坡向对暗紫贝母生长和繁殖特征的影响

在青藏高原东部的牛牛山和卡卡山,在其东、南、西、北4个坡面各设置一个海拔相同(3800m)的样地,每个样地中随机选择30株同龄级的暗紫贝母植株作为研究对象,然后比较各坡面的生态因子以及暗紫贝母的生长和繁殖特征。结果表明:1融雪时间、气温、土壤含水量在南北坡面间有显著的差异,但土壤p H在各坡面间无明显差异。2开始生长期、始花期和盛花期等物候阶段都是北坡最迟,南坡最早,而枯黄期在各坡面间无显著差异。3单叶面积、比叶面积和植株株高以北坡最大,南坡最小。4鳞茎生物量以南坡最大,北坡最小,东、西坡面的值介于南、北坡之间。5单粒果实的生物量在各坡面之间无明显的差异,果实生物量在地上部分中所占的比例以南坡最大,北坡最小。6单粒果实平均种子数以北坡最多,南坡最少;而种子千粒重则以南坡最重,北坡最轻。可见,坡面对暗紫贝母的生长和繁殖特征有显著的影响,尤其是在南北坡面之间大多数性状差异显著。     

Analysis of covariance with pre-treatment measurements in randomized trials: comparison of equal and unequal slopes

In randomized trials, an analysis of covariance (ANCOVA) is often used to analyze post-treatment measurements with pre-treatment measurements as a covariate to compare two treatment groups. Random allocation guarantees only equal variances of pre-treatment measurements. We hence consider data with unequal covariances and variances of post-treatment measurements without assuming normality. Recently, we showed that the actual type I error rate of the usual ANCOVA assuming equal slopes and equal residual variances is asymptotically at a nominal level under equal sample sizes, and that of the ANCOVA with unequal variances is asymptotically at a nominal level, even under unequal sample sizes. In this paper, we investigated the asymptotic properties of the ANCOVA with unequal slopes for such data. The estimators of the treatment effect at the observed mean are identical between equal and unequal variance assumptions, and these are asymptotically normal estimators for the treatment effect at the true mean. However, the variances of these estimators based on standard formulas are biased, and the actual type I error rates are not at a nominal level, irrespective of variance assumptions. In equal sample sizes, the efficiency of the usual ANCOVA assuming equal slopes and equal variances is asymptotically the same as those of the ANCOVA with unequal slopes and higher than that of the ANCOVA with equal slopes and unequal variances. Therefore, the use of the usual ANCOVA is appropriate in equal sample sizes.     

Analysis of covariance with pre-treatment measurements in randomized trials under the cases that covariances and post-treatment variances differ between groups

When primary endpoints of randomized trials are continuous variables, the analysis of covariance (ANCOVA) with pre-treatment measurements as a covariate is often used to compare two treatment groups. In the ANCOVA, equal slopes (coefficients of pre-treatment measurements) and equal residual variances are commonly assumed. However, random allocation guarantees only equal variances of pre-treatment measurements. Unequal covariances and variances of post-treatment measurements indicate unequal slopes and, usually, unequal residual variances. For non-normal data with unequal covariances and variances of post-treatment measurements, it is known that the ANCOVA with equal slopes and equal variances using an ordinary least-squares method provides an asymptotically normal estimator for the treatment effect. However, the asymptotic variance of the estimator differs from the variance estimated from a standard formula, and its property is unclear. Furthermore, the asymptotic properties of the ANCOVA with equal slopes and unequal variances using a generalized least-squares method are unclear. In this paper, we consider non-normal data with unequal covariances and variances of post-treatment measurements, and examine the asymptotic properties of the ANCOVA with equal slopes using the variance estimated from a standard formula. Analytically, we show that the actual type I error rate, thus the coverage, of the ANCOVA with equal variances is asymptotically at a nominal level under equal sample sizes. That of the ANCOVA with unequal variances using a generalized least-squares method is asymptotically at a nominal level, even under unequal sample sizes. In conclusion, the ANCOVA with equal slopes can be asymptotically justified under random allocation.     

Allometry of male genitalia in a species of soldier beetle: support for the one-size-fits-all hypothesis

Hypotheses about the functions of the male genitalia and the male scape in insects were tested by measuring the slopes of allometric relations in six populations of Chauliognathus scutellaris. All allometric relations used elytron length as the indicator of overall body size. Male genitalia have lower slopes than male pronota (a structure not involved in reproduction), male scapes (secondary sexual characters) have higher slopes than male pronota, and female scapes have slopes that are not different from the slopes of female pronota. These results support Eberhard's one-size-fits-all hypothesis regarding the size of male genitalia in insects, and they raise questions about the role of the male scape in reproductive activities.     

Plant community patterns in old embanked grasslands and the survival of halophytic flora

The presence of a halophytic and sub-halophytic flora in grasslands reclaimed from the sea several centuries ago on the west Atlantic coast in France appears very unusual and the reasons for its survival are still uncertain. Our objective is to document its distribution pattern and to investigate whether its persistence is related to abiotic conditions and/or management practices. Vegetation surveys were carried out in seven different sites with 26 relevés on grazed sites (15 on slopes and 10 on flats) and 11 on mown sites (six on slopes and five on flats).This flora shows some important similarity with the vegetation of recent polders and can be classified into groups of species differing by their degree of salt tolerance but also their response to management mode. It was found that halophytes are only present on very saline soils, in a situation where the level of competition with more competitive species is reduced. The sub-halophytes also required low competition on lower soil salinity. In old polders, these two groups only occurred on grazed slopes and declined or even disappeared in the absence of grazing. In exclosures, the community became strongly dominated by competitive species and the soil salinity decreased on the slopes. The maintenance of sub-halophytes in old polders seems to be mainly conditioned by competition limitation whereas halophytes showed also a strong dependency to soil salt level, two requirements, which are met on continuously grazed slopes. Grazing maintains inter-specific competition at a low level while trampling increases soil compaction. Soil compaction modifies water and salt circulation, which could explain the high level of soil conductivity observed on grazed slopes.     

高寒地区路堑边坡植被恢复效果

以大兴安岭地区阿荣旗至博客图段高速公路边坡作为研究对象,研究厚质基层喷附技术和植生混凝土喷附技术的植被恢复效果。结果表明:1)从植物群落组成情况和群落相似性系数来看,两种技术的总体恢复效果差别不明显,但植生混凝土喷附坡面植物群落更为接近自然水平。2)同样基于植物群落组成和群落相似性系数,两种技术在阴坡和阳坡上的恢复效果存在明显不同。3)土壤全氮和有机质含量的适当增长可以促进植物群落发展,而土壤速效磷含量的增长会抑制其发展。4)推荐较为合理的物种搭配为艾蒿、柳蒿、羊草、贝加尔针茅、兴安胡枝子、紫穗槐和兴安柳。研究可改善这两种生态恢复复方式在该地区的应用,优化物种配置,防止二次退化问题的出现,为后期养护、管理提供理论依据。     

Ski slope vegetation at Snoqualmie Pass, Washington State, USA, and a comparison with ski slope vegetation in temperate coniferous forest zones

Ski slope vegetation at Snoqualmie Pass in Washington State, USA, was surveyed in order to identify community types and to compare it with vegetation development patterns in Japan. Ski slopes in Japan, most of which were constructed after 1960, underwent heavy land recontouring, while those at Snoqualmie Pass were constructed before 1950 with less modification. Three points apply to Japanese ski slope vegetation and differentiate these slopes from those at Snoqualmie Pass: (i) grasslands of introduced species are widespread and persistent; (ii) unvegetated patches are uncommon; and (iii) wetland vegetation has developed. These differences are mainly derived from the intensity of human impact, history of the slope and its scale: namely, ski slopes in Washington are older and larger than those in Japan. Ski slope vegetation in Washington was primarily differentiated by a soil moisture gradient. The large size of Washington ski slopes permitted the inclusion and development of wetland habitats, whereas most ski slopes in Japan are constructed on ridges and do not contain wetlands. Most introduced species in Japan are eliminated soon after seeding. In contrast, the long-term management of ski slopes decreased soil erosion and/or unvegetated patches in Washington and created relatively permanent grasslands composed of introduced species. Tsuga heterophylla and Abies amabilis were found established on the ski slopes in Washington, whereas in Japan the pioneer tree species are shade-intolerant broadleaved species. These differences may be a result of the different disturbance histories of ski slopes in the two countries. In addition, along with the conifers, early successional forbs such as Anaphalis margaritacea and Epilobium angustifolium are well established on Washington ski slopes. Results show that disturbances created by ski slope development greatly affect the vegetation, even on older, less heavily impacted ski slopes.     

Ecological factors affecting gene flow between populations of Anarthrophyllum cumingii (Papilionaceae) growing on equatorial- and polar-facing slopes in the Andes of Central Chile

In the Andes of Central Chile, flowering commences 1–2 months earlier on equatorial-(north-) facing than on polar- (south-) facing slopes, and pollinator assemblages also differ between these habitats. In order to understand the potential influence of these differences on gene flow, we monitored flowering periods and insect visitation rates to flowers of 60 individuals of Anarthrophyllum cumingii (Papilionaceae) on two equatorial- and two polar-facing slopes in the Andes of central Chile (33°35 S;70°32 W). Flowering began about 30 days earlier on equatorial-facing slopes. Flowering periods of individuals on slopes with the same aspect had a mean overlap of 0.52, while those on opposite slopes had a mean overlap of 0.15. On equatorial-facing slopes Yramea lathionoides (Lepidoptera) accounted for 60% of the visits to flowers of A. cumingii, while on polar-facing slopes Centris cineraria (Hymenoptera) was responsible for more than 80% of flower visits. Average similarities of visitor assemblages among individual plants on slopes with the same aspect was 0.83, while the mean similarity between individuals on opposite slopes was only 0.23. Within slopes fluorescent dyes were dispersed up to 40 m from the donor plants, but there was no movements of dyes between individuals growing on opposite slopes, even when they were separated by less than 10 m. Synchronous blooming and a common pollen vector are necessary conditions for pollen exchange between individuals. The overall probability of pollen exchange estimated by multiplying the inter-individual overlap for both factors, was nearly 0.5 for individuals growing on slopes with the same aspect, and less than 0.04 for individuals growing on opposite slopes. Consequently, at equivalent distances, the probability of pollen exchange between individuals growing on slopes of opposite aspect is more than 10-times lower than between those growing on the same slopes. Seed dispersal cannot compensate for restricted gene flow through pollination, because seeds of A. cumingii were dispersed less than 2 m away from a parent plant. Presumably, restricted gene flow could enhance genetic divergence between populations on slopes of contrasting aspects. This factor could be important in contributing to the high diversity and endemism in the Chilean Andes.     

Re-evaluation of species limits in the genus Atlapetes based on mtDNA sequence data

Brush-finches of the genus Atlapetes present a complicated pattern of differentiation along the Andes. Forms with different colours may replace each other sharply at different altitudes on the same slopes, in similar humid habitats on different slopes or on adjacent humid and semi-humid slopes. In the current classification, grey and yellow-and-green species are placed in different groups, and similar-coloured populations replacing each other in corresponding ecological zones on different slopes are ranked as subspecies of the same species. However, Remsen and Graves have suggested that different-coloured forms inhabiting adjacent mountains could be representatives of the same species with different pigment saturations, rather than competing species. The relationships between and within Atlapetes species are assessed based on mtDNA sequence data. Three main branches are demonstrated, comprising southern (Bolivian, northwest Argentinean), central (south and central Peruvian] and northern/western species. Clearly, the traditional groupings based on plumage colours did not demonstrate evolutionary trajectories in the genus. The data also show that many forms, currently ranked as subspecies, are genetically more divergent than sympatric species. Species rank is suggested for several forms hitherto treated as subspecies of geographically disjunct species.     

Late Holocene vegetation history suggests natural origin of steppes in the northern Mongolian mountain taiga

Insular occurrences of steppe vegetation are a common feature of the northern Mongolian mountain taiga. Steppe vegetation is limited here to southern slopes, whereas northern slopes and valley bottoms are principally wooded with light and dark taiga forests. In a case study in the valley of the river Eroo at Khonin Nuga Research Station in the western Khentey Mountains, we searched for evidence of an anthropogenic versus natural origin of steppe vegetation on the southern slopes. Pollen data of three profiles covering the last 2500 years showed continuous presence of steppe throughout the late Holocene with human influence restricted to the recent past. Virtual absence of charcoal in the soil on and beneath three steppe slopes suggested that the present steppe grasslands are not replacing former forests burnt by humans or lightning. The floodplains in the center of the Eroo valley were recently deforested. This is suggested by the pollen analysis and by interviews with local people on landuse history. Steppe grasslands of the study area have probably never been used as pastures. Pastoral nomads traditionally avoided the Eroo valley near Khonin Nuga because of difficult access and high densities of wolves and bears. All our data suggest that the present vegetation pattern of the western Khentey with steppes (and single small Ulmus pumila trees) on south-facing slopes occurring as islands in the mountain taiga is driven by climate and relief and is not the result of human activities as suggested for other regions of Asia.     

Flagship bird species habitat management supports the presence of ground-nesting aculeate hymenopterans

Burrowing birds, such as sand martins (Riparia riparia), are tightly bound to resource patches narrowly defined by soil penetrability, clay content, low incidence of parasites, and sufficient amount of aerial prey. Such habitat patches are limited both in number and quality, and their management is expected to affect not only the target flagship species, but also the non-target species represented by solitary ground-nesting aculeate hymenopterans utilizing the same habitat patches. The efficiency of sand martin habitat restoration at 23 localities was evaluated. Since most of the successful efforts resulted in a decrease of soil penetration resistance, whether the observed penetration resistance decrease had an effect on non-target aculeate hymenopterans utilizing vertical or near-vertical slopes was studied. To assess this, penetration resistance and soil granulometric characteristics were measured at 39 randomly selected vertical slopes, and the density of ground-nesting aculeate hymenopterans was evaluated. Ground-nesting aculeate hymenopterans were found to avoid slopes containing only soil strata with high penetration resistance, or with high gravel content. The burrow density in slopes with regular (bi)annual management was similar to the burrow density in slopes with medium to low penetrability but with less frequent management efforts. Removal of the hard-packed crust resulted in the return of both sand martins and aculeate hymenopterans in the respective slopes. Flagship bird species habitat management was found to support not only the the target burrowing bird, but also the non-target ground-nesting aculeate hymenopteran species.     

GIS‐analysis of tree‐line elevation in the Swiss Alps suggests no exposure effect

Abstract. Counter intuition, an analysis of tree‐line position across the Swiss Alps based on a geographical information system (GIS) with a spatial resolution of 100 m (2.5 million points) revealed no difference in climatic tree‐line altitude with slope exposure. Through step wise discrimination procedures our analysis accounts for anthropogenic tree‐line depression. Any land cover bias affects the frequency of GIS‐points corresponding to tree‐line forests rather than the mean elevation of such points, captured by our analysis. We explain this phenomenon (1) by the absence of significant drought effects in the Alps (no disadvantages for southwest slopes), (2) by the fact that tree tops, unlike low stature vegetation, do not profit from greater radiation warming on south slopes during the growing season but are thermally coupled to free air circulation, and (3) by preliminary data for root zone temperatures during the growing season, which do not differ between south and north slopes, as long as the soil is screened by a closed forest canopy. The overall difference in season length and snow cover, often seen between south and north slopes, does not seem to affect tree‐line position but explains greater natural forest fragmentation on north slopes. It is this greater fragmentation and patchiness (avalanche tracks, snow beds etc.) which seem to have nourished the idea of a generally lower limit of tree growth and tree lines at northern slopes. These results are in line with a recently developed theory, which suggests that tree‐line elevations in humid climates correspond to similar isotherms, irrespective of latitude and thus, season length.     

西藏珠穆朗玛峰国家级自然保护区鸟类群落结构与多样性

通过样线法调查并综合有关文献,录得珠峰保护区鸟类342种,并对其鸟类群落结构与多样性进行了分析。其中留鸟218种,夏候鸟67种,冬候鸟43种,旅鸟及迷鸟14种;国家一级保护鸟类8种,二级保护鸟类31种;东洋界132种,古北界156种,广布种54种,特有种19种。多样性指数2.4340,均匀性指数0.4371。研究表明,喜马拉雅山脉将保护区明显阻隔为南坡和北坡两种不同的生态景观。南坡鸟类群落以森林鸟类为主,东洋界成分占67%,垂直分带明显,多样性系数3.3983,均匀度指数0.6396;北坡鸟类群落以湿地和荒漠鸟类为主,古北界成分占77%。呈斑块状分布,多样性指数1.8751,均匀度指数0.4199,南、北坡鸟类群落的相似百分率为15.70,差异显著。     

喀斯特地区坡耕地与退耕地土壤有机碳空间异质性及其影响因素

利用网格采样(10 m×10 m),对比分析了典型喀斯特坡耕地(长期耕作)和退耕地(自然恢复)表层(0—15 cm)土壤有机碳(SOC)的空间变异特征,以期探究退耕恢复20a后SOC的空间异质性及其主要影响因素的变化。结果表明退耕地SOC含量(75.5 g/kg)显著高于坡耕地(15.1 g/kg),为坡耕地的5.0倍,说明自然恢复能显著提高SOC累积量;半变异函数分析结果表明退耕地基台值(521.7)为坡耕地(25.7)的14.9倍,说明退耕地SOC空间异质性远大于坡耕地。坡耕地和退耕地SOC的主要影响因子存在较大差异,土地覆盖类型、坡位、岩石出露率以及三者的交互作用显著控制着坡耕地SOC的空间格局,其贡献率分别为9.1%、6.3%、4.6%以及17.0%;土壤水分、坡度、岩石出露率以及三者的交互作用显著控制退耕地SOC的空间格局,其贡献率分别为26.0%、10.7%、7.2%以及3.6%;尽管岩石出露率对坡耕地和退耕地SOC的空间格局均有显著影响,但坡耕地SOC的主要控制因子为土地覆盖类型以及各因子的交互作用,而退耕地的主要控制因子为土壤水分。以上研究表明随着植被恢复和物种多样性增加,喀斯特坡地SOC的累积量和空间异质性增强,自然因素对SOC空间格局影响凸显,而岩石出露率始终控制SOC空间格局。     

论乌兰敖都地区沙丘坡面直射光的分布

乌兰敖都位于内蒙古自治区东部的科尔沁沙地中部,是西辽河中上游流域干旱地带的中心。境内分布着石质残丘和起伏的风积沙丘而呈现坨甸相间的景观,石质残丘、流动沙丘和固定沙丘占有很大比例,流动沙丘和固定沙丘(包括半固定沙丘在内)占总面积30%左右。由于地形起伏不平,下垫面性质的不同引起小气候、土壤和植被的显著差异。在本地区的半干旱气候条件下,光是决定生态系统生产力的主要因素之一,也是植物生长的唯一能源。本文根据1983—1984年实际观测资料,着重讨论乌兰敖都地区沙丘不同坡面对直射光到达量的影响,为沙地的综合利用和改造提供科学依据。一、计算方法沙丘不同坡面上直射光到达量,是指在单位时间内投射到单位坡面积上的直射光通量,     

北京东灵山不同坡位辽东栎(Quercus liaotungensis)叶属性的比较

植物在山地环境中生存不仅受到海拔等大尺度地形因子的影响,坡位等小尺度地形因子也会对植物产生影响.不同坡位上光照、温度、土壤养分和水分等均会影响到植物的资源利用策略.为比较不同坡位对辽东栎资源利用策略的影响,在北京东灵山海拔1000～1800 m的辽东栎分布范围内针对比叶面积、叶氮含量和叶干物质含量3个重要的叶属性进行了研究.ANOVA统计分析发现,地形和土壤养分及水分等环境因子在不同坡位上出现变化,但只有土壤有机质含量有显著差异.在叶属性中,干物质含量在上坡位最高,下坡位最低,在坡位间差异极显著.比叶面积与叶干物质含量在不同坡位间均成反比关系,在上坡位比叶面积变化一定的情况下,叶干物质含量的变化幅度最小;而比叶面积与叶氮含量仅在上坡位成反比关系.这些结果说明坡位对辽东栎的叶属性有一定的影响,尤其是上坡位的影响最大.     

Peculiarities of the courtship song in the <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> populations adapted to gradient of microecological conditions

In theory of evolution, two chief scenarios of development of sexual isolation—allopatric and sympatric, which act respectively under conditions of geographic separation or without it, are considered. Differences in the courtship behavior and in the used signals can lead to reproduction isolation and prevent gene exchange between sympatric populations or species, in which postmating barriers are absent. The previous studies of natural Drosophila populations inhabiting the opposite, ecologically contrast slopes of evolutional canyon (vicinities of the brook Oren in the mountain ridge Karmel, Israel) revealed statistically significant differences between them by the complex of adaptive and behavioral parameters including courtship behavior and choice of partner for mating. Astonishingly, differentiation of two populations has appeared in spite of a very small distance between two slopes. Here we report the statistically significant differences between males from the opposite slopes in characteristics of the courtship song that is one of signals serving for recognition by female of sexual partner of her species. We suggest that these differences can underlie the earlier revealed female discriminational behavior and can reflect different adaptive strategies in the populations inhabiting opposite canyon slopes.     

Geomorphology and benthic cover of mesophotic coral ecosystems of the upper insular slope of southwest Puerto Rico

The upper insular slope of southwest Puerto Rico is defined as extending from the shelf break at ~20 m water depth down to a depth of ~160 m where there is a pronounced change in geomorphic character and the basal slope begins. The upper slope is divided into two geomorphic zones separated by a pronounced break in slope gradient at ~90 m water depth. Descending from the shelf break, these are Zone I (20–90 m) and Zone II (90–160 m). As orientation of the shelf margin changes, geomorphology of Zone I shows systematic variations consistent with changes in exposure to prevailing waves. Within Zone I, exposed southeast-facing slopes have a gentler gradient and lower relief than more sheltered southwest-facing slopes, which are steep and irregular. Mesophotic coral ecosystems (MCEs) are largely restricted to Zone I and concentrated on topographic highs removed from the influence of active downslope sediment transport. Accordingly, MCEs are more abundant, extensive and diverse on southwest-facing slopes where irregular topography funnels downslope sediment transport into steep narrow grooves. MCEs are more sporadic and widely spaced on southeast-facing slopes where topographic highs are more widely spaced and downslope sediment transport is spread over open, low-relief slopes inhibiting coral recruitment and growth. Relict features formed during preexisting sea levels lower than present include deep buttresses at ~45–65 m water depth and a prominent terrace at ~80 m. Based on correlations with existing reef accretion and sea-level records, it is proposed that the 80-m terrace formed during the last deglaciation ~14–15 ka and subsequently drowned during a period of rapid sea-level rise associated with meltwater pulse 1A at ~14 ka and deep buttresses at ~45–65 m formed between ~11.5 and 13.5 ka and then drowned during a period of rapid sea-level rise associated with meltwater pulse 1B at ~11.3 ka.     

甘南高寒草甸植物元素含量与土壤因子对坡向梯度的响应

通过测定甘南高寒草甸不同坡向条件下25科86种植物叶片氮(N)、磷(P)、钾(K)含量、有机碳(C)含量、叶片含水量和相对叶绿素(SPAD)值,以及不同坡向的土壤含水量、有机碳、全氮、全磷含量等土壤指标,分析了不同坡向植物叶片元素含量与土壤环境因子之间的关系。研究结果表明,在南坡-北坡梯度上,随着土壤含水量的增加,植物叶片P含量、叶K含量和叶片含水量显著增加,而相对叶绿素显著降低。土壤养分含量与植物叶片P、叶K含量和叶含水量显著正相关,与叶片相对叶绿素显著负相关。说明不同坡向条件下叶片养分含量受土壤因子的影响显著,土壤的水分及养分状况对植物叶片元素含量的贡献不同。土壤含水量是坡向梯度上影响植物叶片特征的最主要因子。坡向梯度上土壤含水量对植物叶片各种元素含量的影响和植物叶片含水量对不同土壤因子的响应模式支持了生长在南坡的植物能以提高水分和养分利用效率而适应南坡较为干旱和贫瘠的生境。     

黄土丘陵沟壑区土壤水分环境及植被生长响应——以燕沟流域为例

调查了黄土丘陵沟壑区燕沟流域刺槐(Robinia pseudoacacia)林地、辽东栎(Quercus liaotungensis)林地、荒草地、农地等不同植被类型条件下7种地类的土壤水分环境,分析不同植被类型对水分环境的生长响应.结果认为,各地类均存在一定程度的水分亏缺,亏缺量由大到小依次为:阳坡刺槐林地991.57mm、阳坡荒草地941.21mm、阴坡刺槐林地866.53mm、阳坡辽东栎林地815.89mm、阴坡荒草地790.27mm、阴坡辽东栎林地745.20mm、农地325.55mm.土壤水分的交换深度农地达320cm,阴坡荒草地为240cm,阴坡辽东栎林地为200cm,阴坡刺槐林地和阳坡辽东栎林地均为160cm,阳坡荒草地为140cm,阳坡刺槐林地为120cm.试验期间,林地、荒草地和农地分别约有10%、14%、30%的降水储存于土壤中,林地、荒草地600cm深土壤水库可利用水量62.6～309.0mm,与农地728.6mm相比土壤水库的调节能力很有限.受林木耗水量和土壤供水能力的双重影响,阳坡刺槐林枯梢现象严重,有整株枯死林木;阴坡刺槐林有明显的枯梢,但没有整株枯死的林木;辽东栎林也存在枯梢现象,但较刺槐林轻微,林木生长仍然十分旺盛.人工林地植被较高的截留和蒸腾耗水是造成土壤干燥化的主要原因,在植被建设中应遵循区域植被的演替规律,以水定植,尽量选择低耗水的适生乡土树种,采取自然修复为主、人工栽植为辅的措施,同时实施好水土保持措施.黄土丘陵区天然辽东栎林是当地植被演替的顶级群落,林地土壤的干燥化是黄土高原气候整体趋于旱化造成的,并不是人为干扰导致植被过度耗水造成的,这种土壤干燥化不宜归属于干层的范畴.判别土壤干层应以当地稳定天然植被群落的生物量水平和土壤水分状况为基准.