摘要:

AbstractClimate change may influence pelagic fish by altering advective processes or by changing where fish choose to spawn. Using a simulation model, the effects of altered advection and spatial distribution of spawning by anchovy on recruitment off South Africa were explored. Cape anchovyEngraulis capensisspawn on the region of the Agulhas Bank, south of South Africa. Currents transport eggs and larvae to nursery areas. Transport of eggs and larvae was modelled using a flow field based on averaged Acoustic Doppler Current Profile data, Feasible Scenarious of altered advection were modelled. For modelling purposes, the ocean surrounding South Africa was divided into blocks with dimensions of a quarter‐degree latitude by a quarter‐degree longitude. Acoustically measured distributions of spawner biomass for the years 1986–92 were used to calculate egg production per block. In the model, batches were released from each of these blocks each day of the spawning season. The modelling study indicates that passive transport of young anchovy may account for a substantial proportion of year‐class variability. Model results show that distribution of spawners influences the distribution of young of the year, as well as the number and the location of advective losses across offshore bou

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00091.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractVertical CO2profiles (between 0.02 and 14.0 m) were studied in forest canopies ofPinus contorta, Populus tremuloides, and in a riparian forest withAcer negundoandAcer grandidentatumduring two consecutive growing seasons. Profiles, measured continuously during 1‐ to 13‐day periods in four to five stands differing in overstorey canopy area index (CAI<4.5; including leaves, branches and stems), were well stratified, with highest [CO2] just above the forest floor. Canopy [CO2] profiles were influenced by stand structure (CAI, presence of understorey vegetation), and were highly dependent on vegetation type (deciduous and evergreen). A doubling of CAI inAcerspp. andP. tremuloidesstands did not show an effect on upper canopy [CO2], when turbulent mixing was high. However, increasing understorey biomass inAcerspp. stands had a profound effect on lower canopy [CO2]. In open stands with a vigorous understorey layer, higher soil respiration rates were offset by increased understorey gas exchange, resulting in [CO2] below those of the convective boundary layer (CBL). Midday depletions up to 20 ppmv below CBL values could be frequently observed in deciduous canopies. In evergreen canopies, [CO2] stayed generally above the CBL background values, [CO2] profiles were more uniform, and gradients were smaller than in deciduous stands with similar CAI. Seasonal changes of canopy [CO2] reflected changes in soil respiration rates as well as plant phenology and gas exchange of both dominant tree and understorey vegetation. Seasonal patterns were less pronounced in evergreen than in deciduous fore

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00092.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractRecent predictions that tropospheric aerosols have counterbalanced greenhouse warming assume aerosol emissions were low beforead1850 and then increased dramatically with industrialization of the Northern Hemisphere and biomass burning in the Tropics. We assembled the lake sediment record of emissions across northeastern North America, where temperatures are predicted to have been substantially affected by industrial aerosols. Sediment evidence suggests a systematic shift in source and an overall decline in emissions since the 19th century. The geographical shift results from high presettlement emissions from wildfires in the Midwest that collapsed with tillage and fire suppression. Meanwhile, emissions were increasing in the North‐east with European settlement. These regional changes produced a shift from the continental interior to the North‐east. An overall decline results because decreases in the Midwest more than compensate for increases in the North‐east. Results suggest the Central Plains as an important source of emissions in the recent past, consistent with pioneer accounts of dense smoke clouds emanating from prairie in the 19th century. Contrary to recent models that suggest increased 20th century combustion emissions could have offset warming effects of rising greenhouse gases, our data suggest that aerosols could have actually decreased over this interval. Although we cannot directly quantify aerosols from our methods, the emissions of large particles suggest assumptions of 20th century aerosol declines should be reconsi

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00093.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractRegarding time ranges of years, a rationale has been developed which is capable of explaining observed ‘spruce decline’ symptoms observed when spruce is exposed to air containing ambient levels of SO2. It integrates and interrelates (i) ecophysiological data (tree morphology, assimilate partitioning, canopy turnover, senescence physiology, stomatal conductance, canopy throughfall, sulphur metabolism, tonoplast symport), (ii) pedological data (soil leaching, cation recycling, litter decomposition, forest nutrition), and (iii) meteorological data (site elevation, length of the annual trunk growth period, SO2‐pollution). Furthermore, it can explain field observations at numerous sites of spruce decline in central Europe where SO2is implicated as a factor of forest decline: (i) thinning of the canopy structure; (ii) early needle senescence; (iii) cation deficiency; (iv) low SO2tolerance at sites with depleted soils in the mountains; (v) synergism of SO2pollution and acidic precipitation; (vi) recovery after liming, fertilization and after decreasing SO2pollution; and (vii) higher SO2tolerances of deciduous angiosperms. Different SO2tolerance strategies are identified that are employed by more SO2‐tolerant tree species. Ecophysiological SO2tolerance factors interact in a complex synergistic or antagonistic manner. It is concluded that chronic SO2pollution at ambient concentrations predisposes mainly evergreen gymnosperms to suffer under synergistic environmental stresses (frost, drought, pathogens, etc.). Thinning of the crown structure is massive at extreme sites, where several stresses act simultaneously on the trees (depleted soils, high SO2pollution, acidic rain, etc.). Mathematical formulations allow precise definitions of terms such as cooperativity, synergism, antagonism, vitality, predisposition, latency, etc. This universal rationale, which is applicable to all tree species, is exemplified here for Norway spruce (Picea abies[L.] Karst.). Integration of parameters yields an ordinary differential equation, which can be solved analytically. It predicts reversible dynamics of crown structures and gives an ecophysiological background to

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00094.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractField data on the sulphur and cation budget of growing Norway spruce canopies (Picea abies[L.] Karst.) are summarized. They are used to test a spruce decline model capable of quantifying effects of chronic SO2pollution on spruce forests. At ambient SO2concentrations, acute SO2damage is rare, but exposure to polluted air produces reversible thinning of the canopy structure with a half‐time of a few years. Canopy thinning in the spruce decline model is highest (i) at elevated SO2pollution, (ii) in the mountains, (iii) at unfertilized sites with poor K+, Mg2+or Zn2+supply, (iv) at low spruce litter decomposition rates, and (v) acidic, shallow soils at high annual precipitation rates in the field andvice versa.Model application using field data from Würzburg (moderate SO2pollution, alkaline soils, no spruce decline) and from the Erzgebirge (extreme SO2pollution, acidic soils in the mountains, massive spruce decline) predicts canopy thinning by 2–11% in Würzburg and by 45–70% in the Erzgebirge. The model also predicts different SO2‐tolerance limits for Norway spruce depending on the site elevation and on the nutritional status of the needles. If needle loss of more than 25% (damage class 2) is taken to indicate ‘real damage’ exceeding natural variances, then for optimum soil conditions SO2tolerance limits range from (27.3 ± 7.4) μg m−3to (62.6 ± 16.5) μg m−3. For shallow and acidic soils, SO2tolerance limits range from (22.0 ± 5.5) μg m−3to (37.4 ± 7.5) μ m−3. These tolerance limits, which are calculated on an ecophysiological data basis for Norway spruce are close to epidemiological SO2‐toIerance limits as recommended by the IUFRO, UN‐ECE and WHO. The observed statistical regression slope of the plot (damaged spruce trees vs. SO2‐pollution) in west Germany is confirmed by modelling (6% error). Model application to other forest trees allows deduction of the observed sequence of SO2‐sensitivity:Abies>Picea>Pinus>Fagus>Quercus.Thus, acute phytotoxicity of SO2seems not to be involved in ‘forest decline’. Chronic SO2‐pollution induces massive canopy thinning ofAbies albaandPicea abiesonly at unfavourable sites, where natural stress factors and secondary effects of SO2pol

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00095.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY