As invasive species become increasingly abundant in forests, their presence may influence a number of key nutrient cycling processes. For example, Chinese privet has become well established in southeastern forests and continues to spread. Two studies, a multisite field investigation and a controlled approach on a single site, were conducted to examine the role of Chinese privet (Ligustrum sinense) on decomposition within riparian forests of the Georgia Piedmont. The field study also investigated the effects of privet presence on soil nitrogen (N) mineralization and microbial carbon and N immobilization. Both studies utilized a litterbag approach to examine how increasing proportions of privet in foliar litter influenced mass loss rates and nutrient dynamics. The field investigation included litterbags with representative proportions of the five dominant species from 16 sites. Litterbags in the controlled study were composed of specific levels of privet litter within bags (0, 10, 20, 30, 40, and 50% Chinese privet) as treatments. The litter quality of four native species was compared to Chinese privet in the controlled study. Both studies showed significant positive relationships between percentage of Chinese privet in litterbags and decomposition rates (2.6-fold rate increase with 30% privet in litterfall). Chinese privet leaf litter had lower lignin and cellulose concentrations, higher N concentrations, lower lignin : N ratios, and narrower C : N ratios than the native species. The positive relationship between mass loss rates and the proportion of Chinese privet in litter indicates that Chinese privet enhances decomposition rates as it becomes more abundant. During summer, N mineralization showed approximately a fivefold increase; during winter, microbial biomass N increased by approximately 30% on sites with the highest levels of privet in the understory. Consequently, C and N dynamics in Piedmont riparian forests were significantly influenced in direct proportion to the amount of privet present in the understory.

Rain gardens have become a widespread stormwater practice in the United States, and their use is poised to continue expanding as they are an aesthetically pleasing way to improve the quality of stormwater runoff. The terms rain garden and bioretention, are now often used interchangeably to denote a landscape area that treats stormwater runoff. Rain gardens are an effective, attractive, and sustainable stormwater management solution for residential areas and urban green spaces. They can restore the hydrologic function of urban landscapes and capture stormwater runoff pollutants, such as phosphorus (P), a main pollutant in urban cities and residential neighborhoods. Although design considerations such as size, substrate depth, substrate type, and stormwater holding time have been rigorously tested, little research has been conducted on the living portion of rain gardens. This paper reviews two studies—one that evaluated the effects of flooding and drought tolerance on the physiological responses of native plant species recommended for use in rain gardens, and another that evaluated P removal in monoculture and polyculture rain garden plantings. In the second study, plants and substrate were evaluated for their ability to retain P, a typical water pollutant. Although plant growth across species was sometimes lower when exposed to repeated flooding, plant visual quality was generally not compromised. Although plant selection was limited to species native to the southeastern U.S., some findings may be translated regardless of region. Plant tissue P was higher than either leachate or substrate, indicating the critical role plants play in P accumulation and removal. Additionally, polyculture plantings had the lowest leachate P, suggesting a polyculture planting may be more effective in preventing excess P from entering waterways from bioretention gardens. The findings included that, although monoculture plantings are common in bioretention gardens, polyculture plantings can improve biodiversity, ecosystem resilience, and rain garden functionality.

Since its introduction to the United States in 1852, Chinese privet (Ligustrum sinenseLour.) has spread throughout the Southeast, invading many natural areas. Manual control by cutting or shredding is one of the most common strategies many land managers employ. However, rapid sprouting from the root collar and lateral roots commonly results in poor control. Cutting followed by either glyphosate or triclopyr application to the stumps is generally effective, but the efficacy of these herbicides in relation to treatment timing andL. sinenseroot collar diameter has not been evaluated. The objective of this experiment was to determine the effectiveness of glyphosate and triclopyr cut stump treatments compared with cutting alone at spring and fall timings across a range ofL. sinensesize classes. Studies were conducted at two locations in Auburn, AL. Treatments included cut stump+no herbicide, cut stump+ glyphosate (120 g L−1), or cut stump+triclopyr (90 g L−1). Treatments were applied to at least 50 experimental units each at April and November timings. Root collar diameter was recorded for each stem, stems were cut 2.5 cm above the ground, and herbicide treatments were applied within 30 s.Ligustrum sinensemortality and sprouting were quantified 6, 12, and 18 mo after treatment. Both glyphosate and triclopyr amine were very effective in controllingL. sinenseat both spring and fall timings. However, glyphosate provided slightly better results than triclopyr when lateral sprouting was included. Application timing also was significant, with a lower percentage of sprouting following November treatments than April treatments. Stem size influenced treatment success, as larger stumps tended to sprout more than smaller stumps. These results indicateL. sinensecan be controlled with cut stump herbicide treatment using either glyphosate or triclopyr with spring or fall timings at concentrations much lower than typically used.

Chinese privet is an invasive shrub that commonly infests roadsides and bottomland forests across the southeastern United States. Its aggressive growth and ability to prolifically sprout from the root collar and shallow lateral roots makes control very difficult. Individual plant treatment methods such as low-volume basal bark herbicide application with triclopyr are commonly used for Chinese privet control. However, little research has been done to examine optimal triclopyr concentrations and application timings for the low-volume basal bark method. Furthermore, little is known regarding basal bark treatment efficacy when plant size varies. To address these questions, field studies were conducted from 2009 to 2011 at two locations in east-central Alabama near Auburn and Opelika. The triclopyr butoxyethyl ester formulation was applied in January or March to Chinese privet shrubs across a range of sizes in a commercially available basal oil carrier at 24 (5% v/v−1), 48 (10% v/v−1), and 96 g L−1 (20% v/v−1). Additionally, a triclopyr butoxyethyl ester ready-to-use formulation (90 g L−1) was applied at 100% v/v−1. Canopy defoliation, sprout height, and mortality were quantified at 6, 12, and 18 mo after treatment. Triclopyr at all concentrations was highly effective in defoliating Chinese privet and reducing height of new basal sprouts. However, mortality was concentration dependent. The 90 and 96 g L−1 treatments resulted in 88 and 89% mortality across timings, while the 24 and 48 g L−1 treatments resulted in 63 and 76% mortality. March applications were less effective as basal diameter increased, especially at the lower triclopyr concentrations where mortality fell to less than 40%. These results indicate that triclopyr is an effective treatment for Chinese privet control, but efficacy is influenced by concentration, application timing, and plant size.

Research was conducted to evaluate the effect of phosphorus (P) concentration in irrigation water on growth of a southeastern U.S. native grass Muhlenbergia capillaris in flooded and non-flooded conditions. Plants of Muhlenbergia capillaris (Lam.) Trin. (gulf muhly grass) growing in 3.8 liter (1 gal) containers in 85:15 sand:peat were flooded to the substrate surface for 0 (non-flooded) or 3 days (flooded). Between flooding events, plants were drained for 6 d with no additional irrigation. The flood-drain process was repeated five times. Non-flooded plants were hand watered as needed. Plants were irrigated (non-flooded) or flooded with one of several tap water solutions, each with a different P concentration ranging from 0 to 0.8 mg·liter−1 (ppm) P (hereafter referred to as P irrigation rate). The experiment was repeated once (total two runs). Shoot dry weight (SDW) root dry weight (RDW) were higher in non-flooded plants than in flooded plants in both runs. Shoot dry weight increased linearly with an increasing P irrigation rate, while RDW changed cubically with increasing P irrigation rates in run 1 (no effect on either in run 2). Phosphorus concentration in leachate increased with increasing P irrigation rate in run 1 but not in run 2. Phosphorus concentration in leachate was usually higher in flooded plants than in non-flooded plants in both runs. All plants maintained root and shoot growth when flooded suggesting M. capillaris would be appropriate native species for rain gardens or bioretention areas. Phosphorus concentrations in leachate were lower than what was applied indicating P was removed via plant uptake or substrate adsorption or both.