Showing papers by "Swiss Federal Institute for Forest, Snow and Landscape Research published in 1995"

Unusual twentieth-century summer warmth in a 1,000-year temperature record from Siberia

Abstract: IN the current debate on the magnitude of modern-day climate change, there is a growing appreciation of the importance of long, high-resolution proxies of past climate1–3. Such records provide an indication of natural (pre-anthropogenic) climate variability, either singly at specific geographical locations or in combination on continental and perhaps even hemispheric scales4. There are, however, relatively few records that are well dated, of high resolution and of verifiable fidelity in terms of climate response, and conspicuously few that extend over a thousand years or more5. Here we report a tree-ring-based reconstruction of mean summer temperatures over the northern Urals since AD 914. This record shows that the mean temperature of the twentieth century (1901–90) is higher than during any similar period since AD 914.

The climate-carbon isotope relationship in tree rings and the significance of site conditions

Abstract: Considerable complexity exists regarding the relationship between tree ring δ 13 C and climate. We proceed from the theoretically derived and experimentally confirmed finding that the relative humidity of the atmosphere but also the soil water content can influence the stomatal opening of plant leaves and consequently the δ 13 C of photosynthetically fixed carbon. Therefore, the potential to reconstruct humidity variations by δ 13 C in tree rings should depend on the water conditions at the site where the trees are growing. We analysed δ 13 C series (3-year ring samples) of cellulose of beech trees ( Fagus silvatica ) covering the time period from 1934 to 1989 for 3 sites in Switzerland: a relatively dry and a humid site close together and another dry site 30 km distant. The δ 13 C series from the two dry sites are closely interrelated and are inversely correlated to the total precipitation amount of the months May + June + July This is most expressed for first differences, i.e., differences of consecutive values, while the long-term trends are more strongly influenced by biological effects. A multivariate analysis shows that at the dry sites, δ 13 C is relatively high for dry/warm summers and low for cool/wet summers. The respective correlations for the humid site are less distinct. In addition, we compared average δ 13 C values for beech, pine and spruce trees from sites differing in soil moisture conditions. For all species we found that the drier the sites the more positive the tree δ 13 C values are. We conclude that at relatively dry sites in temperate-moist climatic conditions, short-term precipitation variations can be reconstructed by δ 13 C measurement on tree rings of beech and probably also of the conifers pine and spruce. DOI: 10.1034/j.1600-0889.47.issue3.4.x

Diurnal changes in the radius of a subalpine Norway spruce stem : their relation to the sap flow and their use to estimate transpiration

Abstract: Diurnal changes in the stem radius of a subalpine mature Norway spruce were measured simultaneously with the flow of sap in xylem. Matric potentials in the soil were > -35 kPa. The kinetics of the flow were closely related to the changes in the radius of the stem resulting from depletion of its extensible tissues. The radius of the stem oscillated daily and, fairly independently of this, fluctuated over several days. The daily shrinkage (Δd) was correlated with the daily flow through its base (Qd). When the crown transpired little and was nearly saturated during rainy days, ASd tended to increase relative to Qd. Using a linear relation, the estimates of flow by Δd deviated less than ± 10% from the values measured by heat balance, provided that the periods of calibration in their ratio of dry to rainy days were comparable to those estimated. If the two periods differed in this respect, the estimates of flow deviated up to 42%. A quadratic relation yielded estimates that depended less on weather. It reduced maximal deviations to ±22%. Since Δd additionally may represent the time pattern of the daily transpiration better than Qd, analysing changes in the radius of stems may supplement or partly replace measurements of sap flow in stems.

Nighttime exposure to ozone reduces whole-plant production in Betula pendula.

Abstract: For 20 weeks during the growing season, cuttings of one birch clone (Betula pendula Roth.) were exposed in the Birmensdorf fumigation chambers to O(3)-free air (control) or 75 nl O(3) l(-1). Ozone was supplied either from 1900 until 0700 h (nighttime regime), from 0700 until 1900 h (daylight regime), or all day (24-h regime). By autumn, reductions in whole-plant biomass production, root/shoot biomass and stem weight/length ratios were evident in all three O(3) regimes. The reductions in cuttings receiving the 24-h O(3) treatment were about twofold larger than in cuttings receiving the daylight O(3) treatment. Stomata were open at night, and stomatal conductance was about 50% of its maximum daytime value. We calculated that the rate of O(3) uptake into leaves in the dark approached 4 nmol m(-2) s(-1). Whole-plant production and carbon allocation were more sensitive to O(3) during the night than during the day; however, O(3) exposure caused similar visible leaf injury in both of the 12-h regimes, although the leaves exposed to O(3) at night exhibited delayed O(3)-induced shedding. Overall, changes in production and carbon allocation were determined by the external O(3) dose rather than by the kind of O(3) exposure, indicating that, at the seasonal scale, the internal dose of ozone that was physiologically effective was a constant fraction of the external O(3) dose. We conclude that nighttime O(3) exposures should be included in the daily time period for determining critical concentrations of O(3) causing injury in trees.

Early Development of Transplanted Isidioid Soredia of Lobaria Pulmonaria in an Endangered Population

Abstract: Vegetative diaspores of Lobaria pulmonaria were transplanted to previ- ously uncolonized trees The early development of the corticated but otherwise non-stratified isidioid soredia was studied mainly by low-temperature scanning electron microscopy Anchoring hyphae developed from cortical hyphae after 2-4 months and later apical or lateral pseudomeristematic growth zones were formed After 15 months the growth zones further differentiated into 0-5-mm-broad lobes and revealed a stratified thallus typical for this foliose epiphytic lichen species The experiment showed that the small population size of L pulmonaria was limited by the low reproductive potential of the species and that it might fail to compensate for a relatively high disturbance, natural or anthropogenic, in the stand U 1995 The British Lichen Society

Signal strength, timing, and self-deafening: the evolution of echolocation in bats

Abstract: We propose that the ancestors of bats were small, nocturnal, sylvatic gliders that used echolocation for general orientation. Their echolocation calls were short, low intensity, broadband clicks, which translated into a very short operational range. In the lineage that gave rise to bats, a switch to stronger, tonal signals permitted the use of echolocation to detect, track, and assess flying insects in subcanopy settings. We propose that these animals hunted from perches and used echo- location to detect, track, and assess flying insects, which they attacked while gliding. In this way, the perfection of echolocation for hunting preceded the appearance of flapping flight, which marked the emergence of bats. Flapping flight had appeared by the Eocene when at least eight families are known from the fossil record. Stronger signals and adaptations to minimize self-deafening were central to the perfection of echolocation for locating flying prey. Echolocation constituted a key innovation that permitted the evolution and radiation of bats. At the same time, however, its short effective range imposed a major constraint on the size of bats. This constraint is associated with flight speed and the very small time intervals from detection of, and contact with a flying target. Gleaning and high duty cycle echolocation are two derived approaches to hunting prey in cluttered situations, places where echoes from background and other objects arrive before or at the same time

The influence of ozone and nutrition on δ13C in Betula pendula.

Abstract: In the cellulose of stems and leaves, δ13C was investigated in a birch clone (Betula pendula), which was exposed throughout the growing season to either <3 (control) or 90/40 nl O3 1-1 (day/night). Each regime was split into plants under high or low nutrient supply. δ13C was increased (becoming less negative), in stems rather than leaves, by both high nutrition (+2‰) and O3 stress (+1‰). Whereas high nutrition raised the wateruse efficiency (WUE) while lowering the CO2 concentration in the inner leaf air space (c i), WUE decreased and c i increased under O3 stress. Therefore, only the nutritional effect on the carbon isotope fractionation was reproduced by the model of Farquhar et al. (1982) which estimates WUE by means of δ13C based on c i. c i was not biased by ‘patchiness’ in respect to stomatal opening. The latter was verified by microscopical analysis and the complete water infiltration of the birch leaves through the stomata, independent of the diurnal course of the leaf conductance for water vapour. Under low nutrient supply, the activity of phosphoenol pyruvate carboxylase (PEPC) was roughly doubled by ozone to about 1.3% of the total carboxylation capacity (by PEPC + rubisco), and was increased to 1.7% under high nutrition. The fractionation model, extended to account for varying activities of the carboxylating enzymes, indicated that stimulated PEPC was the cause of elevated δ13C, although c i was increased under O3 stress. The stimulation of PEPC and, as a consequence, elevated δ13C are discussed as part of a whole-plant acclimation to O3 stress.

Structural and functional processes during water vapour uptake and desiccation in selected lichens with green algal photobionts

Abstract: Structural alterations of the photobiont and mycobiont cells of lichens have been related to CO2-gas exchange during experiments involving water vapour uptake and desiccation of liquid-water-saturated thalli. Increasing water vapour uptake of air dry lichens led to a gradual unfolding of the photobiont cells in Lobaria pulmonaria, Pseudevernia furfuracea, Ramalina maciformis and Teloschistes lacunosus as studied by low-temperature scanning electron microscopy. The data indicated that globular, probably turgid, cells and also slightly infolded or even heavily collapsed cells contributed to positive net photosynthesis, which was reached after water vapour uptake by the four species studied. During desiccation of fully water-saturated thalli of L. pulmonaria, extrathalline water films gradually evaporated before maximum values of CO2-gas exchange were measured and before photobiont cells started to shrivel. In contrast, in P. furfuracea the CO2-gas exchange maximum was reached when a considerable percentage of photobiont cells had already collapsed and while other parts of the thalli were still covered with liquid water. Further desiccation led to cavitation of the cortical cells in both species, this occurring at water contents at which net photosynthesis was still positive.

Response Mechanisms of Conifers to Air Pollutants

Abstract: Conifers are known to respond to SO{sub 2}, O{sub 3}, NO{sub x} and acid deposition. Of these pollutants, O{sub 3} is likely the most widespread and phytotoxic compound, and therefore of great interest to individuals concerned with forest resources Direct biological responses have a toxicological effects on metabolism which can then scale to effects on tree growth and forest ecology, including processes of competition and succession. Air pollution can cause reductions in photosynthesis and stomatal conductance, which are the physiological parameters most rigorously studied for conifers. Some effects air pollutants can have on plants are influenced by the presence of co-occurring environmental stresses. For example, drought usually reduces vulnerability of plants to air pollution. In addition, air pollution sensitivity may differ among species and with plant/leaf age. Plants may make short-term physiological adjustments to compensate for air pollution or may evolve resistance to air pollution through the processes of selection. Models are necessary to understand how physiological processes, growth processes, and ecological processes are affected by air pollutants. The process of defining the ecological risk that air pollutants pose for coniferous forests requires approaches that exploit existing databases, environmental monitoring of air pollutants and forest resources, experiments with well-defined airmore » pollution treatments and environmental control/monitoring, modeling, predicting air pollution-caused changes in productivity and ecological processes over time and space, and integration of social values.« less

Fungal endophytes of dryas octopetala from a high arctic polar semidesert and from the swiss alps

Abstract: Endophytes were isolated from leaves, stems and roots of Dryas octopetala sampled in Switzerland and Spitsbergen. Endophyte assemblages from differ? ent sites and at different sampling times were diverse. Seventy-three species were isolated in the four sites examined and 38 had frequencies of more than 10% in at least one sample. Samples from the subalpine region were generally richer in species than those col? lected in the alpine or Arctic regions. Leaves tended to host more endophyte taxa than twigs or roots.

A dendroecological reconstruction of western spruce budworm outbreaks (Choristoneura occidentalis) in the Front Range, Colorado, from 1720 to 1986

Abstract: Radial increment cores from Douglas-fir (Pseudotsuga menziesii) and blue spruce (Picea pungens), defoliated by western spruce budworm (Choristoneura occidentalis), were analyzed by means of dendrochronological methods and compared with cores from undefoliated ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta) growing on the same sites in the Front Range, Colorado. Extensive deforestation during the gold and silver booms in the second part of the nineteenth century led to dense and almost pure stands of shadetolerant budworm host species. By using the skeleton plot method, the number of trees with clear growth reductions is obtained, thus representing an exact record of forest insect attacks. The analysis of abrupt growth reductions revealed at least nine outbreaks of western spruce budworm between 1720 and 1986, the majority occurring in the nineteenth century. The outbreaks were graphically compared with periods of attack in New Mexico and Colorado which were detected by other scientists employing tree-ring measurement techniques. No increase in the frequency of severe outbreaks during the twentieth century was observed, yet there is some evidence that the most recent outbreak might be the most severe ever recorded. Open Douglas-fir stands on higher sites were more susceptible to heavy budworm attack than dense stands on lower sites. Blue spruce was less frequently and less severely attacked than Douglas-fir. The spatial pattern of historical outbreaks generally was very patchy.

Effects of high nitrogen concentrations on ectomycorrhizal structure and growth of seedlings of Picea abies (L.) Karst.

Abstract: SUMMARY High nitrogen concentrations are known to affect ectomycorrhizas and ectomycorrhizal fungi in field and laboratory experiments. Using NH4+ as a nitrogen source in the growth pouch system, a variety of structural modifications were documented on first order lateral roots of Picea abies (L.) Karst. seedlings. Root cells increased in size and number at high levels of NH4+, resulting in a hypertrophic appearance of roots in both uncolonized seedlings and in those inoculated with mycelia of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex St. Amans) Qu6l. A fungal mantle surrounded short roots of inoculated seedlings, and the outer walls of epidermal and cortical cells were often thickened when in contact with fungal hyphae. No Hartig net developed, although intracellular penetration of fungal hyphae into epidermal and cortical cells frequently occurred. At moderate NH-4+ concentrations, Hartig net development was incomplete, but occasional intracellular penetration of Hartig net hyphae into epidermal and cortical cells occurred. The addition of high levels of NH + after ectomycorrhizal development resulted in ectomycorrhizas with distinctly altered apical structures. None of the various NH 4? concentrations resulted in significantly different plant dry weights after two months of exposure, either with or without fungal inoculation. After four months, dry weight, root length and branching indices were higher in both inoculated plants and those exposed to high nitrogen. The root/shoot ratio and number of short roots per seedling were high with fungal inoculation. Shoot nitrogen levels after two and four months and the Ca levels after 4 months were higher with increasing NH4+ in the nutrient solution. Other mineral elements were not influenced by nitrogen concentrations and fungal inoculation.

Concentrations of nutritional and trace elements in needles of Norway spruce (Picea abies [L.] Karst.) as functions of the needle age class

Abstract: The endogenous concentrations of the essential elements Ca, Cl, Cu, Fe, K, Mg, Mn, N, P and Zn, and of the nonessential elements Al, As, Ba, Br, Co, Cr, Cs, Hg, I, La, Na, Rb, Sb, Sc, Si and Sr were determined in 5 successive needle age classes 40 mature spruce trees from 6 different sites were investigated individually A given element usually shows smooth changes with the needle age class t Trees on a given site usually have a similar dynamic behaviour The same holds for the different site means The concentrations can be approximated by functions c = f(t) Three different types of functions are required to describe the dynamic behaviour of 3 groups of elements that increase with t, and one for the elements that decrease with t A given element usually can be described by the same type of function at all sites, even if its concentration differs widely Exceptions are Mn, Co and Zn, which change from a decreasing function at low concentrations to an increasing function at high concentrations Further irregularities are found at some sites with Ca, Sr and Ba These findings are corroborated by a multivariate statistical analysis

Coincidence Between Molecularly or Morphologically Classified Ectomycorrhizal Morphotypes and Fruitbodies in a Spruce Forest

Abstract: In a study of ectomycorrhizal diversity in a spruce stand in Switzerland the macroscopically classified ectomycorrhizal morphotypes were characterised molecularly by Restriction Fragment Length Polymorphism (RFLP)-patterns of the internal transcribed spacer (ITS) region. In four different plots characterised by different levels of species diversity a total of eighteen ectomycorrhizal morphotypes were macroscopically classified. The evaluation of similarities between the different plot types revealed a more or less homogenous distribution of morphotypes which stands in contrast to the different grades of fruitbody diversity in these plots. Characterisation by molecular tools resulted in a minimum of twenty-three RFLP-types. Seven pattern-types could be referred to fungal species found as fruitbodies in the spruce stand which represents about one third of all mapped fungal species. Different types of correlation between morphotypes and fungal species were observed: (i) one morphotype represents one species, (ii) one morphotype represents several species, (iii) several morphotypes represent one species and (iv) a combination of (ii) and (iii). A low coincidence between spatial distribution and abundance of molecularly identified morphotypes and mapped fruitbodies could be found. The problems associated with classification of ectomycorrhizas and the significance of above-ground fruitbody pattern for below-ground mycorrhizal pattern is discussed.

NITREX: The timing of response of coniferous forest ecosystems to experimentally-changed nitrogen deposition

Abstract: In large regions of Europe and eastern North America atmospheric deposition of inorganic nitrogen (N) compounds has greatly increased the natural external supply to forest ecosystems. This leads to N saturation, in which availability of inorganic N is in excess of biological demand and the ecosystem is unable to retain all incoming N. The large-scale experiments of the NITREX project (NITRogen saturation EXperiments) are designed to provide information regarding the patterns and rates of responses of coniferous forest ecosystems to increases in N deposition and the reversibility and recovery of impacted ecosystems following reductions in N deposition. The timing of ecosystem response generally followed a hypothesized “cascade of response”. In all sites N outputs have responded markedly but to very different degrees within the first three years of treatment. Within this time significant effects on soil processes and on vegetation have only been detected at two sites. This delayed response is explained by the large capacity of the soil system to buffer the increased N supply by microbial immobilization and adsorption. We believe that this concept provides a framework for the evaluation and prediction of the ecosystem response to environmental change.

Theoretical and practical criteria for the selection of ecosystem monitoring plots in Swiss forests.

Abstract: A great deal of attention has been paid to the selection of nature reserves. These are important from a conservation viewpoint but, for long-term evaluations, it is important to monitor ecosystems. The need for long-term monitoring plots has been recognized for some time in forest ecology. Of the natural ecosystems, forests are some of the most difficult to monitor because of the time-scales involved in the life-spans of the dominant organisms (100 → 1000 years). The selection of long-term forest ecosystem monitoring plots is a critical process involving decisions that need to remain valid for many years. Traditional sampling theory suggests that some form of systematic or random sampling may be appropriate, but this is usually inappropriate for the selection of ecosystem monitoring plots. Instead, the selection of plots more closely resembles some of the procedures that are used in the selection of nature reserves. In Switzerland, a monitoring programme has been established which uses a number of criteria for the selection of sites. These include site homogeneity, the abundance and sensitivity of the plant communities to change and the presence of pre-existing data series or monitoring equipment. In addition, the human factor is incorporated by selecting sites from throughout the country, with the willingness of the local forest managers to help with the project being an important factor influencing the final choice of plots. In contrast to most inventories, statistical representativeness is not a requirement for the programme, as the plots are treated as a series of case studies.

The structure and dynamics of old-growth Pinus sylvestris (L.) stands in the Wigry National Park, north-eastern Poland

Abstract: The paper describes the structure and the developmental trends of old-growth Pinus sylvestris stands in the Wigry National Park, in north-eastern Poland. The stands represent a transitional zone between deciduous forests of Central Europe and boreal, coniferous forests of north-eastern Europe. Besides P. sylvestris, the most important tree species are Picea abies and Quercus robur. Among the subcanopy species, Corylus avellana and Sorbus aucuparia occur most frequently. On the basis of the data from 6 permanent sample plots (total size: 1.90 ha), several parameters and stand indices are analysed including species composition of the canopy and the regeneration, diameter distribution, age structure of main tree species, and the relationship between canopy and spatial dispersion of woody regeneration. The most striking feature of the stands studied is the almost complete absence of natural regeneration of P. sylvestris. This seems to be in contradiction with the apparently natural origin of this species in the stands, and a common occurrence of natural disturbances resulting in openings and gaps in forest canopy. The main tree species replacing P. sylvestris in the canopy are P. abies and Q. robur. Also increasing are some broad-leaved species typical of high fertility sites: Acer platanoides, Tilia cordata, Ulmus glabra, and Fraxinus excelsior. A shrub C. avellana occurs extensively competing with tree species and delaying tree replacement processes. While no direct data on the changes in the site conditions can be provided and the ‘recovery’ hypothesis appears to be the most straightforward explanation of the changes in P. sylvestris stands, the possible role of the allogenic changes in environmental conditions (climate warming, nitrogen deposition) is also discussed.

Combining field and control team assessments to obtain error estimates for surveys of crown condition

Abstract: Three field teams undertook a survey of crown transparency in Switzerland in 1993. A fourth team (control) also visited a subset of the trees that had already been visited by the field teams and reported estimates for the same. The problem of estimating the proportion (Pc) of trees with total crown transparency at least equal to a (fixed) level c is addressed. The method assumes that the control team estimate is an unbiased estimate of Pc and therefore if the expected difference between a field team estimate and the control team estimate is non‐zero then the field team estimate is biased. This assumption is most likely to be met in those countries or areas where the control team consists of the instructors. When this assumption cannot be met, as long as the bias of the control team remains the same over the years, the estimates of Pc from different years can still be used to study, for example, whether there is any temporal trend in Pc . A weighted average of the bias‐corrected field team estimates is use...

Abundance and emergence of spruce cone insects in different parts of Switzerland

Abstract: In 1989 a total of 4471 spruce cones was harvested at 29 locations distributed over the five main geographic regions of Switzerland, i.e. Jura, Central Plateau, North, Central and South Alps. The cones were incubated in a controlled environment chamber and the emerging insects were collected and identified. This analysis excludes parasitoids except for the most abundant Torymus spp. Twelve insect species and some 14000 individuals in total were identified. On the average, every cone was inhabited by three insects. The most numerous species were Kaltenbachiola strobi (Winn.), Cydia strobilella (L.), and Torymus spp., amounting together to 95% of the total insect number. Though the abundance peaks varied for different species, most insects were reared from cones from the alpine area. Vegetation type (alliance) was related to the abundance of several species but did not correlate with total infestation rate. For two species their number was related to sampling site altitude. Likewise, a positive, linear correlation was found between the frequencies of the parasitoid Torymus spp. and its host K. strobi, the ratio between the two species averaging 0.7. Cone setting did not correlate with infestation level, but tree age was positively related to total insect number per cone. In the laboratory C. strobilella and K. strobi were the earliest species to emerge; they had the shortest emergence period as well. The percentage of K. strobi with prolonged diapause (emergence in second year after cone sampling) was 51%, while the corresponding values for all other species were lower than 20%. Neither sampling site elevation nor cone setting affected diapause length.