Burn Intervals Research Articles

Interacting influence of mycorrhizal symbiosis and competition on plant diversity in tallgrass prairie.

In tallgrass prairie, plant species interactions regulated by their associated mycorrhizal fungi may be important forces that influence species coexistence and community structure; however, the mechanisms and magnitude of these interactions remain unknown. The objective of this study was to determine how interspecific competition, mycorrhizal symbiosis, and their interactions influence plant community structure. We conducted a factorial experiment, which incorporated manipulations of abundance of dominant competitors, Andropogon gerardii and Sorghastrum nutans, and suppression of mycorrhizal symbiosis using the fungicide benomyl under two fire regimes (annual and 4-year burn intervals). Removal of the two dominant C4 grass species altered the community structure, increased plant species richness, diversity, and evenness, and increased abundance of subdominant graminoid and forb species. Suppression of mycorrhizal fungi resulted in smaller shifts in community structure, although plant species richness and diversity increased. Responses of individual plant species were associated with their degree of mycorrhizal responsiveness: highly mycorrhizal responsive species decreased in abundance and less mycorrhizal responsive species increased in abundance. The combination of dominant-grass removal and mycorrhizal suppression treatments interacted to increase synergistically the abundance of several species, indicating that both processes influence species interactions and community organization in tallgrass prairie. These results provide evidence that mycorrhizal fungi affect plant communities indirectly by influencing the pattern and strength of plant competitive interactions. Burning strongly influenced the outcome of these interactions, which suggests that plant species diversity in tallgrass prairie is influenced by a complex array of interacting processes, including both competition and mycorrhizal symbiosis.

Economics of Redberry Juniper Control in the Texas Rolling Plains

Redberry juniper (Juniperus pinchotii Sudw.) is a common invasive brush species that reduces rangeland productivity over vast acreages in the Rolling Plains and Edwards Plateau regions of Texas. The objectives of this study were to evaluate the economic feasibility of redberry juniper control and determine the optimum treatment cycle for maintenance burning. A response equation was used to estimate the relationship between herbage production and redberry juniper canopy. Data to estimate the relationship was obtained for a site in the Texas Rolling Plains. The analysis used chaining as the initial treatment and periodic prescribed burns as maintenance treatments. Additional livestock production resulting from brush treatments and the costs of treatments were estimated and used to calculate net present values of the investment in brush control over a 30-year time horizon. Net present values indicated that juniper control was economically feasible across a wide range of economic and environmental conditions. Prescribed burn intervals were found to be optimal at 7-year intervals under most conditions.

Lone Star Tick Abundance, Fire, and Bison Grazing in Tallgrass Prairie

Lone star ticks (Amblyomma americanum L.) were collected by drag samples of 1 km transects on 12 watersheds at Konza Prairie Research Natural Area near Manhattan, Kans., during summer 1995-1996. Watersheds were treated to 2 experimental treatments: 3 burn intervals (1-year, 4-year, and 20-year) and 2 grazing treatments (grazed by bison (Bos bison L.) or ungrazed). The objectives were to determine whether fire interval, time since most recent burn, and the presence of large ungulate grazers would cause changes in lone star tick abundance in tallgrass prairie in central Kansas. Watersheds burned at 1-year intervals had fewer larvae and adults than watersheds burned at 4-year or 20-year intervals. Watersheds burned during the year of sampling had fewer ticks than watersheds burned one or more years in the past. For watersheds burned 1 or more years in the past there was no effect from time since burn. The presence of bison did not affect tick abundance. Spring burning is an effective method to reduce tick populations in tallgrass prairie during the year of the burn.

Long-term effects of dormant-season prescribed fire on plant community diversity, structure and productivity in a longleaf pine wiregrass ecosystem

A flatwoods longleaf pine wiregrass ecosystem, which regenerated naturally following wildfire in 1942, on the Coastal Plain of southern Georgia was treated over a period of four decades with prescribed fire at annual, biennial and triennial intervals during the winter dormant season. Burning caused substantial changes in the understory plant community, with significant reductions in the foliar cover of Ilex glabra in the shrub layer resulting in corresponding increases in the cover of Vaccinium myrsinites, Sporobolus curtissii, Aristida stricta and Andropogon spp. Understory plant species richness, diversity and evenness also increased as a result of periodic fire. Dormant-season burning decreased the cover of litter on the forest floor and significantly increased the standing biomass of A. stricta, S. curtissii, Andropogon spp., all other grasses and all forbs. Recurrent fire also prevented the development of a vigorous midstory, that impedes understory growth and poses a serious fire hazard to the stand. Overstory trees were largely unaffected by burning. Historical light grazing on the site produced no measurable effects on the plant community. Findings suggest that the biennial burning interval results in declines of I. glabra in the shrub layer and litter cover on the forest floor, leading to the largest increases in understory plant species richness and diversity and the biomass productivity of grasses and forbs. Although flatwoods plant communities evolved in environments characterized by growing-season fires of variable frequency, long-term application of dormant-season fire is also recommended as a useful option for sustaining resource values in this and similar longleaf pine wiregrass ecosystems.

Vegetative Responses to Prescribed Burning in a Mature Red Pine Stand

Abstract We investigated the effects of low-intensity, prescribed spring surface fires at varying intervals in a widely spaced, mature red pine plantation growing on a high quality sandy loam soil in northern Lower Michigan. Measurements of overstory characteristics, as well as the composition and development of the herbaceous and woody understory, were taken in unburned plots and during the seventh growing season following a single burn, the second growing season following the last of two burns at 5 yr intervals, and the growing season immediately following the last of four burns 2 yr intervals. Except for loss of a few trees due to crown scorch early in the study when fuel loadings were high, the red pine overstory was minimally affected by fires at any return interval. Compared to unburned plots, fire had no effect on total species richness or percent cover of ground flora < 1.4 m tall, but species composition shifted; cover of mosses and lichens declined and black cherry seedlings increased at the two shortest fire intervals. Although percent cover of grasses, bracken fern, and Rubus spp. appeared to increase following fire, the clumped distribution of vegetation and interplot variability in overstory density obscured the statistical significance of these trends. Species richness and density of stems in the woody understory (> 1.4 m tall but < 10 cm dbh) declined abruptly as burning interval decreased and number of burns increased. Fewer than two woody understory species, on the average, persisted on plots burned every 2 yr, whereas nearly 12 grew on unburned plots. Postburn conditions were conducive to the re-establishment of black cherry and paper birch in the understory; density of all other major species dropped sharply after more than one fire. As time after the last fire increased, however, red maple, choke cherry, and white ash densities began to recover slowly, largely by sprouting. The significance of these findings to red pine managers in the Lake States is discussed. North. J. Appl. For. 13(3):140-146.

Managing Species Diversity in Tallgrass Prairie: Assumptions and Implications

Conservation and restoration ecology efforts may conserve or restore a particular image of a community, a variety of plausible images, or maximum biological diversity. The choice is a policy decision that should reflect relevant history and sound science. Here I argue that common methods of conserving and restoring tallgrass prairie have a weak scientific rationale, are not consistent with plausible history, and threaten prairie biodiversity. Dormant‐season burns and grazer exclusion are human interventions that may promote artificially consistent dominance of large grasses utilizing the C4 photosynthetic pathway, thereby relegating hundreds of other prairie plants to small populations that are vulnerable to local extinction. I recommend an experimental approach to large remnant conservation and restoration in which varied conditions alter dominance, thereby increasing short‐term species richness. I also recommend prescribed burning during the summer, to simulate the timing of lightning fire, and light‐to‐moderate grazing by different ungulates, to simulate historical grazing history. Both should favor plants that are consistently infrequent or rare in many managed prairies. Varied regimes of burn season, burn interval, and large‐mammal grazing should promote greater overall species diversity and should more realistically represent varied conditions under which grassland taxa evolved.

Soil Chemistry in a Loblolly/Longleaf Pine Forest with Interval Burning.

We examined the 30-yr cumulative effects of prescribed fires at intervals of 1, 2, 3, and 4 yr in a loblolly and longleaf pine forest in the Coastal Plain of South Carolina. The fine fraction of the forest floor (Oe + Oa horizons) contained much more carbon and nitrogen per unit area in the control plots (1.7 and 0.05 kg/m2 , respectively) than in the 1-yr burn interval plots (0.4 and 0.007 kg/m2 , respectively). Mineral soils (0-0.2 m depth) were highly variable in chemistry, and showed only slight differences across the burning treatments for nitrogen and sulfur. No trends were apparent for phosphorus in the forest floor or mineral soil; differences in acidity and extractable cations were also slight. The nutrient content of foliage was generally low, with no differences across burning intervals. Our results are consistent with earlier studies that showed the biogeochemical effects of repeated surface fires in southern pine forests are generally limited to the forest floor, with the possible exception of overall reductions in nitrogen cycling.

Growth Dynamics of Crowns of Eastern Redcedar at 3 Locations in Oklahoma

Eastern redcedar (Juniperus virginiana L.) trees from a location in western, central, and eastern Oklahoma were aged by tree ring analysis to assess the relationship of tree age to tree height and crown area. The relationship of tree age to crown size differed with location. Trees in the oldest age class, 28 to 29 years, ranged in height from 6.2 m on the western Oklahoma location to 8.3 m on the eastern Oklahoma location. The oldest trees at all locations were still actively growing. Height growth rate of the oldest class of trees averaged 0.5 to 0.6 m yr-1 on the western and eastern study locations, respectively. Eastern redcedar reached 2.0 m in height at about 8 years of age on the eastern Oklahoma location. Trees reached 2.0 m in height in 10 to 14 years at the other locations. This suggests that burning intervals should be more frequent on the eastern Oklahoma location than on the central and western Oklahoma locations. Crown area as a function of tree age was not as similar as tree height among the 3 locations. Not only did the relationship differ among locations, but it differed also between 2 central Oklahoma range sites. Crown area of 28-year-old trees ranged from only 15 m(2) on the central Oklahoma Loamy Prairie to 40 m(2) at the eastern Oklahoma location. These data suggest that the smaller crown area of trees at the central Oklahoma location may be a result of an influence other than environment, such as an introduction of plants of a different race with an inherent columnar growth habit. The reduction in forage production associated with eastern redcedar and the efficacy of prescribed burning for controlling eastern redcedar would change more rapidly as trees age on the eastern Oklahoma location than on the other locations.

Debris basin policy and design

Debris flows cause considerable property damage and loss of life. The debris basin is a widely used control alternative, for which accurate design methods are not available. Thus, there is a need for a systematic design procedure, as well as a practical basis for establishing policy elements. A design procedure that accounts for seasonal volumes of debris is presented. The choice of the design return period and burn interval, both of which are important policy elements, is a function of the hazard level associated with failure. The monitoring and maintenance of debris basins are also important policy elements. The frequency of monitoring a basin to ensure adequate storage is a function of the potential hazard presented by a debris flow to the area downstream of the basin, as well as the precipitation, the frequency of burning in the watershed, and the drainage area. A procedure for estimating the temporal accumulation of debris is presented so that public agencies will know when to monitor and dredge each debris basin in their jurisdiction. The adoption of rational design methods and policy elements relating to debris basins should minimize the risk of failure of the basins.

Risk of Debris‐Basin Failure

Debris basins are a common engineering structure used to control debris flows. Knowledge of the risk of failure as a function of important design variables can improve decision making and can be used as a basis for minimizing the total annual cost (i.e., construction and maintenance plus risk cost). The failure risk was computed for four policy elements: the rainfall frequency, the interval between significant watershed burn, construction and dreding accuracy, and the regularity of maintenance of the debris basin. The burn interval and the rainfall magnitude are the two most important variables associated with the failure risk, with the expected annual risk varying from less than 1% to as much as 65% for different burn intervals and rainfall frequencies. A failure to maintain the basin can double the risk of failure. The risk of failure does not appear to change much for typical construction and dreding-volume accuracy. The risk estimates were made using a model developed from data from the southern California area and the conditional expectation variance reduction technique.

Effect of Periodic Burning on Soil Nitrogen Concentrations in Ponderosa Pine

AbstractTo determine the effects of different burning intervals on soil N status in substands of sapling‐, pole‐, and sawtimber‐sized ponderosa pine (Pinus ponderosa Laws.) we sampled plots burned at 1‐, 2‐, and 4‐yr intervals by three strata at two depths (0–5 and 5–15 cm). Generally, NH4+ and NO3‐ concentrations were higher on plots repeatedly burned than on unburned controls. However, plots not reburned for 4 to 5 yr had concentrations similar to controls. No significant difference in total (organically bound) N was found among treatments. We conclude that frequent periodic burning can be used to enhance N availability in southwestern ponderosa pine sites.

Bush control with fire inacacia nigrescens/combretum apiculatumsavanna in Botswana

Abstract The results of a trial to study the effects of periodic burning, or complete resting, on the vegetation and some soil characteristics of semi‐arid Acacia nigrescens/Combretum apiculatum savanna in eastern Botswana are discussed. Plots of 1,2 ha were burned at intervals of O (no burn control), 1,2,3,4 and 5 years from 1958 to 1980. In 1981 these were assessed for bush density by species and by height classes, for grass basal cover and botanical composition, and for soil properties. Bush density increased with increasing burning interval but complete resting suppressed seedling development. All burned plots were visibly more open than the rested plot and hence fire appears to offer the possibility of a low cost means of bush control. The changes in soil properties, grass cover and botanical composition resulting from low frequency burns were small.

Reproductive Ecology of Picea Mariana (Mill.) BSP., at Tree Line Near Inuvik, Northwest Territories, Canada

Picea mariana predominates in even—aged stands of fire origin at the forest—tundra ecotone near Inuvik, Northwest Territories, Canada. Growth rates of P. mariana decrease with increasing latitude and density although growth rates do not change significantly along the ecotone. Field measurements of water relations, when compared with laboratory determinations of leaf water potentials vs. net photosynthesis, suggest no water stress related photosynthetic reduction for mature trees during 1976. Maximum and minimum leaf water potentials for mature trees were —0.6 and —2.1 MPa on 4 August and 1 July, respectively. Winter measurements of water relations also suggest no water stress. In contrast, 1st—yr seedlings demonstrated sensitivity to water stress with high rates of mortality at low levels of water loss. A macro—mesoclimatic gradient of 4°C was found across the tree line (135—km study transect). Picea mariana seed production and germination are limited by this environmental gradient to °40 km south of modern forest line. Germination and survivorship are also affected by microenvironments within a well—developed soil hummock terrain. The lower cardinal germination temperature of 15°C was the determinant of germination timing and success. Seed production estimates suggested little effect on stand reproduction with burn intervals of 100—200 yr. Shorter or longer burn intervals are believed to reduce stand reproduction. Reduced seed longevity, complete stand destruction by wild—fire, and apparent destruction of seed in the soil restrict establishment to 1—8 yr after fire. This may cause local extermination of the species or out—of—equilibrium tree line positions under conditions of deteriorating environment.

Proper Burning Intervals for Tobosagrass in West Texas Based on Nitrogen Dynamics

Highlight: The time required for re-establishment of pre-fire nitrogen levels in tobosagrass (Hilaria mutica) communities in the Rolling Plains of West Texas was studied on five different ages of burns over a 2-year period. Time elapsed after burns varied from one to five growing seasons for both convex and concave topographic sites near Colorado City, Texas. Standing old growth-N returned to pre-fire levels by the end of the third growing season. However, litter-N on the soil surface took 5 years to reach pre-fire levels on concave sites and an estimated 8 years on convex sites. High variation prevented the recognition of any meaningful trends in root or soil nitrogen levels. Based on this data, tobosagrass should not be burned more frequently than 5 to 8 years, depending on the site.

Advances in precision of mass-spectroscopic spark-source analysis of conducting materials

A procedure is described for the mass-spectroscopic analysis of solids by spark sources. This procedure differs from the customary r.f. spark source analysis mainly by 1. the use of a unipolar low-voltage discharge for ion production; 2. rectangular blackening profiles of constant width of the mass-spectral lines due to improvements in the ion optics design; 3. the suppression, by time-resolution (gating) techniques, of ions from unsuitable burning intervals of the discharge; 4. the elimination of large-scale variations of photographic sensitivity by exposure of analytical and reference spectrum on the same plate; 5. a refinement of the evaluation procedure of photographically recorded mass spectra.

A Study of Forward Combustion in a Radial System Bounded by Permeable Media

Abstract A mathematical model of forward combustion in an oil reservoir is treated in this paper. The model describes a radial system having a vertical section of essentially infinite thickness, all of which is permeable to gas flow. Combustion, however, is presumed initiated over a limited thickness of the total vertical section. In the interval supporting combustion, the mechanisms of radial conduction, convection and heat generation are taken into account. Above and below the burning interval, heat transport in the radial direction is by conduction and convection. Vertical heat losses from the ignited interval are accounted for by conduction alone.A general solution is presented for the temperature distribution caused by radial movement of the combustion front. The results show that no feedback of heat occurs into the ignited interval when convection and conduction are acting in the bounding media. Peak temperatures are also 5 to 10 per cent higher than in the case where heat transport in the bounding media is by conduction alone. We arbitrarily define vertical coverage to be that fraction of the total ignited interval which is at 600F above ambient, or greater, at any given time. The radial distance at which the vertical coverage becomes zero is the propagation range of the combustion front. It was found that an increase in vertical coverage results when the oxygen concentration, fuel concentration or gas-injection rate is increased. Moreover, the combustion front can be propagated 10 to 15 per cent further than in the case where only conduction is acting above and below the ignited interval. Introduction In the theoretical treatment of forward combustion in a radial system, one of the problems encountered is the determination of the transient temperature distributions caused by an expanding cylindrical heat source. Bailey and Larkin and Ramey simultaneously presented analytical solutions to the problem assuming heat transport by conduction alone. In a subsequent publication, Bailey and Larkin included the effects of both conduction and convection while treating linear and radial models. In this latter work, however, vertical heat losses were largely neglected. Selig and Couch dealt with a radial model in which both conduction and convection were acting. Only a limiting case involving vertical heat losses was considered, however. Namely, temperatures on the boundary of the bed of interest were set equal to zero. Solutions thus obtained were representative of a system having a maximum vertical heat flux. Chu recently treated a more general case in which a permeable bed was considered bounded by impermeable media. Conduction and convection took place within the bed, and only conduction outside of the bed. The effects of vertical heat losses were included in his study. Solutions were obtained by numerical techniques. This paper is an extension of the theoretical work of other authors pertaining to forward combustion in a radial system. In particular, a mathematical model of the process is treated in which heat generation occurs over a small vertical interval of a larger permeable section. In the interval supporting heat generation, and above and below this interval, the mechanisms of radial conduction and convection are also presumed acting. Heat losses from the ignited interval are accounted for by vertical conduction. An analytical solution for the temperature distribution caused by radial movement of the burning front is presented. The effects of certain process variables are indicated and comparisons with Chu's results are made. THEORY To render the mechanism of forward combustion tractable to mathematical treatment, we idealize the problem to the extent of assuming continuous reservoir media possessing homogeneous and isotropic properties. The following additional assumptions are implicit in this analysis.The thermal parameters, i.e., heat capacities, thermal conductivities and thermal diffusivities are invariant with temperature and pressure. Moreover, the bounding media possess the same thermal properties as the bed of interest.The temperatures of the porous media and its contained fluids at any point and at any time are equal.The reaction rate between the oxidant gas and the fuel is infinite. The assumption implies that the incoming oxygen concentration instantaneously goes to zero within an infinitesimal distance, i.e., the width of the combustion zone is negligible.The rate of gas injection is constant and corresponds to the average rate throughout the lifetime of the project.The fuel concentration is constant throughout the volume of rock swept out by the burning zone.There is complete burnoff of fuel. This assumption demands that the rate of propagation of the burning front equals the rate of fuel burnoff. JPT P. 1145^