Edward P. Farrell

European forest ecosystems : building the future on the legacy of the past

Abstract The viability of the many civilisations of Europe has depended, to a very large extent, on an adequate supply of wood. In the Ancient World, this supply was secured through the exploitation of forest reserves, the conquest of new territories and, when these opportunities no longer presented themselves, through the conservation of diminishing resources. Ultimately, civilisations collapsed because of the shortage of wood. Although some silvicultural techniques were known in the pre-Christian era, the scientific management of forests was not widely practised until the late 18th century. It is argued that the controlled exploitation of ‘nature’, on sustained yield principles, only became possible when men came to view the forest, not as a nuisance, an Arcadia or a pagan horror, but as a centre of wood production, a biological factory. The emergence of scientific forestry, however, did not put an end to the exploitation of forest resources. Unregulated felling and traditional practices such as litter raking exerted an insidious, negative influence on the fertility of the soil. The impact of human exploitation has often been underestimated by scientists, in recent decades, in particular, in the context of forest decline. While sustainable management, seen as sustained yield of wood supply, has been practised in forestry for centuries modern ideas of sustainability are broader in scope, embracing all the goods and services of the forest. Increasingly, forests are being managed as multifunctional ecosystems, often for amenity purposes. Forest ecosystem research, which developed from a range of traditional, highly focused disciplines, requires, if it is to make a meaningful contribution to forest management, long-term interdisciplinary studies. It provides the basis for ecologically intelligent management decisions and as such, is central to the development of sustainable forestry management. Central to the successful implementation of research findings is their efficient transfer from the researcher to the manager. If the research community identifies such an interchange as an important part of their duties, it will be a decisive step towards the better use of forests in Europe. It is only by deepening our knowledge of the past, accepting the challenge of the present and acknowledging that, as researchers, we have also a responsibility to communicate with users, that we can foster the growth in wisdom which is fundamental to the wise use of Europe’s forests in the next millennium.

Atmospheric deposition and soil acidification in five coniferous forest ecosystems: a comparison of the control plots of the EXMAN sites☆

Abstract The five sites of the EXMAN project conducted in Ireland, Denmark, Netherlands, Northern and Southern Germany were compared regarding (1) the marine and anthropogenic components of deposition, (2) the acidification of soil and consequences for Al status, and (3) the nitrate load of seepage. The marine deposition decreases with decreasing rates from the coast inland. It vanishes at a distance of more than 600 km of the sea. The most part of sea salt input in conifer forests is due to dry deposition. Sea salt Mg2+ in throughfall near the coast by far exceeds the demand of trees. The anthropogenic deposition of N and S at the Irish site is about 20%; at the Danish site, about 60% of that at the inland sites. At the Irish site, the anthropogenic deposition is the two- to threefold of the preindustrial deposition. NH4+ prevails at all sites as acid component in throughfall, controlling the pH values that vary between 3.9 and 5.3. In drainage water leaving the root zone, the mean pH values vary only between 4.1 and 4.4. Proton budgets for the forest floor have shown that N turnover dominates as a proton source at the inland sites, whereas at the coastal sites the dominant source results from the production of organic acids. The main proton sink is due to H+ output. Proton budgets for the total root zone indicate that an important proton gain is caused at the most sites by proton excretion of the roots in connection with base cation uptake. In addition, at some sites, the release and output of SO42− appears to be a considerable proton source. At all sites, buffering and output of Al represent the main proton sink. The Al solubility of each layer of the EXMAN sites was compared with the solubility of a synthetic gibbsite. Al saturation exists only at the lower boundary of the main root zone. In the soil layers above, there is an undersaturation that is largest at the humus layer efflux. The relationship between Al dissolved and Al adsorbed, both expressed in cation percentages, is rather weak for the coastal sites in contrast to the inland sites. The importance of the ionic strength effect of sea salt input is discussed with respect to the deep reaching Al saturation and acidification of the soils. Moderate to strong Al stress is indicated at all sites in the mineral soil. The nitrate load of the seepage water depends on the N status of the ecosystems rather than N deposition when the throughfall exceeds 20 kg N ha−1 yr−1. An attempt was made to classify the EXMAN sites with respect to the N status with the aid of the N flux gradient by depth.

Effect of drought experiments using roof installations on acidification/nitrification of soils

Within the framework of the EU-funded EXMAN (EXperimental MANipulation of Forest Ecosystems) project drought experiments were conducted at four different European Norway Spruce (Picea abies (L.) Karst.) plantations in the year 1992–1995. The aim of the project was to investigate if there is an additional risk of soil acidification due to nitrification/acidification pulses after extended periods of summer droughts. The sites included (Ballyhooly/BH, southwest of Ireland. Klosterhede/KH, west coast of Denmark, Hoglwald/HW, northwest of Munich, and Solling/SL, central Germany) cover considerable gradients of climatic and air pollution regimes. Artificial droughts were produced by using different types of roof constructions installed below the forest canopy (non-permanent constructions in BH and HW, permanent installations in KH and SL). Each drought was started in spring time and dry conditions were maintained until the soil water tension was below a potential of −700 hPa at 70 cm depth in the mineral soil. Results given are focused on changes in the soil solution concentrations during the rewetting of severely dried out soils. No marked nitrification pulses were observed after any of the droughts carried out at any site. Only single lysimeters/sample locations showed the hypothesized reaction with increasing aluminum concentrations and decreasing pH values, but spatial heterogeneity was high during rewetting. In the first soil solution samples after the drought, occasionally distinct peaks of NH4+, DOC and K+, and partly also Norg and HPO42− appeared. For the BH site the respective potassium concentrations increased 10 to 20 times compared to the level of the control plot. Presented data indicate a certain potential for nitrification pulses at the BH and KH site, but probably due to a fast root uptake, below the rooting zone no nitrate was determined. At the HW site, the drought induced reactions in the soil solution composition were only visible in humus water samples. At SL, nitrate concentrations were generally reduced at the drought plot. During rewetting in 1992 samples from a single lysimeter indicated a clear nitrification pulse. Applied flux calculations for SL showed a significant increase of the nitrate budget but a distinct decrease of the potassium budget. It is concluded that drought phases can influence the element cycling, but there seems to be no risk that forest soils will be subjected to pronounced acidification after summer droughts.

Interactions between society and forest ecosystems: challenges for the near future

Abstract European forestry is rich and complex both from the ecological and the socio-economical point of view. In this paper, we discuss the human interaction with the forest today, including the influence of management systems and suggest potentially rewarding areas for future ecological research. Changing patterns of land use and the impact of socio-economic factors on management practices have brought about major changes in forest ecosystems. Abandoned farmland, particularly in temperate and northern Europe, is undergoing a process of colonisation by tree and shrub species with implications for carbon sequestration, wood production, regional biodiversity and soil stability. In southern Europe, desertification is occurring particularly where the frequency of fire and/or grazing pressure are high. Multiple use of the forest has usually been described as a way of combining timber utilisation with other uses of forest products and forest land. There is a need to study the influence of multiple use management on ecosystem stability and social structures, especially in regions where forest areas and human settlements are situated in proximity to one another. Fundamental to a discussion of these issues are questions concerning the necessity for forests, the optimum proportion of the land that should be under forest and the appropriate level of management intervention in these forests.

Carbon dioxide dynamics of a restored maritime peatland

ABSTRACT The restoration of cutaway peatlands provides an opportunity to return the carbon (C) sink function and to examine the influence of climate on peat formation and C accumulation. We studied CO2 exchange dynamics in 2002 and 2003 at a rewetted cutaway peatland located within the temperate maritime climatic zone. Gross photosynthesis (PG), ecosystem respiration (RTOT), and net ecosystem exchange (NEE) were observed in a range of microsites representing a hydroseral succession gradient: Typha latifolia – Phalaris arundinacea, Eriophorum angustifolium – Carex rostrata, and Juncus effusus – Holcus lanatus vegetation communities and areas of bare (unvegetated) peat. Annual rainfall was 26% higher in 2002 and 4% lower in 2003 than the long-term average and influenced water table position at all microsites. Observed instantaneous CO2 fluxes varied temporally and spatially at all microsites. Modelled PG was strongly dependent on irradiation (Photosynthetically Active Radiation) and the Vascular Green Area index (VGA). RTOT was influenced by the soil temperature at 5 cm depth (T5cm) and the water table position. All microsites were net sources of CO2 in both years of the study, and higher losses (with the exception of Juncus / Holcus) were observed in 2003 at all microsites. In general, losses followed the trend Juncus / Holcus > Phalaris > Typha > bare peat > Eriophorum– Carex in 2002 and Phalaris > Juncus– Holcus > Typha > Eriophorum / Carex > bare peat in 2003. Losses ranged from −163 to −651 g CO2– C·m−2·y−1 in 2002 and −308 to −760 g CO2 – C·m−2·y−1 in 2003. Considerable wintertime losses were observed at all microsites. The results from this study suggest that these peatlands are vulnerable to interannual variations in climatic inputs and that future predictions of climatic change may make restoration of the C sink function in cutaway peatlands in the temperate maritime climatic zone a considerable challenge in the years ahead. Nomenclature: Moore, 1982.

Forests of the temperate region: gaps in knowledge and research needs.

Abstract Gaps in knowledge of current and past forest ecosystem research in the temperate zone of Europe are discussed and research priorities are defined. Since the last Ice Age the forest ecosystems of this region have undergone fundamental changes mainly caused by climatic and anthropogenic influences. Hence, today’s temperate forests hardly represent the natural ecosystem development state. However, the implementation of the sustainability concept as the dominant principle of modern forestry in the early 19th century allowed to predict and maintain forest productivity in the longer run. Despite timber production forest management has to cover public demands such as recreation, groundwater protection, and biodiversity. But it is still unclear whether all these requirements can be fulfilled economically and in agreement with the concept of ecological sustainability. Even though the understanding of forest ecosystems has increased enormously in recent decades, this improved understanding has resulted, somewhat paradoxically, in a demand for further knowledge, both more precise in nature and broader in scope. The ongoing discussion on forest stability is based on the experience that predictions of an enhanced dieback of forests did not come true. On the contrary, the growth of many European forests has been accelerated since several decades, illustrating a fundamental lack in the understanding of the productivity of forest ecosystems. In conclusion, specific gaps of knowledge are identified with regard to (i) the impacts of elevated CO 2 and nitrogen on the stability and resilience of forest ecosystems, (ii) the functioning of old-growth (semi-)natural forests and the development of scientifically based concepts for forest transformation, (iii) the multiple interactions between forest and adjacent management systems, (iv) the afforestation of set-aside and abandoned areas, and (v) the intensification, methodological complementation and diversification of the monitoring of forest sites belonging to the EU ‘level-two-programme’.

Biological response of five forest ecosystems in the EXMAN project to input changes of water, nutrients and atmospheric loads

Abstract In five coniferous forest ecosystems in Europe, water and nutrient supply, as well as atmospheric loads, were manipulated for 3 or 4 years. Water supply was optimised and nutrients were added according to tree demand in optimal proportions relative to the ambient N supply. Tree growth was strongly enhanced by optimal water supply but not further enhanced by nutrient additions. The nutritional balance in trees was improved for P and K. The increased water and nutrient supply retarded needle shedding in autumn and diminished root production. To date, the manipulated decrease in N input to the soil has decreased the N content in needles in one stand. Water additions tended to lower N contents at two sites. Large applications of N increased N content in needles even though the N nutrition was already optimal. Liming with dolomite stimulated tree growth only in the nutrient-poor stand, but has generally increased Ca content in needles. The number of species and cover of understorey vegetation has increased considerably by liming and, in some cases, by water addition. Ecosystem manipulation experiments have been shown to be a useful tool for the quantification of the growth effects of traditionally limiting factors. Additionally they give indications of the effects on forest ecosystem processes of future changes in atmospheric loads.

A comparison of sites in the EXMAN project, with respect to atmospheric deposition and the chemical composition of the soil solution and foliage☆

Abstract Forest stands, throughfall and the composition of the soil solution in six coniferous forest plantations in Europe were compared as part of the EXMAN project, which was established to quantify biogeochemical cycles and the effects of atmospheric deposition on coniferous forest ecosystems. Even though the EXMAN stands and sites are broadly similar, they represent a wide range of climatic conditions and levels of pollutant deposition. The EXMAN project incorporates treatment of forest plots and in this paper the untreated control plots are compared. The results show marked differences in ionic composition of water between sites, most clearly expressed in throughfall fluxes. At the German and Dutch sites, ionic inputs demonstrate a strong human influence. Throughfall at the Danish and Irish sites is dominated by ions of marine origin. Hydrogen ions are not the most important cations in precipitation at any site, and at only one site (Solling, Germany) was the hydrogen ion flux in throughfall greater than in precipitation. The influence of atmospheric deposition on the composition of the soil water is very evident for most major ions. Exceptions to this are ammonium and nitrate, the complexity of whose behaviour demonstrates the need for greater understanding of nitrogen transformation and uptake in coniferous forest ecosystems.

Atmospheric deposition in maritime environments and its impact on terrestrial ecosystems

Seasalts are the dominant chemical constituents of precipitation in maritime regions. Dry deposition of these salts is also an important process and consequently, canopy interception by forest ecosystems greatly augments wet deposition. The separation of seasalt from non-seasalt sulphur is usually accomplished by reference to the concentration ratio of other major component ions of seawater, such as sodium-, chloride-, or magnesium-to sulphate. Biogenic sulphur, from the oceans or from terrestrial ecosystems is sometimes of importance in maritime regions. Seasalts, which dominate atmospheric deposition in maritime regions can induce short-term acidification in surface waters as a result of ion-exchange reactions following storm events. The results of one large storm in western Ireland in 1991 and the recovery process in a peat soil were clearly discernible in soil water analysis. The seasalt impact on acid mineral soils can be seen in the exchangeable sodium levels and the degree of base saturation of these soils.

A survey of lakes in the Republic of Ireland: hydrochemical characteristics and acid sensitivity.

Abstract In 1997, as part of a national program to determine and map critical loads, a lake survey was carried out in the Republic of Ireland. In total 200 lakes were sampled, which represents approximately 3.3% of the total lake population. The majority of lakes were situated in remote, high-altitude, acid-sensitive areas along the coastal margins of the country. Lake chemistry was dominated by marine inputs. Approximately 50% of the lakes had DOC > 5 mg L−1 due to the presence of organic soils in a large proportion of the catchments. Nonmarine sulfate concentrations were at background levels (< 20 µeq L−1) in 50% of the lakes. Exceedance of critical load was observed in 7% of the sampled lakes (13 lakes). However, there are uncertainties in the critical load calculations due to the interference of sea salts and organic acids; accurate estimation under such conditions requires long-term lake and deposition chemistry.