Cavitation fatigue in conifers: a study on eight European species.

After drought-induced embolism and repair, tree xylem may be weakened against future drought events (cavitation fatigue). As there are few data on cavitation fatigue in conifers available, we quantified vulnerability curves (VCs) after embolism/repair cycles on eight European conifer species. We induced 50% and 100% loss of conductivity (LC) with a cavitron, and analyzed VCs. Embolism repair was obtained by vacuum infiltration. All species demonstrated complete embolism repair and a lack of any cavitation fatigue after 50% LC . After 100% LC, European larch (Larix decidua), stone pine (Pinus cembra), Norway spruce (Picea abies), and silver fir (Abies alba) remained unaffected, while mountain pine (Pinus mugo), yew (Taxus baccata), and common juniper (Juniperus communis) exhibited 0.4-0.9 MPa higher vulnerability to embolism. A small cavitation fatigue observed in Scots pine (Pinus sylvestris) was probably biased by incomplete embolism repair, as indicated by a correlation of vulnerability shifts and conductivity restoration. Our data demonstrate that cavitation fatigue in conifers is species-specific and depends on the intensity of preceding LC. The lack of fatigue effects after moderate LC, and relevant effects in only three species after high LC, indicate that conifers are relatively resistant against cavitation fatigue. This is remarkable considering the complex and delicate conifer pit architecture and may be important considering climate change projections.

Adaptation to local climate in multi-trait space: evidence from silver fir (Abies alba Mill.) populations across a heterogeneous environment.

Heterogeneous environments, such as mountainous landscapes, create spatially varying selection pressure that potentially affects several traits simultaneously across different life stages, yet little is known about the general patterns and drivers of adaptation in such complex settings. We studied silver fir (Abies alba Mill.) populations across Switzerland and characterized its mountainous landscape using downscaled historical climate data. We sampled 387 trees from 19 populations and genotyped them at 374 single-nucleotide polymorphisms (SNPs) to estimate their demographic distances. Seedling morphology, growth and phenology traits were recorded in a common garden, and a proxy for water use efficiency was estimated for adult trees. We tested whether populations have more strongly diverged at quantitative traits than expected based on genetic drift alone in a multi-trait framework, and identified potential environmental drivers of selection. We found two main responses to selection: (i) populations from warmer and more thermally stable locations have evolved towards a taller stature, and (ii) the growth timing of populations evolved towards two extreme strategies, 'start early and grow slowly' or 'start late and grow fast', driven by precipitation seasonality. Populations following the 'start early and grow slowly' strategy had higher water use efficiency and came from inner Alpine valleys characterized by pronounced summer droughts. Our results suggest that contrasting adaptive life-history strategies exist in silver fir across different life stages (seedling to adult), and that some of the characterized populations may provide suitable seed sources for tree growth under future climatic conditions.

Linking dendroecology and association genetics in natural populations: Stress responses archived in tree rings associate with SNP genotypes in silver fir (Abies alba Mill.).

Genetic association studies in forest trees would greatly benefit from information on the response of trees to environmental stressors over time, which can be provided by dendroecological analysis. Here, we jointly analysed dendroecological and genetic data of surviving silver fir trees to explore the genetic basis of their response to the iconic stress episode of the 1970s and 1980s that led to large-scale forest dieback in Central Europe and has been attributed to air pollution. Specifically, we derived dendrophenotypic measures from 190 trees in the Bavarian Forest that characterize the resistance, resilience and recovery during this growth depression, and in the drought year in 1976. By focusing on relative growth changes of trees and by standardizing the dendrophenotypes within stands, we accounted for variation introduced by micro- and macroscale environmental differences. We associated the dendrophenotypes with single nucleotide polymorphisms (SNPs) in candidate genes using general linear models (GLMs) and the machine learning algorithm random forest with subsequent feature selection. Most trees at our study sites experienced a severe growth decline from 1974 until the mid-1980s with minimum values during the drought year. Fifteen genes were associated with the dendrophenotypes, including genes linked to photosynthesis and drought stress. With our study, we show that dendrophenotypes can be a powerful resource for genetic association studies that permit to account for micro- and macroenvironmental variation when data are derived from natural populations. We call for a wider collaboration of dendroecologists and forest geneticists to integrate individual tree-level dendrophenotypes in genetic association studies.

Differences in xylogenesis between dominant and suppressed trees.

PREMISE OF THE STUDY: Most dendroecological studies focus on dominant trees, but little is known about the growing season of trees belonging to different size classes and their sensitivity to biotic factors. The objective of this study was to compare the dynamics of xylem formation between dominant and suppressed trees of Abies fabri of similar age growing in the Gongga Mountains, southeastern Tibetan Plateau, and to identify the association between xylem growth and climate. METHODS: The timing and duration of xylogenesis in histological sections were investigated weekly during the 2013-2015 growing seasons. KEY RESULTS: Our investigation found that timing and duration of xylogenesis varied with canopy position and its associated tree size. Xylogenesis started 6-14 days earlier, and ended 5-11 days later in dominant trees than in suppressed trees, resulting in a significantly longer growing season. Dominant trees also exhibited higher temperature sensitivity of tracheid production rate than suppressed trees. CONCLUSIONS: The observed differences in xylogenesis among trees suggested that competition affects tree growth by reducing the growing period in suppressed trees. Representative climate-growth relationships should involve trees of all size classes when evaluating the effects of the environment on forest dynamics.

Extreme cold consistently reduces seedling growth but has species-specific effects on browse tolerance in summer.

PREMISE OF THE STUDY: Extreme weather events can injure plants, causing decreased survival. However, we may underestimate the ecological importance of extreme events if they have strong sublethal effects that manifest after several months. We tested the hypothesis that late-winter extreme-cold events decrease the ability of woody plants to grow and tolerate stem removal in summer. METHODS: Seedlings from four temperate tree species (Abies balsamea, Pinus resinosa, P. strobus, Quercus rubra) were acclimated to winter conditions in growth chambers, and experienced 1 week of warm temperatures before being exposed to one of three 24-h extreme-cold events (minimum temperature: 8°C control, -8°C, or -16°C). Seedlings were then transferred to a greenhouse where we monitored survival and growth. Three months after the extreme-cold event, we mimicked an herbivore attack by removing either 25% or 75% of new stem growth from seedlings of two species (P. resinosa, Q. rubra). KEY RESULTS: While extreme cold had no immediate effect on seedling survival, the coldest temperature treatment reduced stem growth 51% relative to controls. Stem removal decreased P. resinosa survival in the -16°C treatment, but stem removal treatment had no effect on P. resinosa survival in the intermediate -8°C treatment or 8°C control. Stem removal did not alter Q. rubra survival. CONCLUSIONS: Ephemeral late-winter cold temperatures can have unappreciated effects on growing-season seedling dynamics, including growth and herbivory. For predicting how extreme-cold events might alter large-scale patterns of tree distribution, seedlings should be monitored throughout the growing season following extreme late-winter frosts.

Cessation of annual apical growth and partial death of cambium in stem of Abies sachalinensis under intensive shading.

This study evaluated variation in the height at which absent rings and internodes were detected along stem of Abies sachalinensis trees grown under shade for 39 years. Eight sample trees planted in 1974 under a secondary forest in Japan were felled in 2013 and analyzed. A. sachalinensis is a monopodial species in which it is possible to measure annual apical growth using the distinct internodes. We applied microscopic analysis on 154 stem disks from the stem base to the top to evaluate the cessation of apical and radial growth caused by intensive shading. Cessation of apical stem growth for one or more years was found in 6 out of 8 sample trees. We termed this phenomenon as "absent internode". In addition, the absent growth rings were detected more frequently in the lower part of sample stems, and the number of absent rings at the stem base did not correspond with the number of absent internodes in the six trees. From cellular level observation, the five suppressed trees had no living cambial cells at the stem base but had living cells at the stem top. The cessation of the apical and radial growth did not occur synchronously but did occur independently under a shade environment in A. sachalinensis.

Suppression of growth and death of meristematic tissues in Abies sachalinensis under strong shading: comparisons between the terminal bud, the terminally lateral bud and the stem cambium.

The suppression of apical growth and radial trunk growth in trees under shade is a key factor in the competition mechanism among individuals in natural and artificial forests. However, the timing of apical and radial growth suppression after shading and the physiological processes involved have not been evaluated precisely. Twenty-one Abies sachalinensis seedlings of 5-years-old were shaded artificially under a relative light intensity of 5% for 70 days from August 1, and the histological changes of the terminal bud and terminally lateral bud of terminal leader and the cambial zone of the trunk base were analyzed periodically. In shade-grown trees, cell death of the leaf primordia in a terminal bud of terminal leader was observed in one of the three samples after 56 and 70 days of shading, whereas the leaf primordia in a terminal bud of terminal leader in all open-grown trees survived until the end of the experiment. In addition, the leaf primordia of the terminally lateral buds of terminal leader retained their cell nuclei until the end of the experiment. No histological changes were observed in the cambial cells after shading, but the shade-grown trees had less cambial activity than the open-grown trees through the experiment. Strong shading appeared to inhibit the formation and survival of cells in the terminal bud of terminal leader rather than the terminally lateral buds of terminal leader and the cambium. The suppression of the terminal bud growth and elongation of the surviving lateral buds would result in an umbrella-shaped crown under shade.

Risk of genetic maladaptation due to climate change in three major European tree species.

Tree populations usually show adaptations to their local environments as a result of natural selection. As climates change, populations can become locally maladapted and decline in fitness. Evaluating the expected degree of genetic maladaptation due to climate change will allow forest managers to assess forest vulnerability, and develop strategies to preserve forest health and productivity. We studied potential genetic maladaptation to future climates in three major European tree species, Norway spruce (Picea abies), silver fir (Abies alba), and European beech (Fagus sylvatica). A common garden experiment was conducted to evaluate the quantitative genetic variation in growth and phenology of seedlings from 77 to 92 native populations of each species from across Switzerland. We used multivariate genecological models to associate population variation with past seed source climates, and to estimate relative risk of maladaptation to current and future climates based on key phenotypic traits and three regional climate projections within the A1B scenario. Current risks from climate change were similar to average risks from current seed transfer practices. For all three climate models, future risks increased in spruce and beech until the end of the century, but remained low in fir. Largest average risks associated with climate projections for the period 2061-2090 were found for spruce seedling height (0.64), and for beech bud break and leaf senescence (0.52 and 0.46). Future risks for spruce were high across Switzerland. However, areas of high risk were also found in drought-prone regions for beech and in the southern Alps for fir. Genetic maladaptation to future climates is likely to become a problem for spruce and beech by the end of this century, but probably not for fir. Consequently, forest management strategies should be adjusted in the study area for spruce and beech to maintain productive and healthy forests in the future.

Past and future evolution of Abies alba forests in Europe - comparison of a dynamic vegetation model with palaeo data and observations.

Information on how species distributions and ecosystem services are impacted by anthropogenic climate change is important for adaptation planning. Palaeo data suggest that Abies alba formed forests under significantly warmer-than-present conditions in Europe and might be a native substitute for widespread drought-sensitive temperate and boreal tree species such as beech (Fagus sylvatica) and spruce (Picea abies) under future global warming conditions. Here, we combine pollen and macrofossil data, modern observations, and results from transient simulations with the LPX-Bern dynamic global vegetation model to assess past and future distributions of A. alba in Europe. LPX-Bern is forced with climate anomalies from a run over the past 21 000 years with the Community Earth System Model, modern climatology, and with 21st-century multimodel ensemble results for the high-emission RCP8.5 and the stringent mitigation RCP2.6 pathway. The simulated distribution for present climate encompasses the modern range of A. alba, with the model exceeding the present distribution in north-western and southern Europe. Mid-Holocene pollen data and model results agree for southern Europe, suggesting that at present, human impacts suppress the distribution in southern Europe. Pollen and model results both show range expansion starting during the Bølling-Allerød warm period, interrupted by the Younger Dryas cold, and resuming during the Holocene. The distribution of A. alba expands to the north-east in all future scenarios, whereas the potential (currently unrealized) range would be substantially reduced in southern Europe under RCP8.5. A. alba maintains its current range in central Europe despite competition by other thermophilous tree species. Our combined palaeoecological and model evidence suggest that A. alba may ensure important ecosystem services including stand and slope stability, infrastructure protection, and carbon sequestration under significantly warmer-than-present conditions in central Europe.

Topography and age mediate the growth responses of Smith fir to climate warming in the southeastern Tibetan Plateau.

The Tibetan Plateau holds some of the world's highest undisturbed natural treelines and timberlines. Such extreme environments constitute potentially valuable monitoring sites of the effects of climate warming on high-elevation forests. Here, we analyze a network of 21 Smith fir forests situated in the Sygera Mountains, southeastern Tibetan Plateau, using tree-ring width (TRW) and basal area increment (BAI) chronologies. Sampled sites encompassed a wide elevation gradient, from 3600 to 4400 m, including some treeline sites and diverse aspects and tree ages. In comparison with TRW series, BAI series better capture the long-term warming signal. Previous November and current April and summer temperatures are the dominant climatic factors controlling Smith fir radial growth. The mean inter-series correlations of TRW increased upwards, but the forest limit presented the highest potential to reconstruct past temperature variability. Moreover, the growth responses of young trees were less stable than those of trees older than 100 years. Climate warming is accelerating radial growth of Smith fir forest subjected to mesic conditions. Collectively, these findings confirm that the effects of site elevation and tree age should be considered when quantifying climate-growth relationships. The type of tree-ring data (BAI vs. TRW) is also relevant since BAI indices seem to be a better climatic proxy of low-frequency temperature signals than TRW indices. Therefore, site (e.g., elevation) and tree (e.g., age) features should be considered to properly evaluate the effects of climate warming on growth of high-elevation forests.

February-May temperature reconstruction based on tree-ring widths of Abies fargesii from the Shennongjia area in central China.

February-May temperature strongly affects ecological processes and socio-economics in central China, yet its long-term variability has not been thoroughly assessed due to the shortness of instrumental records. In order to improve the understanding of the regularities of temperature variability in central China, in this study, we present a new tree-ring chronology from the Shengnongjia Mountains in central China which provides a valuable 245-year record of temperature variability. The reconstructed temperature correlated strongly with February-May mean temperature records of the Fangxian meteorological station from AD 1958 to AD 2011, and the derived reconstruction explained 44.5 % of the instrumental temperature variation during this period. The study shows that this region experienced three warm periods and two cool periods, i.e., the major warm periods occurred in AD 1783-1806, AD 1879-1909, and AD 1975 to the present, whereas the cool intervals occurred in AD 1807-1878 and AD 1910-1974. This reconstruction could aid in the evaluation of regional climate variability in subtropical China.

Comparison of δ(18)O and δ(13)C values between tree-ring whole wood and cellulose in five species growing under two different site conditions.

RATIONALE: We investigated the applicability of tree-ring whole-wood material for δ(18)O and δ(13)C analysis in comparison with the more time- and resource-intensive use of cellulose, by considering possible variability between (i) five different tree species (Fagus sylvatica, Quercus robur, Picea abies, Abies alba, Pseudotsuga menziesii), (ii) two sites that differ in soil moisture, and (iii) climate conditions within a 10-year period. METHODS: Stem cores of 30 individual trees (n = 3 trees per each species and site) were sampled from two sites in south Germany (Bavaria), and tree rings within sapwood of the years 2001-2010 were separated. The δ(18)O and δ(13)C values from homogenized tree-ring whole wood and from extracted cellulose were measured by mass spectrometry. Species-specific offsets in isotope values were analyzed and the responses in isotopic signature to climate variability including a single drought event were compared between whole-wood and cellulose. RESULTS: A constant offset in δ(18)O values of ca 5‰ between wood and cellulose was observed for most species independent of site conditions, with a significant difference between beech and Douglas-fir, while inter-annual variability was only observed in oak. The offset in δ(13)C values ranged between 1.45 and 1.84‰ across species, sites and years. Both materials generally showed similar strength in responses to temperature, precipitation and soil water availability, particularly for conifers. Resistance to severe drought stress--partly more strongly reflected in the δ(13)C values of cellulose--was lower for conifers than for the deciduous species. CONCLUSIONS: Wood material from the sapwood of the studied tree species is as useful as cellulose for studying environmental effects on tree-ring δ(18)O and δ(13)C values at a short-term scale as considered in most ecophysiological studies. The more variable response of oak may require further investigations.

Shifts in soil testate amoeba communities associated with forest diversification.

We studied changes of testate amoeba communities associated with the conversion of spruce monocultures into mixed beech-fir-spruce forests in the Southern Black Forest Mountains (Germany). In this region, forest conversion is characterized by a gradual development of beech undergrowth within thinned spruce tree stands leading to multiple age continuous cover forests with a diversified litter layer. Strong shifts in the abundance of testate amoeba observed in intermediate stages levelled off to monoculture conditions again after the final stage of the conversion process had been reached. The average number of species per conversion stage (i.e., local richness) did not respond strongly to forest conversion, but the total number of species (i.e., regional richness) was considerably higher in the initial stage than in the mixed forests, due to the large number of hygrophilous species inhabiting spruce monocultures. Functional diversity of the testate amoeba community, however, significantly increased during the conversion process. This shift was closely associated with improved C and N availability as well as higher niche diversity in the continuous cover stands. Lower soil acidity in these forests coincided with a higher relative abundance of eurytopic species. Our results suggest that testate amoeba communities are much more affected by physicochemical properties of the soil than directly by litter diversity.

ClRTL1 Encodes a Chinese Fir RNase III-Like Protein Involved in Regulating Shoot Branching.

Identification of genes controlling shoot branching is crucial for improving plant architecture and increasing crop yield or biomass. A branching mutant of Chinese fir named "Dugansha" (Cunninghamia lanceolata var. dugan.) has been isolated in our laboratory. We chose the cDNA-AFLP technique and an effective strategy to screen genes that potentially regulate shoot branching in Chinese fir using this mutant. An RNase III-like1 cDNA fragment named ClRTL1 was identified as a potential positive regulator. To investigate the function of ClRTL1 in regulating shoot branching, we cloned the full-length cDNA sequence from C. lanceolata (Lamb.) Hook, deduced its secondary structure and function, and overexpressed the coding sequence in Arabidopsis. The ClRTL1 cDNA is 1045 bp and comprises an open reading frame of 705 bp. It encodes a protein of 235 amino acids. The deduced secondary structure of the ClRTL1 indicates that it is a mini-RNase III-like protein. The expression analysis and phenotypes of 35S: ClRTL1 in A. thaliana implies that ClRTL1 plays a role in promoting shoot branching in Chinese fir.

Constraining 3-PG with a new δ13C submodel: a test using the δ13C of tree rings.

A semi-mechanistic forest growth model, 3-PG (Physiological Principles Predicting Growth), was extended to calculate δ(13)C in tree rings. The δ(13)C estimates were based on the model's existing description of carbon assimilation and canopy conductance. The model was tested in two ~80-year-old natural stands of Abies grandis (grand fir) in northern Idaho. We used as many independent measurements as possible to parameterize the model. Measured parameters included quantum yield, specific leaf area, soil water content and litterfall rate. Predictions were compared with measurements of transpiration by sap flux, stem biomass, tree diameter growth, leaf area index and δ(13)C. Sensitivity analysis showed that the model's predictions of δ(13)C were sensitive to key parameters controlling carbon assimilation and canopy conductance, which would have allowed it to fail had the model been parameterized or programmed incorrectly. Instead, the simulated δ(13)C of tree rings was no different from measurements (P > 0.05). The δ(13)C submodel provides a convenient means of constraining parameter space and avoiding model artefacts. This δ(13)C test may be applied to any forest growth model that includes realistic simulations of carbon assimilation and transpiration.

Combined effect of elevated UVB, elevated temperature and fertilization on growth, needle structure and phytochemistry of young Norway spruce (Picea abies) seedlings.

Simultaneously with warming climate, other climatic and environmental factors are also changing. Here, we investigated for the first time the effects of elevated temperature, increased ultraviolet-B (UVB) radiation, fertilization and all combinations of these on the growth, secondary chemistry and needle structure of 1-year-old Norway spruce (Picea abies (L.) Karst.) seedlings in an outdoor experiment. After one growing season, elevated temperature increased root : shoot ratio and concentrations of needle piperidine alkaloids, while concentrations of needle catechins and acetophenones and bark flavonoids decreased compared with ambient temperature seedlings. UVB-radiation increased concentrations of bark condensed tannins, while fertilization increased total biomass and concentrations of needle catechins. In addition to the main effects, concentrations of some individual phenolic compounds showed UV × temperature or UV × temperature × fertilization interactions, and fertilization modified temperature response on root : shoot ratio. All the treatments described here affected the defence chemistry profiles of the seedlings, which may imply some changes in plant-herbivore interactions in connection with changing climate. The interactions between treatments indicate a need for further experiments involving several simultaneously affecting environmental changes.

Growth, allometry and shade tolerance of understory saplings of four subalpine conifers in central Japan.

The conifers Abies veitchii, A. mariesii, Picea jezoensis var. hondoensis, Tsuga diversifolia dominate in subalpine forests in central Japan. We expected that species differences in shade tolerance and in aboveground and belowground architecture are important for their coexistence. We examined net production and carbon allocation of understory saplings. Although the four species allocated similar amounts of biomass to roots at a given trunk height, the root-zone area of T. diversifolia was greater than that of the three other species. T. diversifolia often dominates shallow soil sites, such as ridge and rocky slopes, and, therefore, a wide spread of lateral roots would be an adaptation to such edaphic conditions. Crown width and leaf and branch mass were greatest for T. diversifolia and A. mariesii, followed in order by A. veitchii and P. jezoensis var. hondoensis. Although leaf mass of P. jezoensis var. hondoensis was lowest among the four species, species differences were not found in the net production per sapling because net production per leaf mass was greatest for P. jezoensis var. hondoensis. The leaf lifespan was longer in the order A. mariesii, T. diversifolia, P. jezoensis var. hondoensis and A. veitchii. The minimum rate of net production per leaf mass required to maintain the current sapling leaf mass (MRNP(LM)) was lowest in A. mariesii and T. diversifolia, and increased in the order of A. veitchii and P. jezoensis var. hondoensis. A. mariesii and T. diversifolia may survive in shade conditions by a lower MRNP(LM) than the two other species. Therefore, species differences in aboveground and belowground architecture and MRNPLM reflected their shade tolerance and regeneration strategies, which contribute to their coexistence.

Fine-scale distribution of ectomycorrhizal fungi colonizing Tsuga diversifolia seedlings growing on rocks in a subalpine Abies veitchii forest.

Numerous species of ectomycorrhizal (ECM) fungi coexist under the forest floor. To explore the mechanisms of coexistence, we investigated the fine-scale distribution of ECM fungal species colonizing root tips in the root system of Tsuga diversifolia seedlings in a subalpine forest. ECM root tips of three seedlings growing on the flat top surface of rocks were sampled after recording their positions in the root system. After the root tips were grouped by terminal-restriction fragment length polymorphism (T-RFLP) analysis of ITS rDNA, the fungal species representing each T-RFLP group were identified using DNA sequencing. Based on the fungal species identification, the distribution of root tips colonized by each ECM fungus was mapped. Significant clustering of root tips was estimated for each fungal species by comparing actual and randomly simulated distributions. In total, the three seedlings were colonized by 40 ECM fungal species. The composition of colonizing fungal species was quite different among the seedlings. Twelve of the 15 major ECM fungal species clustered significantly within a few centimeters. Some clusters overlapped or intermingled, while others were unique. Areas with high fungal species diversity were also identified in the root system. In this report, the mechanisms underlying generation of these ECM root tip clusters in the root system are discussed.

[Changes and influence factors of soil matrix infiltration in Chinese fir plantations with different stand ages in northern Guangxi]. / æ¡‚åŒ—åœ°åŒºä¸åŒæž—é¾„æ‰æœ¨äººå·¥æž—åœŸå£¤åŸºè´¨å ¥æ¸—å˜åŒ–åŠå½±å“å› ç´ .

Soil matrix infiltration is an important pathway for plantations to obtain water, which affects ecological benefits and water conservation function of plantations. The changes of soil matrix infiltration and its influencing factors in different growth stages of Chinese fir plantations remain unclear. We measured soil matrix infiltration process using a tension infiltrometer in Chinese fir plantations (5, 8, 11, and 15 years old) of Beijiang River Forest Farm in Rongshui, Guangxi, and analyzed soil basic physicochemical properties to identify the dominant factors influencing soil matrix infiltration. The results showed that initial infiltration rate, stable infiltration rate, and cumulative infiltration increased with stand ages. The ranges of different stand ages were 141-180 mm·h-1, 109-150 mm·h-1, and 188-251 mm, respectively. The initial infiltration rate, stable infiltration rate, and cumulative infiltration were significantly positively correlated with soil capillary porosity, soil organic matter, soil water stable macroaggregate, sand content, and clay content, while negatively correlated with soil bulk density and silt content. Early thinning had a positive effect on soil matrix infiltration, but thinning measures after 11 years did not enhance soil matrix infiltration further. Philip model was optimal for describing soil matrix infiltration process in this region. In conclusion, soil matrix infiltration capacity of Chinese fir plantations gradually increased from young to middle-aged stands, but matrix infiltration capacity tended to stabilize after 11 years old. Silt content and water stable macroaggregate were the dominant factors influencing matrix infiltration.

[Response of radial growth of different timberline species to climate change in Yading Nature Reserve, Sichuan, China]. / å››å·äºšä¸è‡ªç„¶ä¿æŠ¤åŒºä¸åŒæž—çº¿æ ‘ç§å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å˜åŒ–çš„å“åº”.

The radial growth of trees in alpine timberline is particularly sensitive to climate change. We sampled and disposed tree-ring cores of three coniferous tree species including Juniperus saltuaria, Abies forrestii, and Larix potaninii at alpine timberline in Yading Nature Reserve. The standard tree-ring chronology was used to explore the response of radial growth of different timberline species to climate change. The results showed that radial growth of L. potaninii increased after 2000, while that of A. forrestii declined after 2002, and J. saltuaria showed a significant decreasing growth trend in the past 10 years. Such results indicated divergent growth responses to climate factors among the three tree species at alpine timberline. The radial growth of J. saltuaria was sensitive to temperature, and was positively correlated with the minimum temperature from previous October to current August, the mean tempera-ture from previous November to current April and from current July to October, but was negatively associated with the relative humidity from current July to October. The radial growth of A. forrestii showed negative correlation with mean temperature and the maximum temperature from May to June in the current year, while it exhibited positive association with the relative humidity and the Palmer drought severity index from May to June in the current year. L. potaninii radial growth was positively associated with mean temperature and the maximum temperature of November-December in the previous year, the maximum temperature of current March and mean temperature of current August. The temporal stability of climate-growth relationship varied among different timberline species. The positive correlation between radial growth of A. forrestii and J. saltuaria and temperature gradually decreased, while the posi-tive relationship of L. potaninii radial growth and temperature gradually increased. Under the background of climate warming, rapid rise in surface air temperatures may promote the radial growth of L. potaninii, while inhibit that of J. saltuaria and A. forrestii, which may change the position of regional timberline.