川西高山林线三种灌木凋落叶分解中的无脊椎动物多样性

以无脊椎动物为主体的土壤动物是影响凋落物分解的重要生物因素,对维持陆地生态系统物质循环和能量流动具有重要作用。高山林线交错带是高山植被垂直带谱中重要的过渡区域,拥有比相邻生态系统更高的生境复杂性和物种多样性。林线上温度波动和冻融循环频率显著高于针叶林,为了了解林线交错带上环境差异对凋落物分解过程中的土壤动物群落结构和多样性的影响,采用凋落物分解袋的方法,于高山生态系统的两个主要时期,即雪被末期和生长季末期,研究了林线主要代表性灌木——高山柳(Salix cupularis)、高山杜鹃(Rhododendron lapponicum)和红毛花楸(Sorbus rufopilosa)凋落叶分解的土壤动物多样性特征。结果表明:凋落物中的无脊椎动物群落多样性及个体、类群密度随物种、海拔梯度和季节而变化,且季节差异对无脊椎动物多样性的影响比物种和海拔梯度更显著。3个因子的交互作用不仅影响土壤动物群落多样性和均匀度,而且影响群落个体密度和类群密度。雪被末期,凋落物中的无脊椎动物多样性指数H、均匀度指数J及丰富度指数D以针叶林最高,优势度指数C以林线最高;生长季节末期的无脊椎动物类群密度和个体密度显著高于雪被末期。总体上,凋落物中的无脊椎动物群落丰富度以生长季末期最高,林线较针叶林丰富。这意味着,未来气候变暖情景下,灌丛密度增加,凋落物输入量增大,可能导致无脊椎动物多样性增加。     

Primers designed to amplify a mitochondrial nad1 intron in ponderosa pine, Pinus ponderosa, limber pine, P. flexilis, and Scots pine, P. sylvestris

The b/c intron of the mitochondrial nad1 gene, was sequenced to characterize the indel region of ponderosa pine, Pinus ponderosa. The sequence in ponderosa pine was aligned with the sequence in Scots pine, Pinus sylvestris, to design seven primers that are useful for sequencing and for revealing size variation in amplified fragments in ponderosa pine, Scots pine, and limber pine, Pinus flexilis. These primers reveal variability in all three species, and the pattern of variability within ponderosa pine is described by a preliminary survey. The indel region of ponderosa pine contains three distinct elements with lengths of 31, 32, and 34 bp. Received: 1 March 2000 / Accepted: 14 April 2000<@head-com-p1a.lf>Communicated by P.M.A. Tigerstedt     

Temporal dynamic of wood formation in Pinus cembra along the alpine treeline ecotone and the effect of climate variables

We determined the temporal dynamic of cambial activity and xylem development of stone pine (Pinus cembra L.) throughout the treeline ecotone. Repeated micro-sampling of the developing tree ring was carried out during the growing seasons 2006 and 2007 at the timberline (1,950 m a.s.l.), treeline (2,110 m a.s.l.) and within the krummholz belt (2,180 m a.s.l.) and the influence of climate variables on intra-annual wood formation was determined. At the beginning of both growing seasons, highest numbers of cambial and enlarging cells were observed at the treeline. Soil temperatures at time of initiation of cambial activity were c. 1.5°C higher at treeline (open canopy) compared to timberline (closed canopy), suggesting that a threshold root-zone temperature is involved in triggering onset of above ground stem growth. The rate of xylem cell production determined in two weekly intervals during June through August 2006–2007 was significantly correlated with air temperature (temperature sums expressed as degree-days and mean daily maximum temperature) at the timberline only. Lack of significant relationships between tracheid production and temperature variables at the treeline and within the krummholz belt support past dendroclimatological studies that more extreme environmental conditions (e.g., wind exposure, frost desiccation, late frost) increasingly control tree growth above timberline. Results of this study revealed that spatial and temporal (i.e., year-to-year) variability in timing and dynamic of wood formation of P. cembra is strongly influenced by local site factors within the treeline ecotone and the dynamics of seasonal temperature variation, respectively.     

气候变暖对老秃顶子林线结构特征的影响

运用样带样方法和年轮气候学方法对大海林地区的气候因子和样地数据进行了分析。结果表明 ,近 30 a来老秃顶子地区气候变暖明显 ,尤其是冬季增温最明显 ,月份增温中以 2月份最大 ;寒冷时期 (12月份、翌年 1和 2月份 )和温暖时期 (6～ 9月份 )的温度都有增加 ,但是寒冷时期温度的增加幅度较大 ;冬季与夏季温差稍有减少 ,但积温有所增加 ,整年的热量正在增加。全球变暖导致的大海林地区增温对老秃顶子林线结构特征产生了很大的影响 ,由样地调查和分析可知 ,全球变暖导致林线中上部幼苗、幼树的更新和存活增多 ,森林密度加大 ,树木平均年龄降低 ,年龄结构呈倒 J字型 ,并且多呈聚集分布 ;而在林线的下部 ,幼苗更新很少 ,主要以中龄林存在 ,并且多呈零散分布形式。通过年轮分析得出 ,气候变暖导致林线树木径生长和高生长增加 ,而且增加的趋势和近 30 a来温度的变化基本一致。通过对年轮指数与气候因子的相关性分析 ,表明林线树木年轮指数与温度的相关性较强 ,而与降水的相关性较弱 ,并且年轮指数与温暖时期温度和积温呈正相关 ,而与寒冷时期温度和年平均温度呈负相关 ,表明温暖时期温度和积温控制着林线的海拔高度 ,而寒冷时期的温度和年平均温度主要对林线树种类型起着决定性的作用。从敏感度分析看出 ,林线     

Drought stress limits the geographic ranges of two tree species via different physiological mechanisms

Range shifts are among the most ubiquitous ecological responses to anthropogenic climate change and have large consequences for ecosystems. Unfortunately, the ecophysiological forces that constrain range boundaries are poorly understood, making it difficult to mechanistically project range shifts. To explore the physiological mechanisms by which drought stress controls dry range boundaries in trees, we quantified elevational variation in drought tolerance and in drought avoidance‐related functional traits of a widespread gymnosperm (ponderosa pine – Pinus ponderosa) and angiosperm (trembling aspen – Populus tremuloides) tree species in the southwestern USA. Specifically, we quantified tree‐to‐tree variation in growth, water stress (predawn and midday xylem tension), drought avoidance traits (branch conductivity, leaf/needle size, tree height, leaf area‐to‐sapwood area ratio), and drought tolerance traits (xylem resistance to embolism, hydraulic safety margin, wood density) at the range margins and range center of each species. Although water stress increased and growth declined strongly at lower range margins of both species, ponderosa pine and aspen showed contrasting patterns of clinal trait variation. Trembling aspen increased its drought tolerance at its dry range edge by growing stronger but more carbon dense branch and leaf tissues, implying an increased cost of growth at its range boundary. By contrast, ponderosa pine showed little elevational variation in drought‐related traits but avoided drought stress at low elevations by limiting transpiration through stomatal closure, such that its dry range boundary is associated with limited carbon assimilation even in average climatic conditions. Thus, the same climatic factor (drought) may drive range boundaries through different physiological mechanisms – a result that has important implications for process‐based modeling approaches to tree biogeography. Further, we show that comparing intraspecific patterns of trait variation across ranges, something rarely done in a range‐limit context, helps elucidate a mechanistic understanding of range constraints.     

Drought responses of conifers in ecotone forests of northern Arizona: tree ring growth and leaf δ<Superscript>13</Superscript>C

We sought to understand differences in tree response to meteorological drought among species and soil types at two ecotone forests in northern Arizona, the pinyon-juniper woodland/ponderosa pine ecotone, and the higher elevation, wetter, ponderosa pine/mixed conifer ecotone. We used two approaches that provide different information about drought response: the ratio of standardized radial growth in wet years to dry years (W:D) for the period between years 1950 and 2000 as a measure of growth response to drought, and ¹³C in leaves formed in non-drought (2001) and drought (2002) years as a measure of change in water use efficiency (WUE) in response to drought. W:D and leaf ¹³C response to drought for Pinus edulis and P. ponderosa did not differ for trees growing on coarse-texture soils derived from cinders compared with finer textured soils derived from flow basalts or sedimentary rocks. P. ponderosa growing near its low elevation range limit at the pinyon-juniper woodland/ponderosa pine ecotone had a greater growth response to drought (higher W:D) and a larger increase in WUE in response to drought than co-occurring P. edulis growing near its high elevation range limit. P. flexilis and Pseudotsuga menziesii growing near their low elevation range limit at the ponderosa pine/mixed conifer ecotone had a larger growth response to drought than co-occurring P. ponderosa growing near its high elevation range limit. Increases in WUE in response to drought were similar for all species at the ponderosa pine/mixed conifer ecotone. Low elevation populations of P. ponderosa had greater growth response to drought than high-elevation populations, whereas populations had a similar increase in WUE in response to drought. Our findings of different responses to drought among co-occurring tree species and between low- and high-elevation populations are interpreted in the context of drought impacts on montane coniferous forests of the southwestern USA.     

Neighboring trees affect ectomycorrhizal fungal community composition in a woodland-forest ecotone

Ectomycorrhizal fungi (EMF) are frequently species rich and functionally diverse; yet, our knowledge of the environmental factors that influence local EMF diversity and species composition remains poor. In particular, little is known about the influence of neighboring plants on EMF community structure. We tested the hypothesis that the EMF of plants with heterospecific neighbors would differ in species richness and community composition from the EMF of plants with conspecific neighbors. We conducted our study at the ecotone between pinyon (Pinus edulis)-juniper (Juniperus monosperma) woodland and ponderosa pine (Pinus ponderosa) forest in northern Arizona, USA where the dominant trees formed associations with either EMF (P. edulis and P. ponderosa) or arbuscular mycorrhizal fungi (AMF; J. monosperma). We also compared the EMF communities of pinyon and ponderosa pines where their rhizospheres overlapped. The EMF community composition, but not species richness of pinyon pines was significantly influenced by neighboring AM juniper, but not by neighboring EM ponderosa pine. Ponderosa pine EMF communities were different in species composition when growing in association with pinyon pine than when growing in association with a conspecific. The EMF communities of pinyon and ponderosa pines were similar where their rhizospheres overlapped consisting of primarily the same species in similar relative abundance. Our findings suggest that neighboring tree species identity shaped EMF community structure, but that these effects were specific to host-neighbor combinations. The overlap in community composition between pinyon pine and ponderosa pine suggests that these tree species may serve as reservoirs of EMF inoculum for one another.     

Stand‐replacing fires reduce susceptibility of lodgepole pine to mountain pine beetle outbreaks in Colorado

Aim As climate change is increasing the frequency, severity and extent of wildfire and bark beetle outbreaks, it is important to understand how these disturbances interact to affect ecological patterns and processes, including susceptibility to subsequent disturbances. Stand‐replacing fires and outbreaks of mountain pine beetle (MPB), Dendroctonus ponderosae, are both important disturbances in the lodgepole pine, Pinus contorta, forests of the Rocky Mountains. In the current study we investigated how time since the last stand‐replacing fire affects the susceptibility of the stand to MPB outbreaks in these forests. We hypothesized that at a stand‐scale, young post‐fire stands (< c. 100–150 years old) are less susceptible to past and current MPB outbreaks than are older stands. Location Colorado, USA. Methods We used dendroecological methods to reconstruct stand‐origin dates and the history of outbreaks in 23 lodgepole pine stands. Results The relatively narrow range of establishment dates among the oldest trees in most sampled stands suggested that these stands originated after stand‐replacing or partially stand‐replacing fires over the past three centuries. Stands were affected by MPB outbreaks in the 1940s/1950s, 1980s and 2000s/2010s. Susceptibility to outbreaks generally increased with stand age (i.e. time since the last stand‐replacing fire). However, this reduced susceptibility of younger post‐fire stands was most pronounced for the 1940s/1950s outbreak, less so for the 1980s outbreak, and did not hold true for the 2000s/2010s outbreak. Main conclusions Younger stands may not have been less susceptible to the most recent outbreak because: (1) after stands reach a threshold age of > 100–150 years, stand age does not affect susceptibility to outbreaks, or (2) the high intensity of the most recent outbreak reduces the importance of pre‐disturbance conditions for susceptibility to disturbance. If the warm and dry conditions that contribute to MPB outbreaks concurrently increase the frequency and/or extent of severe fires, they may thereby mitigate the otherwise increased landscape‐scale susceptibility to outbreaks. Potential increases in severe fires driven by warm and dry climatic trends may lead to a negative feedback by making lodgepole pine stands less susceptible to future MPB outbreaks.     

Observations on the genetic structure and mating system of ponderosa pine in the Colorado front range

Summary Variation of peroxidase enzymes is analyzed both in mature needle tissue and in open-pollinated seedling families of ponderosa pine, Pinus ponderosa, and is identified as being controlled by a single Mendelian locus. Variation at this locus, analyzed in 1, 386 individuals, is used in the analysis of population differentiation and the mating system. Significant variation of gene frequencies is detected over distances of several hundred meters, and is found to be associated with slopes of different aspects. Ponderosa pine is wind-pollinated, and an analysis of the mating system indicates that the level of outcrossing is greater than 90 %. Selection specific for different environments is evidently strong enough to overcome the homogenizing force of migration and produce population fissuring in ponderosa pine.     

Connections between climatic variables and the growth and needle dynamics of Scots pine (Pinus sylvestris L.) in Estonia and Lapland

The relationships between climatic variables and Scots pine (Pinus sylvestris L.) growth and needle dynamics were studied in three stands in Estonia and in four stands located near the northern timberline in Lapland. The trees sampled in Estonia had low correlations with the analysed climatic variables (air temperature, precipitation and indices of atmospheric circulation). Moreover, the weak cross-correlation of the time-series of the Estonian sample trees indicated that Scots pine is affected mainly by local factors in that region. In Lapland, however, height increment and needle production correlated strongly among trees within a stand (mean r=0.45 and 0.46, respectively) and between stands (r=0.32 and 0.37). Radial increment also showed a high inter-correlation among the trees within a stand in Lapland (r=0.45). Both height increment and needle production were strongly influenced by the temperature regime of the previous summer in Lapland (mean r=0.64 and 0.64, respectively). Radial increment was correlated with the mean July temperature of the current year (mean r=0.29). The correlations between the indices of atmospheric circulation and tree attributes were weak, while the strongest correlation was between the Ponta Delgada NAO index (PD–NAO) and height increment and needle production in Lapland. Height increment, needle production and radial increment have increased since the 1990s in the trees growing in Lapland. This may indicate a positive effect of climate warming on tree growth in Lapland. In Estonia, where climatic conditions do not limit tree growth, the climate warming seems not to directly influence the growth and needle dynamics of Scots pine.     

Recognizing site adversity and drought-sensitive trees in stands of bristlecone pine (Pinus longaeva)

Bristlecone pine has been called the world’s oldest known living thing. The tree grows in mountainous terrain near timberline in three southwestern states. Because of the species’ longevity, sensitivity to climatic fluctuations, and unique growth form, it has attracted considerable attention from both scientists and recreationists. This paper discusses bristlecone pine in relation to its environment in east-central Nevada and sets forth criteria for recognizing trees that may be old or sensitive to climatic changes.     

Long-term changes in tree-ring–climate relationships at Mt. Patscherkofel (Tyrol,Austria) since the mid-1980s

Although growth limitation of trees at Alpine and high-latitude timberlines by prevailing summer temperature is well established, the loss of thermal response of radial tree growth during last decades has repeatedly been addressed. We examined long-term variability of climate–growth relationships in ring width chronologies of Stone pine (Pinus cembra L.) by means of moving response functions (MRF). The study area is situated in the timberline ecotone (ca. 2,000–2,200 m a.s.l.) on Mt. Patscherkofel (Tyrol, Austria). Five site chronologies were developed within the ecotone with constant sample depth (≥19 trees) throughout most of the time period analysed. MRF calculated for the period 1866–1999 and 1901–1999 for ca. 200- and ca. 100-year-old stands, respectively, revealed that mean July temperature is the major and long-term stable driving force of Pinus cembra radial growth within the timberline ecotone. However, since the mid-1980s, radial growth in timberline and tree line chronologies strikingly diverges from the July temperature trend. This is probably a result of extreme climate events (e.g. low winter precipitation, late frost) and/or increasing drought stress on cambial activity. The latter assumption is supported by a <10% increase in annual increments of ca. 50-year-old trees at the timberline and at the tree line in 2003 compared with 2002, when extraordinary hot and dry conditions prevailed during summer. Furthermore, especially during the second half of the twentieth century, influence of climate variables on radial growth show abrupt fluctuations, which might also be a consequence of climate warming on tree physiology.     

Mountain pine beetle attack associated with low levels of 4-allylanisole in ponderosa pine

Mountain pine beetle (Dendroctonus ponderosae) is the most important insect pest in southern Rocky Mountain ponderosa pine (Pinus ponderosa) forests. Tree mortality is hastened by the various fungal pathogens that are symbiotic with the beetles. The phenylpropanoid 4-allylanisole is an antifungal and semiochemical for some pine beetle species. We analyzed 4-allylanisole and monoterpene profiles in the xylem oleoresin from a total of 107 trees at six sites from two chemotypes of ponderosa pine found in Colorado and New Mexico using gas chromatography-mass spectroscopy (GC-MS). Although monoterpene profiles were essentially the same in attacked and nonattacked trees, significantly lower levels of 4-allylanisole were found in attacked trees compared with trees that showed no evidence of attack for both chemotypes.     

Smith fir population structure and dynamics in the timberline ecotone of the Sejila Mountain, Tibet, China

Smith fir (Abies georgei var. smithii), which grows on cool aspects with elevations ranging between 3600 m and 4400 m, is a major native dominant alpine tree species in Southeast Tibet, China. The smith fir population structure, dynamics and characteristics were investigated in the timberline ecotone of the Sejila Mountain. Results indicate that the minimum crown closure (≤20%) was reached at 4320 m above sea level, where two types of alpine species exist, smith fir and blackseed savin (Sabina saltuaria). On the warm aspects, blackseed savin is a dominant species. Forest line was formed gradually with a wider timberline ecotone. While on the cool aspects, smith fir is a dominant species. Forest line was formed clearly with a narrow timberline ecotone. Furthermore, the upper limits of the distribution of the alpine species were 4570 m and 4390 m on warm and cool aspects, respectively. The timberline ecotone widths of the two species on the warm and cool aspects were 250 m and 70 m, respectively. The optimal distribution of smith fir on the cool aspects was from 3700 m to 3800 m. The smith fir's diameter class distribution was of reversed “J” shape and its density was about 380 stem·hm?2, while the age structure appeared to be of pyramid-shape, suggesting an expanding population. Finally, the static life table and the survivorship curve showed that the populations had experienced severe environmental selection during their first 20 years, self-thinning between 60 to 100 years, and environmental changes related mortality at later stages. The smith fir's physiological life span was around 200 years, and its maximum age was about 400 years old.     

Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic

Aim We examined relationships between climate–disturbance gradients and patterns of vegetation zonation and ecotones on a subtropical mountain range. Location The study was conducted on the windward slopes of the Cordillera Central, Dominican Republic, where cloud forest appears to shift in a narrow ecotone to monodominant forest of Pinus occidentalis. Methods Climate, disturbance and vegetation data were collected over the elevation range 1100–3100 m and in 50 paired plots along the ecotone. Aerial photographs were georeferenced to a high‐resolution digital elevation model in order to enable the analysis of landscape‐scale patterns of the ecotone. Results A Shipley–Keddy test detected discrete compositional ecotones at 2200 and 2500 m; the distributions of tree species at lower elevations were continuous. The elevation of the ecotone determined with aerial photographs was fairly consistent, namely ± 164 m (SD) over its 124‐km length, but it exhibited significant landscape variation, occurring at a lower elevation in a partially leeward, western zone. The ecotone also occurred significantly lower on ridges than it did in drainage gullies. Ecotone forest structure and composition differed markedly between paired plots. In pine paired plots, the canopy height was 1.7 times higher and the basal area of non‐pine species was 6 times lower than in the cloud forest directly below. Fire evidence was ubiquitous in the pine forest but rare in the abutting cloud forest. Mesoclimate changed discontinuously around the elevation of the ecotone: humidity and cloud formation decreased markedly, and frost frequency increased exponentially. Main conclusions The discreteness of the ecotone was produced primarily by fire. The elevational consistency of the ecotone, however, resulted from the overarching influence of mesoclimate on the elevational patterns of fire occurrence. Declining temperature and precipitation combine with the trade‐wind inversion to create a narrow zone where high‐elevation fires extinguish, enabling fire‐sensitive and fire‐tolerant taxa to abut. Once established, mesotopography and contrasting vegetation physiognomy probably reinforce this boundary through feedbacks on microenvironment and fire likelihood. The prominence of the pine in this study – and of temperate and fire‐tolerant taxa in subtropical montane forests in general – highlights the importance of climate‐disturbance–biogeography interactions in ecotone formation, particularly where fire mediates a dynamic between climate and vegetation.     

Persistence and expansion of ponderosa pine woodlands in the west‐central Great Plains during the past two centuries

Aim Woody plant expansion and infilling in grasslands and savannas are occurring across a broad range of ecosystems around the globe and are commonly attributed to fire suppression, livestock grazing, nutrient enrichment and/or climate variability. In the western Great Plains, ponderosa pine (Pinus ponderosa) woodlands are expanding across broad geographical and environmental gradients. The objective of this study was to reconstruct the establishment of ponderosa pine in woodlands in the west‐central Great Plains and to identify whether it was mediated by climate variability. Location Our study took place in a 400‐km wide region from the base of the Front Range Mountains (c. 105° W) to the central Great Plains (c. 100° W) and from Nebraska (43° N) to northern New Mexico (36° N), USA. Methods Dates for establishment of ponderosa pine were reconstructed with tree rings in 11 woodland sites distributed across the longitudinal and latitudinal gradients of the study area. Temporal trends in decadal pine establishment were compared with summer Palmer Drought Severity Index (PDSI). Annual trends in pine establishment from 1985 to 2005 were compared with seasonal PDSI, temperature and moisture availability. Results Establishment of ponderosa pine occurred in the study area in all but one decade (1770s) between the 1750s and the early 2000s, with over 35% of establishment in the region occurring after 1980. Pine establishment was highly variable among sites. Across the region, decadal pine establishment was persistently low from 1940 to 1960, when PDSI was below average. Annual pine establishment from 1985 to 2005 was positively correlated with summer PDSI and inversely correlated with minimum spring temperatures. Main conclusions Most ponderosa pine woodlands pre‐date widespread Euro‐American settlement of the region around c. ad 1860 and currently have stable tree populations. High variability in the timing of establishment of pine among sites highlights the multiplicity of factors that can drive woodland dynamics, including land use, fire history, CO₂ enrichment, tree population dynamics and climate. Since the 1840s, the influence of climate was most notable across the study area during the mid‐20th century, when the establishment of pine was suppressed by two significant droughts. The past sensitivity of establishment of ponderosa pine to drought suggests that woodland expansion will be negatively affected by predicted increases in temperature and drought in the Great Plains.     

Associations Among Breeding Birds and Gambel Oak in Southwestern Ponderosa Pine Forests

Abstract: Ponderosa pine (Pinus ponderosa) forests with Gambel oak (Quercus gambelii) are associated with higher bird abundance and diversity than are ponderosa pine forests lacking Gambel oak. Little is known, however, about specific structural characteristics of Gambel oak trees, clumps, and stands that may be important to birds in ponderosa pine-Gambel oak (hereafter pine-oak) forests. We examined associations among breeding birds and structural characteristics of Gambel oak at a scale similar in size to individual bird territories in pine-oak forests in northern Arizona and western New Mexico, USA. Avian species richness and occurrence of some bird species were associated with specific growth forms of Gambel oak. Estimated probability of Virginia's warblers (Vermivora virginiae), black-headed grosbeaks (Pheucticus melanocephalus), and red-faced warblers (Cardellina rubrifrons) occurring at points increased with increasing density of pole-sized Gambel oak 7–15 cm in diameter at breast height. We also found evidence that large Gambel oak trees (≥23 cm dbh) were associated with increased occurrence of yellow-rumped warblers (Dendroica coronata) at points. Some avian associations with oak were influenced by characteristics of ponderosa pines. For example, bird species richness was positively associated with the abundance of large Gambel oak when density of large pine trees ≥23 cm in diameter at breast height was low. Because large oak trees are rare and their numbers are thought to be declining, efforts should be made to retain and promote growth of additional oaks in this size class. Forest management practices that maintain forest openings, such as prescribed burning, could promote growth of pole-sized Gambel oak, which appears important to some bird species in pine-oak forests.     

Native root xylem embolism and stomatal closure in stands of Douglas-fir and ponderosa pine: mitigation by hydraulic redistribution

Hydraulic redistribution (HR), the passive movement of water via roots from moist to drier portions of the soil, occurs in many ecosystems, influencing both plant and ecosystem-water use. We examined the effects of HR on root hydraulic functioning during drought in young and old-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine (Pinus ponderosa Dougl. Ex Laws) trees growing in four sites. During the 2002 growing season, in situ xylem embolism, water deficit and xylem vulnerability to embolism were measured on medium roots (2–4-mm diameter) collected at 20–30 cm depth. Soil water content and water potentials were monitored concurrently to determine the extent of HR. Additionally, the water potential and stomatal conductance (g_s) of upper canopy leaves were measured throughout the growing season. In the site with young Douglas-fir trees, root embolism increased from 20 to 55 percent loss of conductivity (PLC) as the dry season progressed. In young ponderosa pine, root embolism increased from 45 to 75 PLC. In contrast, roots of old-growth Douglas-fir and ponderosa pine trees never experienced more than 30 and 40 PLC, respectively. HR kept soil water potential at 20–30 cm depth above –0.5 MPa in the old-growth Douglas-fir site and –1.8 MPa in the old-growth ponderosa pine site, which significantly reduced loss of shallow root function. In the young ponderosa pine stand, where little HR occurred, the water potential in the upper soil layers fell to about –2.8 MPa, which severely impaired root functioning and limited recovery when the fall rains returned. In both species, daily maximum g_s decreased linearly with increasing root PLC, suggesting that root xylem embolism acted in concert with stomata to limit water loss, thereby maintaining minimum leaf water potential above critical values. HR appears to be an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure.     

Relationship between soil properties and incidence of pine wilt disease at stand level

This study was conducted to evaluate and compare soil properties between pine stands either damaged or undamaged by pine wilt disease in Jinju and Sacheon Cities, which are areas in Korea severely affected by the disease. Soil physical and chemical properties were generally similar between damaged and undamaged pine stands. There was no significant difference in soil factors related to soil nutrient fertility between damaged and undamaged pine stands, although the incidence of pine wilt disease was affected by soil clay content, which was significantly (P < 0.05) higher in the damaged (24.8%) than in the undamaged (20.1%) pine stands. However, this relationship should be treated with caution because small scale topographical variation may simply reflect the incidence of pine wilt disease. The results suggest that incidence of pine wilt disease was not influenced by soil nutrient properties at a small stand scale.     

Variation in ecophysiological properties among conifers at an ecotonal boundary: comparison of establishing seedlings and established adults at timberline

Question: Environmental limitations on carbon acquisition and use can impact successful establishment and restrict a species range, such as for trees at timberline. How do ecophysiological properties associated with carbon uptake and allocation change along an elevation gradient for adult compared to seedling conifers in a timberline ecotone? Location: Teton Range in the Rocky Mountains, Wyoming, USA Methods: Photochemical efficiency (F_v/F_m), specific leaf area (SLA) and foliar nonstructural carbohydrates (NSC) were compared along an elevation gradient (2200‐3050 m) among two age classes (seedling and adult) and species (Abies lasiocarpa and Pseudotsuga menziesii) at timberline during mid‐summer. Results: F _v/F_m values were relatively high in both seedlings and adults across the elevation gradient, with the exception of a low F_v/F_m for seedlings in the site having the lowest soil temperatures. SLA was surprisingly constant within each age class and species across the timberline ecotone. Foliar NSCs did not increase or decrease consistently with elevation in either age class. Nonetheless, NSCs were highly variable among sites, but only in seedlings and not in adults. Conclusions: Elevation effects on these indicators of the efficiency of interception and use of sunlight in the timberline ecotone were minimal during the optimum period of the growing season. However, establishing seedlings had a tendency to exhibit greater responses to the timberline environment, particularly in their allocation of photosynthate to NSC, which may be a constraint to tree establishment at high elevations.