Contrasting physiological responses of six eucalyptus species to water deficit

BACKGROUND AND AIMS: The genus Eucalyptus occupies a broad ecological range, forming the dominant canopy in many Australian ecosystems. Many Eucalyptus species are renowned for tolerance to aridity, yet inter-specific variation in physiological traits, particularly water relations parameters, contributing to this tolerance is weakly characterized only in a limited taxonomic range. The study tests the hypothesis that differences in the distribution of Eucalyptus species is related to cellular water relations. METHODS: Six eucalypt species originating from (1) contrasting environments for aridity and (2) diverse taxonomic groups were grown in pots and subjected to the effects of water deficit over a 10-week period. Water potential, relative water content and osmotic parameters were analysed by using pressure-volume curves and related to gas exchange, photosynthesis and biomass. KEY RESULTS: The six eucalypt species differed in response to water deficit. Most significantly, species from high rainfall environments (E. obliqua, E. rubida) and the phreatophyte (E. camaldulensis) had lower osmotic potential under water deficit via accumulation of cellular osmotica (osmotic adjustment). In contrast, species from low rainfall environments (E. cladocalyx, E. polyanthemos and E. tricarpa) had lower osmotic potential through a combination of both constitutive solutes and osmotic adjustment, combined with reductions in leaf water content. CONCLUSIONS: It is demonstrated that osmotic adjustment is a common response to water deficit in six eucalypt species. In addition, significant inter-specific variation in osmotic potential correlates with species distribution in environments where water is scarce. This provides a physiological explanation for aridity tolerance and emphasizes the need to identify osmolytes that accumulate under stress in the genus Eucalyptus.     

Forest-scale sap flux responses to rainfall in a dryland eucalyptus plantation

Dryland salinity is caused by rising saline water tables, the result of relatively recent landscape-scale clearance of deep-rooted vegetation. One obvious solution to this problem is the reintroduction of deep-rooted vegetation into these landscapes, most likely non-deciduous trees. Ideally, continually-transpiring deep-rooted trees would remove moisture from throughout the soil profile, increasing the capacity of the soil to store water, thus lowering water tables by effectively reducing the number of rainfall events that contribute to groundwater recharge. In this study, we examined how water use by a Eucalyptus sideroxylon A. Cunn. ex Woolls plantation, growing in a salinity-prone landscape, varied in response to rainfall events across four years of sap flux monitoring. Responses of the plantation were observed across multiple seasons, from above average to well below average rainfall. We observed that the plantation forest, while capable of continuous water use during drought, was also quite responsive to rainfall events. During the driest periods, during which shallow soil moisture was reduced to a stable minimum, the forest continued using water at around 1 mm/day. Generally we observed increases in forest water use following only 5 mm of rainfall, in contrast to 20 mm for neighbouring native vegetation. We compared a range of plausible empirical models for describing forest water use responses to rainfall. The best model demonstrated that rainfall size, post-rainfall PET and the interaction between rainfall size and antecedent soil moisture made significant contributions to variation in forest water use across rainfall events. Interestingly, the model showed that all else equal, higher antecedent soil moisture tended to reduce potential increases in forest water use in response to rainfall.     

Dominant species constrain effects of species diversity on temporal variability in biomass production of tallgrass prairie

Species diversity is thought to stabilize functioning of plant communities. An alternative view is that stability depends more on dynamics of dominant species than on diversity. We compared inter-annual variability (inverse of stability) of aboveground biomass in paired restored and remnant tallgrass prairies at two locations in central Texas, USA. Data from these two locations were used to test the hypothesis that greater richness and evenness in remnant than restored prairies would reduce variability in aboveground biomass in response to natural variation in rainfall. Restored prairies were chosen to be similar to paired remnant prairies in characteristics other than species diversity that affect temporal variability in biomass. Variability was measured as the coefficient of variation among years (square root of variance/mean; CV), where variance in community biomass equals the sum of variances of individual plant species plus the summed covariances between species pairs. Species diversity over five years was greater by a factor of 2 or more in remnant than restored prairies because richness and evenness were greater in remnant than restored prairies. Still, the CV of community biomass during spring and CV of annual biomass production did not differ consistently between prairie types. Neither the sum of species covariances nor total community biomass differed between prairies. Biomass varied relatively little in restored compared to remnant prairies because biomass of the dominant species in restored prairies (the grass Schizachyrium scoparium ) varied less than did biomass of other dominant and sub-dominant species. In these grasslands, biomass response to natural variation in precipitation depended as much on characteristics of a dominant grass as on differences in diversity.     

元阳梯田水源区旱冬瓜水分来源

旱冬瓜(Alnus nepalensis)是元阳梯田水源区的优势树种之一,其作为一种速生树种被发展为当地居民重要的薪炭林和经济林,树种的生长发育和地理分布受到水分制约,其吸收水分和水分利用的变化将会直接影响森林生态系统的水循环。该研究于2014年5－11月间进行,研究时段内累计降雨1262 mm,地下水δD 值在－71‰~－53‰范围,δ18 O 在－10.6‰~－7.0‰范围,受环境因子的影响很小,基本上保持常年稳定。土壤水是可供树种直接吸收利用的水源,基于氢氧稳定同位素技术,对比元阳梯田水源区旱冬瓜树种茎干水δD 和其林地不同深度土壤水δD 的同位素组成情况,结合不同深度土壤含水量,定性分析判断旱冬瓜对土壤水的利用,结果表明旱冬瓜旱季利用的土壤水主要分布在40 cm 土层附近,而雨季利用的土壤水范围较广,分布在0~60 cm 的土层。利用多元线性混合模型 IsoSource 软件定量分析旱冬瓜对土壤水和地下水的利用,结果表明：旱冬瓜水分来源分布较广,各土层土壤水和地下水均有贡献,雨季旱冬瓜主要利用0~60 cm 深土壤水,其中雨后旱冬瓜绝大部分水分来源于0~10 cm 的土壤水分,利用比例为66％~73％;其它时间主要利用40~60 cm 的土壤水,贡献率高达73％;旱季旱冬瓜的绝大部分水分来源于地下水,对地下水的利用比例为18％~68％,同时,40~60 cm 的土壤水也是其重要的水源。从不同时间尺度考察旱冬瓜对土壤水和浅层地下水的需求,更加准确地认识元阳梯田水源区不同森林类型优势树种的水分来源,为梯田森林生态系统经营与维护以及梯田的可持续发展提供了理论依据。     

Effects of neighbouring vegetation on eucalypt seedlings at two sites subject to different levels of abiotic stress

Abstract In spite of numerous studies on the effect of nutrient levels and/or standing crop on the intensity of resource competition the debate has not been resolved. Field studies that have used natural productivity gradients have generally supported the argument that competitive intensity and resource availability are positively correlated, whereas studies that have used artificial resource gradients have generally refuted the same argument. Here we report the results from study in which both approaches were used within the same system. We studied two species of eucalypt that occupy contrasting parts of the same landscape: Eucalyptus camaldulensis, found mostly along creek lines and in valleys with deep alluvial soils, and Eucalyptus microcarpa, found on hillsides and ridges with shallow soils. We studied the response of seedlings of the two species to the combined effects of competition and manipulated nutrient levels in a glasshouse experiment, and also investigated their responses to removal of neighbouring plants in the field. Eucalyptus microcarpa was less responsive to increased resource availability, which is consistent with one of the principal assumptions of Grime’s C‐S‐R model. In the glasshouse experiment both species of eucalypt responded in a qualitatively similar fashion to the combined effects of resource availability and competition: release from competition resulted in increased growth, but only in pots that received additional resources. In the field we found that neighbouring vegetation could severely limit the establishment of E. camaldulensis but the removal of neighbouring vegetation did not affect the performance of E. microcarpa seedlings. Eucalyptus camaldulensis seedlings suffered high levels of damage from herbivores. Our results thus generally support the predications of the C‐S‐R model, however, they indicate that the effects of competition and herbivory may be heavily confounded.     

Soil water depletion by Eucalyptus spp. integrated into dryland agricultural systems

Spatial patterns of soil water depletion by Eucalyptus spp. were surveyed to assess the potential of tree belts and short rotation phase farming with trees for groundwater recharge reduction and salinity control. Soils were sampled to depths of up to 10 m in transects perpendicular to 4- to 7-year-old mallee eucalypt belts (Eucalyptus horistes, E. kochii ssp. plenissima, E. loxophleba ssp. lissophloia, E. polybractea) and in a 4 year-old block of E. astringens. Results indicate that the eucalypt species can exploit soil water to depths of at least 8–10 m within 7 years of planting. The root systems of these eucalypts were able to penetrate clayey subsoils with bulk densities of up to 2.0 g cm⁻³. Leaf area indexes of tree belts were 2–10 times greater than those predicted for natural vegetation, probably as a result of exploiting a greater amount of soil water stored under the agricultural system. The lateral influence of mallee belts, as indicated by soil water contents that were depleted to wilting point, ranged from 15–42 m. The resulting dry soil zone provided an effective barrier to groundwater recharge by incident rainfall thereby lessening the risk of salinisation in the agricultural landscape. The width of this barrier to recharge was predicted to range from 7 m to 54 m based on leaf area.     

Daily, seasonal and annual patterns of transpiration from a stand of remnant vegetation dominated by a coniferous Callitris species and a broad-leaved Eucalyptus species

Quantifying water use of native vegetation is an important contribution to understanding landscape ecohydrology. Few studies provide long-term (more than one growing season) estimates of water use and even fewer quantify interseasonal and interannual variation in transpiration. Globally, changes in land use are significantly altering landscape ecohydrology, resulting in problems such as dryland salinity and excessive groundwater recharge. Estimating stand water use is complex in multispecies forests, due to the differences in relationships among sapwood area, basal area and tree size for co-occurring species. In this article, we examine seasonal and interannual variation in transpiration rate of the tree canopy of two co-occurring species (a conifer Callitris glaucophylla J. Thompson & L.A.S. Johnson and a broad-leaved Eucalyptus crebra F. Muell.) in an open woodland in eastern Australia. Evapotranspiration of understorey species was measured using an open-top chamber, and tree water use was measured using heat-pulse sap flow sensors. Annual stand transpiration was 309 mm in 2003, a year of below average rainfall, and 629 mm in 2004, a year with higher-than-average rainfall. Despite an almost doubling (522 vs. 1062 mm) of annual rainfall between 2003 and 2004, annual tree water use remained a constant fraction (59%) of rainfall, indicative of compensatory mechanisms linking annual rainfall, leaf area index and tree water use. Deep drainage was estimated to be 4% of rainfall (20.8 mm) in 2003 and 2% (21.2 mm) in 2004, indicating that this native woodland was able to minimize deep drainage despite large interannual variability in rainfall.     

Effects of experimental rainfall manipulations on Chihuahuan Desert grassland and shrubland plant communities

Aridland ecosystems are predicted to be responsive to both increases and decreases in precipitation. In addition, chronic droughts may contribute to encroachment of native C₃ shrubs into C₄-dominated grasslands. We conducted a long-term rainfall manipulation experiment in native grassland, shrubland and the grass–shrub ecotone in the northern Chihuahuan Desert, USA. We evaluated the effects of 5 years of experimental drought and 4 years of water addition on plant community structure and dynamics. We assessed the effects of altered rainfall regimes on the abundance of dominant species as well as on species richness and subdominant grasses, forbs and shrubs. Nonmetric multidimensional scaling and MANOVA were used to quantify changes in species composition in response to chronic addition or reduction of rainfall. We found that drought consistently and strongly decreased cover of Bouteloua eriopoda, the dominant C₄ grass in this system, whereas water addition slightly increased cover, with little variation between years. In contrast, neither chronic drought nor increased rainfall had consistent effects on the cover of Larrea tridentata, the dominant C₃ shrub. Species richness declined in shrub-dominated vegetation in response to drought whereas richness increased or was unaffected by water addition or drought in mixed- and grass-dominated vegetation. Cover of subdominant shrubs, grasses and forbs changed significantly over time, primarily in response to interannual rainfall variability more so than to our experimental rainfall treatments. Nevertheless, drought and water addition shifted the species composition of plant communities in all three vegetation types. Overall, we found that B. eriopoda responded strongly to drought and less so to irrigation, whereas L. tridentata showed limited response to either treatment. The strong decline in grass cover and the resistance of shrub cover to rainfall reduction suggest that chronic drought may be a key factor promoting shrub dominance during encroachment into desert grassland.     

Hydraulic redistribution in Eucalyptus kochii subsp. borealis with variable access to fresh groundwater

Salinity caused by land clearing is an important cause of land degradation in the Western Australian wheatbelt. Returning a proportion of the cleared land to higher water use perennial vegetation is one option for reducing or slowing the salinisation of land. Over the course of a year patterns of water use by Eucalyptus kochii subsp borealis (C. Gardner) D. Nicolle, a mallee eucalypt species, were monitored in three landscape positions with different water availability. One treatment had groundwater at 2 m, a second at 4.5 m and a third had groundwater below a silcrete hardpan thought to be impenetrable to roots. Hydraulic redistribution was observed in all landscape positions, and rates were positively correlated with the magnitude of soil water potential gradients within the soil. High rates of hydraulic redistribution, facilitated by abundant deep water may increase tree water use by wetting surface soils and reducing stomatal closure. This effect may be countered by increased soil evaporation of water moved from root to soil following hydraulic redistribution; the net volumes of redistributed water though lateral roots was calculated to be the equivalent of up to 27% of transpiration.     

Drought‐related tree death of savanna eucalypts: Species susceptibility,soil conditions and root architecture

Questions: For eucalypt savanna in northeast Australia subject to multi‐year rainfall deficits this paper asks whether (1) dominant tree species (Ironbarks, Boxes) are more drought susceptible than the sub‐dominant Bloodwoods; (2) whether soil moisture is beyond wilting point in surface soil layers but available at depth; (3) soil conditions (moisture availability and texture) are related to tree death during drought; (4) the root systems of the Boxes and Ironbarks are shallower than the Bloodwoods; and the survivors of drought within species have deeper root systems than those that died. Location: Central Queensland, Australia. Methods: Patterns of tree death between eucalypt species were compared from field data collected after drought. Soil conditions during drought were described and compared with patterns of tree death for the Ironbark Eucalyptus melanophloia. The basal area and orientation of coarse roots were measured on upturned trees after broad‐scale tree clearing, and compared between species, and between live and dead trees with tree size as a covariate. Results: Drought‐induced tree death was higher for dominant Ironbark‐Box than for sub‐dominant Bloodwoods. During a moderate to severe drought in 2004, 41% of 100 cm deep subsoils had soil matric potential less than‐5600 kPa. The drought hardy Bloodwoods had a greater root basal area and particularly so for vertical roots compared to the drought sensitive Ironbark‐Box. Within species there was no significant difference in root basal area characteristics between trees that were recently killed by drought and those that remained relatively healthy. Surface soil moisture availability was lower where tree densities were high, and tree death increased as surface soil moisture became less available. Tree death was also greater as the clay content of sub‐soils increased. Discussion: The study suggests species with roots confined to upper soil layers will suffer severe water stress. The results strongly indicate that root architecture, and the way it facilitates water use during drought, is important for the relative dominance of the tree species. Patchiness in drought‐induced tree death seems to be at least partially a product of heterogeneity in sub‐soil conditions and competition for soil moisture.     

Multi-scale determinants of dung beetle assemblage structure across abiotic gradients of the Kalahari–Nama Karoo ecotone, South Africa

Aim Changing conditions across spatial gradients are primary determinants of biotic regions, local habitats, and distributional edges. We investigate how a climatic gradient and edaphic mosaic interact as multi‐scale drivers of spatial patterns in scarabaeine dung beetles. The patterns are tested for congruency with ecoregion and floral boundaries over the same gradient, as responses to physical factors often differ among higher taxa. Location Southern Africa and the Nama Karoo–Kalahari ecotone, Northern Cape, South Africa. Methods Data consisted of the climatic distributions of 104 species and their abundances at 223 sites in two ecoregions/floral biomes, four bioregions, and 13 vegetation units. Factor analyses determined the biogeographical composition of the species, and regional‐ to local‐scale patterns in species abundance structure. Hierarchical analysis of oblique factors determined the proportional contribution of spatial variance to patterns. One‐way anova was used to test for significant separation of patterns along factor axes. Stepwise multiple regression was used to determine correlations of five physical attributes with species richness, Shannon‐Wiener diversity, and factor loadings for the study sites. Results Four biogeographical influences overlap in the study region, although rank contribution declines from south‐west arid through north‐east savanna to widespread and south‐east highland taxa. Species abundance structure comprises five subregional patterns, two centred to the north‐east (Kalahari, Isolated Kalahari Dune) dominated by Kalahari influence, and three to the south‐west (Nama Karoo subdivisions: Bushmanland, ‘Upper’, ‘Stony Prieska’) dominated by south‐west arid influence. Kalahari deep sands are characterized especially by a warmer, moister climate, whereas the Nama Karoo mosaic of deep or stony soils is characterized especially by north‐west aridity (Bushmanland), south‐east cooler temperatures (‘Upper’), or excessively stony soils (‘Stony Prieska’). Four of the subregional patterns each comprised three localized patterns related primarily to relative stoniness, edge effects from geographical position, or incidence of rainfall. Species richness and diversity declined with decreasing rainfall and increasing stoniness. Main conclusions Climatic and edaphic factors are important multi‐scale determinants of spatial patterns in dung beetle assemblage structure, with edaphic factors becoming more important at local spatial scales. The patterns are roughly congruent with the Kalahari Savanna–Nama Karoo ecotone at the floral biome or ecoregion scale, but show limited coincidence with finer‐scale floral classification.     

Primary lowland dipterocarp forest at Danum Valley, Sabah, Malaysia. Species composition and patterns in the understorey

The spatial distributions of species of tree 10 cm gbh were examined in two 4 ha plots and related to the local variation in topography and soil chemistry. The plots were similar in their species composition, particularly in terms of the densities of small trees, and they showed very similar edaphic characteristics. Size class distributions varied little within and between plots. Ordination of 0.25 ha subplots highlighted parallel gradients in the vegetation of both plots when the densities of trees 10 cm gbh were considered. Focusing on understorey trees in the 10-<50 cm gbh class at the 0.04 ha subplot scale showed a similar vegetation gradient in both plots closely associated with change from lower slope to ridge. No relationship with soil chemistry was found. On the ridges a special group of understorey species formed clumps and these species contributed importantly to the ordinations. Borneo has a regional history of occasionally severe droughts. It is suggested here that the observed patterns in the understorey are due to differential responses to low soil water supply, the ridges probably tending to dryness more than the lower slopes. Within the large and diverse family Euphorbiaceae, which dominates the understorey at Danum, there may be ecophysiological groupings of species. The long-term effects of disturbance interacting with local edaphic factors on forest structure and composition are discussed.     

Tracing water uptake by jarrah (Eucalyptus marginata) trees using natural abundances of deuterium

 Seasonal change in the δ²H content of water from twig sap, soil, rainfall and groundwater were measured to determine the water sources accessed by jarrah (Eucalyptus marginata) trees at three sites in Western Australia with differing soils and depths to water table. During winter and spring the main contributor to the water uptake of the trees was stored water in the surface layers of the soil replenished by predominantly winter rainfall. With the onset of summer drought jarrah became more reliant on water from deeper down the profile. There was no clear evidence that jarrah could tap water from groundwater more than 14 m deep in deep sands. Defining the source of water for trees in deep lateritic soils using stable isotopes is hampered by the uniform deuterium profiles down most of the unsaturated zone and into the groundwater. There was a limited response in the δ²H values of sapwater in twigs to changes in the δ²H of the upper layers of the deep sand following input of rainfall in autumn. The damped response was related to the small variation in the δ²H composition of rainfall in most events during the year and the mixing in the tree of water extracted from different locations in the soil profile. Received: 21 August 1995 / Accepted: 3 December 1995     

Groundwater use and salinization with grassland afforestation

Vegetation changes, particularly transitions between tree- and grass-dominated states, can alter ecosystem water balances and soluble salt fluxes. Here we outline a general predictive framework for understanding salinization of afforested grasslands based on biophysical, hydrologic, and edaphic factors. We tested this framework in 20 paired grassland and adjacent afforested plots across ten sites in the Argentine Pampas. Rapid salinization of groundwater and soils in afforested plots was associated with increased evapotranspiration and groundwater consumption by trees, with maximum salinization occurring on intermediately textured soils. Afforested plots (10–100 ha in size) showed 4–19-fold increases in groundwater salinity on silty upland soils but 50% of the days, and depressed the water table 38 cm on average compared to the adjacent grassland. Soil cores and vertical electrical soundings indicated that ≈6 kg m⁻² of salts accumulated close to the water table and suggested that salinization resulted from the exclusion of fresh groundwater solutes by tree roots. Groundwater use with afforestation in the Pampas and in other regions around the world can enhance primary production and provide a tool for flood control. However, our framework and experimental data also suggest that afforestation can compromise the quality of soils and water resources in predictable ways based on water use, climate, and soil texture.     

Phytogeography of dry ecosystems in the ignimbrite meseta of Guanacaste, Costa Rica]

The dry ecosystems in the ignimbrite meseta of Guanacaste, northwest Costa Rica is mapped. Plant community distribution is intimately related to the type of relief, soils and humidity. In the upper parts of the meseta, characterised by soils which are stony, sandy, and acidic, herbacious vegetation such as savanna and edaphic steppe is dominant. By contrast, woodland is found on the deep and organically rich soils of the valley floors. Within the herbaceous formations dwarf varieties of Byrsonima crassifolia (nance), Curatella americana (raspa guacal) and Quercus oleoides (encino) are found because of the acid and infertile soils.     

Fine roots of <Emphasis Type="Italic">Prosopis flexuosa</Emphasis> trees in the field. Plant and soil variables that control their growth and depth distribution

Fine root growth in natural vegetation is difficult to predict due to its regulation by soil and plant factors. Field studies in arid ecosystems show a variety of root responses to soil resources and to plant aboveground phenology that sometimes differ from root responses predicted by controlled experiments. There is a pressing need to cover a greater diversity of plant species and ecological scenarios in field studies. In this paper, we have studied fine roots of Prosopis flexuosa trees living with or without access to phreatic water in an inter-dune valley and a dune flank, respectively, in the Central Monte Desert, Argentina. We have described fine root growth over time and at different depths by rhizotron observations and soil core auger samples in relation to soil water and nutrients, tree crown phenology, plant water and nutrient status. We have found that surface soil moisture from rainfall is the variable that best predicts seasonal topsoil fine root growth. Access to groundwater advanced leaf sprouting with respect to rainfall, but did not advance root growth that stayed linked to rainfall in valley and dune flank trees. Trees without access to phreatic water produced deeper and thicker or denser roots, which is consistent with the poor soil resource content of dunes. Variations in rainfall dynamics due to global climate change may have a particular impact on fine roots and ecosystem processes such as biogeochemistry and carbon budget in dune flank trees as well as in valley trees.     

Species trait syndrome drives the leaves’ functional variations of dominant grasses to modifications in summer water supply

Climate change models predict a strong reduction of average precipitation, especially of the summer rainfall, and an increase in intensity and frequency of drought events in the Mediterranean region. The research aim was to understand how four dominant grass species (Arrhenatherum elatius, Cynosurus cristatus, Elymus repens, and Lolium perenne) in sub-Mediterranean meadows (central Apennines, Italy) modulate their resource acquisition and conservation strategies to short-term variation of the pattern of summer water supply. During summer 2016, using a randomized block design, we tested the effect of three patterns of summer water supply, differing in water amount and watering frequency, on leaf area, leaf dry mass, specific leaf area (SLA), leaf senescence, and plant height. Our results showed that dominant grass species can modulate their strategies to variation of the pattern of summer water supply, but the response of leaf traits and plant height is mediated by the set of functional characteristics of the species. E. repens and A. elatius, with summer green leaves, lower SLA, later flowering period, and deeper roots, were less influenced by changes in water amount. C. cristatus and L. perenne, which display acquisitive strategies (persistent leaves, higher SLA values), earlier flowering, and shallower roots were more influenced by changes in the pattern of summer water supply. Our results suggest that a short-term decrease in water availability might affect primarily species with trait syndromes less adapted to face summer drought.

     

黄土高原退耕地的生态恢复

在刈割干扰下,黄土高原退耕地恢复进程中植被从沙蓬（Agriophyllum arenarium)单优群落向以达乌里胡枝子（Lespedeza davurica)为优势种的群落演替。物种增加速度初期快,后期慢,退耕后恢复初期的新增物种主要是沙蓬和白草（Pennisetum flaccidum);中前期主要是茵陈蒿（Artemisia capillaris),可成为群落的次优势种;中后期新增物种主要是多年生豆科植物,只是群落的伴生种,群落中1年生和多年生植物地上生物量分别以8.8%的年平均速率减少或增加,豆科植物地上生物量及所占比例上升,在退耕地恢复过程中,上层土壤中植物地下生物量比例与变化幅度增加,表现出浅层化趋势,退耕地恢复演替1-7年,土壤粘粒和粉粒减少,砂粒增加,7年后变化趋势相反,退耕地0-100cm土壤含水量在恢复期间呈逐渐上升趋势,中期增幅显著,全N和速效N在恢复前期减少,后期增加,在刈割利用下,退耕地恢复过程中土壤全P,速效P和有机C持续衰竭,退耕地恢复到当前稳定的群落所需时间分别为优势种群8-9年,群落9-11年和土壤11-12年。     

The eco-hydrology of partly cleared,native ecosystems in southern Australia: a review

Water use by the native vegetation that existed in southern Australia prior to European settlement was largely in balance with rainfall. European settlers altered the landscape by clearing land to grow agricultural crops and pastures, and with the introduction of livestock to graze the partly cleared, native ecosystems. The aim of this review is to contrast the hydrology of grazed, partly cleared ecosystems, intact indigenous ecosystems, and entirely cleared agricultural systems in the intensive land-use zone (350–1000 mm annual rainfall zone) of southern Australia. Since European settlement, the areas of forests and woodlands in the Murray–Darling Basin have declined by approximately 64% to make way for agricultural enterprises. Modern-day vegetation surveys estimate between 52 and 58% of the intensive land-use zone of the Murray–Darling Basin has been entirely cleared, while about 40% is in the partly cleared state (disturbed ecosystems with canopy cover exceeding 5%). The replacement of native vegetation by agricultural crops and pastures has disturbed the water cycle that existed prior to European settlement, and has markedly elevated the amount of water leaking beyond the root zone of introduced species, and contributing to groundwater systems. Estimates of annual leakage beneath the root zone of annual crops range from 0 to 63 mm per annum; however, no estimates of leakage for partly cleared woodlands exist. Yet, because the groundwater beneath partly cleared woodlands rises considerably more slowly than under entirely cleared landscapes, it is likely that less water leaks beneath the roots of grazed woody ecosystem. However, aging of these systems by livestock grazing will reduce the numbers of woody individuals and will impact on groundwater recharge.     

The Plecoptera of Øvre Heimdalsvatn

The stonefly fauna was studied in the exposed zone and on soft bottom in deeper waters. Emergence was recorded by traps. Ten species were found. All were recorded in the exposed zone. Diura bicaudata (L.) and Nemoura avicularis Morton dominated.
During the winter N avicularis occurred in large numbers on soft bottom at nearly all depths while D. bicaudata was only recorded on stony substratum in shallow water. N. avicularis was therefore more susceptible to predation and was recorded in trout stomachs during most of the year, while D. bicaudata was preyed upon only during the short emergence and flight period.
The growth of the most numerous plecopteran species took place partly while the lake was covered by ice. D. bicaudata had two thirds of its growth during this period, while N. avicularis only had one third of its growth during the same period.