Effects of Environmental Stress on Forest Crown Condition in Europe. Part III: Estimation of Critical Deposition and Concentration Levels and Their Exceedances

The stress by air pollution at the systematicPan-European 16 × 16 km² forest (crown) condition monitoring network, is discussed by comparingsite-specific estimates of critical and presentconcentration and deposition levels for S and Ncompounds and ozone. Results indicate that theexceedance of critical levels, related to directabove-ground impacts, decrease going from O₃ >SO₂ > N compounds. Critical N loads related toeffects on the forest understorey are exceeded atapproximately 25% of the plots, located mainly inWestern and Central Europe. Critical N loads relatedto effects on trees are hardly ever exceeded, but mostlikely, this is an under estimate. Critical aciddeposition levels are exceeded at approximately 30%of the plots with a low base saturation, where acidinputs may release toxic Al. This is especially thecase in Central and Eastern Europe, where presentloads are high and in boreal forest in SouthernScandinavia where critical loads are low. Although theuncertainties in the calculated exceedances is large,the spatial pattern, which is most important for acorrelative study, seems reliable, implying that thecritical load concept is suitable for regional risk assessments.     

Effects of Environmental Stress on Forest Crown Condition in Europe. Part IV: Statistical Analysis of Relationships

Site-specific estimates for various environmentalstress factors were related with measured crowncondition data at a systematic 16 ×: 16 km² gridover Europe, according to previously statedhypotheses, using a multiple regression approach,including interactions, and lagged effects of stressfactors. Methodological differences among countriesaccounted for >30% of the variation in defoliation.Nevertheless, crown condition was found to varynaturally with tree age, altitude, drought stress and,most likely, also pathogenic fungi and insects.Significant impacts of air pollution (specificallyozone but also NO_x, SO_x and acid deposition)were found at regional levels in parts of centralEurope, particularly for deciduous species. Impactsseemed less significant for conifers, especially forspruce, but this might be affected by confoundingeffects or strong correlations between (a harsh)climate and (low) atmospheric deposition in the areawhere spruce predominates. National studies indicatethat ozone and acid deposition can have a significanteffect on the defoliation of spruce as well. Weconclude that while forest condition varies naturally,continued emissions will contribute further to forestdecline in the long term.     

Effects of environmental stress on forest crown condition in Europe. Part I: Hypotheses and approach to the study

This paper is the first in a series of four,describing the hypothesis and approach of acorrelative study between observed data on crowncondition in Europe, monitored since 1986 at asystematic 16 × 16 km grid, and site-specificestimations of various natural and anthropogenicstress factors. The study was based on the hypothesisthat forests respond to various natural andanthropogenic stress factors, whose contributiondepend on the geographic region considered. In view ofthis hypothesis, major stand and site characteristics,chemical soil composition, meteorological stressfactors (temperature and drought stress indices) andair pollution stress (concentrations and/ordepositions of SO_x, NO_y, NH_x andO₃) were included as predictor variables. Theresponse variables considered were actual defoliationand changes/trends in defoliation for five major treespecies. The spatial distribution of the averagedefoliation during the period 1986–1995 shows highdefoliation in Central Europe and in parts ofScandinavia and of Southern Europe. There are,however, sharp changes at country borders, which aredue to methodological differences between countries.The spatial distribution of the calculated trends showa distinct cluster of large deterioration in parts ofCentral and Eastern Europe and in Spain and a ratherscattered pattern of positive and negative trends for most of Europe, indicating that other factors than airpollution only have a strong impact on defoliation.The limitations of the study are discussed in view ofthe quality of the considered response and predictor variables.     

Effects of environmental stress on forest crown condition in Europe. Part II: Estimation of stress induced by meteorology and air pollutants

In order to assess the relationship betweenenvironmental stress and crown condition of foresttrees monitored since 1986 in Europe, estimates ofstress factors, including temperature stress, droughtstress and air pollution stress, were derived with thebest data, methods and models currently available.This paper presents information on the methods used toderive such stress factors, and on the overall ranges,the temporal trends, the spatial distribution and thereliability of the calculated stress factors. Thetemperature stress indices did not show much temporalvariation between 1985 to 1995. As expected spatialpatterns were north-south orientated, going fromcolder northern regions to warmer southern regions.The calculated relative transpiration showed a morecomplex pattern, coinciding to a large extend withpatterns of rainfall and temperature. Potential aciddeposition decreased between 1986 and 1992, butremained fairly constant after 1992. The strongdecrease was mainly the result of the decrease inSO_x deposition, and to a small decrease inNO_y deposition. Highest levels of the S and Ndeposition were calculated in Central and WesternEurope. Base cation deposition was largest in coastalareas and in southern Europe. This is mainly due tosoil dust, Sahara dust and sea salt. Base cationdeposition can compensate almost entirely for thepotential inputs in the south of Europe, whereas incentral Europe it equalled about 25% of thepotential acid input. A comparison between sitespecific modelled deposition and deposition derivedfrom throughfall data showed that the total aciddeposition is usually overestimated by the model,whereas the total nitrogen deposition isunderestimated, especially at plots with high nitrogenloads. There is, however, a significant correlationbetween measured and modelled data for all S and Ndeposition, thus allowing their use in a statistical analyses.     

Dynamics of protozoan counts in the rumen of calves during a period of milk feeding]

Protozoan counts were followed in the rumen of calves in the period of milk diet. In the third week of calves' age the total counts of protozoans in 1 ml of rumen contents made 1.48 +/- 0.91 (log 10 +/- SEM). These counts were increasing gradually to reach in the seventh week of age the value of 5.54 +/- 0.19 (log 10 +/- SEM) in 1 ml of rumen contents. An increase in the protozoan counts in the seventh week of age was significant in comparison with the preceding four weeks. Total protozoan counts were converted also per 1 g of rumen content dry matter.