Accurate Measurements of Forest Soil Water Content Using FDR Sensors Require Empirical In Situ (Re)Calibration

Monitoring volumetric soil water content (θv) is the key for assessing water availability and nutrient fluxes. This study evaluated the empirical accuracy of θv measurements using standard and in situ calibrated frequency domain reflectometers (FDR) with gravimetric water content and bulk density measurements of 1512 samples gathered from 15 profiles across 5 ICP Forests level II intensive monitoring plots. The predicted θv, calibrated with standard functions, predominantly underestimated the real water content. The measurement error exceeded the threshold of 0.03 m3 m−3 in 93% of all soil layers. Layer specific calibration removed bias and reduced the overall prediction error with a factor up to 2.8. A simple linear regression often provided the best calibration model; temperature correction was helpful in specific cases. To adequately remove bias in our study plots, a calibration dataset of up to 24 monthly observations was required for topsoils (whereas 12 observations sufficed for subsoils). Based on estimated precision errors, 3 sensors per soil layer proved to be sufficient, while up to 16 sensors are needed to meet the required accuracy in organic topsoils. Validating FDR sensor outputs using in situ gravimetric measurements is essential for quality control and assurance of long term θv monitoring and for improving site specific instrumentalization.

Trends of Scots pine forest health and element flow changes in the ICP Forests monitoring sites in Latvia

Scots pine (Pinus sylvestris L.) is one of the most widespread and economically most important tree species in Latvia. Scots pine forest health and element flow changes have been monitored in Latvia within the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with assessment of crown condition and damaging agents at 115 Level I monitoring sites (mostly oligothrophic and mesotrophic Vacciniosa, Myrtillosa and Hylocomiosa forests) and with sampling and analyses of environmental samples at three Level II monitoring sites representing typical Scots pine forests (Myrtillosa) in hemiboreal conditions in Latvia. This study summarizes the background information and presents the trends of forest health, carbon turnover and environment condition in Scots pine forest since 2009. In general, defoliation rate in Scots pine stands remains stable for the studied period, with some yearly fluctuations, possibly related to regional insect outbreaks, especially well demonstrated in two Level II plots. The share of damaged trees varied by year from 12.8% to 19% of the total number; the main cause of damage was direct action of man. Chemical element flows in Scots pine forests in Level II monitoring plots have been relatively stable as well except the decreasing trend in total N concentration in deposition and SO4-S concentration in soil solution and increasing trends in DOC concentration in soil solution that is in line with common trends in Europe. Carbon input with above-ground litter was relatively stable during the whole period; however, interannual variations were rather wide.

New appetite for the monitoring of European forests

Key message Future international forest monitoring should build upon the existing pan-European programs. There is a renewed interest in the monitoring of European forests. Future monitoring systems should build upon existing international programs, making use of their strengths and solving their weaknesses. This approach will result into win–win solutions for both the existing and future systems. The UNECE ICP Forests has a number of characteristics that makes it a very good and strong basis for developing an advanced international forest monitoring system.

Nitrification in tree canopies of European forests: evidence from oxygen isotopes in nitrate and microbial analyses in rainfall and throughfall water.

<p>There is mounting evidence demonstrating that fluxes and chemical composition of precipitation is substantially changed after passing through tree canopies, particularly in the case of atmospheric nitrogen (N) compounds, with important implications on forest N cycling. However, the processes underpinning those changes – beyond the leaf retention and/or leaching of N compounds - have been less investigated. In a previous study we provided isotopic evidence that biological nitrification in tree canopies was responsible for significant changes in the amount of NO<sub>3</sub><sup>-</sup> from rainfall to throughfall across two UK forests at high nitrogen (N) deposition. This finding strongly suggested that forest canopies are not just passive filters for precipitation water and dissolved nutrients, and that the microbial life hidden within them can be responsible for transforming atmospheric N before it reaches the soil. We extended the isotopic approach at the European scale, and combined it to next-generation sequence analyses with the aim of elucidating canopy nitrification and identify phyllosphere microbes responsible for it. Specifically, in this study we: 1) estimated the relative contribution of NO<sub>3</sub><sup>-</sup> derived from biological canopy nitrification vs. atmospheric deposition by using δ<sup>18</sup>O and δ<sup>17</sup>O of NO<sub>3</sub><sup>-</sup> in rainfall and throughfall water; 2) quantified the functional genes related to nitrification, and finally 3) characterized the microbial communities harboured in tree canopies (i.e., phyllosphere) and in the underlying soils for two dominant tree species in Europe (Fagus sylvatica L. and Pinus sylvestris L.) using metabarcoding techniques. We considered twelve sites included in the European ICP Forests monitoring network, chosen along climate and N deposition gradients, spanning from Fennoscandia to the Mediterranean. We will show that presence of nitrifying microbes (as assessed through qPCR) and their activity (as derived from δ<sup>18</sup>O and δ<sup>17</sup>O) were detected in the tree canopies across most of the sites, and that canopy nitrification was significantly correlated with atmospheric N deposition. Finally, we will discuss differences in microbial community structure and composition across phyllosphere (and between the two tree species considered), water and soil samples in the investigated forests. Our study demonstrates the potential of integrating stable isotopes with microbial analyses to advance our understanding on canopy-atmosphere interactions and their contribution to N cycling.</p>

CHARACTERISATION AND ASSESSMENT OF THE DECLINE OF THE OULED BECHIH FOREST (ALGERIA)

The establishment of the state of the massif by a diagnosis on different forest plots is part of a project of monitoring and silvicultural management. The purpose of this study is to assess the health status of the Ouled Bechih forest. The methodology used was the visual assessment of the tree crown of the dominant species (i.e. Quercus suber and Quercus canariensis) according to the protocols DEPEFEU, DEPERIS and ICP Forests. These protocols were selected for adoption based on field observations and their applicability in record time. The results obtained indicate that the health status of the trees within the studied plots is declining. The DEPEFEU value index shows an average of 1.75 for Quercus suber and 2.6 for Quercus canariensis while the DEPERIS has an average level of 2.36 Q. suber in and 3.37 in Q. canariensis. ICP Forests has also contributed to providing clearer information on the consequences of this health situation by deducting an average visibility rate of 1.20 and 2.63; social status of 1.17 and 3.11 and competition of 1.11 and 2.49 for Q. suber and Q. canariensis respectively. In general, the health status of the tree crown is average and almost adapted to the environmental conditions. In contrast, the carrying capacity of biodiversity is low and needs to be improved.

Tree stands of Scots pine and Norway spruce state assessment using hemispherical photography by Fish-eye lens and subsequent analysis of the digital images

На примере чистых и смешанных древостоев хвойных пород с преобладанием сосны обыкновенной и ели европейской было проведено поисковое исследование возможностей определения состояния древостоев на основе цифровой полусферической съемки полога леса снизу вверх объективом типа «Рыбий глаз» и последующей обработки полученных изображений. Исследования были проведены на 25 пробных площадях, заложенных по европейской методике мониторинга состояния лесов ICP-Forest с регулярным их размещением по территории. На пробных площадях традиционным наземным методом были визуально определены такие показатели состояния древостоев как средние дефолиация верхней 1/3 части кроны деревьев, дефолиация всей кроны деревьев и класс повреждения древостоев. На этих же пробных площадях были получены снимки древесного полога объективом для полусферической съемки «Рыбий глаз», которые были обработаны с помощью программы открытого доступа Gap Light Analyzer. Методами регрессионного и дисперсионного анализа были установлены статистически достоверные связи между показателями состояния древостоев и их индексом листовой поверхности, полученным при обработке цифровых изображений. Показатели состояния древостоев и их индекс листовой поверхности связаны обратной зависимостью с коэффициентами детерминации от 79,8 до 87,4%. Полученные результаты позволяют в принципе разработать измерительную методику оценки состояния древостоев, обладающую свойствами объективности, технологичности, экономичности и точности. Основной целью такой методики является удаление из оценок состояния древостоев субъективного подхода, свойственного всем визуальным определениям. On the example of pure and mixed stands of coniferous species with a predominance of Scots pine and Norway spruce, a search study was conducted to determine the state of stands based on digital hemispherical shooting of the forest canopy from bottom to top with a Fish-eye lens and subsequent processing of the images obtained. The research was carried out on 25 test areas laid down according to the European method of monitoring the state of forests ICP-Forests. On the test areas land-based method to identify indicators of the status of the forest as the average defoliationof upper 1/3 part of the trees, defoliation of all trees and the class of damage of forest stands. At the same test areas, images of the tree canopy were obtained with a Fish-eye hemispherical lens, which were processed using the Gap Light Analyzer open access program. Using regression and variance analysis methods, statistically significant relationships were established between indicators of the state of stands and their leaf area index with determination coefficient from 79,8 to 87,4%. The results obtained allow us to develop a methodology for assessing the state of stands, which are usually determined visually with a high degree of subjectivity, by measuring.

Long-Term Temporal Changes of Precipitation Quality in Slovak Mountain Forests

The paper is focused on the evaluation of long-term changes in the chemical composition of precipitation in the mountain forests of Slovakia. Two stations with long-term measurements of precipitation quality were selected, namely the station of the EMEP (European Monitoring and Evaluation Programme) network Chopok (2008 m a.s.l.) and the station of the ICP Forests (International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests) network Poľana-Hukavský grúň (850 m a.s.l.). All basic chemical components were analyzed, namely sulfur (S-SO4), nitrogen (N-NH4, N-NO3), and base cations (Ca, Mg, and K) contained in precipitation. The time changes of the individual components were statistically evaluated by the Mann–Kendall test and Kruskal–Wallis test. The results showed significant declining trends for almost all components, which can significantly affect element cycles in mountain forest ecosystems. The evaluated forty one-year period (1987 to 2018) is characterized by significant changes in the precipitation regime in Slovakia and the obtained results indicate possible directions in which the quantity and quality of precipitation in the mountainous areas of Slovakia will develop with ongoing climate change.

Assessment of the health status of the Sidi R'Ghies forest, Oum El Bouaghi, north-east Algerian

Rached-Kanouni M, Zerrouki A, Lahmar M, Beldjazia A, Kara K, Ababsa. 2020. Assessment of the health status of the Sidi R'Ghies forest, Oum El Bouaghi, north-east Algerian. Biodiversitas 21: 1980-1988. In recent decades, the forest of Sidi R'Ghies has been degraded by human activity. The establishment of the state of the massif by a diagnosis on different forest plots is part of a project of monitoring and silvicultural management. The purpose of this study is to assess the health status of the Sidi R'Ghies forest. The methodology used was the visual assessment of the tree crown of the dominant species (i.e. Aleppo pine and holm oak) according to the protocols DEPEFEU, DEPERIS, and ICP Forests. These protocols were selected for adoption based on field observations and their applicability in record time. The results obtained indicate that the health status of the trees within the studied plots is declining. The DEPEFEU value index shows an average of 2.20 for Aleppo pine and 1.95 for holm oak while the DEPERIS has an average level of 4.56 in Aleppo pine and 3.07 in holm oak. ICP Forests has also contributed to providing clearer information on the consequences of this health situation by deducting an average visibility rate of 1.24 and 1.63; social status of 2.17 and 2.11 and competition of 1.71 and 2.49 for Aleppo pine and holm oak respectively. In general, the health status of the tree crown is average and almost adapted to the environmental conditions. In contrast, the carrying capacity of biodiversity is low and needs to be improved.