Johan Neirynck

Impact of Tilia platyphyllos Scop., Fraxinus excelsior L., Acer pseudoplatanus L., Quercus robur L. and Fagus sylvatica L. on earthworm biomass and physico-chemical properties of a loamy topsoil

Abstract Impact of hardwoods of different humus forms on earthworm biomass and physico-chemical properties of the topsoil of a loamy acid brown forest soil after a time-span of 60–65 years was examined in the Forest of Halle near Brussels. Three sites were selected in which homogeneous stands of mull-forming tree species (Tilia platyphyllos Scop., Fraxinus excelsior L. and Acer pseudoplatanus L.) were compared with adjacent stands of Fagus sylvatica L. and/or Quercus robur L. where a mullmoder had developed. Total earthworm biomass was conspicuously higher at the sites that supported Tilia and Acer as mull-forming hardwoods. Study of soil acidity revealed that there were marked differences in pH and base saturation in the A- and E-horizon between hardwoods developing different humus forms. The topsoil beneath mull-forming hardwoods was generally higher in pH and base saturation with the largest differences being displayed between Tilia and Fagus/Quercus. C/N ratios were significantly lower in the topsoil under Acer. Significant differences in physical soil properties among humus form were also evident. The A-horizon under mull-forming species was higher in total porosity, aeration porosity and saturated hydraulic conductivity. The bulk density was only significantly lower under Fraxinus. The E-horizon of the mull stands was lower in bulk density and higher in aeration porosity but this was linked by a reduction in water-filled porosity. The study indicated that mull-forming tree species differed in ability to improve or maintain productivity of the studied soil type.

Impact of decreasing throughfall depositions on soil solution chemistry at coniferous monitoring sites in northern Belgium

Abstract Impact of decreasing throughfall depositions on soil solution chemistry at three depths was examined in a Corsican pine (Pinus nigra Arn. ssp. laricio Poiret) stand in Ravels and a Scots pine (Pinus sylvestris L.) stand in Brasschaat within a time-span of 6 years (1992–1997). At Ravels depositions of sulphate, ammonium, nitrate, calcium, magnesium and sodium decreased by 463, 468, 169, 121, 63 and 169xa0molcxa0ha−1 per annum. At Brasschaat deposition reduction rates of sulphate, nitrate, calcium and magnesium were 198, 127, 134 and 46xa0molcxa0ha−1 per annum. In both stands the substantial reductions in inorganic nitrogen deposition were followed by a decline of nitrate fluxes leaving the forest floor and with the seepage water. The decrease of sulphate deposition since 1992 was only manifested by a decline in sulphate concentrations and fluxes during the first half of the measuring period. The increase at the end of the period could be ascribed to the fact that sulphate adsorption which was important between 1993 and 1995 finally ceased. A significant drop of calcium concentrations was discernible at both plots. Magnesium and potassium levels did only fall significantly at Brasschaat. The concentrations of base cations were largely driven by the concentrations of their counter anions, but were influenced by the base cation throughfall fluxes as well. Although a substantial reduction of throughfall acidity occurred, no improvement of the soil water acidity (acid neutralising capacity (ANC)) was noticed. ANC and molar Ca/Al followed decreasing trends at all depths in both plots. For ANC the decline was significant for the topsoil in Ravels. The decrease of molar cation Ca/Al ratio was significant for two out of three depths at both sites. The decrease was due to the drop in calcium concentrations and the raise of Altot in some horizons.

Correction to Multilayered Modeling of Particulate Matter Removal by a Growing Forest over Time, From Plant Surface Deposition to Washoff via Rainfall

Airborne fine particulate matter (PM) is responsible for the most severe health effects induced by air pollution in Europe. Vegetation, and forests in particular, can play a role in mitigating this pollution since they have a large surface area to filter PM out of the air. Many studies have solely focused on dry deposition of PM onto the tree surface, but deposited PM can be resuspended to the air or may be washed off by precipitation dripping from the plants to the soil. It is only the latter process that represents a net-removal from the atmosphere. To quantify this removal all these processes should be accounted for, which is the case in our modeling framework. Practically, a multilayered PM removal model for forest canopies is developed. In addition, the framework has been integrated into an existing forest growth model in order to account for changes in PM removal efficiency during forest growth. A case study was performed on a Scots pine stand in Belgium (Europe), resulting for 2010 in a dry deposit...

Soil Water Chemistry and Revegetation of a Limed Clearcut in a Nitrogen Saturated Forest

A clearcut stand of Pinus sylvestris in Flanders (Belgium) was limed with 3 ton/ha dolomite and reforested with Acer pseudoplatanus and Fagus sylvatica. Soil water monitoring revealed an overall decrease of ion concentrations and an annual peak in September due to seasonal nitrification. Liming reduced concentrations of NO3- and Al3+ and raised concentrations of K+ and Mg2+ and the molar ratio of (Ca+Mg)/Al. Liming also stimulated release of SO42-, which prevented a rise of pH, except during nitrification peaks. Liming had no effect on height increment of Fagus but stimulated Acer, which suffered from severe deficiencies of calcium (Ca), magnesium (Mg), potassium (K), and phosphorus (P) without treatment. Nitrogen (N) was not growth-limiting for Fagus or Acer and liming had no effect on N concentrations in leaves of both species. Liming had a strong impact on ground vegetation. Nutrient-demanding species expanded while species that tolerate nutrient-poor conditions decreased. It is argued that changes in ground vegetation had a greater impact on reduction of NO3- concentration in soil water than increased tree growth.

Relationships between Crown Condition of Beech (Fagus sylvatica L.) and Throughfall Chemistry

A two-step regression procedure was used to predict the impact of throughfall chemistry on the defoliation of Fagus sylvatica L. over a 10-year-monitoring period at three plots in northern Belgium. The impact of throughfall chemistry on crown condition was examined after accounting for influences of site, stand, climate and diseases. In a first step, defoliation was regressed on site, stand, climate and disease parameters. The residual defoliation of this standard set was correlated with 27 throughfall variables.Climatic variables of the year preceding the year of crown assessment accounted for 79% of the variation in current defoliation. Site, stand and disease factors were not included and were still part of the residual defoliation. The study of the residual defoliation revealed that high throughfall depositions of sulphate and ammonium and high throughfall ratios of SO4/Mg enhanced defoliation.

VARIABILITY OF OZONE DEPOSITION VELOCITY OVER A MIXED SUBURBAN TEMPERATE FOREST

A 10-year long dataset of half-hourly ozone (O3) fluxes was used to study the variability in deposition velocity (υd) over a mixed temperate suburban forest. Average (median) υd amounted to 0.70 (0.46) cm s-1, with day- and night-time average (median) of 0.98 (0.73) cm s-1 and 0.46 (0.30) cm s-1, respectively. It was found that the precipitation form had a marked impact on υd and the deposition efficiency (υd/υdmax), with highest values measured when the canopy was dew-wetted or covered with snow. The analysis further evidenced that traffic volume led to increased deposition due to the presence of chemical reactions between O3 and nitric oxide (NO) above the canopy surface. During the working week, daytime values of υd, υd/υdmax and the O3 fluxes (F) were found to be significantly higher than the weekend values, especially during the winter half-year. In a next step, half hourly deposition data were aggregated into day- and night-time monthly values, for a correlative study with measured environmental variables. Monthly average night-time/daytime υd and υd/υdmax were positively correlated with the relative humidity at the canopy surface (RH(z0’)) and negatively correlated with the water levels below the ground surface. During the daytime, monthly υd and υd/υdmax were additionally increased during the working-week when traffic volume was high. There existed, however, substantially different weather conditions, in which unaccounted covariates with a totally different meteorological signature controlled the υd and F. It was speculated that, among other, biogenic volatile compounds (BVOCs) could have contributed to O3 quenching in some (spring) months with severe drought stress.