Simulation of the effect of root distribution on hydraulic redistribution in a desert riparian forest

Hydraulic redistribution (HR) of roots plays an important role in the water relations of desert riparian plants. In order to estimate the effect of vertical root distribution on the HR process of Populus euphratica Oliv. during the entire growth season, we performed simulation and scenario analyses based on the observed soil water potential and root distribution data. The results showed that our simulation model achieved a good accuracy. The initial value of soil water content could significantly affect the simulated soil water content at soil depths of >90 cm, but had only limited effect on soil water content in the 0- to 90-cm soil layers. Scenario analysis revealed that with increase in root distribution depth, the HR process extended from the upper and middle soil layers downward toward the middle and deeper soil layers: the deeper the root distribution, the more likely it was to trigger the HR process in deep soil layers. However, a deeper rooting system led to a decrease in the total amount of hydraulically redistributed water over the entire soil column. Redistributed water also significantly increased the soil water depletion and the soil water storage. However, the effects of redistributed water (HR vs. without HR) on water depletion and soil water storage were reduced with the deepening of root distribution. These results indicate that HR can obviously affect the moisture of the upper soil layers, while vertical root distribution significantly changes the spatial and quantitative characteristics of HR within soil columns.     

The stable carbon and nitrogen isotopic composition of vegetation in tropical forests of the Amazon Basin, Brazil

Here we present the within-site, seasonal, and interannual variations of the carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of leaves, wood, bark and litter from four sites in the Amazon region, Brazil. Samples were collected in Manaus (3° 06′07′′ S; 60°01′30′′ W), Ji-Paraná (10°53′07′′ S; 61°57′06′′ W), and Santarém (2°26′35′′ S; 54°42′30′′ W) with mean annual precipitation of 2207, 2040 and 1909 mm respectively. The overall average for all leaf samples was for δ¹³C and for δ¹⁵N (n=756). The leaf δ values at these sites were often but not always statistically distinct from each other. The δ¹³C values varied from to . Pronounced differences in δ¹³C values occurred with height associated with differences in forest structure. The δ¹³C of leaf dry matter showed seasonal variations associated with the length of the dry season, despite the fact that total annual precipitation was similar among the studied sites. Leaf δ¹⁵N values ranged from to a maximum value of , and the Santarém sites showed more enriched values than Manaus and Ji-Paraná sites. No seasonal variation was detected in the δ¹⁵N of leaves, but significant differences were observed among sites and with changes in canopy height. The isotope ratio data are consistent with our current understanding of the roles of light, water availability, and recycling of soil-respired CO₂ influences on δ¹³C and consistent with our understanding that an open nitrogen cycle can lead to high δ¹⁵N values despite a significant number of legumes in the vegetation.     

Interactive effects of flooding and forest gap formation on tree composition and abundance in the Peruvian Amazon

In order to better understand how flooding and gap formation affect Amazonian rainforests, I set up plots both in three major forest types that differed by flooding duration (referred to here as dry, wet, very wet) and in their respective gaps. Sampling of those plots after 4 years of regeneration showed: (1) common species exist between wet forests and their gaps and between wet and very wet gaps, (2) tree richness is maximum in dry forest and minimum in very wet gaps except in the wet gaps that show the second highest number of species, (3) there were less stems in gaps compared to forests and less stems in forests as flooding increased, except again in the wet gaps, and (4) dominance-diversity curves have more dominance by single species in the dry gap plots compared to other gaps and in dry forest compared to other forests. In general while some aspects of structure such as tree stem density is largely determined by tree-fall gap dynamics, tree composition is determined by flooding regime. Finally a jump in tree richness in wet forests and wet gaps compared to other plots suggests a “mass effects” hypothesis where species from dry and very wet forest and gaps have overlapping ranges in the wet forest and gap. This effect may help explain the high species diversity seen in this part of the Amazon.     

The impact of large herbivores on floral composition and vegetation structure in the Naukluft Mountains, Namibia

Floral composition and vegetation structure were investigated on the Naukluft Mountain Plateau to determine (i) whether or not grazing has had an impact on the flora of the Naukluft Mountains during the last two decades and (ii) if so, whether vegetation recovery is influenced by the nature of the rainy season. Vegetation subjected to grazing to large herbivores and vegetation excluded from grazing for 18 and 19 years was compared. Based on classification (TWINSPAN) and ordination (detrended and canonical correspondence analysis) of 20, 10 × 10 m stands within and outside exclosures in two seasons, a clear difference in floristic composition between grazed and not grazed areas was indicated. Although neither the height of the vegetation, not the growth form spectrum differed significantly between grazed and not grazed sites, leaf-succulents were much more abundant when grazing was excluded. This suggests that changes in the vegetation due to grazing pressure have occurred in the last two decades, but the degree of grazing impact is not severe and may be part of the natural savanna ecosystem of the Naukluft Mountains. Whether this trend also occurs in other vegetation types in the Naukluft Mountains remains to the investigated. This revised version was published online in November 2006 with corrections to the Cover Date.     

The impact of forest transformation on stand structure and ground vegetation in the southern Black Forest, Germany

The goal of this study was to investigate the effects of 'ecologically orientated' forest transformation on forest floor vegetation. Forest transformation, as defined by the BMBF southern Black Forest project group, is the process which converts even-aged spruce forest into structured continuous-cover forest, consisting principally of spruce (Picea abies), fir (Abies alba) and beech (Fagus sylvatica). In order to analyse the transformation process, four transformation stages were defined as part of a 'conceptual forest development model' (pure even-aged, species enrichment, structuring and continuous cover forest stage). Four forest districts representative of the southern Black Forest were selected for the study. The analysis included the separate classification of structures, sites, and ground vegetation. In a second step, the relationships between the three complexes were analysed. The influence of forest structure on ground vegetation was investigated by examining the relationships between so-called substructure types and ground vegetation types. The substructure types associated with the pure spruce stand, species enrichment and continuous cover forest stages exhibited a ground vegetation resembling that of the Luzulo-Fagetum and Luzulo-Abietetum, whereas the structuring stages exhibited a ground vegetation of the Galio-Fagetum type. Transformation of pure, even-aged spruce forest into mixed, uneven-aged continuous cover forest is considered an important silvicultural tool to combine the demands of sustainable timber production and nature conservation. Transformation brings about greater diversity in stand structure and tree species composition. The frequencies of acidophytic mosses and vascular plants in spruce forest decrease during the transformation process. The species requiring moderate base supply increase over the transitional stages. The continuous cover forest, the final stage of transformation, increasingly contains ground species of both, i.e., species normally associated with both conifer and deciduous forest.     

Diversity and composition of understory vegetation in the tropical seasonal rain forest of Xishuangbanna, SW China

Tropical forests vegetation and community research have tended to focus on the tree component, and limited attention has been paid to understory vegetation. Species diversity and composition of the understory of tropical seasonal rain forest were inventoried in a 625 m2 area (for sapling layer) and a 100 m2 area (for herb/seedling layer) in three 1 ha plots. We found 3068 individuals belonging to 309 species, 192 genera and 89 families. The most important family as determined by the Family Importance Value (FIV) was Rubiaceae in both sapling and herb/seedling layers. In terms of Importance Value Index (IVI), the shrub Mycetia gracilis (Rubiaceae) was the most important species in the sapling layer and the pteridophyte Selaginella delicatula (Selaginellaceae) was the most ecological significant species in the herb/seedling layer. Much more vascular plant species were registered in the understory than in the tree layer totaled among the three plots. The species diversity did not differ significantly among the tree layer, sapling layer and herb/seedling layer. Given that we still know little about the understory plant community for growth forms other than trees, the results from the present study indicate that more attention should be paid to the understory vegetation during the decision-making process for biodiversity conservation in the tropical forests.     

Soil and forest structure in the Colombian Amazon

Forests structural differences could result of environmental variations at different scales. Because soils are an important component of plant's environment, it is possible that edaphic and structural variables are associated and that, in consequence, spatial autocorrelation occurs. This paper aims to answer two questions: (1) are structural and edaphic variables associated at local scale in a terra firme forest of Colombian Amazonia? and (2) are these variables regionalized at the scale of work? To answer these questions we analyzed the data of a 6ha plot established in a terra firme forest of the Amacayacu National Park. Structural variables included basal area and density of large trees (diameter > or = 10cm) (Gdos and Ndos), basal area and density of understory individuals (diameter < 10cm) (Gsot and Nsot) and number of species of large trees (sp). Edaphic variables included were pH, organic matter, P, Mg, Ca, K, Al, sand, silt and clay. Structural and edaphic variables were reduced through a principal component analysis (PCA); then, the association between edaphic and structural components from PCA was evaluated by multiple regressions. The existence of regionalization of these variables was studied through isotropic variograms, and autocorrelated variables were spatially mapped. PCA found two significant components for structure, corresponding to the structure of large trees (G, Gdos, Ndos and sp) and of small trees (N, Nsot and Gsot), which explained 43.9% and 36.2% of total variance, respectively. Four components were identified for edaphic variables, which globally explained 81.9% of total variance and basically represent drainage and soil fertility. Regression analyses were significant (p < 0.05) and showed that the structure of both large and small trees is associated with greater sand contents and low soil fertility, though they explained a low proportion of total variability (R2 was 4.9% and 16.5% for the structure of large trees and small tress, respectively). Variables with spatial autocorrelation were the structure of small trees, Al, silt, and sand. Among them, Nsot and sand content showed similar patterns of spatial distribution inside the plot.     

Seed bank and vegetation composition of forest stands of varying age in central Belgium: consequences for regeneration of ancient forest vegetation

Vegetation composition differs significantly between ancientand recent forest, due to slow colonization capacity of typical forest speciesand the higher abundance of early successional species in recent forest.However, little is known about differences in persistent seed bank compositionbetween ancient and recent forest and about the interaction between seed bankand vegetation in relation with forest age. We surveyed the seed bank and theunderstorey vegetationcomposition in transects from ancient to recent forest. Seed bank and fieldlayer vegetation characteristics and similarity between seed bank andvegetationwere analysed in relation to recent forest age and distance to the ancientforest. A total of 39 species and 14,911 seedlings germinated, whichcorresponds with a seed density of 12,426 seeds/m².Total seed density is significantly higher in the youngest recent forest parcel(55 years). Also the seed bank composition in the youngest forest parceldifferssignificantly from the other parcels. After a longer period of reforestation,the seed bank approaches that of the ancient forest, suggesting seed bankdepletion, although the seed bank is permanently replenished to some extent byseed bank forming species from local disturbances. Seed bank composition doesnot change significantly with distance to the ancient forest. Similaritybetween seed bank and vegetation composition, nomatter the forest age, is very low, but decreases with increasing forest age.The most frequent species in the vegetation are absent in the seed bank andvice versa. The contribution of forest species is highin the vegetation and they almost not occur in the seed bank, while species offorest edges and clearings, and species of disturbed environments are morefrequent in the seed bank. The seed bank is mainly composed of earlysuccessional species of former forest stages or species which temporary occurinsmall-scale disturbances. The seed bank may enhance the negative effects ofearlysuccessional, mainly competitive species to the forest species richness in therecent forest. In this respect, forest management should minimise forestdisturbances, to prevent germination of competitive species form buriedseeds.     

Human impact on the forest vegetation in the western part of the Pannonic Plain (Yugoslavia)

A comparative phytosociological study was made out on two types of forest on the southern slopes of Moslavaka gora in the western part of the Pannonic Plain, Yugoslavia: acidophilic oak forest of Festuco-Quercetum petraeae Hruka 1975 and areas where Robinia pseudoacacia has been introduced by man. After cutting, the oakforest reestablishes spontaneously. Reafforestation with Robinia leads to changes irreversible in species composition and vegetational structure and prevents reestablishment of oak forest. The introduction of this allochthonous species prevents the primary wood from being restored. Forestry planting projects with a view to reducing the Robinia have so far proved ineffective.     

Variation in nutrient removal in three wetland blocks in relation to vegetation composition,inflow nutrient concentration and hydraulic loading

Wetlands provide vital ecosystem services such as water quality improvements, and are important sites of biodiversity conservation. Their optimal use and management depends, in part, on vegetation management and the quality and quantity of the water flowing through them. The South-finger wetland, situated on a Wildfowl & Wetlands Trust wetland visitor centre at Slimbridge, UK, receives waters of high nutrient concentrations from the wildfowl collection. The nutrient removal functioning of three constructed beds was compared and related to variations in input nutrient concentrations and hydraulic loading over 1 year (October 2005–October 2006). None of the beds removed nitrate, orthophosphate or total phosphorus over the year as a whole. The beds planted with Iris and mixed vegetation were found to remove the greatest proportion of ammonium, and increased nitrate concentrations in the water to a lesser extent than the Phragmites bed. Nutrient functioning in all three beds varied in a non-linear manner in relation to input nutrient concentrations and water residency time. Possible reasons for the differences in functioning between nitrogen and phosphorus, vegetation types and between seasons are discussed.     

Impact of spruce forest and grass vegetation cover on soil micromorphology and hydraulic properties of organic matter horizon

Two organic matter horizons developed under a spruce forest and grass vegetation were chosen to demonstrate the impact of a different vegetation cover on the micromorphology, porous system and hydraulic properties of surface soils. Micromorphological studies showed that the decomposed organic material in the organic matter horizon under the grass vegetation was more compact compared to the decomposed organic material in the organic matter horizon under the spruce forest. The detected soil porous system in the organic matter horizon under the spruce forest consisted of two clusters of pores with different diameters that were highly connected within and between both clusters. The soil porous system in the organic matter horizon under the grass vegetation consisted of one cluster of pores with the larger diameters and isolated pores with the smaller diameter. The retention ability of the organic matter horizon under the grass vegetation was higher than the retention ability of the organic matter horizon under the spruce forest. Presented at the International Conference on Bioclimatology and Natural Hazards, Poľana nad Detvou, Slovakia, 17–20 September 2007.     

Bird community composition in an actively managed savanna reserve, importance of vegetation structure and vegetation composition

The mosaic of trees, shrubs and open grassland in mesic African savannas is highly dynamic and strongly influenced by mammal herbivory and fire. We investigated the bird fauna in four different savanna habitats to help assess the impacts of vegetation change on this component of faunal diversity. Birds were censused, plant species were identified and vegetation structure was measured in four different vegetation types (Acacia nilotica woodland, Acacia nigrescens woodland, broadleaf thicket and open grassland) in the Hluhluwe-Umfolozi Park in northern KwaZulu Natal, South Africa. Multivariate ordination analyses were used to determine the relative importance of vegetation structure and floristic composition in defining bird assemblages. The bird communities of the grasslands, the acacia woodlands, and the broadleaf woodlands were clearly separated on the first axis of the detrended canonical correspondence analysis (DCCA). Canopy cover and foliage height diversity (FHD) were strongly correlated with the first axis of DCCA, possibly reflecting a secondary successional series from grassland to woodland, known as bush encroachment. Floristic composition (based on presence–absence data only) seemed to be less important for bird community composition than vegetation structure. The results indicate that changes in vegetation structure, caused by bush encroachment, could cause concomitant changes in bird community composition.     

Structure, floristic composition, and vegetation forming factors of three vegetation types in Senegal

Six 1 ha plots were established in a coastal savanna, called Fathala Forest, in Delta du Saloum National Park, Senegal. Two plots were placed in woodland, two in wooded grassland, and two in transition woodland in order to describe structure and floristic composition of the vegetation. All trees ≥ 5 cm dbh were sampled. The three selected vegetation types showed distinct differences in structure as well as in species composition. Woodland had high density (440–449 individuals per ha), many small trees, and high basal area (13.4 m²per ha). Transition woodland was characterised by low density (54–118 individuals per ha) but many large trees and a relatively large basal area (8.6–12.8 m² per ha). Wooded grassland was characterised by medium sized trees, it had low density (86–102 individuals per ha) and low basal area (3.8–5.7 m² per ha). Species richness ranged between 17 and 27 species per ha in the six plots. Only two species were found in all plots, Daniellia oliveri (Caesalpiniaceae) and Prosopis africana (Mimosaceae). Legumes dominated all plots. Wooded grassland and transition woodland had many characteristics of fire-affected vegetation in contrast to woodland. Today wooded grassland encroaches on woodland and transition woodland. Management of the latter two vegetation types should be given priority as they maintain structural and floristic characteristics that are essential to conserve biodiversity and original features of the vegetation, and they are also important for local people who are allowed to make sustainable use of the vegetation.     

Winter bird communities in forest plantations in western England and their response to vegetation,growth stage and grazing

This paper presents the results of a study of wintering bird communities across a wide range of coniferous, broadleaved and mixed forest stands in the Forest of Dean, western England. Bird communities of broadleaved and coniferous woodland differed with respect to their species composition. The mean number of individual birds recorded increased linearly with woodland age and was not influenced by woodland type, stand size or the presence of grazing. Woodland age and type and the presence or absence of grazing all significantly influenced bird species richness and the proportions of the bird community made up by granivores, insectivores and omnivores. Broadleaved stands held more species than coniferous stands. Ungrazed stands held significantly more species, particularly seed-eating species, than grazed stands and this effect was independent of woodland type. Ordination was used to relate variation in tree species composition and stand structure to bird community composition. A larger number of species was associated with broadleaved stands and stands with abundant undergrowth than was associated with coniferous stands or stands with little undergrowth. Woodland age had less effect on bird community composition than the extent of undergrowth and the conifer to broadleaf ratio. The results of this work have relevance to the enhancement of winter bird communities in commercial forests.     

红松阔叶混交林中坑和丘的微立地特征及其对植被更新的影响

2011年8月,在红松阔叶混交林2.55 hm2的样地内,调查了42株倒木及其形成的坑和丘复合体的微立地特征及其植被更新状况,测定了丘顶、丘面、坑壁、坑底、完整立地5个微立地的土壤含水量、土壤温度、空气相对湿度和光合有效辐射.结果表明:在5个微立地中,丘顶的光合有效辐射最高(527.9μmol·m-2·s-1),完整立地最低(58.7 μmol·m-2·s-1);丘顶的土壤温度最高(16.0℃),坑底最低(13.3℃);坑底的土壤含水量最高(34.6％),丘面最低(0.5％);完整立地的空气相对湿度最高(75.9％),丘顶最低(68.0％).形成坑和丘复合体的5个树种的频率大小依次是红松(42.9％)＞云杉(31.0％)＞白桦(16.7％)＞冷杉(7.1％)＞稠李(2.4％).42株掘根倒木中,有2/3偏向西北方向.倒木体积与坑深度、坑长度、丘高度、丘宽度均呈极显著正相关,与丘厚度呈负相关.坑的宽度和长度分别与倒木的胸径呈显著和极显著正相关.不同微立地之间物种丰富度的大小顺序为完整立地＞坑＞丘;所有树种盖度的大小顺序依次为完整立地＞坑＞丘.     

Biomass of primary and secondary vegetation in Rondônia, Western Brazilian Amazon

Biomass estimates of primary and different ages of secondary vegetation are reported for a tropical forest region in Rondônia, Western Brazilian Amazon. The estimates are based on published allometric equations, and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18 years. Primary forest biomass estimates varied from 290 to 495 t ha^–1. Secondary vegetation biomass estimates accounted for 40–60% of the primary forest biomass after 18 years of abandonment. Secondary growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 t ha^–1 y^–1 between the third and the eighteenth years after abandonment. CO₂ sequestration by regrowing vegetation is discussed for two scenarios of land abandonment.