Frost-free Period Research Articles

Climate and Productivity of Major Conifer Species in the Interior of British Columbia, Canada

Abstract Lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Wats.), interior spruce (including Picea glauca (Moench) Voss, P. engelmannii Parry ex. Engelm., P. glauca×engelmannii), and interior Douglas-fir (Pseudotsuga menziesiivar. glauca (Beissn.) Franco) are the most important commercial species in the interior of British Columbia. We develop statistical models to predict site index (a measure of site productivity) from climate for these species. Using data from 193 climate stations, we first developedmodels that predict mean annual temperature, mean temperature of the warmest and coldest months, number of frost-free days, and frost-free period from latitude, longitude, and elevation. With these models and the Parameter-elevation Regressions on Independent Slopes Model (used to predictmean annual and mean summer precipitation), we predict 10 climate attributes for site index plots of lodgepole pine, interior spruce, and interior Douglas-fir. These attributes are then used in regression models to estimate site index. The models allow us to investigate the current relationshipbetween climate (particularly temperature and precipitation) and site productivity for these species. The productivity for all the species studied increased as temperature increased, with lodgepole pine exhibiting the greatest response. The productivity of lodgepole pine and interior Douglas-firalso increased with increasing precipitation, with interior Douglas-fir having a greater response than lodgepole pine. We discuss the application of the models in relation to the impact of climate change on site productivity. FOR. SCI. 50(5):659–671.

Population variation in growth and 15-year-old shoot elongation along geographic and climatic gradients in black spruce in Alberta

Twenty black spruce (Picea mariana (Mill.) BSP) populations from Alberta were tested at one trial to study the variation of shoot elongation at ages of 15 years, height growth at 10 and 15 years, and breast-height diameter (DBH) at 14 years. Significant difference among populations was found for all of the growth traits and some of the shoot elongation traits investigated. Population means for shoot elongation and cumulative growth traits of significant difference were further regressed against the geographic coordinates and climates of seed origins to study patterns of genetic variation in relation to geography and climate. Both linear and quadratic regressions were investigated, but the one with better fit (lower P and standard error) was chosen and further analyzed. Geographic and climatic gradients explained 20%–62.9% of the population variation in regressions that were statistically significant. Shoot elongation and cumulative growth traits were closely related to frost-free periods, but diverged in their relationships to geographic and all other climatic variables considered. While shoot elongation was associated exclusively with latitude, longitude, day length, and negative temperature variables, growth traits were associated with elevation and positive temperature and moisture variables. Climate factors were more effective than geographic coordinates in describing differentiation in shoot elongation and growth traits. The most effective factors in predicting growth traits were mean annual precipitation and summer moisture index of the seed origin.

ARE REPRODUCTIVE TACTICS DETERMINED BY LOCAL ECOLOGY IN ROMALEA MICROPTERA (ORTHOPTERA: ACRIDIDAE)?

We tested whether reproductive tactics of a univoltine insect can be predicted by local ecology, specifically mean length of the frost free period (FFP) as a measure of the potential active season. We measured reproductive tactics and longevity for populations of the lubber grasshopper Romalea microptera (Beauvois) from Miami, Florida (FL; 365 days FFP), Lydia, Louisiana (LA; 280 days FFP), and Athens, Georgia (GA; 224 days FFP). Differences in local climate led us to predict that GA grasshoppers will have shorter interclutch intervals, fewer clutches, and shorter lifespan than FL grasshoppers, with LA grasshoppers intermediate in these traits. When reared in a common laboratory environment, longevity, total reproductive period, and number of clutches produced were not clearly related to FFP. Longevity and reproductive period of LA grasshoppers were significantly less than those of FL grasshoppers, and number of clutches produced by LA grasshoppers was less than that for the FL or GA grasshoppers. First interclutch interval was significantly greater for LA than for GA grasshoppers. Our data suggest that phylogenetic relationships among populations may be a better predictor of reproductive tactics in this species.

The climate of Atndalen

The climate of Atndalen Valley is described by data collected by the standard network of stations currently run by the Norwegian Meteorological institute. It consists of one weather station (Sorneset) with full instrumental equipment, and three precipitation stations with a reduced set of equipment. At the latter stations, precipitation, snow depth, and snow cover are observed. Most of the stations, including the weather station, are situated in the central part of the watershed, near Atnsjoen. The climate of the Atndalen is of a continental type with precipitation minimum in late winter or spring and maximum during summer. The mean annual precipitation is about 500 mm near Atnsjoen (701 m a.s.l.) for the 30 year normal period 1961–1990. At the meteorological station Sorneset the warmest month is July, 11.2 °C, while the coldest month is January, −9.9 °C, i.e. an annual amplitude of 21.1 °C. The mean cloud cover varies from 4.5 oktas in February to 5.4 oktas in July, September and October. The highest ratio of relative sunshine is about 50% in spring. The mean snow depth increases during winter and early spring and reaches its maximum of 68 cm in March. The snow cover disappears on 9 May ±12 days and establishes on 5 November ±18 days. Variations in precipitation (since 1904) and temperature (since 1864) were studied on a decadal time scale by Gaussian filtering technique, and the significance of trends on the 0.05 level were studied by the Mann–Kendall test. For the whole period no significant trend in annual precipitation was detected. The maximum value was located to the 1920s and the minimum value to the 1910s. Annual mean temperature has increased significantly since 1864, and the classical temperature optimum in the 1930s was surpassed in the 1990s. By adopting a sinus model including the first Fourier component, trends and variations in climatological periods as well as heat and frost sums were studied. The frost free period has since 1864 increased by 13 days within 100 years based on a linear trend line. Earlier passing dates in spring largely account for the increase. The length of the growth season also increased up to about 1950. The annual heat sum shows a linear increase of about 103 daydegrees per 100 years while the annual frost sum varies considerably from period to period and fitted badly with a linear model.

Growth patterns of secondary Nothofagus obliqua– N. alpina forests in southern Chile

The environmental factors that influence the diameter-growth of the Nothofagus obliqua and Nothofagus alpina were investigated in secondary forests in southern Chile. A total of 17 edaphic, topographic and climatic variables were studied. The annual periodic diameter increment (API) in 15 and 20 year-old trees was measured using dendrochronological techniques. A multiple correspondence factorial analysis (MCFA) indicated that longitude, minimum precipitation, summer humidity index, frost-free period, maximum drought period, and percentage of silt and sand in the soil were driving variables influencing diameter-growth. The first three factors accounted for 70% of the total variation. Higher diameter-growth rates were associated with intermediate annual rainfall, a short dry period, and sandy soil. Lower rates were associated with an intermediate frost-free period, a low summer humidity index, a long dry period and silty soil. A spatial pattern of the driving variables was found in the study area. The first two factors showed a longitudinal division separating the sites located in the Central Depression, Coastal Range and Andean Range. Using the results generated by MCFA, an ascendant hierarchic classification analysis (AHCA) was conducted to classify the study area into five sites of homogeneous productivity. The highest diameter-growth (>7.1 mm per year) sites were located in the pre-Andes of Valdivia Province, followed by sites in the northern pre-Andes of Cautin Province and the Andean Range of both provinces. Intermediate growth rates corresponded to the coastal site. The lowest diameter-growth (<5.3 mm per year) was located in the Central Depression in both provinces. The use of multivariate methods and the adequate selection of environmental variables enabled us to identify the diameter-growth driving variables, as well as to classify the study area into five productivity categories.

Methane emission from northern wetlands in Europe during Oxygen Isotope Stage 3

Interstadials during the last glacial show a rapid rise of the atmospheric methane concentration at the onset of climatic warming. This is explained by reaction of (northern) wetlands to climate change, or by catastrophic release of methane from sea floor methane clathrates. The wetland hypothesis usually assumes expansion of wetlands, which is a slow process and difficult to reconcile with the rapid rise of the atmospheric methane concentration. Here it is demonstrated by modeling that wetland methane fluxes may have reacted rapidly on climatic warming by its direct effect on methane production, without the assumption of wetland expansion. A bottom-up modeling of methane fluxes in northern Europe during Oxygen Isotope Stage 3 is presented. This study combines paleodata on wetland ecology, climate model output, a process-based methane flux model, and GIS-based modeling of wetland areal distribution. The resulting methane flux during interstadials is twice as high as during stadials. This is attributed to higher bacterial metabolic rates, a longer frost-free period, and a higher ecosystem primary production providing more substrate for methanogenesis.

Growth patterns of secondary Nothofagus obliqua?N. alpina forests in southern Chile

The environmental factors that influence the diameter-growth of the Nothofagus obliqua and Nothofagus alpina were investigated in secondary forests in southern Chile. A total of 17 edaphic, topographic and climatic variables were studied. The annual periodic diameter increment (API) in 15 and 20 year-old trees was measured using dendrochronological techniques. A multiple correspondence factorial analysis (MCFA) indicated that longitude, minimum precipitation, summer humidity index, frost-free period, maximum drought period, and percentage of silt and sand in the soil were driving variables influencing diameter-growth. The first three factors accounted for 70% of the total variation. Higher diameter-growth rates were associated with intermediate annual rainfall, a short dry period, and sandy soil. Lower rates were associated with an intermediate frost-free period, a low summer humidity index, a long dry period and silty soil. A spatial pattern of the driving variables was found in the study area. The first two factors showed a longitudinal division separating the sites located in the Central Depression, Coastal Range and Andean Range. Using the results generated by MCFA, an ascendant hierarchic classification analysis (AHCA) was conducted to classify the study area into five sites of homogeneous productivity. The highest diameter-growth (>7.1 mm per year) sites were located in the pre-Andes of Valdivia Province, followed by sites in the northern pre-Andes of Cautin Province and the Andean Range of both provinces. Intermediate growth rates corresponded to the coastal site. The lowest diameter-growth (<5.3 mm per year) was located in the Central Depression in both provinces. The use of multivariate methods and the adequate selection of environmental variables enabled us to identify the diameter-growth driving variables, as well as to classify the study area into five productivity categories.

Export of dissolved organic carbon, nitrogen and phosphorus following clear-cutting of three Norway spruce forests growing on drained peatlands in southern Finland

The effect of clear-cutting on the concentrations of dissolved organic carbon (DOC), organic nitrogen (DON), NH4+, NO3–, and P in outflow water from three productive, Norway spruce dominated drained peatlands (RCC, VCC-1, VCC-2) were studied. Changes in runoff and transport loads (concentration x runoff) at two of the catchments during the frost-free period are also presented. Approximately 40% of the area was cut at RCC and VCC-2, and 72% at VCC-1. The volume removed was 250 m3 ha–1 at RCC, 259 m3 ha–1 at VCC-1, and for VCC-2, 317 m3 ha–1. The mean annual increase in outflow concentrations of DOC during the first four years after clear-cutting was 9.0 mg l–1 at RCC, 22.8 mg l–1 at VCC-1 and 8.4 mg l–1 at VCC-2. Corresponding increases in the forms of nitrogen were: 0.23, 0.51 and 0.16 mg DON l–1; 0.06, 0.31 and 0.04 mg NH4+-N l–1; and 0.05, 0.12 and 0.22 mg NO3–-N l–1. Clear-cutting did not significantly (p &gt; 0.05) increase P concentrations. The increase in non-frost season runoff over the first three years after clear-cutting was 107 mm at RCC and 207 mm at VCC-1. The export loads of DOC during the non-frost season increased by 80 kg ha–1 at RCC and by 184 kg ha–1 at VCC-1 over the first three years. Corresponding increases for the other studied solutes were: 1.78 and 3.98 kg DON ha–1; 0.39 and 1.49 kg NH4+-N ha–1; 0.45 and 0.48 kg NO3–-N ha–1, and 0.09 and 0.06 kg P ha–1. The study demonstrated that clear-cutting may significantly increase the export of DOC and different forms of nitrogen from drained productive peatlands while only small increases in phosphorus export may occur.

An examination of short- and long-term air–ground temperature coupling

Data from two experimental air–ground climate stations operating at field and wooded sites in Nova Scotia (Canada), monitoring meteorological and ground thermal variables, were examined along with longer-term records of air and soil temperature in order to clarify the energy exchanges at the air–ground interface. A simple, first-order approximation, multilayer numerical model of heat conduction was used to assess whether soil temperatures track air temperature variations at each location. Data indicate that in winter, when soil freezing occurs, the heat transfer regime between the lower atmosphere and the ground is dominated by latent heat released at field and wooded sites. In spring and summer, the ground thermal response at the field site is driven by direct solar radiation heating rather than by conduction. Results from a numerical model indicate that during a frost-free period of 290 days in spring, summer and fall, the soil thermal regime in the forest can be modelled using surface air temperature data as the driver at the upper boundary and assuming a purely conduction dominated scenario, such that at these short time scales, the forest floor and lower atmosphere appear to be coupled. Longer-term records (∼30 years) from selected climatological stations across Canada indicate that soil–air temperature differences appear to be temporally variable at all locations examined. If this variation is common and persistent, then the coupling between air and ground temperatures may not be as straight forward as previously though at some locations.

Variations of the climatological growing season (1951–2000) in Germany compared with other countries

AbstractWe analyse how variations in the climatological growing season, defined by single‐value thresholds of daily minimum and mean air temperature, mirror recent changes in plant phenological phases. In Germany (1951–2000, 41 climate stations), the dates of last spring frost Tmin &lt; 0 °C (&lt;−3 °C and &lt;−5 °C) advance by 0.24 (0.23 and 0.32) days per year on average, and the first day when the daily mean temperature constantly exceeds 5 °C (7 °C and 10 °C) advances by 0.13 (0.21 and 0.09) days per year. The respective autumn dates are delayed up to 0.25 days per year; in total, the climatological growing season is lengthened by 0.11 to 0.49 days per year, depending on the criterion analysed. However, a certain station‐to‐station variability is displayed. Mean trends of phenological phases correspond well to those measures of the climatological growing season having similar seasonal occurrence. Thus, for example, the extension of the growing seasons of trees (up to 0.22 days per year) averages the lengthening of the period where the daily mean temperature constantly exceeds 5 °C (0.23 days per year). However, the greatest changes result for the lengthening of the frost‐free period (0.49 days per year) due to the observed stronger increase in daily minimum rather than maximum temperatures. Consequently, trees may not take advantage of the frost‐free season as before, but may profit from a reduced risk of damage by late spring frosts.A parallel evaluation of trends in the climatological growing season in other European countries (Austria, Switzerland, Estonia) supports this finding of a stronger lengthening of the frost‐free period than that of the growing season based on daily mean air temperature. The mean lengthening of the frost‐free period of 0.50 days per year in Austria and Switzerland (1951–99, 18 stations &lt;950 m a.s.l.) and 0.34 days per year in Estonia (1951–2000, two stations) is quite similar to that in Germany. The lengthening of the growing season (Tmean≥7 °C) in Austria and Switzerland (0.39 days per year) also approximates the respective result for Germany (0.36 days per year). However, in several cases, the trends increase with altitude (up to 500–900 m a.s.l.), but at high‐elevation climate stations (&gt;950 m a.s.l.) weaker trends are again generally observed. Copyright © 2003 Royal Meteorological Society

Distribution and ecology of meningeal worm, Parelaphostrongylus tenuis (Nematoda), in northcentral North America.

Meningeal worm (Parelaphostrongylus tenuis), a common nematode parasite in white-tailed deer (Odocoileus virginianus) and pathogenic for several species of ungulates in eastern North America, is not known to occur in the west. Heads of 1,902 white-tailed deer were examined for adult meningeal worm to determine geographic distribution of the parasite in Saskatchewan and Manitoba (Canada) and North Dakota (USA). Finding the parasite in a deer in eastern Saskatchewan near the Manitoba border established the current northern and western limits in Canada. Prevalence of infection was < 1, 18.6, and 8.2% in Saskatchewan, Manitoba, and North Dakota, respectively. Infected deer occurred throughout southern Manitoba and eastern North Dakota. Distribution appears to have changed little since the last published survey for P. tenuis in the region in 1972. We examined precipitation, temperature, deer density, and forest cover as likely correlates to prevalence and distribution of P. tenuis. Deer management units used for hunting purposes were the scale of analysis in the three jurisdictions. Presence of P. tenuis was positively correlated with precipitation during frost-free periods and deer density, and it was negatively correlated with winter and spring temperatures. Landscapes with > 25 and < 75% forest cover were most likely to have infected deer. Low rainfall and low density of white-tailed deer likely influence the westernmost limit of P. tenuis.

Mapping Frost Occurrence Using Satellite Data

Abstract Detailed maps of the date of the first and last frost, the length of the frost-free period, and the number of days of frost during spring have been produced for the Otago region of New Zealand. These frost occurrence variables are estimated using a combination of channel-5 (11.5–12.5 μm) infrared brightness temperature data and the normalized difference vegetation index (NDVI) from the Advanced Very High Resolution Radiometer (AVHRR) satellite instrument. It is shown that a generalized linear model with quasi-likelihood estimation is best suited to the estimation of these frost occurrence variables. The maps show that frosts occur earlier in the autumn and later in the spring with increasing distance away from the coast and from major rivers and lakes. Frost is most prevalent on the top of high mountain ranges where the air temperature is coldest and is shown to be more common near the bottom of inland basins as compared with the sides of the surrounding hills because of cold-air drainage and pon...

Use of non-selective herbicides for wheat physiological and harvest maturity acceleration

Double cropping of wheat ( Triticum aestivum L.) and soybean ( Glycine max (L.) Merr.) in the southeast of Buenos Aires Province, Argentina, is risky because of the short frost-free period after wheat harvest and the probability of water deficits during the soybean cropping period. Soybean yield declines rapidly with delays in the sowing date. The objective of this work is to evaluate the potential to anticipate wheat harvest through the application of non-selective herbicides prior to physiological maturity. Two experiments were carried out in Tandil during the 1997 (wet year) and 1998 (dry year) growing seasons. Treatments consisted of herbicide (Glyphosate and Paraquat) applications to two wheat cultivars at different moments prior to physiological maturity. Herbicide applications produced greater grain moisture decreases than in the checks. The contact product exhibited greater drying rates than the systemic one in the water-deficient year. No differences in herbicide effect were observed between cultivars. Grains continued to accumulate dry weight after herbicide applications. In 1997, herbicide applications with grain moisture of 45% produced grain weight decreases close to 9% and a 7 days anticipation in harvest time. In the same year, herbicide applications with grain moisture of 40% decreased grain weight non-significantly and anticipation in harvest time was close to 5 days. In 1998, applications with both 40 and 45% grain moisture, did not significantly decrease grain weight and the anticipation in harvest time was close to 3 days. Considering both years and cultivars, harvest anticipation and grain dry weight decreases due to herbicide applications were better associated with the current rates of grain filling ( r=0.87 and 0.76 for harvest anticipation and grain dry weight decrease, respectively, on the basis of chronological time, and r=0.85 and 0.79, respectively, on the basis of thermal time) than with grain moisture during that time.

Early growth differentiation among Prosopis flexuosa D.C. provenances from the Monte phytogeographic province, Argentina

Early-growth differentiation among seven provenances of Prosopis flexuosa (algarrobo dulce) from the Monte phytogeographic province, Argentina, was studied by comparing their height growth; whole-seedling dry mass gain; allocation to root, stem and leaves; leaf number and leaf area in a common garden. Differentiation among provenances was detected for all the seedling characters examined except leaf number. Family variation within provenances was significant for height growth and leaf number. Variation on the provenance level was related to the elevation, geographic location, and some abiotic conditions of the seed source such as mean annual temperature and frost free period. Latitudinal clines were evident for almost all the growth traits. They were more pronounced for height and aboveground mass, and moderate for total plant mass and leaf area per plant. In addition, a good correspondence in growth traits between young seedlings and older trees of this species (studied by others authors) was also assessed. This fact would permit an early selection and genetic advances in the short term in breeding programs.

Characteristics of Daily and Extreme Temperatures over Canada

Recent studies have shown that, since 1900, mean annual temperature over southern Canada has increased by an average of 0.9°C, with the largest warming during winter and early spring. Every season was associated with greater increases in minimum temperature as opposed to maximum, thus resulting in a significant decrease in the daily temperature range (DTR). The second half of the twentieth century was associated with significant winter and spring warming in the south and west, and cooling in the northeast. However, no significant changes in DTR were observed during this period. This investigation goes beyond the annual/seasonal scales by examining trends and variability in daily minimum and maximum temperature with particular emphasis on extremes. Using recently updated, homogenized daily data, spatial and temporal characteristics of daily and extreme temperature-related variables are analyzed on a seasonal basis for the periods of 1900–98 (southern Canada), and 1950–98 (the entire country). From 1900 to 1998, the majority of southern Canada shows significantly increasing trends to the lower and higher percentiles of the daily minimum and maximum temperature distribution. The findings translate into fewer days with extreme low temperature during winter, spring, and summer and more days with extreme high temperature during winter and spring. No consistent trends are found for the higher percentiles of summer daily maximum temperature, indicating little change to the number of extreme hot summer days. Over the southwest, increases are larger to the left-hand side of the daily minimum and maximum temperature distribution, resulting in significant decreases to the intraseasonal standard deviation of daily temperature. The 1950–98 results are somewhat different from the entire century, especially, during winter and spring. This result includes significant increases to the low and high percentiles over the west, and decreases over the east. This analysis reveals that the largest individual daily temperature trends (both minimum and maximum) occur during winter and early spring, when substantial warming is observed. For summer, increases are only associated with daily minimum temperature. Autumn displays varying results, with some late season cooling, mainly over western regions. The observed warming trends have a substantial effect on several economically sensitive indices. This effect includes significant increases in the number of growing and cooling degree days and significant decreases in heating degree days. In addition, the length of the frost-free period is significantly longer over most of the country.

A Geographic Information System for identification of potential alternative crops utilizing soil and climatic variables in the Bighorn Basin, Wyoming

AbstractThe Bighorn Basin is an important agricultural region in Wyoming. To promote expansion of economic prospects within the Bighorn Basin, we explored the feasibility of introducing alternative crops into the area. Currently, the major crops in this region are sugar beet, barley, alfalfas, and dry beans. Diversification of agricultural cropping systems within the Bighorn Basin is an important step in enhancing the state's economy. This research provides preliminary results for evaluating diversification by determining crops that may potentially be cultivated in the Bighorn Basin region. Four of the 28 alternative crops investigated in this project include amaranth, buckwheat, canola, and faba bean. A Geographic Information System (GIS) was used to combine spatial data identifying areas with unique combinations of characteristics (e.g., soils, frost-free period, temperature, etc.) for introduction of new crops. The GIS was used to compile data layers for different soil and climatic variables. A soils data layer was developed for the study area using a predictive model based on the region's surficial geology, bedrock geology, and elevation. Monthly minimum, mean, and maximum summer temperatures, precipitation, growing degree-days and frost-free season were obtainedfrom weatherstations located in the Bighorn Basin, where 30-year averages have been collected by the National Climate Data Center. Using geostatistics, information obtainedfrom weather stations was utilized to develop continuous data layers for 31 climatic conditions related to the study area. A compilation of growth parameters for 28 alternative crops included various soil and climatic conditions that were used to identify areas with potential to support these new crops. Maps of alternative crop production areas suggested that 8 crops (amaranth, chickpea, onion, quinoa, saffiower, sesame, sorghum, and sunflower) could potentially be cultivated in eastern Bighorn Basin where temperatures are warmer, another 12 crops (broccoli, buckwheat, canola, carrot, cauliflower, crambe, Kentucky bluegrass turf seed, leek, lentil, lettuce, mint, and radish) could be produced in western Bighorn Basin where temperatures are cooler, and 8 additional crops (asparagus, beet, cabbage, cowpea, faba bean, field pea, medic seed, and tall fescue turf seed) may possibly be cultivated throughout the Bighorn Basin study area in suitable soils. The alternative crop production area maps derived from this projectwillbe useful to potential growers, land-use planners, and county and state agencies in the Bighorn Basin seeking information on different agricultural practices and new production systems.

Ecological biogeography of North American mammals: species density and ecological structure in relation to environmental gradients

AbstractAim To evaluate the relationship of climate and physiography to species density and ecological diversity of North American mammals.Location North America, including Mexico and Central America.Methods Species density, size structure and trophic structure of mammalian faunas and nine environmental variables were documented for quadrats covering the entire continent. Spatial autocorrelation of species density and the environmental variables illustrated differences in their spatial structure at the continental scale. We used principal component analysis to reduce the dimensionality of the climatic variables, linear multiple regression to determine which environmental variables best predict species density for the continent and several regions of the continent, and canonical ordination to evaluate how well the environmental variables predict ecological structure of mammalian faunas over North America.Results In the best regression model, five environmental variables, representing seasonal extremes of temperature, annual energy and moisture, and elevation, predicted 88% of the variation in species density for the whole continent. Among different regions of North America, the environmental variables that predicted species density vary.Changes in the size and trophic structure of mammalian faunas accompany changes in species density. Redundancy analysis demonstrated that environmental variables representing winter temperature, frostfree period, potential and actual evapotranspiration, and elevation account for 77% of the variation in ecological structure.Main conclusions The latitudinal gradient in mammalian species density is strong, but most of it is explained by variation in the environmental variables. Each ecological category peaks in species richness under particular environmental conditions. The changes of greatest magnitude involve the smallest size categories (&lt; 10 g, 11–100 g), aerial insectivores and frugivores. Species in these categories, mostly bats, increase along a gradient of decreasing winter temperature and increasing annual moisture and frostfree period, trends correlated with latitude. At the opposite end of this gradient, species in the largest size category (101–1000 kg) increase in frequency. Species in size categories 3 (101–1000 g), 5 (11–100 kg) and 6 (101–1000 kg), herbivores, and granivores increase along a longitudinal gradient of increasing annual potential evapotranspiration and elevation.Much of the spatial pattern is consistent with ecological sorting of species ranges along environmental gradients, but differential rates of speciation and extinction also may have shaped the ecological diversity of extant North American mammals.

Improvements of stochastic weather data generators for diverse climates

Weather data generators can be used to produce long periods of synthetic weather records from a limited amount of input data. They provide a useful tool for supplementing existing climate data for risk assessment and decision support systems. They also can be adapted for use in climate change studies where only limited data are available on a course spatial grid. A number of studies have demon- strated the failure of data produced with stochastic weather data generators to mimic the statistical properties of observed daily climate data. Differences may be large enough to limit the usefulness of the output data. This study suggests that the lack-of-fit is related to simplifying assumptions incorpo- rated in these models which may be acceptable in some climates but lead to significant discrepancies when applied under very different climate conditions. Methods are proposed to address these limita- tions. The challenge related to choosing an appropriate probability distribution for each climate vari- able is addressed by approximating the probability distribution of the data using an observed fre- quency distribution. It is becoming increasingly clear that the correlation between climate variables may differ significantly on a seasonal and regional basis. To account for this, the interrelationship between climate parameters is evaluated for each site once every 2 mo. The way the relationship between the wet or dry status of the day and temperature and solar radiation is accounted for is improved in the model. Observed climate data for 3 selected Canadian climatological stations are used to assess the proposed weather data generator. The results indicate an overall improvement in the cor- respondence between the means, standard deviations, correlations, probability distributions and extreme values of the observed and estimated weather data series when compared with previously reported results. Related parameters such as the length of wet periods, the length of dry periods and the length of frost-free periods are also found to compare favourably with the observed values.

Decomposition of cellulose strips in relation to climate, litterfall nitrogen, phosphorus and C/N ratio in natural boreal forests.

The decomposition of cellulose strips in relation to climatic variables was studied in a wide range of forested sites with minimal anthropogenic influence. The 22 study sites located in four catchments (61°–69°N in Finland) had stands composed of varying proportions of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karst.) and deciduous species (mainly Betula spp.). The cellulose strips were placed both on and buried in the forest floor of upland and peatland sites for two 1-year periods and the weight loss measured. The decomposition data from all plots had the highest correlations with evaporation of canopy intercepted water, actual transpiration and actual evapotranspiration out of the 17 climatic variables studied. These variables (calculated using SOIL-model) incorporate the effects of climate and vegetation. The decomposition in the Scots pine dominated upland plots was additionally well related to the temperature variables of the frost-free period (May–September mean temperature, temperature sum, soil temperature and July mean temperature) and the number of frost days. Some of the correlations between decomposition and climatic variables are among the highest reported for boreal forests (up to r = 0.98, p <0.001). The nutrients of litterfall were also measured. The weight loss of the cellulose strips, the evaporation of canopy intercepted water and the actual transpiration correlated positively to litterfall amounts of N and P. The same parameters correlated negatively to the litterfall C/N ratio. The results emphasize the need to consider vegetation when effects of climatic factors on decomposition are being studied in boreal forests.

Atmospheric research program for studying changing emission patterns after German unification

A dramatic decrease in emission of sulphur dioxide (SO 2, 60%), dust (82%), nitrogen oxide (NO, 30%) and other pollutants (hydrochloric acid (HCl); ammonia (NH 3)) has been observed in East Germany after German unification in 1989. The smaller decrease in total NO is due to significant increase of NO from traffic. Air-pollutant concentrations in both parts of Germany before and after 1989 will be compared and their development will be discussed, based on precipitation and cloud chemistry data from long-term continuous record. Sectoral rain data, based on backward trajectory calculations, clearly show that the significant decline in annual volume weighted precipitation ions (sulphate, calcium, ammonium, chloride) in rain water from sector “East” since 1989 and particularly since about 1992 is roughly correlated with a similar percentage decline in SO 2, dust and NH 3 emissions for the region East Germany. The acidity of the precipitation from sector “East” has increased very strikingly from 1993 up to 1995 threefold more than from sector “West”. Despite the strong decrease in SO 2 emission, this decrease of the atmospheric neutralising capacity was caused by the much steeper decline in atmospheric base cations in that region. Precipitation data from all transport directions show high variation, but no significant trend in the annual average H + ion concentration. At Mt. Brocken the annual average volume weighted cloud-water acidity during frost-free periods increased by a factor of three between 1992 and 1995. This result, confirmed also by the annual frequency distributions of the pH values, reflects the atmospheric pollutant loading also from all entry sectors. After 1995 this trend is reversed. Detailed classification of the cloud-water data by entry sector, and by meteorological and especially microphysical factors is currently being carried out and preliminary results are presented.