Quality Assurance and measurement errors in monitoring tree crown conditions in Italy (original) (raw)
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Crown Condition Surveys in Italian Forests: Issues in Reporting Findings
Environmental Monitoring and Assessment, 2003
This study examines defoliation and discoloration findings collected throughout the Italian Level I network between 1997 and 2000. Prior to this period no Quality Assurance procedures had been implemented, so that earlier findings cannot be considered reliable. The aim of the study is to compare differentindices used in reporting findings, in order to determine the full potential and limitations of each. In international surveys,findings are normally expressed in terms of individual trees presenting a defoliation level greater than 2 %; this criterion,however, has been challenged since it is not based on scientificevidence. By analysing the distribution of defoliation values(grouped in 5% classes) relating to the main species (Fagus sylvatica, Quercus pubescens, Quercus cerris, Picea abies), the study examines the behaviour of statistical indices such as the median, the mode and the mean. Instead of using the traditional 25% threshold to determine the part of the population with the highest defoliation values, a procedureis suggested whereby a different threshold can be determined foreach species. It is established based on the 90° percentile of cumulative defoliation values recorded over the four-year period. Each index used to report findings possessesits own information potential, and the findings may at times appear contradictory. The use of a combined defoliation and discoloration index (Ilce = Lacking Crown Equivalent Index) is also proposed, but the results obtained do not differin substance from the results relating to defoliation alone. Thefunctional limitations of this index are due mainly to the way the data are collected: for this reason suggestions are made onhow to improve the procedure in future surveys.
Agro Food Industry Hi-tech, 2000
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 SOx, NOy, NHx 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.
Water Air and Soil Pollution, 2000
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 NOx, SOx 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.
Forest Ecology and Management, 2002
Assessments of tree health using scoring systems based on the visual appearance of the tree crown are used throughout Europe. The principal parameter assessed is the amount of defoliation in the sample tree when compared to a healthy tree of the same species. Different methods are used to select sample trees. This study compares the results of 2 years of assessment on matched pairs of plots in oak (Quercus robur and Q. petraea) and Scots pine (Pinus sylvestris L.), where assessments of crown condition of trees selected from the edge of a stand were compared with trees selected from within the stand. Trained forest surveyors carried out the assessments as part of the UK's national annual tree health survey and the same methods were used. Results showed there were no significant differences in any of the parameters assessed between trees within the forest stand and those on the edge of a forest road or ride. This suggests that the practice of selecting sample trees from ride or road edge trees within a forested area does not affect the health scores for trees in Britain. # 2002 Published by Elsevier Science B.V.
Status and change of tree crown condition at the CONECOFOR plots, 1996-2005
Between 1996 and 2005 crown condition at Italian Level II plots was assessed annually within the CONECOFOR programme. Three different assessment forms and manuals were adopted over this period of time (the first in 1996-97, the second between 1998 and 2004, the last starting in 2005); as a result, many of the parameters investigated and the data collected are neither homogeneous nor comparable over time. Since, however, neither the definition nor the assessment criteria for transparency changed, this parameter was chosen to represent crown condition variations over time. (In this survey, transparency is used as a proxy for defoliation.) Yearly field surveys were always preceded by an inter-calibration course, and were followed up by Quality Control surveys done by one or more Reference Teams. After 10 years, the results suggest that statistically significant variations in transparency, from one year to the next, are only scattered and display no recognizable trend. Overall, there were 15 variations, of which 7 were positive (i.e. increase in transparency), and 8 negative (i.e. decrease in transparency). The majority of variations is concentrated in the 1997-98 period. Significant defoliation trends were identified in 11 out of the 27 considered plots. In 4 cases these trends were positive (increased transparency).
Acta Silvae et Ligni, 2014
Data from the forest monitoring programme in Slovenia were used to assess the relationship between tree phenology, crown defoliation and meteorological conditions in Fagus sylvatica, Quercus robur and Picea abies forests in the 2004-2013 period. We hypothesized a species-specific response of first leaf unfolding, general leaf colouring, the length of the growing season to crown defoliation, air temperature, precipitation and soil water. In accordance with the hypothesis, we found a high sensitivity of first leaf unfolding to air temperature and precipitation for all species, exhibiting contrasting responses. We observed strong sensitivity of beech defoliation to precipitation and soil water conditions. Oak crown defoliation and next-year phenology were correlated, with higher crown defoliation contributing to earlier leaf unfolding, later autumn leaf colouring and longer growing season of oak in next year. Correlation between crown defoliation and phenology was found neither for bee...