Westward Expansion by Juniperus virginiana of the Eastern United States and Intersection with Western Juniperus Species in a Novel Assemblage

Eastern redcedar (Juniperus virginiana L.) is increasing in density in the eastern United States and expanding in range to the west, while western Juniperus species also are increasing and expanding, creating the potential for a novel assemblage. I estimated range expansion and intersection by comparing recent USDA Forest Service Forest Inventory and Analysis surveys (mean year = 2009) to the oldest available surveys (mean year = 1981), with adjustments for sampling changes, and predicted climate envelopes during the following year ranges: 1500–1599, 1800–1849, 1850–1899, 1900–1949, and 1960–1989. During approximately 28 years, eastern redcedar range expanded by about 54 million ha (based on ≥0.5% of total stems ≥12.7 cm in diameter in ecological subsections). Combined range of western species of juniper did not expand. Range intersection of eastern redcedar and western Juniperus species totaled 200,000 km2 and increased by 31,600 km2 over time, representing a novel assemblage of eastern and western species. Predicted ranges during the other time intervals were 94% to 98% of predicted area during 1960–1989, suggesting major climate conditions have been suitable for centuries. The southern western Juniperus species and Rocky Mountain juniper (Juniperus scopulorum Sarg.) have the greatest potential for intersection with eastern redcedar, whereas eastern redcedar may have concluded westward expansion.

Effects of post oak Quercus Stellata and Smooth Brome Bromus Inermis Competition on Water Uptake and Root Partitioning of Eastern Redcedar Juniperus Virginiana

Water availability may alter species competitive interactions, resulting in different outcomes as plants compete for available water. Eastern redcedar Juniperus virginiana (hereafter ERC) will likely continue to encroach into new habitats, which will affect soil and water budgets. We designed a greenhouse experiment to investigate changes in water uptake and rooting depths of two-year old ERC saplings in the presence of an invasive grass (Bromus inermis) and a native tree (Quercus stellata). We measured soil moisture content over two growing seasons. When grown together, ERC took up water from the deeper layers (21–40 cm) whereas B. inermis used water from the top layers of the soil (0–20 cm). Similarly, when ERC grew with Q. stellata, ERC took up water from the deeper layers and Q. stellata used water mostly from the top layers. This root partitioning can allow the co-existence of ERC, grasses, and other trees, which can facilitate ERC encroachment into grasslands and woodlands. However, when the three species grew together, we found root overlap between the ERC and Q. stellata. This overlap can affect ERC establishment and encroachment in habitats where grasses and trees co-occur. A major factor that affected ERC performance was higher mortality in treatments with B. inermis than in the ERC-alone or with Q. stellata. This indicates that competition with grasses is a major factor affecting ERC sapling establishment.

Economic Feasibility of Mixed-Species Grazing to Improve Rangeland Productivity

Pasture and grazing land in the southern and central Great Plains is being invaded by woody species, especially eastern redcedar. As a result of woody plant encroachment, cattle production on native rangeland is becoming less profitable because stocking rates must be decreased. Eastern redcedar encroachment can be controlled by grazing management, herbicide use, prescribed fire, mechanical control and mixed species grazing. This study utilizes traditional management practices, prescribed fire and three types of mixed species grazing operations to determine the most economically feasible way to manage redcedar encroachment on rangeland. The cost-benefit analysis in this study found that the source of redcedar management on rangeland with the highest net present value was the use of a breeding goat operation in which goats were grazed alongside cattle with the use of prescribed fire. This suggests that producers who are fighting redcedar encroachment will likely be able to implement a mixed species grazing operation with breeding goats to better manage their land and increase returns.

Shade is the most important factor limiting growth of a woody range expander

The expansion of woody plants into grasslands and old fields is often ascribed to fire suppression and heavy grazing, especially by domestic livestock. However, it is also recognized that nutrient availability and interspecific competition with grasses and other woody plants play a role in certain habitats. I examined potential factors causing range- and niche expansion by the eastern redcedar Juniperus virginiana, the most widespread conifer in the eastern United States, in multifactorial experiments in a greenhouse. Historical records suggest that the eastern redcedar is a pioneer forest species, and may be replaced as the forest increases in tree density due to shading. Another possible factor that affects its distribution may be nutrient availability, which is higher in old fields and other disturbed lands than in undisturbed habitats. In its historic range, eastern redcedars are particularly abundant on limestone outcrops, often termed ‘cedar barrens’. However, the higher abundance on limestone could be due to reduced interspecific competition rather than a preference for high pH substrates. I manipulated shade, fertilization, lime, and interspecific competition with a common dominant tree, the post oak Quercus stellata. In a separate experiment, I manipulated fire and grass competition. I measured growth rates (height and diameter) and above- and belowground biomass at the end of both experiments. I also measured total non-structural carbohydrates and nitrogen in these plants. Shade was the most important factor limiting the growth rates and biomass of eastern redcedars. I also found that there were significant declines in nitrogen and non-structural carbohydrates when shaded. These results are consistent with the notion that the eastern redcedar is a pioneer forest species, and that shade is the reason that these redcedars are replaced by other tree species. In the second experiment, I found that a single fire had a negative effect on young trees. There was no significant effect of competition with grass, perhaps because the competitive effect was shading by grasses and not nutrient depletion. Overall, the effects of shade were far more apparent than the effects of fire.

Stand-Level Transpiration Increases after Eastern Redcedar (Juniperus virginiana L.) Encroachment into the Midstory of Oak Forests

Eastern redcedar (Juniperus virginiana L., redcedar) encroachment is transitioning the oak-dominated Cross-Timbers of the southern Great Plain of the USA into mixed-species forests. However, it remains unknown how the re-assemblage of tree species in a semiarid to sub-humid climate affects species-specific water use and competition, and ultimately the ecosystem-level water budget. We selected three sites representative of oak, redcedar, and oak and redcedar mixed stands with a similar total basal area (BA) in a Cross-Timbers forest near Stillwater, Oklahoma. Sap flow sensors were installed in a subset of trees in each stand representing the distribution of diameter at breast height (DBH). Sap flow of each selected tree was continuously monitored over a period of 20 months, encompassing two growing seasons between May 2017 and December 2018. Results showed that the mean sap flow density (Sd) of redcedar was usually higher than post oaks (Quercus stellata Wangenh.). A structural equation model showed a significant correlation between Sd and shallow soil moisture for redcedar but not for post oak. At the stand level, the annual water use of the mixed species stand was greater than the redcedar or oak stand of similar total BA. The transition of oak-dominated Cross-Timbers to redcedar and oak mixed forest will increase stand-level transpiration, potentially reducing the water available for runoff or recharge to groundwater.

Surface Quality of Wood Plastic Composites as Function of Water Exposure

The objective of this study was to evaluate the surface quality of experimentally manufactured wood plastic composite (WPC) samples exposed to water soaking. Eastern redcedar (Juniperus virginiana L.), which is one of the invasive species in Oklahoma, USA, and recycled plastic were used to manufacture WPC samples. Three types of samples, namely with 0%, 3% and 6% nano-clay were soaked in water for up to one month. Stylus-type equipment was employed to evaluate their surface roughness as a function of water exposure. Two accepted roughness parameters, average roughness (Ra) and mean peak-to-valley (Rz), were used to determine changes in the surface quality of the specimens due to water exposure. Average roughness values of 1.5 µm and 4.1 µm were determined for the samples with no clay in dry conditions and those soaked for one month in water, respectively. Corresponding values were lower in the case of those with clay in their content. Based on the findings in this work, it appears that the stylus technique can be successfully applied to such samples to quantitatively evaluate their surface quality when they are exposed to water for an extended time span. It is expected that data from this work could help to produce a better understanding of the behavior of WPCs under environmental conditions.