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1.
Transpirations of three dominated tree species, namely Mongol Scotch Pine (Pinus sylvestris var. mongolica Litvin), White elm (Ulmus pumila) and Gansu Poplar (Populus gansuensis Wang et Yang) in oasis shelter forest (Linze site) and of two dominated tree species, namely Euphrates Poplar (Populus euphratica Oliv.) and Russia olive (Elaeagnus angustifolia Linn.) in lowland desert (Erjinaqi site) have been estimated using measured sapflow in summer, autumn and winter, 2002 and in spring, 2003. An ENVIS System was used for each site to measure microclimate variables, soil moisture and sapflow every half an hour, and the study time scale is one day. In the 104 days of observation during the growing season at the Linze site, the average daily sapflow of Gansu Poplar is 9.93 L· d-1, and the average transpiration per unit leaf area is 1.99 mm · d-1. For White elm tree, the daily average sapflow is 4.08 L· d-1, while the daily average transpiration per unit leaf area is 0.49 mm · d-1. The values for Mongol Scotch Pine are 3.91 L· d-1 and 0.25 mm · d-1, respectively. In the total 73 days of observation during the growing season at the Erjinaqi site, the daily average sapflows of Russia olive and Euphrates Poplar are 12.1 and 20.97 L· d-1, respectively, and the average transpirations per unit leaf area are 0.22 and 0.31 mm · d-1, respectively. In the observation period of the growing season, tree conductances of Mongol Scotch Pine, White elm, Gansu Poplar or Russia olive show an exponential relationship with the daily average air temperature or vapour pressure deficit, but the relationship is not so obvious between tree conductance and global radiation. The transpiration process of each tree species is affected by all the observed four environmental variables. The response of tree conductance to different climatic factors changes with tree species. The effect of the same factor to the same tree species is also variable in different growing stages. The sapflow of every tree species is relatively large in later spring to early summer, and low in summer, and then reaches its largest value in later September. In the mid-November, the sapflow is relatively large, especially the deciduous tree species. This may be characteristic of the tree species in Arid Regions of Northwest China.  相似文献   

2.
Brush removal is widely practiced as a tool for increasing groundwater recharge, but its efficacy depends greatly on the way in which the removed species interact with the hydrological system relative to the vegetation replacing it. We examined the effects of Ashe juniper removal in the recharge zone of the Edwards Aquifer, Texas, USA, a karst aquifer. The study was conducted in an Ashe juniper (Juniperus ashei)–live oak (Quercus fusiformis) woodland on a hill slope composed of rocky, shallow soils over fractured limestone bedrock. Ashe juniper is a native species that has been encroaching grasslands and savannas over the past century. In September 2008, a plot was cleared of 90% of its juniper trees. Tree transpiration, predawn water potentials and vegetation cover across the cleared plot and an adjacent reference site were measured from May 2009 to December 2011. Stand‐level tree transpiration from May 2009 to March 2010 was diminished by a severe summer drought in 2009, from which trees were slow to recover. Subsequently, tree transpiration was 5–10× higher in the woodland compared to the clearing. For all of 2011, also a drought year, tree transpiration in the woodland exceeded precipitation inputs, indicating a high capacity for water storage at the study site. However, site differences for oak trees were generally larger than for juniper trees. While juniper removal accounted for a 431 mm year?1 difference in tree transpiration between sites, vegetation cover in the clearing increased from 42% to 90% over two years, suggesting that understory growth was increasingly compensating for the loss of juniper transpiration. We conclude that the removal of a relatively shallow‐rooted tree, when replaced with herbaceous vegetation and low shrubs, has little effect on deep recharge. By contrast, successive years of precipitation extremes may be more effective increasing recharge by lowering the water transport capacity of trees in the aftermath of severe drought. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
Forests comprise approximately 37% of the terrestrial land surface and influence global water cycling. However, very little attention has been directed towards understanding environmental impacts on stand water use (S) or in identifying rates of S from specific forested wetlands. Here, we use sapflow techniques to address two separate but linked objectives: (1) determine S in four, hydrologically distinctive South Carolina (USA) wetland forests from 2009–2010 and (2) describe potential error, uncertainty and stand‐level variation associated with these assessments. Sapflow measurements were made from a number of tree species for approximately 2–8 months over 2 years to initiate the model, which was applied to canopy trees (DBH > 10–20 cm). We determined that S in three healthy forested wetlands varied from 1.97–3.97 mm day?1 or 355–687 mm year?1 when scaled. In contrast, saltwater intrusion impacted individual tree physiology and size class distributions on a fourth site, which decreased S to 0.61–1.13 mm day?1 or 110–196 mm year?1. The primary sources of error in estimations using sapflow probes would relate to calibration of probes and standardization relative to no flow periods and accounting for accurate sapflow attenuation with radial depth into the sapwood by species and site. Such inherent variation in water use among wetland forest stands makes small differences in S (<200 mm year?1) difficult to detect statistically through modelling, even though small differences may be important to local water cycling. These data also represent some of the first assessments of S from temperate, coastal forested wetlands along the Atlantic coast of the USA. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

4.
In this study, artificial neural network analyses (ANN) were used to identify the forcing environmental variables that are most significant in governing the transpiration rates of an Austrian Pine stand and its forest floor. Latent heat flux densities (Lh) of the Austrian Pine stand and its forest floor were separately measured using the eddy covariance technique. To assess the sensitivity of the ANNs to input information on the soil water status, the site calibrated soil hydrological model SWIF was used to compute average volumetric soil water contents of different depth intervals. Results show that forest floor transpiration dynamics can be adequately modelled using the global radiation reaching the forest floor and the topsoil water content (0–50 cm). The response functions of the total forest and forest floor showed a clear difference in sensitivity of latent heat fluxes to global radiation, air temperature and soil water content. Most significantly, results demonstrate that the presented ANN analysis is suited for assessing effective rooting depths from measured transpiration rates and soil water contents.  相似文献   

5.
The heat pulse method was used to estimate stand transpiration from a radiata pine (Pinus radiata) plantation in southeastern Australia over a period of four days. The diurnal pattern of sapflow was related to net radiation with a time lag of about 1.5 hours. Despite high soil moisture levels, sapflow did not keep up with evaporative demand in the afternoon. Sapflow estimates of transpiration exceeded estimates for evaporation based on Bowen ratio measurements for all four days of the study.  相似文献   

6.
David McJannet 《水文研究》2008,22(16):3079-3090
Water table fluctuations and transpiration were monitored in a seasonally inundated Melaleuca quinquenervia floodplain forest at Cowley Beach, north Queensland, Australia. Techniques were developed to reconstruct inundation duration and seasonal and inter‐annual variability at this site using long‐term stream flow data. It was estimated that the median duration of inundation in any year was 75 days with maximum and minimum durations of 167 days and 8 days, respectively. Measurements of individual tree transpiration using heat‐pulse techniques showed a strong relationship between tree size and tree water use, which was used for scaling to stand transpiration. Stand transpiration rates were found to be closely tied to atmospheric drivers of evaporation, and transpiration of M. quinquenervia was found to be unaffected by inundation. This ability to transpire during inundation may be due to physiological adaptations of this species. These adaptations are believed to include dynamic root systems that can quickly respond to rising and falling water tables and dense networks of fine apogeotropic roots, which grow on and within the papery bark. Rates of stand transpiration remained low throughout the study (0·46 mm d?1, 164 mm y?1) despite the fact that transpiration was not limited by solar energy inputs or soil moisture deficit. Low stand transpiration was attributed to the low density, stunted nature and small sapwood area of trees at this site. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

7.
M5 model tree based modelling of reference evapotranspiration   总被引：1，自引：0，他引：1  
This paper investigates the potential of M5 model tree based regression approach to model daily reference evapotranspiration using climatic data of Davis station maintained by California irrigation Management Information System (CIMIS). Four inputs including solar radiation, average air temperature, average relative humidity, and average wind speed whereas reference evapotranspiration calculated using a relation provided by the CIMIS was used as output. To compare the performance of M5 model tree in predicting the reference evapotranspiration, FAO–56 Penman–Monteith equation and calibrated Hargreaves–Samani relation was used. A comparison of results suggests that M5 model tree approach works well in comparison to both FAO–56 and calibrated Hargreaves–Samani relations. To judge the generalization capability of M5 model tree approach, model created by using the Davis data set was tested with the datasets of four different sites. Results from this part of the study suggest that M5 model tree could successfully be employed in modeling the reference evapotranspiration. Further, sensitivity analysis with M5 model tree approach suggests the suitability of solar radiation, average air temperature, average relative humidity, and average wind speed as input parameters to model the reference evapotranspiration Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
Spatial and temporal variation in wet canopy conditions following precipitation events can influence processes such as transpiration and photosynthesis, which can be further enhanced as upper canopy leaves dry more rapidly than the understory following each event. As part of a larger study aimed at improving land surface modelling of evapotranspiration processes in wet tropical forests, we compared transpiration among trees with exposed and shaded crowns under both wet and dry canopy conditions in central Costa Rica, which has an average 4200 mm annual rainfall. Transpiration was estimated for 5 months using 43 sap flux sensors in eight dominant, ten midstory and eight suppressed trees in a mature forest stand surrounding a 40‐m tower equipped with micrometeorological sensors. Dominant trees were 13% of the plot's trees and contributed around 76% to total transpiration at this site, whereas midstory and suppressed trees contributed 18 and 5%, respectively. After accounting for vapour pressure deficit and solar radiation, leaf wetness was a significant driver of sap flux, reducing it by as much as 28%. Under dry conditions, sap flux rates (Js) of dominant trees were similar to midstory trees and were almost double that of suppressed trees. On wet days, all trees had similarly low Js. As expected, semi‐dry conditions (dry upper canopy) led to higher Js in dominant trees than midstory, which had wetter leaves, but semi‐dry conditions only reduced total stand transpiration slightly and did not change the relative proportion of transpiration from dominant and midstory. Therefore, models that better capture forest stand wet–dry canopy dynamics and individual tree water use strategies are needed to improve accuracy of predictions of water recycling over tropical forests. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

9.
2004年6月甘肃临泽震群地震精确定位   总被引：1，自引：0，他引：1       下载免费PDF全文
利用"双差地震定位法"对2004年6月甘肃临泽发生的地震震群进行了精确定位,结合地质构造资料讨论了本次震群的发震构造.结果表明:该震群震中沿着榆木山北缘断裂呈NNW向分布,震源深度优势分布于10～25 km,平均深度为16.3 km;发震断裂为榆木山北缘断裂东段局部断裂,走向NNW,倾向SW,倾角约为60°.  相似文献   

10.
Zhang  Rongfei  Xu  Xianli  Liu  Meixian  Zhang  Yaohua  Xu  Chaohao  Yi  Ruzhou  Luo  Wei  Soulsby  Chris 《中国科学:地球科学(英文版)》2019,62(11):1744-1755
The critical zone(CZ) represents the intersection of the biosphere with the atmosphere, hydrosphere and lithosphere.Understanding the hydrological processes and human impact factors on the CZ is fundamental to sustainable water resources management for agroforestry. Transpiration(T) is an important component of terrestrial evapotranspiration(ET), and understanding the time lag(TL) between vegetation transpiration and meteorological factors can improve our knowledge of the mechanisms of vegetation adaptability to a changing environment. However, the controlling factors on the TL remain poorly understood. Therefore, the objective of this study is identifying the temporal dynamics of key controlling factors on the TL, using a typical deciduous broad-leaved tree species(Zenia insigins Chun) of CZ in subtropical humid karst regions. This species is used as an example to explore the characteristics of the TL between SF(sap flow) and hydro-meteorological forcing. Sap flow in these 6 trees was monitored using the thermal dissipation probes(TDP). Results showed that:(1) the peak of diurnal sap flow generally lagged behind PAR but preceded Ta(air temperature), RH(relative humidity) and VPD(vapor pressure deficit), with the mean TL of-67.4 min(PAR), 90.5 min(Ta), 91.6 min(RH) and 92.9 min(VPD), respectively;(2) TL had no significant relationships with the daily mean meteorological factors and soil moisture, but was highly(R~20.66) correlated to CRs(changing rates of meteorological factors) in the morning;(3) At seasonal scale, the sap flow rate and TL both were controlled by the seasonality of precipitation and temperature. Overall, the seasonality of the TL was caused by plants' high water loss and strongly active physiological response in hot seasons, leading to close stomata earlier than in cold seasons;(4) The reason why CRs proposed can explain the TL better than mean values of metrological factors is that the CRs considered the distribution and change processes of metrological factors in the daytime. This study may be helpful for understanding the physiological response of vegetation to climatic change, and may be useful for constructing models to simulate transpiration processes more accurately during a day.  相似文献   

11.
Relations between the spatial patterns of soil moisture, soil depth, and transpiration and their influence on the hillslope water balance are not well understood. When determining a water balance for a hillslope, small scale variations in soil depth are often ignored. In this study we found that these variations in soil depth can lead to distinct patterns in transpiration rates across a hillslope. We measured soil moisture content at 0.05 and 0.10 m depth intervals between the soil surface and the soil–bedrock boundary on 64 locations across the trenched hillslope in the Panola Mountain Research Watershed, Georgia, USA. We related these soil moisture data to transpiration rates measured in 14 trees across the hillslope using 28 constant heat sapflow sensors. Results showed a lack of spatial structure in soil moisture across the hillslope and with depth when the hillslope was in either the wet or the dry state. However, during the short transition period between the wet and dry state, soil moisture did become spatially organized with depth and across the hillslope. Variations in soil depth and thus total soil water stored in the soil profile at the end of the wet season caused differences in soil moisture content and transpiration rates between upslope and midslope sections at the end of the summer. In the upslope section, which has shallower soils, transpiration became limited by soil moisture while in the midslope section with deeper soils, transpiration was not limited by soil moisture. These spatial differences in soil depth, total water available at the end of the wet season and soil moisture content during the summer appear responsible for the observed spatial differences in basal area and species distribution between the upslope and midslope sections of the hillslope.  相似文献   

12.
Street and garden trees in urban areas are often exposed to advection of strong vapour pressure deficit (VPD) air that can raise the whole‐tree transpiration rate (ET), known as the oasis effect. However, urban trees tend to have small soil volume compared with natural conditions, and so they are believed to strongly regulate stomata. ET characteristics of such urban trees have not been well understood because of a lack of reliable measurement methods. Therefore, we propose a novel weighing lysimeter method and investigate the whole‐tree water balance of an isolated container‐grown Zelkova serrata to examine (a) which biotic and abiotic factors determine ET and (b) which spatial and temporal information is needed to predict ET under urban conditions. Whole‐tree water balance and environmental conditions were measured from 2010 to 2012. Although leaf area substantially increased in the study period, daily ET did not vary much. ET increased with VPD almost linearly in 2010 but showed saturation in 2011 and 2012. Root water uptake lagged ET by 40 min in 2012. These results suggest that the small planter box interfered with root growth and that hydraulic supply capacities did not increase sufficiently to support leaf area increase. From analysis of water balance, we believe that neglecting soil drought effects on street trees without irrigation in Japan will overestimate ET over 4–5 sunny days at the longest. This is unlike previous studies of forest.  相似文献   

13.
Transpiration of four different rainforest types in north Queensland, Australia, was determined using the heat pulse technique for periods ranging between 391 and 657 days. Despite the complexity of the natural rainforest systems being studied, the relationship between sample tree size and daily water use was found to be strong, thus providing a robust means by which to scale transpiration from individual trees to the entire forest stand. Transpiration was shown to be dependent on solar radiation and atmospheric demand for moisture with little evidence of limitation by soil moisture supply. Total stand transpiration was controlled by forest characteristics such as stem density, size distribution and sapwood area. Annual transpiration for each of the four sites ranged between 353 mm for cloud forest and 591 mm for montane rainforest. In comparison with the international literature, transpiration from Australian rainforests is low; the reasons for this could be related to a combination of differences in forest structure, climatic conditions, canopy wetness duration and tree physiology. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

14.
The flow of precipitation from the surface through to groundwater in karst systems is a complex process involving storage in the unsaturated zone and diffuse and preferential recharge pathways. The processes associated with this behaviour are not well understood, despite the prevalence of karst aquifers being used as freshwater supplies. As a result, uncertainty regarding the ecohydrological processes in this geological setting remains large. In response to the need to better understand the impact of woody vegetation on groundwater recharge, annual evapotranspiration (ET) rates and tree water sources were measured for two years above a shallow, fresh karst aquifer. Water use strategies of the co‐occurring Eucalyptus diversifolia subsp. diversifolia Bonpl. and Allocasuarina verticillata (Lam.) L. Johnson were investigated using a monthly water balance approach, in conjunction with measurement of the stable isotopes of water, leaf water potentials and soil matric potentials. The results suggest that it is unlikely groundwater resources are required to sustain tree transpiration, despite its shallow proximity to the soil surface, and that similarities exist between ET losses and the estimated long‐term average rainfall for this area. Irrespective of stand and morphological differences, E. diversifolia and A. verticillata ET rates showed remarkable convergence, demonstrating the ability of these co‐occurring species to maximise their use of the available precipitation, which avoids the requirement to differentiate between these species when estimating ET at a landscape scale. We conclude that the water holding capacity of porous geological substrates, such as those associated with karst systems, will play an important role in equilibrating annual rainfall variability and should be considered when assessing ecohydrological links associated with karst systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

15.
We investigated canopy transpiration and canopy conductance of peach trees under three irrigation patterns: fixed 1/2 partial root zone drip irrigation (FPRDI), alternate 1/2 partial root zone drip irrigation (APRDI) and full root zone drip irrigation (FDI). Canopy transpiration was measured using heat pulse sensors, and canopy conductance was calculated using the Jarvis model and the inversion of the Penman–Monteith equation. Results showed that the transpiration rate and canopy conductance in FPRDI and APRDI were smaller than those in FDI. More significantly, the total irrigation amount was greatly reduced, by 34·7% and 39·6%, respectively for APRDI and FPRDI in the PRDI (partial root zone drip irrigation) treatment period. The daily transpiration was linearly related to the reference evapotranspiration in the three treatments, but daily transpiration of FDI is more than that of APRDI and FPRDI under the same evaporation demand, suggesting a restriction of transpiration water loss in the APRDI and FPRDI trees. FDI needed a higher soil water content to carry the same amount of transpiration as the APRDI and FPRDI trees, suggesting the hydraulic conductance of roots of APRDI and FPRDI trees was enhanced, and the roots had a greater water uptake than in FDI when the average soil water content in the root zone was the same. By a comparison between the transpiration rates predicted by the Penman–Monteith equation and the measured canopy transpiration rates for 60 days during the experimental period, an excellent correlation along the 1:1 line was found for all the treatments (R2 > 0·80), proving the reliability of the methodology. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

16.
W. Zhao  X. Chang  Z. Zhang 《水文研究》2009,23(10):1461-1470
As an important source of income in the region's economy, the jujube plantations are very common in arid north‐western China, and their planted areas continue to expand. In the central Heihe River Basin of arid north‐western China, Linze jujube (Zizyphus jujuba Mill. var. inermis (Bunge) Rehd.) plantations cover more than 10,000 ha, too. Water use by this species is expected to change or modify catchment hydrological process. To our knowledge, there is no information on the transpiration and canopy conductance of the jujube plantations in arid north‐western China. Therefore, Transpiration and canopy conductance were monitored in a 14‐year‐old Linze jujube orchard. The experiment was carried out in the central Heihe River Basin, near Pingchuan Town (Linze County, Gansu Province, China) during growing season of 2006, from May to the first ten days of October. Eight trees were used to measure sap flow using the heat‐pulse‐velocity method. The orchard was irrigated adequately during the study. Transpiration was estimated from the sap flow measurements. During the experiment, the transpiration rate of the orchard ranged from 0·32 to 1·40 mm per day. Canopy conductance was obtained from estimated daily transpiration and climatic variables measured on a half‐hour basis, and canopy conductance for water vapour transfer was between 1·20 to 82·57 mm s?1, with a mean of 11·86 ± 6·84 mm s?1 during the observation period. Air temperature and vapour‐pressure deficit exhibited a linear relationship with sap flow velocity and the relationship between these factors and canopy conductance could be represented by an exponential decay function. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

17.
Quantifying the spatial variability of species-specific tree transpiration across hillslopes is important for estimating watershed-scale evapotranspiration (ET) and predicting spatial drought effects on vegetation. The objectives of this study are to (1) assess sap flux density (Js) and tree-level transpiration (Ts) across three contrasting zones a (riparian buffer, mid-hillslope and upland-hillslope, (2) determine how species-specific Js responds to vapour pressure deficit (VPD) and (3) estimate watershed-level transpiration (Tw) using Ts derived from each zone. During 2015 and 2016, we measured Js in eight tree species in the three topographic zones in a small 12-ha forested watershed in the Piedmont region of central North Carolina. In the dry year of 2015, loblolly pine (Pinus taeda), Virginia pine (Pinus virginiana) and sweetgum (Liquidambar styraciflua) Js rates were significantly higher in the riparian buffer when compared to the other two zones. In contrast, Js rates in tulip poplar (Liriodendron tulipifera) and red maple (Acer rubrum) were significantly lower in the buffer than in the mid-hillslope. Daily Ts varied by zone and ranged from 10 to 93 L/day in the dry year and from 9 to 122 L/day in the wet year (2016). Js responded nonlinearly to VPD in all species and zones. Annual Tw was 447, 377 and 340 mm based on scaled-Js data for the buffer, mid-hillslope and upland-hillslope, respectively. We conclude that large spatial variability in Js and scaled Tw was driven by differences in soil moisture at each zone and forest composition. Consequently, spatial heterogeneity of vegetation and soil moisture must be considered when accurately quantifying watershed level ET.  相似文献   

18.
Black ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non-forested conditions. The vulnerability to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site-dependent vulnerability and our ability to predict it is unknown. Here, we assessed vulnerability potential as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. Further, we used high-resolution (1-cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Although we observed similar ET and groundwater exchange rates among settings, lowland sites were generally drier because of elevated landscape position and greater water level drawdowns (via lower specific yield). We predict that such drier sites will exhibit greater water level increases following EAB-induced ash mortality, compared to wetter sites where open water evaporation and shallow-rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibited minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss. These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, we assessed the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts.  相似文献   

19.
We examined the water balance of a forested ombrotrophic peatland and adjacent burned peatland in the boreal plain of western Canada over a 3‐year period. Complete combustion of foliage and fine branches dramatically increased shortwave radiation inputs to the peat surface while halting all tree transpiration at the burned site. End‐of‐winter snowpack was 7–25% higher at the burned site likely due to decreased ablation from the tree canopy at the unburned site. Shrub regrowth at the burned site was rapid post‐fire, and shading by the shrub canopy in the burned site approached that of the unburned site within 3 years after fire. Site‐averaged surface resistance to evaporation was not different between sites, though surface resistance in hollows was lower in the burned site. Water loss at both burned and unburned sites is largely driven by surface evaporative losses. Evaporation at the burned site marginally exceeded the sum of pre‐fire transpiration and interception at the unburned site, suggesting that evapotranspiration during the growing season was 20–40 mm greater at the burned peatland. Although the net change in water storage during the growing season was largely unchanged by fire, the lack of low‐density surface peat in the burned site appears to have decreased specific yield, leading to greater water table decline at the burned site despite similar net change in storage. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

20.
Measurements of transpiration from individual trees of Eucalyptus from plantations at four different sites in Karnataka, Southern India, are presented. These show large (as much as tenfold) differences in the transpiration between premonsoon and postmonsoon periods, a reflection of the effects of soil-moisture stress in the premonsoon periods. For trees with diameters at breast height (DBH) less than 10 cm the transpiration rate of individual trees is proportional to the square of the DBH. For trees which are not experiencing soil-water stress the daily transpiration rate of individual trees, q, is well represented by the relation: q = (6.6 ± 0.3)g (m3 day−1 where g (m2) is the tree basal area. On a unit ground area basis the transpiration rate, expressed as a depth per day is given by the relation: Et = (0.66 ± 0.03)G (mm day−1 where g(m2ha−1) is the total basal area per hectare. For all the sites studied, although there is evidence for the ‘mining’ of soil water as roots penetrate deeper depths in the soil each year, there is no evidence for direct abstraction from the water table.  相似文献   

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