Ursula Falkengren-Grerup

Soil acidification and vegetation changes in deciduous forest in southern Sweden

SummaryThirtyfour deciduous forest sites in southern Sweden, originally studied in 1949–1970, were resampled in 1984/85. The average pH change in the humus layer was-0.78 and-0.23 in soils originally studied 30–35 and 15–20 years ago, respectively. Cover changes in the field layer were measured and related to pH changes. The number of species had increased in spite of pH decreases, reaching a maximum at pH 4.0–5.0, while the total cover of the field layer was unchanged.Two groups of species showed no correlation with pH decreases in the humus layer. A large number of species had increased in cover on a majority of sites over the entire species specific pH interval, including nitrophilic species (Rubus idaeus, Chamaenerium angustifolium, Aegopodium podagraria, Stellaria nemorum). A few species had decreased in cover on a majority of sites (Polygonatum multiflorum, Pulmonaria officinalis, Dentaria bulbifera). Some species showed a covariation with pH changes, decreasing in cover in sites in the acidic part of the pH interval (Mercurialis perennis, Lamium galeobdolon, Galium odoratum, Oxalis acetosella, Luzula pilosa). Without excluding other factors, this paper suggests that the increased nitrogen deposition and the increased acidity in the humus layer might cause some of the cover changes in the presented species.

Long-term changes in pH of forest soils in southern Sweden

Changes in pH in 22 forest soils (Fagus, Carpinus, Quercus, Picea) and one Calluna health from southern Sweden were examined in 1984 by repeating studies originally made in 1949-1970. The topsoil had become more acid in 1984 with pH decreases in the old profiles of more than 1.0 in less acid soils and of 0.5 in acid soils. Younger profiles also showed pH decreases, although of a smaller magnitude. Soil pH had, on the whole, declined, and acid deposition is probably a main contributor. Acidification has also occurred in deeper horizons, most markedly in 30-35-year-old horizons. Podsols had largest pH decreases in deeper horizons, and grey-brown soils in the upper profile.

Changes in acidity and cation pools of south Swedish soils between 1949 and 1985

Abstract The pH of south Swedish soils have decreased considerably during the last 15–35 years. The decrease has occurred throughout the soil profile, not only in the rhizosphere, and is particularly marked in the originally less acid soils. The pH decrease was accompanied by considerable losses of exchangeable Na, K, Mg and Ca, as well as of Zn and (in the originally less acid soils) of Mn. The changes can be prognosticated from the current relationship between soil pH and base saturation and from budget calculations based on lysimeter data.

Herb layer vegetation of south Swedish beech and oak forests—effects of management and soil acidity during one decade

Abstract Effects of forest management and soil acidity on herb layer vegetation were studied after 10 years on 190 permanent plots in south Swedish beech (Fagus sylvatica) and oak (Quercus robur) forests. Species richness generally increased with management intensity, mainly due to establishment of ruderal species from the seed bank. Species richness of the typical forest flora was unaffected by management. Moderate management of oak stands favoured several species which are commonly found in semi-natural pastures. Classification and ordination of the data showed that the main floristic gradient within Swedish beech and oak forest vegetation is related to soil acidity. Species richness of the typical forest flora was strongly positively correlated with soil pH in beech forests, but this correlation was weaker in oak forests. The number of herbaceous plants with a broader habitat range increased with pH only in the oak forest plots. Long term changes in the forest environment, which may affect the vegetation, are the decline of grazing 150-50 years ago and soil acidification mainly caused by atmospheric pollutants during the last 50 years. In the one-decade perspective of this study, however, we did not find a general trend towards a more acid-tolerant flora. Neither could we find a general decrease of pasture species in currently ungrazed oak stands. The results indicate that most typical forest plants are well adapted to and partly depend on occurrence of canopy gaps and soil disturbance. If canopy thinning is followed by periods of canopy closure the characteristic shade tolerant flora of Swedish beech and oak forests may be able to persist as long as soil chemical limits of existence are not exceeded.

Interspecies differences in the preference of ammonium and nitrate in vascular plants

Three solution experiments were performed to test the importance of NH4+versus NO3-+NH4+to growth of 23 wild-forest and open-land species, using field-relevant soil solution concentrations at pH 4.5. At N concentrations of 1–200 μM growth increased with increasing N supply in Carex pilulifera, Deschampsia flexuosa, Elymus caninus and Bromus benekenii. Geum urbanum was the most N demanding species and had little growth below 200 μM. The preference for NH4+or NO3-+NH4+was tested also at pH 4.0; no antagonism was found between NH4+and H+, as indicated by similar relative growth in both of the N treatments at both pH levels. Growth in solution with NH4+relative to NO3-+NH4+, 200 μM, was negatively related to the mean pH of the field occurrence of the species tested; acid-tolerant species grew equally well with only NH4+as with NO3-+NH4+(Oxalis acetosella, Carex pilulifera, Festuca gigantea, Poa nemoralis, Deschampsia flexuosa, Stellaria holostea, Rumex acetosella), while species of less acid soils were favoured by NO3-+NH4+(Urtica dioica, Ficaria verna, Melandrium rubrum, Aegopodium podagraria, Geum urbanum, Bromus benekenii, Sanguisorba minor, Melica ciliata, Silene rupestris, Viscaria vulgaris, Plantago lanceolata). Intermediate species were Convallaria majalis, Elymus caninus, Hordelymus europaeus and Milium effusum. No antagonism between NH4+and Ca2+, Mg2+ and K+ was indicated by the total uptake of the elements during the experiment.

Modelling long-term cation supply in acidified forest stands

A dynamic soil chemistry model was used to explain the observed decrease in soil base saturation between 1949 and 1984 at three stands in southern Sweden. The results show that acid deposition has caused soil acidification. The model, SAFE (Soil Acidification in Forest Ecosystems), includes the fundamental physical processes such as leaching and accumulation, and chemical processes such as cation exchange, mineral weathering, nutrient uptake and solute equilibrium reactions. The sources and sinks of base cations in the soil system were quantified, showing that weathering, deposition of base cations and depletion of exchangeable base cations supply cations to the soil solution in similar amounts in the upper 1 m during the acidification phase. This demonstrates that budget studies alone cannot be used to distinguish between long-term capacity to resist acidification, represented by weathering, from short-term buffering caused by cation exchange.

Changes in soil, vegetation and forest yield between 1947 and 1988 in beech and oak sites of southern Sweden.

Abstract The upper C-horizon was analyzed in 19 beech and oak stands in southern Sweden over a period of 40 years. The results confirmed a study of ten other stands of the same period. The exchangeable base and metal cations had decreased, on average, in the following order: Na>Mn>Zn>Ca>, Mg>K and 20–70% was recovered in 1988. Exchangeable Al had doubled. In spite of soil acidification, which according to earlier results should also have occurred in the upper soil horizons, many field-layer species had increased in cover. Among these were several nitrophilous species. However, a few species had decreased in cover, especially in the most-acid pH range. The yield of beech and oak has been measured since 1945. Beech had increased more than expected in both basal area and site index (height) in 1976–1985, while oak showed no stable changes in yield. The simultaneous increase of nitrogen deposition and decrease of soil macronutrients leads to the conclusion that the higher availability of N has been of greater influence on the ground flora and yield of beech than the loss of other macronutrients.

Regional differences in floristic change in South Swedish oak forests as related to soil chemistry and land use

Abstract. Changes of the ground layer vegetation between1983 and 1993 were studied on permanent oak forest plots inSkane and eastern Smaland, two regions of South Sweden richin oak but with different climatic conditions. 79 of the 123more common species differed considerably in frequencybetween Skane and Smaland. The oak forests in Skane con-tained more typical forest species, whereas the number oflight-demanding grassland species was higher in Smaland.Almost half of the more common species showed significantchanges in frequency between 1983 and 1993. Several speciesof clearings and some light-demanding grassland species in-creased their frequency in Skane. They were probably fa-voured by canopy thinning which occurred in 65 out of 95permanent plots. Only two species decreased in frequency inSkane, but 14 species showed a decrease in Smaland. All weretypical grassland species and their decline may be regarded asa long-term response to ceased grazing and tree canopy clo-sure as almost no tree cutting occurred during the study periodin Smaland. Total species richness increased with manage-ment intensity in Skane. This was due to decreasing specieslosses and increasing establishment of new species at intensemanagement. A small general increase in species numberswas recorded in Smaland. Species richness was more closelyrelated to soil pH in Skane than in Smaland. The floristicvariability between the oak forest plots was closely related tosoil pH in both Skane and Smaland. We suggest that changesof light conditions as a result of changes in forest managementare important for current secondary succession in South Swed-ish oak forests, whereas the general floristic pattern is to alarge extent controlled by soil acidity.Keywords: Detrended Correspondence Analysis; Forest man-agement; Ground layer vegetation; Secondary succession;Soil acidity; Species richness.Nomenclature: Lid (1987).

Experimental evidence for the relative sensitivity of deciduous forest plants to high soil acidity

Abstract Thirteen species of deciduous forest vascular plants were established from seeds: Brachypodium sylvaticum, Carex sylvatica, Circaea lutetiana, Deschampsia flexuosa, Galium odoratum, Lamium galeobdolon, Lathyrus vernus, Luzula pilosa, Milium effusum, Poa nemoralis, Sanicula europaea, Stellaria holostea and Stellaria nemorum. An acid beech forest soil was variously treated with carbonates (CaCO3 + MgCO3 or SrCO3) to obtain a soil solution pH of 3.3–5.2. The experimental results were compared with the field distribution of the same species in 230 south Swedish deciduous forests with regard to soil pH. In general, the species reacted to increasing soil pH in accordance with their field distribution. Addition of SrCO3 was almost equally effective as CaCO3 + MgCO3 (both at pH 4.2 in the soil solution) in promoting establishment and growth, whereas most species failed in the untreated soil (pH 3.3). There were no indications that the Ca or Mg concentrations of the soil solution were below minimum or even suboptimal for plant growth in the untreated soil. Within the pH range (pH ⩽ 3.5–4.3) which proved critical to establishment and growth in most of the species, the reactive Al3+ concentration of the soil solution did not vary significantly. It is suggested that the high acidity of the rhizosphere solution, possibly aggravated by Al3+, obstructed the uptake or retention of mineral nutrients by the roots in the untreated acid beech forest soil.

Nitrogen mineralisation in deciduous forest soils in south Sweden in gradients of soil acidity and deposition

Abstract Net nitrogen mineralisation was studied in 600 deciduous forests in four geographically separate regions of southern Sweden. The total nitrogen deposition in the forests varied between 7 and 17 kg ha −1 year −1 . The most frequent canopy-dominant tree species was Quercus robur , others being Acer platanoides, Carpinus betulus, Fraxinus excelsior, Tilia cordata and Ulmus glabra . Soil pH (0.2 M KCl), varied between 3.1 and 7.7 and the C/N ratio between 8 and 50 in soil sampled 5 cm below the litter layer. The potential net mineralisation rate, measured in a 15-week laboratory incubation experiment, could be explained to 20% by soil pH and to 4.5. The most striking finding was that rates of net nitrogen mineralisation and nitrification were by far the highest in the southernmost region, especially in the most acid soils, rates about twice as high as in the other regions. Sites that differed in the dominant tree species did not differ in net nitrogen mineralisation. Nitrogen deposition explained 30% of the variation in mineralisation rate. It is suggested that the high nitrogen deposition in recent decades has favoured ammonification through increasing the nitrogen pool in the soil and altering the quality of the organic matter, the microbial community adapting to the acidified soils and the increased nitrification.