Caroline Vincke

Frequency responses of radial growth series after different thinning intensities in Norway spruce (Picea abies (L.) Karst.) stands

A thinning intensity experiment started in 1971 on two experimental 22-year-old stands of Norway spruce in the Belgian Ardenne. The stands had strongly contrasting water availability conditions. Heavy thinning resulted in up to 77% removal of the basal area. In 1995, tree ring-area series were measured from dendrochronological cores sampled in three different thinning intensity treatments and on a control plot. Radial growth variations at different frequencies (low, medium and high) were isolated by standardisation with polynomials and differencing. Results showed that long, medium and short-term radial growth variations are widely altered by heavy thinning. At low-frequency, growth tended to increase during 15 years, until the stand basal area reached 26-29 m(2) ha(-1) again. At medium-term, the positive growth lasted for 10 years: after this period radial growth was limited by an undetermined factor. Medium-frequency growth variation showed an inverse cycling behaviour between treatments during the entire period studied (25 years). At short-term, positive growth variation lasted 4 years. We showed empirical evidences that stand density alters the classical climate-growth relationship. At individual tree level, thinning could be a method to increase tree resistance to drought stress. This effect is limited when site conditions,are limiting

Predicting transpiration from forest stands in Belgium for the 21st century

Canopy transpiration is a major element of the hydrological cycle of temperate forests. Levels of water stress during the 21st century will be largely controlled by the response of canopy transpiration to changing environmental conditions. One year of transpiration measurement in two stands (Quercus robur L. and Fagus sylvatica L.) was used to calibrate the ASPECTS model on a(1) and D-0, two parameters of a modified version of Leunings equation of stomatal conductance. A second year of data was used to validate the model. The results indicate a higher sensitivity of g(sc), to vapour pressure deficit (DS) in oak than in beech (D-0 (oak) < D-0 (beech)). To simulate future forest transpiration, site specific weather data sets were constructed from GCM outputs, spatially and temporally downscaled with local climatic data. Temperature increase between the end of the 20th and 21st centuries was predicted to be 2.8 degreesC in the beech stand and 3.1 degreesC in the oak stand. Based solely on temperature change, ASPECTS predicted an increase in transpiration of 17% in the beech and 6% in the oak stand, the difference being due to variation in local climate and the sensitivity of both species to D-s. Based solely on increased atmospheric CO2 (355 ppm in 1990 to 700 ppm in 2100), ASPECTS predicted that transpiration would decrease by 22% in beech and 19% in oak. With the combined scenarios of climatic change and increased atmospheric CO2, ASPECTS showed a decrease of 7% in transpired water in the oak stand and only 4% in the beech stand, which are not significant differences from zero. Consequently, water stress should not increase in either stand during the 21st century

Current status and predicted impact of climate change on forest production and biogeochemistry in the temperate oceanic European zone: review and prospects for Belgium as a case study

Reviews of the current statuses of forests and the impacts of climate change on forests exist at the (sub)continental scale, but rarely at country and regional levels, meaning that information on causal factors, their impacts, and specific regional properties is often inconsistent and lacking in depth. Here, we present the current status of forest production and biogeochemistry and the expected impacts of climate change on them for Belgium. This work represents a case study for the temperate oceanic zone, the most important bioclimatic zone in northwestern Europe. Results show that Belgian forests are mainly young, very productive, and have a high C-sequestration capacity. Major negative anomalies in tree vitality were observed in the 1990s and—as result of disturbances—in the last decade for sensitive species as poplars and European beech. The most severe disturbances were caused by extreme climatic events, directly (e.g. storms) or indirectly (e.g. insect outbreaks after a mild autumn with an early/severe frost). Because of atmospheric deposition and soil fertilization (due to the previous use of the land), nutrient stocks of Belgian forests are likely to sustain the future enhancement in productivity which is expected to follow the increase in atmospheric CO2 concentration that will occur in years to come. However, in the long term, such (enhanced) forest production is likely to be limited by nutrient deficiencies at poor sites and by drought for sensitive species such as beech and (particularly) Norway spruce. Drought conditions will likely increase in the future, but adverse effects are expected on a relatively limited number of tree species. The potential impacts of windstorms, insects and fungi should be carefully investigated, whereas fires are less of a concern.

Porosity and available water of temporarily waterlogged soils in a Quercus robur (L.) declining stand

Pedunculate oak (Quercus robur L.) is particularly sensitive to decline in clayey soils presenting a high-perched temporary water table. These soils induce two successive constraints in one-year cycle: water excess (and hypoxy) in winter and early spring, and water shortage in summer (water stress being more restrictive to oak). We determined the porosity and water properties of temporarily waterlogged clayey soils supporting forest stands of decliningQuercus robur trees in a 101 yr-old oak stand in Belgium (50°06′N, 4°16′E). Roots unevenly colonized the soil down to 1.6 m: fine roots (diameter < 5 mm) were mostly distributed on the surface horizons (0–0.3 m) and around 1.3 m deep, despite dense clayey horizons appearing at 0.35 m depth. Clay content below this depth reached 46–51. Illite and vermiculite were the dominant clay minerals. The clayey horizons exhibited marked shrink–swell properties: bulk density at 30 kPa increased from 1.41 to 1.88 g cm−3 from the surface to 2 m depth. There was also evidence of hypoxic conditions caused by water saturation of pore space in the rooting zone from October to mid-April. Extractable water (EW), calculated between moisture tensions of 5 and 1600 kPa was 152.8 mm. The level of perched temporary water table strongly depended on the seasonal rhythm of water uptake by trees and on the shrink–swell behaviour of soil.

Characterization of black locust ( Robinia pseudoacacia L.) heartwood extractives: identification of resveratrol and piceatannol

Robinia pseudoacacia L. heartwood is characterized by a very high natural durability. However, a significant difference was observed between the mature and juvenile heartwood, the latter presenting less durability against fungi decay, which could be attributed to lower extractive content. In order to elucidate this idea, extractives from mature and juvenile heartwoods of black locust trees were investigated. Results showed that extractive and phenolic contents were higher in mature than in juvenile heartwoods. The identification of phenolic compounds by UPLC–DAD–MS/MS revealed, for the first time, the presence of resveratrol and piceatannol. These two stilbenes as well as the flavonoid dihydrorobinetin were present at the highest level in mature heartwood, and as they are known antifungals, they could account for the great durability of mature heartwood. The stilbenes were detected in significant amounts particularly in mature heartwood where piceatannol reached a level tenfold higher than that reported for Japanese knotweed roots, the primary natural source of these stilbenes, whereas resveratrol level was comparable with reported values. As resveratrol and piceatannol receive increasing demand for nutraceutical, cosmetic and, possibly, pharmaceutical purposes, due to their beneficial health effects, this study underlines the use of R. pseudoacacia as a promising sustainable and economical source of resveratrol and piceatannol.

Reduction of tree cover in West African woodlands and promotion in semi-arid farmlands

Woody vegetation in farmland acts as a carbon sink and provides ecosystem services for local people, but no macroscale assessments of the impact of management and climate on woody cover exist for drylands. Here we make use of very high spatial resolution satellite imagery to derive wall-to-wall woody cover patterns in tropical West African drylands. Our study reveals that mean woody cover in farmlands along all semi-arid and sub-humid rainfall zones is 16%, on average only 6% lower than in savannahs. In semi-arid Sahel, farmland management promotes woody cover around villages (11%), while neighbouring savannahs had on average less woody cover. However, farmlands in sub-humid zones have a greatly reduced woody cover (21%) as compared with savannahs (33%). In the region as a whole, rainfall, terrain and soil are the most important (80%) determinants of woody cover, while management factors play a smaller (20%) role. We conclude that agricultural expansion causes a considerable reduction of trees in woodlands, but observations in Sahel indicate that villagers safeguard trees on nearby farmlands which contradicts simplistic ideas of a high negative correlation between population density and woody cover.Farmland management promotes tree cover around villages in the semi-arid Sahel of West Africa, according to analyses of satellite imagery. This implies that a higher population density does not always lead to reduced tree cover.

Forest cover correlates with good biological water quality. Insights from a regional study (Wallonia, Belgium)

Forested catchments are generally assumed to provide higher quality water in opposition to agricultural and urban catchments. However, this should be tested in various ecological contexts and through the study of multiple variables describing water quality. Indeed, interactions between ecological variables, multiple land use and land cover (LULC) types, and water quality variables render the relationship between forest cover and water quality highly complex. Furthermore, the question of the scale at which land use within stream catchments most influences stream water quality and ecosystem health remains only partially answered. This paper quantifies, at the regional scale and across five natural ecoregions of Wallonia (Belgium), the forest cover effect on biological water quality indices (based on diatoms and macroinvertebrates) at the riparian and catchment scales. Main results show that forest cover - considered alone - explains around one third of the biological water quality at the regional scale and from 15 to 70% depending on the ecoregion studied. Forest cover is systematically positively correlated with higher biological water quality. When removing spatial, local morphological variations, or population density effect, forest cover still accounts for over 10% of the total biological water quality variation. Partitioning variance shows that physico-chemical water quality is one of the main drivers of biological water quality and that anthropogenic pressures often explain an important part of it (shared or not with forest cover). The proportion of forest cover in each catchment at the regional scale and across all ecoregions but the Loam region is more positively correlated with high water quality than when considering the proportion of forest cover in the riparian zones only. This suggests that catchment-wide impacts and a fortiori catchment-wide protection measures are the main drivers of river ecological water quality. However, distinctive results from the agricultural and highly human impacted Loam region show that riparian forests are positively linked to water quality and should therefore be preserved.

Trees dynamics (1955-2012) and their uses in the Senegal's Ferlo region: insights from a historical database, local knowledge and field inventories

Sahelian ecosystems are undergoing increas- ing anthropogenic and climatic pressures with long-lasting consequences for woody vegeta- tion. As trees play a vital role for the local popu- lation, the main challenge is to ensure that they will endure. This study characterizes the woody vegetation, its uses and its long-term dynamics (1955-2012) in Senegal’s sandy Ferlo region, in an anthropized zone near two boreholes. In 2012, inventories were made of 30 plots and surveys on vegetation dynamics and uses of tree species were conducted among herders from 30 camps. A historical vegetation data- base provided further information about the species diversity of the woody vegetation since 1955, and all potential uses of the species were listed through a review of the literature. We then attempted to convert these data in terms of the dynamics of provisioning services, by calcu- lating use indices for the species and service indices for the ecosystem. With 3% tree cover in 2012, made up of 12 different tree species, the tree stands were dominated by two Sahe- lian species, Balanites aegyptiaca and Boscia senegalensis . The ratio between saplings and adults was up to 70.5%, which seemed to indi- cate a good balance among trees in the stands, but 95% of the saplings belonged to the spe- cies Balanites aegyptiaca , Boscia senegalensis and Acacia tortilis . Regarding the use value of woody species, the most commonly used were B. aegyptiaca and B. senegalensis , but also the rare A . senegal , Adansonia digitata and Ziziphus mauritiana . The data showed a decline in species diversity and numbers of saplings from 1955 to 2012 with a shift towards Sahe- lian species, while the uses and services trends suggest a decline in provisioning services. This could indicate an increase in the vulnerability of these ecosystems.