Tree crown defoliation data collected on 102 managed forest plots of the RENECOFOR programme in F... more Tree crown defoliation data collected on 102 managed forest plots of the RENECOFOR programme in France were investigated to identify (i) short-term (annual) changes and medium term (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009) trends, and (ii) possible correlates of such changes and trends. Methodological aspects (trees assessed, changes in methods and reporting units, observers, assessment dates) were considered. To account for the specificity of individual plots in terms of tree provenance, age, site condition and management regime, an individual plot approach was adopted. Results showed highly frequent, statistically significant and methodologically meaningful (>5% of the expected measurement error) annual defoliation changes, with pulses of increasing defoliation occurring in 1994-1997 (with a possible methodological bias), in 2002-2004 and 2008-2009. A meta-analysis of individual plot results revealed a significant overall increase, in defoliation over the examination period; when the potentially biased 1994-1996 data were excluded from the analysis, the increase in defoliation was also significant. Within this overall increasing trend, cases of stability (11-24% of the plots) or even decreasing defoliation (11-18%) were frequent. We used a Partial Least Square (PLS) regression to model defoliation on 87 plots where sufficient data was available for a standard set of predictors, including meteorology, nutrition, phenology, reported health problems, management regime and assessment methodology. The most frequent correlates of defoliation were precipitation-related variables (of the current and previous years), tree density and frequency of trees with reported health problems. Foliar nutrients, air temperature, assessment method and observers were never found to be important predictors. Within this general pattern, interactions among predictors varied on a plot basis, leading to divergent estimated effects for the same predictor. The adopted plotbased approach avoids the bias that affects traditional cross-sectional, correlative studies and makes it possible to estimate correlates of change at the scale of individual plots; it is therefore a powerful tool to identify response patterns that can be of value when considering (or re-considering) management options.
Since the 1980s, atmospheric deposition acidity has generally decreased in European forest ecosys... more Since the 1980s, atmospheric deposition acidity has generally decreased in European forest ecosystems. However, at many sites, little or no sign of recovery has been observed yet. Concerns are rising about the sustainability of these ecosystems because of reduced nutrients inputs in atmospheric deposition and the increase in biomass harvesting to supply bio-energy. Nutrient input-output budgets are widely used tools to diagnose the forest ecosystem nutrient status and the changes in soil fertility over time. This approach was applied to two different poor forest ecosystems: a 60-year old silver fir stand in the Vosges Mountains (Lorraine, France) and a 30-year old beech stand in the Morvan Mountains (Burgundy, France). The monitoring data of the silver fir stand was used to calibrate a process-orientated biogeochemical model (NuCM) over a 12 year period which was used to simulate the consequences on soil fertility of two main scenarios and their combinations: constant or reduced atm...
International Journal of Environmental Studies, 2008
Forest condition in Europe has been monitored for 20 years jointly by the United Nations Economic... more Forest condition in Europe has been monitored for 20 years jointly by the United Nations Economic Commission for Europe (UNECE) and the European Union (EU). Large‐scale variations of forest condition over space and time in relation to natural and anthropogenic factors are assessed on about 6000 plots systematically spread across Europe. Causal relationships are studied in detail on about 860
Since the late 1970s, several long-term ecological studies were conducted to better understand th... more Since the late 1970s, several long-term ecological studies were conducted to better understand the biogeochemical functioning of Norway spruce stands in the Ardennes as these nutrient-poor ecosystems were subject to high levels of acid deposition and exhibited symptoms of tree health decline. Between 1978 and 2009, acid deposition declined sharply, especially sulfur and to a lesser extent nitrogen deposition. The aim of this study was (i) to determine if the Norway spruce stands recovered after the reduction of acid deposition and (ii) to explain why such a recovery occurred or not. Therefore, we collected data from different projects carried out in the Ardennes to characterize the long-term temporal trends in soil solution chemistry, foliar nutrition, and crown condition. In parallel, a model describing the nutrient cycling in forests (NuCM) was calibrated and used to check the consistency of the observed temporal trends and to explain them. The soil solution concentration of most of the elements decreased between 1978 and 2002, which was ascribed to a decrease in atmospheric deposition. For potassium, a decline in the exchangeable pool was also showed based on the simulation carried out with NuCM. As nitrogen (N) deposition remained at an elevated level, Norway spruce stands were progressively saturated in N and mineral nutrition became more and more unbalanced. Except the foliar N and Al concentration that remained constant and increased respectively, the foliar concentration of all other nutrients decreased between 1993 and 2009, which can be explained by the decrease in ion concentration in solution. These nutritional disorders weakened trees and were probably exacerbated during the 2003 summer drought, after which symptoms of vitality loss progressively appeared. In these N-saturated ecosystems, the N cycle was disrupted by this health decline, which increased NO 3 À leaching reinforcing soil acidification and risk of aluminum (Al) toxicity.
Forest conditions in Europe have been monitored over 20 years jointly by the International Cooper... more Forest conditions in Europe have been monitored over 20 years jointly by the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and the European Union (EU). Maps for mean bulk SO4, NO3 and NH4 deposition at around 400 intensive monitoring plots in the years 1999–2001, as well as time trends for the period
This paper summarizes the results of the project "Ozone at the intensive monitoring plots in... more This paper summarizes the results of the project "Ozone at the intensive monitoring plots in South-Western European Forests - Levels, risk, actual and potential effects". Ozone (O3) concentration was measured by passive sampling at 83 forest monitoring sites in France, Italy, Spain and Switzerland. Distinct latitudinal and altitudinal trends are detected. On the basis of passive sampling, cumulated exposure AOT40
Vegetation phenology is the chronology of periodic phases of development. It constitutes an effic... more Vegetation phenology is the chronology of periodic phases of development. It constitutes an efficient bio-indicator of impacts of climate changes and a key parameter for understanding and modelling vegetation-climate interactions and their implications on carbon cycling. Numerous studies were devoted to the remote sensing of vegetation phenology. Most of these were carried out using data acquired by AVHRR instrument onboard NOAA meteorological satellites. Since 1999, multispectral images were acquired over the whole earth surface every one to two days by MODIS instrument onboard Terra and Aqua platforms. In comparison with AVHRR, MODIS constitutes a significant technical improvement in terms of spatial resolution, spectral resolution, geolocation accuracy, atmospheric corrections scheme and cloud screening and sensor calibration. In this study, 250 m daily MODIS data were used to derive precise vegetation phenological dates over deciduous forest stands. Phenological markers derived from MODIS time-series and provided by MODIS Global Land Cover Dynamics product (MOD12Q2) were compared to field measurements carried out over the main deciduous forest stands across France and over five years. We show that the inflexion point of the asymmetric double-sigmoid function fitted to NDVI temporal profile is a good marker of the onset of green-up in deciduous stands. At plot level, the prediction uncertainty is 8.5 days and the bias is 3.5 days. MODIS Global Land Cover Dynamics MOD12Q2 provides estimates of onset of green-up dates which deviate substantially from in situ observations and do not perform better than the null model. RMSE values are 20.5 days (bias -17 days) using the onset of greenness increase and 36.5 days (bias 34.5 days) using the onset of greenness maximum. An improvement of prediction quality is obtained if we consider the average of MOD12Q2 onset of greenness increase and maximum as marker of onset of green-up date. RMSE decreases to 16.5 days and bias to 7.5 days.
This study presents a multivariate geostatistical approach for the mapping of atmospheric deposit... more This study presents a multivariate geostatistical approach for the mapping of atmospheric deposition at the scale of the entire French territory, including precipitation as an auxiliary variable. By applying cokriging, deposition maps were produced with the corresponding uncertainty and with an improved level of detail in comparison to previous studies.
Water Air and Soil Pollution - WATER AIR SOIL POLLUT, 1998
Bulk precipitation was sampled weekly from 1993 to 1994 at 27 sites, covering the whole country. ... more Bulk precipitation was sampled weekly from 1993 to 1994 at 27 sites, covering the whole country. In this paper the relations between decreasing concentrations of 4-weekly mean weighted samples with increasing 4-weekly precipitation are studied using two types of equations: (i) y = a+b/x; (ii) y+1= axb, where y = concentration of an ion and x = 4-weekly precipitation quantity. Relationships were studied for the major ions. H+ did not show any relationship with the rainfall amount. From the 216 regressions (27 sites × 8 ions) for all the other ions, 55.6% showed a good fit (r equal or above 0.6) and 16.2% a very good fit (r equal or above 0.85). Good fits were found for 85% of the regressions for N-NO3-, 81% for S-SO42-, 63% for Ca2+, 59% for K+, 55% for N-NH4+, 37% for Mg2+, 33% for Cl- and 29% for Na+. The comparison between sites for the same ions showed: (i) the ranking of the sites after the regressions from lower to higher concentration levels does not necessarily correspond to ...
The influence of climate on the radial growth of Fagus sylvatica was investigated using 15 chrono... more The influence of climate on the radial growth of Fagus sylvatica was investigated using 15 chronologies developed from mature stands of the French Permanent Plot Network (RENECOFOR) growing under different climatic and soil conditions. The relationships between climate and ring widths were analyzed using extreme growth years, simple correlations and response functions analysis.
This study is one of very few dealing with the distribution and the origin of heavy metals in Fre... more This study is one of very few dealing with the distribution and the origin of heavy metals in French soils from a priori non-polluted forest areas. The abundance of heavy metals measured in these soils decreases as follows: Cr) Zn)Pb)Ni)Cu)Co4Cd. Total concentrations of Pb, Cr and Ni in some soils exceed the European thresholds for non-polluted soils and even the French association of normalization critical values for sludge spreading. The lowest heavy metal contents are observed in acid soils while the highest concentrations are in the calcaric cambisol and in the mollic andosol, which is rather scarce as compared with the other French forest soils. With the exception of the podzol, Cr and Ni concentrations increase with depth in all soil profiles. The distribution pattern of Co, Cu, Zn depends on the soil characteristics. In some acid soils, however, Cu and Zn decrease with depth. Pb and Cd are accumulated in the upper soil horizons. Heavy metals accumulate in deep soil horizons in relation to important clay content in the dystric planosol and stagnic luvisol. The concentration of each heavy metal is always controlled by different parameters (soil pH, iron and aluminum oxide content, clay content, organic matter and cation exchange capacity), which are heavy metal specific. This study highlights the metal-trapping character of andosol and calcaric soil, the weak heavy metal retention in acid soils, the leaching and trapping character in leached clayed soils, and the migration of heavy metals in the podzol. Pb and Cr concentrations indicate a significant enrichment in surface horizons from various soils in areas which receive significant acid atmospheric pollution. Particularly, the highest Pb content is observed in a soil located in the N-NE part of France. Lead isotope ratios measured in the cambic podzol and the calcaric cambisol, exhibit the importance of the anthropogenic sources and particularly the influence of global atmospheric inputs from leaded gasoline compared to regional and local industrial emissions. The anthropogenic Pb contribution is estimated to 83, 30 and 11%, respectively, for surface, intermediate and deep horizons of the cambic podzol located in the northern part of France, and to 68% in surface horizon of the calcaric cambisol located in the Alps.
Vegetation phenology is the chronology of periodic phases of development. It constitutes an effic... more Vegetation phenology is the chronology of periodic phases of development. It constitutes an efficient bio-indicator of impacts of climate changes and a key parameter for understanding and modelling vegetation-climate interactions and their implications on carbon cycling. Numerous studies were devoted to the remote sensing of vegetation phenology. Most of these were carried out using data acquired by AVHRR instrument onboard NOAA meteorological satellites. Since 1999, multispectral images were acquired over the whole earth surface every one to two days by MODIS instrument onboard Terra and Aqua platforms. In comparison with AVHRR, MODIS constitutes a significant technical improvement in terms of spatial resolution, spectral resolution, geolocation accuracy, atmospheric corrections scheme and cloud screening and sensor calibration. In this study, 250 m daily MODIS data were used to derive precise vegetation phenological dates over deciduous forest stands. Phenological markers derived from MODIS time-series and provided by MODIS Global Land Cover Dynamics product (MOD12Q2) were compared to field measurements carried out over the main deciduous forest stands across France and over five years. We show that the inflexion point of the asymmetric double-sigmoid function fitted to NDVI temporal profile is a good marker of the onset of green-up in deciduous stands. At plot level, the prediction uncertainty is 8.5 days and the bias is 3.5 days. MODIS Global Land Cover Dynamics MOD12Q2 provides estimates of onset of green-up dates which deviate substantially from in situ observations and do not perform better than the null model. RMSE values are 20.5 days (bias -17 days) using the onset of greenness increase and 36.5 days (bias 34.5 days) using the onset of greenness maximum. An improvement of prediction quality is obtained if we consider the average of MOD12Q2 onset of greenness increase and maximum as marker of onset of green-up date. RMSE decreases to 16.5 days and bias to 7.5 days.
The number of species (species richness) is certainly the most widely used descriptor of plant di... more The number of species (species richness) is certainly the most widely used descriptor of plant diversity. However, estimating richness is a difficult task because plant censuses are prone to overlooking and identification errors that may lead to spurious interpretations. We used calibration data from the French ICP-level II plots (RENECOFOR) to assess the magnitude of the two kinds of errors in large forest plots. Eleven teams of professional botanists recorded all plants on the same eight 100-m 2 plots in 2004 (four plots, eights teams) and 2005 (four plots, nine teams including six from 2004), first independently and then consensually. On average, 15.5% of the shrubs and trees above 2 m were overlooked and 2.3% not identified at the species level or misidentified. On average, 19.2% of the plant species below 2 m in Electronic supplementary material The online version of this article (height were overlooked and 5.3% were misidentified and 1.3% were misidentified at the genus level (especially bryophytes). The overlooking rate also varied with plant species, morphological type, plot and team. It was higher when only one botanist made the census. It rapidly decreased with species cover and increased with plot species richness, the recording time of the census in the tree layer and the number of the censuses carried out during the day in the ground layer. Familiarity of the team with the local flora reduced the risk of overlooking and identification errors, whereas training had little impact. Differences in species richness (over space or time) in large plots should be cautiously interpreted, especially when several botanists participate in the survey. In particular, the quality of the data needs to be evaluated using calibration training and, if necessary, may be improved by involving more experienced botanists working in teams and by fixing a minimum recording time.
Questions: (1) How do extreme climatic events and climate variability influence radial growth of ... more Questions: (1) How do extreme climatic events and climate variability influence radial growth of conifers (silver fir, Norway spruce, Scots pine)? (2) How do elevation and soil water capacity (SWC) modulate sensitivity to climate? Location: The sampled conifer stands are in France, in western lowland and mountain forests, at elevations from 400 to 1700 m, and an SWC from 50 to 190 mm. Methods: We established stand chronologies for total ring width, earlywood and latewood width for the 33 studied stands (985 trees in total). Responses to climate were analysed using pointer years and bootstrapped response functions. Principal component analysis was applied to pointer years and response function coefficients in order to elucidate the ecological structure of the studied stands.
, were used to calculate empirical relationships between DOC and the difference between the sum o... more , were used to calculate empirical relationships between DOC and the difference between the sum of cations and the sum of anions, with the aim to evaluate a formal charge per mg of organic C. Regression coefficients were obtained for data from each laboratory, as well as for all the data combined. The coefficients were further tested using an independent set of data from each country. The differences between the individual laboratory and the overall regression coefficients are discussed. The results are also considered in the light of formal charge values for DOC/TOC obtained in studies on freshwater. The formal DOC charge proved to be useful for estimating the contribution of organic acids in the ion balance test, thus considerably improving the applicability of the ion balance as a validation criterion for samples with high DOC values.
A Working Ring Test (WRT) was organised in the framework of the EU Regulation (EC) No 2152/2003 (... more A Working Ring Test (WRT) was organised in the framework of the EU Regulation (EC) No 2152/2003 ("Forest Focus") and of the UN/ECE Program "ICP Forests" to evaluate the overall performance of the laboratories monitoring atmospheric deposition and soil solution in European Forests. Seven natural samples of atmospheric deposition and soil solutions and 5 synthetic solutions were distributed to 52 laboratories, which analysed them using their routine methods. Thirteen variables are considered in this paper: pH, conductivity, calcium, magnesium, sodium, potassium, ammonium, sulfate, nitrate, chloride, total alkalinity, total dissolved nitrogen and dissolved organic carbon. For each variable, the relative standard deviation of the results was evaluated, after outlier rejection, to estimate the analytical error of the measurements. The results are evaluated considering the Quality Assurance/Quality Control (QA/QC) procedure included in the ICP Forests monitoring manual: consistency check of the data and use of control charts and internal standards. A Data Quality Objective (DQO) is defined for each of the variables and the number of data meeting the DQOs are discussed in relation to the QA/QC procedures adopted. Although 38% of the results did not meet the DQO, the laboratories adopting QA/QC procedures produced a larger proportion of results meeting the objective and a consistent part of the outliers could be detected a posteriori checking analyses consistence.
After modeling the large-scale climate response patterns of leaf unfolding, leaf coloring and gro... more After modeling the large-scale climate response patterns of leaf unfolding, leaf coloring and growing season length of evergreen and deciduous French temperate trees, we predicted the effects of eight future climate scenarios on phenological events. We used the ground observations from 103 temperate forests (10 species and 3,708 trees) from the French Renecofor Network and for the period 1997-2006. We applied RandomForest algorithms to predict phenological events from climatic and ecological variables. With the resulting models, we drew maps of phenological events throughout France under present climate and under two climatic change scenarios (A2, B2) and four global circulation models (HadCM3, CGCM2, CSIRO2 and PCM). We compared current observations and predicted values for the periods 2041-2070 and 2071-2100. On average, spring development of oaks precedes that of beech, which precedes that of conifers. Annual cycles in budburst and leaf coloring are highly correlated with January, March-April and October-November weather conditions through temperature, global solar radiation or potential evapotranspiration depending on species. At the end of the twenty-first century, each model predicts earlier budburst (mean: 7 days) and later leaf coloring (mean: 13 days) leading to an average increase in the growing season of about 20 days (for oaks and beech stands). The A2-HadCM3 hypothesis leads to an increase of up to 30 days in many areas. As a consequence of higher predicted warming during autumn than during winter or spring, shifts in leaf coloring dates appear greater than trends in leaf unfolding. At a regional scale, highly differing climatic response patterns were observed.
Tree crown defoliation data collected on 102 managed forest plots of the RENECOFOR programme in F... more Tree crown defoliation data collected on 102 managed forest plots of the RENECOFOR programme in France were investigated to identify (i) short-term (annual) changes and medium term (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009) trends, and (ii) possible correlates of such changes and trends. Methodological aspects (trees assessed, changes in methods and reporting units, observers, assessment dates) were considered. To account for the specificity of individual plots in terms of tree provenance, age, site condition and management regime, an individual plot approach was adopted. Results showed highly frequent, statistically significant and methodologically meaningful (>5% of the expected measurement error) annual defoliation changes, with pulses of increasing defoliation occurring in 1994-1997 (with a possible methodological bias), in 2002-2004 and 2008-2009. A meta-analysis of individual plot results revealed a significant overall increase, in defoliation over the examination period; when the potentially biased 1994-1996 data were excluded from the analysis, the increase in defoliation was also significant. Within this overall increasing trend, cases of stability (11-24% of the plots) or even decreasing defoliation (11-18%) were frequent. We used a Partial Least Square (PLS) regression to model defoliation on 87 plots where sufficient data was available for a standard set of predictors, including meteorology, nutrition, phenology, reported health problems, management regime and assessment methodology. The most frequent correlates of defoliation were precipitation-related variables (of the current and previous years), tree density and frequency of trees with reported health problems. Foliar nutrients, air temperature, assessment method and observers were never found to be important predictors. Within this general pattern, interactions among predictors varied on a plot basis, leading to divergent estimated effects for the same predictor. The adopted plotbased approach avoids the bias that affects traditional cross-sectional, correlative studies and makes it possible to estimate correlates of change at the scale of individual plots; it is therefore a powerful tool to identify response patterns that can be of value when considering (or re-considering) management options.
Since the 1980s, atmospheric deposition acidity has generally decreased in European forest ecosys... more Since the 1980s, atmospheric deposition acidity has generally decreased in European forest ecosystems. However, at many sites, little or no sign of recovery has been observed yet. Concerns are rising about the sustainability of these ecosystems because of reduced nutrients inputs in atmospheric deposition and the increase in biomass harvesting to supply bio-energy. Nutrient input-output budgets are widely used tools to diagnose the forest ecosystem nutrient status and the changes in soil fertility over time. This approach was applied to two different poor forest ecosystems: a 60-year old silver fir stand in the Vosges Mountains (Lorraine, France) and a 30-year old beech stand in the Morvan Mountains (Burgundy, France). The monitoring data of the silver fir stand was used to calibrate a process-orientated biogeochemical model (NuCM) over a 12 year period which was used to simulate the consequences on soil fertility of two main scenarios and their combinations: constant or reduced atm...
International Journal of Environmental Studies, 2008
Forest condition in Europe has been monitored for 20 years jointly by the United Nations Economic... more Forest condition in Europe has been monitored for 20 years jointly by the United Nations Economic Commission for Europe (UNECE) and the European Union (EU). Large‐scale variations of forest condition over space and time in relation to natural and anthropogenic factors are assessed on about 6000 plots systematically spread across Europe. Causal relationships are studied in detail on about 860
Since the late 1970s, several long-term ecological studies were conducted to better understand th... more Since the late 1970s, several long-term ecological studies were conducted to better understand the biogeochemical functioning of Norway spruce stands in the Ardennes as these nutrient-poor ecosystems were subject to high levels of acid deposition and exhibited symptoms of tree health decline. Between 1978 and 2009, acid deposition declined sharply, especially sulfur and to a lesser extent nitrogen deposition. The aim of this study was (i) to determine if the Norway spruce stands recovered after the reduction of acid deposition and (ii) to explain why such a recovery occurred or not. Therefore, we collected data from different projects carried out in the Ardennes to characterize the long-term temporal trends in soil solution chemistry, foliar nutrition, and crown condition. In parallel, a model describing the nutrient cycling in forests (NuCM) was calibrated and used to check the consistency of the observed temporal trends and to explain them. The soil solution concentration of most of the elements decreased between 1978 and 2002, which was ascribed to a decrease in atmospheric deposition. For potassium, a decline in the exchangeable pool was also showed based on the simulation carried out with NuCM. As nitrogen (N) deposition remained at an elevated level, Norway spruce stands were progressively saturated in N and mineral nutrition became more and more unbalanced. Except the foliar N and Al concentration that remained constant and increased respectively, the foliar concentration of all other nutrients decreased between 1993 and 2009, which can be explained by the decrease in ion concentration in solution. These nutritional disorders weakened trees and were probably exacerbated during the 2003 summer drought, after which symptoms of vitality loss progressively appeared. In these N-saturated ecosystems, the N cycle was disrupted by this health decline, which increased NO 3 À leaching reinforcing soil acidification and risk of aluminum (Al) toxicity.
Forest conditions in Europe have been monitored over 20 years jointly by the International Cooper... more Forest conditions in Europe have been monitored over 20 years jointly by the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and the European Union (EU). Maps for mean bulk SO4, NO3 and NH4 deposition at around 400 intensive monitoring plots in the years 1999–2001, as well as time trends for the period
This paper summarizes the results of the project "Ozone at the intensive monitoring plots in... more This paper summarizes the results of the project "Ozone at the intensive monitoring plots in South-Western European Forests - Levels, risk, actual and potential effects". Ozone (O3) concentration was measured by passive sampling at 83 forest monitoring sites in France, Italy, Spain and Switzerland. Distinct latitudinal and altitudinal trends are detected. On the basis of passive sampling, cumulated exposure AOT40
Vegetation phenology is the chronology of periodic phases of development. It constitutes an effic... more Vegetation phenology is the chronology of periodic phases of development. It constitutes an efficient bio-indicator of impacts of climate changes and a key parameter for understanding and modelling vegetation-climate interactions and their implications on carbon cycling. Numerous studies were devoted to the remote sensing of vegetation phenology. Most of these were carried out using data acquired by AVHRR instrument onboard NOAA meteorological satellites. Since 1999, multispectral images were acquired over the whole earth surface every one to two days by MODIS instrument onboard Terra and Aqua platforms. In comparison with AVHRR, MODIS constitutes a significant technical improvement in terms of spatial resolution, spectral resolution, geolocation accuracy, atmospheric corrections scheme and cloud screening and sensor calibration. In this study, 250 m daily MODIS data were used to derive precise vegetation phenological dates over deciduous forest stands. Phenological markers derived from MODIS time-series and provided by MODIS Global Land Cover Dynamics product (MOD12Q2) were compared to field measurements carried out over the main deciduous forest stands across France and over five years. We show that the inflexion point of the asymmetric double-sigmoid function fitted to NDVI temporal profile is a good marker of the onset of green-up in deciduous stands. At plot level, the prediction uncertainty is 8.5 days and the bias is 3.5 days. MODIS Global Land Cover Dynamics MOD12Q2 provides estimates of onset of green-up dates which deviate substantially from in situ observations and do not perform better than the null model. RMSE values are 20.5 days (bias -17 days) using the onset of greenness increase and 36.5 days (bias 34.5 days) using the onset of greenness maximum. An improvement of prediction quality is obtained if we consider the average of MOD12Q2 onset of greenness increase and maximum as marker of onset of green-up date. RMSE decreases to 16.5 days and bias to 7.5 days.
This study presents a multivariate geostatistical approach for the mapping of atmospheric deposit... more This study presents a multivariate geostatistical approach for the mapping of atmospheric deposition at the scale of the entire French territory, including precipitation as an auxiliary variable. By applying cokriging, deposition maps were produced with the corresponding uncertainty and with an improved level of detail in comparison to previous studies.
Water Air and Soil Pollution - WATER AIR SOIL POLLUT, 1998
Bulk precipitation was sampled weekly from 1993 to 1994 at 27 sites, covering the whole country. ... more Bulk precipitation was sampled weekly from 1993 to 1994 at 27 sites, covering the whole country. In this paper the relations between decreasing concentrations of 4-weekly mean weighted samples with increasing 4-weekly precipitation are studied using two types of equations: (i) y = a+b/x; (ii) y+1= axb, where y = concentration of an ion and x = 4-weekly precipitation quantity. Relationships were studied for the major ions. H+ did not show any relationship with the rainfall amount. From the 216 regressions (27 sites × 8 ions) for all the other ions, 55.6% showed a good fit (r equal or above 0.6) and 16.2% a very good fit (r equal or above 0.85). Good fits were found for 85% of the regressions for N-NO3-, 81% for S-SO42-, 63% for Ca2+, 59% for K+, 55% for N-NH4+, 37% for Mg2+, 33% for Cl- and 29% for Na+. The comparison between sites for the same ions showed: (i) the ranking of the sites after the regressions from lower to higher concentration levels does not necessarily correspond to ...
The influence of climate on the radial growth of Fagus sylvatica was investigated using 15 chrono... more The influence of climate on the radial growth of Fagus sylvatica was investigated using 15 chronologies developed from mature stands of the French Permanent Plot Network (RENECOFOR) growing under different climatic and soil conditions. The relationships between climate and ring widths were analyzed using extreme growth years, simple correlations and response functions analysis.
This study is one of very few dealing with the distribution and the origin of heavy metals in Fre... more This study is one of very few dealing with the distribution and the origin of heavy metals in French soils from a priori non-polluted forest areas. The abundance of heavy metals measured in these soils decreases as follows: Cr) Zn)Pb)Ni)Cu)Co4Cd. Total concentrations of Pb, Cr and Ni in some soils exceed the European thresholds for non-polluted soils and even the French association of normalization critical values for sludge spreading. The lowest heavy metal contents are observed in acid soils while the highest concentrations are in the calcaric cambisol and in the mollic andosol, which is rather scarce as compared with the other French forest soils. With the exception of the podzol, Cr and Ni concentrations increase with depth in all soil profiles. The distribution pattern of Co, Cu, Zn depends on the soil characteristics. In some acid soils, however, Cu and Zn decrease with depth. Pb and Cd are accumulated in the upper soil horizons. Heavy metals accumulate in deep soil horizons in relation to important clay content in the dystric planosol and stagnic luvisol. The concentration of each heavy metal is always controlled by different parameters (soil pH, iron and aluminum oxide content, clay content, organic matter and cation exchange capacity), which are heavy metal specific. This study highlights the metal-trapping character of andosol and calcaric soil, the weak heavy metal retention in acid soils, the leaching and trapping character in leached clayed soils, and the migration of heavy metals in the podzol. Pb and Cr concentrations indicate a significant enrichment in surface horizons from various soils in areas which receive significant acid atmospheric pollution. Particularly, the highest Pb content is observed in a soil located in the N-NE part of France. Lead isotope ratios measured in the cambic podzol and the calcaric cambisol, exhibit the importance of the anthropogenic sources and particularly the influence of global atmospheric inputs from leaded gasoline compared to regional and local industrial emissions. The anthropogenic Pb contribution is estimated to 83, 30 and 11%, respectively, for surface, intermediate and deep horizons of the cambic podzol located in the northern part of France, and to 68% in surface horizon of the calcaric cambisol located in the Alps.
Vegetation phenology is the chronology of periodic phases of development. It constitutes an effic... more Vegetation phenology is the chronology of periodic phases of development. It constitutes an efficient bio-indicator of impacts of climate changes and a key parameter for understanding and modelling vegetation-climate interactions and their implications on carbon cycling. Numerous studies were devoted to the remote sensing of vegetation phenology. Most of these were carried out using data acquired by AVHRR instrument onboard NOAA meteorological satellites. Since 1999, multispectral images were acquired over the whole earth surface every one to two days by MODIS instrument onboard Terra and Aqua platforms. In comparison with AVHRR, MODIS constitutes a significant technical improvement in terms of spatial resolution, spectral resolution, geolocation accuracy, atmospheric corrections scheme and cloud screening and sensor calibration. In this study, 250 m daily MODIS data were used to derive precise vegetation phenological dates over deciduous forest stands. Phenological markers derived from MODIS time-series and provided by MODIS Global Land Cover Dynamics product (MOD12Q2) were compared to field measurements carried out over the main deciduous forest stands across France and over five years. We show that the inflexion point of the asymmetric double-sigmoid function fitted to NDVI temporal profile is a good marker of the onset of green-up in deciduous stands. At plot level, the prediction uncertainty is 8.5 days and the bias is 3.5 days. MODIS Global Land Cover Dynamics MOD12Q2 provides estimates of onset of green-up dates which deviate substantially from in situ observations and do not perform better than the null model. RMSE values are 20.5 days (bias -17 days) using the onset of greenness increase and 36.5 days (bias 34.5 days) using the onset of greenness maximum. An improvement of prediction quality is obtained if we consider the average of MOD12Q2 onset of greenness increase and maximum as marker of onset of green-up date. RMSE decreases to 16.5 days and bias to 7.5 days.
The number of species (species richness) is certainly the most widely used descriptor of plant di... more The number of species (species richness) is certainly the most widely used descriptor of plant diversity. However, estimating richness is a difficult task because plant censuses are prone to overlooking and identification errors that may lead to spurious interpretations. We used calibration data from the French ICP-level II plots (RENECOFOR) to assess the magnitude of the two kinds of errors in large forest plots. Eleven teams of professional botanists recorded all plants on the same eight 100-m 2 plots in 2004 (four plots, eights teams) and 2005 (four plots, nine teams including six from 2004), first independently and then consensually. On average, 15.5% of the shrubs and trees above 2 m were overlooked and 2.3% not identified at the species level or misidentified. On average, 19.2% of the plant species below 2 m in Electronic supplementary material The online version of this article (height were overlooked and 5.3% were misidentified and 1.3% were misidentified at the genus level (especially bryophytes). The overlooking rate also varied with plant species, morphological type, plot and team. It was higher when only one botanist made the census. It rapidly decreased with species cover and increased with plot species richness, the recording time of the census in the tree layer and the number of the censuses carried out during the day in the ground layer. Familiarity of the team with the local flora reduced the risk of overlooking and identification errors, whereas training had little impact. Differences in species richness (over space or time) in large plots should be cautiously interpreted, especially when several botanists participate in the survey. In particular, the quality of the data needs to be evaluated using calibration training and, if necessary, may be improved by involving more experienced botanists working in teams and by fixing a minimum recording time.
Questions: (1) How do extreme climatic events and climate variability influence radial growth of ... more Questions: (1) How do extreme climatic events and climate variability influence radial growth of conifers (silver fir, Norway spruce, Scots pine)? (2) How do elevation and soil water capacity (SWC) modulate sensitivity to climate? Location: The sampled conifer stands are in France, in western lowland and mountain forests, at elevations from 400 to 1700 m, and an SWC from 50 to 190 mm. Methods: We established stand chronologies for total ring width, earlywood and latewood width for the 33 studied stands (985 trees in total). Responses to climate were analysed using pointer years and bootstrapped response functions. Principal component analysis was applied to pointer years and response function coefficients in order to elucidate the ecological structure of the studied stands.
, were used to calculate empirical relationships between DOC and the difference between the sum o... more , were used to calculate empirical relationships between DOC and the difference between the sum of cations and the sum of anions, with the aim to evaluate a formal charge per mg of organic C. Regression coefficients were obtained for data from each laboratory, as well as for all the data combined. The coefficients were further tested using an independent set of data from each country. The differences between the individual laboratory and the overall regression coefficients are discussed. The results are also considered in the light of formal charge values for DOC/TOC obtained in studies on freshwater. The formal DOC charge proved to be useful for estimating the contribution of organic acids in the ion balance test, thus considerably improving the applicability of the ion balance as a validation criterion for samples with high DOC values.
A Working Ring Test (WRT) was organised in the framework of the EU Regulation (EC) No 2152/2003 (... more A Working Ring Test (WRT) was organised in the framework of the EU Regulation (EC) No 2152/2003 ("Forest Focus") and of the UN/ECE Program "ICP Forests" to evaluate the overall performance of the laboratories monitoring atmospheric deposition and soil solution in European Forests. Seven natural samples of atmospheric deposition and soil solutions and 5 synthetic solutions were distributed to 52 laboratories, which analysed them using their routine methods. Thirteen variables are considered in this paper: pH, conductivity, calcium, magnesium, sodium, potassium, ammonium, sulfate, nitrate, chloride, total alkalinity, total dissolved nitrogen and dissolved organic carbon. For each variable, the relative standard deviation of the results was evaluated, after outlier rejection, to estimate the analytical error of the measurements. The results are evaluated considering the Quality Assurance/Quality Control (QA/QC) procedure included in the ICP Forests monitoring manual: consistency check of the data and use of control charts and internal standards. A Data Quality Objective (DQO) is defined for each of the variables and the number of data meeting the DQOs are discussed in relation to the QA/QC procedures adopted. Although 38% of the results did not meet the DQO, the laboratories adopting QA/QC procedures produced a larger proportion of results meeting the objective and a consistent part of the outliers could be detected a posteriori checking analyses consistence.
After modeling the large-scale climate response patterns of leaf unfolding, leaf coloring and gro... more After modeling the large-scale climate response patterns of leaf unfolding, leaf coloring and growing season length of evergreen and deciduous French temperate trees, we predicted the effects of eight future climate scenarios on phenological events. We used the ground observations from 103 temperate forests (10 species and 3,708 trees) from the French Renecofor Network and for the period 1997-2006. We applied RandomForest algorithms to predict phenological events from climatic and ecological variables. With the resulting models, we drew maps of phenological events throughout France under present climate and under two climatic change scenarios (A2, B2) and four global circulation models (HadCM3, CGCM2, CSIRO2 and PCM). We compared current observations and predicted values for the periods 2041-2070 and 2071-2100. On average, spring development of oaks precedes that of beech, which precedes that of conifers. Annual cycles in budburst and leaf coloring are highly correlated with January, March-April and October-November weather conditions through temperature, global solar radiation or potential evapotranspiration depending on species. At the end of the twenty-first century, each model predicts earlier budburst (mean: 7 days) and later leaf coloring (mean: 13 days) leading to an average increase in the growing season of about 20 days (for oaks and beech stands). The A2-HadCM3 hypothesis leads to an increase of up to 30 days in many areas. As a consequence of higher predicted warming during autumn than during winter or spring, shifts in leaf coloring dates appear greater than trends in leaf unfolding. At a regional scale, highly differing climatic response patterns were observed.
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Papers by Erwin Ulrich