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Forests modify their productivity, composition, and distribution in response to global change. We studied the radial growth trends of the Western Mediterranean oak Quercus pyrenaica over the last two centuries to analyze whether trees exhibited instability in productivity in response to climatic changes. Trees were sampled to build annual growth chronologies following climatic gradients of increasing moisture availability and decreasing temperature with altitude and latitude. The species' response to climate showed high variability linked to local climatic conditions. The strength in the positive response of trees to moisture availability was inversely related to precipitation (that is, enhanced by higher water stress) whereas high temperature in the growing season was positive for tree-growth only at cold sites. The oldest ages of trees expanded back to the late 1500 s. These old-growth trees were located at the coldest sites and exhibited a long-term increase in productivity starting 150 years ago which could express a dominant positive effect of warming temperatures since the mid 1800 s at cold-humid sites. Conversely, trees at dry sites exhibited negative growth trends. Particularly low elevation stands located at latitudes below 40° displayed enhanced growth constraints with the increase in water stress around 1970, which suggests vulnerability of Quercus pyrenaica at the sampled altitudinal dry edge. The response of trees to future changes in climate should be monitored, particularly in threatened transitional zones. [ABSTRACT FROM AUTHOR]

Background and Aims: The dependence of oak decline on climatic stressors is fairly well documented, but little is known about the impact of soil properties on growth plasticity and as predisposing factors to decline. Here we investigate if oak dieback and individual responses to climatic stresses are related to soil nutrient availability. Methods: Chemical properties of surrounding soil and tree-ring series of healthy, declining, and dead oaks were analysed in four replicated forest stands under Atlantic wet climate conditions in NW Spain, where massive death has occurred. Results: Current nutrient availability significantly predicted oak death risk. Lower concentrations of macronutrients (N, Ca, Mg, and Na) were found in soil surrounding dead trees than living trees. Water excess before the growing season negatively affected growth, and trees showing declining symptoms were more responsive to climate. Trees with greater Ca availability in the surrounding soil were able to respond more plastically to the stress caused by water excess, while trees with lower Ca levels were less responsive to the stress and more predisposed to die. Conclusion: This work revealed that both climatically-induced dieback and the individual dendroclimatic response of oaks may be linked to the uneven distribution of soil resources in declining Atlantic forests. [ABSTRACT FROM AUTHOR]

Spatial and temporal differences in the crown condition of sugar maple ( Acer saccharum Marsh) in Ontario remain largely unexplained. In this study, the potential role of metals in sugar maple dieback was explored by measuring metal concentrations in foliage and forest floor (LFH) at 35 forest stands in south-central Ontario that exhibit varying levels of decline and span a climatic, soil acidity and acid deposition gradient. Foliar and forest floor metal concentrations varied among sites by between two and ten-fold, with acidic sites exhibiting the highest concentrations of many metals in the forest floor and foliage. Sites with moderate decline symptoms (decline index (DI) > 10, averaged between 1986 and 2004) had significantly greater Cd, Zn, Cu, Pb and Mn concentrations and lower Ca concentrations in the forest floor compared with healthy sites (DI < 10). Foliar concentrations of Cd, Sr and Mn were also significantly greater and Ca was significantly lower in sites with moderate decline symptoms compared with healthy sites. However the highest metal concentrations in foliage and the forest floor found in this study are lower than critical values reported in the literature. The notable exception is Mn where values at acidic sites may be high enough to negatively impact sugar maple. [ABSTRACT FROM AUTHOR]

Our study focuses on the ground vegetation dynamics and its dependence on microsite conditions in declined climax mountain Norway spruce forests during the recovery period (1995–2006) following upon the considerable decrease of SO2 pollution. We showed that ground vegetation development shifted from prevailing mosses and vegetation-free sites covered with spruce litter to dominance by Avenella flexuosa during the earlier period of massive decline of the observed ecosystems. The expansion of Vaccinium myrtillus seems to occur mainly under the gradually defoliating tree crowns whereas larger canopy gaps and quickly deforested areas are more successfully colonized by grasses, especially Calamagrostis villosa. The gradual spruce stand decline, as well as the corresponding ground vegetation dynamics, proceeded until the end of the twentieth century. Afterwards, the ground vegetation responded to the interruption of trees dying and stopped its expansion on spruce litter microsites. Retreat of both dominant grasses accompanied by the remarkable increase in cover of mosses occurred. [ABSTRACT FROM AUTHOR]

Natural disturbances such as fires, windstorms, floods, and herbivory often act on plant communities, affecting their structure and the abundance and composition of their species. Most research has focused on the effects of single disturbances on plant communities whereas the synergistic effects of several disturbances have received less attention. In this study, we evaluated how timing and severity of tree mortality modified plant use by introduced deer and early post-mortality successional trajectories in northern Patagonian conifer forests. We sampled understory composition and deer use in Austrocedrus chilensis (ciprés de la cordillera) forest stands undergoing varying timing and severity of forest mortality as reconstructed using dendroecological techniques. In addition, we evaluated the effect of fallen logs on plant composition and deer use of plants by monitoring areas of massive dieback where fallen logs had been removed for fire hazard reduction, and nearby control areas not subjected to such removal. Stepwise regression analyses showed that history and severity of tree mortality strongly influence plant composition and deer use of plants. For deer use (with pellet counts and browsing index as response variables), results showed a positive relationship with degree of stand mortality and a negative relationship with cover of fallen logs. Similarly, cover of unpalatable shrub species was explained by canopy mortality history, whereas cover of palatable shrub species was positively associated with severity of canopy mortality. In areas where fallen logs had been removed, pellet counts were six times higher than those in control areas. Though total shrub species cover was similar between log removal and control areas, proportion of unpalatable shrubs increased in areas where fallen logs had been removed. In conclusion, deer use of plants was strongly limited by tall fallen logs, allowing palatable species to establish and grow. Fallen log removal... [ABSTRACT FROM AUTHOR]

A serious forest decline of Betula ermanii Cham. has been observed at Mt. Mae-Shirane, Oku-Nikko, Japan, where high ozone (O3) concentration and severe water deficiency have been measured. In order to consider the possibility whether O3 and/or water stresses could have been the causes of the forest decline of B. ermanii, plant growth experiments were conducted in environment-controlled growth cabinets. Two-year-old seedlings of B. ermanii were exposed to either charcoal-filtered air (O3 concentration <5 ppb) or 50 ppb O3 (daily average, ranging between 20–100 ppb) for 123 days at 20.0/12.5 ± 1.0°C (day/night) and 70/80 ± 7% relative humidity (day/night). Simultaneously, seedlings were treated with three watering regime: 1.0 < pF < 1.8 (no water stress), 1.8 < pF < 2.5 (mild water stress) or 2.5 < pF < 3.0 (severe water stress). O3 exposure significantly reduced the dry weights of leaf, root and the whole plant, while water stress significantly reduced the dry weights of each organ and the whole plant. Significant reductions of net photosynthesis, transpiration and stomatal conductance were also observed under O3 and/or water deficiency treatments, while contents of RuBP carboxylase/oxygenase (Rubisco), chlorophyll a+ b and some essential nutrient elements (N, P, K, Mg and Ca) were not markedly changed. It was suggested that the decrease in net photosynthetic rate induced mainly by stomatal closure was the major cause of the growth reduction under O3 and/or water stresses. No significant interactions between O3 and water stresses were observed in terms of the depression of dry matter production, which suggested that simultaneous stress treatments of O3 exposure and water deficiency could affect the tree growth of B. ermanii additively. [ABSTRACT FROM AUTHOR]

Soil acidification and the disruption of nutrient cycles appear to be important factors that weaken sugar maple resistance to both abiotic and biotic stresses and predispose it to decline symptoms. Although connections between edaphic stress and decline symptoms have been identified, very little is known about the physiological and biochemical mechanisms that underlie this relationship. In this study, we tested the hypothesis that foliar nutrient imbalances impair the photosynthetic apparatus of sugar maple through oxidative stress. We examined leaf nutrition, photosynthesis and antioxidant enzyme activity (a biomarker of oxidative stress) from early June to late August in three-paired overstory sugar maple stands on Pennsylvania’s Allegheny Plateau that contrast in soil nutrient availability according to slope position. Beginning in early June, trees on upper slopes (nutrient-poor) had significantly lower foliar Ca and Mg concentrations and significantly higher foliar Mn concentrations than trees on lower slopes. These differences increased throughout summer peaking in late August. Photosynthesis and antioxidant enzyme activity closely reflected changes in foliar nutrient status throughout the summer. In the latter half of the summer, leaf gas exchange and chlorophyll content were significantly lower and antioxidant enzyme activity was significantly higher in stands on upper slope soils. At the end of August, leaf nutrient imbalances corresponded with lower rates of photosynthesis and higher antioxidant enzyme activity, suggesting that foliar nutrient imbalances may impair sugar maple function through mechanisms of oxidative stress. [ABSTRACT FROM AUTHOR]

Critical load calculations in the Czech part of 'the Black Triangle' show exceedance of critical load in 75% of the forest area. A comparison with forest damage data shows an insignificant tendency toward more forest damage in areas with high exceedance. We conclude that high exceedance of critical load is a probable contributing factor to forest damage in the area. [ABSTRACT FROM AUTHOR]

Austrocedrus chilensis forests in Argentina suffer a widespread mortality, locally known as `mal del ciprés', whose causes remain unknown. `Mal del ciprés' occurs throughout the cypress range in Argentina, being Río Grande Valley, in Central Patagonian Andes, an area where the disease has notoriously increased its extension and importance in the last years. The purpose of this work was to characterize Río Grande Valley soils where declining cypress stands develop and to determine what soil properties are associated with the disease. Four sampling sites with pure cypress forests expressing `mal del ciprés' were selected. In each of them, 3 declining and 3 asymptomatic plots were established and were characterized by edaphic features. Selected morphological, physical and chemical soil properties were related to the occurrence of the decline by means of analysis of variance. The cypress forest developed in a wide range of soils with different parent materials: glacifluvial, alluvial, volcanic with a glacifluvial discontinuity, volcanic on an andesitic substratum, and soils derived from andesite alteration. All the soils presented dark superficial horizons, rich in organic matter and with granular structure. Cypress growing on volcanic soils with a glacifluvial discontinuity presented symptoms of decline in areas where the discontinuity, and therefore the clayey horizon and the redoximorphic features, were close to the surface. In soils derived from andesite alteration, the declining forest was also present on shallow soils with redoximorphic features near the surface. In volcanic soils with a lithological discontinuity of andesite, the decline was restricted to areas near a water stream. In alluvial soils, declining trees appeared related with the flood plain of the river; healthy forest stands developed on higher lands, where soils were well drained. Glacifluvial soils, presenting clayey textures and great difficulties for rooting, were the soils submitted to the worst drainage conditions. In these soils, the decline presented a random pattern of distribution, suggesting that the whole area is prone to develop the decline. Results showed cypress capacity to inhabit different soils; however microsite features related to poor drainage (i.e., low slope, nearness to water streams, the presence of clay and redoximorphic features near to the surface) determined a higher risk of disease occurrence. [ABSTRACT FROM AUTHOR]

The Canadian Forest Service, the Ontario Ministry of Natural Resources, and the Ontario Ministry of the Environment all conduct monitoring of forest health in Ontario. Among these agencies over 1500 permanent sample plots are monitored for purposes of assessing tree condition and/or site productivity. The data and length of record differ depending on the original intent of the plot system. However, a number of common variables are collected including basic tree measurements (tree height, stem diameter), mortality and site condition. Other variables collected at certain sites include crown condition, pest damage, ground vegetation, soils descriptions, and soils and foliage chemistry. A co-operative has been formed to compile this information from various sources and to make it more easily accessible. Information from these projects is available through the co-operative web site and can be extracted to report on forest health in a region of the province, or on an individual tree species. Information from these sources provide a picture of forest health in Ontario. [ABSTRACT FROM AUTHOR]

Species composition of the understory of spruce (Picea abies (L.) Karsten) and beech (Fagus sylvatica L.) forests subjected to intense air pollution stress in the Krkonoše Mts., Czech Republic, showed directional changes over the last 15 years. The changes were documented with repeated observations of 29 permanent plots, initiated in 1980 and analysed with constrained ordination methods (Canonical Correspondence Analysis). Ground layer changes were mainly associated with the loss of canopy foliage from air pollution stress. The increased amount of the light at ground level resulted in increased herb cover. The initially dominant species (e.g., Calamagrostis villosa (Chaix) J. F. Gmelin, Deschampsia flexuosa (L.) P. B., Vaccinium myrtillus L., Athyrium distentifolium Tausch) were those that increased in cover. Moss cover, and moss and herb richness, declined over the course of the study. Thus, the changes in tree canopy are accompanied with changes in the forest understory, which in turn can affect the dynamics of these forests. [ABSTRACT FROM AUTHOR]

Changes in seasonal temperature and precipitation, as predicted by several global climate models, were utilized together with a stochastic daily weather stimulation model to evaluate the ecological impacts of projected global climate change scenarios on temperate forest ecosystems in northern Michigan, USA. The model simulated the impacts of these projected changes on ecologically significant weather variables, such as the length of the frost-free period, average growing season temperature, average growing season degree days (4.4° C basis), summer precipitation, potential evaporation during the growing season, and the ratio of precipitation to potential evaporation during July and August. The results indicate that even the lower range of predicted climate changes could lead to ecologically and commercially significant changes in the composition and productivity of these forests. Of particular concern is the possibility of climatically induced regional decline episodes for a number of important commercial species in the northern temperate forests of central North America. [ABSTRACT FROM AUTHOR]

Canopy dieback in patches was discovered in an otherwise undisturbed very humid lower montane forest on a quartzitic sandstone plateau of the middle Caroní river basin, Venezuela. The patches vary in size from about 0.1 to 2 ha (50 to 700 upper story dead trees per ha). Preliminary inventories were carried out at 3 selected sites comparing 4 dieback patches (M) with adjacent not affected (V) forests. In the M plots, 40 to 61% of all trees with dbh ≥ 10 cm were dead. They consisted mostly (81–100%) of the endemic tree species Terminalia quintalata of the upper story (dbh > 20 to 60 cm, height up to 30 m), which is much sparser in the V stands. Data on stand structure and species composition are presented. They seem to indicate a spatial variation in the density of Terminalia quintalata, but also of other dominant species, and reproductive problems of Terminalia, which is hardly present in the diameter classes below 10 cm dbh. V and M stands grow on similar soils with a perched high water table. They are practically free of clay and rich in humus. The exchange complex is dominated by H+. Low pH and dilution of base cations represent the main chemical stress factors. Different concepts of the dieback process are discussed, including cyclic reproductive patterns, nutrient sequestering and drought frequency. [ABSTRACT FROM AUTHOR]

A comparative field study was conducted to study the correlation between forest vitality and the abundance of soil microarthropods. During 5 years the vitality of six pine forests within the Veluwe area, the Netherlands, was estimated by the number of needle year-classes, while soils were sampled and extracted for various soil microarthropod groups. Within sites the number of needle year-classes in the forest stands fluctuated over the 5 years, while the collembolan family Sminthuridae showed a trend towards a decreasing population density and the density of the cryptostigmatid mite Platynothrus peltifer Koch increased. Among sites there was a significant positive correlation between the number of needle year-classes and the relative abundance of P. peltifer. The results imply that soil microarthropods may indicate changes in physical and chemical factors in relation to soil fertility and vitality of the trees. [ABSTRACT FROM AUTHOR]

Contents of organic sulfur, sulfate and the inorganic cations K, Ca, Mg, Mn and Na were compared in needles of three conifer species differing in tolerance to chronic SO immissions. Sulfate and organic sulfur compounds were also measured in bark and wood. Field material was collected from Norway Spruce ( Picea abies (L.) Karst.), Colorado Spruce ( Picea pungens Engelm.) and Scots Pine ( Pinus sylvestris L.) at sites where the SO concentration in air was high, and at another site where it was low. In general, sulfate contents were higher but cation contents lower at the sites where SO concentrations were high than where they were low. Up to 114mmol · (kg DW) sulfate was measured in fouryear-old needles of Norway Spruce from the Erzgebirge (annual mean of SO in air 32 nl · 1). Sulfate accumulation in this SO-sensitive conifer increased with SO concentration in ambient air and with needle age, indicating that the main part of the sulfate resulted from the oxidative detoxification of SO. Loss of inorganic cations from ageing needles was reduced, or cation levels even increased, with increasing needle age, while sulfate accumulated. Apparently, cations served as counter-ions for sulfate, which is sequestered in the vacuoles. Individual trees differed in regard to the nature of cations which accumulated with sulfate. Calcium, potassium and magnesium were the dominating cations. Sodium levels were very low. Needles of the SO-tolerant conifers Colorado Spruce and Scots Pine growing next to Norway Spruce in the Erzgebirge did not accumulate, or accumulated less, sulfate with increasing needle age as compared to needles of Norway Spruce. However, somewhat more sulfate was found in the bark of the SO-tolerant species than in the bark of Norway Spruce. Scots Pine contained distinctly more sulfate in the wood than the other conifers. Since accumulation of organic sulfur compounds could not be observed with increasing needle age, or in bark and wood, reduction does not appear to play a major role in the detoxification of SO by the investigated species. Physiological mechanisms permitting Colorado Spruce and Scots Pine to avoid the sulfate accumulation in the needles and the accompanying sequestration of cations that are observed in neighbouring Norway Spruce are discussed on the basis of the obtained data. [ABSTRACT FROM AUTHOR]

Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce ( Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The δC values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (δC between-25.3 and-27.8‰) were significantly less depleted in C than needles (δC between-27.3 and-29.1‰), and δC in twigs increased consistently with age. The δN values of needles ranged between-2.5 and-4.1‰ and varied according to stand and age. In young needles δN decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. δN values in twigs were more negative than in needles (-3.5 to-5.2‰) and showed age- and stand-dependent trends that were similar to the needles. δN values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4‰ in the mineral soil. The δN values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed. [ABSTRACT FROM AUTHOR]

A declining, closed-canopy Picea abies (L.) Karst. stand produced as much crown biomass as a healthy stand, although some trees were chlorotic due to magnesium deficiency. The production of wood per unit of leaf area in both stands was related to the foliar magnesium concentration. Although leaf area index and climate were similar at both sites, stemwood production was 35% lower in the declining than in the healthy stand. Nutritional disharmony, rather than a deficiency in a single element, was identified as the mechanism for reduced tree vigor. The role of nutrient stress in forest decline was detected by partitioning the season into three periods reflecting different phenological stages: a canopy growth period in spring, a stem growth period in summer, and a recharge period during the non-growing season. Needle growth was associated with nitrogen supply. Most of the magnesium supply required to meet the demand for foliage growth was retranslocated from mature needles. Magnesium retranslocation was related to concentration of nitrogen and magnesium in those needles before bud break. Retranslocation from mature needles during the phase of canopy production resulted in chlorosis in initially green needles if the magnesium concentration before bud break was low. Nitrogen concentration in 0-year-old needles generally remained constant with increasing supply, indicating that foliage growth was restricted by the supply of nitrogen. In contrast, magnesium concentration generally increased with supply, indicating that magnesium supply for needle growth was sufficient. Much of the magnesium required for wood production was taken up from the soil because stored magnesium was largely used for canopy growth. Uptake at the declining site was probably limited because of restricted root expansion and lower soil magnesium compared to the healthy site. For this reason only wood growth was reduced at the declining site. Because the recharge of magnesium during the non-growing period is dependent on uptake from the soil, it was more limited at the declining that at the healthy stand. However, as nitrogen uptake from the atmosphere may account for an appreciable proportion of the total uptake, and as its supply in the soil at both sites was similar, an unbalanced recharge of nitrogen and magnesium may have occurred at the declining site. If mature needles are unable to recharge with magnesium in proportion to the uptake of nitrogen, chlorosis is likely to occur during the next canopy growth period. [ABSTRACT FROM AUTHOR]

The nutrient relations (nitrogen, magnesium, calcium, potassium, and manganese) of the xylem sap of spruce trees, Picea abies (L.) Karst., growing at a healthy and a declining site in Northern Bavaria, were followed on a diurnal and seasonal basis between April and October 1985. There were significant differences between the two sites in the xylem sap concentrations of all elements investigated except nitrogen. Nutrient concentrations remained constant diurnally despite changes in transpiration and xylem water potential. However, during periods between precipitation events, concentrations of elements in xylem sap decreased with decreasing xylem water potential. Apparent differences in needle chlorosis of spruce trees at the two sites were associated with consistent differences in nutrient contents of their xylem sap and needles. [ABSTRACT FROM AUTHOR]

The development of root tips and apparent ectomycorrhizas was compared in the Fichtelgebirge (FRG) over one growing season in two 30-year-old Picea abies stands, both on soils derived from phyllite but showing varying symptoms of decline. Visual symptoms of tree decline reflected a lower relative and absolute mycorrhizal frequency, a lower number of ectomycorrhizas per m leaf area and an uneven vertical distribution of root tips and ectomycorrhizas. The number of apparent ectomycorrhizas per ground area was correlated with the amount of magnesium, calcium, and ammonium, and the pH in the free-drainage soil solution, and with the molar calcium to aluminium ratio in mineral soil extracts. The foliage concentrations of magnesium and calcium were correlated with the numbers of apparent ectomycorrhizas per m leaf or ground area. These observations were used to formulate testable hypotheses concerning the role of the root system and the soil environment in forest decline. [ABSTRACT FROM AUTHOR]

CO assimilation rate ( A) and leaf conductance ( g) were measured in the field on intact branches of 35-year-old Picea abies (L.) Karst. trees, in five plots each in a healthy and a declining stand. The declining site included trees with yellow needles. In order to separate atmospheric effects on gas exchange from effects of nutrient deficiency, direct effects of atmospheric pollutants were studied on green needles of different age classes in plots of trees at different stages of visible decline. The effects of nutrient deficiency on gas exchange were studied on a different group of trees showing needles of various degrees of yellowing. CO assimilation of green needles at the same leaf conductance fell somewhat only when needles had reached 5 years of age, the oldest age examined in this study. Leaf conductance decreased with increasing needle age, but green needles in the declining stand had leaf conductances similar to those of needles in the healthy stand. Stomata of needles with different magnesium concentrations responded to light and air humidity in all age classes. Thus, as long as needles were green, no dese effect was detectable up to 5 years of exposure to atmospheric emissions. Since all needles, green and yellow, were exposed to the same pollution levels, differences in gas exchange between green and yellow needles could not be explained simply in terms of long-term direct effects of air pollution. Needle magnesium contents were correlated with needle yellowing. Neither needle color change nor the magnesium concentration were related to g, but CO uptake at ambient CO levels declined with lower magnesium concentration and greater degrees of needle yellowing. [ABSTRACT FROM AUTHOR]

The water relations of Picea abies in a healthy stand with green trees only and a declining stand with trees showing different stages of needle yellowing were investigated in northern Bavaria. The present study is based on observations of trees differing in their nutritional status but apparently green on both sites in order to identify changes in the response pattern which might be caused by atmospheric concentrations of air pollutants and could lead to the phenomenon of decline. Transpiration was measured as water flow through the hydroactive xylem using an equilibrium mass-flow measurement system. Total tree transpiration was monitored diurnally, from July 1985 until October 1985 at both sites. The relationship between transpiration and meteorological measurements indicated that transpiration was a linear function of the vapor pressure deficit. No differences in transpiration of green trees were observed between the two sites. Canopy transpiration was 57%-68% of total throughfall and 41%-54% of total rainfall. Due to this positive water balance, soil water potential at 10 and 20 cm depths remained close to-0.02 MPa (max.-0.09 MPa) for most of the summer. Soil water potential was correlated with the difference between the weekly precipitation and transpiration. No differences in the water relations of apparently healthy trees in the two P. abies stands were observed. It is concluded that differences between green trees at the two sites in terms of nutrient relations or growth rate cannot be explained by changes in whole-tree transpiration or soil water status. [ABSTRACT FROM AUTHOR]

Spruce ( Picea abies) damage in the Fichtelgebirge (FRG) occurs as needle bleaching and a depression of CO assimilation. Such injury may primarily result from the direct, above-ground effects of air pollution or indirect, below-ground changes in mineral uptake. Typically, the new flush of spruce needles is green and exhibits high photosynthetic capacity. Mies and Zöttl concluded that the older foliage is damaged when nutrients are withdrawn to supply the current year's needles. By removing the terminal buds of single branches in the spring, we produced an experimental set of the previous year's needles with greater mineral reserves than the control needles. During the course of the growing period, the performance of the experimental needles, which lacked competition from the new flush, was compared to that of the control needles of the same age-class on intact branches with the new flush. Throughout the experiment, chloroplast pigments of a healthy control tree were not affected by the elimination of the new flush. However, the chlorophyll and carotenoid content as well as the photosynthetic capacity of the previous year's needles on those branches of a heavily damaged tree where the new flush had been eliminated increased substantially. This increase was associated with an increase in minerals, which seemed to be deficient in the control needles with the new flush. Thus, in contrast to needles of the same age-class on intact branches with undisturbed new growth in the same atmospheric environment, the experimental needles escaped bleaching and a decrease in photosynthesis. It would seem that the bleaching and the loss in photosynthetic capacity typical of trees damaged by forest decline indirectly result from nutrient deficiencies through soil environment changes and/or root damage than directly from atmospheric pollutants. [ABSTRACT FROM AUTHOR]

The article examines the history of forest declines, and presents a concise account of the European forest monitoring and research programs of the last 15 years. The critical loads approach is identified asa key mechanism for taking scientific evidence through to policy formulation. For forest ecosystems the approach is of particular importance because is provides a quantification of the link between pollutant inputs and biological sustainability. [ABSTRACT FROM AUTHOR]

Sulfate, nitrogen, and hydrogen ion deposition in the Laurel Hill region of the Appalachian Plateau province in Pennsylvania has been very high. Records indicate that losses of rainbow trout (Oncorhynchus mykiss) first occurred about 1960, although unrecorded losses probablypreceded that date. Research has also attributed loss of brook trout(Salvelinus fontinalis) in this region to chronic and episodic stream acidification. Relatively recently, mortality of northern red oak has become a problem in parts of the region with mortalities as high as 60 percent of standing trees evident in some areas. Preliminary analysis indicates that soil acidification may play a significant role in the observed mortality. If this is the case, it would appear that fish losses due to watershed acidification in the region were evident about 30 years prior to the current mortality of northern red oak Therefore, fish loss caused by acidification may be a prelude to more widespread ecosystem damage as a consequence of chronic deposition of acidifying elements. [ABSTRACT FROM AUTHOR]

Between 1988 and 1993 six surveys on the condition of forests in Navarra (North Spain were carried out. The results, relating to 408 trees in 17 sampling points, showed that the overall percentage of damaged trees increased from 2.86% in 1988 to 18.6% in 1993, which indicates a general large-scale deterioration of forest condition. Among the most common groups of trees, the most severely affected species were Quercus faginea, Quercus robur and Pinus sylvestris. Furthermore, it was observed that defoliation and discoloration processes did not occur randomly between stand trees, but the trees that were damaged one year (1992) were more predisposed to suffer damage in the next year (1993). [ABSTRACT FROM AUTHOR]