Tree Crown Defoliation Degree as a Predictor of Silver Fir (Abies alba Mill) and Norway Spruce (Picea abies (L.) Karst.) Timber Value

Key messageWe found a significant increase in the latewood density of European beech, and a decrease in the latewood and mean wood density of silver fir and Norway spruce in European mountain forests over the period 1901–2016. In the past century, drought did not directly influence the wood density trend of the three studied species. However, for both fir and spruce, drought indirectly affected the mean wood density via changes in the latewood to earlywood ratio, i.e., in the case of extreme drought, trees with high values of latewood to earlywood ratio experienced a slight attenuation in the declining trend of their mean wood density.ContextCentury-long wood density measurements can provide novel information on tree response to climate change and the carbon sequestration potential of forest ecosystems. Still, the knowledge about long-term changes in wood density of European beech (Fagus sylvatica L.), silver fir (Abies alba Mill.), and Norway spruce (Picea abies (L.) H.Karst.) in European mountain forests needs to be further explored.AimsWe assessed long-term changes in tree-ring mean wood density, earlywood density, and latewood density in trees of the three species between 1901 and 2016. We investigated the influence of endogenous factors (i.e., tree-ring width, current tree diameter, and latewood to earlywood ratio) and drought events on wood density.MethodsIn total, 150 tree cores were sampled from mountain forests in Bulgaria, Bosnia and Herzegovina, Slovenia, Switzerland, and Germany. The mean, early, and latewood density of these samples were measured with the LIGNOSTATION™ system. To address our research aims, we applied a linear mixed-effect modelling approach using the data from 101 correctly cross-dated cores that spanned the entire period of analysis.ResultsIn the absence of drought, the latewood density of European beech increased by 7.1%, the late and mean wood density of silver fir decreased by 16.8% and 11.0%, respectively, and the late and mean wood density of Norway spruce decreased by 16.1% and 7.2%, respectively, between 1901–2016. In the past century, drought influenced the trends of wood density through an effect mediated by changes in the latewood to earlywood ratio. Specifically, in cases of extreme drought, silver fir and Norway spruce trees with a latewood to earlywood ratio value 50% higher than the median experience a slight attenuation in the declining trend of their mean wood density, making the negative impact of drought marginally less severe.ConclusionsOur findings have significant implications for the accuracy of carbon stock assessments, national greenhouse gas inventories, and the utilization of wood from the three species. Given the fact that changes in wood density follow species-specific patterns and the expectation of more frequent drought events in Europe, in the future, it is essential to build further tree-ring density time series for other species and sites to improve our understanding of how climate change alters wood density and carbon sequestration of forest ecosystems.

In the Mediterranean area, numerous decline and mortality processes have been reported during recent decades, affecting forest dynamics. They are likely due to increases in summer drought severity and therefore especially affect drought-sensitive species, such as silver fir (Abies alba Mill.). To understand the relationships between tree growth, crown condition and mortality probability, radial growth trends of healthy, declining (showing crown damages) and dead trees were compared using tree-ring analysis. Factors involved in determining this mortality were also examined at the plot and tree level using altitudinal gradients on three contrasted sites in southeastern France. Individuals with higher inter-annual variability in growth were more prone to dieback. At two sites, dead trees displayed lower growth rates over their entire lifetime, while, on the last site, their juvenile growth rate was higher. Trees with crown damage had higher growth rates than healthy trees on one site, and their radial growth trends over time always differed from those of dead trees. Mortality and crown damage were little related to altitude, but strongly differed between sites and among plots underlining the importance of local edaphic and topographic conditions. These results suggest that the relationships among mortality probability, crown condition and growth can differ among sites, and highlight the impact of soil conditions and the need to assess them in tree mortality studies.

We examined manganese uptake and translocation in 30-year-old silver fir trees (Abies alba Mill.) showing severe symptoms of needle chlorosis by analyzing both xylem and phloem sap of shoots and an extract of root sap originating from both xylem and phloem elements. Manganese concentrations in shoot xylem and phloem sap were significantly lower in chlorotic trees than in neighboring healthy trees. The Mn concentration of root sap was also lower in these Mn-deficient trees than in healthy trees, indicating reduced Mn uptake by Mn-deficient trees. Although Mn deficiency had no effect on the Mn concentration of whole roots, separation of root tissue into root cortex and stele (wood) suggested impaired translocation of Mn from the cortex to the stele in Mn-deficient trees. Triphenyltetrazolium chloride (TTC) tests indicated that there was no decrease in reducing capacity of the fine roots (< 1 mm in diameter) of Mn-deficient trees. Fine roots of Mn-deficient trees contained significantly more organic acids than fine roots of healthy trees, including increased concentrations of malic, quinic, trans-acontic and formic acid; however, concentrations of pyruvic and acetic acid were lower than in fine roots of healthy trees. The total amounts of organic acids in the rhizospheric soil were similar for healthy and Mn-deficient trees. Pyruvic acid concentration was significantly increased in the rhizospheric soil of Mn-deficient trees, and concentrations of simple aliphatic acids like formic and acetic acid also tended to be higher in the rhizospheric soil of Mn-deficient trees. Both pH and water content were higher in bulk soil and rhizospheric soil around Mn-deficient trees compared with soil around healthy trees. Although lower concentrations of exchangeable Mn were found in the soil around Mn-deficient trees, the active Mn concentration (sum of exchangeable and reducible Mn) did not differ between healthy and Mn-deficient trees. A considerable proportion of manganese was in an oxidized form in the soil around Mn-deficient trees.

Growth patterns as indicators of impending tree death in silver fir

The research on incidence of mistletoe (Viscum album ssp. abietis) on silver fir (Abies alba) was carried out in natural fir stands in Croatia. In the area of Gorski Kotar 32.8 % of the examined dominant fir trees were infected with mistletoe. The mistletoe incidence was presented according to the damage degrees of silver fir from 0 (healthy trees) to 4 (dead trees), rated by the crown defoliation and needle discoloration. With the increase of incidence, mistletoe spreads more onto more vital, i.e. less damaged trees. In the Dinaric Alps 28.6% of the examined fir trees were infected, this percentage amounting to 27.1% for the mountainous regions between the Sava and Drava rivers.

Bark beetle infestations and other natural disturbances have increasingly affected Norway spruce (Picea abies (L.) Karst.) forests across Europe resulting in devaluation and decreased applicability of woody biomass of such trees. The aim of this research was to investigate the extractive content of bark beetle-attacked and dead wind-damaged Norway spruce trees relative to healthy trees, in order to assess their potential for extractives recovery. After harvesting, three discs were dissected along the stem height of each tree, and samples of sapwood, heartwood, knots, and bark were collected. Sequential extraction of the samples was performed using cyclohexane and acetone–water mixture in an accelerated solvent extractor. Lipophilic and hydrophilic extractives were determined gravimetrically, while total phenols and proanthocyanidins were measured by UV–Vis spectrophotometry. Results showed that knotwood contained the highest amounts of hydrophilic extractives and total phenols among investigated tissues. Knots of healthy trees contained the highest amount of hydrophilic extractives (52.4% w w−1), while knots of dead wind-damaged trees contained significantly higher content of total phenols (8.8% w w−1). The total phenols in bark beetle-attacked and healthy trees were 7.1% w w−1 and 7.2% w w−1, respectively. The sapwood and heartwood of dead wind-damaged trees had higher content of hydrophilic extractives (3.4% and 2.3% w w−1) than healthy and bark beetle-attacked trees. Bark from healthy trees contained more total phenols (2.7% w w−1) than bark of bark beetle-attacked trees, while proanthocyanidin contents in bark were comparable among three groups of trees. Our findings revealed that woody biomass from bark beetle-attacked and dead wind-damaged Norway spruce trees contains significant levels of phenolics, indicating high potential for extracting valuable compounds in biorefineries.

In Romania Viscum album ssp. abietis is one of the most significant biotic factors that affect Silver fir situated on Eastern border of its natural area. The aim of our research is to assess the incidence and distribution of mistletoe in representative Silver fir stands from the Eastern Carpathians (at four forest districts level - Gura Humorului, Vaduri, Manastirea Casin and Agas). According with this purpose a statistical inventory of Silver fir stands based on 2 x 2 km grid was performed. At the intersection of the gridlines, stands older than 70 years were searched for on a distance of 500 m around. Each Silver fir stand chosen in this way represents a sample plot. In each plot 30 dominant Silver fir trees were chosen. For all this trees, the mistletoe infection degree was quantified using a 4-class rating system: no infection, low infection, moderate infection and heavy infection. The incidence of Silver fir was presented according to the damage degree. The site and stand parameters - elevation, exposure and canopy closure - were analysed to establish whether correlation between these parameters and mistletoe incidence exists. The volume of dead trees (due to the mistletoe infection) in 2004 - 2007 was also compared with mistletoe incidence in order to establish the correlation between these variables. Silver fir trees infected by mistletoe have been found in 55% of all 86 sample plots. Within the studied area 22% out of 2147 Silver fir trees were infected by mistletoe (42.2% - 1st infection class, 32.7% - 2nd class and 25.1% - 3rd class). The highest percentage of infected trees was found in the forest district Manastirea Casin where 42% of examined trees were infected, mostly of the trees being in the 2nd and 3rd infection classes. There was a significant negative correlation between the elevation and mistletoe incidence. Up to 600 m, the most of the trees are heavily infected, while above 800 m the trees are incipiently infected. Regarding the canopy closure, sample plots with understocked and sparsely closed stands have shown a high level of infection compared with plots with closed stands. A significant correlation has been found between the volume of dead Silver fir tees and mistletoe incidence. The highest mistletoe infection was registrated in Silver fir stands at the eastern border of the Eastern Carpathians. There was noticed a decrease of mistletoe infection from the East to the West.Â

Глобальні зміни клімату вже зараз суттєво змінили умови ведення лісового господарства в Українських Карпатах. Зокрема внаслідок масового всихання ялини багато підприємств змушені переорієнтовувати свої лісівничі заходи на вирощування товарної деревини інших порід. Виявлено два основних напрями кліматогенних змін у лісах регіону: зміна едафотопів лісових ділянок у напрямі покращення їхньої родючості з одночасним зменшенням вологості, зміна конкурентоздатності різних деревних видів, зміна породного складу лісів. Найбільші зміни відбуваються в ялинових лісах, де місце ялини, що всихає, природним шляхом займають ялиця і бук, однак під час створення лісових культур вибір головної породи може бути й іншим. Тому актуальним є виявлення закономірностей цих змін для правильного вибору головних порід за типами лісу і висотними рослинними смугами. Тенденції динаміки лісорослинних умов і породного складу лісів регіону були ідентифіковані за відомчими даними метеостанцій та лісовпорядкування. Встановлено, що кліматогенні зміни лісів Українських Карпат відбуваються у таких напрямах: а) дубово-букові ліси трансформуються в буково-дубові зі зміною гігротопу зі «свіжого» на «сухий»; б) буково-ялицеві ліси – в ялицево-букові зі зміною гігротопу з «вологого» на «свіжий»; в) грабово-букові ліси – в грабово-дубово-букові зі зміною гігротопу з «вологого» на «свіжий»; г) смереково-буково-ялицеві ліси – в смереково-ялицево-букові або ялицево-букові зі зміною гігротопу з «вологого» на «свіжий»; д) буково-ялицево-смерекові ліси – в смереково-ялицево-букові або ялицево-букові зі зміною гігротопу з «сирого» і «вологого» на «свіжий»; е) щільнодернинні луки та полонини інтенсивно заростають смерековими, ялівцевими та душекієвими угрупованнями. Констатується нагальна потреба в лісотипологічному картуванні лісогосподарських підприємств Карпатського регіону під час проведення їх повторного лісовпорядкування.

The stochastic backward shifts model better corresponds to the fine-scale structural heterogeneity of old-growth Abies-Fagus-Picea forests than the ontogenic life cycle model

Eighty-four mature Norway spruce (Picea abies L. Karst), silver fir (Abies alba Mill) and Scots pine (Pinus sylvestris L.) trees were winched over to determine the maximum resistive turning moment (M(a)) of the root-soil system, the root-soil plate geometry, the azimuthal orientation of root growth, and the occurrence of root rot. The calculation of M(a), based on digital image tracking of stem deflection, accounted not only for the force application and its changing geometry, but also for the weight of the overhanging tree, representing up to 42% of M(a). Root rot reduced M(a) significantly and was detected in 25% of the Norway spruce and 5% of the silver fir trees. Excluding trees with root rot, differences in M(a) between species were small and insignificant. About 75% of the variance in M(a) could be explained by one of the four variables--tree mass, stem mass, stem diameter at breast height squared times tree height, and stem diameter at breast height squared. Among the seven allometric variables assessed above ground, stem diameter at breast height best described the root-soil plate dimensions, but the correlations were weak and the differences between species were insignificant. The shape of the root-soil plate was well described by a depth-dependent taper model with an elliptical cross section. Roots displayed a preferred azimuthal orientation of growth in the axis of prevailing winds, and the direction of frequent weak winds matched the orientation of growth better than that of rare strong winds. The lack of difference in anchorage parameters among species probably reflects the similar belowground growth conditions of the mature trees.

Silver fir growth responses to drought depend on interactions between tree characteristics, soil and neighbourhood features

Silver fir (Abies alba Mill.) is one of the major tree species (with beech and spruce) in the Polish Carpathians which during the last twenty years significantly improved its vitality. In our study we analyzed the degree of fir stands infestation by fungal pathogens using computer tomography. The test stands at age from 60 to 200 years were located in four different parts of the Polish Carpathians. Our results confirmed large share of fir trees in selected stands with wood decay that was proportionally increasing with stand age. It was also found that the percentage of silver fir with damaged wood by fungal pathogens was similar, and in some stands even bigger than of the Norway spruce, which is generally considered to be susceptible to damage by fungi. Among inspected silver fir trees in seed stands we found also some healthy individuals despite their age above 150 years. We suggest further investigations to determine potential differences between silver fir and Norway spruce in damages caused by fungi in Carpathian forests.

Summary This paper describes dendrochronological and silvicultural investigations in natural or near-natural, and selectively managed, uneven-aged Dinaric silver fir‐beech forests in Slovenia. The results indicate that relatively old understorey silver fir and Norway spruce trees still have a high capacity to tolerate shading and suppression, and can show a vigorous growth response after release. This capacity for growth after suppression did not depend on the tree age or duration of the juvenile stage. The tree-ring width trends of the released understorey trees shows that they have clearly been increasing since around 1950. The current growth rate of released trees is from 3.2 (Norway spruce) to 5.7 (silver fir) times higher than that of suppressed trees. The results suggest that understorey silver fir and Norway spruce trees still have a high potential for application of single tree or small group selection silvicultural systems.

Phytohormones in Needles of Healthy and Declining Silver Fir ( Abies alba Mill.): II. Abscisic Acid

Improving our understanding of the potential of forest adaptation is an urgent task in the light of predicted climate change. Long-term alternatives for susceptible yet economically important tree species such as Norway spruce (Picea abies) are required, if the frequency and intensity of summer droughts will continue to increase. Although Silver fir (Abies alba) and Douglas fir (Pseudotsuga menziesii) have both been described as drought-tolerant species, our understanding of their growth responses to drought extremes is still limited. Here, we use a dendroecological approach to assess the resistance, resilience, and recovery of these important central Europe to conifer species the exceptional droughts in 1976 and 2003. A total of 270 trees per species were sampled in 18 managed mixed-species stands along an altitudinal gradient (400-1200m a.s.l.) at the western slopes of the southern and central Black Forest in southwest Germany. While radial growth in all species responded similarly to the 1976 drought, Norway spruce was least resistant and resilient to the 2003 summer drought. Silver fir showed the overall highest resistance to drought, similarly to Douglas fir, which exhibited the widest growth rings. Silver fir trees from lower elevations were more drought prone than trees at higher elevations. Douglas fir and Norway spruce, however, revealed lower drought resilience at higher altitudes. Although the 1976 and 2003 drought extremes were quite different, Douglas fir maintained consistently the highest radial growth. Although our study did not examine population-level responses, it clearly indicates that Silver fir and Douglas fir are generally more resistant and resilient to previous drought extremes and are therefore suitable alternatives to Norway spruce; Silver fir more so at higher altitudes. Cultivating these species instead of Norway spruce will contribute to maintaining a high level of productivity across many Central European mountain forests under future climate change.