Synergistic effects of past historical logging and drought on the decline of Pyrenean silver fir forests

The causal factors and effects of forest declines are not well understood in temperate conifer forests. Most studies have focused on climatic and environmental stressors and have obviated the potential role of historical forest management as a predisposing factor of decline. Here, we assess if the recent silver fir (Abies alba) decline observed in the Spanish Pyrenees was predisposed by historical logging and incited by warming-induced drought stress. We analysed a dataset of environmental, structural, and historical variables at the tree and stand level including 32 sites with contrasting degrees of defoliation distributed over 5600 km². We followed a dendroecological approach to reconstruct historical logging and to infer the effects of warming-induced drought stress on growth. The silver fir decline was more severe and widespread in western low-elevation mixed forests dominated by trees of small size and slow growth. These sites were subject to higher water deficits than eastern sites, where late-summer rainfall as the key climatic variable controlling silver fir growth was higher. Declining sites showed more frequent growth releases induced by historical logging than non-declining sites. Historical logging and warming-induced drought acted as long-term predisposing and short-term inciting factors of silver fir decline in the Pyrenees, respectively. We suggest that biomass increases caused by past intense logging affected the vulnerability of silver fir against late-summer water deficit. Future research in declining temperate conifer forests should consider the interacting role of predisposing historical management and inducing climatic stressors such as droughts.     

Mistletoe effects on Scots pine decline following drought events: insights from within-tree spatial patterns, growth and carbohydrates

Forest decline has been attributed to the interaction of several stressors including biotic factors such as mistletoes and climate-induced drought stress. However, few data exist on how mistletoes are spatially arranged within trees and how this spatial pattern is related to changes in radial growth, responses to drought stress and carbon use. We used dendrochronology to quantify how mistletoe (Viscum album L.) infestation and drought stress affected long-term growth patterns in Pinus sylvestris L. at different heights. Basal area increment (BAI) trends and comparisons between trees of three different infestation degrees (without mistletoe, ID1; moderately infested trees, ID2; and severely infested trees, ID3) were performed using linear mixed-effects models. To identify the main climatic drivers of tree growth tree-ring widths were converted into indexed chronologies and related to climate data using correlation functions. We performed spatial analyses of the 3D distribution of mistletoe individuals and their ages within the crowns of three severely infested pines to describe their patterns. Lastly, we quantified carbohydrate and nitrogen concentrations in needles and sapwood of branches from severely infested trees and from trees without mistletoe. Mistletoe individuals formed strongly clustered groups of similar age within tree crowns and their age increased towards the crown apex. Mistletoe infestation negatively impacted growth but this effect was stronger near the tree apex than in the rest of sampled heights, causing an average loss of 64% in BAI (loss of BAI was ～51% at 1.3 m or near the tree base). We found that BAI of severely infested trees and moderately or non-infested trees diverged since 2001 and such divergence was magnified by drought. Infested trees had lower concentrations of soluble sugars in their needles than non-infested ones. We conclude that mistletoe infestation causes growth decline and increases the sensitivity of trees to drought stress.     

Individual vulnerability factors of Silver fir (Abies alba Mill.) to parasitism by two contrasting biotic agents: mistletoe (Viscum album L. ssp. abietis) and bark beetles (Coleoptera: Curculionidae: Scolytinae) during a decline process

? Context

In recent decades, there have been increasing reports of forest decline, especially in Mediterranean forest ecosystems. Decline in tree vitality is usually due to complex interactions between abiotic factors and biotic agents that attack weakened trees.

? Aims and methods

Estimating dendrometrical characteristics [basal area increment (BAI), age at DBH from tree ring counting, social status, height, and diameter], tree health status, and a competition index, we investigated the individual vulnerability of a French declining silver fir forest to both mistletoe (Viscum album L. ssp. abietis) and bark beetles (Pityophthorus pityographus Ratz., Pityokteines vorontzovi Jac., and Pityokteines spinidens Reitt.).

? Results

BAI was negatively correlated with both mistletoe infection (via mistletoe biomass) and bark beetle attack (number of insects per square meter), but there was evidence of divergence in tree choice between two groups of parasites. Mistletoe preferentially infected isolated and dominant trees that showed higher past growth rates than non-infected ones. Conversely, bark beetles mainly attacked defoliated and preferably declining trees with diameter (DBH) lower than 44.5 cm and slower past growth.

? Conclusion

While successive severe drought periods are thought to greatly weaken southern silver fir populations, mistletoe and bark beetles may contribute actively to their decline processes as inciting and contributing factors, respectively.     

CLIMATE AND SILVICULTURAL IMPLICATIONS IN MODIFYING STAND COMPOSITION IN MIXED FIR-PINE STANDS

ABSTRACT

A growing concern exists over the decreasing proportion of Scots pine (Pinus sylvestris L.) trees in mixed Trojan fir (Abies nordmanniana subsp. equi-trojani [Asch. & Sint. Ex Boiss] Coode & Cullen)-Scots pine forests in northern Turkey. Given the changes in mean annual temperature and annual precipitation for the last 40 years in the region, understanding of the sensitivity of Trojan fir and Scots pine trees to changing climate seems to be critical so that better management strategies can be developed against the potential climate extremes of the future in the region. Moreover, our knowledge on the influence of current silvicultural methods on seedling density and growth in these forests is limited. Therefore, in this study, the growth response (i.e., radial growth) of Trojan fir and Scots pine trees to the changing climate were examined. In addition, the influence of current silvicultural practices on seedling growth and density in these forests was also monitored. Trojan fir appeared more sensitive to the climatic variables (i.e., temperature and precipitation) than Scots pine in the region. It was also found that the current silvicultural practices might favor Trojan fir over Scots pine in these forests. Natural dynamics and current silvicultural implications would benefit Trojan fir, however, given the species’ potential sensitivity to the changing climate, current silvicultural approaches can be modified to favor Scots pine, and to increase the resilience of these forests against climate extremes expected in the region’s future.     

Growth responses of three coexisting conifer species to climate across wide geographic and climate ranges in Yukon and British Columbia

This work aimed to compare radial growth–climate relationships among three coexisting coniferous tree species across a wide geographic and climate range from southern British Columbia (BC) to central Yukon, Canada. Tree-ring data were collected from 20 mature stands of white spruce (Picea glauca), lodgepole pine (Pinus contorta var. latifolia), and subalpine fir (Abies lasiocarpa). Linear relationships between annual growth variation and monthly and seasonal climate were quantified with correlation and regression analyses, and variation in climate–growth responses over a climatic gradient were quantified by regressing growth responses against local mean climatic conditions. Temperatures had more consistent and stronger correlations with growth for all three species than precipitation, but growth–climate responses varied among species and among sites. In particular, pine and fir populations showed different responses between BC and Yukon, whereas spruce showed a more consistent response across the study domain. Results indicate that (1) the response and sensitivity of trees to seasonal climate variables vary among species and sites and (2) winter temperatures prior to growth may have significant impacts on pine and fir growth at some sites. The capacity to adapt to climate change will likely vary among the study species and across climatic gradients, which will have implications for the future management of mixed-species forests in Yukon and BC.     

Sugar maple (Acer saccharum Marsh.) decline during 1979–1989 in northern Pennsylvania

Sugar maple decline has been observed in northern Pennsylvania since the early 1980s. We investigated the interactions between soil moisture stresses in sugar maple and other factors, such as soil chemistry, insect defoliation, geology, aspect, slope, topography, and atmospheric deposition. In the summer of 1998, we sampled 28 sugar maple (Acer saccharum Marsh.) plots drawn from the USFS Forest Inventory and Analysis (FIA) plots, containing declining and non-declining sugar maple trees across northern Pennsylvania for a variety of soil physical and chemical parameters, site characteristics, and tree health. Foliage from declining plots was found to have significantly lower base cations and higher Mn as compared to that from non-declining plots. Soils in declining plots had lower base cations and pH, a Ca:Al⁻≤1, lower percent clay and higher percent sand and rock fragments than soils on non-declining plots, suggesting that trees on declining plots are at risk of nutritional and drought stress. Regression relationships between foliar and soil chemistry indicated that foliar nutrition was highly correlated with soil chemistry in the upper 50 cm of the soil. Declining sugar maple plots in this study occurred at higher elevations on sandstone dominated geologies. Soils were found to be base poor-sandy soils that contained high percentages of rock fragments. Soils below 50 cm on declining plots had lower soil pH and foliar chemistry indicated lower foliar base cations. A trend, while not significant was found with declining plots experiencing a greater number of and more severe insect defoliations.     

Climatic signal in annual growth variation of silver fir (Abies alba Mill.) and spruce (Picea abies Karst.) from the French Permanent Plot Network (RENECOFOR)

This paper explores the growth/climate relationships in earlywood, latewood and total ring-width chronologies of five Norway spruce (Picea abies) and six silver fir (Abies alba) stands sampled in the French permanent plot network (RENECOFOR) (327 trees). The relationships between climate and ring widths were analyzed using extreme growth years, simple correlations and response functions analysis (bootstrapped coefficients). Monthly climatic regressors were derived by a physiological water balance model that used daily climatic data and stand parameters to estimate soil water deficits. Pointer years underline the high sensitivity to winter frosts (1956, 1986) and exceptional annual droughts (1962, 1976, 1991) for both species. For those years, growth variations were higher for Abies alba than for Picea abies. For each species, the climate information of tree ring series is not modified by local site characteristics (altitude, slope, aspect, soil water reserve). Moreover, strong specific differences appear among species. Earlywood and latewood spruce growth mainly depends on current summer soil water deficit conditions. For silver fir, winter and early summer temperatures, as well as the water supply of the previous year (August to October) play a major role for the production of earlywood, after which the current early summer water supply influences mainly latewood width.     

Dendroecological assessment of the complex causes of decline and recovery of the growth of silver fir (Abies alba Mill.) in Southern Germany

Causes of decline and silver fir (Abies alba Mill.) mortality in Central Europe have been controversially discussed for a long time. This contribution details a comprehensive dendroecological investigation of two basic and alternative hypotheses that explain the decline by either climatic influences or by SO₂ pollution as the primary factors. Growth reduction between the 1960s and 1980s as well as the recovery of growth during recent decades have be seen as a response to complex interactions of multiple factors. Herein, we undertake a multidisciplinary evaluation of a broad database, representing the long-term growth of 1010 firs from 51 sites, long-term climate records as well as data assessing the long-term pollution situation in Southern Germany. The results provide clear evidence that SO₂-immissions play a key role in decline and that tree growth corresponds with the regional and temporal pattern of SO₂ pollution. Calculations with a new complex growth model indicate that tree-ring widths of fir at many sites were more influenced by SO₂ than by any other growth-determining factor during the second half of the last century. Strongest coherence between measured and modelled ring widths are found if – in addition to temperature, available soil water content, heavy frost events and long-term growth trends – the site-specific trend of SO₂ pollution is included. Both the immediate response to SO₂ pollution and the quick recovery of fir since the beginning of the 1980s after the decrease of SO₂ emissions indicate a direct impact of SO₂ in gaseous form and not via the soil in terms of soil acidification. Tree-ring widths document that radial growth response occurs at air concentrations above 10 μg SO₂ m⁻³ (annual average), which can be thought of as a critical threshold for silver fir health. Since the beginning of the 1980s, increasing growth trends have been observed which predominantly result from decreased SO₂ pollution in most parts of Central Europe, although climate change, fertilization by nitrogen deposition and a reduced tree-to-tree competition are also relevant factors. The drastic reduction of SO₂ emission during the recent decades significantly improved the environmental conditions for fir. Consequently, an increased cultivation of silver fir on suitable sites is recommended.     

Detecting changes in tree health and productivity of silver fir in Slovenia

Cambial electrical resistance (CER) was used as an objective measure of vitality of silver fir (Abies alba) in the forests of Slovenia. Trees were rated during the growing season by CER and a subjective crown status index (CSI). Both CER and CSI were inversely correlated to annual ring width increment. Using both CER and CSI, fir were assigned to vitality and vigour categories. Inferences made from these categories and radial growth trends indicated that ring growth decreased prior to the development of canopy symptoms. This decrease in ring growth would have been detected as an increase in CER. This pattern of decline is consistent with the decline of trees due to chronic below-ground stress. Variation in CER was due both to the vascular cambium and to the thickness of the nonconducting phloem.     

Drought sensitivity of Norway spruce is higher than that of silver fir along an altitudinal gradient in southwestern Germany

Context

For Central Europe, climate projections foresee an increase in temperature combined with decreasing summer precipitation, resulting in drier conditions during the growing season. This might negatively affect forest growth, especially at sites that are already water-limited, i.e., at low elevation. At higher altitudes trees might profit from increasing temperatures.

Aims

We analyzed variations in radial growth of silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) Karst.) along an altitudinal gradient from 400 until 1,140 m a.s.l. in the Black Forest, to assess climate responses with increasing elevation.

Methods

Climate–growth relationships were analyzed retrospectively using tree-ring and climate data. In total, we sampled stem discs of 135 trees to build 27 species- and site-specific chronologies (n _fir?=?13, n _spruce?=?14).

Results

Our results indicate distinct differences in climate–growth relations between fir and spruce along the gradient. Growth of high-altitude fir was positively related to temperature from January till March. Growth of low-altitude fir and spruce at all elevations was positively related to precipitation and negatively to temperature during the growing season, particularly in July. A self-calibrating Palmer drought severity index underlined summer drought sensitivity of these trees.

Conclusion

Overall, we found that climatic control of tree growth changes over altitude for fir. For spruce, a remarkable synchrony in growth variation and climate response was shown, which indicates that this species is drought sensitive at all studied elevations. In a future warmer climate, the growth of low-altitude fir and spruce along the entire studied gradient may be negatively affected in the Black Forest, if an increased evaporative demand cannot be compensated by increased water supply.     

Synergistic effect of drought and chestnut blight (Cryphonectria parasitica) on growth decline of European chestnut (Castanea sativa)

The chestnut blight fungus [Cryphonectria parasitica (Murill) Barr] has threatened European chestnut stands (Castanea sativa Mill.) in the 20th century, but infected trees recovered because of the appearance of hypovirulent strains. However, within a dry inner Alpine valley (Italy), blight‐infected C. sativa showing various degrees of crown dieback and dead trees were found. We conducted a dendroecological analysis to retrospectively evaluate a possible synergistic effect of blight infection in the early 1970s and climate stress on the growth decline of C. sativa. In the Eisack Valley (Italy), where annual precipitation is <700 mm, increment cores were taken from blight‐infected C. sativa (n = 103) showing different levels of decline symptoms, i.e. extent of crown dieback (healthy, moderate, severe), and from dead trees. Ring width and basal area increment (BAI) chronologies were developed based on dendroecological methods. Growth–climate relationships were explored using response function analysis and Pearson correlation coefficients. Major findings of our study were: (i) C. sativa growth is limited by low precipitation from December to February and high temperatures in June, (ii) BAI of all vitality classes except healthy trees shows a decreasing trend since 1980; and (iii) a severe drought in 1996 accelerated growth decline and caused death of infected C. sativa individuals. Because of the strong influence of climate on radial tree growth within the study area and observed divergent growth trends in selected vitality classes after infestation by hypovirulent C. parasitica strains in the early 1970s, we conclude that although blight infection is a prerequisite for observed growth declines, soil water availability in the years of drought strongly affects susceptibility to tree death.     

Quantifying stem growth loss at the tree-level in a Pinus radiata plantation to repeated attack by the aphid, Essigella californica

Since its detection in 1998, the exotic aphid pest, Essigella californica Essig (Hemiptera: Aphididae) has caused extensive defoliation in commercial Pinus radiata plantations throughout Australia. A total of one hundred and twenty plots encompassing thirty tree ages, and three thinning treatments were established in September 2006 in southern New South Wales, Australia to assess crown health and tree growth. Assessments were carried out annually during 2006-2009 to quantify the relationship between natural aphid-induced defoliation and growth loss at the individual tree level. Over the course of the four years, particularly in 2006, trees were subjected to moisture stress, as indicated by average annual rainfalls that were below the long-term average. In general, the diameter growth of individual trees appeared unaffected by crown damage severity across most tree ages, indicating that the productivity in Green Hills was limited by the interactive effects of climatic and biotic stressors (both cause premature loss of foliage). Furthermore, the results from this four-year experiment demonstrated that both moisture stress and aphid-induced defoliation constrained the growth response to thinning. However, thinning may have assisted damaged trees to maintain growth rates similar to trees with little or no damage. Understanding the impact of disturbances such as insect pest outbreaks on growth yield models is critical for optimal modelling of long-term plantation growth and management. Our results highlight the difficulty in quantifying the effect of aphid-induced defoliation when combined with chronic moisture stress.     

Long-term realised and projected growth impacts caused by autumn gum moth defoliation of 2-year-old Eucalyptus nitens plantation trees in Tasmania,Australia

Insect damage to production forests has the potential to reduce financial returns by retarding tree growth and causing mortality, however, long-term realised quantification of these losses is rare. In order to help elucidate economic damage thresholds for making spray decisions we capitalised on a natural outbreak of autumn gum moth, Mnesampela privata, in a 2-year-old Eucalyptus nitens plantation. Following the partial chemical control of this insect outbreak we measured the tree growth variables diameter at breast height over bark and height of five differing tree defoliation classes for 75 months following tree damage. At the end of this period a threshold model was fitted to describe the relationship between tree defoliation and realised tree wood volumes. The model revealed that realised stand wood volume was not significantly affected up until defoliation exceeded 60% and then declined sharply after this defoliation level was reached. Further support for this defoliation threshold was evident from multiple comparisons among defoliation classes that showed 50% defoliated trees did not have significantly different wood volume compared to more lightly defoliated trees, but did have significantly greater wood volume compared to trees that were 72% or more defoliated. To determine if the realised differences in wood volume resulted in differences in yield over a plantation rotation the E. nitens growth model NITGRO was used to on-grow trees to age 15 years for a ‘best case’ (type 1 growth response, constant growth rates from last inventory until harvest) and ‘worst case’ (type 2 growth response, divergent growth rates from last inventory until harvest) scenario. The threshold model was then fitted to the outcomes of both scenarios and the economic consequences of defoliation were clearly dependent on the growth function assumed.     

Recent growth changes in Western European forests are driven by climate warming and structured across tree species climatic habitats

Key message

Recent growth changes (1980–2007) in Western European forests strongly vary across tree species, and range from +42% in mountain contexts to ?17% in Mediterranean contexts. These changes reveal recent climate warming footprint and are structured by species' temperature (?) and precipitation (+) growing conditions.

Context

Unprecedented climate warming impacts forests extensively, questioning the respective roles of climatic habitats and tree species in forest growth responses. National forest inventories ensure a repeated and spatially systematic monitoring of forests and form a unique contributing data source.

Aims

A primary aim of this paper was to estimate recent growth changes in eight major European tree species, in natural contexts ranging from mountain to Mediterranean. A second aim was to explore their association with species’ climatic habitat and contemporary climate change.

Methods

Using >315,000 tree increments measured in >25,000 NFI plots, temporal changes in stand basal area increment (BAI) were modelled. Indicators of climate normals and of recent climatic change were correlated to species BAI changes.

Results

BAI changes spanned from ?17 to +42% over 1980–2007 across species. BAI strongly increased for mountain species, showed moderate/no increase for generalist and temperate lowland species and declined for Mediterranean species. BAI changes were greater in colder/wetter contexts than in warmer/drier ones where declines were observed. This suggested a role for climate warming, further found more intense in colder contexts and strongly correlated with species BAI changes.

Conclusion

The predominant role of climate warming and species climatic habitat in recent growth changes is highlighted in Western Europe. Concern is raised for Mediterranean species, showing growth decreases in a warmer climate with stable precipitation.

     

Long-term dynamics of a mixed conifer stand in Slovenia managed with a farmer selection system

The single-tree selection system is an important option for management of Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) forests because it provides continuous cover, requires low investments for tending, and promotes natural regeneration as well as high stand resistance and elasticity. It is often regarded as a very conservative system that usually results in only minor spatiotemporal changes in forest structure and composition. We studied management history, structural changes, regeneration dynamics, and light climate of a traditional single-tree farmer selection silver fir-Norway spruce forest (site typology Bazzanio-Abietetum). Stand structure was analyzed on five 0.25 ha permanent plots in 1994, 2001, and 2008. Regeneration density and height growth, forest floor vegetation, and light climate were also assessed on 1.5 × 1.5 m regeneration subplots in 2001 and 2008. Tree cores extracted from dominant trees from both species in two plots were used for reconstructing stand history and age structure of the canopy layer. We documented the forest response to three types of selection management regimes: excessive, normal, and conservative. Excessive management with harvest intensity significantly above the increment was documented until the late 1950s, including two peaks of heavy fellings (diameter limit cut) in the 1880s and 1930s, which favoured establishment of Norway spruce and released regeneration. The period that followed was characterized by normal selection management, but was nevertheless marked by a decline of silver fir as a result of air pollution and several droughts. This led to sanitary fellings that were carried out from the late 1970s to the early 1990s. In the last two decades conservative management followed, which led to suppression and decline of regeneration, especially of Norway spruce, and loss of selection structure. Although we recorded lower regeneration potential of silver fir compared with Norway spruce within the seedling category, silver fir outcompeted Norway spruce within the small-sized tree category (1 cm < dbh ? 10 cm) because of its superior height growth in low light levels (diffuse light <6%) and occupied a greater share of the canopy. Nevertheless, we anticipate that over the long-term the low light regime will also cause regeneration decline of silver fir and broadleaves. Our research revealed significant structural changes in a single-tree farmer selection forest during the last 150 years. These were a result of variable management regime and environment. A farmer single-tree selection system could better mimic the natural disturbance regime if spatiotemporal combinations of diverse felling regimes would be used.     

Phenological and water-use patterns underlying maximum growing season length at the highest elevations: implications under climate change

Consequences of climate change on tree phenology are readily observable, but little is known about the variations in phenological sensitivity to drought between populations within a species. In this study, we compare the phenological sensitivity to temperature and water availability in Abies pinsapo Boiss., a drought-sensitive Mediterranean fir, across its altitudinal distribution gradient. Twig growth and needle fall were related to temperature, precipitation and plant water status on a daily scale. Stands located at the top edge of the distributional range showed the most favourable water balance, maximum growth rates and little summer defoliation. Towards higher elevations, the observed delay in budburst date due to lower spring temperatures was overcome by a stronger delay in growth cessation date due to the later onset of strong water-deficit conditions in the summer. This explains an extended growing season and the greatest mean growth at the highest elevation. Conversely, lower predawn xylem water potentials and early partial stomatal closure and growth cessation were found in low-elevation A. pinsapo trees. An earlier and higher summer peak of A. pinsapo litterfall was also observed at these water-limited sites. Our results illustrate the ecophysiological background of the ongoing altitudinal shifts reported for this relict tree species under current climatic conditions.     

Epidemiology of Heterobasidion abietinum and Viscum album on silver fir (Abies alba) stands of the Pyrenees

In the last two decades, stand decline and increased mortality has affected silver fir (Abies alba) forests in the Spanish Pyrenees. Simultaneously severe occurrences of the root rot fungus Heterobasidion annosum s.l. and of the mistletoe Viscum album have been reported. We aimed to improve the understanding of the epidemiology of both pathogens in our region. All H. annosum isolates found on silver fir were typed as H. abietinum. H. abietinum was more frequently observed where cuttings had targeted fir trees rather than other species. H. abietinum fruiting bodies were observed in the most recently cut stumps. V. album was more abundant on more dominant fir trees, and in southern aspect stands. The number of V. album colonies in the stand correlated (R² = 0.40) with silver fir mortality. Stands with a high level of V. album infection tended to have a smaller percentage of basal area in species other than silver fir, and they tended to be located on more south‐facing slopes. H. abietinum was widespread in silver fir forests of the Pyrenees. Our data suggest that, in the Pyrenees, the observed H. abietinum incidence may represent a combination of both primary and secondary spread of the pathogen. Favouring mixed forests should be tested as a potential control method for V. album. The correlation between silver fir mortality and V. album infection warrants further study, as the observed tree mortality could have occurred due to other factors than V. album, such as drought damage.     

Tree spatial patterns of Abies alba and Fagus sylvatica in the Western Carpathians over 30 years

The decline of Abies alba (fir) in natural fir–beech forests in Europe has fascinated scientists for over a century. During this period, Fagus sylvatica (beech) became the dominant species in this forest type. We hypothesised that (1) the success of beech over fir is significantly connected with the fact that beech suffers less than fir from the presence of conspecific neighbours; that (2) shade tolerance is not a factor which favours beech over fir; and that (3) this is due to a significantly reduced proportion of litter treethrow mounds with suitable conditions for the successful regeneration of fir. We investigated these hypotheses by means of tree spatial pattern analysis. Eight rectangular plots (2–8 ha) were analysed in mountain fir–beech forests of the Outer Western Carpathians, Czech Republic. Various types of the pair correlation function and L function were used to describe the tree density variability of trees with DBH ≥10 cm. The analyses were carried out on datasets from the 1970s, 1990s and 2000s. Our results suggest that negative density dependence is not responsible for the current decline of fir. It seems that a higher shade tolerance of the advanced regeneration could be one of the factors which favour beech over fir. It is evident that fir trees have a markedly stronger positive association to mounds than beech trees.     

Retrospective analysis of tree architecture in silver fir (Abies alba Mill.): ontogenetic trends and responses to environmental variability

Context

Understanding the effects of exogenous factors on tree development is of major importance in the current context of global change. Assessing the structure development of trees is difficult given that they are large and complex organisms with lifespan of several decades.

Aims

We used a retrospective analysis to derive the ontogenetic trends in silver fir development and assess the effects of climate or light environment on tree architecture.

Methods

Thanks to the identification of relevant growth markers (bud cataphylls and pseudo-whorl branches), a retrospective analysis allowed to record annual shoot extension and to date them on silver firs of various sizes under different environmental conditions.

Results

The length of successive annual shoots located on different axes clearly show gradual trends related to the physiological age of meristems. Within- and between-tree variations are noted due to the plasticity of development and growth induced by light environment and climate.

Conclusion

Retrospective analysis is an efficient method for getting information on the history of trees architecture and subsequently to relate it to environmental factors.     

Long-term growth trends of red spruce and fraser fir at Mt. Rogers,Virginia and Mt. Mitchell,North Carolina

Cross-sectional area growth and height growth of Fraser fir and red spruce trees growing in Virginia and North Carolina were analyzed to identify possible long-term growth trends. Cross-sectional area growth provided no evidence of growth decline. The individual discs were classified according to parameter estimates of the growth trend equation. The predominant pattern of growth was a steady increase followed by fluctuation about a horizontal line. Other cross-sections exhibited a steady increase throughout the series. The only discs that represent declining growth patterns were from trees in subordinate crown position or which had previous top damage. No unexplained growth decline was present in any disc. The results regarding height growth were uncertain. A slight decline in height growth was present although we suggest that this observation was due to problems with the data or the model used to fit height growth. These findings contradict other studies suggesting that a recent growth decline has occurred in red spruce in the southern Appalachians.