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1.
Growth response of subalpine fir (Abies lasiocarpa) to climate was studied across its local geographical and elevation range in the Olympic Mountains, Washington. A dendroecological analysis of subalpine fir across a range of elevations (1350-1850 m) and annual precipitation (125-350 cm y?1), was used to compare environmental factors affecting growth. Climate-growth relationships were explored using Pearson product-moment correlation coefficients; partial correlation analysis was used to assess relationships among site chronologies and climatic variables. Radial growth is negatively correlated with winter precipitation at high elevation and wet sites, but not at low and middle elevation dry sites. Growth is positively correlated with current growing season temperature at all sites; however, growth is negatively correlated with previous year August temperature, indicating that climate affects growth in subsequent years. Positive correlations between growth and summer precipitation during the growing season at low and middle elevation dry sites suggest that soil moisture is partially limiting to growth on these sites. If the climate of the Pacific Northwest becomes warmer and drier, then subalpine fir growth may increase at high elevation and wet sites, but may decrease at lower elevation dry sites in the Olympic Mountains. However, the growth response of subalpine fir to potentially rapid climate change will not be uniform because subalpine fir grows over a wide range of topographic features, habitats, and local climates at different geographical scales. A comparison of growth response to current growing season temperature suggests that the temperature-related growth response of subalpine fir is not adequately described by the parabolic curve used in JABOWA-based models. 相似文献
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Leaf tolerance to high temperatures, as determined by electrolyte leakage and chlorophyll a fluorescence, was compared for Artemisia tridentata (Asteraceae), a widespread shrub of the Great Basin, Colorado Plateau, and western slope of the Rocky Mountains, and Potentilla gracilis (Rosaceae), a herbaceous forb common to high-elevation meadows of the western United States. Species-specific and treatment-specific differences in leaf temperature, high-temperature tolerance and chlorophyll a fluorescence from photosystem II were compared, to test the hypothesis that plants at ecosystem borders will exhibit species-specific responses to climate change. Measurements were made for plants exposed to a climate change warming manipulation on a major ecosystem border at the Rocky Mountain Biological Laboratory, Colorado, United States, in July and August 1995. In July, daily maximal leaf temperatures were significantly higher for P. gracilis than for A. tridentata. Leaf temperatures were slightly lower in August than July for leaves of both species, on control and heated plots, despite the fact that daily maximum air temperatures were not significantly different for the two months. High-temperature tolerance was determined for leaves treated for 1 h at temperatures ranging from 15°C to 65°C. LT50 was approximately 46°C for both species on control plots, but was 43°C for leaves of both species from heated plots, contrary to the predictions of the hypothesis. No shift in LT50 (acclimation) was apparent between July and August. Changes in chlorophyll a fluorescence from photosystem II (F
V
/F
M
) were used to characterize the photosynthetic response to high temperatures. For both A. tridentata and P. gracilis in July, F
V
/F
M
was about 0.7, but decreased for temperatures above 40°C. The results suggest that plant responses to global warming at ecosystem borders may be influenced by factors other than leaf-level physiological tolerance to elevated temperatures. 相似文献
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《Plant Ecology & Diversity》2013,6(3):319-333
ABSTRACTBackground: Topoclimate can influence tree establishment within treeline ecotones. Yet much less is known about how regional topography, such as the Continental Divide, Rocky Mountains, mediates the role of climate in governing treeline dynamics.Aims: To utilise the Continental Divide to test whether contrasts in growing-season moisture regimes to the west (summer-dry) and east (summer-wet) impact the spatio-temporal patterns of tree establishment and rates of treeline advance in the Northern Rocky Mountains.Methods: We sampled trees at sites on north- and south-facing slopes, west and east of the Continental Divide. We used dendroecological techniques to reconstruct patterns of tree establishment. Age-structure data were quantitatively compared with climate to evaluate possible mechanistic linkages.Results: Across all sites, 96% of trees established after 1950. There was a treeline advance (range = 39–140 m) accompanied by increases in tree density. Significantly more trees established during wet springs on both sides of the Divide.Conclusions: Overall, snow duration in spring and autumn temperatures appear to influence patterns of tree recruitment at the treeline. Continued warming will likely amplify the role of autumn climate in regulating tree establishment throughout treeline ecotones in the Northern Rocky Mountains, particularly west of the Divide where summer-dry conditions persist. 相似文献
4.
Scott Bennett Thomas Wernberg Euan S. Harvey Julia Santana‐Garcon Benjamin J. Saunders 《Ecology letters》2015,18(7):714-723
Climate‐mediated changes to biotic interactions have the potential to fundamentally alter global ecosystems. However, the capacity for novel interactions to drive or maintain transitions in ecosystem states remains unresolved. We examined temperate reefs that recently underwent complete seaweed canopy loss and tested whether a concurrent increase in tropical herbivores could be maintaining the current canopy‐free state. Turf‐grazing herbivorous fishes increased in biomass and diversity, and displayed feeding rates comparable to global coral reefs. Canopy‐browsing herbivores displayed high (~ 10 000 g 100 m?2) and stable biomass between 2006 and 2013. Tropical browsers had the highest abundance in 2013 and displayed feeding rates approximately three times higher than previously observed on coral reefs. These observations suggest that tropical herbivores are maintaining previously kelp‐dominated temperate reefs in an alternate canopy‐free state by grazing turfs and preventing kelp reestablishment. This remarkable ecosystem highlights the sensitivity of biotic interactions and ecosystem stability to warming and extreme disturbance events. 相似文献
5.
Recent increases in temperature over the semi-arid western United States have been shown to exacerbate drought, reducing streamflow, and increasing stress on ecosystems. Our understanding of the role temperature played during drought in the more distant past is far from complete. While numerous tree-ring proxy records of moisture provide evidence for past extreme droughts in this region, few contemporaneous tree-ring proxy records of temperatures exist. This limits our ability to evaluate the variable influence of temperature on drought over past centuries and to contextualize the present interplay of moisture and temperature during more recent drought events. It is also important to understand the complexity of climatic interactions that produced drought under natural variability prior to evaluating the potential impacts of future climate change. In response to this knowledge gap, we undertook the first extensive evaluation of climate sensitivity in Rocky Mountain bristlecone pine (Pinus aristata Engelm.), focusing on the potential for developing new multi-century proxy records of both temperature and precipitation. We isolated dominant patterns of growth variability among trees from ten ring-width datasets across the Southern Rocky Mountains of Colorado and New Mexico and assessed their response to climate. We utilized both an empirical orthogonal function (EOF) analysis and a modified form of hierarchical cluster analysis to produce time series representing growth patterns in P. aristata. The results indicate a widespread June drought stress signal with a high potential for multi-millennial reconstruction. We also found a positive minimum temperature response during late summer, evident only at lower frequency and co-occurring at locations with the June drought stress signal. The potential for temperature reconstruction will require further investigation into the physiological linkages between P. aristata and climate variability. The presence of multiple climate responses within P. aristata sampling sites highlights the need for particular care when including P. aristata in regional climate reconstructions. 相似文献
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理解植物群落组成结构的演化对于阐明荒漠化的过程与驱动机制、制定有效的干旱区生态系统恢复措施具有重要价值。研究干旱区植物群落的空间格局的演化过程有助于深入理解荒漠化和生态恢复的过程与机理。目前大量研究关注于植被退化过程中的群落组成结构变化,而对于生态恢复过程中的植物群落空间格局演化的研究尚不多见。干旱区生态系统中植物通常较为稀疏且个体较小,准确提取植物的分布往往需要分辨率极高的遥感数据。近年来,低空无人机遥感技术的快速发展为精细尺度上植被空间格局的研究提供重要技术支持。利用2 cm空间分辨率的低空无人机遥感数据结合地面群落调查,在精细尺度上研究了宁夏沙坡头草方格生态恢复区内植物群落的空间格局变化。研究结果表明,沙坡头地区草方格生态恢复工程实验区域,相对于未实施生态恢复工程的裸露沙丘区域,植物物种多样性和植被盖度显著提高。恢复工程实施4年后,平均植被盖度增加3倍,物种丰富度增加1倍。在植被恢复过程中,随着植被盖度的增加,植被斑块表现出规模上升、破碎化程度下降、形状复杂化、空间自相关减弱等格局特征变化。这些空间格局特征的变化表明大型植被斑块趋于恢复,整体微环境的改善有利于单独生长的植物个体存活,整体上生态系统退化为裸地的风险降低。利用低空无人机遥感手段,对草方格生态恢复工程的植被恢复过程进行了详细、高分辨率的空间格局调查及分析,结合地面群落调查,从多个方面证明了草方格生态恢复措施的有效性。基于无人机的系统格局连续长期监测有助于深入理解干旱区生态恢复机理,对于科学开展荒漠化生态恢复措施也具有重要价值。 相似文献
8.
In an effort to explore the thermal limitations of Colorado River cutthroat trout Oncorhynchus clarkii pleuriticus, the critical thermal maxima (Tcmax) of 1+ year Lake Nanita strain O. c. pleuriticus were evaluated when acclimated to 10, 15 and 20° C. The mean ±s.d. Tcmax for O. c. pleuriticus acclimated to 10° C was 24·6 ± 2·0°C (n = 30), for 15° C‐acclimated fish was 26·9 ± 1·5° C (n = 23) and for 20° C‐acclimated fish was 29·4 ± 1·1° C (n = 28); these results showed a marked thermal acclimation effect (Q10 = 1·20). Interestingly, there was a size effect within treatments, wherein the Tcmax of larger fish was significantly lower than that of smaller fish acclimated to the same temperature. The critical thermal tolerances of age 0 year O. c. pleuriticus were also evaluated from three separate populations: Lake Nanita, Trapper Creek and Carr Creek reared under ‘common‐garden’ conditions prior to thermal acclimation. The Trapper Creek population had significantly warmer Tcmax than the Lake Nanita population, but that of the Carr Creek fish had Tcmax similar to both Trapper Creek and Lake Nanita fish. A comparison of these O. c. pleuriticus Tcmax results with those of other stream‐dwelling salmonids suggested that O. c. pleuriticus are less resistant to rapid thermal fluctuations when acclimated to cold temperatures, but can tolerate similar temperatures when acclimated to warmer temperatures. 相似文献
9.
Peter R. Last William T. White Daniel C. Gledhill Alistair J. Hobday Rebecca Brown Graham J. Edgar Gretta Pecl 《Global Ecology and Biogeography》2011,20(1):58-72
Aim South‐eastern Australia is a climate change hotspot with well‐documented recent changes in its physical marine environment. The impact on and temporal responses of the biota to change are less well understood, but appear to be due to influences of climate, as well as the non‐climate related past and continuing human impacts. We attempt to resolve the agents of change by examining major temporal and distributional shifts in the fish fauna and making a tentative attribution of causal factors. Location Temperate seas of south‐eastern Australia. Methods Mixed data sources synthesized from published accounts, scientific surveys, spearfishing and angling competitions, commercial catches and underwater photographic records, from the ‘late 1800s’ to the ‘present’, were examined to determine shifts in coastal fish distributions. Results Forty‐five species, representing 27 families (about 30% of the inshore fish families occurring in the region), exhibited major distributional shifts thought to be climate related. These are distributed across the following categories: species previously rare or unlisted (12), with expanded ranges (23) and/or abundance increases (30), expanded populations in south‐eastern Tasmania (16) and extra‐limital vagrants (4). Another 9 species, representing 7 families, experienced longer‐term changes (since the 1800s) probably due to anthropogenic factors, such as habitat alteration and fishing pressure: species now extinct locally (3), recovering (3), threatened (2) or with remnant populations (1). One species is a temporary resident periodically recruited from New Zealand. Of fishes exhibiting an obvious poleward movement, most are reef dwellers from three Australian biogeographic categories: widespread southern, western warm temperate (Flindersian) or eastern warm temperate (Peronian) species. Main conclusions Some of the region's largest predatory reef fishes have become extinct in Tasmanian seas since the ‘late 1800s’, most likely as a result of poor fishing practices. In more recent times, there have been major changes in the distribution patterns of Tasmanian fishes that correspond to dramatic warming observed in the local marine environment. 相似文献
10.
Regime shifts are abrupt transitions between alternate ecosystem states including desertification in arid regions due to drought or overgrazing. Regime shifts may be preceded by statistical anomalies such as increased autocorrelation, indicating declining resilience and warning of an impending shift. Tests for conditional heteroskedasticity, a type of clustered variance, have proven powerful leading indicators for regime shifts in time series data, but an analogous indicator for spatial data has not been evaluated. A spatial analog for conditional heteroskedasticity might be especially useful in arid environments where spatial interactions are critical in structuring ecosystem pattern and process. We tested the efficacy of a test for spatial heteroskedasticity as a leading indicator of regime shifts with simulated data from spatially extended vegetation models with regular and scale‐free patterning. These models simulate shifts from extensive vegetative cover to bare, desert‐like conditions. The magnitude of spatial heteroskedasticity increased consistently as the modeled systems approached a regime shift from vegetated to desert state. Relative spatial autocorrelation, spatial heteroskedasticity increased earlier and more consistently. We conclude that tests for spatial heteroskedasticity can contribute to the growing toolbox of early warning indicators for regime shifts analyzed with spatially explicit data. 相似文献
11.
Andrés Holz Sam W. Wood Thomas T. Veblen David M.J.S. Bowman 《Global Change Biology》2015,21(1):445-458
Athrotaxis cupressoides is a slow‐growing and long‐lived conifer that occurs in the subalpine temperate forests of Tasmania, a continental island to the south of Australia. In 1960–1961, human‐ignited wildfires occurred during an extremely dry summer that killed many A. cupressoides stands on the high plateau in the center of Tasmania. That fire year, coupled with subsequent regeneration failure, caused a loss of ca. 10% of the geographic extent of this endemic Tasmanian forest type. To provide historical context for these large‐scale fire events, we (i) collected dendroecological, floristic, and structural data, (ii) documented the postfire survival and regeneration of A. cupressoides and co‐occurring understory species, and (iii) assessed postfire understory plant community composition and flammability. We found that fire frequency did not vary following the arrival of European settlers, and that A. cupressoides populations were able to persist under a regime of low‐to‐mid severity fires prior to the 1960 fires. Our data indicate that the 1960 fires were (i) of greater severity than previous fires, (ii) herbivory by native marsupials may limit seedling survival in both burned and unburned A. cupressoides stands, and (iii) the loss of A. cupressoides populations is largely irreversible given the relatively high fuel loads of postfire vegetation communities that are dominated by resprouting shrubs. We suggest that the feedback between regeneration failure and increased flammability will be further exacerbated by a warmer and drier climate causing A. cupressoides to contract to the most fire‐proof landscape settings. 相似文献
12.
Brian J. Harvey Daniel C. Donato Monica G. Turner 《Global Ecology and Biogeography》2016,25(6):655-669
Aim Climate warming and increased wildfire activity are hypothesized to catalyse biogeographical shifts, reducing the resilience of fire‐prone forests world‐wide. Two key mechanisms underpinning hypotheses are: (1) reduced seed availability in large stand‐replacing burn patches, and (2) reduced seedling establishment/survival after post‐fire drought. We tested for regional evidence consistent with these mechanisms in an extensive fire‐prone forest biome by assessing post‐fire tree seedling establishment, a key indicator of forest resilience. Location Subalpine forests, US Rocky Mountains. Methods We analysed post‐fire tree seedling establishment from 184 field plots where stand‐replacing forest fires were followed by varying post‐fire climate conditions. Generalized linear mixed models tested how establishment rates varied with post‐fire drought severity and distance to seed source (among other relevant factors) for tree species with contrasting post‐fire regeneration adaptations. Results Total post‐fire tree seedling establishment (all species combined) declined sharply with greater post‐fire drought severity and with greater distance to seed sources (i.e. the interior of burn patches). Effects varied among key species groups. For conifers that dominate present‐day subalpine forests (Picea engelmannii, Abies lasiocarpa), post‐fire seedling establishment declined sharply with both factors. One exception was serotinous Pinus contorta, which did not vary with either factor. For montane species expected to move upslope under future climate change (Larix occidentalis, Pseudotsuga menziesii, Populus tremuloides) and upper treeline species (Pinus albicaulis), establishment was unrelated to either factor. Greater post‐fire tree seedling establishment on cooler/wetter aspects suggested local topographic refugia during post‐fire droughts. Main conclusions If future drought and wildfire patterns manifest as expected, post‐fire tree seedling establishment of species that currently characterize subalpine forests could be substantially reduced. Compensatory increases from lower montane and upper treeline species may partially offset these reductions, but our data suggest important near‐ to mid‐term shifts in the composition and structure of high‐elevation forests under continued climate warming and increased wildfire activity. 相似文献
13.
Shalik Ram Sigdel Eryuan Liang Yafeng Wang Binod Dawadi Jesús Julio Camarero 《Journal of Biogeography》2020,47(8):1816-1826
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In the Sierra Nevada, distributions of forest tree species are largely controlled by the soil-moisture balance. Changes in
temperature or precipitation as a result of increased greenhouse gas concentrations could lead to changes in species distributions.
In addition, climatic change could increase the frequency and severity of wildfires. We used a forest gap model developed
for Sierra Nevada forests to investigate the potential sensitivity of these forests to climatic change, including a changing
fire regime. Fuel moisture influences the fire regime and couples fire to climate. Fires are also affected by fuel loads,
which accumulate according to forest structure and composition. These model features were used to investigate the complex
interactions between climate, fire, and forest dynamics. Eight hypothetical climate-change scenarios were simulated, including
two general circulation model (GCM) predictions of a 2 × CO2 world. The response of forest structure,species composition, and the fire regime to these changes in the climate were examined
at four sites across an elevation gradient. Impacts on woody biomass and species composition as a result of climatic change
were site specific and depended on the environmental constraints of a site and the environmental tolerances of the tree species
simulated. Climatic change altered the fire regime both directly and indirectly. Fire frequency responded directly to climate's
influence on fuel moisture, whereas fire extent was affected by changes that occurred in either woody biomass or species composition.
The influence of species composition on fuel-bed bulk density was particularly important. Future fires in the Sierra Nevada
could be both more frequent and of greater spatial extent if GCM predictions prove true.
Received 5 May 1998; accepted 4 November 1998. 相似文献
17.
基于2008年和2013年对位于秦岭山脉西端、甘肃东南部小陇山林区的林分调查数据,选取树种锐齿栎、膀胱果和青榨槭为研究对象,运用点格局O-ring O(t)函数分析法,探讨5年前后锐齿栎林种群空间分布格局与关联性变化情况(其中,对树种锐齿栎进行分林层讨论,而对于膀胱果和青榨槭则不分层,空间关联性分析均不分层)。结果显示:(1)5年前后,锐齿栎林的空间格局整体上表现为随机分布;林上层锐齿栎分布稳定,主要为随机分布,林间层多均匀分布,林下层聚集分布明显;树种膀胱果和青榨槭因株数较少,在大部分尺度上仍随机分布,但随时间变化在局部尺度上则出现轻微的聚集分布。(2)分析林木空间关联性变化,则膀胱果与锐齿栎在幼树期因相互竞争而大部分尺度上互为负相关,其生长发育到一定阶段相互促生且小部分尺度上相互独立;树种锐齿栎与青榨槭、膀胱果与青榨槭在整体上保持无关联,逐渐发展为小范围内互为相关性。研究表明:不同调查时间锐齿栎林主要树种空间分布格局变化对其尺度依赖性强,林木分布格局的尺度吻合程度较高,林分整体上为随机分布,说明五年前后林分空间分布格局基本没变;就主要树种而言,锐齿栎分布格局变化符合群落中种群发育的规律,膀胱果和青榨槭分布格局变化受株数影响较大;林木种间关联性变化与种群结构及其演替阶段有关;但就群落演替过程而言,5年期限不足以表征整座林分的演替规律,需进一步拓宽研究年限。 相似文献
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Abstract Aim The research explores how changes in disturbance regime resulting from human settlement may affect landscape structure. A spatially explicit grid‐based simulation model is used to explore the interplay between humans, fire regime and landscape composition. Location The study site for this research is the botanical reserve at Mont Do, New Caledonia. The endemic conifer Araucaria laubenfelsii (Araucariaceae) forms a key component of the landscape at Mont Do. This species is unusual in that it is found scattered as an emergent in maquis and as a canopy species in adjacent rain forest patches. Although now dominated by a low maquis, prior to human settlement of New Caledonia, montane landscapes such as Mont Do are likely to have been heavily forested. Methods A spatially explicit simulation model, based on field data and palaeoecological information, was used to explore interactions between disturbance regime and the landscape. The model is described briefly here and more fully in Perry & Enright (2002) Ecological Modelling, 152 , 279. Results The model suggests that human‐influenced changes to the fire regime at Mont Do have been important in generating the current landscape structure. The origin and maintenance of forest landscapes and maquis‐forest mosaic landscapes are considered in the context of alternative stable states. Strong feedback loops between fire size and landscape composition, mediated at the smaller scale by other similar mechanisms, are capable of driving landscape change. The utility of a spatial state and transition modelling approach is demonstrated. Main conclusions The current landscape pattern on Mont Do is likely the result of changes to the fire regime occurring since human settlement. The specific mechanisms for this change outlined here may occur in a number of other similar systems. Understanding the origin and persistence of these ‘fire landscapes’ in New Caledonia and in the south‐west Pacific in general is crucial for their effective management. 相似文献
19.
Young KR León B 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2007,362(1478):263-272
The Andes provide an extensive latitudinal and topographical framework for studying the factors that control the spatial patterns of forests (timberlines) and their species components expressed through the presence of tree growth forms (tree lines). Despite consistent overall similarities in landscape patterns, many processes must be unique, given the dramatic differences in species richness and biophysical constraints along the Andes. In all cases evaluated to date, morphological plasticity is a common trait of plant species that dominate at tree lines. In fact, many changes observed can be related to species-specific traits. Physiological limitations on tree growth form only explain species limits, while disturbances and cyclical climate fluctuations interact to affect many landscape patterns. Over long periods of time, tree lines provide unique habitats and perhaps opportunities for speciation. Understanding the spatial organization of tree-line dynamics is one viable research approach for evaluating the likely past fluxes and possible future changes. 相似文献
20.
The evergreen coniferous creeping shrub, Sabina vulgaris, is widely distributed in China, from high and cold mountain sites to low-elevation arid desert areas. This paper performed dendroclimatological analysis of the samples of S. vulgaris from three sampling sites (2700–2900 m a.s.l.) at sites in the northern border of the middle Qilian Mountains, Northwest China. We found that the radial growth of S. vulgaris was mainly limited by rainfall during the growing season, especially in May and June, but was also limited by low temperatures in the late growing season. It presents the regional differention of the climate response of the shrub radial growth from the other distributed areas, such as the sandland and mountains. We constructed a 274-year drought record by calibrating growth-ring data and relating this data to the regional monthly Palmer Drought Severity Index (PDSI56), which represents regional moisture conditions. The PDSI56 reconstruction accounted for 35.5 % of the variation of the actual May to June PDSI56 during the period for which meteorological data was available (1950–2014). The most severe drought occurred during the 1920s, followed by the 1950s, 1740s, and the period from the 1870s to the 1880s; the wettest years were during the 1980s, followed by the 2010s, 1770s, and 1750. The changes between drought, normal, and wet periods were consistent with the reconstructed results from previous conifer ring series for Sabina przewalskii and Picea crassifolia in the study area. Our results demonstrate the value of S. vulgaris in dendrochronology. 相似文献