Lieven Nachtergale

Earthworm biomass and species diversity in windthrow sites of a temperate lowland forest

Summary In temperate forests, disturbance by uprooting of trees is a key process in maintaining species richness and diversity. Nevertheless, very little is known about the changing role and abundance of earthworm communities in different windthrow microsites. The aim of the study was to find (i) whether single-tree uprooting causes significant changes in earthworm biomass and species composition and (ii) which changes in chemical and physical soil properties can be related to it. Twelve single-tree gap sites in an Ulmo-Fraxinetum aceretosum were selected, six sites locally dominated by beech ( Fagus sylvatica ) and six by poplar ( Populus x euramericana ). At each site, 7 microsites were sampled for soil chemical and soil physical properties: undisturbed soil beneath closed canopy, undisturbed soil beneath the gap in the canopy layer, the outer side of the pit, the inner side of the pit, the soil fallen from the mound into and away from the pit, and the mound itself. At six sites also earthworms were collected. The impact of microsite on earthworm biomass and species diversity was more important than the impact of tree species. A significant decrease in earthworm biomass and species number was detected from closed canopy over gaps to zones with soil disturbance and finally to windthrow mounds which never contained earthworms. The most pronounced reaction was the negative impact of uprooting on endogeic biomass. Epigeic biomass or species number of any ecological group changed more moderately. Six years after uprooting, microsites with direct soil disturbance were still adverse for earthworms though some – epigeic – species could profit from the absence of competitive species. It is concluded that in temperate lowland forests, the early uprooting phases induce changes in earthworm communities due to changes in soil physical parameters and food availability.

Soil acidification along an ammonium deposition gradient in a Corsican Pine stand in northern Belgium

Abstract In a homogeneous Corsican pine ( Pinus nigra ssp laricio ) stand, situated in a region of intensive livestock breeding, effects of different NH x doses on soil acidification were studied. Throughfall collectors were placed every 25 m on a transect of 1.4 km, oriented according to the dominant wind direction. The throughfall water was analysed on NH 4 + . A permanent monitoring plot is situated in the middle of the transect where quantity and chemical composition of different water fractions are monitored fortnightly. Along the transect, soil samples of the upper mineral soil (0–10 cm) were taken and analysed on pHH 2 O and pHKCl. The measured deposition of NH 4 + N was very high, especially in the forest edge at the prevailing wind direction (55 kg ha −1 year −1 ), where up to twice as much NH 4 + N was found as in the monitoring plot. A forest edge zone of 180 m with significantly higher NH 4 + deposition could clearly be delineated. Serious indications were found that all NH 4 + was nitrified but that this process was slowed down. The variation in NH 4 + depositions was clearly reflected in the state of soil acidification: pHH 2 O and pHKCl values varied between 3.1 (edge) and 3.8 (centre), and 2.4 (edge) and 2.8 (centre) respectively.

Increase of biodiversity in homogeneous Scots pine stands by an ecologically diversified management

Three important parameters of biodiversity in first generation Scots pine (Pinus sylvestris) forests on sandy soils have been evaluated: herbal layer diversity, natural regeneration and stand structure. The study took place in the Belgian Campine region, where the original oak–birch forest, degraded to heathlands in the course of time, were finally replaced by monocultures of Scots pine. These first generation pine forests are characterized by a low biodiversity. In maturing stands of this type, however, a spontaneous increase of biodiversity is noticed. Herbal species richness is very limited in all age classes. Different natural regeneration patterns are found. Referring to stand structure, the lengthening of the rotation favours the ingrowth of several hardwood species. As a consequence, the homogenous Scots pine stands are gradually and spontaneously transformed into heterogeneous mixed stands, featuring a noticeable increase in biodiversity. Selected human interventions may further increase biodiversity. The fundamental management principles are discussed: avoidance of major disturbances, lengthening of the rotation period, use of native tree species and natural regeneration, protection of microbiotopes and permanent monitoring.

Comparison of nitrate leaching under Silver birch (Betula pendula) and Corsican pine (Pinus nigra ssp laricio) in Flanders (Belgium)

In a forest in Flanders (Belgium), situated in a region of intensive livestock production, comparable stands of Corsican pine and silver birch were studied for (1) NH4+ and NO3- concentrations in throughfall water and soil solution and (2) depositions and leaching of NH4+ and NO3- to groundwater. In each stand, throughfall collectors and porous cup lysimeters at three depths (0.1m, 0.5m and 1m) were installed in three replicated sets. Throughfall concentrations of ammonium and nitrate were significantly different for both species as well as soil solution concentrations of nitrate at all depths. Under pine, nitrate concentrations of the soil solution at 1m depth clearly exceeded the Belgian critical level for drinking water (50 mg.1-1). Under birch, this level was only sporadically exceeded. During the sampling period, the depositions of NH4+-N and NO3--N reached respectively 21.6 kg/ha and 6.3 kg/ha under birch and 81.3 and 15.2 kg/ha under Corsican pine. Nitrate-N leaching under silver birch amounted 25.4 kg/ha whereas 56.4 kg/ha was measured under Corsican pine.

Spatio-temporal litterfall dynamics in a 60-year-old mixed deciduous forest

IntroductionTo increase our understanding of litterfall dynamics in mixed-species forests, seasonal and annual variations in litterfall mass and nutrient concentrations were assessed for a 60-year-old spontaneously developed forest dominated by silver birch (Betula pendula Roth), pedunculate oak (Quercus robur L.), and northern red oak (Quercus rubra L.) in Belgium.ResultsTotal quantities and seasonal patterns of most litterfall fractions were similar over the 29-month study period, but the species differed in start and duration of their leaf shedding period. The spatial distribution of litterfall persisted over the years for leaves, but not for total litterfall because of the varying spatial pattern of fallen twigs and reproductive structures. Consequently, predicting humus build-up based on short-term litterfall measurements may be difficult in mixed forests. Nutrient concentrations in leaf litter differed considerably between the species and throughout the year, but the seasonal pattern did not depend on the species. Betula returned significantly more nutrients to the soil per mass unit than Quercus, except for sodium.ConclusionAs the present stand conditions only allow recruitment of Q. rubra, Betula is being outcompeted, which decreases the nutrient return to the soil and may negatively affect biogeochemical cycling.

Medium-term evaluation of a forest soil restoration trial combining tree species change, fertilisation and earthworm introduction

A mixed stand of red oak (Quercus rubra) and common beech (Fagus sylvatica) on a compacted and acidified sandy loam soil was harvested and reforested with ash (Fraxinus excelsior in 1992. The ecosystem restoration trial in this newly established ash plantation included 180 trees and was set up in a block design with 4 blocks, 3 experimental groups per block and 15 trees per experimental group. Experimental groups were: (1) application of P, K, Ca and Mg fertiliser to the planting pit; (2) combined application of fertiliser and earthworms to the planting pit; and (3) a control without additional restoration measures. Fertiliser application consisted of 500 g dolomite, 100g Thomas slags and 100g kieserite; earthworm introduction consisted of 40 individuals, being 20 anecics (Lumbricus terrestris L. and Nicodrilus longus Ude) and 20 endogeics (Aporrectodea caliginosa Sav., Aporrectodea rosea Sav. and Allolobophora limicola Michaelsen). Tree growth was monitored annually. The control trees failed to grow and died after two years. Excellent growth was found for treated trees, and treatment-related growth patterns were observed: fertilised trees grew faster than fertilised trees with earthworms during the first two years, with the trend reversed from year 4 onwards. Although this trend suggested that introduced earthworms provided a more sustained response to fertiliser, this was not conclusively confirmed by an evaluation of 24 trees 10 years after planting (based on nutrient concentration in above-ground biomass and soil, litter biomass, earthworm biomass, and aggregate stability of organic particles in the soil); although statistically significant differences were found between treated and untreated plots, differences between fertilised plots with and without earthworms were not significant. Endogeic earthworms recolonised most fertilised plots, with or without earthworm introduction. Anecic earthworms did not colonize any plots. Although our findings suggest that earthworm introduction might contribute to a sustained fertiliser response in ash trees, more experiments are needed to demonstrate the precise role of earthworm introduction as part of integrated forest soil restoration.