Soil Disturbance Regimes Research Articles

Faunal Soil Disturbance Regime of a Longleaf Pine Ecosystem

Abstract Pocket gophers (Geomys pinetis), Gopher Tortoises, armadillos, and fire ants were the primary soil disturbance agents in a longleaf pine ecosystem. Pocket gopher mounds were the most abundant soil disturbance and covered the greatest percentage of the study area. The most prominent feature of the pocket gopher soil disturbance regime was a strong peak in mound formation from November to January each year in the three-year study, with the location of mound clusters shifting from year to year. During the three-year study, the area disturbed in 0.25-ha plots ranged from 0.7–1.0% yr−1. Pocket gopher mound formation rates were negatively correlated with air temperature and influenced by soil type in some cases, but mostly unaffected by prescribed fires.

Origins of the southeastern Australian vegetation

Australia is an ancient continent with an interesting geological history that includes a recent major shift in its position, both globally and compared with neighbouring land masses. This has led to a great deal of confusion over many years about the origins of the Australian biomes. The plant fossil record is now clarifying this, and it is clear that the ancient Gondwanan rainforests that covered Australia while it was still part of that supercontinent contained many of the elements of the modern vegetation. However, major climatic sifting, along with responses to other factors, including soil nutrient levels, disturbance regimes, atmospheric CO2 levels, fire frequency and intensity, glaciations and the arrival of humans, have had profound impacts on the Australian vegetation, which today reflects the sum of all these factors and more. The origins of Australian vegetation and its present-day management cannot be properly understood without an appreciation of this vast history, and the fossil record has a vital role to play in maintaining the health of this continent's vegetation into the future.

Quantifying Harvesting Impacts using Soil Compaction and Disturbance Regimes at a Landscape Scale

Several indicators have been identified for the conservation and maintenance of soil criterion in the Montreal Protocol. The objective of this study was to use soil compaction and disturbance measures to determine harvesting impacts at a landscape scale in the boreal forest of Saskatchewan. Forest harvesting impacts were studied pre and postharvest for five harvested sites by (i) sampling soil bulk density (Db) at prescribed grid‐points, and (ii) measuring soil disturbance regimes on two 30‐m transects at each grid‐point. Mean soil Db in the harvested area increased significantly (8–11%) from pre to postharvest conditions for the two winter‐harvested sites at both the 10‐ and 20‐cm depths, while two of the three summer harvested sites also showed significant Db increases (7–15%) at the 10‐cm depth. Combining all five sites, showed that after harvest 32% of all the grid‐points had an increased Db of >15%. Mean soil Db at a 10‐cm depth for roadways and landings was significantly higher (8–14%) than postharvest Db for postharvest levels at four of the five harvested sites. Surface soil disturbance regimes were higher for the summer‐harvested sites than that for the winter‐harvested sites. Landscape position showed no significant differences in Db between the shoulder, backslope, and footslope positions; however, within each landscape position, significant differences in Db were found between pre and postharvest conditions. Soil Db and soil disturbance regimes measured on a grid basis provided a simple, but reliable method for monitoring soil compaction and disturbance effects from harvesting at a landscape scale.

Soil disturbance regime in relation to micro-scale landforms and its effects on vegetation structure in a hilly area in Japan

To clarify vegetation-landform relationships, we examined the soil disturbance regime in relation to micro-scale landforms and its effects on vegetation structure in a mixed temperate forest in a hilly area in northeastern Japan. Soil profiles in each micro-landform unit were surveyed to elucidate the effects of soil disturbances on the vegetation structure. The hilly area studied consisted of an upper and a lower hillslope area divided by an erosion front, which differed considerably with respect to vegetation structure. In the upper hillslope area, canopy was closed and dominated by Pinus densiflora and Quercus serrata. In the lower hillslope area, on the other hand, canopy was less closed and shrubs, ferns, and herbaceous species were abundant. The species composition changed gradually from the crest slope to the upper sideslope to the head hollow in the upper hillslope area. However, micro-landforms in the lower hillslope area seemed to have less effect on the vegetation structure. This may be because the lower hillslope area, in contrast to the upper hillslope area, has suffered from soil disturbances, and hence shrubs, ferns, and herbs have developed irrespective of micro-landforms. Thus, vegetation can be quite different depending on whether or not sites have suffered from soil disturbance. In disturbed stands, it is suggested that the frequency and intensity of disturbance are more important for species composition than the type of soil disturbance.

Identifying Sites for Riparian Wetland Restoration: Application of a Model to the Upper Arkansas River Basin

AbstractWe present a conceptual model for identifying restoration sites for riparian wetlands and discuss its application to reaches within the Upper Arkansas River basin in Colorado. The model utilizes a Geographic Information System (GIS) to analyze a variety of spatial data useful in characterizing geomorphology, hydrology, and vegetation of riparian wetland sites. The model focuses on three basic properties of riparian wetland sites: relative soil moisture, disturbance regime, and vegetative characteristics. A relative wetness index is used to define nominal soil moisture classes within the watershed. These classes generally coincide with uplands (low), channel margins (moderate), and channels or open water (high). Vegetative conditions are characterized using color infrared aerial photographs. Land cover types are grouped into five major land cover classes: riparian, moist herbaceous, bare ground, upland, and open water. Disturbance regime is characterized by a reach‐based index of specific power (ω). Preliminary results indicate that reaches within the Upper Arkansas River basin can be classified as high energy (ω≥ 8 W/m2) or low energy (ω≤ 3W/m2), using discharge estimates that reflect the 10‐year flood event. Field surveys of channel and floodplain conditions show that high‐energy reaches (ω≥ 8W/m2) are characterized by sites where the channel occupies a large proportion of the valley bottom. By contrast, low‐energy reaches (ω, ≤ 3 W/m2) are characterized by meandering channels with wide alluvial valleys. Restoration potential is evaluated as a combination of nominal scores from wetness, land cover, and disturbance indices. Application of these methods to field sites within the Upper Arkansas River basin identifies a wide range of riparian wetland sites for preservation or restoration. Potential sites within identified reaches are prioritized using size and proximity criteria.

Identifying Sites for Riparian Wetland Restoration: Application of a Model to the Upper Arkansas River Basin

AbstractWe present a conceptual model for identifying restoration sites for riparian wetlands and discuss its application to reaches within the Upper Arkansas River basin in Colorado. The model utilizes a Geographic Information System (GIS) to analyze a variety of spatial data useful in characterizing geomorphology, hydrology, and vegetation of riparian wetland sites. The model focuses on three basic properties of riparian wetland sites: relative soil moisture, disturbance regime, and vegetative characteristics. A relative wetness index is used to define nominal soil moisture classes within the watershed. These classes generally coincide with uplands (low), channel margins (moderate), and channels or open water (high). Vegetative conditions are characterized using color infrared aerial photographs. Land cover types are grouped into five major land cover classes: riparian, moist herbaceous, bare ground, upland, and open water. Disturbance regime is characterized by a reach‐based index of specific power (ω). Preliminary results indicate that reaches within the Upper Arkansas River basin can be classified as high energy (ω≥ 8 W/m2) or low energy (ω≤ 3W/m2), using discharge estimates that reflect the 10‐year flood event. Field surveys of channel and floodplain conditions show that high‐energy reaches (ω≥ 8 W/m2) are characterized by sites where the channel occupies a large proportion of the valley bottom. By contrast, low‐energy reaches (ω≤ 3 W/m2) are characterized by meandering channels with wide alluvial valleys. Restoration potential is evaluated as a combination of nominal scores from wetness, land cover, and disturbance indices. Application of these methods to field sites within the Upper Arkansas River basin identifies a wide range of riparian wetland sites for preservation or restoration. Potential sites within identified reaches are prioritized using size and proximity criteria.

The biogeography and historical ecology of Lobelia urens L.(r)(the heath lobelia) in southern England

This paper examines the past and present ecology and biogeography of Lobelia urens L. (the heath lobelia) which is threatened with extinction in southern England. A survey of the historical and documentary evidence of the distribution of the species is presented. Historical records exist for nineteen sites in the south but nowhere else in England. The status of L. urens is in decline in Britain with ten populations having been lost this century. The six remaining sites have been surveyed to describe the phytosociology of L. urens communities and the variability of the environmental factors controlling its distribution. A total of ninety‐five quadrats containing 122 species were recorded and analysed using two‐way indicator species analysis. Canonical correspondence analysis was used to assess the correlations between twenty‐eight environmental variables and the floristic variation in the ninety‐five quadrats. These were reduced to sixteen variables for the final analysis. L. urens is shown to be a member of rough, grass‐heath communities (NVC M25 and W23) dominated by Molinia caerulea and situated on seasonally waterlogged, moderately acidic, nutrient‐poor soils. The species is suited to both cyclical and sporadic soil disturbance regimes. The final discussion argues that existing populations will only be maintained and expansion of the species distribution occur, if conservationists prevent woodland succession in L. urens sites and periodically disturb the ground in locations where the species survives at present and also where it has been observed in the recent past. This link between historical ecology and present‐day conservation management would appear very important. Further demographic and experimental work is needed to explore these predictions and their implications for the future conservation management of L. urens.

Geographic differentiation among populations ofArabis serrata Fr. & Sav. (Brassicaceae)

Geographic variation in morphological traits of thirteen populations ofArabis serrata was analyzed to characterize the life history of each particular population in the field. These localities varied in altitude, topography, soil type, humidity, vegetation structure and degree of disturbance. Twelve morphological characters were measured in each plant, and populations were compared using both univariate and multivariate analyses. Populations showed significant differences for most of the traits measured. Principal component analyses revealed a significant differentiation among populations although a continuous variation for some traits was noted. Length of capsules and leaf length of inflorescence's stalks were correlated with the number of frost free days and with temperature, precipitation and number of days of the growing season. The number of rosettes was also correlated with the same variables but negatively. Seed weight was correlated positively with altitude but negatively with temperature and length of the growing season. Populations were also differentiated according to soil conditions and disturbance regimes distinguishing different types of populations: I) populations with many small rosettes, and few heavy seeds per capsule in volcanic soils with low disturbance; ii) plants with many small seeds and few rosettes in very disturbed localities along asphalt roadways and mountain trails; and iii) large plants with intermediate seed size and intermediate number of seeds per plant in limestone and serpentine soils under different conditions of disturbance. Populations ofA. serrata displayed a complex pattern of differentiation in morphological and life history traits in relation to several biotic and abiotic factors. The quantitative nature of the differences among populations ofA. serrata observed in the field deserves further studies (e.g., quantitative genetics and phenotypic plasticity) under controlled conditions in order to assess the extent of differentiation within this species complex.

Plant nutrient changes in a semi‐arid Mediterranean shrubland after fire

Abstract. Alkaline xeric soils from SE Spain weathered from kakiritized dolomitic rocks and subjected to recurrent fires, show phosphorus immobilization, low nutrient availability and high cation content, which might affect plant nutrition. Currently, Ulex shrubland, with a variety of dolomitophilous endemics, is colonizing eroded areas and replacing the original shrubland communities. Variation in nutrient content during post‐fire regeneration was studied in six species which differ widely in their successional status. All species showed a high consumption of nutrients immediately after the fire. A pattern of decline in internal nutrient levels, especially P, with time since fire was detected in mid‐to‐late successional shrubs: Juniperus oxycedrus, Genista spartioides, and to a lesser extent in Rosmarinus officinalis, a shrub species of intermediate successional status. This pattern of decline may represent a progressive change towards a metabolism with a low turnover along the age gradient. Early successional shrub species behaved in a different way. Cistus clusii showed a nutrient‐cumulative strategy, especially for P, across the fire‐age gradient. Ulex rivasgodayanus maximized internal N concentrations due to its symbiotic activity with N2‐fixing bacteria. Cistus and Rosmarinus held high cation levels in their tissues. The nutritional characteristics of these shrub species are seen as advantageous adaptations to the specific soil properties and disturbance regime of the area.

Biogeography of island floras in the Great Lakes. I. Species richness and composition in relation to gull nesting activities

Species–area relations of vascular plants and the effect of nesting colonies of gulls on plant species composition were investigated for 77 islands in Georgian Bay and Lake Huron in the Great Lakes region of Canada. The percentage of plant species classed as alien, annual, or biennial was significantly greater on islands with gull colonies. The slope of the species–area curve was significantly steeper on islands supporting gull colonies compared with islands lacking gull colonies. The expected decline in species richness with increased island remoteness was not detected statistically using multiple regression analysis. The difference in species–area slopes does not appear to reflect a lower propagule immigration rate to islands with gull colonies, because gulls are important in the dispersal of alien plant species to these islands. Larger islands with gull colonies tended to have richer floras than islands of similar size without gull colonies. It is suggested that on these larger islands the presence of gull colonies produces a gradient of soil nutrient and disturbance regimes, thus increasing habitat heterogeneity and species richness.