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Fire Intervals (fire + interval)
Selected AbstractsA spatial model of coexistence among three Banksia species along a topographic gradient in fire-prone shrublandsJOURNAL OF ECOLOGY, Issue 5 2002J. Groeneveld Summary 1A spatially explicit, rule-based model for three co-occurring Banksia species was developed to investigate coexistence mediating processes in a fire-prone shrubland in western Australia. Fecundity, recruitment, mortality and other biological data for two non-sprouting (B. hookeriana, B. prionotes) and one resprouting (B. attenuata) species were available from 15 years of empirical field studies. 2Without interspecific competition, each species could persist for a wide range of fire intervals (10 to > 20 years). The resprouting species performed better under shorter fire intervals (10,13 years), while both non-sprouting species were favoured by longer (15 to > 20 years) fire intervals. These results conform with those obtained from single-species, non-spatial population models. 3When interspecific competition for space was included in the model, all three species exhibited optima at shorter fire intervals and with a narrower range than in isolation. The three species did not co-occur under any fire regime. At intermediate fire frequencies (11,13 years), B. hookeriana excluded the other species, while for longer intervals between fires B. prionotes became dominant. 4The introduction of temporal (stochastic) variability in fire intervals (drawn from a normal distribution) failed to produce coexistence, unless spatial variability as a spatial ignition gradient was also included. The spatial arrangement of the non-sprouters observed in the field was then reproduced. 5Observed patterns of coexistence and spatial distributions of all species occurred when a spatial establishment gradient for the resprouter species was included in the model (individuals of B. attenuata are known to produce more seeds in swales than on dune crests and recruit seedlings here more frequently). 6Coexistence appears to be highly dependent upon the mean interfire period in combination with subtle gradients associated with fire propagation and recruitment conditions. Variation around the mean fire interval is less critical. When the system is modelled over a long time period (1500 years) coexistence is most strongly favoured for a narrow window of mean fire intervals (12,14 years). [source] Latitudinal trends in foliar oils of eucalypts: Environmental correlates and diversity of chrysomelid leaf-beetlesAUSTRAL ECOLOGY, Issue 2 2010MARTIN J. STEINBAUER Abstract Eucalypts are characterized by their oleaginous foliage, yet no one has considered the universality of oil expression or its ecological associations and implications for biodiversity. Published literature on the oils of 66 eucalypts was combined with geographic distribution information contained in the Australian National Herbarium (ANHSIR) database to investigate continent-scale changes in oil yield and composition. The exposure to fire and rainfall of each eucalypt was considered in reference to Walker's data on fire frequency and Australian Bureau of Meteorology 97-year records of rainfall variability. Host collection records for 69 species of chrysomelid leaf-beetle were collated from entomologists to consider patterns of association with a subset of 16 eucalypts. Eucalypts endemic to the seasonally arid, sub-tropical to tropical climates of northern Australia have less oleaginous and aromatic leaves than species endemic to the mesic, temperate climates of the southern parts of the continent. Maximum oil yield and the concentrations of cineole and pinene were positively correlated with minimum fire interval but not with rainfall variability. Low oil contents in more northerly distributed species may facilitate persistence in highly fire-prone habitats. There were no patterns in the diversity of chrysomelid leaf-beetles with either the oil yield or the concentrations of 1,8-cineole or ,-pinene in their hosts. When taken in consideration with the apparent strategy of eucalypts to tolerate insect herbivory, current evidence augurs against high concentrations of cineole or pinene acting alone as antibiotic plant secondary metabolites. [source] Californian mixed-conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, MexicoJOURNAL OF BIOGEOGRAPHY, Issue 1 2000R. A. Minnich Abstract Aim,This study appraises historical fire regimes for Californian mixed-conifer forests of the Sierra San Pedro Mártir (SSPM). The SSPM represents the last remaining mixed-conifer forest along the Pacific coast still subject to uncontrolled, periodic ground fire. Location,The SSPM is a north,south trending fault bound range, centred on 31°N latitude, 100 km SE of Ensenada, Baja California. Methods,We surveyed forests for composition, population structure, and historical dynamics both spatially and temporally over the past 65 years using repeat aerial photographs and ground sampling. Fire perimeter history was reconstructed based on time-series aerial photographs dating from 1942 to 1991 and interpretable back to 1925. A total of 256 1-ha sites randomly selected from aerial photographs were examined along a chronosequence for density and cover of canopy trees, density of snags and downed logs, and cover of non-conifer trees and shrubs. Twenty-four stands were sampled on-the-ground by a point-centred quarter method which yielded data on tree density, basal area, frequency, importance value, and shrub and herb cover. Results,Forests experience moderately intense understory fires that range in size to 6400 ha, as well as numerous smaller, low intensity burns with low cumulative spatial extent. SSPM forests average 25,45% cover and 65,145 trees per ha. Sapling densities were two to three times that of overstory trees. Size-age distributions of trees , 4 cm dbh indicate multi-age stands with steady-state dynamics. Stands are similar to Californian mixed conifer forests prior to the imposition of fire suppression policy. Livestock grazing does not appear to be suppressing conifer regeneration. Main conclusions,Our spatially-based reconstruction shows the open forest structure in SSPM to be a product of infrequent, intense surface fires with fire rotation periods of 52 years, rather than frequent, low intensity fires at intervals of 4,20 years proposed from California fire-scar dendrochronology (FSD) studies. Ground fires in SSPM were intense enough to kill pole-size trees and a significant number of overstory trees. We attribute long fire intervals to the gradual build-up of subcontinuous shrub cover, conifer recruitment and litter accumulation. Differences from photo interpretation and FSD estimates are due to assumptions made with respect to site-based (point) sampling of fire, and nonfractal fire intensities along fire size frequency distributions. Fire return intervals determined by FSD give undue importance to local burns which collectively use up little fuel, cover little area, and have little demographic impact on forests. [source] The millennial dynamics of a boreal forest stand from buried treesJOURNAL OF ECOLOGY, Issue 3 2004DOMINIQUE ARSENEAULT Summary 1We reconstructed the dynamics of a black spruce (Picea mariana) and jack pine (Pinus banksiana) forest stand in northern Québec using a continuous, 5200-year-long sequence of stem remains buried in adjacent peatland. Simulations of recruitment of such remains provided guidelines for inferring past ecosystem structure and composition at the stand scale. 2Compared with the late Holocene (4650,0 cal. year BP (CYBP)), the mid Holocene (5200,4650 CYBP) period was characterized by faster tree growth, larger stems and higher stem density, indicating higher forest productivity in association with a milder climate. 3The presence of stem remains of both species from 17 out of 20 contiguous 250-year time intervals suggests that the spruce-pine stand exhibited high compositional stability, with both species regenerating after fire from canopy-stored seed banks. 4Relative species abundance closely followed the duration of past fire intervals deduced from the number of tree rings in buried conifers. Time periods of long (4650,3950, 3400,1850 and 250,0 CYBP) and short fire intervals (4950,4650, 3950,3400 and 1850,250 CYBP) were associated, respectively, with decreasing and increasing pine abundance, probably reflecting faster juvenile growth, lower shade tolerance, earlier sexual maturity and shorter longevity in jack pine compared with black spruce. 5We conclude that both climate change and climate-induced fire disturbance have been driving long-term ecosystem dynamics. Our field evidence supports the idea that interactions between disturbances and the life-history traits of species modulate the impact of climate change at the scale of forest stands. At the same time, disturbances may result in long-term stability of disturbance-adapted ecosystems. [source] A spatial model of coexistence among three Banksia species along a topographic gradient in fire-prone shrublandsJOURNAL OF ECOLOGY, Issue 5 2002J. Groeneveld Summary 1A spatially explicit, rule-based model for three co-occurring Banksia species was developed to investigate coexistence mediating processes in a fire-prone shrubland in western Australia. Fecundity, recruitment, mortality and other biological data for two non-sprouting (B. hookeriana, B. prionotes) and one resprouting (B. attenuata) species were available from 15 years of empirical field studies. 2Without interspecific competition, each species could persist for a wide range of fire intervals (10 to > 20 years). The resprouting species performed better under shorter fire intervals (10,13 years), while both non-sprouting species were favoured by longer (15 to > 20 years) fire intervals. These results conform with those obtained from single-species, non-spatial population models. 3When interspecific competition for space was included in the model, all three species exhibited optima at shorter fire intervals and with a narrower range than in isolation. The three species did not co-occur under any fire regime. At intermediate fire frequencies (11,13 years), B. hookeriana excluded the other species, while for longer intervals between fires B. prionotes became dominant. 4The introduction of temporal (stochastic) variability in fire intervals (drawn from a normal distribution) failed to produce coexistence, unless spatial variability as a spatial ignition gradient was also included. The spatial arrangement of the non-sprouters observed in the field was then reproduced. 5Observed patterns of coexistence and spatial distributions of all species occurred when a spatial establishment gradient for the resprouter species was included in the model (individuals of B. attenuata are known to produce more seeds in swales than on dune crests and recruit seedlings here more frequently). 6Coexistence appears to be highly dependent upon the mean interfire period in combination with subtle gradients associated with fire propagation and recruitment conditions. Variation around the mean fire interval is less critical. When the system is modelled over a long time period (1500 years) coexistence is most strongly favoured for a narrow window of mean fire intervals (12,14 years). [source] Dispersal and recruitment dynamics in the fleshy-fruited Persoonia lanceolata (Proteaceae)JOURNAL OF VEGETATION SCIENCE, Issue 6 2007Tony D. Auld Abstract Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy-fruited obligate seeding plant species in fire-prone habitats? Location: Southeastern Australia. Methods: We used a long-term study of a shrubby, fleshy-fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post-fire seedling densities 6-7 times pre-fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77-100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0-5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7,8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five-fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished. [source] Increased early growth rates decrease longevities of conifers in subalpine forestsOIKOS, Issue 8 2009Christof Bigler For trees, fast growth rates and large size seem to be a fitness benefit because of increased competitiveness, attainment of reproductive size earlier, reduction of generation times, and increased short-term survival chances. However, fast growth rates and large size entail reduced investment in defenses, lower wood density and mechanical strength, increased hydraulic resistance as well as problems with down-regulation of growth during periods of stress, all of which may decrease tree longevity. In this study, we investigated the relationship between longevity and growth rates of trees and quantified effects of spatial environmental variation (elevation, slope steepness, aspect, soil depth) on tree longevity. Radial growth rates and longevities were determined from tree-ring samples of 161 dead trees from three conifer species in subalpine forests of the Colorado Rocky Mountains (Abies lasiocarpa, Picea engelmannii) and the Swiss Alps (Picea abies). For all three species, we found an apparent tradeoff between growth rate to the age of 50 years and longevity (i.e. fast early growth is associated with decreased longevity). This association was particularly pronounced for larger P. engelmannii and P. abies, which attained canopy size, however, there were also significant effects for smaller P. engelmannii and P. abies. For the more shade-tolerant A. lasiocarpa, tree size did not have any effect. Among the abiotic variables tested only northerly aspect significantly favored longevity of A. lasiocarpa and P. engelmannii. Trees growing on south-facing aspects probably experience greater water deficits leading to premature tree death, and/or shorter life spans may reflect shorter fire intervals on these more xeric aspects. Empirical evidence from other studies has shown that global warming affects growth rates of trees over large spatial and temporal scales. For moist-cool subalpine forests, we hypothesize that the higher growth rates associated with global warming may in turn result in reduced tree longevity and more rapid turnover rates. [source] Bird responses to fire severity and time since fire in managed mountain rangelandsANIMAL CONSERVATION, Issue 3 2010P. Pons Abstract Broom matorrals are subjected to extensive burning in the Pyrenees to improve grazing value, despite being a habitat of conservation interest in Europe. Our aim here is to evaluate the impact of such management practices over the long term, and of fire severity over the short term, on avifauna. Bird-habitat stations were distributed in broom shrublands from a few months to 51 years after fire, at 1400,2100 m a.s.l. Overall, shrub cover was the main habitat variable affecting the bird community composition. The abundance trends of bird species for half a century after fire were varied, but population recovery seemed slower (especially in the Dartford warbler Sylvia undata) than it had been reported at a lower altitude. Three species of European conservation concern (Alauda arvensis, Lullula arborea and Lanius collurio) showed abundance peaks at 10,19 years after fire. This time interval showed the highest species richness, abundance and conservation value, whereas shrub cover continued to increase afterwards. The bird assemblage tended to impoverish with increasing fire severity in the first year after a fire. Our results emphasize: (1) the slow recovery of bird community of burnt mountain shrublands; (2) the need for long-term biodiversity assessments to help improve planning of fire intervals at different altitudes; (3) the relevance of reducing fire severity due to its impact on fauna. [source] | ||||||||||