Abies Research Articles

Species delimitation and invasion history of the balsam woolly adelgid, Adelges (Dreyfusia) piceae (Hemiptera: Aphidoidea: Adelgidae), species complex

AbstractThe Adelges (Dreyfusia) piceae (Ratzeburg) species complex is a taxonomically unstable group of six species. Three of the species are cyclically parthenogenetic [Ad. nordmannianae (Eckstein), Ad. prelli (Grossmann), and Ad. merkeri (Eichhorn)] and three are obligately asexual [Ad. piceae, Ad. schneideri (Börner), and Ad. nebrodensis (Binazzi & Covassi)]. Some species are high‐impact pests of fir (Abies) trees, so stable species names are needed to communicate effectively about management. Therefore, to refine species delimitation, guided by a reconstruction of their biogeographic history, we genotyped adelgids from Europe, North America, and the Caucasus Mountains region with 19 microsatellite loci, sequenced the COI DNA barcoding region, and compared morphology. Discriminant analysis of principal components of microsatellite genotypes revealed four distinct genetic clusters. Two clusters were morphologically consistent with Ad. nordmannianae. One of these clusters consisted of samples from the Caucasus Mountains and northern Turkey, and the other included samples from this region as well as from Europe and North America, where Ad. nordmannianae is invasive. A third cluster was morphologically consistent with Ad. piceae, and included individuals from Europe, where it is native, and North America, where it is invasive. In North America, the majority of Ad. piceae individuals were assigned to two geographically widespread clones, suggesting multiple introductions. The fourth cluster included individuals morphologically consistent with Ad. prelli or Ad. merkeri. However, based on genetic assignments, hybrid simulations, and approximate Bayesian computation, we find it likely that these are contemporary hybrids between Ad. nordmannianae and Ad. piceae that arose independently in Europe and North America, so we propose that Ad. prelli and Ad. merkeri are invalid. Finally, we synonymise Ad. schneideri (syn.n.) with Ad. nordmannianae and designate Ad. nebrodensis as subspecies Ad. piceae nebrodensis (stat.n.). Our revised taxonomy therefore recognises two species: Ad. nordmannianae and Ad. piceae, which we estimate to have diverged recently, during one of the last two interglacial periods. Finally, we comment on this species complex being in the midst of transition between sexual and asexual reproduction, a pattern that is probably common in Adelgidae.

Wind and Snow Loading of Balsam Fir during a Canadian Winter: A Pioneer Study

Widely distributed across Quebec, balsam fir (Abies balsamea (L.) Mill) is highly vulnerable to wind damage. The harsh winter conditions, freezing temperatures, and snow pose an additional risk. It is important to find the mechanical loads experienced by trees during winter to adapt forest management and minimize the risk of damage to this species. Many studies have been carried out on wind and snow loading damage risks in Northern Europe, mostly based on post-storm damage inventories. However, no study has continuously monitored the applied turning moment during a period with snow loading, and no study has investigated wind and snow loading on balsam fir. Therefore, our main objective was to conduct a pioneering study to see how trees bend under wind loading during winter, and to see how snow cover on the canopy contributes to the loading. Two anemometers placed at canopy height and 2/3 canopy height, air and soil temperature sensors, a hunting camera, and strain gauges attached to the trunks of fifteen balsam fir trees, allowed us to measure the wind and snow induced bending moments experienced by the trees together with the meteorological conditions. Data were recorded at a frequency of 5 Hz for more than 2000 h during summer 2018 and winter 2019. Two mixed linear models were used to determine which tree and stand parameters influence the turning moment on the trees and evaluate the effect of winter. The selected model for measurements made during winter found that including the snow thickness on crowns was better than those models that did not consider the effect of snow (ΔAICc > 25), but the effect of snow depth on the bending moment appears to be minor. However, overall, the turning moment experienced by trees during winter was found to be higher than the turning moment experienced at the same wind speed in summer. This is probably a result of increases in the rigidity of the stem and root system during freezing temperatures and the change in wind flow through the forest due to snow on the canopy and on the ground during the winter season.

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

Mixed forests are expected to be more productive and resilient against disturbances than pure forests. However, tree to tree interactions are complex and vary depending on tree characteristics and multiple site features including soil properties. Such complexity is not normally accounted for in studies of mixing effects on tree response to drought. Here, we evaluate if neighbourhood tree identity influence soil biotic and abiotic characteristics in three mature, mixed Silver fir (Abies alba) forests. Further, we investigate the relationships between radial growth response to drought, tree characteristics (growth rate, size and competition pressure), tree neighbourhood, and soil physico-chemical and biological properties. Patterns of covariation between tree size, competition pressure, soil microbial composition, and growth recovery after drought were observed among different neighbourhood types. Slow-growing, small Silver fir trees experiencing high competitive pressure were associated with higher proportions of Scots pine (Pinus sylvestris) in the neighbourhood, high soil C:N ratios, and showed a faster growth recovery after drought. A neighbourhood dominated by broadleaf species (mainly European beech, Fagus sylvatica) was associated with high biomass of arbuscular mycorrhizal fungi, and low biomass of Gram-positive bacteria and Eukaryote, together with lower tree growth recovery. Therefore, coexistence with other Silver fir, Scots pine or European beech trees is associated to different covariation patterns of tree, soil and drought performance variables of the target Silver fir trees. Finally, our study remarks that combining tree, soil and neighbour variables at individual level helps to understand patterns of tree growth and growth response to drought under different stand mixtures.

Soil fungal diversity and biological activity as indicators of fertilization strategies in a forest ecosystem after spruce disintegration in the Karpaty Mountains

Forest soils are being exposed to nutrient deficiency and acidification at increasing rates as a result of intensive management. Mineral fertilization, however, provides a way to improve soil nutrient balance. The aim of this study is to present the effects of mineral fertilization on the properties of forest soil 11 years after fertilization. Our research investigated the effects of dolomite, magnesite and serpentinite fertilization on the physicochemical properties of the soil, soil biological activity, and fungal diversity. We also determined the condition of a new generation of fir trees after mineral fertilization. In autumn, 2008, fertilizers (dolomite, magnesite and serpentinite, specifically) in the amount of 4000 kg.ha−1 were added to plots in the Wisła Forest District in Poland; one area was left unfertilized to act as the control area for this research. Our results reveal that all fertilization improved the selected soil's physicochemical properties (pH, Ca and Mg content) and accordingly, its biochemical activity; in particular, we found that dolomite (4000 kg.ha−1) contributed heavily to soil improvement. The findings also showed that soil pH and calcium content were strongly dependent on enzymatic activity, while dolomite fertilization resulted in a significant increase in biomass size in the fir trees included in this study. In addition to being associated with the highest plant biomass and amounts of enzymatic activity, dolomite-fertilized soil also had the highest number of fungal operational taxonomic units (OTUs): 403, compared to 322 OTUs in the control soil. Finally, the fungal communities in the control soil varied significantly from the fungal communities in soils fertilized with dolomite and serpentinite. The results of this research support mineral fertilization, and in particular, fertilization using dolomite in amounts of 4000 kg.ha−1, to improve soil nutrient supply and to shape the biological activity expressed by the enzymatic activity of forest soils.

Recent decline of high altitude coniferous growth due to thermo-hydraulic constrains: evidence from the Miyaluo Forest Reserve, Western Sichuan Plateau of China

Tree growth decline has been reported in many places around the globe under the context of increasingly warming climate, and strengthening drought intensity is detected to be the primary factor for such decline, particularly in northern forest sites, as well as arid and semi-arid areas. Yet, the forest growth decline in high altitude, high mountain sites certainly merits investigation. Here, we reported faxon fir (Abies fargesii var. faxoniana) forest growth decline (slope = -0.64) at the tree line (4150 m above sea level) in Miyaluo Forest Reserve (MFR) at the Western Sichuan Plateau, southwestern China since 2000. We investigated the cause of tree growth decline by applying dendrochronological approaches. We took tree-ring samples from fir trees at the tree line and developed tree-ring width (TRW) chronology. The tree growth – climate relationship analysis showed that maximum temperature (Tmax) was the primary factor limiting the radial growth of fir trees in the investigated area. The moving correlation analysis indicated the strengthening positive influence of Tmax, spring precipitation, and cloud cover during winter and monsoon period on radial growth since 2000s. Our results have shown that both thermal and hydraulic constrains accounted for the radial growth decline of fir trees at the tree line of MFR in the western Sichuan Plateau.

Intraspecific structural signs of curly silver fir (Abies alba Mill.) growing in the Ukrainian Carpathians

The aim of this paper is to present the intraspecific differentiation of the curly silver fir (Abies alba Mill.) by the wood structure growing in the Ukrainian Carpathians. To find the morphological distinctions by using the silvicultural and biometric methods, 50 silver fir trees with anomalous wavy-relief stemwood formations were investigated. The trees aged from 94 to 132 years were characterised by the diameter at breast height of 32–59 cm. The length of the wave-grained stemwood varied from 6 to 11.5 m. The amplitude of the wood fibre waves varied from 4.4 to 24.1 mm. The smallest values of the amplitude of the wave-grained wood corresponded to the smaller wavelengths. The significant differences in the wood density and annual growth between the silver fir trees with the straight-grained and wave-grained stem wood were determined. The number of annual rings in 1 cm of the curly silver fir was 27.1% lower and 22.7% higher than the same characteristics for the straight-grained stem wood. The obtained linear equation described the relationship between the number of annual rings in 1 cm and the basic wood density of the silver fir with the straight-grained wood. The aesthetic features of the curly silver fir stem wood were discussed in the subject area of a new niche of exclusive wood products.

Testing an individual tree wind damage risk model in a naturally regenerated balsam fir stand: potential impact of thinning on the level of risk

Abstract Widely distributed in Quebec, balsam fir (Abies balsamea (L.) Mill.) is highly vulnerable to wind damage. Recently, there has been a trend in forest management to increase the use of partial cuttings in naturally regenerating stands, leaving the remnant trees at increased risk of wind damage. In order to limit wind damage after partial cuttings, it is therefore important to find silvicultural practices that minimize the risk of wind damage in these fir stands. Our main objective was to find balsam fir-specific values of parameters to integrate into the wind risk model ForestGALES, in order to simulate the impact of different types of commercial thinning on wind damage risk, and to determine which practice potentially minimizes the risk in a naturally regenerated stand. An anemometer placed at canopy height and strain gauges attached to the trunks of balsam firs allowed us to measure the wind-induced bending moments experienced by a sample of balsam fir trees. This enabled the calculation of the turning moment coefficients specific to each of the trees in order to compare them with the ForestGALES model predictions and to adapt the model for balsam fir stands. The model was tested first with only tree diameter and height as input variables to calculate the turning moment coefficient, then with the addition of a competition index, and finally with the addition of crown dimensions. Wind climate parameters for prediction of the probability of damage were calculated using the Wind Atlas Analysis and Application Program airflow model. The model with the highest accuracy was then used to simulate two types of thinning and determine the impact on wind damage risk for each tree in the stand. According to the model’s predictions, thinning from below has a reduced risk of wind damage compared with thinning from above.

Changes in Siberian Fir Crown Architecture under Impaired Homeostasis

The crown of the Siberian fir (Abies sibirica) is characterized by a specific organization, namely, a narrow-pyramidal form, apical dominance, tiering by types of sexualization, and whorled branching. The gravitational vector is clearly manifested at all levels of the organization of the crown, that is, in the architecture (diageotropism of branches), morphostructure (dorsoventrality of tissues and organs of shoots, as well as the location of reproductive organs in the tree crown and on the shoot), and physiological processes. It was shown that the internal state of the tree is a determining factor in graviperception. When Siberian fir trees weaken, the diageotropism of branches is lost, which can serve as a universal biomarker of impairment of homeostasis.

Collective growth patterns reveal the high growing potential of older silver fir trees in a primeval forest in Romania’s Southern Carpathians

The trees’ ability to respond and adjust to very different growing conditions during their lifespans varies depending on tree species and the site-specific situations. Identifying the underlying mechanisms and the individual drivers that may affect the patterns of tree growth is crucial in ecological and economic terms. How long can forest trees grow and sustain biomass accumulation, with increasing age, is still under debate. In order to determine the factors that influence growth releases for silver fir (Abies alba Mill.) trees in a temperate old-growth forest of Romania's Southern Carpathians, an analysis of radial and basal area growth patterns was initiated. Dendroecological methods were used to reconstruct radial growth both at the individual level, but especially at the group level, in four clusters obtained by a prior k-cluster analysis depending on social status. The study results showed that the growth rate of older trees increases continuously for this species at stand level, even after the typical harvesting age in managed forests. Although the direction and intensity of the climate-growth correlations at individual level were very different, the considered climatic variables explaining little to none of the growth variation, the cumulative response of the analysed trees to climate change is directly correlated with the mean July-August temperature, confirming the capacity of the silver fir to tolerate drought. Our results demonstrate that the trees of the same species are able to obtain together a temporal plasticity in strategies, exceeding the adaptability of individuals considered separately and suggest the positive impact of facilitative intraspecific interactions on forest growth.

Попередні результати досліджень потомств кращих та нормальних дерев псевдотсуги Мензіса (Pseudotsuga menziesii (Mirb.) Franco) в умовах Лісостепу України

Стаття репрезентує результати обстеження потомств кращих та нормальних дерев псевдотсуги Мензіса (Pseudotsuga menziesii (Mirb.) Franco), відібраних у дослідних культурах ДП «Харківська ЛНДС». Досліджено особливості росту дворічних сіянців 22 потомств у теплиці ДП «Гутянське ЛГ» та 17 потомств на родинній насінній плантації у Вінницькій області. Відзначено добрі збережуваність рослин (61,5 %) та стан, велику частку прямостовбурних дерев та високу інтенсивність росту. За результатами комплексного оцінювання потомств у 8-річному віці 5 дерев псевдотсуги можуть бути попередньо рекомендовані для заготівлі насіння й живців із метою створення лісонасінних плантацій в умовах Лісостепу України. Решту 10 слід у подальшому вивчати на основі дослідження їхнього потомства. Насіння від загального збору з дерев, які оцінювали, може бути рекомендовано для створення постійних лісонасінних ділянок.

Species-specific drought resilience in juniper and fir forests in the central Himalayas

Abstract With increased frequency and intensity of drought occurrence in the changing climate, the drought resilience of forest trees is of widespread interest. Particularly, it is not clear as to how the resilience differs between tree species and whether or not such resilience changes over time. Understanding tree resilience to drought requires observations not only from recent events but also from the historical past, information of which is usually hardly available. Here we defined historical drought based on isotope data and compared drought resilience in Juniperus tibetica and Abies spectabilis forest in the central Himalayas in five extreme droughts during the past two centuries. We found that juniper trees had a stronger resistance than fir trees in the three extreme droughts in the nineteenth century but this pattern reversed in the two drought events in the twentieth century. The length of response time to droughts and recovery time to pre-drought state were shorter in juniper trees than in fir trees. The proportion of declining trees showed a decreasing trend in fir trees but not in juniper trees. Our results indicate that the species-specific resilience might be related to the anisohydric (junipers) and isohydric (firs) strategies of stomatal regulation in response to droughts plants. The differences in species-specific drought resilience should be taken into account when developing forest management policies against the influence of extreme droughts in future.

Rango altitudinal: factor de vigor forestal y determinante en la regeneración natural del oyamel

Objetivo: evaluar el vigor del arbolado y la regeneración natural de oyamel al oriente del Estado de México, considerando variables topográficas y forestales.Método: se usó muestreo sistemático, con sitios cada 100 m s. n. m. entre los 2900 y 3600 m s. n. m. Con el programa SAS se hicieron pruebas de normalidad, tablas de frecuencia y análisis de varianza para analizar la relación entre altitud, vigor y regeneración de Abies religiosa (Kunth) Schltdl. et Cham.Resultados: hay relación entre la altitud, el vigor y la densidad arbórea. La regeneración es nula en las cotas más bajas e incrementa con la altitud hasta los 3 400 m s. n. m. y no muestra gran reducción más arriba. La densidad de los estratos A (DAP ≥12.5 cm) y B (DAP <12.5 cm y >1 m de altura) incrementa conforme a la altitud; las densidades más altas se registran en la cota 3 400 m s. n. m.Limitaciones: se requiere investigación de otros factores que intervienen en la distribución de la especie.Principales hallazgos: la regeneración tiene más éxito en zonas medias y altas, y la condición del arbolado tiende a ser mejor ahí también. Se evidencia que el oyamel migra a zonas más elevadas, debido al cambio climático global.

Тенденції динаміки типів лісорослинних умов і породного складу деревостанів Українських Карпат у зв’язку зі змінами клімату

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.

Peculiarities of cambial growth of some woody plants introduced in Kakheti region

The paper deals with the study of cambial growth of 32 species of woody plants, carried out in Kakheti region during six years. We have studied several plants and found out that they begin their cambial growth (with the exception of some oak species) after bud opening. According to calendar time, two groups of plants were distinguished: the first group of the plants began cambial growth in late March and at the beginning of April. These plants are as follows: Larix decidua Mill and Larix leptolepis Gord., Acer negundo L., Aesculus carnea Haine., Aesculus hippocastanum L. and 20 other species. The second group of the plants began cambium activity in May. These are plant species like Picea orientalis (L.) Link., Pinus griffithii Mc Cleland, Quercus occidentalis J. Gay., Magnolia grandiflora L. and others. The earliest completion of cambial growth was observed in the lateral branches of spruce, fir and other trees. The latest accomplishment (the first half of October) of cambial growth occurred in case of Cedrus atlantica Mannetti. and Cedrus deodara Loud., Pinus griffithii Mc Clel., Magnolia grandiflora L., Firmiana platanifolia Schott., etc. The endogenous rhythm of the investigated plants (with few exceptions) is in synchronous connection with the climate of Kakheti region, so we consider these plants to be interesting species for the decorative gardening and forestry of Telavi district, and deserve widespread distribution.

STRUCTURAL AND DYNAMIC CHANGES IN MIXED FORESTS OF BEECH AND FIR ON MT. GOČ

The primary goal of this research was to analyze the structural, production and dynamic changes of theforests of beech and fir in permanent sample plots of Mt. Goč, excluded from regular management fora period of 35 years (1977–2011). The established principles of spontaneous development and selfregulatoryprocesses could have implications on the regular management in these forests located in thearea of Mt. Goč and other areas.The results of this research in the permanent sample plots indicate that the mixed forests of beech andfir have suffered a number of changes in terms of structure and production in the investigated period.Structural disruptions have been the result of a decrease in the share of small and medium-diametertrees, as well as an increase in the share of trees of large dimensions in the total number of trees. Thecurves of distribution have been moved to the right and in terms of shape they differ from the lines thatare typical of selection forests. A relatively large number of trees per hectare and the described distributionby diameter classes have resulted in the high values of basal area and stand volume. In addition,a high volume increment has also been recorded. The quality and incremental capacity of the standshave been reduced due to a significant share of old beech and fir trees. The accumulation of volumeslowed down the dynamics of stand development and hindered rejuvenation and recruitment, as thenecessary prerequisites for structural stability and functionality in selection forests.The observed trends of development in these forests in the sample plots clearly indicate that a structurallystable, socio-economically and ecologically valuable selection forest is possible to achieve only withan active and continuous implementation of a set of management procedures, which primarily refersto selection cutting. Self-regulatory processes that are allowed over time, as in the case of the analyzedsample plots, are increasingly distancing us from this goal.

Реконструкция истории древостоев и оценка воздействия инвазивного короеда в пихтовых лесах с помощью анализа пространственной структуры

The most devastating insect invasion of forest ecosystems in Russia is the recent mass reproduction of the four-eyed fir bark beetle (Polygraphus proximus Blandf.) in southern Siberian fir (Abies sibirica Ledeb.) forests. The objective of our research was to study the spatial structure of fir forests and their change under the impact of the four-eyed fir bark beetle in its secondary (invasive) distribution range. We selected two fir stands located near the villages of Itatka and Malinovka in the Tomsk region. Both stands represent natural ripe succession forests on sites that previously experienced logging activities, which were triggered by settlement activities in the second half of the nineteenth century. We used Field-Map technology for gathering non-spatial and spatial stand data. The analysis showed that height, diameter and radial increment of fir trees, killed or severely weakened by attacks of the four-eyed fir bark beetle, were significantly lower than that of healthy individuals. The social status of fir trees, seriously attacked or already killed by Polygraphus proximus was indicated by the Ui index as moderately suppressed. In contrast to the distribution pattern of living firs, the pattern of dead or severally weakened firs killed by the four-eyed fir bark beetle was significantly clumped over short distances (sample plots (SP) Itatka and Malinovka). This finding coincides with visual observations in other stands, that dead trees are grouped to some extent. However, the hypothesis of spatial independence of the tree positions of living and dead firs was accepted for both plots.Funding: The research was funded by the Russian Foundation for Basic Research and the government of Tomsk region, grant No. 16-44-700782, and carried out as part of a state assignment of the Center for Forest Ecology and Productivity of the Russian Academy of Sciences (No. АААА-А18-118052400130-7).For citation: Debkov N.M., Gradel A., Aleinikov A.A. Reconstruction of Stand History and Impact Evaluation of an Invasive Bark Beetle in Siberian Fir Forests with the Help of Spatial Structure Analysis. Lesnoy Zhurnal [Russian Forestry Journal], 2020, no. 3, pp. 24–41. DOI: 10.37482/0536-1036-2020-3-24-41

The paradox of defoliation: Declining tree water status with increasing soil water content

Defoliation can enhance tree water status by reducing canopy transpiration under drought. During long-lasting insect outbreaks however, this effect can be transient as reduced foliage affects not only transpiration but also the entire soil-plant-atmosphere continuum. In this study, we investigated the effects of defoliation and vapor pressure deficit (VPD) on plant and soil water status in balsam fir and black spruce defoliated by spruce budworm, Choristoneura fumiferana (Clemens). We sampled 48 fir trees and 36 spruce trees subjected to differing severities of defoliation. In May–September 2014 and 2015, we monitored the relative shoot water content (RWC) and soil volumetric water content (VWC), and midday shoot water potential (Ψmd, only in 2015). We applied linear mixed models (LMMs) to assess changes in RWC, Ψmd, and VWC to defoliation and VPD and we ran structural equation models (SEM) to determine the causal relationships between the measured variables in relation to defoliation and VPD. In LMMs models, defoliation and VPD, as individual factors, reduced Ψmd in both balsam fir and pooled species models but did not affect RWC. Defoliation alone increased VWC in balsam fir and in pooled models. We observed no interaction between VPD and defoliation on tree water status, but significant effect on VWC (in balsam fir and pooled models), indicating that both factors had independent and additive effects on plants but not on soil. However, in SEM models, RWC was negatively correlated to defoliation, suggesting a hydraulic safety margin. Under conditions of multiple-years of natural defoliation during a spruce budworm outbreak, the decrease in Ψmd reflects the amount of internal water capacitance that could be caused by both a lower Ψmd due to larval feeding and a negative feedback between defoliation and xylem vulnerability.

Pit and pit aperture dimensions in plantation-grown Douglas fir as affected by local growth conditions and height in stem

Abstract This study assessed whether allometric scaling applied to pit sizes in stems of Douglas fir. Pit and pit aperture diameters were measured in xylem from stems of four plantation-grown Douglas fir (Pseudotsuga menziesii) trees from each of two different sites in Denmark. One site had fertile soil, the other had poor soil fertility. Three different heights were accessed for each tree, and 40 pits were measured per height. Results showed that pit diameter varied between 17 and 24 μm and decreased significantly with increasing height above ground. Representing the position in the tree as a power function of distance from the top of the tree (L0.2) rather than the height above ground improved the model fit for pit diameter as expressed by the R2 value. However, the pit diameter relationship was found to be significantly affected by site, suggesting that anatomic dimensions relate not only to tree size but also to growth conditions. This would imply that even though pit size supposedly has a strong biophysical determination, some xylem plasticity may still be induced by environmental factors.

Genome Sequencing of the Endangered Kingdonia uniflora (Circaeasteraceae, Ranunculales) Reveals Potential Mechanisms of Evolutionary Specialization.

SummaryKingdonia uniflora, an alpine herb, has an extremely narrow distribution and represents a model for studying evolutionary mechanisms of species that have adapted to undisturbed environments for evolutionarily long periods of time. We assembled a 1,004.7-Mb draft genome (encoding 43,301 genes) of K. uniflora and found significant overrepresentation in gene families associated with DNA repair, underrepresentation in gene families associated with stress response, and loss of most plastid ndh genes. During the evolutionary process, the overrepresentation of gene families involved in DNA repair could help asexual K. uniflora reduce the accumulation of deleterious mutations, while reducing genetic diversity, which is important in responding to environment fluctuations. The underrepresentation of gene families related to stress response and functional loss of ndh genes could be due to lack or loss of ability to respond to environmental changes caused by long-term adaptation to a relatively stable ecological environment.

The interactive effect of competition and climate on growth of boreal tree species in western Canada and Alaska

Understanding interactions between competition and climate in relation to their effects on individual tree growth is crucial to the development of climate-sensitive growth models required for modelling boreal forest succession in a changing climate. We used data from permanent growth and yield sample plots in western Canada and Alaska to investigate the impact of competition within a regional gradient of climatic conditions for lodgepole pine (Pinus contorta Douglas ex Loudon), jack pine (Pinus banksiana Lamb.), trembling aspen (Populus tremuloides Michx.), balsam poplar (Populus balsamifera L.), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.). We characterized the effects of competition (basal area of spruce–fir, deciduous, and pine trees larger than the focal tree) and climate (mean annual temperature and precipitation) and their interactions on basal area growth of individual trees using linear mixed-effects models. Our results indicated that intraspecific competition had stronger effects on growth than interspecific competition and climate. Moreover, significant interactions between intraspecific competition and climate suggest that an increase in intraspecific competition will lead to a reduction in tree growth for warmer regions (lodgepole pine, trembling aspen, balsam poplar, and white spruce) and wetter regions (jack pine). The manner in which interspecific competition altered tree growth responses to climate was variable, depending on tree species and competition type. These results indicate that the relationships between growth and climate may differ according to the degree of competition and the structure of the stand.