Spatial and temporal variations in boreal forest fire frequency in northern Alberta

Abstract. Spatial and temporal variations in fire frequency in the boreal forest of Wood Buffalo National Park (WBNP) were assessed using forest stand age, fire scar and historical data. I test the hypotheses that (1) fire frequency is higher in jack pine forests and aspen forests than in black spruce forests and white spruce forests, (2) these variations in fire frequency can be related to the mean waterbreak distance (MWD) around a site and (3) fire frequency has changed over the past 300 years. The fire cycles (the time required to burn an area equal in size to the entire study area) in jack pine forests (39 years) and in aspen forests (39 years) were significantly shorter than those in black spruce forests (78 years) and in white spruce forests (96 years). The length of the fire cycle varies inversely with the MWD around a site, and the MWD was significantly higher in jack pine and aspen forests than in black or white spruce forests. It is suggested that covariations between soil type and the MWD influence, respectively, variations in forest dominant and fire frequency. A change in fire frequency at 1860 was apparent in the fire history for all of WBNP, the black spruce dominated stands, and the near and medium MWD classes. The fire cycle estimates for these classes were all significantly shorter during the period 1750 to 1859 (fire cycles = 25–49 years) than they were in the period 1860 to 1989 (fire cycles = 59–89 years). The possible roles of changes in climate and aboriginal burning practices in causing the temporal change in fire frequency are discussed.     

Late Glacial and Holocene environmental and climatic changes from a limnological transect through Colombia, northern South America

We present a synthesis of the palaeolimnological and palaeoclimatic reconstructions of four sites in Colombia. The record from Lake El Caimito, the westernmost site on the Pacific Coast, dates from the Late Holocene and shows lacustrine sedimentation frequently interrupted by fluvial pulses. These pulses probably reflect periods of increased precipitation related to La Niña phases. East of El Caimito site is the Patía swamp, situated between the Western and Central Andean Cordilleras. The Patía records the dynamics of forest expansion/reduction and changes in water levels. Although the climatic signal of the Patia core is difficult to reconstruct, there is a clear increase in humidity in the Mid-Holocene. The Fúquene Lake record, on the Eastern Andean Cordillera, records dry and cold conditions during the Late Pleistocene, very humid conditions for the early Mid-Holocene, and dry conditions during the mid-Late Holocene. Las Margaritas site, on the eastern savannas, records dry conditions during the Early Holocene and overall humid conditions for the Mid- and Late Holocene. Climate conditions from the Fuquene and Las Margaritas sites seem to reflect the Holocene movements of the Intertropical Convergence Zone (ITCZ); the latter site being more affected by humidity coming from the Amazon region.     

Interactions between rainfall, deforestation and fires during recent years in the Brazilian Amazonia

Understanding the interplay between climate and land-use dynamics is a fundamental concern for assessing the vulnerability of Amazonia to climate change. In this study, we analyse satellite-derived monthly and annual time series of rainfall, fires and deforestation to explicitly quantify the seasonal patterns and relationships between these three variables, with a particular focus on the Amazonian drought of 2005. Our results demonstrate a marked seasonality with one peak per year for all variables analysed, except deforestation. For the annual cycle, we found correlations above 90% with a time lag between variables. Deforestation and fires reach the highest values three and six months, respectively, after the peak of the rainy season. The cumulative number of hot pixels was linearly related to the size of the area deforested annually from 1998 to 2004 (r2=0.84, p=0.004). During the 2005 drought, the number of hot pixels increased 43% in relation to the expected value for a similar deforested area (approx. 19000km2). We demonstrated that anthropogenic forcing, such as land-use change, is decisive in determining the seasonality and annual patterns of fire occurrence. Moreover, droughts can significantly increase the number of fires in the region even with decreased deforestation rates. We may expect that the ongoing deforestation, currently based on slash and burn procedures, and the use of fires for land management in Amazonia will intensify the impact of droughts associated with natural climate variability or human-induced climate change and, therefore, a large area of forest edge will be under increased risk of fires.     

Above ground woody community attributes, biomass and carbon stocks along a rainfall gradient in the savannas of the central lowveld, South Africa

Enumeration of carbon stocks at benchmark sites is a necessary activity in assessing the potential carbon sequestration and possible generation of credits through restoration of intensively impacted sites. However, there is a lack of empirical studies throughout much of the savannas of sub-Saharan Africa, including South Africa. We report an estimation of species specific and site biomass and carbon stocks, and general vegetation structural attributes from three protected areas along a rainfall gradient in the central lowveld, South Africa. Estimates of biomass and carbon stocks were effected through destructive sampling to establish locally derived allometric equations. There was a gradient of increasing woody density, height of the canopy, number of species, density of regenerative stems and a greater proportion of stems in small size classes from the arid locality to the mesic locality, with the semi-arid locality being intermediate. The proportion of spinescent species decreased with increasing rainfall. The mesic locality was significantly more woody than either the arid or semi-arid sites, having double the biomass, four times the density and 40% higher basal area. Above ground carbon pools were also higher; carbon stocks were approximately 9 t/ha for the arid and semi-arid sites and 18 t/ha for the mesic site.     

Annual and inter-annual variability of the present climate in northern South America and southern Mesoamerica

Present climate of northwestern South America and the southern Isthmus is detailed in terms of major hydro-climatic controls, supported by evidence from station records, reanalysis data and satellite information. In this tropical region, precipitation is the principal hydro-climatological variable to display great variability. The primary objective is to view the controls that operate at intra-seasonal to inter-decadal time scales. This is a topographical complex region whose climate influences range in provenance from the South Atlantic to the Canadian Prairies, and from the North Atlantic to the Eastern Pacific. The situation is further complicated by interactions and feedbacks, in time and space, between these influences, which are interconnected over various scales. The greatest single control on the annual cycle is the meridional migration of the Inter-tropical Convergence Zone and its pattern of associated trade winds. Consideration of these alone and their interaction with the Cordilleras of the Andes and Central America produce a variety of unimodal and bimodal regimes. Regionally, two low level jet streams, the westerly Choco jet (5°N) and the easterly San Andrés jet (12-14°N), and their seasonal variability, have tremendous significance, as do mesoscale convective storms and mid-latitude cold fronts from both the northern (“nortes”) and southern (“friagems”) hemispheres. There are many examples of hydro-climatological feedbacks within the region. Of these the most notable is the interaction between evaporation over the Amazon, precipitation onto the eastern Andes and streamflow from the headwaters of the Amazon. This is further compounded by the high percentages of recycled precipitation over large areas of the tropics and the potential impacts of anthropogenic modification of the land surface. The El Niño-Southern Oscillation phenomenon (ENSO) is the greatest single cause of interannual variability within the region, yet its effects are not universal in their timing, sign or magnitude. A set of regional physical connections to ENSO are established and their varying local manifestations are viewed in the context of the dominant precipitation generating mechanisms and feedbacks at that location. In addition, some potential impacts of longer run variations within the ocean-atmosphere system of the Atlantic are examined independently and in conjunction with ENSO. This review of the climatic controls and feedbacks in the region provides a spatial and temporal framework within which the highly complex set of factors and their interactions may be interpreted from the past.     

Assessing the response of area burned to changing climate in western boreal North America using a Multivariate Adaptive Regression Splines (MARS) approach

Fire is a common disturbance in the North American boreal forest that influences ecosystem structure and function. The temporal and spatial dynamics of fire are likely to be altered as climate continues to change. In this study, we ask the question: how will area burned in boreal North America by wildfire respond to future changes in climate? To evaluate this question, we developed temporally and spatially explicit relationships between air temperature and fuel moisture codes derived from the Canadian Fire Weather Index System to estimate annual area burned at 2.5° (latitude × longitude) resolution using a Multivariate Adaptive Regression Spline (MARS) approach across Alaska and Canada. Burned area was substantially more predictable in the western portion of boreal North America than in eastern Canada. Burned area was also not very predictable in areas of substantial topographic relief and in areas along the transition between boreal forest and tundra. At the scale of Alaska and western Canada, the empirical fire models explain on the order of 82% of the variation in annual area burned for the period 1960–2002. July temperature was the most frequently occurring predictor across all models, but the fuel moisture codes for the months June through August (as a group) entered the models as the most important predictors of annual area burned. To predict changes in the temporal and spatial dynamics of fire under future climate, the empirical fire models used output from the Canadian Climate Center CGCM2 global climate model to predict annual area burned through the year 2100 across Alaska and western Canada. Relative to 1991–2000, the results suggest that average area burned per decade will double by 2041–2050 and will increase on the order of 3.5–5.5 times by the last decade of the 21st century. To improve the ability to better predict wildfire across Alaska and Canada, future research should focus on incorporating additional effects of long‐term and successional vegetation changes on area burned to account more fully for interactions among fire, climate, and vegetation dynamics.     

Diversity and occurrence of herbaceous communities in West African savannas in relation to climate,land use and habitat

In the face of the current changes in land use and climate as well as habitat destruction, it is important to study herbaceous vegetation as an indicator of changes occurring in savanna ecosystems. We investigated the effects of climate, land use and habitat, both alone and in combination, on the diversity and occurrence of West African savanna herbaceous plant communities. Floristic data and environmental variables were sampled in Burkina Faso and subjected to ordination and indicator species analysis to explore the variation in nine vegetation types. Regression analyses showed that climate, land use, humidity gradient, soil fraction and vegetation structure discriminate herbaceous plant communities. Climate, habitat and their interaction had the greatest effect on the occurrence of these communities. Changes in species richness of the studied communities were mainly due to climate, land use and their interaction, which were more important for increasing rather than decreasing diversity. In all cases, climate conditions remained the most important environmental factor driving vegetation variation in West African savannas. Beside this, the effects of habitat degradation in interaction with land use and climatic conditions indicate land use to be a threat for the diversity of the herbaceous vegetation.     

Spatial and temporal variability in the net primary production of grassland in China and its relation to climate factors

As an important component of the terrestrial carbon (C) cycle, variability in net primary productivity (NPP) plays a crucial role in the C input and accumulation in grasslands system. In this study, the spatial and temporal variability of grassland NPP in China during 2001–2010 and its relation to climate factors were analyzed by using a modified model of Carnegie–Ames–Stanford Approach based on the Comprehensive and Sequential Classification System. The results show that monthly grassland NPP increases from January to July. While the seasonal variability of NPP indicates peak productivity in summer. Annual mean grassland NPP follows a significant increasing trend with fluctuation from 2001 to 2010. The spatial pattern of grassland NPP shows increasing gradients from the west to the east and from the north to the south of China. Annual NPP differs significantly among different grassland types, with the highest NPP in the grassland distributed in sub-tropical perhumid evergreen broad leaved forest and tropical-perhumid rain forest. Time-lag correlation analysis at the monthly scale shows that grassland NPP responded more rapidly to changes in temperature than to precipitation. Among the climate factors, grassland NPP shows the strongest correlation at 1-month lag with moisture index K. There is a significant positive correlation between seasonal NPP and K. The seasonal NPP is significantly correlated with >0 °C annual cumulative temperature. The highest and the lowest NPP sensitivity to precipitation, K, and temperature were observed in the grassland distributed in tropical forest and semi-desert. The results indicate a complex mechanism of climate factors that control grassland C sequestration in terrestrial ecosystems.     

Rainforest understory beetles of the Neotropics, Mizotrechus Bates 1872, a generic synopsis with descriptions of new species from Central America and northern South America (Coleoptera, Carabidae, Perigonini)

Information on the single previously described species, Mizotrechus novemstriatus Bates 1872 (type locality: Brazil - Amazonas, Tefé), is updated and 17 new species for the genus from Nicaragua, Costa Rica, Panamá, Colombia, Venezuela, and Guyane are described. The species records in the literature and on determined specimens in some collections of Mizotrechus novemstriatus Bates from Central America are not that species; currently, Mizotrechus novemstriatus is known only from its type locality in Amazonian Brazil. For the new species described, their known general distributions are as follows: Mizotrechus batesisp. n. (Guyane), Mizotrechus bellorumsp. n. (Guyane), Mizotrechus bruleisp. n. (Guyane), Mizotrechus belevederesp. n. (Guyane), Mizotrechus costaricensissp. n. (Costa Rica), Mizotrechus dalensisp. n. (Guyane), Mizotrechus edithpiafaesp. n. (provenance unknown), Mizotrechus fortunensissp. n. (Panamá), Mizotrechus gorgona. sp. n. (Colombia), Mizotrechus grossussp. n. (Guyane), Mizotrechus jefesp. n. (Panamá), Mizotrechus marielaforetaesp. n. (Guyane), Mizotrechus minutussp. n. (Guyane), Mizotrechus neblinensissp. n. (Guyane, Venezuela), Mizotrechus poirierisp. n. (Guyane), and Mizotrechus woldaisp. n. (Panamá). Long-term use of flight intercept traps in Guyane provided so many new species that apparently the use of FITs is the way to collect adults of this taxon, previously known from very few specimens. Many more species of this genus can be expected to be discovered throughout the Neotropics; the present contribution is a preliminary synopsis with identification key and adult images of all known species. Likely numerous species are yet to be discovered throughout tropical climes.     

Spatial and temporal patterns of carbon storage from 1992 to 2002 in forest ecosystems in Guangdong, Southern China

Aims

The overall goal of this study was to examine the spatial and temporal patterns of C storage from 1992 to 2002 in forest ecosystems in Guangdong, China.

Methods

We used 2237, 2103, and 1978 plot data from three continuous forest inventory in 1992, 1997, and 2002, respectively, four TM images and one soil survey data in Guangdong to examine the spatial and temporal patterns of C storage in forest ecosystems during 1992–2002. The uncertainty analysis of forest C storage in Guangdong in 1992 and 2002 was also conducted to provide the range of estimations.

Results

The forest coverage percent in Guangdong increased from 37.1 % in 1992 to 57.2 % in 2002 while the total forest C storage in Guangdong increased from 144.73?±?6.20 Tg in 1992 to 215.03?±?8.48 Tg in 2002. The order of average forest biomass C storage increase during 1992–2002 among the four regions is Western Guangdong (GW)?>?Eastern Guangdong (GE)?>?the Pearl River Delta (PRE)?>?Northern Guangdong (GN). The factors including tree species and altitude and slope aspect can explain 58–67 % variation of Veg C storage multiple regression model in Guangdong. However, the multiple regression model for SOC storage can only explain about 18–39 % variation of SOC storage in Guangdong. Total ecosystem C is mainly determined by SOC storage.

Conclusions

The total forest C storage in Guangdong increased about 49 % from 1992 to 2002 partially due to the increasing forest coverage percent over the period. The spatial distribution of forest C storage in Guangdong was uneven and this pattern reflects differences in forest management and economic and social development. Future forest management should focus on the selection of tree species, management of forest stand structures and implementation of sustainable practices so that Veg C sequestration potentials can be maximized.     

Spatial and temporal variability of the phenological seasons in Germany from 1951 to 1996

Various indications for shifts in plant and animal phenology resulting from climate change have been observed in Europe. This analysis of phenological seasons in Germany of more than four decades (1951–96) has several major advantages: (i) a wide and dense geographical coverage of data from the phenological network of the German Weather Service, (ii) the 16 phenophases analysed cover the whole annual cycle and, moreover, give a direct estimate of the length of the growing season for four deciduous tree species. After intensive data quality checks, two different methods – linear trend analyses and comparison of averages of subintervals – were applied in order to determine shifts in phenological seasons in the last 46 years. Results from both methods were similar and reveal a strong seasonal variation. There are clear advances in the key indicators of earliest and early spring (?0.18 to ?0.23 d y^?1) and notable advances in the succeeding spring phenophases such as leaf unfolding of deciduous trees (?0.16 to ?0.08 d y^?1). However, phenological changes are less strong during autumn (delayed by + 0.03 to + 0.10 d y^?1 on average). In general, the growing season has been lengthened by up to ?0.2 d y^?1 (mean linear trends) and the mean 1974–96 growing season was up to 5 days longer than in the 1951–73 period. The spatial variability of trends was analysed by statistical means and shown in maps, but these did not reveal any substantial regional differences. Although there is a high spatial variability, trends of phenological phases at single locations are mirrored by subsequent phases, but they are not necessarily identical. Results for changes in the biosphere with such a high resolution with respect to time and space can rarely be obtained by other methods such as analyses of satellite data.     

Spatial and temporal variability in the structure of a tropical forest

This study examines spatial and temporal variation in the forest structure of the Kibale National Park, Uganda by contrasting tree density, tree size, and forest composition among four areas each separated by less than 15 km, and by quantifying changes in the composition of one of these forests over a 20‐year period. Densities of some tree species differed markedly between sites, and some species common at one location were absent at others. Monthly phenological monitoring demonstrated that it was not uncommon for phenological patterns to differ between the forests. To examine temporal variation in the tree composition over a 20‐year period, a sampling regime that was carried out in the early 1970s was replicated on the floristic composition of one of these sites, using identical methods in the same sampling areas. While no form of human intervention occurred in this area between the early 1970s and 1992, there were marked changes in the densities of some tree species. Twenty‐seven percent of the identified species increased in abundance, 33% decreased, and 40% remained relatively unchanged. The observed spatial and temporal variation in forest composition could be the result of abiotic factors, such as altitude or rainfall, or biotic factors such as elephant and/or human influences on ecosystem dynamics; the implications of this variation for frugivores are discussed.     

Spatial and temporal variability of antibiotic resistance in freshwater bacterial assemblages

Abstract Spatial and temporal variability in antibiotic resistance was examined in bacterial assemblages from streams and ponds on the US Department of Energy's Savannah River Site (SRS) in South Carolina. Sites sampled have been impacted to varying degrees by contamination with organic compounds, heavy metals, and radioactive materials because of production of nuclear materials on the site. Antibiotic resistance in the culturable portion of the bacterial assemblage was determined from coloby formation on media containing antibiotics. Eight antibiotics, chloramphenicol, cycloserine, kanamycin, neomycin, novobiocin, rifampicin, streptomycin, and tetracycline, were used at concentrations of 50 and 200 μg ml⁻¹. Statistically significant differences in frequency of antibiotic resistance were observed among sites and among dates at a single site. Bacterial densities (total and culturable), dissolved organic carbon (DOC) concentration, and human impact also varied among sites but bore no overall relationship to resistance frequency. SRS operations did not have a detectable impact on antibiotic resistance.     

Spatial and temporal variability of internal and external phosphorus loads in Mona Lake,Michigan

A study was conducted in Mona Lake, a small eutrophic lake located in western Michigan (USA) to address the temporal and spatial variability of external and internal phosphorus loading. External P load varied among subbasins, which was mostly related to discharge, but also to land use. Black Creek, which drains lands with natural cover and agriculture, accounted for the majority of flow, and total phosphorus (TP) and soluble reactive phosphorus (SRP) load, to Mona Lake. However, the relative contribution of SRP load was greater in Little Black Creek, which flows through a mostly urbanized subbasin, than in Black Creek. The relative importance of internal loading was strongly related to season, as internal TP loads contributed only ∼9% of the overall P load in April 2005, but ∼68–82% of the overall P load in the summer and early fall seasons. Internal TP and SRP loading was greater under anaerobic than aerobic conditions. Mean anaerobic TP release rates ranged from 0.80 to 15.56 mg P m⁻² d⁻¹, varying with site and season. Spatial variability in both internal phosphorus loading and sediment P concentration was also evident. By taking into account the spatial and temporal variability of different loading sources, management practices can be targeted to optimize nutrient source control strategies.     

Spatial variability and major controlling factors of CO2 sink strength in Asian terrestrial ecosystems: evidence from eddy covariance data

Asian terrestrial ecosystems cover an extensive area characterized by a large variety in climates and ecosystem properties. The observations of ecosystem CO₂ flux in this area are increasing both in duration and spatial density, but no synthesis has yet been conducted. We surveyed CO₂ flux observation data obtained by eddy covariance methods at 49 sites in terrestrial Asia. The measurements at most sites (44 of 49) began after 2000. The net ecosystem uptake of CO₂ (NEE) varied greatly among sites and years and averaged −132.6±73.7, −250.1±206.1, and −180.1±361.7 g C m⁻² yr⁻¹, in boreal, temperate, and tropical Asia, respectively, and the coefficient of variation among sites increased from boreal to tropical Asia. The site-averaged annual NEE was correlated linearly with the mean annual temperature (T_air) and also correlated logarithmically with the precipitation. Multiple regression analysis and stepwise analysis indicated that photosynthetic active radiation (PAR) and T_air were the most significant predictors of the annual NEE. The study results suggest that Asian terrestrial ecosystems are currently significant net CO₂ sinks and that the sink strength is largely controlled by temperature, moisture, and light conditions.     

Spatial distribution and temporal variability of some aquatic insects in the Franco-Geneva River,Allondon

The Allodon River, a tributary of the Rhône, has suffered considerably from the recent expansion of human activities in the Geneva region. This study documents changes in its benthic fauna by comparing species richness before and after 1986 and by considering the possibilities of recolonization by drift.

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Résumé L'Allondon, affluent du Rhône, est une rivière qui a considérablemen t souffert d'une expansion récente des activités humaines dans la région genevoise. Cette étude met en lumière l'évolution de certains éléments de la faune benthique en comparant les richesses specifiques avant et après 1986, année critique pour la macrofaune benthique du bassin genevois. Elle met en évidence les possibilités de recolonisation par dérive de certains recours de l'Allondon à partir d'affluents moins perturbés.

     

Spatial and temporal dynamics of diffusive methane emissions in the Okavango Delta,northern Botswana,Africa

Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH₄) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH₄ in the world contributing between 100 and 231 Tg year^?1 to the total budget of 503–610 Tg year^?1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH₄ emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH₄ emission rates varied between 0.24 and 293 mg CH₄ m^?2 h^?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH₄ m^?2 h^?1 or 558 ± 53 mg CH₄ m^?2 day^?1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher (P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH₄ m^?2 h^?1 than in floodplains (20.4 ± 2.5 mg CH₄ m^?2 h^?1) and lagoons (16.9 ± 2.6 mg CH₄ m^?2 h^?1). Diffusive CH₄ emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH₄ m^?2 h^?1) and lowest (0.2–3.0 mg m^?2 h^?1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km², the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH₄ emission from global tropical wetlands.