Radial Growth Patterns Research Articles

Tree-ring record in Ethiopian church forests reveals successive generation differences in growth rates and disturbance events

Forests provide fundamental ecosystem services. Environmental changes are predicted to affect forest growth directly through increased environmental stressors, and indirectly by amplifying disturbance. To increase our understanding of effects of environmental changes and disturbance on Afromontane forest growth, we used tree-ring data collected from Juniperus procera trees from church forests in the northwest highlands of Ethiopia. We used structural change models to detect structural shift in growth trends. We applied Linear Mixed Effect Models (LMM) to compare growth rate differences between successive tree generations. The running mean method and radial growth pattern analysis were used to detect disturbance events. Three groups of generations were identified based on Basal Area Increment (BAI) rates. There are significant differences (χ2 = 204.64, P < .001) among generations in pace of BAI, indicating that old generation trees grew at a slower pace than younger ones. Radial growth patterns were homogeneous for the old generation, but diverse in young trees. The observed high growth rates in the younger generation may have a negative effect on the longevity of the individuals and positively affect carbon accumulation in the biomass. Disturbance was detected in all generations, but worsened in the 20th century. About 35% of disturbances matched with climate extreme events, providing evidence that the disturbance is both human-induced (i.e., site-specific) and climate-induced. Thus, forest management plans should emerge from a sound understanding of climate-forest-human interaction.

Morphological characterization of Ampelomyces spp., a hyperparasite of Bhendi (Abelmoschus esculentus (L.) Moench) powdery mildew

Ampelomyces is a naturally occurring hyperparasite on powdery mildews. Survey was conducted in major bhendi (Abelmoschus esculentus (L.) Moench) growing districts of Tamil Nadu during June 2014 to assess the incidence of powdery mildew and to collect different isolates of Ampelomyces spp. The results of the survey revealed that the disease incidence ranged from 15.54 to 63.45 %. Ten isolates of Ampelomyces spp. were collect-ed from surveyed areas of powdery mildew. Isolation of Ampelomyces spp. was done from powdery mildew infected bhendi leaf parasitized by Ampelomyces spp. using tissue segment method. All the isolates were identified by their morphological characters. The colour of the colonies in various medium was brownish black to greenish white. Most of the isolates showed radial and fluffy growth pattern with raised growth. The pycnidia of different isolates of Ampelomyces varied in their shape and were mostly ovoid, ellipsoid, cylindrical, pyriform to globose in shape. The size of pycnidia varied from 29.2-72.5×22.4-43.1 ?m. The number of pycnidia was found to be more in isolates viz., TNAU-AQ101 and TNAU-AQ103. Pycnidiospores are hyaline, unicellular and guttulate in shape. The pycnidial production was higher in TNAU-AQ101 and TNAU-AQ103. Application of agrochemicals is one of the oldest and most effective methods to manage powdery mildew disease. However, incessant use of these agrochemicals has many demerits such as development of resistance to pathogens, residual toxicity and environmental pollution. Hence, search for an alternative means for disease management is envisaged. The genus Ampelomyces are the major antagonists as an alternative of Erysiphales fungi being a significant group of phytopathogens.

Wild Apple Growth and Climate Change in Southeast Kazakhstan

Wild populations of Malus sieversii [Ldb.] M. Roem are valued genetic and watershed resources in Inner Eurasia. These populations are located in a region that has experienced rapid and on-going climatic change over the past several decades. We assess relationships between climate variables and wild apple radial growth with dendroclimatological techniques to understand the potential of a changing climate to influence apple radial growth. Ring-width chronologies spanning 48 to 129 years were developed from 12 plots in the Trans-Ili Alatau and Jungar Alatau ranges of Tian Shan Mountains, southeastern Kazakhstan. Cluster analysis of the plot-level chronologies suggests different temporal patterns of growth variability over the last century in the two mountain ranges studied. Changes in the periodicity of annual ring-width variability occurred ca. 1970 at both mountain ranges, with decadal-scale variability supplanted by quasi-biennial variation. Seascorr correlation analysis of primary and secondary weather variables identified negative growth associations with spring precipitation and positive associations with cooler fall-winter temperatures, but the relative importance of these relationships varied spatially and temporally, with a shift in the relative importance of spring precipitation ca. 1970 at Trans-Ili Alatau. Altered apple tree radial growth patterns correspond to altered climatology in the Lake Balkhash Basin driven by unprecedented intensified Arctic Oscillations after the late 1970s.

Intra-annual leaf phenology, radial growth and structure of xylem and phloem in different tree parts of Quercus pubescens

Basic knowledge of the intra-annual timings of leaf development and radial growth (including the phloem part) in different tree parts is generally missing although such rudimentary data are crucial to link the structure and function of vascular tissues at the whole tree level. To understand better the time course of leaf development and radial growth patterns in different tree parts, we studied leaf phenology and intra-annual xylem and phloem formation and structure in the stem and at two locations in branches of sub-Mediterranean Quercus pubescens in 2015. Onset and end dates of cambial cell production were synchronized at the two locations in branches, but were different at the stem base. The period of cell production was thus a month longer in the stem, resulting in 82.8 and 45.1% wider xylem and phloem increments, respectively. In addition, the xylem ring was wider than the phloem ring in all three parts. Thus, phloem ring widths in stem represented 24.8% and in branches 79.4% of the xylem ring width. Earlywood occupied 52.9% (stem) and 74.9% (branches) of the xylem ring, and early phloem 53.7% (stem) and 43.3% (branches) of the phloem ring. Most of the annual radial increment (i.e. xylem and phloem increments) in stem and branches was formed prior to full leaf development. Latewood and late phloem were formed in the period of full leaf unfolding. Our study confirmed that the temporal sequence of leaf development and radial growth are not contemporary in Q. pubescens. Different intra-annual patterns of radial growth in different tree parts result in different structures of xylem and phloem, which is in line with different roles of stem and branches in terms of tree functioning.

Growth rate reduction causes a decline in the annual incremental trunk growth in masting Fagus crenata trees

Tree trunk annual increments are markedly reduced in mast years. There are two hypotheses that could explain the mechanism for this phenomenon: (1) a reduction in the duration of growth due to switching the resource allocation from somatic growth to seed production; (2) reduction of growth rate due to resources being shared between somatic growth and reproduction simultaneously. In this study, we aimed to test these hypotheses in Fagus crenata Blume from the point of view of resource allocation. The radial growth patterns in F. crenata during a year without reproduction (2014) and a masting year (2015) were monitored using a digital dendrometer. At the same time, shoot growth patterns were monitored by sampling branches from the top of the canopy. Data obtained using the digital dendrometer were fitted to a sigmoidal function, and the parameters of the function were evaluated with a hierarchal Bayesian approach; estimated parameters were used to represent the properties of trunk growth phenology. Trunk growth started synchronously just after leaf unfurling in both mass-fruiting (F15) and limited-fruiting (NF15) trees in 2014 and 2015. Reproduction reduced the growth rate in 2015. This was due to the resources being allocated for the development of cupules and for formation of relatively thick branches, both of which occurred simultaneously with trunk growth. There was no clear difference in the duration of radial growth between F15 and NF15 trees in the 2 years, although seed maturation started after trunk growth ceased. As a result, the annual trunk radius increment was reduced in the F15 trees in 2015. These results suggested that reduction of radial growth rate (Hypothesis 2) caused the reduction in annual trunk increment of reproducing trees of this species.

Stand structure, recruitment and growth dynamics in mixed subalpine spruce and Swiss stone pine forests in the Eastern Carpathians

Natural subalpine forests are considered to be sensitive to climate change, and forest characteristics are assumed to reflect the prevalent disturbance regime. We hypothesize that stand history determines different stand structures. Based on large full inventory datasets (including tree biometric data, spatial coordinates, tree age, and basal area increment) we assessed the size structure, tree recruitment dynamics and radial growth patterns in three permanent plots along an altitudinal gradient in a mixed coniferous forest (Picea abies and Pinus cembra) in the Eastern Carpathians. Both discrete disturbances (large scale or small scale) and chronic disturbances (climate change) were identified as drivers of stand structure development in the studied plots. A stand replacing wind disturbance generated a unimodal bell-shaped size and age distribution for both species characterized by a sharp increase in post-disturbance recruitment. By contrast, small-scale wind-caused gaps led to a negative exponential diameter distribution for spruce and a left-asymmetric unimodal for pine. Climate-driven infilling processes in the upper subalpine forest were reflected as J-shaped size and age distributions for both species, but with pine predating spruce. The growth patterns for both species demonstrated an increased basal area increment since the early 1900s, with an emphasis in the last few decades, irrespective of stand history. Pine demonstrated a competitive advantage compared to spruce due to the higher growth rate and size at the same age. Recognition of combined discrete and chronic disturbances as drivers of the tree layer characteristics in a subalpine coniferous forest is essential in both stand history analyses and growth predictions.

Understanding tree growth responses after partial cuttings: A new approach.

Forest ecosystem management heads towards the use of partial cuttings. However, the wide variation in growth response of residual trees remains unexplained, preventing a suitable prediction of forest productivity. The aim of the study was to assess individual growth and identify the driving factors involved in the responses of residual trees. Six study blocks in even-aged black spruce [Picea mariana (Mill.) B.S.P.] stands of the eastern Canadian boreal forest were submitted to experimental shelterwood and seed-tree treatments. Individual-tree models were applied to 1039 trees to analyze their patterns of radial growth during the 10 years after partial cutting by using the nonlinear Schnute function on tree-ring series. The trees exhibited different growth patterns. A sigmoid growth was detected in 32% of trees, mainly in control plots of older stands. Forty-seven percent of trees located in the interior of residual strips showed an S-shape, which was influenced by stand mortality, harvested intensity and dominant height. Individuals showing an exponential pattern produced the greatest radial growth after cutting and were edge trees of younger stands with higher dominant height. A steady growth decline was observed in 4% of trees, represented by the individuals suppressed and insensitive to the treatment. The analyses demonstrated that individual nonlinear models are able to assess the variability in growth within the stand and the factors involved in the occurrence of the different growth patterns, thus improving understanding of the tree responses to partial cutting. This new approach can sustain forest management strategies by defining the best conditions to optimize the growth yield of residual trees.

Disturbance severity and canopy position control the radial growth response of maple trees (Acer spp.) in forests of northwest Ohio impacted by emerald ash borer (Agrilus planipennis)

Radial growth of silver and red maples was investigated across three forests in northwest Ohio following the outbreak of the invasive emerald ash borer. The growth response of maples was driven by an advancement in canopy class and disturbance severity. Forest disturbances resulting in species-specific diffuse mortality cause shifts in aboveground and belowground competition. This competition may differentially affect non-impacted trees, depending on crown class, disturbance severity, and species-specific responses. The purpose of this study is to elucidate the primary drivers of silver and red maple (Acer saccharinum and A. rubrum) growth following emerald ash borer (EAB, Agrilus planipennis)-induced ash tree (Fraxinus spp.) mortality in riparian forests of northwest Ohio. Using dendroecological approaches, we analyzed the pattern of radial growth in red and silver maples in conjunction with the EAB outbreak. This study revealed growth rates of maples increased 72% following EAB arrival and trees advancing in crown class grew 41% faster than those not advancing. The growth response varied by initial crown class, with trees in the intermediate class responding most dramatically. Furthermore, the positive correlation between relative basal area of ash and the radial growth response of maples indicates the important role of disturbance severity in post-disturbance dynamics. These findings suggest that, although advancement in crown class may allow predictions of “winners” in forest succession post-disturbance, even trees not changing crown class benefit from decreased competition. Results from this study provide a detailed account of radial growth responses in maples following EAB-induced ash mortality and lend insight into the future canopy composition of ash-dominated riparian forests.

An empirical method that separates irreversible stem radial growth from bark water content changes in trees: theory and case studies.

Substantial uncertainty surrounds our knowledge of tree stem growth, with some of the most basic questions, such as when stem radial growth occurs through the daily cycle, still unanswered.We employed high‐resolution point dendrometers, sap flow sensors, and developed theory and statistical approaches, to devise a novel method separating irreversible radial growth from elastic tension‐driven and elastic osmotically driven changes in bark water content. We tested this method using data from five case study species. Experimental manipulations, namely a field irrigation experiment on Scots pine and a stem girdling experiment on red forest gum trees, were used to validate the theory.Time courses of stem radial growth following irrigation and stem girdling were consistent with a‐priori predictions. Patterns of stem radial growth varied across case studies, with growth occurring during the day and/or night, consistent with the available literature. Importantly, our approach provides a valuable alternative to existing methods, as it can be approximated by a simple empirical interpolation routine that derives irreversible radial growth using standard regression techniques. Our novel method provides an improved understanding of the relative source–sink carbon dynamics of tree stems at a sub‐daily time scale.

Tree responses to moisture fluctuations in a neotropical dry forest as potential climate change indicators

Trees in tropical dry forests (TDFs) have manifold drought coping strategies including succulence of different plant organs, wood anatomical traits and leaf phenology. As water availability to plants is the limiting factor for physiological activity, changes in precipitation patterns are assumed to have strong influences on tree phenology, growth and water turnover. Our objectives were to assess patterns in leaf phenology, radial stem circumference changes and sap flux responses to fluctuating moisture regimes of selected species. Based on these findings we evaluated the potential suitability as indicator species for climate change effects. The study was implemented at different elevational positions in a submontane dry forest of southern Ecuador. Annual rainfall is 600mm with an eight months dry period; moisture availability slightly increases with altitude because of moist air coming from the Pacific. At three altitudes, we studied the tree species Ceiba trichistandra (leaf deciduous, stem succulent), Eriotheca ruizii (leaf deciduous, root succulent) and Erythrina velutina (leaf deciduous). Reversible stem swelling and shrinking was observed for all three species during the whole study period and at all positions at the altitudinal gradient. However, it was most pronounced and sensitive in the stem succulent C. trichistandra and at the lowest (driest) position. C. trichistandra flushed leaves at dry season intermittent rain events, and from dry to wet season leaf out was earlier, and in this period sap flux was high while stem circumference decreased. Length of the leaved periods of all species increased with altitude. Thus, clear differences among species, topographic positions, radial growth and tree water use patterns are revealed; especially C. trichistandra responded very sensitive to fluctuating moisture regimes with leaf phenology, sap flux and stem diameter variations, and can be regarded as a sensitive indicator for assessing climatic variations.

A synthesis of radial growth patterns preceding tree mortality.

Tree mortality is a key factor influencing forest functions and dynamics, but our understanding of the mechanisms leading to mortality and the associated changes in tree growth rates are still limited. We compiled a new pan-continental tree-ring width database from sites where both dead and living trees were sampled (2970 dead and 4224 living trees from 190 sites, including 36 species), and compared early and recent growth rates between trees that died and those that survived a given mortality event. We observed a decrease in radial growth before death in ca. 84% of the mortality events. The extent and duration of these reductions were highly variable (1-100years in 96% of events) due to the complex interactions among study species and the source(s) of mortality. Strong and long-lasting declines were found for gymnosperms, shade- and drought-tolerant species, and trees that died from competition. Angiosperms and trees that died due to biotic attacks (especially bark-beetles) typically showed relatively small and short-term growth reductions. Our analysis did not highlight any universal trade-off between early growth and tree longevity within a species, although this result may also reflect high variability in sampling design among sites. The intersite and interspecific variability in growth patterns before mortality provides valuable information on the nature of the mortality process, which is consistent with our understanding of the physiological mechanisms leading to mortality. Abrupt changes in growth immediately before death can be associated with generalized hydraulic failure and/or bark-beetle attack, while long-term decrease in growth may be associated with a gradual decline in hydraulic performance coupled with depletion in carbon reserves. Our results imply that growth-based mortality algorithms may be a powerful tool for predicting gymnosperm mortality induced by chronic stress, but not necessarily so for angiosperms and in case of intense drought or bark-beetle outbreaks.

Climatic Sensitivity of a Mixed Forest Association of White Spruce and Trembling Aspen at Their Southern Range Limit

Climatic sensitivity of white spruce (Picea glauca (Moench) Voss) was examined growing in association with trembling aspen (Populus tremuloides Michx.) at their southern limit of distribution in a transitional ecotone between the southern boreal forest and northern prairie region. The study was carried out in the Spruce Woods Provincial Park (SWPP) located in southwestern Manitoba, Canada. The dry regional climate restricted trembling aspen growth during the growing season via moisture deficiency and temperature induced drought stress. Warm, mild winters also negatively affected radial growth of trembling aspen. Growth of white spruce was moderated by conditions within the aspen stands as radial growth patterns showed low variability from year to year, a low common growth signal, and a stronger response to temperature than to precipitation. Nonetheless, the dry regional climate still restricted growth of white spruce during the growing season via temperature induced drought stress. The findings of the study for white spruce support the stress gradient hypothesis in which facilitative interactions between tree species are expected under harsher environmental conditions.

In vitro assays for determining the metastatic potential of melanoma cell lines with characterized in vivo invasiveness.

The metastatic potential of cancer cells is an elusive property that is indicative of the later stages of cancer progression. The ability to distinguish between poorly and highly metastatic cells is invaluable for understanding the basic biology of cancer and to develop more treatments. In this paper, we exploit a A375 melanoma cell line series (A375P, A375MA1, A375MA2) that vary in metastatic potential, to demonstrate an in vitro screening assay using polydimethylsiloxane (PDMS) microbubble well arrays that can distinguish these cell lines by their growth characteristics in including morphology, migratory potential, and clonogenic potential. These cell lines cannot be distinguished by their growth characteristics when cultured on standard tissue culture plastic or planar PDMS. Results show that the more metastatic cell lines (A375MA1, A375MA2) have a higher proliferative potential and a distinctive radial spreading growth pattern out of the microbubble well. The A375MA2 cell line also has a higher tendency to form multicellular spheroids. The ability to successfully correlate the metastatic potential of cancer cells with their growth characteristics is essential first step toward developing a high-throughput screening assay to identify aggressive tumor cells in primary samples. The capability to culture and recover aggressive cells from microbubble wells will enable identification of candidate metastatic biomarkers which has immense clinical significance.

Pointer Years in Tree-Ring Width of European Ash with Different Crown Condition and Their Relationships with Climatic Factors in Latvia

Abstract The effect of climatic factors on tree-ring width (TRW) of European ash (Fraxinus excelsior L.) with healthy and damaged crowns growing in the central and eastern part of Latvia was assessed by dendrochronological techniques. Pointer year indices were calculated to assess the variability of TRW. Positive pointer years were more frequent than negative, similarly for damaged and healthy trees, suggesting similar limiting factors. The relationships between TRW and climatic factors differed regionally and locally. In the eastern part of Latvia, TRW was affected by temperature in spring of current and preceding years. In the central part of Latvia, weather conditions in current and preceding summer mainly affected TRW; temperature and precipitation had positive effect suggesting occurrence of water deficit, but the daily range of temperature had a negative effect. Hence, regional diversification of radial growth patterns might be expected. Some differences in sensitivity to climate were observed between the damaged and healthy trees. In the central part of Latvia, the damaged trees appeared additionally sensitive to temperature in summer. In the eastern part of Latvia, damaged trees were additionally sensitive to temperature in May. Nevertheless, some additional factors were significant for the healthy trees.

Climatic responses of Pinus pseudostrobus and Abies religiosa in the Monarch Butterfly Biosphere Reserve, Central Mexico

Understanding the effects of climate on the growth of trees is important to project the response of forests to climate change. Dendrochronological analysis offers a “proxy” source for the effects of climatic variation on tree growth at different spatial and temporal scales. To examine influences of temperature and precipitation on radial growth of Pinus pseudostrobus and Abies religiosa, this study combines measurements of radial growth patterns of forest trees in the Monarch Butterfly Biosphere Reserve (MBBR) in central Mexico with temperature and precipitation variables from instrumental records. Dendrochronological samples were collected as cross sections and increment cores by using a chainsaw and increment borers, respectively. Total ring-width chronologies were developed for each site. Principal component analyses (PCA) were used to identify common temperature, precipitation and tree growth variation patterns. Correlation and response function analyses between chronologies and records of temperature and precipitation were used to evaluate the relation of climate variables on tree growth. The months during which tree growth was most strongly affected by precipitation were January, February and October from the previous year; only the temperature of September from the previous year affected the tree growth. In some chronologies, May’s average monthly maximum temperature was negatively correlated with tree growth. PCA and a comparison of PCA factor scores of climatic variables and chronologies showed no significant differences between northern, central or southern portions of the MBBR. Apparently, tree growth in the MBBR is reduced in years of low January–May precipitation combined with high summer (September of the previous year) temperatures, a scenario which is likely to occur as a consequence of global climate change.

Monitoring intra-annual dynamics of wood formation with microcores and dendrometers in Picea abies at two different altitudes.

Seasonal analyses of cambial cell production and day-by-day stem radial increment can help to elucidate how climate modulates wood formation in conifers. Intra-annual dynamics of wood formation were determined with microcores and dendrometers and related to climatic signals in Norway spruce (Picea abies (L.) Karst.). The seasonal dynamics of these processes were observed at two sites of different altitude, Savignano (650 m a.s.l.) and Lavazè (1800 m a.s.l.) in the Italian Alps. Seasonal dynamics of cambial activity were found to be site specific, indicating that the phenology of cambial cell production is highly variable and plastic with altitude. There was a site-specific trend in the number of cells in the wall thickening phase, with the maximum cell production in early July (DOY 186) at Savignano and in mid-July (DOY 200) at Lavazè. The formation of mature cells showed similar trends at the two sites, although different numbers of cells and timing of cell differentiation were visible in the model shapes; at the end of ring formation in 2010, the number of cells was four times higher at Savignano (106.5 cells) than at Lavazè (26.5 cells). At low altitudes, microcores and dendrometers described the radial growth patterns comparably, though the dendrometer function underlined the higher upper asymptote of maximum growth in comparison with the cell production function. In contrast, at high altitude, these functions exhibited different trends. The best model was obtained by fitting functions of the Gompertz model to the experimental data. By combining radial growth and cambial activity indices we defined a model system able to synchronize these processes. Processes of adaptation of the pattern of xylogenesis occurred, enabling P. abies to occupy sites with contrasting climatic conditions. The use of daily climatic variables in combination with plant functional traits obtained by sensors and/or destructive sampling could provide a suitable tool to better investigate the effect of disturbances on response strategies in trees and, consequently, contribute to improving our prediction of tree growth and species resilience based on climate scenarios.

Effect of gases and particulate matter from electricity generation process on the radial growth of teak plantations surrounding Mae Moh power plant, Lampang province

The objectives of this study were to investigate radial growth patterns and influences of polluting gases and particulate matter on the radial growth of teak plantations surrounding the Mae Moh Power Plant. Twenty-four 32-year-old teak trees were selected from Mae Jang and Mae Moh plantations, which were 5 km and 15 km from the Mae Moe power plant, respectively. Forty-eight sample cores were collected from the 24 trees (two cores per tree). The growth patterns of all the cores were analyzed following the standard methods of dendrochronology. The relationships between the growth pattern and the amounts of sulfur dioxide, nitrogen dioxide, carbon monoxide and particulate matter were measured as average daily rates and then analyzed. The study showed that the best-fit model for the relationship between the radial current annual increment at breast height (CAIdbh) and time (Y) was an exponential equation. The fitted equations were: CAIdbh = 10.657e(−0.031Y) for Mae Moh plantation and CAIdbh = 12.518e(−0.032Y) for Mae Jang plantation. The coefficient of determination for the fitted equations was 0.410 and 0.423 for the Mae Moh and Mae Jang plantations, respectively. Moreover, carbon monoxide (CO) and sulfur dioxide (SO2) had a statistically significant effect on radial teak growth (RT) in the Mae Jang plantation, with a coefficient of determination of 0.69 (RTmj = 0.571 + 0.429(CO) − 0.023(SO2)).

Antineoplastic effects of Rhodiola crenulata treatment on B16-F10 melanoma.

Melanoma is an aggressive form of skin cancer with limited treatment options for advanced stage disease. Early detection and wide surgical excision remain the initial mode of treatment for primary tumors thus preventing metastases and leading to improved prognosis. Through this work, we have evaluated the antineoplastic effects of Rhodiola crenulata (R. crenulata) root extracts on the B16-F10 melanoma cell line, both in vitro and in vivo. We observed that R. crenulata treatment resulted in increased cell death as well as a reduction in tumor cell proliferation and migration in vitro. Additionally, we observed that R. crenulata decreased the expression of integrin β1 and vimentin and increased the expression of E-cadherin. Further, in mice treated with a topical R. crenulata-based cream therapy, tumors were more likely to have a radial growth pattern, a reduction in mitotic activity, and an increase in tumor necrosis. We also observed that mice drinking water supplemented with R. crenulata displayed a reduction of metastatic foci in disseminated models of melanoma. Collectively, these findings suggest that R. crenulata exhibits striking antitumorigenic and antimetastatic properties and that this extract may harbor potential novel adjuvant therapy for the treatment of melanoma.

Does drought incite tree decline and death in Austrocedrus chilensis forests?

AbstractQuestionsIs mal del ciprés, the widespread decline and death of Austrocedrus chilensis trees, caused by a single pathogen or multiple factors? Using a novel dendrochronological approach, we disentangled the influences of climatic variation on the radial growth decline and death of A. chilensis trees in declining forests. We distinguish possible causes of reduced radial growth and mortality from autogenic processes driven by stand development. We present a conceptual model of forest decline including multiple factors that predispose, incite and contributed to decreased radial growth and death of A. chilensis.LocationA. chilensis forests on mesic sites in northern Patagonia, Argentina.MethodsWe used dendrochronology to determine the years of (1) onset of radial growth decline of 301 living and dead trees stratified by canopy position at decline onset, and (2) mortality of 339 trees stratified by radial growth patterns and canopy position at death. Events were years with low or high numbers of trees initiating decline or dying. We tested the hypothesis that onset of decline and mortality were concurrent with drought for individual trees, using contingency tables, and for events, using superposed epoch analysis.ResultsClimatic variability acts as an environmental stress inciting and contributing to stand‐level forest decline. The onset of radial growth decline and mortality of individual trees were significantly associated with summer moisture deficits. High‐magnitude onset‐of‐decline and mortality events were concurrent with adverse climatic conditions.ConclusionsClimatic variation and drought incite and contribute to tree‐ and stand‐level decline and mortality in A. chilensis forests. Deciphering the effects of stand development is critical as autogenic processes independently drive tree mortality and mediate the effects of climatic variability on A. chilensis forest decline. Based on our results, we present a conceptual model within the framework of a forest decline process, and conclude A. chilensis mortality is a forest decline process driven by complex interactions between allogenic abiotic and biotic factors and autogenic stand development processes. Site conditions, genetic variation and sex of trees are predisposing factors that likely interact with the pathogen Phytophthora.

Morphological, physiological and molecular characterization of Phytophthora alni isolates from Western Spain

During extensive surveys for Phytophthora associated with alder mortality in western Spain, isolates were consistently recovered from necrotic bark of the collar and lower stem of Alnus glutinosa. Morphological and molecular characteristics of the selected isolates together with their physiology were examined. Morphologically, the isolates were homothallic and characterized by abundant production of terminal oogonia predominantly with two-celled amphigynous antheridia exhibiting ornamentation. Simple sporangiophores were observed bearing terminal, non-papillate, ellipsoid to ovoid sporangia. Colony growth patterns developed on V8 juice agar (V8A), carrot agar (CA), corn-meal agar (CMA) and potato-dextrose agar (PDA) showed uniform, radial or irregular growth patterns with appressed and/or woolly morphology. Temperature (2 °C, 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 27 °C, 30 °C and 32 °C), pH (5, 7, 9 and 11) and osmotic potential (−0.6, −1.2, −1.8 and −2.4 MPa) significantly influenced radial mycelial growth of the isolates under laboratory conditions. Molecular analyses including ITS DNA region sequencing and subspecies specific primers amplification confirmed identification of the isolates as Phytophthora alni ssp. alni. Further research is under way to carry out more surveys in order to determine the extent of damage and severity of the disease in different regions of Spain.