Decline In Radial Growth Research Articles

Differences in ecological resilience of radial growth between Larix principis-rupprechtii and Picea meyeri after drought.

To understand the responses of radial growth to climatic factors and the differences in ecological resilience to drought between a heliophilous species Larix principis-rupprechtii and a shade species Picea meyeri in mixed forests, we developed the tree-ring width chronologies of L. principis-rupprechtii and P. meyeri in three mixed forests based on the samples collected from Toudaogou of Saihanba in Hebei, Ningwu County and Kelan County in Shanxi Province. We analyzed the correlation between climatic factors and various chronologies and examined the differences in resistance (Rc), recovery (Rt), and resilience (Rs) of L. principis-rupprechtii and P. meyeri in response to drought stress. The results showed that the radial growth of L. principis-rupprechtii and P. meyeri was negatively correlated with the mean and maximum air temperature from May to July in three mixed forests, and was positively correlated with the Palmer drought index (PDSI) from May to September. Radial growth decline in trees due to drought stress was significantly different between the two species among the three sites, indicating different physiological and ecological regulation strategies. The resistance of P. meyeri was stronger than that of L. principis-rupprechtii at the three study sites, with stronger resilience and resilient elasticity of L. principis-rupprechtii than P. meyeri. As a result, P. meyeri exhibited greater drought resistance than L. principis-rupprechtii. Under global warming condition, L. principis-rupprechtii might be at greater risk of growth decline than P. meyeri in this region.

Эколого-биологические аспекты формирования дубрав на возвышенностях и равнинных ландшафтах Нижнего Поволжья

The article presents data on the current topic of conservation and reproduction of oak forests in the arid conditions of the Lower Volga region on various relief elements. The article contains the result of long-term studies of oak forests of the Lower Volga region, the main predominant species of which is the petiolate oak (Quercusrobur L.). It was found that on soils of the Lower Volga region poor in humus composition with dissected relief and difficult weather conditions, the plantations of the petiolate oak fully justified themselves. It was revealed that oaks have good growth on chestnut, light chestnut and chernozem soils, and moderate on sandy, biologically stable, moreover, species with a high content of chlorophyll show the best performance. It was determined that the most effective way to create oak forests is to exclude 25-40% of the parent trees that showed the worst results during research. Otherwise, the plantings may face a decline in radial growth, loss of part of the crown and often shrinkage. Рurpose of the research. Bio-ecological assessment of species of the genus Quercus, aspects of the formation of oak forests on uplands and flat landscapes for afforestation in arid conditions of the south of the European territory of Russia. The object of research was the plantings of the pedunculate oak (Quercusrobur L.), which has an extensive range. Observations were carried out in the Volgograd region in the arboretum collections of the Federal Research Center of Agro-ecology of the Russian Academy of Sciences, at the Shemyakinskaya dacha – the oak grove of the Uryupinsky forestry, geographical oak cultures in the Oktyabrsky forestry, genetic and breeding complexes of oak in the Novoanninsky forestry, in the Rossoshansky forestry of the Voronezh region, the system of protective forest plantations in the Bogdinsky forestry of the Astrakhan region and the Elistinsky forestry of the Republic of Kalmykia. Research methodology. The water content in oak leaves was determined by the weight method by the hour during the day (1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 12 h, 24 h). Weather conditions and oak habitats were studied using the sites "Climate monitor" and "Agroatlas". The typology of forest growing conditions within the ALMR was characterized taking into account the forest suitability of soils developed by VNIALMI (now the Federal Research Centre for Agro-ecology, Complex Reclamation and Protective Afforestation). Based on the analysis of the results of all experimental materials, an integral indicator of the frost resistance of prototypes and control was calculated. Individual indicators of reproductive processes of clones were compared with the characteristics of control trees, revealing their correlations. The chlorophyll content was measured using the MS-100 device. Statistical data processing was carried out in the programs Statistica and Fractan. Research results and discussion. The intensity of growth of this species is determined by the geographical environment and the conditions of the place of growth. According to the results of the research, the petiolate oak showed excellent ecological and geographical plasticity and the ability to grow and develop in various conditions – from fine-grained leached sands of the Astrakhan and Elista experimental stations to light chestnut and dark chestnut soils of the Volgograd region, chernozem soils of the Novoanninsky and Uryupinsky forestry. The best growth and development were distinguished by the plants of the petiolate oak in conditions of macro-subsidence with dark-colored humus soils. A high percentage of oak trees with good condition were noted by the authors on micropropagations, meadow-chestnut slightly saline soils. There were no oak trees in good condition on flat, settled areas with the presence of saline spots. In the southern part of the Lower Volga region (Elista), oak forests with an age of 30 years or more are in poor condition, characterized by low growth rates and trunk diameter. In the Kamyshinsky arboretum, the annual growth of oaks decreases with increasing age, but the plants are characterized by the best resistance to high summer and low winter air temperatures, undemanding to soil conditions. Conclusion. Oaks of 30 years of age have good characteristics in the Novoanninsky forestry, which belongs to the moderately arid zone and is distinguished by chernozem soils. The upland ecotype prevails in this zone (85 %), the floodplain ecotype has the largest crown projection, an increase of 25 cm is observed in the oak ecotype of this zone, which determines the requirements for the soil and climatic conditions of the introduction regions.

Radial growth decline of white spruce (Picea glauca) during hot summers without drought: preliminary results from a study site south of a boreal forest border

If the modern climate trend continues for an additional 20–40 years, forests along the southern border of Canadian taiga may shift into new ranges of annual temperature and precipitation that are similar to the modern climate of central New York State, United States. Here we investigate the possible future response of white spruce (Picea glauca (Moench) Voss) to a warmer climate by studying trees planted 90 years ago near the southern limit of their climate tolerance in central New York, 300 km south of the boreal forest where this species is prevalent. We employed high-frequency recording dendrometers to determine radial growth phenology of six mature white spruce trees during 2013–2017. The results demonstrate significant reductions in the length of radial growth periods inversely proportional to the number of hot days with air temperature exceeding 30 °C. During years with very hot summers, the start of radial growth began about 3 days earlier than the 2013–2017 average. However, in those same years, the end of radial growth was also about 17 days earlier resulting in a shorter (70 days versus 100 days) radial growth season. Abundant (350–500 mm) summer precipitation, which resulted in soil moisture values of 20%–30%, allowed us to dismiss drought as a factor. Instead, a likely cause of reduced radial growth was mean temperature that exceeded optimal growth ranges, exacerbated by temperature extremes in ranges that lead to photoinhibition. The latter case was evident in the two warmest growing seasons (2013 and 2017), marked by extended periods of high daytime temperature (>30 °C) followed by early cessation of radial growth independent of seasonal precipitation.

气候变暖背景下云南西北部大果红杉径向生长衰退及其气候驱动因子分析

PDF HTML阅读 XML下载 导出引用 引用提醒 气候变暖背景下云南西北部大果红杉径向生长衰退及其气候驱动因子分析 DOI: 10.5846/stxb202011303065 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（32061123008）；云南省教育厅科学研究基金项目（2021Y013） The decline in radial growth of Larix potaninii in Northwestern Yunnan and its driving factors under the background of climate warming Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:气候变化背景下森林生态系统的内部结构和功能发生转变，并减弱了其固碳能力，评估与预测森林生态系统对气候变化响应势在必行。基于采自云南西北部的大果红杉树木年轮样本，建立树轮宽度标准化年表，运用相关分析、空间相关、波谱分析等方法，探讨了滇西北大果红杉径向生长的主控因子及其对气候变化的响应。结果表明：（1）温度是限制滇西北大果红杉树轮径向生长的主要因素，季节性高低温变化交替影响大果红杉树轮径向生长。（2）相对湿度变化与滇西北大果红杉树轮的径向生长紧密关联，对滇西北大果红杉树轮的径向生长起促进作用。（3）波谱分析结果显示滇西北大果红杉径向生长呈周期性变化，受ENSO等外强迫影响显著。（4）气候变暖背景下，滇西北大果红杉的径向生长出现衰退趋势。研究结果为加强云南西北部天然林保护和构建西南绿色生态屏障提供了基础性资料。 Abstract:Due to the change of carbon sequestration capacity and internal structure and function of forest ecosystems under global warming, it is imperative to assess and predict the response of forest ecosystems to climate change. Based on tree-ring samples collected from Northwestern Yunnan, some tree-ring width chronologies were developed. The main limiting factors of radial growth and the temporal stability of the tree growth response to climate change were analyzed by correlation analysis, spatial correlation, and spectral analysis. The results showed that (1) Temperature was the main factor limiting the radial growth of Larix potaninii in Northwestern Yunnan, and seasonal high and low temperatures alternately affected the radial growth of the Larix potaninii. (2) The relative humidity was closely positively related to the radial growth of Larix potaninii in Northwestern Yunnan. (3) The results of spectral analysis showed that the radial growth of Larix potaninii in Northwestern Yunnan periodically changed and was significantly affected by ENSO and other external forcing. (4) Under the background of climate warming, the growth of Larix potaninii in Northwestern Yunnan presented a decline trend. It provides a scientific decision basis for us to strengthen the protection of natural forest and construct green ecological barrier in Northwestern Yunnan. 参考文献 相似文献 引证文献

Disentangling Mechanisms of Drought-Induced Dieback in Pinus nigra Arn. from Growth and Wood Isotope Patterns

The increased frequency and intensity of warming-induced droughts have triggered dieback episodes affecting many forest types and tree species worldwide. Tree plantations are not exempt as they can be more vulnerable to drought than natural forests because of their lower structural and genetic diversity. Therefore, disentangling the physiological mechanisms leading to growth decline and tree mortality can provide tools to adapt forest management to climate change. In this study, we investigated a Pinus nigra Arn. plantation situated in northern Spain, in which some trees showed canopy dieback and radial-growth decline. We analyzed how radial growth and its responses to drought events differed between non-declining (ND) and declining (D) trees showing low and high canopy defoliation, respectively, in combination with carbon (δ13C) and oxygen (δ18O) isotope ratios in tree rings. The radial growth of P. nigra was constrained by water availability during the growing season and the previous autumn. The radial growth of D trees showed higher sensitivity to drought than ND trees. This fact is in accordance with the lower drought resilience and negative growth trends observed in D trees. Both tree classes differed in their growth from 2012 onwards, with D trees showing a reduced growth compared to ND trees. The positive δ13C-δ18O relationship together with the uncoupling between growth and intrinsic water-use efficiency suggest that D trees have less tight stomatal regulation than ND trees, which could involve a high risk of xylem embolism in the former class. Our results suggest that different water use strategies between coexisting ND and D trees were behind the differences in growth patterns and point to hydraulic failure as a possible mechanism triggering dieback and growth decline.

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.

IMPACT OF DROUGHT AND SITE CHARACTERISTICS ON VITALITY AND RADIAL GROWTH OF CEDRUS ATLANTICA MANETTI IN THE OUARSENIS MASSIF (ALGERIA)

This work investigates the impact of drought and site characteristics on vitality and radial growth of Atlas cedar (Cedrus atlantica Manetti) in Ouarsenis cedar forests (Algeria). The choice of this zone was dictated by the appearance of the phenomenon of decline since the 1980s and the lack of study on this subject. Our hypothesis seeks to understand how climatic factors interacted with site characteristics affected radial growth and vitality of Atlas cedar. We used the dendroecological approach where 09 populations of Atlas cedar distributed on the two cedars of Ouarsenis (Theniet El Had and Ain Antar) and covering a varied range of environmental conditions (substrate, altitude, exposure) were studied. The climatic signal recorded in ring-width series of Atlas cedar trees was investigated by bootstrapped response function over the period 1936-2010. The results show a good agreement between the individual curves and those of mean site chronologies, which reflects the influence of climatic factors on tree radial growth. Atlas cedar is very sensitive to rainfall fluctuations throughout the year. This sensitivity is more pronounced for populations located at low altitude, on steep slopes and on sand stone or marl substrates. The dry years induced a significant radial growth decline and triggered massive tree mortality, particularly in 1983, 1984, 1988, 1994 and 2002. The vitality of the species seems to be conditioned by the frequency of drought years.

Physiological and Growth Responses to Increasing Drought of an Endangered Tree Species in Southwest China

Research Highlights: We compared annually resolved records of tree-ring width and stable isotope of dead and surviving Fokienia hodginsii (Dunn) Henry et Thomas trees. We provide new insights into the relationships and sensitivity of tree growth to past and current climate, and explored the underlying mechanism of drought-induced mortality in F. hodginsii. Background and Objectives: Drought-induced tree decline and mortality are increasing in many regions around the world. Despite the high number of studies that have explored drought-induced decline, species-specific responses to drought still makes it difficult to apply general responses to specific species. The endangered conifer species, Fokienia hodginsii, has experienced multiple drought-induced mortality events in recent years. Our objective was to investigate the historical and current responses to drought of this species. Materials and Methods: We used annually resolved ring-width and δ13C chronologies to investigate tree growth and stand physiological responses to climate change and elevated CO2 concentration (Ca) in both dead and living trees between 1960 and 2015. Leaf intercellular CO2 concentration (Ci), Ci/Ca and intrinsic water-use efficiency (iWUE) were derived from δ13C. Results: δ13C were positively correlated with mean vapor pressure deficit and PDSI from previous October to current May, while ring widths were more sensitive to climatic conditions from previous June to September. Moreover, the relationships between iWUE, basal area increment (BAI), and Ci/Ca changed over time. From 1960s to early 1980s, BAI and iWUE maintained a constant relationship with increasing atmospheric CO2 concentration. After the mid-1980s, we observed a decrease in tree growth, increase in the frequency of missing rings, and an unprecedented increase in sensitivity of 13C and radial growth to drought, likely related to increasingly dry conditions. Conclusions: We show that the recent increase in water stress is likely the main trigger for the unprecedented decline in radial growth and spike in mortality of F. hodginsii, which may have resulted from diminished carbon fixation and water availability. Given that the drought severity and frequency in the region is expected to increase in the future, our results call for effective mitigation strategies to maintain this endangered tree species.

Assessing the stability of radial growth responses to climate change by two dominant conifer trees species in the Tianshan Mountains, northwest China

As global climate warming intensified in the latter half of the 20th century, the radial growth of trees exhibited unstable climate responses and growth trends, thereby reducing the accuracy of growth-climate ecological relationship and the scientificity of forest management based on tree rings. We assessed the temporal stability of radial growth responses and determined the growth patterns of two dominant co-occurring conifer tree species, Siberian larch (Larix sibirica) and Schrenk spruce (Picea schrenkiana), in the Tianshan Mountains of northwest China under a climate that shifted from warm-dry to warm-wet. The primary conclusions were as follows: (1) drought in the growing season was the main limiting factor of radial growth of the two tree species in recent decades through the analysis of the dynamic relationships between tree radial growth and climate factors; (2) Siberian larch had divergent responses to mean temperature in summer of the previous year, while Schrenk spruce had relatively stable responses to the mean temperature, total precipitation and monthly standardized precipitation-evapotranspiration index (SPEI) in spring of the current year by comparing the response variations before and after the abrupt increases in temperature and the moving correlation function; and (3) Siberian larch showed first increasing and then decreasing trends, while Schrenk spruce showed continuously decreasing trends based on calculating the basal area increment (BAI). The study results confirmed that forests in arid and semiarid environments would be subjected to more serious drought impacts, resulting in radial growth decline, tree mortality and community degradation with climate warming in the future. Therefore, it is important to adopt effective management measures for different species according to their response characteristics to climate change.

Impact of extreme drought on tree-ring width and vessel anatomical features of Chukrasia tabularis

Multiple sources of evidence suggest an increasing frequency of extreme climatic events during the past century. In Bangladesh, a country strongly influenced by the South Asian monsoon climate, the years 1999 and 2006 were the most severe droughts among the ten drought events identified over the last four decades. We investigated the impact of these two drought events on radial growth and xylem anatomical features of the brevi-deciduous tree species Chukrasia tabularis in a moist tropical forest in Bangladesh. Tree radial growth declined by 54% during the 1999 and 48.7% during the 2006 droughts, respectively. Among the wood anatomical features, the number of vessels (NV) showed the highest sensitivity to drought, with a 45% decrease in the 1999 drought year, followed by total vessel area (TVA) and mean vessel area (MVA). On the other hand, Vessel density (VD) increased by 13% during the 1999 drought but the increase in VD was very low in the drought year 2006. The decreasing vessel area and increasing vessel density indicate xylem hydraulic adaptation of C. tabularis to minimize drought induced cavitation risk and to avoid hydraulic failure. The significant correlations between the Standardized Precipitation Evapotranspiration Index (SPEI) and time series of tree-ring width and vessel variables imply that decline in radial growth and changes in vessel features in C. tabularis are likely to be caused by drought induced water stress. Our analyses suggest that radial growth and wood anatomical features of C. tabularis are highly sensitive to extreme drought events in South Asian moist tropical forests and can be used to reconstruct past droughts and to model tree response to drought stress under future climate conditions.

Climate effects on growth differ according to height and diameter along the stem in Pinus pinaster Ait.

Abstract: Climate-growth relationships in forest trees are increasingly the focus of research aimed at understanding and assessing responses to climate change. Many studies have been confined to annual radial growth at breast height as an easy-to-measure dendrological standard variable, although its validity as a proxy for overall annual growth patterns in trees has scarcely been addressed. In this study, we test this hypothesis by exploring additional information on climate-growth relationships as well as analyzing both the radial growth at different stem heights and the height increment. For this purpose, past annual radial growth and shoot elongation were measured in 10 dominant Pinus pinaster Ait. trees in a 130-year-old stand. Radial increments were measured on disks taken from five different trunk heights up to 15 meters. Height increments were obtained by measuring the distance between consecutive branch whorls, which appear as knots after sawing a longitudinal section of the stem. The relationships between climate and both radial growth and height increment were analyzed through Pearson’s correlations and the response to extreme climatic episodes was analyzed using resilience indices. Results revealed that the climatic variables affecting growth were different for height and stem diameter. Additionally, in the case of stem diameter, the climatic variables affecting growth also depended on the height at which the sample was taken. Precipitation prior to bud break, both in the year in which the studied shoot elongation takes place and in the previous year, has a positive effect on height increment. Radial growth in the upper part of the stem was mainly influenced by spring temperatures and precipitation, whereas in the case of basal radial growth it was the autumn and winter temperatures and precipitation of the previous year to growth which had the greatest influence. Similarly, severe droughts cause greater decline in height increment, while the decline in radial growth of the upper part of stem is smaller than that of radial growth at breast height. In conclusion, the analysis of height increment and upper radial growth provides important information to complement the dendroclimatology data for radial growth at breast height, thus improving our understanding of the impact of climate change on tree growth.

Declining Radial Growth Response of Coastal Forests to Hurricanes and Nor'easters

AbstractThe Mid‐Atlantic coastal forests in Virginia are stressed by episodic disturbance from hurricanes and nor'easters. Using annual tree ring data, we adopt a dendroclimatic and statistical modeling approach to understand the response and resilience of a coastal pine forest to extreme storm events, over the past few decades. Results indicate that radial growth of trees in the study area is influenced by age, regional climate trends, and individual tree effects but dominated periodically by growth disturbance due to storms. We evaluated seven local extreme storm events to understand the effect of nor'easters and hurricanes on radial growth. A general decline in radial growth was observed in the year of the extreme storm and 3 years following it, after which the radial growth started recovering. The decline in radial growth showed a statistically significant correlation with the magnitude of the extreme storm (storm surge height and wind speed). This study contributes to understanding declining tree growth response and resilience of coastal forests to past disturbances. Given the potential increase in hurricanes and storm surge severity in the region, this can help predict vegetation response patterns to similar disturbances in the future.

Anthropogenic-management could mitigate declines in growth and survival of Qinghai spruce (Picea crassifolia) in the east Qilian Mountains, northeast Tibetan Plateau

Ongoing climate changes posed significant threats to forest growth, structure and ecological functions. However, in our field survey in the east Qilian Mountains, we found that growth condition of Qinghai spruce under climate changes was better in anthropogenic management forest than disturbance-free stands. Accordingly, we suggested a hypothesis that the environmental change induced suppression in Qinghai spruce growth could be mitigated by anthropogenic management. Such a hypothesis was tested by comparing Qinghai spruce growth and population dynamic patterns between anthropogenic-managed forests and disturbance-free ones. We found that Qinghai spruce radial growth persistently declined since the late 1950s in the disturbance-free forests, while the radial growth of anthropogenic-managed trees almost kept steady-going trends since the 1970s in which anthropogenic-management appeared. Besides, some anomalous growth-declining years occurred in disturbance-free forests did not appear in anthropogenic-managed forests in the same year after anthropogenic-management emerged. Moreover, missing ring and tree mortality took place in disturbance-free stands and became increasingly frequent after the mid-1980s. The frequencies and proportions of missing rings and tree die-off were much lower in anthropogenic-managed forests than disturbance-free ones. Additionally, the occurrence of Qinghai spruce radial growth decline and increased mortality in recent time in our disturbance-free forests could be well explained by global-change-type drought in conjunction with elevated temperature and warming-related pest outbreaks. These results would be of fundamental significance for the further understanding of the changing forests, which could provide new clues for forest management and conservation in the future.

Recent radial growth decline in response to increased drought conditions in the northernmost Nothofagus populations from South America

Abstract An emerging phenomenon of forest decline in Mediterranean-type ecosystems has been detected in response to climate change during the last century. It is expected that the Mediterranean regions will likely experience drought events during this century with consequences for biodiversity maintenance. Although the Chilean Mediterranean-type forests are among the most threatened forest ecosystems in South America, their responses to recent increased drought events due to global warming are poorly documented. In the same region, the endangered and endemic forests of Nothofagus macrocarpa (Nothofagaceae) are found on mountain peaks. It is unclear how N. macrocarpa forests are responding to increased drought conditions occurring in the area over the last few decades. Here, we analyzed how recent climatic variability has affected the growth of N. macrocarpa. We selected five sites along the whole geographic distribution of N. macrocarpa forests in central Chile (32.5–34.5°S) to develop tree-ring chronologies. Climate-growth relationships were analyzed through correlations with local (precipitation, temperature and drought index) and large-scale climate data (ENSO index and Antarctic Oscillation). N. macrocarpa growth was positively influenced by May to November precipitation (austral winter-spring seasons) and negatively influenced by temperature from October to December (austral spring/early-summer seasons). Using a piecewise regression analysis, we identified a significant decrease in growth from 1980 onwards that resembled a precipitation decline and temperature increase in central Chile during the same time period. Tree-ring chronologies were positively correlated to the ENSO index and negatively correlated to the Antarctic Oscillation index during the current growing season, and more strongly from 1980 onwards. Based on our results, we conclude that increased drought conditions have produced a decline in radial growth of N. macrocarpa forests in the last decades. We propose that increased drought conditions predicted for this century in this region will exacerbate this declining N. macrocarpa growth trend with unknown consequences for the survival of these endemic and endangered forest ecosystems.

Observed and projected impacts of climate on radial growth of three endangered conifers in northern Mexico indicate high vulnerability of drought-sensitive species from mesic habitats

A decline in productivity and radial growth in conifer forests from mesic areas has been associated with increased drought stress induced by climate warming. Nevertheless, studies showing how vulnerable tree species will be in response to forecasted warming conditions are scarce in such mesic habitats. Here we address this issue by analyzing how growth responds to drought and to observed and projected climate conditions in a conifer forest from northern Mexico, which is a hotspot of conifer diversity. We quantify the trends in radial growth (quantified as basal area increment, BAI) of three species (Abies durangensis, Picea chihuahuana, Cupressus lusitanica) using dendrochronology and a process-based model of tree growth. Growth decreased in A. durangensis and P. chihuahuana from the late 1980s onwards in response to warmer and drier conditions, whereas C. lusitanica growth showed very low sensitivity to precipitation and increased as temperature did. Winter-spring dry conditions adversely affected the growth of A. durangensis and P. chihuahuana. Our modeling approach anticipates growth reductions and an increase in the vulnerability of A. durangensis and the endangered P. chihuahuana against the warmer and more arid conditions predicted after the 2050s. Future warmer and drier climatic conditions could reduce the productivity and lead to growth decline of these mesic conifer forests triggering dieback episodes in highly drought-sensitive species as A. durangensis and P. chihuahuana.

Using changes in basal area increments to map relative risk of HWA impacts on hemlock growth across the Northeastern U.S.A

Eastern hemlock (Tsuga canadensis) is a critical species in eastern North American forests, providing a multitude of ecological and societal benefits while also acting as a foundation species in many habitats. In recent decades, however, hemlock has become threatened by hemlock woolly adelgid (HWA; Adelges tsugae), an invasive sap-feeding insect from Asia. In addition to causing the more commonly assessed metrics of foliar damage, crown decline, and hemlock mortality, HWA also decreases hemlock growth and productivity. Dendrochronological methods provide a more nuanced assessment of HWA impacts on hemlock by quantifying variable rates of radial-growth decline that follow incipient infestation. This information is necessary to better understand the variable response of hemlock to HWA, and identify the characteristics of stands with the highest potential for tolerance and recovery. To quantify decline, we calculated changes in hemlock yearly radial growth using basal area increment (BAI) measurements to identify periods of growth decline from 41 hemlock stands across New England covering a range of infestation density, duration and hemlock vigor. The onset of growth decline periods were predominantly associated with either HWA infestation or drought. However, the magnitude of change in BAI values pre- and post-decline was significantly related to HWA infestation density and crown impacts, indicating that radial growth metrics can be used to identify locations where HWA infestations have incited significant reductions in hemlock health and productivity. Additional site characteristics (slope, hillshade, and January minimum temperatures), were also significantly associated with hemlock health and productivity decline rates. In order to develop a model to identify stands likely to tolerate HWA infestation, these metrics were used to build a logit model to differentiate high- and low-BAI-reduction stands with 78% accuracy. Independent validation of the model applied to 15 hemlock sites in Massachusetts classified high and low BAI reduction classes with 80% accuracy. The model was then applied to GIS layers for New England and eastern New York to produce a spatially-explicit model that predicts the likelihood of severe hemlock growth declines if/when HWA arrives. Currently 26% of the region’s hemlock stands fall into this high risk category. Under projected climate change, this could increase to 43%. This model, along with knowledge of current HWA infestation borders, can be used to direct management efforts of potentially tolerant hemlock stands in eastern North America, with the intention of minimizing HWA-induced hemlock mortality.

Winter drought impairs xylem phenology, anatomy and growth in Mediterranean Scots pine forests.

Continental Mediterranean forests face drought but also cold spells and both climate extremes can impair the resilience capacity of these forests. Climate warming could amplify the negative effects of cold spells by inducing premature dehardening. Here we capitalize on a winter drought-induced dieback triggered by a cold spell which occurred in December 2001 affecting Scots pine forests in eastern Spain. We assessed post-dieback recovery by quantifying and comparing radial growth and xylem anatomy of non-declining (ND, crown cover>50%) and declining (D, crown cover≤50%) trees in two sites (VP, Villarroya de los Pinares; TO, Torrijas). We also characterized xylogenesis in both sites and aboveground productivity in site VP. Dieback caused legacy effects since needle loss, a 60% reduction in litter fall and radial-growth decline characterized D-trees 3 years after dieback symptoms started appearing in spring 2002. D-trees formed collapsed tracheids in the 2002-ring, particularly in the most affected VP site where xylogenesis differences between ND and D trees were most noticeable. The lower growth rates of D-trees were caused by a shorter duration of their major xylogenesis phases. In site VP the radial-enlargement and wall-thickening of tracheids were significantly reduced in D-trees as compared to ND-trees because these xylogenesis phases tended to start earlier and end later in ND-trees. Gompertz models fitted to tracheid production predicted that maximum growth rates occurred 11-12 days earlier in ND than in D-trees. The formation of radially-enlarging tracheids was enhanced by longer days in both study sites and also by wetter conditions in the driest TO site, but xylogenesis sensitivity to climate was reduced in D-trees. Winter-drought dieback impairs xylem anatomy and phenology, aboveground productivity, xylogenesis and growth in Mediterranean Scots pine populations. Affected stands show a costly post-dieback recovery challenging their resilience ability.

Depression and growth recovery of silver fir in uneven-aged Dinaric forests in Croatia from 1901 to 2001

The causes of the decline of silver fir across Europe in the 1960s and 1970s and its subsequent recovery remain open to debate. We studied the radial growth of silver fir and possible influential factors on growth decline in uneven-aged silver fir-Norway spruce- European beech forests in the Dinaric Mountains of Croatia (180 000 ha) since 1900 using dendrochronological methods. Data on the radial growth of large firs (diameter at breast height >50 cm) sampled in 2002 across the region (151 plots, 491 m(2) each), regional climatic data (temperature, precipitation and drought) and SO2 emissions were used in both statistical and dynamic factor analyses. Two main growth patterns of fir trees were identified: the first features a sharp decline in radial growth in the period 1966-1983, followed by a dramatic recovery, while the second is characterized by a relatively constant increase in radial growth. The most influential climatic factors were mean monthly temperatures in February, July and August ; mean precipitation in May and September ; and summer drought. However, SO2 emissions explained a larger part of the total variability of radial growth than climatic factors (46-60 per cent and 0-42 per cent, respectively). The growth recovery of silver fir supports further application of uneven-aged silviculture in the region.

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.

Climate warming shifts carbon allocation from stemwood to roots in calcium‐depleted spruce forests

Increased greening of northern forests, measured by the Normalized Difference Vegetation Index (NDVI), has been presented as evidence that a warmer climate has increased both net primary productivity (NPP) and the carbon sink in boreal forests. However, higher production and greener canopies may accompany changes in carbon allocation that favor foliage or fine roots over less decomposable woody biomass. Furthermore, tree core data throughout mid‐ and northern latitudes have revealed a divergence problem (DP), a weakening in tree ring responses to warming over the past half century that is receiving increasing attention, but remains poorly understood. Often, the same sites exhibit trend inconsistency phenomenon (TIP), namely positive, or no trends in growing season NDVI where negative trends in tree ring indexes are observed. Here we studied growth of two Norway spruce (Picea abies) stands in western Russia that exhibited both the DP and TIP but were subject to soil acidification and calcium depletion of differing timing and severity. Our results link the decline in radial growth starting in 1980 to a shift in carbon allocation from wood to roots driven by a combination of two factors: (a) soil acidification that depleted calcium and impaired root function and (b) earlier onset of the growing season that further taxed the root system. The latter change in phenology appears to act as a trigger at both sites to push trees into nutrient limitation as the demand for Ca increased with the longer growing season, thereby causing the shift in carbon allocation.