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991.
N. Kljun T. A. Black T. J. Griffis A. G. Barr D. Gaumont-Guay K. Morgenstern J. H. McCaughey Z. Nesic 《Ecosystems》2006,9(7):1128-1144
In 2001–03, continuous eddy covariance measurements of carbon dioxide (CO2) flux were made above mature boreal aspen, black spruce, and jack pine forests in Saskatchewan, Canada, prior to and during
a 3−year drought. During the 1st drought year, ecosystem respiration (R) was reduced at the aspen site due to the drying of surface soil layers. Gross ecosystem photosynthesis (GEP) increased as
a result of a warm spring and a slow decrease of deep soil moisture. These conditions resulted in the highest annual net ecosystem
productivity (NEP) in the 9 years of flux measurements at this site. During 2002 and 2003, a reduction of 6% and 34% in NEP,
respectively, compared to 2000 was observed as the result of reductions in both R and GEP, indicating a conservative response to the drought. Although the drought affected most of western Canada, there was
considerable spatial variability in summer rainfall over the 100−km extent of the study area; summer rainfalls in 2001 and
2002 at the two conifer sites minimized the impact of the drought. In 2003, however, precipitation was similarly low at all
three sites. Due to low topographic position and consequent poor drainage at the black spruce site and the coarse soil with
low water-holding capacity at the jack pine site almost no reduction in R, GEP, and NEP was observed at these two sites. This study shows that the impact of drought on carbon sequestration by boreal
forest ecosystems strongly depends on rainfall distribution, soil characteristics, topography, and the presence of vegetation
that is well adapted to these conditions. 相似文献
992.
Wildfire is the major natural agent of disturbance in interior Alaska. We examined the magnitude of human impact on fire by
comparing fire regime between individual 1-km2 grid cells designated for fire suppression with lands where fires are allowed to burn naturally. Two-thirds of interior Alaska
has an essentially natural fire regime, with few human ignitions, negligible suppression activity, and many large lightning-caused
fires. In the 17% of land that is designated for fire suppression due to its proximity to communities and roads, there was
a 50% reduction in the proportion of area burned from 1992–2001, relative to areas without suppression. The remaining 16%
of land serves as a buffer, receives some suppression, and has an intermediate fire regime. Even though there were 50 times
more fires and the fire season began two months earlier in lands designated for suppression, most of these fires were lit
by people and remained small because fires tended to occur at times and places less favorable for fire spread and were more
accessible to fire fighters compared to lands not designated for suppression. Even in the absence of fire suppression, human-caused
fires were less likely to exceed 400 ha compared to lightning-caused fires. Fire suppression reduced area burned in all fuel
types but was somewhat more effective in less flammable (non-forest) vegetation. Alaska’s fire policy of focusing suppression
efforts on a small proportion of the fire-prone region maximizes the ecological and social benefits associated with fire-dependent
ecosystem services, while minimizing the social and ecological costs of suppression. Application of this policy to other areas
would require well-informed managers and stakeholders to make difficult decisions about the relative costs and benefits of
fire across ecologically and culturally variable landscapes. 相似文献
993.
Aim We explored the relative contributions of climatic and land-cover factors in explaining the distribution patterns of butterflies in a boreal region.
Location Finland, northern Europe.
Methods Data from a national butterfly atlas survey carried out during 1991–2003, with a 10-km grain grid system, were used in these analyses. We used generalized additive models (GAM) and hierarchical partitioning (HP) to explore the main environmental correlates (climate and land-cover) of the realized niches of 98 butterfly species. The accuracy of the distribution models (GAMs) was validated by resubstitution and cross-validation approaches, using the area under the curve (AUC) derived from the receiver operating characteristic (ROC) plots.
Results Predictive accuracies of the 98 individual environment–butterfly models varied from low to very high (cross-validated AUC values 0.48–0.99), with a mean of 0.79. The results of both the GAM and HP analyses were broadly concordant. Most of the variation in butterfly distributions is associated with growing degree-days, mean temperature of the coldest month and cover of built-up area in all six phylogenetic groups (butterfly families). There were no statistically significant differences in predictive accuracy among the different butterfly families.
Main conclusions About three-quarters of the distributions of butterfly species in Finland appear to be governed principally by climatic, predominantly temperature-related, factors. This indicates that many butterfly species may respond rapidly to the projected climate change in boreal regions. By determining the ecological niches of multiple species, we can project their range shifts in response to changes in climate and land-cover, and identify species that are particularly sensitive to forecasted global changes. 相似文献
Location Finland, northern Europe.
Methods Data from a national butterfly atlas survey carried out during 1991–2003, with a 10-km grain grid system, were used in these analyses. We used generalized additive models (GAM) and hierarchical partitioning (HP) to explore the main environmental correlates (climate and land-cover) of the realized niches of 98 butterfly species. The accuracy of the distribution models (GAMs) was validated by resubstitution and cross-validation approaches, using the area under the curve (AUC) derived from the receiver operating characteristic (ROC) plots.
Results Predictive accuracies of the 98 individual environment–butterfly models varied from low to very high (cross-validated AUC values 0.48–0.99), with a mean of 0.79. The results of both the GAM and HP analyses were broadly concordant. Most of the variation in butterfly distributions is associated with growing degree-days, mean temperature of the coldest month and cover of built-up area in all six phylogenetic groups (butterfly families). There were no statistically significant differences in predictive accuracy among the different butterfly families.
Main conclusions About three-quarters of the distributions of butterfly species in Finland appear to be governed principally by climatic, predominantly temperature-related, factors. This indicates that many butterfly species may respond rapidly to the projected climate change in boreal regions. By determining the ecological niches of multiple species, we can project their range shifts in response to changes in climate and land-cover, and identify species that are particularly sensitive to forecasted global changes. 相似文献
994.
P. Rosenkranz N. Brüggemann H. Papen Z. Xu L. Horváth K. Butterbach-Bahl 《Plant and Soil》2006,286(1-2):301-322
During two intensive field campaigns in summer and autumn 2004 nitrogen (N2O, NO/NO2) and carbon (CO2, CH4) trace gas exchange between soil and the atmosphere was measured in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N2O emission rates were 1.5 μg N m−2 h−1 in summer and 3.4 μg N m−2 h−1 in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m−2 h−1) as compared to summer (6.0 μg N m−2 h−1). However, as NO2 deposition rates continuously exceeded NO emission rates (−9.7 μg N m−2 h−1 in summer and −18.3 μg N m−2 h−1 in autumn), the forest soil always acted as a net NO
x
sink. The mean value of CO2 fluxes showed only little seasonal differences between summer (81.1 mg C m−2 h−1) and autumn (74.2 mg C m−2 h−1) measurements, likewise CH4uptake (summer: −52.6 μg C m−2 h−1; autumn: −56.5 μg C m−2 h−1). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N2O/CH4 soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO2 resp ΔO2 resp−1) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg−1 SDW d−1) and autumn measurements (0.89 μg N kg−1 SDW d−1). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg−1 SDW d−1) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg−1 SDW d−1). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N2O emissions and negatively correlated with CH4 uptake, whereas soil CO2 emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn. 相似文献
995.
996.
Leaf morphology, longevity, and demography were examined in Quercus ilex and Phillyrea latifolia growing in a holm oak forest in Prades mountains (northeast Spain). Four plots (10 × 15 m) of this forest were submitted
to an experimental drought during three years (soil moisture was reduced about 15 %). Leaf area, thickness and leaf mass per
area ratio (LMA) were measured in sun and shade leaves of both species. Leaf longevity, the mean number of current-year shoots
produced per previous-year shoot (Sn/Sn-1), the mean number of current-year leaves per previous-year shoot (Ln/Sn-1), and
the percentage of previous-year shoots that developed new ones were measured once a year, just after leaf flushing. LMA and
leaf thickness increased since leaf unfolding except in summer periods, when stomatal closure imposed low photosynthetic rates
and leaves consumed their reserves. LMA, leaf area, and leaf thickness were higher in Q. ilex than in P. latifolia, but leaf density was higher in the latter species. Drought reduced the leaf thickness and the LMA of both species ca. 2.5 %. Drought also increased leaf shedding up to ca. 20 % in Phillyrea latifolia and decreased it up to ca. 20 % in Q. ilex. In the later species, Sn/Sn-1 decreased by 32 %, Ln/Sn-1 by 41 %, percentage of shoots developed new ones by 26 %, and leaf
area by 17 %. Thus the decrease of leaf number and area was stronger in the less drought-resistant Q. ilex, which, under increasingly drier conditions, might lose its current competitive advantage in these Mediterranean holm oak
forests. 相似文献
997.
Recent speciation research has generally focused on how lineages that originate in allopatry evolve intrinsic reproductive isolation, or how ecological divergence promotes nonallopatric speciation. However, the ecological basis of allopatric isolation, which underlies the most common geographic mode of speciation, remains poorly understood and largely unstudied. Here, we explore the ecological and evolutionary factors that promote speciation in Desmognathus and Plethodon salamanders from temperate eastern North America. Based on published molecular phylogenetic estimates and the degree of geographic range overlap among extant species, we find strong evidence for a role for geographic isolation in speciation. We then examine the relationship between climatic variation and speciation in 16 sister-taxon pairs using geographic information system maps of climatic variables, new methods for modeling species' potential geographic distributions, and data on geographic patterns of genetic variation. In contrast to recent studies in tropical montane regions, we found no evidence for parapatric speciation along climatic gradients. Instead, many montane sister taxa in the Appalachian Highlands inhabit similar climatic niches and seemingly are allopatric because they are unable to tolerate the climatic conditions in the intervening lowlands. This temporal and spatial-ecological pattern suggests that niche conservatism, rather than niche divergence, plays the primary role in promoting allopatric speciation and montane endemism in this species-rich group of vertebrates. Our results demonstrate that even the relatively subtle climatic differences between montane and lowland habitats in eastern North America may play a key role in the origin of new species. 相似文献
998.
Wesley W. Boone Christopher E. Moorman David J. Moscicki Bret A. Collier Michael J. Chamberlain Adam J. Terando Krishna Pacifici 《The Journal of wildlife management》2024,88(2):e22524
Temperature and precipitation have been identified as factors that potentially influence eastern wild turkey (Meleagris gallopavo silvestris) reproduction, but robust analyses testing the relationship between weather parameters and turkey nest success are lacking. Therefore, we assessed how weather influenced turkey daily nest survival using 8 years of data collected from 715 nests across the southeastern United States. We also conducted exploratory analyses investigating if weather conditions during or prior to nesting best predicted nest success. We then assessed the possible implications of climate change through 2041–2060 for future eastern wild turkey daily nest survival and nest success for variables determined significant in analyses. During incubation, positive anomalies of minimum daily temperature were associated with greater daily nest survival. Precipitation during nesting was not a good predictor of daily nest survival. Exploratory analyses unexpectedly indicated that weather conditions in January prior to incubation were more important to nest success than weather conditions during incubation. In January, negative anomalies of minimum temperature and greater average daily precipitation were associated with greater nest success. Projections of future nest success or daily nest survival based on these relationships with the predictive covariates, and informed by climate models, suggest that nest success may increase as January precipitation increases and that daily nest survival may increase as temperature during incubation increases. These positive associations could be offset by a negative association between nest success and the expected increases in January minimum average temperature. Additional research is needed to investigate causes of these relationships and assess the implications of climate change for eastern wild turkey poult survival. 相似文献
999.
Spatial patterns in brown bear Ursus arctos diet: the role of geographical and environmental factors
- 1 We reviewed worldwide spatial patterns in the food habits of the brown bear Ursus arctos in relation to geographical (latitude, longitude, altitude) and environmental (temperature, snow cover depth and duration, precipitation, primary productivity) variables.
- 2 We collected data from 28 studies on brown bear diet based on faecal analysis, covering the entire geographical range of this widely distributed large carnivore. We analysed separately four data sets based on different methods of diet assessment.
- 3 Temperature and snow conditions were the most important factors determining the composition of brown bear diet. Populations in locations with deeper snow cover, lower temperatures and lower productivity consumed significantly more vertebrates, fewer invertebrates and less mast. Trophic diversity was positively correlated with temperature, precipitation and productivity but negatively correlated with the duration of snow cover and snow depth. Brown bear populations from temperate forest biomes had the most diverse diet. In general, environmental factors were more explicative of diet than geographical variables.
- 4 Dietary spatial patterns were best revealed by the relative biomass and energy content methods of diet analysis, whereas the frequency of occurrence and relative biomass methods were most appropriate for investigating variation in trophic diversity.
- 5 Spatial variation in brown bear diet is the result of environmental conditions, especially climatic factors, which affect the nutritional and energetic requirements of brown bears as well as the local availability of food. The trade‐off between food availability on the one hand, and nutritional and energetic requirements on the other hand, determines brown bear foraging decisions. In hibernating species such as the brown bear, winter severity seems to play a role in determining foraging strategies. Large‐scale reviews of food habits should be based on several measures of diet composition, with special attention to those methods reflecting the energetic value of food.
1000.
Long-term functional plasticity in plant hydraulic architecture in response to supplemental moisture