Discovery and enumeration of Swahilian Coastal Forests in Lindi region,Tanzania, using Landsat TM data analysis

The Swahilian Coastal Forests in eastern Africa are recognised to be a globally important habitat containing large numbers of endemic species, yet are still poorly known over much of their extent. Floristic diversity and endemism in these forests appears to peak in SE Tanzania, where only a few forests have hitherto been surveyed. We carried out a digital analysis of Landsat Thematic Mapper (TM) data to identify other potential areas of Coastal Forest in Lindi and Kilwa Districts, SE Tanzania, followed by a field survey to ground truth and fine-tune our analysis. Our analysis has identified, mapped and sub-classified all remaining areas of Coastal Forest in Lindi and Kilwa Districts, and includes the discovery of a large and hitherto undescribed area of Coastal Forest at Namatimbili, which would make it one of the largest known blocks of contiguous Coastal Forest in eastern Africa. This forest furthermore appears to be minimally impacted by human disturbance. Given the rapidly increasing threats to forested vegetation in this area, urgent efforts are required by the conservation community to ensure the immediate and continued protection of Namatimbili forest.     

Characterization of changes in land cover and carbon storage in Northeastern China: An analysis based on Landsat TM data

We use Landsat TM time series data for the years of 1991/1992, 1995/1996 and 1999/2000 to characterize land-cover change in northeast China. With the information on land-cover change and the density of vegetation and soil carbon, we assess the potential effect of land-cover change on vegetation and soil carbon in this region. Our results show a large decrease of 2.76(104km2 in forest area and a rapid increase of 2.32(104km2 in urban area. Land-cover changes in northeast China have resulted in a potential maximum loss of 273.2 Tg C for the period of 1991-2000, with a net loss of 95.7 Tg C in vegetation and 177.5Tg C in soil. . The conversion of forests into other land-cover types could have potentially resulted in a loss of 254.6 Tg C for the study period, accounting for 68.8% of the total potential carbon loss in the northeast China. To quantify the net effect of land-cover change on carbon storage will require accounting for vegetation regrowth and soil processes. Our results also imply that forest protectionand reforestation are of critical importance to carbon sequestration in China.     

Effect of acid rain on pine needles as food for capercaillie in winter

The effects of long-range air pollution on the chemical composition of needles of Scots pinePinus sylvestris and consequences for capercaillieTetrao urogallus feeding on the needles were studied. Samples of pine needles from localities receiving different amounts of acid rain were taken in early March. Concentrations of N and P were highest in needles from the most acidified areas, and N concentration was 35% higher in the most heavily polluted area than in the least polluted. Secondary chemicals decreased significantly with increasing acidification. Concentrations of Cd in pine needles were closely correlated with the acid deposition levels, with highest concentrations in the most polluted area. Al concentration also increased with increasing acidification. These results provide evidence that acid rain increases the nutritive value of pine needles through a fertilizing effect. Enhanced levels of certain metals are considered too low to be directly toxic to capercaillie. However, behavioural anomalies cannot be excluded.     

Conversion of hardwood forests to spruce and pine plantations strongly reduced soil methane sink in Germany

Well‐drained forest soils are thought to be a significant sink for atmospheric methane. Recent research suggests that land use change reduces the soil methane sink by diminishing populations of methane oxidizing bacteria. Here we report soil CH₄ uptake from ‘natural’ mature beech forests and from mature pine and spruce plantations in two study areas of Germany with distinct climate and soils. The CH₄ uptake rates of both beech forests at Solling and Unterlüß were about two–three times the CH₄ uptake rates of the adjacent pine and spruce plantations, indicating a strong impact of forest type on the soil CH₄ sink. The CH₄ uptake rates of sieved mineral soils from our study sites confirmed the tree species effect and indicate that methanotrophs were mainly reduced in the 0–5 cm mineral soil depth. The reasons for the reduction are still unknown. We found no site effect between Solling and Unterlüß, however, CH₄ uptake rates from Solling were significantly higher at the same effective CH₄ diffusivity. This potential site effect was masked by higher soil water contents at Solling. Soil pH (H₂O) explained 71% of the variation in CH₄ uptake rates of sieved mineral soils from the 0–5 cm depth, while cation exchange capacity, soil organic carbon, soil nitrogen and total phosphorous content were not correlated with CH₄ uptake rates. Comparing 1998–99, annual CH₄ uptake rates increased by 69–111% in the beech and spruce stands and by 5–25% in the pine stands, due primarily to differences in growing season soil moisture. Cumulative CH₄ uptake rates from November throughout April were rather constant in both years. The CH₄ uptake rates of each stand were separately predicted using daily average soil matric potential and a previously developed empirical model. The model results revealed that soil matric potential explains 53–87% of the temporal variation in CH₄ uptake. The differences between measured and predicted annual CH₄ uptake rates were less than 10%, except for the spruce stand at Solling in 1998 (17%). Based on data from this study and from the literature, we calculated a total reduction in the soil CH₄ sink of 31% for German forests due in part to conversion of deciduous to coniferous forests.     

Assessment of denitrification in organogenic forest soil by regulating factors

One of the dominating sources of the increase in atmospheric N₂O are elevated emissions from terrestrial ecosystems. The N₂O production in soil is probably dominated by two microbial processes, i.e. nitrification and denitrification, and their N₂O production is regulated by an array of soil and environmental factors. This contributes to the large both spatial and temporal variability of emission rates measured in the field. To obtain reasonable estimates of large-scale emission rates this variability has to be dealt with, and one possible way could be to relate measured emission rates to relevant soil and/or environmental factors. In this study the relationship between soil factors (temperature, soil organic matter, soil moisture, pH, and NH₄ ⁺, NO₃ ^- and NO₂ ^- contents) and the denitrification activity in organogenic forest soil was investigated. About 40% or less of the variation of the denitrification rates could be accounted for by soil factors, either by multiple regression or by partial least squares analysis of latent variables (PLS analysis). Interpretation of the relationships obtained was, however, difficult since many of them were unexpected, and some of the soil factors were internally related. In conclusion, the possibility to obtain significant and useful relationships between momentary denitrification rates and soil factors for spatial and temporal extrapolations was limited in this system.     

林隙对小兴安岭阔叶红松林树种更新及物种多样性的影响

研究了小兴安岭阔叶红松林不同林隙梯度(林隙中心、林隙近中心、林隙边缘)中主要树种的数量特征,以及林隙大小对树种更新的影响.结果表明:不同梯度林隙内灌木树种的密度均明显高于非林隙,同种灌木密度的比值在1.08～18.15之间;随林隙面积增加,乔木幼苗更新密度逐渐增大,幼树Ⅰ(高度H≥1 m,胸径DBH≤2 cm)和幼树Ⅱ(H≥1 m,2 cm＜DBH≤5 cm)的更新密度呈多峰曲线.林隙灌木总体更新密度主要随幼苗和幼树Ⅰ数量而变化.林隙内不同位置幼苗的平均树高、平均基径、种密度和个体密度有所差异.从林隙中心到非林隙,更新层乔木幼苗重要值的大小顺序为:林隙中心＞林隙近中心＞林隙边缘＞非林隙;物种均匀度呈高-低-高的变化,物种多样性的变化为早期林隙＞中期林隙＞晚期林隙.     

长白山阔叶红松林蒸散量的测算

2001年7－9月应用水量平衡法对长白山阔叶红松林蒸散量进行了测定,同时应用波文比（BREB）法对其蒸散量进行了估算,两种方法得到的总蒸散量分别为288.18mm和214.94mm,均小于该时段的降雨量301.9mm。通过两种方法分别得出了各月平均日蒸散量,并通过第二种方法计算出每日的蒸散量及每日不同时刻的蒸散速率,从而对水量平衡法和BREB方法测算阔叶红松林蒸散量的可行性及其精度进行了验证。     

投加石灰石和菱镁矿对酸化土壤上马尾松(Pinus massoniana)林的影响

为了确定酸化森林生态系统的修复效果,在重庆铁山坪的马尾松林内设立了6个10m×10m的样地,其中2个作为对照样地,另外4个分别在土壤表面施撒石灰石和菱镁矿粉末,各有2个重复。在处理前和处理1a后的生长季末各进行了一次植被观测,协方差分析和多重比较的结果显示投加修复剂对马尾松生长的影响已经初步显现,马尾松的胸径增量和针叶平均长度都有显著的增加,而针叶中Ca、Mg元素含量也表现出显著的差别。另外,立木更新的变化、细根生物量的增加和物种多度的变化也较明显,总体来说生态系统有恢复的趋势。土壤上层细根的增加较快,这与在土壤表面施撒修复剂,上层土壤的化学变化较显著是一致的。而两种修复剂对生态系统的影响也表现出明显的差异,相对而言,施撒菱镁矿的效果可能会更好。由于土壤修复的效果是长期的,其影响观测还将继续下去。     

Monitoring the recovery of Juncus roemerianus marsh burns with the normalized difference vegetation index and Landsat Thematic Mapper data

Nine atmospherically corrected Landsat Thematic Mapper images were usedto generate mean normalized difference vegetation indices (NDVI) at 11burn sites throughout a coastal Juncus roemerianus marsh in St. MarksNational Wildlife Refuge, Florida. Time-since-burn, the time lapse from thedate of burn to the date of image collection, was related to variation inmean NDVI over time. Regression analysis showed that NDVI increasedfor about 300 to 400 days immediately after the burn, overshooting thetypical mean NDVI of a nonburned marsh. For about another 500 to 600days NDVI decreased until reaching a nearly constant NDVI of about0.40. During the phase of increasing NDVI the ability to predicttime-since-burn was within about ±60 days. Within the decreasingphase this dropped to about ±88 days.Examination of each burn site revealed some nonburn related influences onNDVI (e.g., seasonality). Normalization of burn NDVI by site-specificnonburn control NDVI eliminated most influences. However, differentialresponses at the site-specific level remained related to either storm impactsor secondary burning. At these sites, collateral data helped clarify theabnormal changes in NDVI. Accounting for these abnormalities,site-specific burn recovery trends could be broadly standardized into fourgeneral phases: Phase 1 – preburn, Phase 2 – initial recovery (increasingNDVI), Phase 3 – late recovery (decreasing NDVI), and Phase 4 – finalcoalescence (unchanging NDVI). Phase 2 tended to last about 300 to 500days, Phase 3 an additional 500 to 600 days, and finally reaching Phase 4,900 to 1,000 days after burn.     

非线性状态方程模拟异龄林径阶动态--以长白山阔叶红松林为例

以矩阵模型为基础,利用林分直径生长、进界生长和枯损的资料。用非线性动态模型模拟长白山阔叶红松林动态生长,并预测短期内在不同的采伐强度下林分的径阶变化,分析不同采伐强度对年生长量、年收获量和恢复年数的影响。结果表明,非线性动态模型在模拟林分生长上具有结构严谨和精度高的优点。将模型推广到采伐林分中,为科学地经营阔叶红松林,制定合理的采伐方案提供科学依据。     

水分胁迫对长白山阔红松林主要树种生长及生物量分配的影响

以长白山阔叶红松林主要树种红松、水曲柳、胡桃楸和椴树为研究对象 ,设置 3个水分处理 ,土壤含水量分别为田间持水量的 85 %～ 10 0 % (对照 )、6 5 %～ 85 % (MW )、4 5 %～ 6 5 %(LW )。对不同树种在不同处理下的生长进行测定 ,结果表明 :土壤水分含量对供试树种的单叶面积、单叶干重、叶片数量、茎干重、根长等生长指标均有显著影响。但各个树种对土壤水分胁迫的响应存在明显差异。在中度水分胁迫下 ,红松和水曲柳在总生物量降低的同时增加了地下生物量的比例 ,地下生物量 /地上生物量值比对照组分别提高了 79 31%和 2 3 91%。而胡桃楸和椴树的地下生物量 /地上生物量分别比对照组降低了 4 2 32 %和 7 92 %。在重度水分胁迫条件下 ,供试树种中只有红松的的地下生物量 /地上生物量比对照组提高了 2 7 5 % ,水曲柳、胡桃楸和椴树均呈下降趋势。由此可见 ,在供试树种中 ,红松对土壤水分胁迫的适应性最强 ,水曲柳仅对中度水分胁迫具有一定的适应性 ,而胡桃楸和椴树均不适宜在干旱的环境中生长。     

Influence of soil factors and cultural practice on biological control of sheath blight of rice with antagonistic bacteria

Fluorescent and nonfluorescent strains of bacteria isolated from rice rhizospheres on the International Rice Research Institute (IRRI) farm were evaluated for in vitro antibiosis towards the sheath blight (ShB) pathogen Rhizoctonia solani, and for suppression of ShB in detached rice leaves. Efficient strains were located on the basis of consistent performance in two laboratory tests. Among nine efficient strains, 3 strains were identified as Pseudomonas fluorescens, 5 strains were tentatively identified as Bacillus spp. and one strain was identified as Enterobacter. In three greenhouse tests lowland rice soils with optimum pH for rice growth (pH 5.5–6.5), acidic pH (pH 5.0) and boron toxicity were found more suitable for biological control of ShB and, less frequently, also yield increases than were alkaline (pH 6.9) and zinc-deficient soils. Bacterial treatments afforded significant ShB reductions in 3 field experiments, but no significant yield increases resulted. In direct-seeded rice best performances by bacterial treatments in terms of ShB suppression were 66 and 98% during DS 1988 and WS 1988, respectively, which were comparable to or better than the performance of validamycin (a fungicide routinely used for ShB control) which afforded 42 and 63% disease suppression, respectively, in the same experiments. Although bacterial treatments caused ShB reductions both in direct-seeded and transplanted rice crops, disease control was more pronounced in direct-seeded than in transplanted crops. These results indicate that carefully selected strains of bacterial antagonists have the potential for ShB suppression in rice at least in areas where direct-seeding is practised.     

Activity and activation state of ribulose-1,5-bisphosphate carboxylase of spruce trees with varying degrees of damage relative to the occurrence of novel forest decline

The aim was to determine whether a reduced carboxylation efficiency in needles of damaged spruce trees (Picea abies), is derived from a direct impairment of the ribulose-1,5-bisphosphate carboxylase (RuBP carboxylase) or there is an indirect inhibition of the RuBP carboxylase. In 1985, 1986 and 1987 measurements of RuBP carboxylase activity were carried out at three locations. Trees of different ages and degrees of damage were examined. RuBP carboxylase was assayed using both a rapid extraction method to determine the initial activity and an in vitro test after total activation to determine the total activity. The activation state was calculated as the ratio of initial activity to total activity.Within three vegetation periods the total activity in needles of damaged and apparently healthy or slightly damaged spruce trees indicated no definite difference in the annual average. On the other hand, in damaged needles a continued decline of the actual activation of RuBP carboxylase was established. The observation of continued depression of the activation state of the enzyme in needles of damaged spruce trees can possibly be due to a reduced photosynthetic electron transport rate.The measurements of the soluble protein content indicate a tendency to increased amounts in the needles of damaged trees. In accordance, a considerable increase of the activity of some enzymes like glutamine synthethase, phosphoenol-pyruvate carboxylase, and catalase could be noticed. However, there is no clear connection between the RuBP carboxylase and the content of soluble proteins.Abbreviations chl chlorophyll a+b, dw-dry weight, i.a-initial activity - P-700 reaction center of photosystem I - PVP polyvinylpyrrolidone 25 - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase - t.a. total activity     

Photosynthesis of ground vegetation in different aged pine forests: Effect of environmental factors predicted with a process‐based model

Question: How do stand age and environmental factors affect the species‐specific photosynthesis of ground vegetation? Location: Five different aged pine forests in Southern Finland. Methods: We measured photosynthesis of common species of ground vegetation during the growing season of 2006. Results: The measured vascular species, especially those with annual leaves, had a clear seasonal cycle in their measured photosynthetic activity (P_maxⁱ). A simple model that uses site‐specific temperature history, soil moisture and recent frost as input data was able to predict the changes in photosynthetic activity in dwarf shrubs with perennial leaves. The P_maxⁱ values of mosses did not have a clear seasonal cycle, but low values occurred after rain‐free periods and high values after precipitation. We modified the model for mosses and included temporary rain events. The model was able to predict most of the large changes in P_maxⁱ of mosses resulting from varying weather events but there was still some uncertainty, which was probably due to difficulties in measuring fluxes over a moss population. Conclusions: Temperature history, recent frosts and soil moisture determine the changes in P_maxⁱ of dwarf shrubs with perennial leaves. The P_maxⁱ of mosses depends mostly on recent precipitation.     

The simulation of soil organic matter and nitrogen accumulation in Scots pine plantations on bare parent material using the combined forest model EFIMOD

The individual-based combined forest model EFIMOD including the soil-sub model SOMM has been used for the simulation of Scots pine stand growth and soil organic matter (SOM) accumulation on a humus-free bare mineral surface. The growth of Scots pine plantation, with an initial density of 10 000 trees ha⁻¹ and average tree biomass of 0.01 kg was simulated for 50 yr under Central European climatic conditions (i) with varying atmospheric nitrogen inputs and (ii) different rates of initial application of raw undecomposed organic material or compost, on humus-free parent material. The accumulation of typical raw humus was simulated in all cases. The accumulation was most intensive in the simulation of high atmospheric nitrogen input. The humus pool in the mineral topsoil was small but achieved its maximum value with compost application. SOM nitrogen accumulation was scant in all cases, except the compost applications with low atmospheric nitrogen input. No statistically significant differences of SOM and stand parameters were found between variants without organic matter and those with low input of organic manure. However, the maximum relative rate of SOM and nitrogen accumulation was found in the scenario without organic manure, under slowly growing unstable Scots pine plantation. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Natural oak forest vs. ancient pine plantations: lizard microhabitat use may explain the effects of ancient reforestations on distribution and conservation of Iberian lizards

Natural vegetation in Europe appears nowadays deeply modified by human activities. In the Guadarrama Mountains (Central Spain), ancient reforestations with Scots pines, Pinus sylvestris, replaced original deciduous pyrenean oak, Quercus pyrenaica, forests (since the Roman period). However, the effect of reforestations on fauna remains little known, especially in reptiles. We described patterns of microhabitat selection in several species of Lacertid lizards, and analyzed whether the modification of the original vegetation affected distribution and population densities of lizards. The species of lacertid lizards found in oak forests (Psammodromus algirus, Lacerta lepida and Podarcis hispanica) were different to those of in pine plantations (Podarcis muralis and Podarcis hispanica). Lizards did not use habitat at random and this could explain differences in species found in both forests, which differed in some microhabitat structure characteristics. Most lizards selected microhabitats with rocky outcrops, with low cover of trees, and close to refuges. These microhabitat preferences also explained abundance of lizards in transects. From the perspective of conservation and management of lizards, pine plantations seem not to contribute too much to the diversity of lizard species because species typical from oak forests were lost. This study has implications for pine reforestation management, because allowing the recolonization by understory␣oaks, and leaving some open areas, without trees but with dense shrubs and rocks inside reforestations would contributed to maintain lizard populations.     

Tropical forest and savanna ecosystems show differential impact of N and P additions on soil organic matter and aggregate structure

Landscape transformation and atmospheric nutrient depositions, important global change drivers, are affecting the vegetation and soil properties of natural dry tropical forest and derived savanna ecosystems in India. This study assessed the effect of continuous N and P additions for 6 years on the size distribution and properties of soil aggregates in forest–ecotone–savanna gradient. Addition of N significantly increased the proportion of macroaggregates in forest and ecotone, whereas the same input significantly decreased their proportion in the savanna. Consequently, the stability of soil aggregates increased significantly in forest and ecotone, whereas it decreased significantly in the savanna. The effect of P addition on soil aggregate stability was marginal. N addition also altered the biological and chemical qualities of soil aggregates. It caused increase in microbial biomass C (MBC) associated with macroaggregates in forest and ecotone; however, in savanna, MBC increased in the microaggregates. P addition did not affect the amount of MBC in both types of soil aggregates. Because of rapid accumulation of applied N and P in the microbial biomass, the ratios of MBC to microbial biomass nitrogen (MBN) as well as microbial biomass phosphorous (MBP) were decreased in both aggregates. Overall, the effect of N addition was more marked than that of P addition, suggesting that N is more limiting than P in these dry tropical ecosystems. In the current scenario of N loading, continued soil N loading in forest may lead to increased macroaggregates with associated MBC and MBN and greater aggregate stability. In contrast, the extensively distributed savannas may show the reverse trend leading to a decrease in soil fertility.     

Reduction of forest floor respiration by fertilization on both carbon dioxide-enriched and reference 17-year-old loblolly pine stands

Elevated atmospheric carbon dioxide (CO₂^e) increases soil respiration rates in forest, grassland, agricultural and wetland systems as a result of increased growth, root biomass and enhanced biological activity of soil microorganisms. Less is known about how forest floor fluxes respond to the combined effects of elevated CO₂ and nutrient amendments; until now no experiments have been in place with large forest trees to allow even preliminary investigations. We investigated changes in forest floor respiration (S_ff) in a Pinus taeda L. plantation fumigated with CO₂ by using free‐air CO₂ enrichment (FACE) technology and given nutrient amendments. The prototype FACE apparatus (FACEp; 707 m²) was constructed in 1993, 10 years after planting, on a moderate fertility site in Duke Forest, North Carolina, USA, enriching the stand to 55 Pa (CO₂^e). A nearby ambient CO₂ (CO₂^a) plot (117 m²) was designated at the inception of the study as a reference (Ref). Both FACEp and Ref plot were divided in half and urea fertilizer was applied to one half at an annual rate of 11.2 g N m^?2 in the spring of 1998, 1999 and 2000. Forest floor respiration was monitored continuously for 220 days – March through November 2000 – by using two Automated Carbon Efflux Systems. Thirty locations (491 cm² each) were sampled in both FACEp and Ref, about half in each fertility treatment. Forest floor respiration was strongly correlated with soil temperature at 5 cm. Rates of S_ff were greater in CO₂^e relative to CO₂^a (an enhancement of ～178 g C m^?2) during the measurement period. Application of fertilizer resulted in a statistically significant depression of respiration rates in both the CO₂^a and CO₂^e plots (a reduction of ～186 g C m^?2). The results suggest that closed canopy forests on moderate fertility sites cycle back to the atmosphere more assimilated carbon (C) than similar forests on sites of high fertility. We recognize the limitations of this non‐replicated study, but its clear results offer strong testable hypotheses for future research in this important area.     

Altered patterns of soil carbon substrate usage and heterotrophic respiration in a pine forest with elevated CO2 and N fertilization

To assess how heterotrophic microorganisms may alter their activities and thus their CO₂‐C return to the atmosphere with elevated CO₂ and changing N availability, we examined soil organic matter (SOM) dynamics at the Duke Free Air Carbon Enrichment (FACE) site, after N fertilizer was applied. We measured heterotrophic respiration during early and late stages of SOM mineralization in soil incubations to capture activity on relatively labile and refractory SOM pools. We also measured δ¹³C of respired CO₂‐C and phospholipid fatty acids (PLFAs) during early mineralization stages to track the microbial groups involved in substrate use. We calculated , a measure of δ¹³C_PLFA normalized by respired δ¹³CO₂, to assess microbial function with C substrates formed with elevated CO₂ and altered N availability, via the distinct δ¹³C of the supplemental CO₂. We also quantified extracellular enzyme activity (EEA) during labile and recalcitrant SOM mineralization. Early in the incubations, increased N availability reduced heterotrophic CO₂‐C release. By the later stages of SOM mineralization, elevated CO₂ soils with fertilization had respired 72% of the CO₂‐C respired by all other soils. values suggest that fungi in elevated CO₂ plots took up C substrates possessing the δ¹³C signature of recently formed SOM, and added N promoted the activity of Gram‐negative bacteria and reduced that of Gram‐positive bacteria, particularly actinomycetes. Consistent with this, the enzyme responsible for the degradation of peptidoglycan and chitin, compounds produced by Gram‐positive bacteria and fungi, respectively, experienced a decline in activity with N fertilization. If patterns observed in this study with N additions are reversed with progressive N limitation at this site, actinomycetes and other Gram‐positive bacteria responsible for mineralizing relatively recalcitrant substrates may experience increases in their activity. Such shifts in microbial functioning may result in increased turnover of, and C release from, relatively decay‐resistant material.     

鼎湖山针阔叶混交林优势种树干液流特征及其与环境因子的关系

运用Granier热扩散式探针法,于2010年干湿季对鼎湖山自然保护区针阔混交林4种优势树种马尾松、锥栗、木荷和广东润楠的树干液流密度进行连续监测,并同步观测气温、相对湿度和光合有效辐射等环境因子的变化,研究其树干液流特征及其对环境因子的响应.结果表明:在干湿季,4种优势树种的树干液流速率日变化均呈“昼高夜低”的典型单峰曲线,阔叶树锥栗、木荷和广东润楠的平均液流速率和峰值以及日液流量均显著大于针叶树马尾松;马尾松、锥栗、木荷和广东润楠的最大树干液流密度分别为29.48、38.54、51.67、58.32g H2O·m-2·s-1.优势树种树干液流速率的变化与环境因子的昼夜变化存在时滞;液流速率变化与光合有效辐射、水汽压亏缺和气温等环境因子的变化呈显著正相关,其中湿季以光合有效辐射为主导因子,干季以气温为主导因子.