 9b) caught on fire, with flame heights reaching 20 feet or more.…”

Impact of Eastern Redcedar Proliferation on Water Resources in the Great Plains USA—Current State of Knowledge

“…The Great Plains is a transition region between relatively moist eastern deciduous forest and arid desert to the West. Reductions in the number and frequency of fires in the region and minimal active grassland management are two key factors leading to woody plant encroachment into grassland areas [3], as well as the densification and mesophication of forests [4]. Over the past century, redcedar has increased and become dominant at many rangeland sites in the Central Great Plains where it was historically absent.…”