Grass Removal Research Articles

Restoration of a Restinga Sandy Coastal Plain in Brazil: Survival and Growth of Planted Woody Species

Abstract In this article we report the results of an experiment introducing 17 native shrub and tree species into a Brazilian restinga (i.e., coastal sandy plain vegetation). Restingas have been affected by human impact for about 8,000 years, and human occupation for housing, tourism, and land speculation has recently increased in such a way that there is a need for conservation of remnant patches and restoration of degraded areas throughout the coast to protect biodiversity. Our study site is a remnant located in Rio de Janeiro, the second largest city in the country, and has been subjected in the past to deforestation, man‐made fire, and sand extraction. Although trees and shrubs predominantly compose natural restinga vegetation, local vegetation after impact was replaced by an exotic grass cover, which meant a drastic reduction in species richness. Thus, in this experiment we removed the grass cover, introduced shrub and tree species, and monitored survival and growth of 20 plants per species for 2 years. Despite the adversities imposed by the nutrient‐poor sandy soil, 70% of the species showed high survival percentage and considerable growth. This report on restoration initiatives in the restingas points out the viability of shrub and tree plantation following exotic grass removal as a strategy to restore Brazilian coastal vegetation.

Community response to removals of plant functional groups and species from a Chihuahuan Desert shrubland

Arid and semi‐arid ecosystems often exhibit diverse plant growth forms in water‐limited environments, but it is unclear whether resource competition (interference) is actually important in structuring communities. We chose a diverse Chihuahuan desert shrubland to examine the response of the plant community to experimental removals of selected perennial plant species or groups of species. Four treatments involved the removal of all individuals of all species of a single functional group (functional group removals: shrub removal, succulent removal, subshrub removal, perennial grass removal). Three other treatments involved removing species within functional groups. These seven treatments plus a control (no plants removed) were replicated six times each in 25×25 m experimental plots, in summer 1995. Permanent belt transects were surveyed for number and sizes of all vascular plants in spring and fall in 1997, 1999, 2000, and 2001. Those plots from which the dominant shrub, Larrea tridentata, was removed had not recovered in total plant cover or volume by 2001, but cover and volume in all other treatments were similar to those in control plots. Relatively few species demonstrated a positive response to the removal of other species or functional groups. The perennial grass group and forbs were the most responsive; perennial grass cover increased in the shrub removal treatment relative to the control but treatment differences diminished after dry growing seasons in 2000 and 2001. Results over the first five years suggest that either environmental conditions or intrinsic biological characteristics limit the ability of most plant species to respond to the removal of substantial fractions of community biomass and composition in the short term. Such slow response by both dominant and less abundant components of the community has implications for the recovery of semi‐arid systems after human disturbance or other events leading to the reduction of biological diversity.

The Effects of Exotic Grasses on Litter Decomposition in a Hawaiian Woodland: The Importance of Indirect Effects

Exotic grasses and grass-fueled fires have altered plant species composition in the seasonal submontane woodlands of Hawaii Volcanoes National Park. These changes have altered both structural and functional aspects of the plant community, which could, in turn, have consequences for litter decomposition and nitrogen (N) dynamics. In grass-invaded unburned woodland, grass removal plots within the woodland, and woodland converted to grassland by fire, we compared whole-system fluxes and the contributions of individual species to annual aboveground fine litterfall and litterfall N, and litter mass and net N loss. We assessed the direct contribution of grass biomass to decomposition and N dynamics, and we determined how grasses affected decomposition processes indirectly via effects on native species and alteration of the litter layer microenvironment. Grasses contributed 35% of the total annual aboveground fine litterfall in the invaded woodland. However, total litterfall mass and N were not different between the invaded woodland and the grass removal treatment because of compensation by the native tree Metrosideros polymorpha, which increased litter production by 37% ± 5% when grasses were removed. The 0.3 g N m−2/y−1 contained in this production increase was equal to the N contained in grass litter. Litter production and litterfall N was lowest in the grassland due to the loss of native litter inputs. Decomposition of litterfall on an area basis was highest in the grass-invaded woodland. We attributed this effect to increased inherent decomposability of native litter in the presence of grasses because (a) the microenvironment of the three vegetation treatments had little effect on decomposition of common litter types and (b) M. polymorpha litter produced in the invaded woodland decomposed faster than that produced in the grass removal plots due to higher lignin concentrations in the latter than in the former. Area-weighted decomposition was lowest in the grassland due to the absence of native litter inputs. Across all treatments, most litter types immobilized N throughout the incubation, and litter net N loss on an area basis was not different among treatments. Our results support the idea that the effects of a plant species or growth form on decomposition cannot be determined in isolation from the rest of the community or from the direct effects of litter quality and quantity alone. In this dry woodland, exotic grasses significantly altered decomposition processes through indirect effects on the quantity and quality of litter produced by native species.

EXOTIC GRASSES ALTER CONTROLS OVER SOIL NITROGEN DYNAMICS IN A HAWAIIAN WOODLAND

Exotic invasive grasses and fire have altered plant species composition in the seasonal submontane woodlands of Hawaii Volcanoes National Park. These changes have affected both structural and functional aspects of the plant community, which could have consequences for soil nitrogen (N) dynamics and N availability to plants. To determine if, when, and how soil N dynamics were altered by grass invasion, we measured net and gross N mineralization and nitrification during wet and dry seasons across three vegetation types: (1) experimental grass removal plots within unburned woodland created to simulate the native ecosystem that may have existed prior to invasion; (2) woodland invaded by grasses; and (3) invaded woodland converted to grassland by fire. Grass invasion into woodland shifted the timing, but not the amount, of N available. After conversion to grassland, N-cycling rates were 3.4 times greater. The wet season accounted for 35% of annual net N mineralization in the grass removal treatment, 75% in the...

Abiotic constraints on the establishment ofQuercusseedlings in grassland

AbstractHigh evaporative demand and periodic drought characterize the growing season in midwestern grasslands relative to deciduous forests of the eastern US, and predicted climatic changes suggest that these climatic extremes may be exacerbated. Despite this less than optimal environment for tree seedling establishment, deciduous trees have expanded into adjacent tallgrass prairie within the last century leading to a dramatic land cover change. In order to determine the role of light and temperature on seedling establishment, we assessed carbon and water relations and aboveground growth of first‐yearQuercus macrocarpaseedlings exposed to one of three conditions: (1) intact tallgrass prairie communities (control), (2) aboveground herbaceous biomass removed (grass removal), and (3) shade plus biomass removal to reduce light (PFD) to levels typical of the grassland‐forest ecotone (shade). In the 2000 growing season, precipitation was 35% below the long‐term average, which had a significant negative effect on oak seedling carbon gain at midseason (photosynthesis declined to 10% of maximum rates). However, net photosynthesis and stomatal conductance in the shade treatment was ca. 2.5 and 1.5 times greater, respectively, than in control treatment seedlings during this drought. During this period, leaf and air temperatures in control seedlings were similar whereas leaf temperatures in the shade treatment remained below air temperature. A late‐season recovery period, coincident with decreased air temperatures, resulted in increased net photosynthesis for all seedlings. Increased photosynthetic rates and water relations in shaded seedlings compared to seedlings in full sun suggest that, at least in dry years, high light and temperature may negatively impact oak seedling performance. However, high survival rates for all seedlings indicate thatQ. macrocarpaseedlings are capable of tolerating both present‐day and future climatic extremes. Unless historic fire regimes are restored, forest expansion and land cover change are likely to continue.

Impacts of Exotic Annual Brome Grasses (Bromus spp.) on Ecosystem Properties of Northern Mixed Grass Prairie

Annual brome grasses, Bromus japonicus and B. tectorum, are common exotic plants in the northern mixed grass prairies of North America. As annuals, the bromes die following seed set in late spring, creating a functional difference between them and native perennial grasses because perennials continue to maintain live shoots into the summer and root systems throughout the year. Our objective was to investigate how this functional difference alters ecosystem properties over the growing season, including soil moisture content, quantity of plant biomass, litter accumulation and aboveground litter decomposition. We conducted an experiment in which the annual bromes were removed from treatment plots to compare with adjacent reference plots. While this experiment served as a direct test for brome impacts, observational plots also were sampled to determine if impacts were apparent in an unmanipulated system. A litter bag experiment was conducted to evaluate impacts of brome grasses on decomposition. Experimental removal of brome grasses led to more biomass both above- and belowground at the end of the growing season, and high brome observational plots averaged 28% less aboveground biomass and 40% less belowground biomass than low brome plots. In contrast, removal of brome grasses did not produce a consistent impact on soil moisture content between sites or among months, and none of measurable impacts from the removal experiment were significant in the observational study. Bromes slowed decomposition of aboveground litter at both sites. However, the overall impact on litter accumulation was only significant at one site, where brome removal reduced surface litter in the latter half of the growing season and high brome observational plots averaged 36% more litter than low brome plots. This study demonstrates how the brome functional type alters several properties in an ecosystem traditionally dominated by perennial grasses.

Rosette Recruitment of a Rare Endemic Forb (Gaura neomexicanaSubsp.coloradensis) with Canopy Removal of Associated Species

AbstractGaura neomexicanasubsp.coloradensisMunz (Onagraceae), (Colorado butterfly plant), a short‐lived perennial forb, became listed as a threatened species by the U.S. Fish and Wildlife Service in October 2000 because of its small global range and population size. This endemic subspecies consists of only 18 extant populations within southeastern Wyoming, southwestern Nebraska, and northeastern Colorado. Wyoming occurrences are on private land with the exception of three occurrences on F. E. Warren Air Force Base, near Cheyenne.Gaura neomexicanasubsp.coloradensismay be displaced by many competitors, includingCirsium arvense(L.) Scop. (Canada thistle), an invasive, noxious weed. In June 1998, threeG. neomexicanasubsp.coloradensispopulations were examined for rosette establishment in the presence of and after removal of associated species. The four study treatments removed: (1)Cirsium arvense, (2) grass and forb canopy and associated litter, (3) grass and forb canopy, litter, andC. arvense, and (4) no removal of associated plant species (control). MatureG. neomexicanasubsp.coloradensisplants were evaluated for height, number of leaves, and capsule production. The mature plant characteristics monitored in 1998 were not good indicators of subsequentG. neomexicanasubsp.coloradensisrosette densities in the following spring. Recruitment was assessed by counting new rosettes in the fall 1999. Although bothG. neomexicanasubsp.coloradensisand the exoticC. arvensehave comparable habitat, removal ofC. arvensedid not increaseG. neomexicanasubsp. coloradensis vegetative growth, seed capsule production, or rosette density. Removal of other forbs, grass, and litter, however, increasedG. neomexicanasubsp.coloradensisrosette density in the following two years, indicating that canopy removal of associated species can enhance rosette establishment of this rare native. The accumulation of dense vegetative cover and litter associated with the absence of herbivory and fire may contribute to the decline of rare species in rich riparian habitats. Return of herbivory and fire in mesic sites to reduce standing biomass accumulations should be considered in restoring recruitment potential to rare monocarpic species.

Effect of timing of pasture grass removal on subsequent take-all incidence and yield in wheat in southern New South Wales

Winter cleaning is the removal of grasses from pasture using selective herbicides applied during winter. We compared the effectiveness of an early (June) and late (July) winter cleaning with an early spring herbicide fallow (September), spring (October) herbicide and no disturbance of the pasture on development of the root disease take-all in the subsequent wheat crop. Experiments were done at 5 sites in the eastern Riverina of New South Wales in 1990 and 1991. The winter clean treatments reduced soil inoculum of Gaeumannomyces graminis var. tritici (Ggt) compared with the other treatments at all sites as measured by a bioassay, with reductions from the undisturbed treatments of 52–79% over 5 sites. The winter clean treatments also significantly reduced the amount of take-all that developed in the subsequent wheat crop by between 52 and 83%. The early and late winter clean treatments increased the number of heads/m2 at 3 and 1 sites, respectively. Dry matter at anthesis was increased by the winter clean treatments at 3 sites. Grain yield was increased by the winter cleaning treatments over the other treatments at the 4 sites harvested, with yield increases of the early winter clean over the undisturbed treatment from 13 to 56%. The autumn bioassay of Ggt was positively correlated with spring take-all and negatively correlated with grain yield of the subsequent wheat crop at each site. However, there was a significant site and site × bioassay interaction so that the autumn bioassay could not be used to predict the amount of take-all that would develop.

Crop productivity in relation to species of previous crops and management of previous pasture

An experiment at Rutherglen in north-eastern Victoria compared 5 grass-removal methods in subterranean clover-based pastures that were grown before cropping sequences of canola–wheat–lupin–wheat or wheat–wheat–lupin–wheat. The cropping sequences were started in 3 successive years to provide replication in time. Grass removal from the pasture was more effective in winter than in spring and led to yield increases by the first and second crops. The largest increase (80%) was by the first canola crop after winter-cleaned pasture. The yield increase by the equivalent wheat crop was 42%. Since annual grasses and canola do not host the same root pathogens, we conclude that the yield responses were not due to root-disease control but probably to increased N supply. Assays of wheat roots confirmed that root disease was negligible throughout the experiment. Wheat growing in the year after canola yielded 11% more than wheat growing after wheat. The most surprising result was a 17% increase in the yield of wheat growing 3 years after canola compared with wheat growing 3 years after wheat, with wheat–lupin sequences in the intervening years for both systems. We suggest that canola and lupin, both of which are non-hosts of arbuscular mycorrhizal fungi, reduced mycorrhizal root colonisation in the fourth-year wheat crop, leading to less drain on assimilates.

Dose responses of weeds and winter wheat to MKH 6561

Abstract Greenhouse studies determined dose responses of winter annual weeds and winter wheat to preemergence (PRE) and postemergence (POST) treatments of MKH 6561 and the residual effects on kochia. MKH 6561 at 11 to 45 g ha−1 did not affect wheat. MKH 6561 at 11, 34, and 45 g ha−1 reduced winter annual weed densities compared to an untreated control. Weed growth was inhibited as the rate of MKH 6561 was increased, but downy brome, cheat, and Japanese brome were three to six times more susceptible than jointed goatgrass. The GR70 values for cheat, downy brome, Japanese brome, and jointed goatgrass were 7, 11, 4, and >45 g ha−1, respectively. Dry weights of kochia seeded after removal of the winter annual grasses decreased as MKH 6561 rate increased, with average control being 77% compared to the nontreated control. Regression analysis indicated that kochia was controlled 80% with MKH 6561 at 28 g ha−1. Nomenclature: MKH 6561, methyl 2-[[[(4-methyl-5-oxo-3-propoxy-4,5-dihydro-1H-1,2,4-triazol-1-yl)carbony...

PLANT REMOVALS IN PERENNIAL GRASSLAND: VEGETATION DYNAMICS, DECOMPOSERS, SOIL BIODIVERSITY, AND ECOSYSTEM PROPERTIES

The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or “functional groups” of the flora. We monitored vegetation and soil biotic and chemical properties over a 3-yr period. Plant competitive effects were clear: removal of the C3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C3 grasses reduced total root biomass and drastically enhanced overall shoot-to-root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora. Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe-feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe-feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community-level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil-associated herbivorous arthropods and microbial-feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C4 grasses enhanced diversity; there were negative correlations between plant and arthropod diversity, presumably because of negative influences of C4 species in the most diverse treatments. There was evidence of lag relationships between diversity of plants and that of the three decomposer groups, indicating multitrophic effects of altering plant diversity. Relatively small effects of plant removal on the decomposer food web were also apparent in soil processes regulated by this food web. Decomposition rates of substrates added to soils showed no relationship with treatment, and rates of CO2 evolution from the soil were only adversely affected when all plants were removed. Few plant functional-group effects on soil nutrient dynamics were identified. Although some treatments affected temporal variability (and thus stability) of soil biotic properties (particularly CO2 release) throughout the experiment, there was no evidence of destabilizing effects of plant removals. Our data provide evidence that permanent exclusion of plant species from the species pool can have important consequences for overall vegetation composition in addition to the direct effects of vegetation removal, and various potential effects on both the above- and belowground subsystems. The nature of many of these effects is driven by which plant species are lost from the system, which depends on the various attributes or traits of these species.

Plant Removals in Perennial Grassland: Vegetation Dynamics, Decomposers, Soil Biodiversity, and Ecosystem Properties

The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or “functional groups” of the flora. We monitored vegetation and soil biotic and chemical properties over a 3-yr period. Plant competitive effects were clear: removal of the C3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C3 grasses reduced total root biomass and drastically enhanced overall shoot-to-root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora. Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe-feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe-feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community-level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil-associated herbivorous arthropods and microbial-feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C4 grasses enhanced diversity; there were negative correlations between plant and arthropod diversity, presumably because of negative influences of C4 species in the most diverse treatments. There was evidence of lag relationships between diversity of plants and that of the three decomposer groups, indicating multitrophic effects of altering plant diversity. Relatively small effects of plant removal on the decomposer food web were also apparent in soil processes regulated by this food web. Decomposition rates of substrates added to soils showed no relationship with treatment, and rates of CO2 evolution from the soil were only adversely affected when all plants were removed. Few plant functional-group effects on soil nutrient dynamics were identified. Although some treatments affected temporal variability (and thus stability) of soil biotic properties (particularly CO2 release) throughout the experiment, there was no evidence of destabilizing effects of plant removals. Our data provide evidence that permanent exclusion of plant species from the species pool can have important consequences for overall vegetation composition in addition to the direct effects of vegetation removal, and various potential effects on both the above- and belowground subsystems. The nature of many of these effects is driven by which plant species are lost from the system, which depends on the various attributes or traits of these species.

Monitoring and modelling open savannas using multisource information: analyses of Kalahari studies

SummaryIn the Kalahari of Botswana, as in many other open savannas, the main ecological change following cattle‐based agricultural intensification is one of grass removal and bush encroachment. Changes to vegetation communities in Kalahari rangelands have been expressed in terms of a state‐and‐transition model. However, there remain uncertainties as to the mechanisms and conditions for ecological change. In part, this is due to previous (inadequate) spatial and temporal scales of data collection. This paper describes the results of ongoing ecological studies in the Makoba ranches and analyses the contribution that fine‐scale ground‐based surveys and interpretation of Earth observation data can make to reducing uncertainties in state‐and‐transition models. This detailed case study provides a mechanism for evaluating the role of multi‐source information for monitoring and modelling open savannas.

Species composition and inter-annual dynamics of a freshwater tidal plant community following removal of the invasive grass, Phragmites australis

We document the regeneration of native freshwater wetland plant assemblages following removal of the common reed, Phragmites australis (Cav.) Trin. ex Steudel from two sites at Chapman Pond, East Haddam, Connecticut, USA. We gathered field data on composition of the vegetation 1 year before and for each of the 3 years after the removal in fall 1995/spring 1996 of Phragmites by two slightly different methods (hand-removal and herbiciding in one area, mowing/mulching and herbiciding in another). An area where Phragmites was left intact was similarly monitored. Our goals for this monitoring were: (1) to document plant species composition and richness before and after Phragmites removal and (2) to examine temporal and spatial variability in patterns of plant recruitment. Phragmites declined in both density and extent in both plots where removal treatments were applied. Richness, evenness, and density of non-Phragmites species increased steadily from 1996 to 1997 in all removal and intact plots. However, the species composition of the removal plots was richer than that of the intact plot, and more closely resembled that of comparable, uninvaded freshwater tidal wetlands. Rates of recovery of species richness in the removal plots declined from 1997 to 1998, potentially reflecting saturation of available colonization space, or the return of Phragmites. Phragmites has expanded its range in both of the removal plots since 1997. A model of its colonization indicates that Phragmites occupies space through localized proliferation of dense rhizomes rather than diffusely foraging with long tillers. Vigilance in monitoring is needed to document the spread of invasives, to evaluate the multi-faceted ecological effects of eradication efforts on both the invader and the regenerating community, and develop strategies for preventing re-invasion.

The response of native species to removal of invasive exotic grasses in a seasonally dry Hawaiian woodland

Abstract. Non‐native perennial grasses form 30% of the live understory biomass in seasonally dry, submontane forests in Hawaii Volcanoes National Park, yet their effects on native species are unknown. We removed these grasses from plots of 20 m × 20 m in 1991 and maintained removal and control areas over the next three years. Two fast growing shrub species, Dodonaea viscosa and Osteomeles anthylidifolia, increased in size significantly more in removal areas than in controls. Individuals of the most abundant shrub species, Styphelia tameiameia showed no net growth response to grass removal. They did, however, change their architecture: many branches along the mid and upper sections of the main trunk died and a proliferation of new leaves and shoots occurred in the lower 40 cm of trunk. Basal diameter increase was very small in Metrosideros polymorpha, the dominant tree species in these sites.All species except Styphelia had significantly increased leaf tissue nitrogen in removal plots by 18 months after removal when compared to shrubs in control areas suggesting that removal plot shrubs had greater access to soil nitrogen. Available soil‐N pools, which were generally higher in the removal plots, support this interpretation. Light levels near the soil surface were also higher where grasses were removed than where they were present which may have contributed to increased shrub growth. By contrast, soil moisture was consistently lower where grasses were removed than where they were still present. Shrub tissue carbon isotope values were consistent with the interpretation that shrubs in removal plots had less rather than more water available to them. Hence, the increased growth observed in removal plot shrubs could not be due to release from moisture competition.Lastly, our results showed that seedlings of all woody species except Metrosideros were significantly more abundant in removal plots at both one and three years after removal and initially high sapling mortality was balanced by high recruitment into the sapling class. We believe that over time this will result in increased densities of native shrubs if grasses are kept out. With the presence of grasses, shrub growth in these woodlands is reduced and biomass is shifting towards grasses.

Experimental Restoration of Native Vegetation in Indiana Dunes National Lakeshore

AbstractWe investigated the effects of prescribed fire, herbicide treatment, and sod removal on the eradication of exotic grasses and the establishment of native plant species in 24 experimental restoration plots in three razed residential sites within the boundary of Indiana Dunes National Lakeshore. During 1992–1995, herbicide treatment and sod removal decreased the combined cover of Poa pratensis (Kentucky blue grass) and Agropyron repens (quackgrass) significantly (from 82% to 13%, and 85% to 8%, respectively), whereas fire did not suppress such exotic lawn grasses. In 1993, several opportunistic species, represented by Cyperus spp. (umbrella sedges), Digitaria sanguinalis (crab grass), and Ambrosia artemisiifolia (common ragweed), filled the gaps left by the removal of lawn grasses. For the same period, Detrended Correspondence Analysis revealed a clear vegetation divergence between the control‐fire plots and the herbicide‐sod removal plots. While Poa pratensis and Agropyron repens continued to dominate the control and fire plots, the planted native species, represented by Schizachyrium scoparium (little blue‐stem), Sorghastrum nutans (Indian grass), Rudbeckia hirta (black‐eyed Susan), and Monarda punctata (horsemint), began to dominate in the herbicide and sod removal plots from 1994. In both herbicide and sod removal plots, the ground cover of grasses (68%) was much higher than the forbs (10%). The herbicide plots, where exotic species were removed but nitrogen‐rich top soils were not removed, showed a higher diversity of planted native species than the sod removal plots (where both exotic species and top soils were removed) and the control‐fire plots (where neither was removed). This finding suggests that an optimum but not excessive concentration of soil nitrogen is needed to support a maximum species diversity in such infertile substrate as sandy soil. In addition, the decrease in potassium in all plots, regardless of treatment, suggests that potassium may become a limiting factor for our restored native vegetation.

Increasing production of an annual medic - wheat rotation by grazing and grass removal with herbicides in the Victorian Mallee

Summary. The productivity of an annual medic-based pasture–pasture–wheat rotation in response to chemical grass control and stocking rate treatments was evaluated over 3 years. Fluazifop applied in 1991 reduced the annual grass component during the pasture years (to <2% in 1991 and <5% in 1992) and grass densities in the 1993 wheat phase. This improved winter herbage production in 1992 (>50%) and the 1993 wheat yield (>40%). Glyphosate applied during the winter of 1991 reduced the grass component and the winter and total herbage production in that year, and grass populations in 1992. Glyphosate applied during the spring of 1991 reduced the medic seed yields and the grass and medic densities in 1992. There were no pasture or cereal production benefits measured from the 1991 glyphosate applications. All the above comparisons were made with no herbicide in 1991 followed by glyphosate applied during the winter of 1992, a common district practice. Stocking at twice the district average, over all herbicide treatments, reduced the 1991 winter herbage production but maintained or improved the 1992 winter and total herbage production, compared with the district average stocking rate. The high stocking rate resulted in lower grass densities in the 1993 wheat crop and increased the wheat grain yield by 0.5 t/ha.

Studies on the Nesting Behaviour and Control of the Graminivorous ant Messor galla Mayr (Hymenoptera: Formicidae) in Ilorin area of Nigeria

Messor galla invaded parks and grounds at the University of Ilorin in 1994. This graminivorous ant constructs subterranean nests commonly on dark brown loamy sand soils on the lawns and elsewhere. Foraging for food and other materials are common in the dry season while nest clearing and minor duties are performed during rainy season. It is a diurnal insect with peak activities at noon when temperature is about 31.5 C, Trail lengths vary between 97 and 144 111 and the average nest crater measured 47.5 cm radius. Foraging activities also led to massive removal of planted grass wherever the nest occurs leading to economic loss apart from declining aesthetic values. Although, applications of Dieldrex 20 and Aldrex 40 gave little measure of control, Gammalin 20 proved best in the control of the ants.

Exotic Grass Competition in Suppressing Native Shrubland Re‐establishment

AbstractDisturbance of coastal sage scrub in southern California has led to extensive displacement of native shrubs by exotic annual grasses. The initial conversion from shrubland to exotic grassland is typically associated with disturbance caused by intense grazing, high fire frequency, or mechanical vegetation removal. While native shrubs have been shown to recolonize annual grasslands under some conditions, other annual grasslands are persistent and show no evidence of shrub recolonization. This study examined the mechanisms by which annual grasses may exclude native shrubs and persist after release from disturbance. Grass density was manipulated in experimental plots to achieve a series of prescribed densities. Artemisia californica, a dominant native shrub, was seeded or planted into the plots and responses to the grass density treatments were measured over two growing seasons. A. californica germination, first season growth, and survival were all negatively related to the density of neighboring annual grasses. The most probable mechanism underlying the reduction of first season growth and survival was depletion of soil water by the grasses. The effects of the grasses on A. californica were no longer significant in the second season. The results of this study indicate that Mediterranean annual grasses reduce recruitment and can persist by inhibiting post‐disturbance establishment of A. californica from seed. Although succession alone may not return disturbed annual grasslands to their former shrubland composition, the results suggest that restoration can be achieved by using container plantings or grass removal followed by seeding.

Grass-mediated Capture of Resource Flows and the Maintenance of Banded Mulga in a Semi-arid Woodland

It has been proposed for semi-arid and arid regions that the scarce resources of water and nutrients normally limiting plant growth are distributed patchily in the landscape in order to maintain both stability and productivity (Tongway 1990). ‘Fertile patches’ are maintained by the concentration of resources during flows and when resource control is weakened their persistence is threatened. This proposition was tested by comparing water relations of perennial life-forms in the nutrient and water rich ‘island-bands’ of mulga (Acacia aneura F.Muell. ex Benth.) shrubs, with and without perennial grasses. Dawn xylem water potential (dawn ψx) and stable hydrogen isotope composition data showed that A. aneura and companion grasses competed for soil water, whereas the poplar box (Eucalyptus populnea F.Muell.) trees accessed additional sub-soil water. During a drying cycle, dawn ψx of A. aneura on the upslope portion of ‘island-bands’ was –2 MPa where grass was abundant, and –4.8 MPa where grasses were killed by heavy grazing. On the downslope portions, dawn ψx of A. aneura was similar at –4.2 MPa. Recruitment of A. aneura was occurring in the upslope portion, but was less where there were no grasses. There were more dead A. aneura shrubs on the downslope portion and in grass-free ‘island-bands’. The results suggest that removal of perennial grasses by grazing shortens the period of water supply to A. aneura shrubs in ‘island-bands’ and they prematurely die during low rainfall periods. Furthermore, continued grazing pressure from domestic and non-domestic herbivores will prevent restoration of landscape processes necessary for the survival of these shrubs and associated flora.