Herbaceous Vegetation Control Research Articles

Harmonized site preparation and postplant herbaceous weed control for establishment of southern pine plantations on coastal bedded sites

AbstractLoblolly pine or slash pine response and vegetation colonization are summarized for a region-wide study that included five locations on coastal soils in the southern United States. The objective was to evaluate timing of postplant herbaceous weed control (HWC) treatments following preplant site preparation with imazapyr applied at two timings (August and November) and at three rates (0.56, 0.84, and 1.12 kg ha−1). All imazapyr site preparation treatments were applied after bedding. Site preparation treatments resulted in fast-growing stands without HWC at all locations with average Year 3 dominant tree height ranging from 2.6 to 3.7 m. Imazapyr plus sulfometuron was an effective HWC treatment on loblolly pine. Vegetation control and pine response varied by surface soil texture. On coarser-textured soils, the site preparation treatments resulted in <10% vegetation cover in June of the first pine growing season. On these coarser-textured soils, loblolly pine growth was increased by second-year and not first-year HWC. On finer-textured soils, vegetation colonization was aggressive, with >20% cover in June of the first pine growing season, such that early first-year HWC provided the largest loblolly pine response of single-pass HWC treatments. Pines were highly tolerant to imazapyr site preparation treatments as evidenced by the lack of differences in slash or loblolly pine survival and growth from the doubling of imazapyr rates for applications in either August or November. There was little meaningful residual control of herbaceous vegetation into the second pine growing season from site preparation treatments or first-year HWC regardless of location. There was no consistent pine response benefit from increasing the imazapyr site preparation rate for included treatments. Cost-effective treatments would utilize low site-preparation herbicide rates followed by the appropriate timing of HWC if longer-term vegetation control is the objective.

APPLICATION OF HERBICIDES IN THE CONTROL OF THE INVASIVE SPECIES<i> HERACLEUM SOSNOWSKYI</i> MANDEN. (SOSNOWSKY’S HOGWEED) IN FORESTRY

A representative of the family Apiacea, Sosnowsky's hogweed ( Heracleum sosnowskyi Manden.) previously cultivated as a fodder plant and now occupying vast territories along roads and railways, in and near settlements, uncultivated agricultural lands, on farms and in many other areas, poses a serious threat to human health. On these lands, an active eradication campaign has been going on for over 15 years. This invasive species also spreads actively on the lands of the forest fund including plantations, felling sites, young stands of natural origin, clearings and hayfields, forest stands of different ages with a small basal area, and in the most productive forest conditions. As a result, in forest plantations growth of woody plants (primarily of coniferous species) is inhibited, their death is observed, and environmental, aesthetic and industrial damage increases due to the growth and dominance of Sosnowsky's hogweed. As a result of field experiments in the Leningrad Region, a high effectiveness of a number of modern herbicides (Roundup, Anchor-85, and Magnum) for control of Sosnowsky's hogweed and other unwanted herbaceous vegetation, as well as their selectivity in relation to pine and spruce, has been demonstrated.

Effects of plant traits and their divergence on runoff and sediment retention in herbaceous vegetation

Plant species diversity impacts ecosystem processes, but its effects on runoff and soil erosion are not fully understood. Herbaceous vegetation control concentrated runoff and soil erosion through the increase of hydraulic roughness which leads to sediment retention. This study aims to investigate the effect of aboveground traits and their divergence (i.e., stem diameter and density, and leaf area and density) on hydraulic roughness and sediment retention in plant communities. Runoff experimentations were performed, using a sediment input, on three mono-specific and one multi-specific conditions composed of plant species with contrasting traits furthering hydraulic roughness and sediment retention. No effect of trait diversity was found on the hydraulic roughness and sediment retention; which would be explained by the absence of an optimal space use by the traits involved in the increase of the hydraulic roughness. The dominant effect of the community-weighted traits in the plant community drives the effects of the vegetation on the hydraulic roughness and sediment retention. This absence of positive effects of the trait diversity on hydraulic roughness and sediment retention constitutes an important knowledge to model runoff and soil erosion processes and to design herbaceous infrastructures for soil erosion control.

Impacts of under-canopy vegetation on stand growth in two pine saw-timber stands, South Africa

BackgroundIn pine plantations, shading following canopy closure reduces the growth of competing vegetation. However, canopy closure is not always achieved if low initial planting density, pruning and thinning are practised. This means that complete shading does not occur, resulting in stands with potentially competitive levels of under-canopy vegetation.MethodsAt the time of the first pruning operation, two trials were established to determine the competitive effect of under-canopy vegetation on pine tree growth in South Africa, one on a Pinus patula Schiede ex Schltdl. & Cham. (4.5 years) and one on a Pinus tecunumanii F.Schwerdtf. ex Eguiluz & J.P.Perry (2.9 years) stand. This paper documents results at the final thinning operation carried out at 17–18 years. Treatments were weedy (no vegetation control), herbaceous (complete sustained control of woody vegetation), woody (complete sustained control of herbaceous vegetation), weedfree (complete sustained control of all competing vegetation) and operational (only the woody perennial broadleaves were removed prior to any pruning/thinning event in the commercial weed control treatment). From the time vegetation management treatments were first imposed, they were maintained and tree performance monitored over 14–15 successive growing seasons, including and up to the second and final thinning to 250 stems ha−1.ResultsThe presence of vegetation for up to 15 years had no significant impact on the volume of P. patula and P. tecunumanii following two thinning operations (813 to 400 stems ha−1; 400 to 250 stems ha−1). For P. patula, but not P. tecunumanii, there was a significant and negative impact of under-canopy vegetation on the total basal area removed during two thinning operations. This may result in a reduction in the selection of stems to remain following thinning, as well as any profit that may be obtained if the thinnings were of commercial value.ConclusionsFor the species (P. patula and P. tecunumanii) and sites tested, the results indicate that if good establishment weed control is carried out (from planting until the first pruning event), the development and subsequent impact of under-canopy vegetation over the subsequent 14–15 years (between the first pruning event and the final thinning to 250 stems ha−1) on the growth of the remaining stems is negligible.

How do management techniques affect carbon stock in intensive hardwood plantations?

Recent studies in temperate regions have shown that agroforestry systems, especially silvopastoral systems, have greater carbon (C) sequestration potential than monocropping systems or pastures, or even forest plantations. In Europe, there is growing interest in establishing high quality wood plantations with intensive management comprising irrigation, fertilisation and chemical weed control to reduce rotation length. However, these operations can have major environmental impacts similar to the effects of intensive agriculture, such as impoverishment of soil C. The aim of this study is to identify optimum management practices for intensive systems of quality wood production to optimise soil C stock and plantation productivity. An experiment was conducted in Extremadura, mid-west Spain, from 2011 to 2014, in a 13-year-old hybrid walnut (Juglans major×regia mj 209xra) plantation with a density of 333 trees ha−1. Two essays were established: one with three techniques to control competition from herbaceous strata beneath trees – mowing, ploughing and sheep grazing (1 sheep ha−1) – and the other to test implementation of legumes (mixture of Trifolium michelanium and Ornithopus compressus complemented by the same quantities of phosphorous and potassium as mineral treatment) as an alternative to traditional mineral fertilisation (40kgNha−1, 40kg P2O5 ha−1 and 50kg K2O ha−1). The C stock estimate was based on soil organic carbon (SOC) and aboveground (tree trunks and branches) and belowground biomass (tree and pasture roots). Most of the C stock was contained in SOC, at 50% in the uppermost soil layer (0–25cm), followed by aboveground biomass. The response of SOC in each treatment was higher than the other parameters analysed, suggesting that SOC is a more sensitive pool to management techniques. Grazing as control of herbaceous vegetation and legume implementation as nitrogen supply are suitable techniques for optimising soil C stocks and also achieve adequate tree growth in the longer term.

Optimum Vegetation Conditions for Successful Establishment of Planted Eastern White Pine (Pinus strobus L.)

The 10th-growing season performance of planted eastern white pine (Pinus strobus L.) seedlings was evaluated in response to herbaceous and woody vegetation control treatments within a clearcut and two variants of the uniform shelterwood regeneration system (single vs. multiple future removal cuts). Herbaceous vegetation control involved the suppression of grasses, forbs, ferns and low shrubs for the first 2 or 4 growing seasons after planting. Deciduous woody vegetation control treatments, conducted in combination with the herbaceous treatments within a response-surface design, involved the permanent removal of all tall shrubs and deciduous trees at the time of planting, at the end of the 2nd or 5th growing seasons, or not at all. In general, the average size of planted pine was related positively to the duration of herbaceous vegetation control and negatively to delays in woody control. White pine weevil (Pissodes strobi Peck) altered these trends, reducing the height of pine on plots with little or no overtopping deciduous woody vegetation or mature tree cover. Where natural pine regeneration occurred on these plots, growth was similar but subordinate to the planted pine. Data from the three sites indicate that at least 60% of planted pine may be expected to reach an age-10 height target of 2.5 m when overtopping cover (residual overstory + regenerating deciduous) is managed at approximately 65% ± 10%, and total herbaceous cover is suppressed to levels not exceeding 50% in the first five years. On productive sites, this combination may be difficult to achieve in a clearcut, and requires fairly rigorous vegetation management in shelterwood regeneration systems. Currently, synthetic herbicides offer the only affordable and effective means of achieving such vegetation control.

Effects of overstory retention, herbicides, and fertilization on sub-canopy vegetation structure and functional group composition in loblolly pine forests restored to longleaf pine

The desirable structure of longleaf pine forests, which generally includes a relatively open canopy of pines, very few woody stems in the mid-story, and a well-developed, herbaceous ground layer, provides critical habitat for flora and fauna and contributes to ecosystem function. Current efforts to restore longleaf pine to upland sites dominated by second-growth loblolly pine require information about how restoration treatments affect sub-canopy vegetation. We established a field experiment at Fort Benning in Georgia and Alabama, USA to determine the effects of four levels of approximately uniform canopy density (Control [∼16m2/ha basal area], MedBA [∼9m2/ha basal area], LowBA [∼5m2/ha basal area], and Clearcut [0m2/ha basal area]) and three cultural treatments (NT [untreated], H [chemical control of woody and herbaceous vegetation] and H+F [chemical control plus fertilization]) on vegetation structure and functional group composition for three growing seasons following canopy removal. In general, cover (a measure of abundance) of ground layer vegetation increased with the amount of canopy removal. The ground layer was dominated by herbaceous vegetation in each year. Canopy trees generally suppressed the cover of graminoids in the first two years after treatment but only the Control plots had lower graminoid cover than Clearcut plots after the third growing season. Forb cover was significantly lower on Control plots than on Clearcut plots after only the first growing season, and woody stems/shrubs had lower cover on Control plots than on LowBA or Clearcut plots in each year. Vegetation cover increased following the first year after canopy removal, and the relative dominance of functional groups did not change through time. Canopy retention limited the development of mid-story woody stems, with the greatest stem densities in the Clearcut plots. The herbicide treatment (on both H and H+F) significantly reduced woody stem density in the mid-story in 2009, but the effect was no longer significant in 2010. Traditional methods for converting stands of other pine species to longleaf pine commonly include clearcutting followed by planting, but our results suggest that clearcutting may release woody vegetation to increase mid-story stem densities and will reduce the amount of pine needles in the fuel bed. Retaining low to moderate levels of canopy density (5–9m2/ha basal area) in loblolly pine stands may provide an effective balance for reaching multiple restoration objectives that include maintaining desirable vegetation structure and creating fuel conditions for a frequent fire regime.

Influence of herbaceous and woody vegetation control on seedling microclimate, leaf gas exchange, water status, and nutrient relations of Pinus strobus L. seedlings planted in a shelterwood

The influence of herbaceous and woody vegetation control applied over four consecutive growing seasons (GS) on microclimate, leaf gas exchange, water status, nutrient relations, and growth of planted eastern white pine (Pinus strobus L.) seedlings was examined in a central Ontario shelterwood. Treatment effects on pine seedling ecophysiology were closely associated with temporal changes in the structure and species composition of the developing understory plant communities. Vegetation control had minimal influence on air temperature, but herbaceous control, sometimes in combination with woody control, improved the soil thermal regime in every GS. Herbaceous vegetation control increased soil moisture availability in GS one and two, but only during mid-summer periods of little precipitation. Light availability showed a relatively large treatment response, with highest light levels created where both herbaceous and woody vegetation were suppressed. Herbaceous and woody vegetation control had additive or interactive effects on net carbon assimilation (An) and leaf conductance to water vapour (Gwv) in a given GS, while water use efficiency and midday leaf water potential (ψm) were largely independent of treatment. The effects of vegetation control on An, Gwv, and ψm were often correlated with treatment-induced changes in total vegetative cover, light, and soil moisture availability. Vector analysis of leaf nutrient (N, P, K, Ca, and Mg) relations suggested that herbaceous vegetation control relieved foliar N, P, and K deficiencies in 5-year-old white pine seedlings, woody vegetation control did not affect leaf nutrient relations, and total vegetation control provided non-limiting conditions. In GS four, white pine growth responses were highest where both herbaceous and woody vegetation control had been conducted, likely in response to improved microclimate, resource availability, leaf gas exchange, and foliar nutrition.

Influence of herbaceous and woody competition on white pine regeneration in a uniform shelterwood

We investigated the effects of herbaceous and woody vegetation control on the survival and growth of planted and natural eastern white pine (Pinus strobus L.) seedlings through six growing seasons following a uniform shelterwood regeneration harvest on two independent sites. Subsequent to chain scarification, white pine seedlings were planted at 2-m spacing, augmenting natural regeneration (full stocking and >3000 seedlings per ha). Herbaceous vegetation control involved the suppression of grasses, forbs, ferns, and low shrubs, and was maintained for zero, two, or four growing seasons after planting. Woody control involved the removal of all tall shrubs and deciduous trees, and was conducted at the time of planting, at the end of the second or fifth growing seasons, or not at all. White pine seedling growth responded positively to increased duration of herbaceous vegetation control and negatively to delayed woody control. Maximum growth was not realized unless both types of vegetation were suppressed. During the first six growing seasons, the height growth of planted pine was more than twice that of naturally regenerating pine, regardless of tending regime. The study suggests that successful white pine regeneration may be achieved by thinning from below to allow 50% to 60% of full sunlight in the understory, followed by the proactive, early suppression of woody and herbaceous vegetation to maintain optimum light levels and reduce competition for soil moisture and nutrients.

Effect of early age woody and herbaceous competition control on wood properties of loblolly pine

Early age competition control has been reported to significantly improve the growth and yield of plantation grown loblolly pine. The objective of this paper is to understand the changes in wood properties: basal area weighted whole disk SG, earlywood SG (EWSG), latewood SG (LWSG) and latewood percent (LWP) of 14 year-old trees which received early age herbaceous and hardwood competition control, using data collected from 13-sites across 4-physiographic regions in the southeastern USA. The study was laid out in a randomized complete block design and had four levels of weed control (no weed control; woody vegetation control; herbaceous vegetation control; and woody and herbaceous vegetation control), with four blocks at each site. Increment cores 12 mm in diameter were collected at breast height (1.37 m) from 9-trees in each plot and ring-by-ring SG, EWSG, LWSG and LWP measured using a X-ray densitometer. Whole disk basal area weighted SG and LWP were determined for each tree and used for analysis. A reduction in whole disk SG of 0.039 and 0.0014 and LWP of 7.38% and 3.62% was observed for trees which received total weed control compared to no weed control, for lower and upper Coastal Plain sites, respectively. For trees receiving total weed control compared to no weed control, it was observed that the diameter of the juvenile core increased by 20% on average across all physiographic regions. However, no change in the length of the juvenile period was observed among treatments other than the regional differences.

Songbird Breeding Season Use of Pine Plantations Treated Chemically for Herbaceous Vegetation Control

AbstractPine plantations, a common early successional habitat in the southeastern United States, have been subject in recent years to increased use of herbicides to control herbaceous vegetation immediately postestablishment. Such treatments may affect songbird use during the breeding season, but studies documenting bird response are limited. Furthermore, songbirds that breed in early successional habitats have experienced sustained population declines in recent decades. Therefore, we examined the influence of herbaceous vegetation control on songbird use during the breeding season within pine plantations on the Piedmont Plateau in Virginia. We evaluated 35 plantations characterized by one of five treatments: herbaceous vegetation control applied during the establishment year and that were 1, 2, or 3 y old when sampled, and those that had not received herbaceous vegetation control at establishment and that were 1 or 2 y old when sampled. There was no difference (P > 0.05) in detections of birds between plantations with and without herbicide treatment. However, 1-y-old plantations (both treated and untreated) had fewer detections (P < 0.05) than 2-y-old plantations for 3 individual species and for all 16 species combined.

Timing and duration of herbaceous vegetation control in northern conifer plantations: 15th-year tree growth and soil nutrient effects

A 15-year re-measurement of a study designed to identify the optimum timing and duration of herbaceous vegetation control in plantations of four commercial conifer species was completed in northern Ontario. Few differences were revealed in conifer growth when contrasting early and delayed timing of vegetation control. Conversely, each conifer species responded positively to increased duration of vegetation control, with stand volume gains of up to 209% achieved with four to five years of vegetation control following planting. Compared to earlier assessments, the timing of vegetation control appeared less important than duration. Diminishing returns in the fastest-growing species (jack pine [Pinus banksiana Lamb.] and red pine [Pinus resinosa Ait.]) are consistent with intraspecific competition related to the onset of crown closure in these stands. Quantification of a suite of soil nutrient pools along the gradient of increased duration of vegetation control indicated that the more intensive levels of vegetation control did not adversely affect the assessed soil nutrient pools in red pine or jack pine, but a cautionary approach should be considered for white pine (Pinus strobus L.) and black spruce (Picea mariana [Mill.] BSP), where some declines were evident. Vegetation control for two to three years following planting should maximize early conifer growth potential without adverse longer-term effects on soil nutrient pools.

Influence of woody and herbaceous vegetation control on leaf gas exchange, water status, and nutrient relations of eastern white pine ( Pinus strobus L.) seedlings planted in a central Ontario clearcut

The influence of herbaceous and woody vegetation control, either singly or in combination, on leaf gas exchange, water status, and nutrient relations of planted eastern white pine ( Pinus strobus L.) seedlings was examined in a central Ontario clearcut over four consecutive growing seasons (GSs). Net carbon assimilation ( A n), leaf conductance to water vapour ( G wv), water use efficiency (WUE), and midday leaf water potential ( ψ m) were measured periodically during the second to fourth GSs of vegetation control treatments, while leaf nutrient relations were examined in GS five. Leaf A n and G wv were reduced ( p ≤ 0.05) in the presence of herbaceous vegetation in GS two, by both herbaceous and woody vegetation in GS three, and only by woody vegetation (largely trembling aspen ( Populus tremuloides Michx.)) in GS four. Leaf WUE was increased ( p ≤ 0.05) in all three GSs in which herbaceous vegetation control was applied and where woody vegetation provided partial shading of planted white pine. Leaf water status was comparatively less responsive to vegetation control treatments, but leaf ψ m was increased ( p ≤ 0.05) in the presence of woody vegetation in GSs two and four, likely due to shading and reduced atmospheric evaporative demand of the white pine seedling environment. Within a given GS, the effects of vegetation control on A n, G wv, and ψ m were strongly linked to treatment-induced changes in total vegetative cover, and light and soil moisture availability. Seedling height, diameter, and volume growth rates were positively correlated with A n and WUE in GSs two and three, but less so in GS four. Vector analysis suggested that herbaceous competition induced foliar N, P, and K deficiencies in five-year-old white pine seedlings while competition from aspen resulted in foliar Ca deficiency.

Early vegetation control for the regeneration of a single-cohort, intimate mixture of white spruce and trembling aspen on upland boreal sites

In Canada’s boreal forest region, there is increasing demand for practical regeneration strategies that will recreate mixed stands of white spruce ( Picea glauca (Moench) Voss) and trembling aspen ( Populus tremuloides Michx.). In 2002, we implemented an experiment in both west-central Alberta and northeastern Ontario to better understand the effects of herbaceous and woody vegetation control on crop tree survival and growth, within the context of prescription development for the regeneration of a single-cohort, intimate mixture of spruce and aspen. After five growing seasons, good spruce growth, health, and survival were observed with 2 m radial treatments consisting of herbaceous and woody (i.e., complete) vegetation control centred on trees planted at 5 m spacing. These spruce were 4%–64% taller and 68%–178% larger in stem diameter than untended trees, leading to 167%–1166% gains in stem volume, and were at least equivalent to the same stock grown at 2.5 m spacing and provided with complete, continuous relief from competition. Removing only the woody vegetation within treated radii stimulated herbaceous competition, resulting in reduced survival and growth of spruce and reduced height of surrounding aspen. Early results suggest that spot treatments that provide 2–4 years of relief from herbaceous and woody competition may offer a practical strategy for growing spruce with aspen.

The effects of herbaceous and woody competition on planted white pine in a clearcut site

We investigated the effects of herbaceous and woody vegetation control on the survival and growth of planted eastern white pine ( Pinus strobus L.) seedlings through six growing seasons. Herbaceous vegetation control involved the suppression of grasses, forbs, ferns, and low-shrubs, and was maintained for 0, 2, or 4 years after white pine seedlings were planted. Woody control involved the removal of all tall-shrub and deciduous trees, and was conducted at the time of planting, at the end of the second or fifth growing seasons, or not at all. Seedling height and basal diameter responded positively and proportionally to duration of herbaceous vegetation control. Gains associated with woody control were generally not significant unless some degree of herbaceous vegetation control was also conducted. Only herbaceous control increased pine crown closure and rate of crown closure. Herbaceous control and the presence of 5000–15,000 stems per ha of young overtopping aspen were associated with reduced weevil ( Pissodes strobi Peck.) injury and increased pine height growth. The study suggests that white pine restoration strategies on clearcut sites should focus on the proactive, early management of understory vegetation and the gradual reduction of overtopping cover from woody vegetation to create a seedling light environment that supports acceptable growth with minimal weevil damage.

A Comparison of Herbicide and Mulch Mat Treatments for Reducing Grass, Herb, and Shrub Competition in the BC Interior Douglas-Fir Zone—Ten-Year Results

Abstract We present results from a study established in 1993 in the Interior Douglas-fir biogeoclimatic zone of southwestern British Columbia to test the effectiveness of several herbicide and mulch mat treatments for reducing grass, herbaceous, and shrub competition. The effectiveness of the preplant herbicide applications of hexazinone (Velpar L) at 2.1 kg ai/ha, glyphosate (Vision) at 2.1 and 1.0 kg ai/ha, and the installation of plastic mulch mats (Tredegar 90 × 90-cm mats) for controlling competing vegetation, improving seedling growth and survival of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings and improving soil moisture availability was evaluated. Ten-year results indicate that application of hexazinone and glyphosate enhanced the survival, diameter, and height growth of planted Douglas-fir seedlings. These herbicide treatments provided effective control of grass and herbaceous vegetation for three to four growing seasons. Plastic mulch mats did result in improvements in growth and survival, but these were not statistically different from untreated seedlings. The results of soil moisture monitoring from within the various treatments indicated delay in the onset of soil drought as a key determinant of the seedling growth improvement noted. West. J. Appl. For. 20(3):167–176.

Ten Years of Vegetation Succession Following Ground-Applied Release Treatments in Young Black Spruce Plantations

Abstract Responses of planted black spruce [Picea mariana (Mill.) BSP] and associated vegetation were studied for 10 years after conifer release options on two northeastern Ontario sites. Six treatments were compared to untreated check plots, including directed foliar application of glyphosate herbicide, basal bark treatment with triclopyr herbicide, glyphosate capsule injection with the EZ-Ject system, spot-treatment with hexazinone herbicide, manual cutting with brushsaw, and five growing seasons of annual vegetation removal with repeat applications of glyphosate. Ten years after treatment, black spruce survival averaged 86% and varied little among treatments (P > 0.5). Annual vegetation removal treatments resulted in nearly complete domination by spruce, with treated trees exhibiting 16–55% gains in height and 112–476% gains in stem volume growth over untreated trees. Despite rigorous vegetation control on these plots, each of the vegetation groups studied were well represented at the end of the observation period, including deciduous trees, tall shrubs, low shrubs, forbs, ferns, and grasses/sedges. Directed foliar treatment provided good control of herbaceous and woody vegetation around individual crop trees, providing an 8–46% gain in height and a 43–246% gain in stem volume growth. Both spruce and hardwoods shared dominance on these plots. Spot treatments with hexazinone provided similar short-term reductions in herbaceous vegetation, but tended to release shrub species that had a negative net effect on spruce growth. The other release treatments provided only short-term reductions in woody vegetation, which ultimately led to young stands dominated by deciduous tree species. North. J. Appl. For. 21(3):123–134.

Natural Product Herbicides for Control of Annual Vegetation Along Roadsides

Natural product herbicides for vegetation control are being considered as alternatives to synthetic herbicides by many public agencies. Studies were conducted along roadsides at the Hopland Research and Extension Center (HREC) in 2001 and 2002 and on California State Route 29 (SR29) in 2002 to evaluate acetic acid, pine oil, and plant essentials compared with glyphosate for control of herbaceous vegetation. In 2001, annual grass control after a single application of pine oil at HREC was 40% or less effective, whereas acetic acid was at least 79% effective. A second application of pine oil or acetic acid did not control regrowth or new plants. In 2002, plant essentials was the most effective (>80%) natural product at HREC for control of annual grasses, except slender oat. Pine oil often provided similar control of slender oat as plant essentials (71 and 69%, respectively). At SR29, five applications of acetic acid provided 83% or better control of slender oat, hare barley, medusahead, and broadleaf filaree. Plant essentials and pine oil controlled hairy vetch, broadleaf filaree, and hare barley at least 83%, but yellow starthistle, soft chess, buckhorn plantain, and medusahead control never exceeded 85%. Glyphosate controlled all vegetation in these experiments with one or two applications. The cost of one or more applications of the natural products was greater than 10 times the cost of using one or two applications of glyphosate. Natural products were neither efficaciously nor economically comparable with glyphosate for control of annual roadside vegetation.

Stand Dynamics and Plant Associates of Loblolly Pine Plantations to Midrotation after Early Intensive Vegetation Management—A Southeastern United States Regional Study

Abstract Increasingly, pine plantations worldwide are grown using early control of woody and/or herbaceous vegetation. Assured sustainable practices require long-term data on pine plantation development detailing patterns and processes to understand both crop-competition dynamics and the role of stand participants in providing multiple attributes such as biodiversity conservation and wildlife habitat. This study examined loblolly pine (Pinus taeda L.) plantations across 13 southeastern sites grown for 15 yr with near-complete control of woody, herbaceous, and woody plus herbaceous components during the first 3–5 yr compared to no plant control. This multiple objective experiment (the COMProject) documents stand dynamics at the extreme corners of a response surface that encompasses most conditions of woody and herbaceous competition common to pine plantations in the region. This is the first of two companion reports. After 15 yr, patterns of stand development remained significantly altered by early control treatments and were influenced most by the amounts of hardwoods and shrubs present or controlled. Herbaceous components were more similar across the region. Associated plants in these plantations included 68 species of trees, 33 species/genera of shrubs, and 140 genera of herbaceous and semiwoody plants, woody vines, clubmoss, and ground lichen—241 total taxa or an estimated 490 total species—more richness than previously reported or assumed. Hardwood rootstock numbers were on average maintained at fairly constant levels from yr 1–15 when not controlled, with no initial lag phase evident for reestablishment, indicating prior stand origin. Dynamics of associated vegetation were significantly altered with woody control initially increasing herbaceous cover, while herbaceous control increased hardwood cover and decreased shrub cover. After early herbaceous control, hardwood basel area (BA) was increased by an average of 28%. After rapid early colonization, herbaceous plants began to decline on all treatments about yr 8 as pine and/or hardwood canopy cover reached a total of 50–60%, while woody vines continued to increase. By age 15, plant component richness remained significantly changed by early treatments at all locations, most notably fewer tree species after early woody control. South. J. Appl. For. 27(4):221–236.

Carbon isotope composition of various tissues of beech (Fagus sylvatica) regeneration is indicative of recent environmental conditions within the forest understorey.

• Here, the effects were assessed of local climate and canopy thinning on the carbon isotope composition (δ13 C) signatures of different plant groups in the understorey of a beech (Fagus sylvatica) forest in southern Germany. The relationship between δ13 C and environmental parameters, within different time integrals, was also studied. • δ13 C was analysed in different tissues of beech regeneration, and herbaceous and woody understorey vegetation, in thinned and untreated control stands differing in aspect and, hence, local climate, on three dates during the growing season. • Generally, tissues were 13 C-depleted on the north-east, compared with the south-west aspect. Thinning had variable effects on δ13 C, depending on plant group and sampling date. δ13 C in beech leaves and roots in control stands was mostly influenced by mean soil water potential in 4- and 8-wk integrals before sampling, respectively, and in leaves, additionally, by mean radiation in a 4-wk time integral. Shoot water potential and transpiration influenced foliar δ13 C of beech whereas δ13 C in the beech wood was modulated by soil temperature integrated over a 4-wk period before sampling. Above-ground tissues of woody and herbaceous plants were 13 C-enriched in mid-summer; their δ13 C was poorly related to environmental factors. • δ13 C of various tissues of beech regeneration appears to be indicative of recent environmental conditions within the forest understorey and, consequently, this easy-to-determine physiological parameter could be used widely to assess effects of silvicultural treatments.