共查询到17条相似文献,搜索用时 312 毫秒
1.
《林业研究》2017,(3)
Recently, canopy transpiration(Ec) has been often estimated by xylem sap-flow measurements. However, there is a significant time lag between sap flow measured at the base of the stem and canopy transpiration due to the capacitive exchange between the transpiration stream and stem water storage. Significant errors will be introduced in canopy conductance(gc) and canopy transpiration estimation if the time lag is neglected. In this study, a cross-correlation analysis was used to quantify the time lag, and the sap flowbased transpiration was measured to parameterize Jarvistype models of gcand thus to simulate Ecof Populus cathayana using the Penman–Monteith equation. The results indicate that solar radiation(Rs) and vapor pressure deficit(VPD) are not fully coincident with sap flow and have an obvious lag effect; the sap flow lags behind Rsand precedes VPD, and there is a 1-h time shift between Ecand sap flow in the 30-min interval data set. A parameterized Jarvis-type gc model is suitable to predict P. cathayana transpiration and explains more than 80% of the variation observed in gc, and the relative error was less than 25%, which shows a preferable simulation effect. The root mean square error(RMSEs)between the predicted and measured Ecwere 1.91 9 10-3(with the time lag) and 3.12 9 10-3cm h-1(without the time lag). More importantly, Ecsimulation precision that incorporates time lag is improved by 6% compared to the results without the time lag, with the mean relative error(MRE) of only 8.32% and the mean absolute error(MAE) of1.48 9 10-3cm h-1. 相似文献
2.
Ana I. Leal Ricardo A. Correia Jorge M. Palmeirim José P. Granadeiro 《Agroforestry Systems》2013,87(2):355-363
Semi-natural cork oak woodlands are a biodiversity rich agro-silvo-pastoral system covering large areas in the Mediterranean. Canopies of adult oaks are often pruned, but nothing is known about the consequences of this treatment on biodiversity. We evaluated the impact of pruning on birds that forage in cork oak canopies in an area of southern Portugal. We characterized the use of trees by foraging birds with focal observations, and analysed the effects of pruning on density with point counts on pruned and control areas. As pruning reduces the foraging substrate for foliage gleaners, we predicted that these species would have lower densities in pruned areas. Pruning did not substantially affect overall bird density or species richness. However, as predicted, the density of species that foraged mostly by gleaning in the canopy tended to be lower in pruned areas, especially in winter when differences were statistically significant. In this season the combined density of foliage gleaners in the pruned stations was only half of that in controls. Pruning is also common in other managed Mediterranean woodlands that are important for birds, such as holm oak woodlands and olive groves, and foliage gleaners are likely to be affected in those too. The cumulative effects of pruning on all these habitats need to be assessed, but our results already indicate that pruning has negative consequences that should be properly considered in management decisions. 相似文献
3.
In this study we measured δ13C in various carbon pools along the basipetal transport pathway in co-occurring Pinus pinaster and Acacia longifolia trees under Mediterranean climate conditions in the field. Overall, species differences in photosynthetic discrimination resulted in more enriched δ13C values in the water-conserving overstory P. pinaster relative to the water-spending understory invasive A. longifolia. Post-photosynthetic fractionation effects resulted in differences in δ13C of water-soluble organic matter pools along the plant axis with progressive depletion in δ13C from the canopy to the trunk (~6.5‰ depletion in A. longifolia and ~0.8‰ depletion in P. pinaster). Regardless of these fractionation effects, phloem sap δ13C in both terminal branches and the main stem correlated well with environmental parameters driving photosynthesis for both species, indicating that phloem sap δ13C has potential as an integrative tracer of changes in canopy carbon discrimination (Δ13C). Furthermore, we illustrate that a simple model based on sap flow estimated canopy stomatal conductance (G(S)) and phloem sap δ13C measurements has significant potential as a tool for estimating canopy-level carbon assimilation rates. 相似文献
4.
Tropical moist forests are notable for their richness in tree species. The presence of such a diverse tree flora presents potential problems for scaling up estimates of water use from individual trees to entire stands and for drawing generalizations about physiological regulation of water use in tropical trees. We measured sapwood area or sap flow, or both, in 27 co-occurring canopy species in a Panamanian forest to determine the extent to which relationships between tree size, sapwood area and sap flow were species-specific, or whether they were constrained by universal functional relationships between tree size, conducting xylem area, and water use. For the 24 species in which active xylem area was estimated over a range of size classes, diameter at breast height (DBH) accounted for 98% of the variation in sapwood area and 67% of the variation in sapwood depth when data for all species were combined. The DBH alone also accounted for > or = 90% of the variation in both maximum and total daily sap flux density in the outermost 2 cm of sapwood for all species taken together. Maximum sap flux density measured near the base of the tree occurred at about 1,400 h in the largest trees and 1,130 h in the smallest trees studied, and DBH accounted for 93% of the variation in the time of day at which maximum sap flow occurred. The shared relationship between tree size and time of maximum sap flow at the base of the tree suggests that a common relationship between diurnal stem water storage capacity and tree size existed. These results are consistent with a recent hypothesis that allometric scaling of plant vascular systems, and therefore water use, is universal. 相似文献
5.
Recently, canopy transpiration (Ec) has been often estimated by xylem sap-flow measurements. However, there is a significant time lag between sap flow measured at the base of the stem and canopy transpiration due to the capacitive exchange between the transpiration stream and stem water storage. Significant errors will be introduced in canopy conductance (gc) and canopy transpiration estimation if the time lag is neglected. In this study, a cross-correlation analysis was used to quantify the time lag, and the sap flow-based transpiration was measured to parameterize Jarvis-type models of gc and thus to simulate Ec of Populus cathayana using the Penman–Monteith equation. The results indicate that solar radiation (Rs) and vapor pressure deficit (VPD) are not fully coincident with sap flow and have an obvious lag effect; the sap flow lags behind Rs and precedes VPD, and there is a 1-h time shift between Ec and sap flow in the 30-min interval data set. A parameterized Jarvis-type gc model is suitable to predict P. cathayana transpiration and explains more than 80% of the variation observed in gc, and the relative error was less than 25%, which shows a preferable simulation effect. The root mean square error (RMSEs) between the predicted and measured Ec were 1.91 × 10?3 (with the time lag) and 3.12 × 10?3 cm h?1 (without the time lag). More importantly, Ec simulation precision that incorporates time lag is improved by 6% compared to the results without the time lag, with the mean relative error (MRE) of only 8.32% and the mean absolute error (MAE) of 1.48 × 10?3 cm h?1. 相似文献
6.
? Context
The knowledge of how shrub–seedling interactions vary with summer drought, canopy opening, and tree species is crucial for adapting forest management to climate change.? Aims
The aim of this study was to assess variation in shrub–oak recruitment associations along a south–north drought climate gradient and between two levels of canopy cover in coastal dune forest communities in a climate change-adapted forest management perspective.? Material and methods
Mapped data of associational patterns of seedlings of three oak species with interspecific pooled shrubs were analyzed using a bivariate pair correlation function in 10 (0.315 ha) regeneration plots located in forest and recent gap sites along the climate gradient. An index of association strength was calculated in each plot and plotted against a summer moisture index.? Results
The association strength increased with increasing summer drought from wet south to dry north and from closed forests to gaps.? Conclusion
Consistent with facilitation theory, our results suggest that climate change may shift associational patterns in coastal dune forest communities towards more positive associations, in particular in canopy gaps. In a perspective of climate change, foresters may need to conserve understory shrubs in gaps in order to promote oak species regeneration. 相似文献7.
We investigated central Mediterranean Pinus halepensis plantations under semi-arid climate in order to evaluate the combined effect of soil treatment and afforestation practices on spontaneous plant species composition,richness and evenness,and on the trend and speed of vegetation dynamics.Phytosociological relevés of three different plot typologies,i.e.(1) soil-treatment and plantation,(2) only soil-treatment,(3) no soil-treatment and no plantation,were compared by(a) multivariate analysis and(b) with reference to species richness and evenness.Moreover,in order to compare vegetation dynamics within the plantations with those ones ongoing in semi-natural garrigue communities,we compared life form and syntaxonomic spectra between phytosociological relevés taken at 8 years of distance.DCA showed that floristic species composition and similarity are influenced by the canopy cover of Pine trees as well as by soil-treatment practices.Although species richness and evenness are not clearly related to neither soil treatment nor Pine afforestation,canopy cover clearly plays a major role:in fact,the highest Ph cover rates correspond to the lowest values of understory species richness.This is true also if only species of biogeographical/conservation interest are considered.Regarding vegetation dynamics,sites with dense Pine canopy cover evolve much slower than the adjacent garrigue communities.The same factors invoqued to explain the patterns of floristic composition and similarity(i.e.allelopathy and competition for light,water and nutrients) may also explain the lowering of diversity of therophytes and the strong decline of the cover perfomed by both therophytes and hemicryptophytes underneath the canopy of dense Ph plantations.Thus,in sites where Ph cover exceeds about 80%,thinning is recommended not only in order to accelerate succession,but also to give a natural ’shape’ to afforestations. 相似文献
8.
Offermann C Ferrio JP Holst J Grote R Siegwolf R Kayler Z Gessler A 《Tree physiology》2011,31(10):1088-1102
The carbon (δ(13)C) and oxygen (δ(18)O) stable isotope composition is widely used to obtain information on the linkages between environmental drivers and tree physiology over various time scales. The tree-ring archive can especially be exploited to reconstruct inter- and intra-annual variation of both climate and physiology. There is, however, a lack of information on the processes potentially affecting δ(13)C and δ(18)O on their way from assimilation in the leaf to the tree ring. As a consequence, the aim of this study was to trace the isotope signals in European beech (Fagus sylvatica L.) from leaf water (δ(18)O) and leaf assimilates (δ(13)C and δ(18)O) to tree-ring wood via phloem-transported compounds over a whole growing season. Phloem and leaf samples for δ(13)C and δ(18)O analyses as well as soil water, xylem water, leaf water and atmospheric water vapour samples for δ(18)O analysis were taken approximately every 2 weeks during the growing season of 2007. The δ(13)C and δ(18)O samples from the tree rings were dated intra-annually by monitoring the tree growth with dendrometers. δ(18)O in the phloem organic matter and tree-ring whole wood was not positively related to leaf water evaporative enrichment and δ(18)O of canopy organic matter pools. This finding implies a partial uncoupling of the tree-ring oxygen isotopic signal from canopy physiology. At the same time, internal carbon storage and remobilization physiology most likely prevented δ(13)C in tree-ring whole wood from being closely related to intra-annual variation in environmental drivers. Taking into account the post-photosynthetic isotope fractionation processes resulting in alterations of δ(13)C and δ(18)O not only in the tree ring but also in phloem carbohydrates, as well as the intra-annual timing of changes in the tree internal physiology, might help to better understand the meaning of the tree-ring isotope signal not only intra- but also inter-annually. 相似文献
9.
XIEFu-ju XIAODu-ning LIXiu-zhen WANGXu-gao SHIBao-dong 《林业研究》2005,16(2):125-131
The restoration of forest landscape has drawn much attention since the catastrophic fire took place on the northern slope of Great Xing‘an Mountains in 1987. Forest canopy density, which has close relation to forest productivity, was selected as a key factor to find how much the forest quality was changed 13 years after fire, and how fire severity, regeneration way and terrain factors influenced the restoration of forest canopy density, based on forest inventory data in China, and using Kendall Bivariate Correlation Analysis, and Distances Correlation Analysis. The results showed that fire severity which was inversely correlated with forest canopy density grade was an initial factor among all that selected. Regeneration way which did not remarkably affect forest canopy density restoration in short period, may shorten the cycle of forest succession and promote the forest productivity of conophorium in the future, Among the three terrain factors, the effect of slope was the strongest, the position on slope was the second and the aspect was the last. 相似文献
10.
Reyes Tárrega Leonor Calvo Ángela Taboada Elena Marcos José Antonio Marcos 《European Journal of Forest Research》2011,130(6):949-957
We compared the structure of the arboreal layer and the diversity and species composition of the understory vegetation of
three types of mature forest communities: oak (Quercus pyrenaica) and beech (Fagus sylvatica) forests and Scots pine (Pinus sylvestris) plantations. Our main aim was to determine whether differences in these variables existed and were due to the identity of
the dominant tree species. We selected four stands or replicates per forest type located geographically close and with relatively
similar conditions. We found no differences in the arboreal structure of oak and beech forests, which were characterised by
great variability in tree size, while in case of plantations, this variability was lower at both the intra-stand (estimated
by the coefficient of variation) and inter-stand (i.e. the four replicates harboured trees of similar sizes) scales. However,
the highest variability in the canopy layer of natural forests was not consistently linked to greater understory species richness.
Indeed, the lowest plant species richness was found in beech forests, while oak forests harboured the highest value at either
the sampling unit (per m2) or stand scales. The greatest negative correlation between plant diversity and the environmental variables measured was
found for litter depth, which was the highest in beech forests. The results obtained by the CCA indicated that the four replicates
of each forest type clustered together, due to the presence of characteristic species. We concluded that pine plantations
did not approach the environmental conditions of native forests, as plantations were characterised by singular understory
species composition and low arboreal layer variability, compared to natural woodlands. 相似文献
11.
Decomposition patterns of leaf litter of seven common canopy species in a subtropical forest: dynamics of mineral nutrients 总被引:2,自引:0,他引:2
XU Xiao-niu Hideaki SHIBATA Tsutomu ENOKI 《林业研究》2006,17(1):1-6
Dynamical patterns of mineral elements during decomposition processes were investigated for seven common canopy species in a subtropical evergreen broad-leaved forest by means of litterbag technique over 2 years. The species studied are representative for the vegetation in the study area and differed significantly in chemical qualities of their litter. No significant relationships were found between decomposition rate (percentage dry mass remaining and decomposition constant k) and initial element cuncentrations.However, there were significant correlations betweeu the percentage of dry mass remaining and the mineral element concentrations in the remaining litter for most cases. The rank of the element mobility in decomposition process was as follows: Na = K 〉 Mg ≥ Ca 〉 N ≥ Mn ≥ Zn ≥ P 〉 Cu 〉〉 Al 〉〉 Fe. Concentrations of K and Na decreased in all species as decomposition proceeded. Calcium and Mg also decreased in concentrntion but with a temporal increase in the initial phase of decomposition, while the concentrations of other elements (Zn, Cu, AL and Fei increased for all species with exception of Mn which revealed a different pattern in different species. In most species, microelements (Cu, Al, and Fe) significantly increased in absolute amounts at the end of the litterbag incubation, which could be ascribed to a lange extent to the mechanism of abiotic fixation to humic substances rather than biological immobilization. 相似文献
12.
Fude Liu Wenjie Yang Ming Zhang Yuhong Liu Jianwei Zheng Wenjin Wang Shiting Zhang Zhongsheng Wang Shuqing An 《European Journal of Forest Research》2010,129(6):1093-1108
In order to test whether the strategy of resource acquisition varies with life form, leaf texture and canopy gradient, we
measured light-saturated net photosynthetic capacity (A
max-mass) and leaf nitrogen and phosphorus concentrations (N
mass and P
mass) for 127 woody species of understory (small shrubs and tree seedlings) and 47 woody species of canopy (large shrubs and tree
adults) in a tropical montane rain forest of Hainan Island, South China. Photosynthetic nitrogen use efficiency (PNUE) and
photosynthetic phosphorus use efficiency (PPUE) were studied by taking into account functional groups, which classified by
either life form (FG1) or leaf texture (FG2). For FG1, there were significant (P < 0.05) differences between trees and shrubs in A
mass, N
mass and P
mass, but not in PNUE and PPUE; whereas for FG2, there were significant (P < 0.05) differences between the papery-leaved species and those with leathery leaves in the measured leaf traits inclusive
of PNUE and PPUE. Within the same classification systems, significant allometric scaling relationships were found in the leaf
trait pairs of A
mass-N
mass and A
mass-P
mass. Considered separately, the slope and y-intercept of the linear regression between A
mass and N
mass did not differ among functional groups nor between understory and canopy, but those for the linear regression between A
mass and P
mass differed significantly (P = 0.001) between understory and canopy species regardless of functional groups. The results of phylogenetic comparative analyses
were in accordance with the observed positive scaling relationships. The overall results indicate that there are no fundamentally
different nitrogen capture strategies in tropical woody species regardless of their life form, leaf texture and canopy gradient.
However, the strategies of phosphorus acquisition of tropical woody species differ with canopy layer increases. This variation
may correspond to the special soil conditions in this ecosystem, as phosphorus is an element limiting plant growth in tropical
areas. 相似文献
13.
Subcanopy tree species are an important component of temperate secondary forests.However,their biomass equations are rarely reported,which forms a "vertical gap" between canopy tree species and understory shrub species.In this study,we destructively sampled six common subcanopy species(Syringa reticulate var.amurensis(Rupr.) Pringle,Padus racemosa(Lam.) Gilib.,Acer ginnala Maxim.,Malus baccata(Linn.) Borkh.,Rhamnus davurica Pall.,and Maackia amurensis Rupr.et Maxim.) to establish biomass equatio... 相似文献
14.
ZOU Chun-jing ZHANG Chao MA Yong-liang XU Wen-duo 《林业研究》2006,17(3):221-225
In sandy forest with a forest canopy gap for a period of over 30 years, the spruce(Picea mongolica) seedlings were monitored on two 5-m- wide transects from the center of a large gap into the surrounding forest. The farther they were to the far center, the taller grew the seedling and the more is the number of seedling. There were many seedlings under the canopy but almost all seedlings died before they grow up. Along the forest edge, growth of seedlings was temporarily enhanced by lateral penetration of light from the gap. The implications for natural forest regeneration dynamics are discussed. Our results prove that in P mongolica forest a gap disturbance creates a non-uniform environment for regeneration of the species, and determines that the forest was a non-even aged forest. 相似文献
15.
Atmospheric deposition(dry and wet deposition) is one of the primary sources of chemical inputs to terrestrial ecosystems and replenishes the nutrient pool in forest ecosystems. Precipitation often acts as a primary transporting agent and solvent; thus, nutrient cycles in forests are closely linked to hydrological processes. We collected precipitation data during a growing season to explore variations in nutrient cycling and nutrient balances in the rainfall redistribution process(wet deposition... 相似文献
16.
Xiaojun Xu Huaqiang Du Guomo Zhou Fangjie Mao Xuejian Li Dien Zhu Yangguang Li Lu Cui 《Annals of Forest Science》2018,75(1):33