Productivity and vitality of spruce stands: dynamic feedback simulation for responses to different annual and seasonal levels of magnesium supply from soil

Responses of Norway spruce stands to gradually decreased annual magnesium supply from soil, with two seasonal courses, are evaluated by computer simulation. At low supply, magnesium concentrations in the needles are reduced to levels inducing chlorosis, but annual growth of new needles remains at the same level as stands with adequate magnesium. Above-ground permanent biomass shows a decreased annual production with lower supply, mainly because of shorter net carbon gain caused by decreased assimilation which is due to magnesium deficiency in needles. An additional but less important reason is the magnesium deficiency in stem and branch cambium, which is most severe during summer at low magnesium supply rates. The interaction of magnesium and carbon balance is emphasized.Modeling and simulation are not used for prediction but to test the consistency of scientific hypotheses.     

Effects of toxic heavy metals (Cd,Pb) on growth and mineral nutrition of beech (Fagus sylvatica L.)

The beech (Fagus sylvatica L.) is the dominant tree in Middle Europe under many different ecological conditions. But like other tree species, it is suffering in the last ten years increasingly by air pollutants including heavy metals which have been deposited and accumulated for decades in many forest soils. Increasingly mobilized by acidification processes, these metals may have toxic effects on trees.In autecological studies (dose-response-experiments) effects of root-applied Pb and Cd on various growth parameters, on uptake of mineral nutrients and on transpiration of young beech trees were evaluated, and critical concentrations (threshold levels) could be established. Significant leaf area reduction was found with 6 ppm Pb (0.3 ppm Cd) in the leaves (DW), but biomass reduction only with 18 ppm Pb (3.6 ppm Cd). Root elongation rates of seedlings were significantly reduced with 44 ppm plant-available Pb in the soil by about 30%, but only with 24 ppm Pb when combined with 2 ppm Cd, exhibiting synergistic effects. After treatments with 20 ppm Pb and 1 ppm Cd in sand culture, a considerable decrease in the contents of K, Ca, Mg, Fe, Mn, and Zn in roots and leaves of saplings was coincident with high (roots) and moderate (leaves) accumulation of Pb and Cd. A 20% reduction of transpiration rates was measured in ten-year-old beech trees after three months of exposure to a forest soil containing 2.5 ppm plant-available Cd.The data indicate that present-day concentrations mainly of Pb, but not yet of Cd, in acidified European forest soils are sufficiently high to affect germination, growth and mineral nutrition of natural rejuvenation of beech.The data published here are part of a doctoral and of various diploma theses: Mrs. Christiane Bertels, Barbara Buschmann, Martina Hücker, Gritli Noack, Ute Röder, Swantje von Oy and Mr. Rüdiger Ahrend, Peter Rüther and Frank Weisser.     

Temporal instability in tree-growth/climate response in the Lower Bavarian Forest region: implications for dendroclimatic reconstruction

This paper explores the temporal stability of growth/climate relationships in ring-width chronologies of Norway spruce [ Picea abies (L.) Karst] and silver fir ( Abies alba Mill) in the Lower Bavarian Forest region in southern Germany. These chronologies were compiled, using both historic and living tree-ring data, with the main aim of developing a dendroclimatic reconstruction for the region covering the last 500 years. Moving window correlation analysis shows that prior to the twentieth century, both species co-vary in a similar way (1480–1899 mean r =0.66). There is no significant correlation between the species chronologies since ca. 1930, which partly reflects anomalous growth trends in the fir chronology since ca. 1960. Multiple regression analysis was utilised to assess the ability of both species chronologies to model March–August precipitation. The precipitation signal of the spruce data was found to be both stronger than the fir data (1872–1930 calibration: r ²=0.45 vs 0.25) and more time stable. After ca. 1930, the fir chronology loses it ability to model March–August precipitation until there is no climate signal at all in the fir data in recent decades. The spruce data also express a later weakening in their climate signal in the mid 1970s. We present compelling evidence indicating that the anomalous trends observed in the fir data, since the mid 1960s, appear to be predominantly related to local SO₂ emissions from power plants and refineries. It is also likely that this local anthropogenic forcing is the cause of the weakening of the climate signal in the spruce data since the mid 1970s. The conclusions from this study are: (1) The fir tree-ring data cannot be used for traditional dendroclimatic calibration, although prior to the twentieth century the decadal variability in the fir data is very similar to spruce and so these data could be used to extend potential reconstructions in the future; (2) The recent decline and recovery event in the fir data appears to be unique to the twentieth century and is not part of a natural episodic phenomenon; (3) Traditional dendroclimatic calibration of March–August precipitation will be made using solely the spruce ring-width data. However, due to SO₂ forcing in recent decades, the calibration period will be shortened to the 1871–1978 period.     

Performance of two Picea abies (L.) Karst. stands at different stages of decline

Summary This is the first in a series of papers on the growth, photosynthetic rate, water and nutrient relations, root distribution and mycorrhizal frequency of two Norway spruce forests at different stages of decline. One of the stands was composed of green trees only while the other included trees ranging in appearance from full green crowns to thin crowns with yellow needles. In this paper we compare the growth and carbohydrate relations of the two stands and examine relationships among growth variables in ten plots. The declining stand produced 65 percent of the wood per ground area compared with the stand in which all trees were green because its foliage produced less wood at any level of leaf area index. The difference in foliage efficiency between the sites could not be explained by differeneces in climate, competition or stand structure. The declining stand appeared to have lower carbon gain as indicated by a smaller increase in reserve carbohydrates before bud break, and weaker sinks for carbohydrates as indicated by less use of the stored carbohydrates than the healthy stand. Thus, growth reduction was probably related to factors which affect both photosynthesis and, even more, the sinks for carbohydrate.     

Forest dieback in Czechoslovakia

The article reviews the literature dealing with levels of air pollution in Central Europe and Czechoslovakia particulary in connection with the rate of forest damage and dieback since the fifties. To date 57 percent of forests on an area of 15.000 square km are damaged in Czech republic and more than 40.000 ha of dead Norway spruce forest had to be cut out. Deforested hills are vegetated mostly by Calamagrostis villosa only. The reforestation faces many obstacles of which the change of mezoclimate, the acidification and intoxication of the soil, the disappearance of mycorrhizal fungi and pressure of consumers may be named.     

Belowground ectomycorrhizal communities in three Norway spruce stands with different degrees of decline in the Czech Republic

We investigated the ectomycorrhizal communities on the roots of adult trees and seedlings associated with three Norway spruce stands in the Czech Republic using morphological and molecular tools. The stands had different degrees of forest decline due to air pollution. The aims of the study were to obtain information about the belowground ectomycorrhizal community in a heavily damaged spruce forest and to assess whether missing ectomycorrhizal fungal partners could be one of the reasons for the observed lack of regeneration. The ectomycorrhizal species richness on the roots of adult trees was significantly lower in the heavily damaged site Mumlavska hora than in the other two, but less drastically so than that found in a fruitbody survey. The roots of adult trees and seedlings were fully mycorrhizal at this site although they were less species-rich. The most abundant ectomycorrhizal species on the root system of adult trees in all three forest stands was Tylospora fibrillosa, a member of the athelioid clade. It made up over 60% of root tips in Mumlavska hora and its proportion was at least twice that in the other two sites. This species was also an efficient colonizer of roots from seedlings, in particular, in the most damaged site. The different soil properties in this site may have caused the observed differences in the ectomycorrhizal species richness and composition. For example, cation exchange capacity and soil base saturation were lower and the soil more often saturated. However, the number of living trees and their defoliation status may well directly impact the ectomycorrhizal species composition by presumably affecting the amount of carbon delivered to the symbiotic fungal partners. Athelioids and thelephoroids are an important component of the belowground ectomycorrhizal community in most temperate and boreal forests, but the role they play might even be more crucial in stressed forest ecosystems. Based on our results, we suggest that factors other than missing ectomycorrhizal inoculum constrain natural regeneration in the heavily damaged site Mumlavska hora.     

峨嵋山冷杉森林衰退状况研究

报道和分析了峨嵋山冷杉森林的衰退状况。对冷杉种群的受害程度、分布规律、症状特点及其与海拔、特定生境、立木径级和林型的关系进行了研究分析。指出峨嵋山冷杉森林衰退是全球森林衰退的组成部份,而不是个别的或偶然的现象;肯定了当地冷杉林衰退具有某些个性特征。由此认为,导致当地冷杉衰退的主要原因可能是某种或某些作用范围广、持续时间长、发生频率高、对全球森林系统构成威胁的因素所致。     

Vegetation changes in forests of the Krkonoše Mts. over a period of air pollution stress (1980–1995)

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 Krkonoe 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.     

Response of Citrus Seedlings to Radopholus similis in Two Soils

Radopholus similis was less pathogenic to greenhouse-grown citrus seedlings in Leon loamy sand than in Lakeland fine sand. This was not affected by different watering regimes. Seedling growth reduction by the burrowing nematode in either soil, compared with noninfected controls, was significant at the 1% level.     

Forest-level analysis of stability under exploitation: depensation responses and catastrophe theory

Stability analysis of whole forests is proposed as a qualitative tool for the study of forest responses to partial or patchy harvests or mortality. Instead of modeling every tree or stand, aggregate tree biomass is modeled. In order to aggregate stands, spatial effects must be incorporated. It is shown that depensation growth responses (reduced growth at low biomass) are common because forests often modify harch environments to be more suitable for their growth. Depensation can result from thinning, partial mortality, patchy cutting, or clearcutting, depending on forest type and abiotic factors. Examples of these types of behaviors are given. Stability analysis of different growth regimes under exploitation are related to catastrophe theory and to optimal harvesting policies. Such qualitative analysis is shown to be applicable to data-poor regions such as the tropics where there is great concern over responses of forests to exploitation.     

Photosynthesis and transpiration in the upper crown of a mature spruce in purified and ambient atmosphere in a natural stand

Summary This study addresses the question of whether gaseous air pollutants are capable of damaging spruce foliage. For this purpose, several twig pairs of an adult tree in a natural stand from the western part of the Bavarian Forest were supplied with pure and ambient air and gas exchange was monitored. With the exception of insignificant and unexplained differences during winter, the gas exchange of the twigs showed no negative deviation due to the influence of gaseous air pollutants. Because visible damage arises only in older needles, the duration of measurement is not sufficient to exclude a long-term influence of gaseous air pollutants.     

Rapid field determination of photosynthetic capacity of cut spruce twigs (Picea abies) at saturating ambient CO2

Summary Routine field determination of the parameters characterizing the activity of the photosynthetic apparatus is often difficult when attached branches of tall trees have to be used for gas exchange measurement. If severed twigs could be used, determining these parameters would be greatly facilitated. Because stomatal conductance changes when twigs or leaves are detached, CO₂ assimilation is usually altered. Thus, measurements made at ambient CO₂ concentration fail to accurately assess the activity of the photosynthetic apparatus because photosynthetic rates greatly depend on the supply of carbon dioxide. However, when photosynthetic carboxylation reactions are saturated by increased CO₂ partial pressure in the mesophyll, CO₂ assimilation rates no longer depend on instantaneous stomatal conductance, as shown by gas exchange measurements of spruce (Picea abies) twigs prior to and following detachment. Because net photosynthesis following detachment at saturating CO₂ remains constant for a minimum of 15 min, photosynthetic measurements of severed twigs may be reliable. This length of time is sufficient for detaching and recutting the twig, assembling a portable minicuvette system, re-establishing steady-state conditions with the gas analyser system, and reading the data over a reasonable period of time. The method described measures the maximal photosynthetic CO₂ assimilation of spruce needles of a single age-class from detached spruce twigs under the following conditions: saturating light, saturating external CO₂-partial pressure, standardized temperature and air humidity in the field. The method is applicable as a routine procedure to characterize the status of the photosynthetic apparatus of spruce trees that may be damaged in the process of forest decline.