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Key message: Repeated defoliation soon after full leaf expansion reduces xylem hydraulic transport safety in beech trees. Japanese beech trees undergo branch dieback and eventual mortality following years of repeated leaf loss due to leaf-feeding insects attacking immediately after full leaf expansion. To study the impact of recurrent defoliation on beech debilitation and mortality, we investigated xylem hydraulic transport safety and observed the xylem vessel architecture in field-grown medium-sized Japanese beech trees that had been artificially defoliated repeatedly for 4 years immediately after full leaf expansion. Multiple years of defoliation immediately after full leaf expansion increased the susceptibility to xylem cavitation (P50 value; − 4.46 ± 0.38 MPa (mean ± SD) for non-defoliated control beeches, and − 2.32 ± 0.20 MPa for defoliated beeches), despite a decrease in their vessel diameter and an increase in their vessel density. In defoliated beech, many irregularly shaped, axially wrinkled and partially cracked vessels, mountain-folded intervessel pits, and fibers with thin and less-lignified cell walls were observed. The intervessel double-wall thickness of the defoliated beech was thinner than that of the control beech. Furthermore, the size and shape of intervessel pits did not change in defoliated beech, but the density of intervessel pits and the total number and total area of intervessel pits per 1 mm of vessel length increased. We conclude that the increased susceptibility to xylem cavitation caused by repeated defoliation immediately after full leaf expansion may be due to an increased total area of intervessel pits with thin pit membranes per unit vessel wall area, in addition to cell wall alteration and vessel deformation and damage. [ABSTRACT FROM AUTHOR]

Persian oak (Quercus brantii) is a dominant species in the ecosystems of western Iran. Over the past decade, its decline has become a cause of concern, and still, the effect of some factors such as drought and dust on this decline is unknown. So this study monitored the impact of those factors on declining patches of Q. brantii in the Zagros region in western Iran via the improved Temperature Vegetation Drought Index (iTVDI) and aerosol optical depth (AOD) indices and examined their relationship with Normalized Difference Vegetation Index (NDVI). The indices were obtained from the moderate-resolution imaging spectroradiometer (MODIS) products for declining patches in northern Khuzestan and Ilam provinces from 2001 to 2021. In addition, the spatiotemporal variations in NDVI, iTVDI, SPI, and AOD were also used, and were evaluate their correlations with NDVI. According to the trend results, the highest increased slope value from 20001 to 2021 was to iTVDI and AOD, while NDVI and SPI had a decreased trend value in all declined patches except for the Malekshahi3. In the most decline iTVDI, AOD had an upward slope while the slope of the drought index decreased in most of them. The slope of the NDVI index was increasing in the most decline patches. Pearson correlation analysis also showed NDVI has a negative relationship with AOD. Results indicate that AOD, SPI, and iTVDI influence the forest dynamics and, as a result, contribute to forest degradation. The use of indices derived from the MODIS time series to monitor forest areas might help to improve long-term decision-making. As a result, it may be concluded that oak decline occurs in the Zagros area as dust events and drought become more prevalent, and soil water and vegetation products are scarce. So drought and dust occurrences should be considered for managing these forests. [ABSTRACT FROM AUTHOR]

The dieback of Picea rubens Sarg. (red spruce) in the Appalachian Mountains of New England has been correlated with emissions transported from the Great Lakes region, including acids, metals, and oxidants. In 1994–1995, metal stress in red spruce foliage evidenced by phytochelatin concentrations increased with red spruce damage index in spruce-fir dominated stands in high elevation forests. In this study, we revisited those same forests after two decades to examine metal stress impacts on high-elevation forests following reductions in atmospheric pollutant loading. We measured metal concentrations in soils, lichens, and foliage, and concentrations of phytochelatin and its precursors in foliage of red spruce trees at 1000 m along a west–east transect from New York to New Hampshire, and along an 800–1000 m elevational transect on Whiteface Mountain, NY. Path analysis showed that foliar Hg had a direct positive effect on foliar phytochelatins, metal-binding peptides produced by the metal stress response in plants. Essential metals Cu and Zn decreased the concentration of Hg in foliage. However, we could not determine the relative importance of atmospheric vs soil pathways for metal exposure. While metal stress was still occurring on Whiteface Mountain in 2013, the overall visual health of red spruce trees across the region was significantly improved compared to 1993–1995. Thus, although metal stress is still measurable in red spruce, the physiological impact may be lessened by decreases in the deposition of metals and acids, thus providing evidence of positive forest health outcomes from improvements in regional air quality in the Northeastern US. [ABSTRACT FROM AUTHOR]

Sweet chestnut forests occupy an important role in Italy and Europe, its resilience is often affected by aggressive pathogen attack. In the last times some chestnut wood colour aberrations have attracted attention suggesting intercorrelation with biotic attacks. The present study analyses chestnut wood from a coppice-with-standards stand in Central Italy aiming to understand the reasons for discolorations in respect to a possible effect on wood physical and mechanical character. Wood specimens with different chromatic aberrations were analysed by mechanical tests, microscopic techniques (SEM), specific density measurements, and ATR-FTIR spectroscopy. Standing trees and logs were investigated by IML-RESI. Results by SEM show as all stained wood zones correspond to mycelium presence and abnormal cell wall morphologies. No real trend was found between specific density, or compressive strength, with coloured samples, infact some test samples with colour aberrations had the highest value for specific gravity. Comparing sound wood with stained wood, the semiquantitative analysis by ATR-FTIR spectroscopy allowed to detect a change in the ratio lignin/cellulose which might be due to a white rot fungus. IML-Resi has showed wood decay symptoms at root collar in coppice standards with a decrease in amplitude at least of 30%. The results find an agreement with similar studies carried out in Spanish chestnut suggesting to indeep the analysis to investigated the geographical distribution and the impact of the damage. [ABSTRACT FROM AUTHOR]

Context: Many forest ecosystems around the world are facing increasing drought-induced dieback, causing mortality patches across the landscape at multiple scales. This increases the supply of biological legacies and differentially affects forest insect communities. Objectives: We analysed the relative effects of local- and landscape-level dieback on local saproxylic beetle assemblages. We assessed how classical concepts in spatial ecology (e.g., habitat-amount and habitat-patch hypotheses) are involved in relationships between multi-scale spatial patterns of available resources and local communities. Methods: We sampled saproxylic beetle assemblages in commercial fir forests in the French highlands. Through automatic aerial mapping, we used percentage of dead tree crown pixels to assess dieback levels at several nested spatial scales. We analysed beetle taxonomic, phylogenetic and functional diversity related to differing levels of multi-scale dieback. Results: We found that taxonomic, functional, and phylogenetic diversity of saproxylic beetle assemblages significantly benefitted from forest dieback, at both local and landscape scales. We detected significant effects in the multiplicative models combining local and landscape variables only for phylogenetic diversity. Increased landscape-scale dieback also caused a functional specialisation of beetle assemblages, favouring those related to large and well-decayed deadwood. Conclusions: Increasing tree mortality under benign neglect provides conservation benefits by heterogenising the forest landscape and enhancing deadwood habitats. Legacy retention practices could take advantage of unharvested, declining forest stands to promote species richness and functional diversity within conventionally managed forest landscapes. [ABSTRACT FROM AUTHOR]

The global rise in temperature and associated changes in climate have led to decline of forests around the globe, across multiple species and ecosystems. A particularly severe example of this is yellow-cedar (Callitropsis nootkatensis) decline along the coast of British Columbia and Alaska, where anthropogenic climate change has led to reduced insulating snowpack, leaving yellow-cedar roots vulnerable to thaw-freeze events, resulting in freezing damage to fine roots and water stress during the subsequent growing season. This includes abundant evidence of tree decline and mortality on the islands of Haida Gwaii. Yellow-cedar decline is complex, with the potential for freezing injury over multiple years and damage that can accumulate over time. We found trees in various stages of decline, from long dead to currently declining, and multiple growth patterns at each study site. We conducted a principal component analysis and identified patterns of divergent growth and divergent response to climate among yellow-cedars within the same stands, across all sites, including three distinct periods of an onset of growth decline (1960s, 1990s, 2000s). Yellow-cedars affected by decline were decreasing in growth and negatively associated with warmer drier winter conditions, whereas yellow-cedars not affected by decline were increasing in growth and positively associated with warmer growing season temperatures. The limiting factors for declining trees, warm dry winter conditions, are consistent with the hypothesis from the mainland that climate warming has led to root freezing. Our research highlights the need to consider multiple signals within a site that would be masked by a single site-level chronology. This is especially relevant within the context of forest decline, where stressors may have differing effects on individual trees. [ABSTRACT FROM AUTHOR]

Global climate change impacts the functioning and productivity of forest ecosystems at various spatiotemporal scales across a wide range of biomes. Although summer temperatures are considered the main driver of boreal tree growth, the importance of soil moisture availability is likely to rise with decreasing latitude and increasing warming. Here, we combine dendrochronological measurements with evidence from tree growth modeling and remote sensing to quantify the effect of climate on phenology and productivity of Scots pines (Pinus sylvestris L.) in southern Siberia. Between 1960 and 2017, pine ring widths along a latitudinal transect from 53° to 56°N were mainly controlled by the availability of summer soil moisture. This finding challenges the common belief that summer temperatures are the predominant growth control in boreal forests. Moreover, we show that earlier growing season onsets can compensate for warming-induced drought stress. Despite the phenotypic plasticity of Scots pines to adapt to warmer and drier conditions, we speculate that predicted climate change will likely exceed the species' physiological tolerance in much of Eurasia's forest-steppe by the end of the twenty-first century. [ABSTRACT FROM AUTHOR]

In the Trans-Mexican Volcanic Belt in central-western Mexico, drought stress causes the decline of two of the most ecologically and economically important conifers: Abies religiosa and Pinus pseudostrobus. Since P. pseudostrobus is distributed immediately below the lower elevation limit of A. religiosa, it would be a logical choice of species to fill gaps that may be created by the decline of A. religiosa. We assessed the feasibility of upward assisted migration and explored the effect of rain reduction using four P. pseudostrobus provenances in a rain exclusion field test at the border of the Monarch Butterfly Biosphere Reserve (MBBR) in Mexico. Our results show that, although populations were transferred between − 1.4 and − 3.3 °C mean annual temperature, and 30% of the precipitation (− 200 mm) was excluded, no statistically significant differences were found among treatments or populations for height increment (overall average 1.52 m) or survival (overall average 87%). These findings suggest that it is feasible to migrate P. pseudostrobus upward, towards the MBBR border, which also coincides with the sites where A. religiosa is in decline. This may present the additional benefit of discouraging change in land use from forestry to potato production by maintaining a healthy barrier of trees. If assisted migration is not included in management and reforestation programs, climate change could induce significant mortality in the present A. religiosa forest, facilitating expansion of the agricultural frontier toward the MBBR. [ABSTRACT FROM AUTHOR]

Assessing the vulnerability of forest ecosystems in the climate change context is a challenging task as the mechanisms that determine this vulnerability cannot be directly observed. Based on the ecological interrelationships between forests and climate, the present review focused on providing current information about vulnerability assessments of cork oak (Quercus suber L.) forests in the Mediterranean basin, especially, in the Kroumirie region (northwest Tunisia), currently under historic extreme drought conditions. From comparing recent findings in this region, we synthesized data on cork oak decline and mortality collected during the historic drought years 1988–1995 period. Climate change impacts cork forest decline, with special interest shown in elevated temperatures and drought; cork oak forest regeneration, and the adaptation of the Kroumirie forest to climate change, are reviewed herein. The studied region has been influenced largely by frequent prolonged drought periods, especially from 1988 to 1995. Droughts were found to consistently have a more detrimental impact on the growth and mortality rates of cork oak populations. Cork oak mortality was recorded for up to 63,622 trees. In the future, more research studies and observational data will be needed, which could represent an important key to understand ecosystem processes, and to facilitate the development of better models that project climate change impacts and vulnerability. The study is useful for researchers and forestry decision makers to develop the appropriate strategies to restore and protect ecosystems, and to help anticipate potential future droughts and climate change. [ABSTRACT FROM AUTHOR]

Conifer decline (Abies sibirica Ledeb. stands) as a result of complex biotic effects on the territory of Krasnoyarsk krai by 2018 reached an area of 541 400 ha; the potential area of further death of A. sibirica is up to 10 million ha. The main reason is the phytopathogenic fungi Armillaria mellea s.l. and Heterobasidion annosum s.l. combined with bark beetle Polygraphus proximus. Trees affected by root pathogens are centers of forest dieback, from which pathological outbreaks spread, including the effects of P. proximus and its phytopathogenic mycoassociates. Neonectria fuckeliana (C. Booth) Castl & Rossman is among the concomitant pathogens in the scale of the lesion, which causes a resin flow that is similar to the effects of P. proximus attack. The phytopathogenicity of pure cultures of the dominant root pathogens of Armillaria borealis Marxm. & Korhonen and Heterobasidion annosum (Fr.) Bref., as well as the stem pathogen of N. fuckeliana, has been confirmed by a series of experiments in vitro. Promising natural agents for the regulation of P. proximus abundance are highly virulent aboriginal strains of Beauveria bassiana (Bals.–Criv.) Vuill., resulting in maximum insect death (up to 100%) for 7–11 days and retaining activity in the temperature range of 16–24 ± 1°C. [ABSTRACT FROM AUTHOR]

Forests worldwide have been recently affected by severe decline and mortality, while our understanding about forest decline across spatial scale is still limited. In this work, we study how Quercus suber trees adjust their physiology, in terms of water use efficiency and secondary growth, to pathogen-induced oak decline at the whole-tree, local and landscape scales. This work was carried out in Mediterranean mixed forests where their dominant key species Q. suber is affected by a severe decline and mortality induced by the exotic soil-borne pathogen Phytophthora cinnamomi. Significant differences were not observed between defoliated and healthy trees, either in terms of water use efficiency or growth at the whole-tree scale. We found that limiting conditions, such as low soil depth and high pathogen abundance, induced trees to higher water use efficiency at local and landscape scales. Overall our findings point out that Q. suber trees subjected to soil drought and root pathogens increase water use efficiency to some extent, while this response might not be enough for the trees to overcome the physiological stress associated with the pathogen-induced dieback. We discuss the complex way by which adult Q. suber trees physiologically respond to P. cinnamomi-induced mortality, improving our understanding of the likely consequences of chronic oak decline in the future. [ABSTRACT FROM AUTHOR]

In the continued quest to explain the decline in productivity and vigor with aging forest stands, the most poorly studied area relates to root system change in time. This paper measures the wood production, root and leaf area (and mass) in a chronosequence of fire-origin lodgepole pine ( Pinus contorta Loudon) stands consisting of four age classes (12, 21, 53, and ≥100 years), each replicated ~ five times. Wood productivity was greatest in the 53-year-old stands and then declined in the ≥100-year-old stands. Growth efficiency, the quantity of wood produced per unit leaf mass, steadily declined with age. Leaf mass and fine root mass plateaued between the 53- and ≥100-year-old stands, but leaf area index actually increased in the older stands. An increase in the leaf area index:fine root area ratio supports the idea that older stand are potentially limited by soil resources. Other factors contributing to slower growth in older stands might be lower soil temperatures and increased self-shading due to the clumped nature of crowns. Collectively, the proportionally greater reduction in fine roots in older stands might be the variable that predisposes these forests to be at a potentially greater risk of stress-induced mortality. [ABSTRACT FROM AUTHOR]

Keymessage: Under non-extreme drought conditions, reduced stem growth is not associated with reserve or hydraulic impairment in beech suffering from long-term decline. Abstract: Global change is expected to increase the frequency and the intensity of drought events in temperate ecosystems. In some regions, this might be associated with an increase in tree decline. Of the ecophysiological mechanisms that have been proposed to explain tree decline, an impairment of the vascular transport system and/or carbon function are two of the most discussed. In a context of long-term decline caused by droughts, we investigated the functional differences between the carbon, nitrogen, and hydraulic functions of healthy and declining mature beech ( Fagus sylvatica L.) trees. The study was carried out over two consecutive years with contrasting water availabilities. The radial growth of declining trees was clearly less than that of healthy trees, due to a lower growth rate, associated during the wet year with a shorter growth period. Leaf functional characteristics and hydraulic parameters (native embolism and cavitation vulnerability curves) were similar in healthy and declining trees. However, at the end of a growing season characterized by a dry spring, carbon reserves concentrations in young branches of declining trees were lower than those in healthy trees, though they recovered during the following non-constraining growing season. Our results did not indicate carbon starvation, nitrogen deficiency, or hydraulic failure. However, there seems to be some compensation mechanism related to reserve dynamics in the remaining living tissue of the declining trees. This study shows that the climate conditions of successive years are probably crucial for these functional adjustments to be operational. [ABSTRACT FROM AUTHOR]

Key message: This study provides new data and an alternative framework to the debate of tree carbon economy in a context of increasing stress. Abstract: For long-living trees, the resilience in times of stress is directly linked to the amount of accessible reserves. Despite the simplicity of this principle, the understanding of how carbon reserves limit growth and/or induce mortality under global change is still debated. In this study, we quantify how anatomical properties of rays-one of the main container for carbon reserves in tree stems-vary among sites, individuals, and annual rings of Larix gmelinii growing in contrasting sites in Siberia to verify if (1) the ray proportion and anatomical structure is linked to the environment, and/or (2) to changes in other wood tissues. Our observations have highlighted that ray proportion mainly varies among individuals, but little among sites and consecutive annual rings. We also observed that ray size and density scale to the wood structure with a relatively constant ratio of ~2.5 rays per tracheid, independent of site conditions. These results suggest that the functional connection between the anatomy of rays and tracheid is unaffected by environment and highlight the importance of considering allometric relations in ecological comparisons. Comparative studies of long-term trajectory of ray proportion of living and dead trees might unravel observed variability among individuals validating the link between long-term depleted reserves and mortality. [ABSTRACT FROM AUTHOR]

Plant scientists, conservationists, and land managers have expressed a need for more research into causal mechanisms behind whole-plant senescence and mortality, especially where increased rates and incidence of forest decline are projected owing to climate change. However, these disciplines use the terminology of senescence in different ways, and this impedes communication between them. We highlight three common difficulties with senescence terminology as used in the ecological literature and propose some solutions. Specifically, we recommend (1) distinguishing between physiological and demographic senses of the term 'senescence'; (2) discarding the qualifiers 'exogenous' and 'endogenous' as applied to disturbances that can contribute to senescence; and (3) using care in attributing mortality of individual woody perennials to senescence. [ABSTRACT FROM AUTHOR]

Previous studies show that Masson pine ( Pinus massoniana L.) stands grown at the industrially-polluted site have experienced unprecedented growth decline, but the causal mechanisms are poorly understood. In this study, to understand the mechanisms of growth decline of Mason pine strands under pollution stresses, we determined the reactive oxygen species levels and chemical composition of the current-year (C) and one-year-old (C + 1) needles, and calculated the needle construction costs (CC) of Masson pine trees grown at an industrially-polluted site and an unpolluted remote site. Pine trees grown at the polluted site had significantly higher levels of hydroxyl radical and superoxide anion in their needles than those grown at the unpolluted site, and the former trees eventually exhibited needle early senescence. The contents of lipids, soluble phenolics and lignins in C and C + 1 needles were significantly higher at the polluted site than at the unpolluted site, but the total amounts of non-construction carbohydrates were lower in non-polluted needles than in polluted needles. Elevated levels of the reactive oxygen species and early senescence in polluted needles together led to significant increases in CC and a longer payback time. We infer that the lengthened payback time and needle early senescence under pollution stress may reduce the Masson pine tree growth and consequently accelerate tree decline. [ABSTRACT FROM AUTHOR]

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]

The historical Japanese city of Kyoto boasts a great many old Buddhist temples and Shinto shrines, many of which are surrounded by sizable forests that have long been preserved as sacred forests. However, acidic deposition has been fallen on the forests in Kyoto for many years. For this study, we conducted soil surveys and investigated the extent of decline of the trees in two Shinto shrines as historic monuments of ancient Kyoto. Our study revealed clear decline in two key tree species ( Cryptomeria japonica (Japanese cedar) and Chamaecyparis obtusa (Japanese cypress)) in both shrines, with some trees showing signs of mortality. The soil was acidic, with an average pH of 4.35. Nutrient salt content too was only about one tenth the national average, with exchangeable Ca (0.52 cequiv./kg) and Mg (0.23 cequiv./kg) for 0-20 cm surface soil. The (Ca+Mg+K)/Al molar ratios were also very low, with 80% of all soil samples having a ratio of 10 or below. Such soil conditions are thought to hamper the sound growth of both Japanese cedar and Japanese cypress, and soil acidification is one of the most likely causes of the decline of temple and shrine forests in Kyoto. [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]

Forests in the Changbai Mountains are important timber sources for economic development of the society and provide ecological services in northeast China. In order to strengthen forest resource management, this paper analyzed management-induced changes in forest structure, tree species composition and forest landscape pattern from 1987 to 2000 for Baihe Forestry Bureau in Jilin Province based on digitized forest parcel maps and forest survey data. The results suggested that the area of Mature, High-Stocking, and Close-Canopy Forests decreased by 31.4%, 55.9% and 10.7% respectively; volume of Mixed Forest, the native forest vegetation type, decreased by 17.8%; the number of patches increased tremendously but the mean patch density decreased sharply for Mature, High-Stocking, Close-Canopy, and Mixed Forests. All the changes in forest structure, species composition, and landscape pattern indicated severe degradations going on with the forests in Baihe Forestry Bureau. Because of the effect of degradation to forest services, restoring forest resources and protecting biodiversity has become urgently important. The strategies of sustainable forest management need to be worked out and implemented. [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]

DOI: http:/dx.doi.org/10.1065/espr2005.06.262 The anthropogenic environmental emissions of chloroacetic acids and volatile organochlorines have been under scrutiny in recent years because the two compound groups are suspected to contribute to forest dieback and stratospheric ozone destruction, respectively. The two organochlorine groups are linked because the atmospheric photochemical oxidation of some volatile organochlorine compounds is one source of phytotoxic chloroacetic acids in the environment. Moreover, both groups are produced in higher amounts by natural chlorination of organic matter, e.g. by soil microorganisms, marine macroalgae and salt lake bacteria, and show similar metabolism pathways. Elucidating the origin and fate of these organohalogens is necessary to implement actions to counteract environmental problems caused by these compounds. While the anthropogenic sources of chloroacetic acids and volatile organochlorines are relatively well-known and within human control, knowledge of relevant natural processes is scarce and fragmented. This article reviews current knowledge on natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soils, with particular emphasis on processes in the rhizosphere, and discusses future studies necessary to understand the role of forest soils in the formation and degradation of these compounds. Reviewing the present knowledge of the natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soil has revealed gaps in knowledge regarding the actual mechanisms behind these processes. In particular, there remains insufficient quantification of reliable budgets and rates of formation and degradation of chloroacetic acids and volatile organochlorines in forest soil (both biotic and abiotic processes) to evaluate the strength of forest ecosystems regarding the emission and uptake of chloroacetic acids and volatile organochlorines, both on a regional scale and on a global scale. It is concluded that the overall role of forest soil as a source and/or sink for chloroacetic acids and volatile organochlorines is still unclear; the available laboratory and field data reveal only bits of the puzzle. Detailed knowledge of the natural degradation and formation processes in forest soil is important to evaluate the strength of forest ecosystems for the emission and uptake of chloroacetic acids and volatile organochlorines, both on a regional scale and on a global scale. As the natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soil can be influenced by human activities, evaluation of the extent of this influence will help to identify what future actions are needed to reduce human influences and thus prevent further damage to the environment and to human health caused by these compounds. [ABSTRACT FROM AUTHOR]

Using a representative sample of stands from a cross section through the Bavarian portion of the northern Calcareous Alps, this study evaluates the plausibility and significance of causal hypotheses for an explanation of the poor crown condition of Norway spruce in mountain forests: (1) ozone exposure in conjunction with (a) drought and (b) ample water supply; (2) soil-borne nutrient deficiency; (3) drought; and (4) tree age. Site index and, in a subset of stands, foliar nutrient concentrations are considered as additional indicators of tree vigour. According to principal component analysis and multiple regression, crown condition was controlled by soil chemistry (transparency increased towards shallow calcareous soils), stand age and, to a smaller degree, by an interaction between ozone exposure and drought. Site index was best explained by a model including elevation, soil chemistry and drought. Tree nutrition clearly reflected the main soil chemical gradient, and P, N and Fe deficiencies were found in transparent stands, which had markedly smaller needles. The similar distributions of crown transparency, site index and nutrition present a strong argument for the hypothesis that soil chemistry has constrained the vigour of spruce trees in the Calcareous Alps for a long time. By leaving unproductive stands to age naturally, forest management has accentuated the pattern of crown condition. In the heterogeneous alpine landscape, possible effects of recent increases in ozone exposure have to be viewed extremely carefully against the background of these natural and anthropogenic covariables. [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 impact on an ecosystem of an environmental stress, such as climate change or air pollution, can be studied through experimentation, through comparisons of sites across a gradient of the stress, through long-term studies at a single site, or through theoretical or modelling approaches. Although the former three techniques often are used to develop and test models, it is much rarer to explicitly link experimental, comparative or long-term studies together. Here we present a concept for combining experimental and comparative research to assess the direction and rate of change, the expected long-term state, and the rate at which the long-term state is achieved after an ecosystem is exposed to an environmental stress. We do this by comparing the response of a forest in Denmark to experimentally increased N deposition with the expected long-term response based on a European database of forests exposed to different levels of N deposition over long time periods. The analysis suggests that if N deposition were to increase by 3-fold to about 50 kg N ha-1 a-1 at the Danish site, and remain at this level, the N concentration in needles would respond within 2–4 yr after the onset of the enhanced N deposition, and would rapidly plateau to an expected mean value of 18.0 mg N g-1 dry mass (95% confidence interval ± 2.5 mg g-1). The N concentration of new litter also would respond rapidly (1–2 yr) to reach an expected value of 16.6 mg N kg-1 dry mass (± 3). The N concentration of the organic layer in the soil would increase much more slowly, but a significant increase would be expected within 5–10 yr. Mineral soil pH would take more than 7 yr to change. Finally, the flux of dissolved inorganic N in leachate would begin to increase immediately, but would take many years to reach the expected level of 22.4 kg N ha-1 a-1 (± 4). [ABSTRACT FROM AUTHOR]

Rainfall, stemflow, and throughfall were collected from 1996 to 1999 at two types of forest sites: (1) forests near the traffic roads and urban areas and (2) forests away from the urban areas at Mt. Gokurakuji, Hiroshima, western Japan in order to estimate the effects of anthropogenic activities on atmospheric deposition. Rainfall deposition for major ions showed small differences between the sites. The NO3- and SO42- concentrations in stemflow were higher at the urban-facing slope than at the mountain-facing slope. Throughfall deposition of NO3- and SO42- was also higher at urban-facing slopes. Net throughfall (NTF) deposition (throughfall minus rainfall) of NO3- and SO42- accounted for 77 and 50% of the total throughfall deposition on urban-facing slopes, respectively, while it accounted for 44 and 23% on the mountain-facing slopes, respectively. These results indicated a higher contribution from dry deposition on urban-facing slopes compared to mountain-facing slopes. Atmospheric N (NO3- + NH4+) deposition from throughfall was estimated to be around 17–26 kg N ha-1 yr-1 on urban-facing slopes, which was greater than the threshold of N deposition that could cause nitrogen leaching in Europe and the United States. The high load of atmospheric N deposition may be one of the factors bringing about the decline of pine forests on urban-facing slopes of Mt. Gokurakuji. [ABSTRACT FROM AUTHOR]

In declining forests of the Vosges mountains (northeast of France), we previously observed that the yellowing of spruce ( Picea abies L. cv. Karsten) needles was associated with impairment of the free radical scavenging capacity of the cells and coincided with chronic exposure to ozone. Chloroplasts of yellow needles were characterized by an abnormal accumulation of photosystem II (PSII) D1-protein in the thylakoids. Further experiments carried out on declining and decline-resistant individual spruce trees characterized in previous studies showed that needle yellowing was associated with impairment of the overall anti-oxidative defense in both the cytosol and the chloroplasts. Both enzymic (peroxidases) and non-enzymic (carotenoids) oxidant scavengers were shown to be affected in the declining spruce. PSII D1-protein accumulation seemed to result from a stabilization of the polypeptide, which led us to hypothesize that oxidative processes might interfere with the specific degradation of this protein in declining spruce, with destructive consequences for the photosystems. [ABSTRACT FROM AUTHOR]

There is a concern that soil acidification by acidic deposition, along with the resulting depletion of the labile pool of nutrient cations (e.g. Ca, Mg) and enhanced leaching of Al from soil may contribute to forest dieback. The molar ratios of Ca/Al or (Ca+Mg+K)/Al in the soil solution have been widely used as a criterion for risk of tree damage due to acidification. Intensity and quality of the crown and branch structure transformation due to formation of secondary shoots in successive series is a very sensitive indicator of long-term tree damage, and the subsequent regenerative processes. Soil water chemistry and crown structure transformation of Norway spruce were observed at 16 forest plots within the Czech Republic with the following results: parameters, expressing degradation processes in the crown (defoliation of primary structure), regeneration processes (percentage of secondary shoots) or synthetic stages of crown structure transformation showed high correlation with soil water (Ca+Mg+K)/Al ratio in organic horizons. No relationships were found for mineral horizons. The correlations between soil water and crown status parameters were considerably stronger when using the (Ca+Mg+K)/Al ratio rather than the Ca/Al ratio. [ABSTRACT FROM AUTHOR]

Since the early eighties air pollution by SO2 and Pb and, to a lesser degree by NOx and NH3, have been significantly reduced in Europe. This was done in part for the protection of forest ecosystems. The reductions are reflected in the pollutant impacts and inputs and have been verified through the bioindicator Norway spruce. In contrast, ozone concentrations increased at most of the evaluated measuring locations and trends were calculated based on the results of about 100 stations in Austria and Germany. Despite reduced emissions, large parts of the forest ecosystems are still affected by air-pollution impacts. Negative effects can be assessed using different legal standards and Critical Levels and Critical Loads, respectively: The legal standard for the evaluation of SO2 impact, as used in Austria, is well suited. The provisional European Critical Level for ozone, the AOT40 must, in order to be a meaningful criterion for field applications, be further refined. Continuing the Critical Load concept, the spatial risk of acid depositions in areas of high geomorphic variability were evaluated using the new parameter of ‘critical soil depth’. With the help of the newly defined ‘lead accumulation index’, the accumulation of Pb from air pollution could be evaluated. Air-pollution inputs and the spatial acidification risk is directly related to altitude. Up to altitudes of 1000 m and 1100 m, SO2 impact and acid depositions, respectively were indicated and elevated ozone doses and Pb inputs were observed in the sensitive sub-alpine areas. These results underline the necessity for increased protection of mountain forest ecosystems, among others through a further reduction of emissions or forest-related strategies. [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]

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Since the early 1970s, more than 25% of Japanese red pine forests have died or declined in Hiroshima Prefecture, Japan. Mass mortality phenomenon of pine trees has appeared throughout Japan, expanding northward from the Prefectures in southern Japan such as Nagasaki, Kogashima. The mortality was above 80% in Nagasaki, Kumamoto, Miyazaki and Tokyo. This study shows that the massive mortality of pines forest mainly occurred in south-facing slopes, where mortality was 90% in Gokurakujisann Mount, Hiroshima. The mortality was very low, < 3.7%, on north-facing slopes and mountain peaks. On west-facing slopes, the mortality was 20–40%. The foliar phenological development on south-facing slopes was 14 days earlier than that on north-facing slopes, 18 days earlier than that on mountain peaks. The mortality of pine trees in Gokurakujisann Mount increased with earlier phenological development and was significantly correlated (R = 0.98$^**$). The mortality of pine trees in each Prefecture increased from south to north with earlier phenological progress and was significantly correlated (R = 0.56$^**$). The outbreak of pine tree mortality was closely related to appearance of abnormally extreme lowest air temperature in February and March. The annual ring width in Gokurakujisann Mount was decreased from 1972 to 1984, concomitantly the abnormally extreme lowest air temperature in February and March. Based on these, it may be concluded that the combined effects of accelerated phenological progress and reduced frost hardiness caused by acid deposition, mainly nitrogen deposition, and extreme abnormally lowest air temperature in late winter and early spring in February and March are the original main factors of mortality of pine trees on a large scale. [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]

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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]

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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]