Bruno De Vos

Linking variability in soil solution dissolved organic carbon to climate, soil type, and vegetation type

Lateral transport of carbon plays an important role in linking the carbon cycles of terrestrial and aquatic ecosystems. There is, however, a lack of information on the factors controlling one of the main C sources of this lateral flux, i.e., the concentration of dissolved organic carbon (DOC) in soil solution across large spatial scales and under different soil, vegetation, and climate conditions. We compiled a database on DOC in soil solution down to 80u2009cm and analyzed it with the aim, first, to quantify the differences in DOC concentrations among terrestrial ecosystems, climate zones, soil, and vegetation types at global scale and second, to identify potential determinants of the site-to-site variability of DOC concentration in soil solution across European broadleaved and coniferous forests. We found that DOC concentrations were 75% lower in mineral than in organic soil, and temperate sites showed higher DOC concentrations than boreal and tropical sites. The majority of the variation (R2u2009=u20090.67–0.99) in DOC concentrations in mineral European forest soils correlates with NH4+, C/N, Al, and Fe as the most important predictors. Overall, our results show that the magnitude (23% lower in broadleaved than in coniferous forests) and the controlling factors of DOC in soil solution differ between forest types, with site productivity being more important in broadleaved forests and water balance in coniferous stands.

Phosphorus nutrition of beech (Fagus sylvatica L.) is decreasing in Europe

Key messageFoliar phosphorus concentrations have decreased in Europe during the last 20xa0years. High atmospheric nitrogen deposition and climate change might be responsible for this trend. Continued decrease in foliar P concentrations might lead to reduced growth and vitality of beech forests in Europe.ContextIncreased forest soil acidification, atmospheric nitrogen deposition, and climate change have been shown to affect phosphorus nutrition of forest trees. Low foliar phosphorus levels and high nitrogen/phosphorus ratios have been observed in different European countries and have been related to reduced growth in forests.AimsWe test the hypothesis that phosphorus concentrations of European beech (F. sylvatica L.) foliage are decreasing at the European scale.MethodsFoliar phosphorus concentrations in beech were monitored on the basis of the “International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests.” Here, data from 12 European countries, comprising 79 plots and a 20-year sampling period (1991–2010), were evaluated.ResultsFoliar phosphorus concentrations ranged from 0.81 to 1.66xa0mgxa0g−1 dw (plot median of the 20-year sampling period). On 22xa0% of the plots, phosphorus concentrations were in the deficiency range of beech (Mellert and Göttlein 2012). On 62xa0% of the plots, the nitrogen/phosphorus ratio was above 18.9, which is considered to be disharmonious for beech. In addition, foliar phosphorus concentrations were significantly decreasing by, on average, 13xa0% from 1.31 to 1.14xa0mgxa0g−1 in Europe (pu2009<u20090.001).ConclusionOur results show that phosphorus nutrition of beech is impaired in Europe. Possible drivers of this development might be high atmospheric nitrogen deposition and climate change. Continued decrease in foliar phosphorus concentrations, eventually attaining phosphorus deficiency levels, might lead to reduced growth and vitality of beech forests in Europe.

Predicting forest site productivity in temperate lowland from forest floor, soil and litterfall characteristics using boosted regression trees

AimsThe aim of this study is on the one hand to identify the most determining variables predicting the site productivity of pedunculate oak, common beech and Scots pine in temperate lowland forests of Flanders; and on the other hand to test whether the accuracy of site productivity models based exclusively on soil or forest floor predictor variables is similar to the accuracy achieved by full ecosystem models, combining all soil, vegetation, humus and litterfall composition related variables.MethodsBoosted Regression Trees (BRT) were used to model in a climatically homogeneous region the relationship between environmental variables and site productivity. A distinction was made between soil (soil physical and chemical), forest floor (vegetation and humus) and ecosystem (soil, forest floor and litterfall composition jointly) predictors.ResultsOur results have illustrated the strength of BRT to model the non-linear behaviour of ecological processes. The ecosystem models, based on all collected variables, explained most of the variability and were more accurate than those limited to either soil or forest floor variables. Nevertheless, both the soil and forest floor models can serve as good predictive models for many forest management practices.ConclusionsSoil granulometric fractions and litterfall nitrogen concentrations were the most effective predictors of forest site productivity in Flanders. Although many studies revealed a fertilising effect of increased nitrogen deposition, nitrogen saturation seemed to reduce species’ productivity in this region.

The analysis of spatio-temporal forest changes (1775–2000) in Flanders (northern Belgium) indicates habitat-specific levels of fragmentation and area loss

IntroductionSpatio-temporal forest changes can have a progressive negative impact on the habitat of species that need forest continuity, i.e. the continuous presence of forest. Long-term species data that demonstrate such an impact are often not available. Instead we applied a spatial analysis on maps of the historical and present-day forests, by calculating landscape indices that explain forest plant species diversity.MethodsWe digitized for this purpose, forests in Flanders (northern Belgium, ~13,500 km2) at four time slices (1775, 1850, 1904–1931, 2000) and created a map of forest continuity in 2000. The ecological relevance of the analysis was further enhanced by a site classification, using a map of potential forest habitat types based on soil–vegetation relationships.ResultsOur results indicated that, between 1775 and 2000, forests occupied 9.7–12.2 % of the total study area. If continuity was not taken into consideration, forest fragmentation slightly increased since 1775. However, only 16 % of the forest area in 2000 remained continuously present at least since 1775 and is therefore called ancient forest (AF). Moreover, connectivity of forest that originated after 1775, called recent forest, was low and only 14 % was in physical contact with AF. The results were habitat-specific as forest on sites that are potentially suitable for a high number of slow-colonizing species, e.g. ancient forest plants, were affected most.ConclusionWe discuss that a GIS analysis of this kind is essential to provide statistics for forest biodiversity conservation and restoration, in landscapes with a dynamic and heterogeneous forest cover.

Forest structure and soil fertility determine internal stem morphology of Pedunculate oak: a modelling approach using boosted regression trees

This study aims at the explanation of internal stem morphology of vital (co)dominant Pedunculate oak (Quercus robur L.) trees in homogeneous even-aged high-forests by the factors tree age, forest structure and site quality, using boosted regression trees as a powerful modelling technique. The study area covers the region of Flanders (Northern Belgium), which is characterised by the absence of strong topographic and climatic gradients. For 76 adult sample trees covering the entire productivity range of Pedunculate oak, morphological characteristics were derived from measurements of ring width or heartwood area on wood cores. Forest structure, soil physicochemical properties, humus quality, vegetation indices and litter nutrient contents were quantified at each sample location. Model predictive performance and generality are good. Tree age effects correspond to expected trends in age-related radial growth and heartwood portion. Even if management of oak trees in even-aged high-forests is rather similar over Flanders, forest structure is the most important factor determining ring width, followed by soil fertility. Heartwood portion is determined by soil fertility and crown structure. Effects of topsoil and humus physicochemical characteristics, litter nutrient contents and water supply mainly confirm autecological knowledge on oak. However, variables related to soil water availability are only occasionally relevant, and always of lower importance than soil fertility. The low importance of water availability in the models contradicts results from other studies, and the potential effect of confounding is discussed. The observed growth reduction at low litter N/P ratios might be indirectly linked to early litterfall.

Effects of soil mechanical treatments combined with bramble and bracken control on the restoration of degraded understory in an ancient beech forest

This paper describes the ground floor vegetation that developed four years after tillage implements in an ancient beech forest in central Belgium. The purpose of this study was twofold: (1) to explore whether tillage has a lasting effect on soil compaction and soil moisture as well as on vegetation characteristics; and (2) to analyse whether two distinct tillage treatments (rotary plough vs. disc plough), combined with vegetation control when necessary, have the same effect on soil compaction, soil moisture and plant establishment. Of the 29 species recorded, 15 showed a significant recovery after soil loosening in the studied forest area. Interestingly, different tillage treatments did not have the same influence on plant establishment. Treatment effects on soil structure and/or moisture status can be considered as causing the observed growth response.RésuméCette étude décrit la flore herbacée qui s’est développée quatre années après la mise en place d’expériences de traitement mécanique du sol dans une ancienne hêtraie dans le centre de la Belgique. Les objectifs furent : (1) explorer si le traitement mécanique du sol a un effet durable sur la compaction et l’humidité du sol et sur les caractéristiques de la végétation; et (2) analyser si deux traitements effectués avec des machines différentes (crabe et fraise rotative), combinés à un contrôle de la végétation si nécessaire, ont le même effet sur la compaction et l’humidité du sol et sur l’établissement des plantes. Parmi les 29 espèces inventoriées, 15 ont montré un développement significatif suite au labour du sol dans les zones expérimentales étudiées. Il est intéressant de constater que les différents traitements n’ont pas eu la même influence sur l’établissement des espèces végétales. L’effet des traitements sur la structure et/ou l’humidité du sol peut être considéré comme étant la cause de la réponse végétale observée.

The assessment of mulch sheets to inhibit competitive vegetation in tree plantations in urban and natural environment

Abstract Weed control is often crucial for successful tree establishment. Removal or suppression of competitive vegetation has most often been done by either mowing or the use of herbicides. The Institute of Forestry and Game Management in Flanders (Belgium) has been conducting a three-year experiment (as part of a five-year programme) to assess 18 treatments for newly planted deciduous trees established on ex-agricultural sites. On grass-covered sites mortality of English oak(Quercus roburL.) decreased significantly when mulch sheets were applied. Mulch sheets increased growth of all species in a pasture. An unequivocal relation was found between the diameter of the weed-free area around the tree and the Relative Growth Rate of Common alder (Alnus glutinosa (L.) Gaertn.). Rigid sheets, such as those made of polypropylene could severely damage the trunk of the trees. Bark mulch decreased growth of English oak in the first year, but increased it significantly after 3 years. The application of bark mulch was time-consuming compared to the other treatments. Usage of herbicides on a clay soil was nefarious to both survival and growth of the treated trees. Mowing, often used by the Flemish Forestry Service, had no significant effect on the growth of the trees.

Application of the Ancient Forest Concept to Potential Natural Vegetation Mapping in Flanders, A Strongly Altered Landscape in Northern Belgium

Construction of potential natural vegetation (PNV) poses particular challenges in landscapes heavily altered by human activity and must be based on transparent, repeatable methods. We integrated the concept of ancient forest (AF) and ancient forest species (AFS) into a four-step procedure of PNV mapping: 1) classification of forest vegetation relevés; 2) selection of those vegetation types that can serve as PNV units, based on AF and AFS; 3) merging of selected vegetation types into five PNV units that can be predicted from a digital morphogenetic soil map; 4) mapping of three additional PNV units based on additional environmental data. The second step, concerning the selection of reference forest vegetation, is of particular interest for PNV construction in Flanders (northern Belgium), where forest cover has been subject to temporal disruption and spatial fragmentation. Among the variety of extant forest recovery states, we chose as PNV units those vegetation types for which a high proportion of relevés had been located in AF and that contained many AFS. As the frequency of AFS depends on site conditions, we only compared and selected vegetation types that are found on similar sites according to average Ellenberg indicator values. While succession is irrelevant for the definition of PNV, colonization rates of AFS can be used to estimate the time required for PNV to be restored in a site.

Data Quality in Laboratories: Methods and Results for Soil, Foliar, and Water Chemical Analyses

Abstract Chemical analyses are an essential part of forest ecosystem monitoring activities. Harmonized, well-defined, and documented analytical methods are an important part of a laboratory Quality Control program and are essential to maximize spatial and temporal comparability of monitoring data. Different quality and data consistency checks, plausible ranges for analytical results, use of reference materials, and control charts are described for internal laboratory Quality Control. On the other side, coordinated ring tests among participating laboratories are an integral part of external Quality Control. Organization of ring tests, evaluation, and the benchmark with tolerable limits are described and specified. Results for water, foliage, and soil ring tests and the evaluation of quality indicators within the European forest ecosystem monitoring program are reported.Chemical analyses are an essential part of forest ecosystem monitoring activities. Harmonized, well-defined, and documented analytical methods are an important part of a laboratory Quality Control program and are essential to maximize spatial and temporal comparability of monitoring data. Different quality and data consistency checks, plausible ranges for analytical results, use of reference materials, and control charts are described for internal laboratory Quality Control. On the other side, coordinated ring tests among participating laboratories are an integral part of external Quality Control. Organization of ring tests, evaluation, and the benchmark with tolerable limits are described and specified. Results for water, foliage, and soil ring tests and the evaluation of quality indicators within the European forest ecosystem monitoring program are reported.

Nutritional imbalance caused by nitrogen excess is correlated with the occurrence of watermark disease in white willow

Willows in the Flemish region are threatened by the watermark disease, a wood disease caused by the bacterium Brenneria salicis (Hauben et al. Syst Appl Microbiol 21:384–397, 1998). Affected trees are observed to grow at specific sites which seem more sensitive to periodical watermark symptom development than other sites. In this study we aim at revealing abiotic site factors that could play a role in triggering the watermark disease. During three consecutive years we analyzed stands of young isogenic willows (Salix alba L. cv. Lichtenvoorde), which were planted on four different sites in an agricultural environment. These test sites were chosen, based on the occurrence/absence of watermark disease in the old willows that grow on these sites. Two sites had old willow pollards with clear watermark symptoms, and on the two other sites the old willows were unaffected. Differences in abiotic characteristics between the sites were analysed and their effects on the nutrient status in willow were measured in the isogenic willows that were newly planted. Brenneria salicis-specific multiplex PCR revealed the presence of this pathogenic bacterium in both the old and the freshly planted young willows. At each site, the physical and chemical characteristics of soil and groundwater were investigated; the young tree growth was monitored and nutritional status of the willow plantings was assessed by foliar analysis. Physical soil properties including soil type and profile water availability, and chemical soil analysis were unable to explain differences between healthy and affected sites. Diseased sites, however, had significantly higher N concentrations and traces of herbicides in the groundwater. In young trees, foliar levels of N and S were always greater at the affected sites, while P contents were lower. Dry mass based N concentration in the leaves of the newly planted trees increased systematically over the years, but more at affected than at healthy sites. Also, chlorophyll content was significantly greater at the affected sites. Growth rate of the young isogenic trees was twice as fast at the diseased sites. The presented data suggest that application of fertilisers in agriculture causes an imbalance in the nutritional status of Salix alba L. Excess nitrogen makes this species fast-growing, reflected by an average foliar N:P ratio >10, and more susceptible for watermark disease, indicated by an average foliar N:Ca ratio exceeding 1.5.