Amount Of Bare Ground Research Articles

Conservation of Species in Dynamic Landscapes: Divergent Fates ofSilene tataricaPopulations in Riparian Habitats

In transient environments, where local extinctions occur as a result of destruction or deterioration of the local habitat, the long-term persistence of a species requires successful colonizations at new, suitable sites. This kind of habitat tracking should be associated with the asynchronous dynamics of local populations, and it can be especially important for the conservation of rare plant species in riparian habitats. We determined spatiotemporal variation in the demography of the perennial Silene tatarica (L.) Pers. in 15 populations (1998-2003) located in periodically disturbed riparian habitats. The habitats differed according to their morphology (flat shores, slopes) and the amount of bare ground (open, intermediate, closed) along a successional gradient. We used elasticity and life-table response analyses and stochastic simulations to study the variation in population demography. Finite population growth rate was higher in intermediate habitats than in open and closed habitats. In stochastic simulations population size increased in most cases, but four populations were projected to become extinct within 12-70 years. The viability of local populations depended most on the survival and growth of juvenile individuals and on the fecundity of large fertile individuals. On a regional scale, the persistence of this species will require a viable network of local populations as protection against local extinctions caused by natural disturbances and succession. Accordingly, the long-term persistence of riparian species may depend on habitat changes; thus, their conservation requires maintenance of natural disturbance dynamics. Along regulated rivers, management activities such as the creation of open habitats for new colonization should be implemented. Similarly, these activities can be rather general requirements for the conservation of endangered species dependent on transient habitats along successional gradients.

Physically based modelling of sediment generation and transport under a large rainfall simulator

A series of large rainfall simulator experiments was conducted in 2002 and 2003 on a small plot located in an experimental catchment in the North Island of New Zealand. These experiments measured both runoff and sediment transport under carefully controlled conditions. A physically based hydrological modelling system (SHETRAN) was then applied to reproduce the observed hydrographs and sedigraphs. SHETRAN uses physically based equations to represent flow and sediment transport, and two erodibility coefficients to model detachment of soil particles by raindrop erosion and overland flow erosion. The rate of raindrop erosion also depended on the amount of bare ground under the simulator; this was estimated before each experiment. These erodibility coefficients were calibrated systematically for summer and winter experiments separately, and lower values were obtained for the summer experiments. Earlier studies using small rainfall simulators in the vicinity of the plot also found the soil to be less erodible in summer and autumn. Limited validation of model parameters was carried out using results from a series of autumn experiments. The modelled suspended sediment load was also sensitive to parameters controlling the generation of runoff from the rainfall simulator plot; therefore, we found that accurate runoff predictions were important for the sediment predictions, especially from the experiments where the pasture cover was good and overland flow erosion was the dominant mechanism. The rainfall simulator experiments showed that the mass of suspended sediment increased post-grazing, and according to the model this was due to raindrop detachment. The results indicated that grazing cattle or sheep on steeply sloping hill-country paddocks should be carefully managed, especially in winter, to limit the transport of suspended sediment into watercourses. Copyright © 2006 John Wiley & Sons, Ltd.

Interest group standards for recreation and tourism impacts at ski areas in the summer

Many contemporary recreation and tourism management frameworks including the Limits of Acceptable Change (LAC) require multi-stakeholder input for measuring and monitoring indicators and standards of quality. Most studies, however, have used visitor norms to formulate standards for indicators, whereas the norms of other stakeholders have received less empirical attention. This paper examines the acceptability norms of several groups regarding indicators of summer use at the Whistler Mountain ski area in British Columbia, Canada. Data were obtained from surveys conducted with 432 visitors and 21 representatives of 12 companies, government agencies, and recreation and environmental interest groups. Respondents evaluated photographs of impacts for the density of hikers/ sightseers and amount of bare ground at a campsite indicators. Responses were plotted on social norm curves. Results showed that standards for each indicator differed among the groups. The importance of each indicator (i.e., norm intensity) was high among the groups, but was highest for the density of hikers/sightseers, suggesting that it may be a more important indicator for this tourism-oriented setting. Management implications and future research topics are discussed.

Rodent Communities in a Grazed and Ungrazed Arizona Grassland, and a Model of Habitat Relationships Among Rodents in Southwestern Grass/Shrublands

We live-trapped rodents in 2000–2001 at eight sites on a 3160 ha grassland and mesquite-oak savanna in southeastern Arizona that had been ungrazed since 1968, and on eight paired sites on adjacent cattle ranches. There were 917 captures of 14 species during 5760 trap-nights. Four species of Muridae (Sigmodon fulviventer, Baiomys taylori, Reithrodontomys megalotis and R. fulvescens) were significantly more common on ungrazed plots, while no species was more abundant on grazed plots. However, Heteromyidae as a group (especially Chaetodipus hispidus and Perognathus flavus) comprised a significantly higher proportion of total captures on grazed plots, and heteromyids as a percentage of total captures was positively correlated across all plots with amount of bare ground. One of the eight cross-fence sites also had been trapped in 1981–1983. In the 17 y between trapping events at this site: (1) the grass canopy on both grazed and ungrazed plots had become dominated by taller species, (2) a kangaroo rat (Dipodomys merriami) that had been the second most common species in grazed areas disappeared from both plots, (3) pocket mice increased on the grazed plot and declined on the ungrazed plot and (4) Muridae (excluding Peromyscus) as a percent of all captures increased by greater than 1.5-fold on both plots. Based on these results, and those from other field studies, we propose a model for the composition of rodent communities in grass/shrublands of the Southwest and Intermountain West, based on ground cover. Kangaroo rats (Dipodomys spp.) are abundant in areas with the most bare soil, Muridae (specifically, Sigmodon, Baiomys and Reithrodontomys) dominate areas with the most and tallest ground cover, and pocket mice (Chaetodipus and Perognathus) are common in areas of intermediate cover. In relatively mesic grasslands, livestock grazing and fire drive the rodent community toward one dominated by heteromyids instead of murids. In more arid landscapes, grazing and fire favor kangaroo rats over pocket mice.

Hydrologic and Sediment Responses to Vegetation and Soil Disturbances

Soil erosion has been linked to stream sedimentation, ecosystem degradation, and loss of rangeland productivity. However, knowledge of soil loss, as it affects rangeland productivity or ecosystem sustainability is lacking. We evaluated the effects of 3 levels of vegetation cover reduction (0, 27%, and 43%) and soil removal (0, 12, and 24 tonnes ha - 1 ) on soil surface runoff and sediment yield in a sagebrush [Artemisia tridentata var. vasseyana (Rydb.) Beetle] steppe under simulated rainfall. Time to runoff initiation was affected by the vegetation cover reduction treatments, but not by the soil removal treatments. The 43% vegetation canopy reduction treatment resulted in a shorter time to runoff initiation than did the 27% and 0% canopy reduction treatments (p = 0.002). Results from analysis of covariance indicated that vegetation reduction and soil removal did not significantly affect sediment yield or runoff quantities in the first year following treatments. Multiple regression analysis revealed total sediment yield was related to forb cover, sand in the upper soil profile (0-5 cm), and the amount of bare ground. Time to runoff initiation was positively correlated with slope. Despite the lack of significant treatment differences, we do not conclude that these soil removal and vegetation reduction treatments had no affect on soil surface hydrology and sediment yield. There are numerous studies that show a strong relationship between vegetation reduction and soil erosion. Future research at this site may reveal long-term treatment effects that were not apparent in first year results.

Hydrologic and sediment responses to vegetation and soil disturbances

Soil erosion has been linked to stream sedimentation, ecosystem degradation, and loss of rangeland productivity. However, knowledge of soil loss, as it affects rangeland productivity or ecosystem sustainability is lacking. We evaluated the effects of 3 levels of vegetation cover reduction (0, 27%, and 43%) and soil removal (0, 12, and 24 tonnes ha-1) on soil surface runoff and sediment yield in a sagebrush [Artemisia tridentata var. vasseyana (Rydb.) Beetle] steppe under simulated rainfall. Time to runoff initiation was affected by the vegetation cover reduction treat- ments, but not by the soil removal treatments. The 43% vegeta- tion canopy reduction treatment resulted in a shorter time to runoff initiation than did the 27% and 0% canopy reduction treatments (p = 0.002). Results from analysis of covariance indicated that vegetation reduction and soil removal did not significantly affect sediment yield or runoff quantities in the first year following treatments. Multiple regression analysis revealed total sediment yield was related to forb cover, sand in the upper soil profile (0-5 cm), and the amount of bare ground. Time to runoff initiation was positively correlated with slope. Despite the lack of significant treatment differences, we do not conclude that these soil removal and vegetation reduction treatments had no affect on soil surface hydrology and sediment yield. There are numerous studies that show a strong relationship between vegetation reduction and soil erosion. Future research at this site may reveal long-term treatment effects that were not apparent in first year results.

Vegetation Structure and Soil Properties in Ecuadorian Páramo Grasslands with Different Histories of Burning and Grazing

High-altitude grasslands in the north Andes (páramos) are subject to frequent fires that are usually set by farmers to support traditional cattle-raising systems. Apparently, this practice has caused dramatic changes in the structure and composition of native vegetation, but the mechanisms, magnitude, and direction of these changes still need to be documented for a broader range of conditions. This paper describes the differences in selected soil properties, ground cover, grass tussock structure, and populations of giant Andean rosettes (Espeletia pycnophylla) in four páramo sites in northwestern Ecuador, characterized by contrasting patterns of burning and grazing. The only differences between the soil properties of the sites were the higher pH in the least disturbed site, and the high concentration of P in the more recently burned site. Along the sequence of least impacted to most impacted sites, we observed a decrease in grass tussock cover, and an increase in the amount of bare ground and number of fragments per tussock. In the most undisturbed site tussock coverage was extremely low due to the dominance of shrubs. The density of giant Andean rosettes was higher in the sites with intermediate disturbance regimes, while the mortality of adult stem rosettes was significantly higher at the more recently burned site. The significance of these differences is discussed in the context of the regeneration of páramo vegetation after burning and grazing disturbance.

Factors controlling vegetation change in long‐term experiments designed to restore heathland in Breckland, UK

Abstract. This paper describes the vegetation change in an 18‐year experiment designed to test a range of control of Pteridium aquilinum (Pteridium) and heathland restoration treatments; cutting, asulam application and Calluna vulgar is seeding, in a range of combinations at Cavenham Heath in Breckland, UK between 1978 and 1996. Vegetation change was recorded in two Phases; in Phase I (1978‐1986) species biomass was sampled and in Phase II (1986‐1996) cover was measured. Initially, Calluna establishment was good in some treatments, especially where Calluna seed was added and Pteridium was controlled. Other plots developed either a grass‐heath flora dominated by Agrostis capillaris, Deschampsia flexuosa, Dicranum scoparium, Festuca ovina and Rumex acetosella or were dominated by clonal species such as Calamagrostis epigejos or Carex arenaria.An unconstrained ordination showed significant vegetation change through time and that several treatments influenced the vegetation, especially those involving asulam application. When variation partitioning with constrained ordination was used a different explanation emerged. In Phase I the most important factors were the management treatments applied, elapsed time and spatial factors, with little overlap. In Phase II, elapsed time became irrelevant because the variation time explained overlapped that which could be explained by other variables. The most important of these were management treatments, spatial effects, weather, the amount of bare ground caused by disturbance and Pteridium litter cover (an index of Pteridium recovery). The implications of these results in interpreting vegetation change are discussed.

Comparative Effects of Stock and Wild Vertebrate Herbivore Grazing on Treeless Subalpine Vegetation, Eastern Central Plateau, Tasmania

The existence of two 25-year-old grazing exclosures on Liawenee Moor, Eastern Central Plateau, Tasmania, created an opportunity to investigate the impacts of vertebrate herbivores on treeless subalpine vegetation. There were three treatments: sheep-, native herbivore- and rabbit-grazed; native herbivore- and rabbit-grazed; no grazing. The amount of bare ground was highest in the sheep-grazed plots, while vegetation cover was greatest in the ungrazed exclosure. The cover of all lifeform groups, except small herbs, was greater in the exclosures than in the sheep-grazed plots. The percentage frequency of tall herbs was significantly less in the sheep-grazed plots than either of the grazing exclosures. Tall herbs were more likely to be found under the canopy of other vegetation in the sheep-grazed plots while the same species were found to be growing in locations with no other vegetation cover in the ungrazed exclosure. Revegetation of bare ground averaged 1% per year over a 20-year period in the ungrazed exclosure. While percentage bare ground has also decreased in the native- and rabbit-grazed exclosure, it has increased in the sheep-grazed plots. Domestic stock grazing appears to have a much greater impact on vegetation cover, species composition and community structure than grazing by native herbivores and rabbits. No grazing allows for the fastest rehabilitation of the area. Our results are consistent with those from alpine and treeless subalpine areas of the Australian mainland.

Vehicle track damage to salt marsh soil and vegetation at Culbin Sands, NE Scotland

Summary The effects of 3 year old vehicle tracks on salt marsh soil and vegetation within Culbin Sands SSSI on the Moray Firth, Scotland were investigated. Vehicle tracks destroyed the organic layer which was present in the later successional communities. Soil penetration resistance and bulk density were increased, and moisture content and salinity were decreased inside all the tracks, thus soil characteristics were shifted towards those typical of lower marsh zones. Penetration resistance within tracks reached levels which may inhibit root elongation. Vegetation inside tracks remained in earlier successional stages than the surrounding communities, particularly on the lower marsh where recovery may be slowed by repeated disturbance by tidal water. Vegetation on the mid and upper marsh showed less successional shift, but was still changed, being more diverse within the tracks. There was also a significant amount of bare ground within these tracks, which could facilitate erosion. Effects of vehicle tracks ...

Vulpia ciliata Dumort. ssp. ambigua (Le Gall) Stace & Auquier (Vulpia ambigua (Le Gall) More, Festuca ambigua Le Gall)

<i>Vulpia ciliata</i> Dumort. ssp. <i>ambigua</i> (Le Gall) Stace &amp; Auquier (<i>Vulpia ambigua</i> (Le Gall) More, <i>Festuca ambigua</i> Le Gall)

A Survey of CRP Land in Minnesota: II. Weeds on CRP Land

The federal Conservation Reserve Program (CRP) funded the conversion of eroding cropland to grass or grass-legume cover that was not to be tilled, hayed, or grazed for 10 yr. It was not known what the species composition of CRP fields would be after years of minimal disturbance. Our objective was to document the presence and percentage groundcover of weeds in 151 CRP fields located in 10 Minnesota counties; including 108 Conservation Practice (CP)-1 (cool-season legumes and grasses) fields, 17 CP-2 (native grasses) fields, and 26 CP-10 (existing vegetation) fields. Groundcover of each species present and of bare ground was scored in six 106-sq-ft sample plots per field. The most prevalent species were the primary noxious weed Canada thistle [Cirsium arvense (L.) Scop.], the secondary noxious weed quackgrass [Efytrgia repens (L.) Dew. ex. Nevski], and the non-noxious weeds dandelion (Tarmacurn oflcinale Weber.) and goldenrod (Solidago spp.). Weed percentage groundcover was higher in CP-10 fields than in CP-1 or CP-2 fields, probably because many CP-IO stands were already thinning at the start of the CRP contract. Volunteer legumes and grasses were common in CP-10 fields. In CP-1 fields, legume and grass percentage groundcover usually was correlated negatively with weed percentage groundcover. Weed percentage groundcover and species richness were correlated positively. Gopher mounding was correlated positively with the amount of bare ground and with the percentage groundcover of annual and biennial weed species. Primary, secondary, and non-noxious weeds were each found in nearly 90% of the fields studied. Widespread presence of noxious weeds on CRP fields is a cause for concern. Weed control issues should be addressed in planning a new CRP. Research Question Most lands in the Conservation Reserve Program (CRP) were to remain in grass or grass-legume cover for 10 yr with no tillage, haying, or grazing. It was not known what changes in vegetation would occur during that time. Establishment of noxious weeds in CRP fields is a concern because they may supply weed seeds to adjacent cropland. This study documented weed presence on CRP fields in Minnesota; and related groundcover by weeds to species diversity, groundcover of grasses and legumes, soil pH, P, and K, and gopher damage. Literature Summary On land retired from haying or grazing, the number of species increases over time. Destruction of vegetation and mounding of soil by small mammals contributes to weed invasion by providing bare ground in which seedlings may become established. Invasion by annual species is common in the first few years after removal of land from cropping. In later years, tall perennials and woody species increase. Species initially present in low numbers may eventually become dominant. A study of pasture adjacent to cropland showed that pasture weeds supplied seed to the field edge. Many of the Minnesota primary noxious weeds have seeds adapted to wind dispersal. Study Description Six 106-sq-ft sample plots were marked in each of 151 fields, selected from 10 Minnesota counties with a high amount of land in CRP contracts. Within each plot all species were identified and their percentage groundcover determined; percentage of bare ground was also determined. Soil samples were taken from each field and amount of gopher mounding was scored. The relationship of weed percentage groundcover with soil pH, P, and K; weed groundcover with number of weed species; weed groundcover with grass-legume groundcover; and weed groundcover with gopher mounding was determined. Applied Questions How many and what kinds of weeds are invading CRP lands, and how does weed invasion relate to soil fertility and groundcover of planted legumes and grasses? Primary noxious weeds were found in 88% of the fields studied. Canada thistle was the most common primary noxious weed. Secondary noxious weeds and non-noxious weeds were found in 89 and 90% of fields, respectively. Quackgrass was the most common secondary noxious weed; dandelion and goldenrod were the most common non-noxious weeds. Fields planted to grasdlegume mixtures at the start of the CRP contract had the lowest ground-cover of weeds for all weed types. Fields accepted into the CRP with existing vegetation had the highest groundcover of primary, secondary, and non-noxious weeds. High groundcovers of planted legumes and grasses were associated with low groundcover for some weed species. Soil pH, P, and K levels had little effect on the groundcover of weed species. Gopher mounding was associated with increased bare ground and presence of annual and biennial weeds.

Monitoring the effects of pastoral use on upland and high country soils in South Island, New Zealand

This paper reports on chemical changes that have occurred since 1978 in topsoils (O-7.5 cm depth) of upland and high country farms at 3 sites: Longslip and Glencaim Stations near Omarama, north Otago, and the east Otago uplands between Middlemarch and Alexandra. Between 1978 and 1992 on Longslip, on fertilised and oversown hilly and steep slopes, mean soil organic C increased by 67%, total N value changed little, and pH declined by 0.41 units. Associated with the soil changes were declines in the amount of bare ground and snow tussock cover, and increases in legume and hieracium cover. The organic C change was equivalent to an increase of about 11 t C/ha between 1978 and 1992. Over the same time period no topsoil changes on lower landscape positions were apparent. On Glencairn, under grazing but no topdressing, mean organic C declined by lo%, total N declined by 25% and pH declined by 0.43 units between 1978 and 1993). The organic C and N changes were equivalent to a decline of about 1.7 t C/ha and 0.4 t N/ha between 1978 and 1993. In contrast, within unfertilised and fertilised plots of exclosures that had not been mown or grazed for 9 years, organic C rose by 40-55%, total N rose by 21-36%, and there was no significant change of pH. Vegetation changes outside the exclosures included an increase of hieracium and briar cover. On the east Otago uplands under light grazing and little or no fertiliser application no significant changes of pH, organic C or total N were~recorded between 1978 and 1994. The results show that soil monitoring can give useful information about the changes associated with pastoral use and the options available to maintain or enhance soil organic matter and pH levels. Keywords: high country, monitoring, organic C, pH, sustainability, total N

Long-Term Vegetation Change in Relation to Cattle Grazing in Sub-Alpine Grassland and Heathland on the Bogong High-Plains: an Analysis of Vegetation Records From 1945 to 1994

Changes in vegetation composition and structure are described for grassland and heathland communities on the Bogong High Plains, in the Victorian Alpine National Park. The data are based on long-term records collected from permanent reference plots over the period 1945 to 1994 from plots established in 1945, 1946 and 1979. In the Pretty Valley grassland plots, established in 1946, cattle grazing has prevented the large-scale regeneration of a number of tall, palatable forbs and short, palatable shrubs, while in the absence of grazing, the cover of these Life forms increased substantially. The amount of bare ground and loose litter was significantly greater on the grazed compared with the ungrazed plot. Between 1979 and 1994, there was little or no identifiable trend in the cover of Vegetation or bare ground at either the Pretty Valley grazed site, or two additional grazed grassland sites established nearby in 1979. The current condition of grazed grassland on the Bogong High Plains is interpreted as stable, yet degraded. Improvement in condition will occur in the absence of grazing. In the Rocky Valley open heathland plots, established in 1945, increases in shrub cover over the study period were due to growth of shrubs following the 1939 bushfires that burnt much of the Bogong High Plains. From 1945-1979 shorter-lived shrubs increased in cover; since 1979, these shrubs have senesced, and are being replaced mainly by grasses. On the grazed plot longer lived, taller shrubs have continued to increase in cover and are not senescing. Between 1979 and 1989, total shrub cover declined on the ungrazed plot, but increased on the grazed plot. There was no evidence that grazing has reduced shrub cover, and therefore potential fire risk, in open heathland. These findings have significant management implications for the Alpine National Park and are consistent with those from other regions in the Australian alps.

The effects of military tank traffic on prairie: A management model

The effect of various frequencies and seasons of military tank traffic on native mixed-grass prairie was examined in a randomized and replicated field experiment. Vegetation (in 10×10 m plots) was subjected to tank traffic at the following rates: (a) one pass per day of training from May until August; (b) one pass per day in May and June; (c) one pass per day in July and August; (d) one pass every three weeks from May until August; (e) zero (control). Species composition and the amount of bare ground were found to vary significantly with traffic frequency. Plant species alien to North America invaded plots subjected to spring driving. Regression analysis showed spring driving to produce more bare ground than summer driving. The regression models suggested that much higher intensities of training could be conducted without damage if spring driving were avoided. Regression models were also used to estimate the frequency of traffic associated with a significant change in species composition, where species composition was expressed as the ratio ofBouteloua gracilis toStipa spartea, an indicator of disturbance-induced change in prairie vegetation. This relationship predicted the capacity of the vegetation of a training area of any given width to support tank traffic without changing species composition. The predictive ability of the model was tested by comparing predicted traffic capacities with the amount of traffic actually applied to two training areas in 1986. Where traffic capacity was exceeded, the model successfully predicted a significantly higher frequency of bare ground and ratio ofBouteloua gracilis toStipa spartea.

Slope, aspect, and slope position as factors controlling grassland communities in the coulees of the Oldman River, Alberta

Vegetation and environmental variables were examined in some coulees of the Oldman River near Lethbridge, Alta. Principal components analysis of environmental variables indicated that solar energy, aspect, soil Mg2+, [Formula: see text], and moisture were related to the first axis of variation. Slope position, soil [Formula: see text], moisture, K+, [Formula: see text], and amount of bare ground were related to a second axis of variation. There was a large range in species diversity among plots; most diverse plots were on north-facing slopes. Direct ordination of vegetation data indicated that slope position and aspect were most important in describing distribution of species. Koeleria macrantha, Bouteloua gracilis, Stipa comata, and Artemisia frigida were found on most coulee positions. Hymenoxys richardsonii, Machaeranthera grindeloides, Astragalus spatulatus, and Eriogonum flavum were mostly restricted to summit and upper slope positions. Anemone patens, Geum triflorum, Thermopsis rhombifolia, and others were most abundant on north- and east-facing slopes. Fewer species (e.g., the C4 Aristida longiseta and the cactus Coryphantha vivipara) were mostly confined to south-facing positions.

The effect of cattle and sheep grazing on salt-marsh vegetation at Skallingen, Denmark

The aggregated effect of cattle and sheep grazing on Puccinellion maritimae and other salt-marsh vegetation has been studied together with changes in species composition, the percentage cover of each species, total cover and the percentage of bare ground, six years after grazing had been prevented by construction of experimental exclosures. The results of these experiments are discussed in relation to the natural development of the vegetation that occurred in a permanent plot in the ungrazed part of the salt marsh. Six years without grazing caused a marked increase in total cover and a dramatic reduction in the amount of bare ground. The species composition of the Puccinellia maritima community did not change during these six years, but all species increased in cover. Whereas Artemisia maritima migrated into the Festuca rubra community and only two species Festuca and Halimione portulacoides, increased in cover, all other species showed reduced cover and Salicornia europaea disappeared from the plot after six years without grazing. During the same period of time, three species, Salicornia europaea, Suaeda maritima, and Glaux maritima, disappeared from the plot in the ungrazed marsh as a result of natural development. During thirty-five years the vegetation originally dominated by Puccinellia maritima and Salicornia europaea has changed into a community dominated by Halimione portulacoides, whereas the grazed salt marsh is still dominated by Puccinellia maritima and Salicornia europaea.

Infiltration and Sediment Production on a Deep Hardland Range Site in North Central Texas

Greatest infiltration rate and lowest sediment production most closely associated with variations in infiltration capacity and occurred in the honey mesquite canopy zone. Infiltration on sediment production. shortgrass interspace areas was about one-half of the canopy zone rate. Terminal infiltration rates within the canopy zone and Study Area shortgrass interspace areas were affected little by brush control treatments. Infiltration rate improvement due to treatment occurred primarily in the midgrass interspace areas. Water-stable aggregates and the interaction of soil aggregate stability with the amount of bare ground were the dominant factors controlling infiltration. Sediment production on the shortgrass interspace was double that of the canopy zone or midgrass interspace areas. Low rate of sediment production on the midgrass interspace areas occurred on areas aerially sprayed or root plowed 3 years earlier. Sediment production was controlled primarily by an interaction of soil organic matter and amount of above-ground biomass or grass cover. Past land management practices have resulted in large increases of honey mesquite (PTosopis glandulosa Torr. var. glandulosa) which now occurs on 56 million acres of Texas rangeland, including 34 million acres which are moderately to heavily infested (Fisher et al. 1973). Most of the heavily and moderately infested rangelands currently produce much less forage than their potential and require control of the honey mesquite to improve forage production. Herbicides and root plowing are widely accepted tools for improving honey mesquite dominated rangelands. However, little information exists for Texas rangelands relative to the impact of honey mesquite control on infiltration rates and sediment production. In other areas, brush control practices have apparently increased infiltration rates and decreased erosion (Rosa and Tigerman 1951, Rich 1961, Rowe and Reimann 1961, Dragoun 1969, Blackbum and Skau 1974). Yet, in some cases, these practices have failed to improve watershed condition (Rowe and Reimann 1961, Blackburn and Skau 1974, Gifford and Busby 1974). Blackburn (1975) reported sagebrush (Artemesia spp.) canopy zones to have exceedinalv high infiltration rates. sometimes 3 to 4 Field research was conducted on the W.T. Waggoner Estate southwest of Vernon, Texas. Theestate is part of the Rolling Plains land resource area which comprises approximately 6.32 million ha of rolling to rough topography in northwest Texas (Gould 1975). Normal annual precipitation for Vernon, Texas, is about 65 cm, with May, June, and October being the months of highest precipitation and January being the driest month (USDC 1976). The average frost-free period is 232 days (Koos et al. 1962). Climax vegetation of the Rolling Plains include tall and midgrasses, but continuous heavy utilization by cattle has reduced the vegetation to primarily short and midgrasses with varying densities of woody plants. Honey mesquite, with a mean height of 1.6 m, a mean density of 437 plants/ ha and a 21% canopy cover, dominated the study area prior to treatment. Lotebush (Ziziphus obrusifolia (T.G.) Gray), tasajillo (Opuntia leprocaulis D.C. var leptocaulis), and grassland prickly pear (Opuntia rnacrorhiza Engelm.) were common on the study area. Herbaceous vegetation was typified by Texas wintergrass (Sripa feucotricha Trin. and Rupr.), Arizona cottontop (Digitaria calryornica (Benth.) Henr.), little barley(Hordeum pusillum (Nutt.)), rescuegrass (Bromus unioloides (Willd.) H.B.K.), buffalograss (Buchloe dacfyloides (Nutt.) Engelm.), sand dropseed (Sporobolus cryptandrus (Torr.) Gray), and purple threeawn (Aristida purpurea (Nutt.)).

Changes in the Vegetation of Sclerophyll Shrubby Woodland Associated With Invasion by Phytophthora cinnamomi

Changes in the vegetation of a sclerophyll shrub woodland community growing on deep infertile sands at the northern end of Wilson's Promontory National Park were monitored for infected and control plots over a 5- year period and compared with changes due to disease on a ridge site. In all cases disease appeared as a mosaic of chlorotic and dying plants. The plant community changed to an open sedge woodland characterized by a rediction in tree density, loss of susceptible species, an increase in cover by resistant sedges and increased amount of bare ground. There were highly significant changes in plant density for 12 of the 16 species and in the proportion of these species in the total vegetation. The changes are continuing and there is no evidence as to whether they are irreversible or likely to become part of a cyclic process of disease and recovery. Changes in soil temperature and soil matric water potential were monitored continuously during the 5 years and were correlated with changes in pathogen disease potential, symptom expression and deaths. Disease was most severe not on the plots but on nearby ridge sites with exposed shallow, gravelly soils, and in these plant deaths were more frequent and occurred in more species.

Trends in Vegetation at Kosciusko. II. Subalpine Range Transects, 1959-1978

Changes in vegetation during the 20-yr period from 1959 to 1978 were measured along permanent transects and on photographic quadrats in four subalpine areas at elevations between 1660 and 1770 m at Kosciusko: Thompsons Plain, Wragges Creek, The Piper and Piper West. The plant communities sampled include more or less natural tussock understorey vegetation in mature subalpine woodland; disclimax tussock, disclimax intertussock and more open vegetation with large bare areas, all in sites formerly dominated by woodland; and disclimax ground-water vegetation with shrubs, derived from Sphagnum bogs. On the dense tussock transects under woodland the vegetation underwent little change, except for an increase in the number and abundance of species of major and intermediate herbs within the snowgrass tussocks; strong competition from the perennial snowgrasses and other herbs suppressed the development of shrubs. On the disclimax tussock transects there was a progressive decrease in the amount of bare ground to minimal values, corresponding with increases in the cover of herbaceous species and shrubs. the increases in shrubs being generally proportional to the amount of bare ground initially exposed. On the disclimax intertussock transects there was a substantial decrease in the amount of bare ground owing to the increased cover of snowgrasses, shrubs and colonizing minor herbs. The cover provided by major non-gramineous herbs remained low, but showed signs of increasing towards the end of the period of measurement. On some transects, the shrubs began to senesce without regeneration as competition from the perennial herbs increased. The bare transects on which there were initially large areas of bare ground continued to lose soil. The main colonizers under these conditions were leguminous shrubs. On the ground-water transects the initial cover of short, grazing-adapted herbs was replaced by tallergrowing sedges and shrubs, with some adjacent regeneration of Sphagnum moss. The results of the transect and associated quadrat measurements were supplemented by other observations throughout the Kosciusko National Park, on the variable regeneration of snowgum, and on the regeneration of kangaroo grass.(Themeda australis) in the Poa-dominated sod tussock grasslands in lower-subalpine cold air plains. The contrasting condition of subalpine vegetation in the Snowy Plains area, just outside the Park, was also recorded. Trends and associated plant successions reflect the effects of the last 20 years' protection from burningoff and livestock grazing and the occasional periods of unfavourable weather including drought, prolonged snow cover and low temperatures. The vegetation trends, which are still continuing, are generally beneficial to water catchment and nature conservation values. Grazing potential has suffered through the replacement of minor herbs by less palatable grasses and shrubs, and although palatable major herbs have increased these could not sustain grazing at the previous stocking rates. Unless grossIy disturbed, some of the associated plant successions are likely to continue for at least another 30 years before near-climax stages are reached, and on severely disturbed sites subclimax conditions may persist indefinitely.