Vegetation asymmetry in Hawaii under the trade wind regime

Abstract. Interpretation of aerial photographs (1962–1965) revealed vegetation asymmetry on opposite valley slopes in the semi-arid to semi-humid zones of the island of Oahu. Field studies after 5 and 10 yr showed that this asymmetry is a transitional feature during recovery from disturbance (fire). The types of asymmetry ranged from difference in vigour of shrub canopies to total difference in floristic composition. Slopes exposed to the trade winds are typically characterized by grassy vegetation and landslides, whereas on the protected part of the upper west-facing slope immediately behind a ridge, vigorous shrubs and trees grow without any mechanical damage or deformation of crowns. This part of the slope is richer in species, including rare ones, than other parts. It is also characterized by the invasion of grasses from more exposed sites and the elongation of shrub canopies above the crest line. Different levels of exposure to exceptionally strong trade winds and salt spray at different parts of slopes seem to allow different speeds of recovery and thus contrasting vegetation structure and species composition. The existence of many shrub seedlings on the exposed upper slope suggests that succession is taking place and the vegetation asymmetry seems at least structurally to be a transitional feature.     

Vegetation structure in relation to micro-landform in an evergreen broad-leaved forest on Amami Ohshima Island,south-west Japan

The relationship between micro-landform and vegetation structure was studied in a plot that was established on a slope from the ridge to the valley bottom in an evergreen broad-leaved forest on Amami Ohshima Island, south-west Japan. Five micro-landform units recognized in the plot were grouped into the upper and lower slopes by their location in relation to the erosion front, and plant distributions and vegetation structure were compared between them. Although small trees with d.b.h. less than 10 cm occurred almost all over the plot, the occurrence of larger trees was limited mostly to the upper slope. Based on the spatial distribution pattern in the plot, woody species are classified into three groups: group A mostly or strictly confined to the upper slope; group B confined to the lower slope; and group C associated statistically with neither slope. A well-developed forest stand, whose dominant species wereCastanopsis sieboldii ssp.lutchuensis andSchima wallichii, was seen on the upper slope, whereas only a poorly developed stand was seen on the lower slope. The difference in stability of the land surface is likely to be the major cause of the observed differences in stand structure between the upper and lower slopes. It is suggested that the erosion front is important as a line demarcating different habitats within a slope from the ridge to the valley bottom.     

Variations in carbon source–sink relationships in subalpine fir across elevational gradients

• Cold‐adapted trees display acclimation in both carbon source and carbon sink capacity to low‐temperature stress at their upper elevational range limits. Hence a balanced carbon source–sink capacity might be required for their persistence and survival at the elevational tree limits.
• The present study examined the spatial dynamics of carbon source–sink relationship in subalpine fir (Abies fargesii) trees along elevational gradients in the northern slope of the temperate region and in the southern slope of the subtropics in terms of climate in the Qinling Mountain range, north‐central China.
• The results showed that non‐structural carbohydrate (NSC) concentrations in both the source and sink tissues increased with the increase in elevation. The ratio of carbon source–sink displayed a consistent decreasing trend with the increase in elevation and during growing season, showing that it was lowest at a ratio of 2.93 in the northern slope and at a ratio of 2.61 in the southern slope at the upper distribution elevations in the late growing season. Such variations of carbon source–sink ratio might be attributable to the balance between carbon source and sink activities, which changed seasonally across the elevational distribution range.
• We concluded that a ratio of carbon source–sink of at least 2.6 might be essential for subalpine fir trees to persist at their upper range limits. Therefore, a sufficient source–sink ratio and a balanced source–sink relationship might be required for subalpine fir trees to survive and develop at their upper elevational distribution limits.

     

Topographical pattern of the forest vegetation on a river basin in a warm-temperate hilly region,central Japan

The relationship between tree distribution and topography was examined in a small river basin (3.4 ha) comprising a complex mosaic of topographical units at 10² to 10³ m² order, each of which had a shallow valley bordered by small ridges or breaks of slopes. Twenty-five major woody species were divided into two groups (groups A and B) based on a cluster analysis using the distribution data in the basin. Group A, which mainly consisted of early-successional species, was distributed around the valley sites of the topographical units, while group B, which mainly consisted of late-successional species, was distributed around the ridge sites of the topographical units. This vegetation pattern coincided with erosional condition in the basin. That is, the valley sites were eroded more actively than the ridge sites, as soil depth tended to be thin in the valley sites and thick in the ridge sites, and because large (canopy) trees were restricted in the ridge sites. There was no tendency that group B was replacing group A, and hence it was suggested that repeated disturbance by slope failures or small-scale shallow landslides have prevented compositional change from the early-successional (group A) to the late-successional (group B) species by preventing the invasion of the latter into valley sites.     

南方红壤侵蚀区芒萁叶片对微地形的响应

植物功能性状可以反映植物应对环境变化的响应策略。该文以芒萁为研究对象,主要采用单因素方差分析和冗余分析,比较了3种微地形(沟脊、沟壁、沟底)中环境因子和芒萁叶片功能性状的差异,分析了芒萁对浅沟微地形的响应及其适应策略。结果表明:(1)芒萁叶片功能性状的总体变异程度在0.05～0.47之间,叶厚和叶面积均表现为沟底>沟壁>沟脊(P<0.05),沟壁的叶氮含量显著高于沟脊和沟底,沟脊的叶磷含量显著低于沟壁和沟底,比叶面积和叶碳含量在3种微地形间均无显著差异。(2)沟脊的芒萁通过减小叶面积来降低水分散失进行自我保护,沟壁的芒萁通过增加叶氮含量来提高叶片光合速率而促进生长,沟底的芒萁通过增大叶面积来提高光捕获能力而促进生长。综上结果认为,土壤养分和温湿条件的差异,促使芒萁通过调节营养物质含量和改变叶片形态以更好地适应环境。     

Fine‐scale habitat heterogeneity influences browsing damage by elephant and giraffe

Effects of large mammalian herbivores on woody vegetation tend to be heterogeneous in space and time, but the factors that drive such heterogeneity are poorly understood. We examined the influence of fine‐scale habitat heterogeneity on the distribution and browsing effects of two of the largest African terrestrial mammals, the elephant and giraffe. We conducted this study within a 120‐ha (500 x 2,400 m) ForestGEO long‐term vegetation monitoring plot located at Mpala Research Center, Kenya. The plot traverses three distinct topographic habitats (“plateau,” “steep slopes,” and “valley”) with contrasting elevation, slope, soil properties, and vegetation composition. To quantify browsing damage, we focused on Acacia mellifera, a palatable tree species that occurs across the three habitat categories. Overall tree density, species richness, and diversity were highest on the steep slopes and lowest on the plateau. Acacia mellifera trees were tallest and had the lowest number of stems per tree on the steep slopes. Both elephant and giraffe avoided the steep slopes, and their activity was higher during the wet season than during the dry season. Browsing damage on Acacia mellifera was lowest on the steep slopes. Elephant browsing damage was highest in the valley, whereas giraffe browsing damage was highest on the plateau. Our findings suggest that fine‐scale habitat heterogeneity is an important factor in predicting the distribution of large herbivores and their effects on vegetation and may interact with other drivers such as edaphic variations to influence local variation in vegetation structure and composition.     

Spatial variation in diurnal surface temperatures and the distribution and abundance of an alpine grasshopper

We studied the influence of spatial differences in diurnal surface temperatures due to topography on an alpine grasshopper (Aeropedellus clavatus). Temperature measurements on east-and west-facing alpine dry meadow slopes on Niwot Ridge in Colorado demonstrated a significant difference in diurnal surface temperatures between the two slopes throughout the growing season. A. clavatus body temperature was found to be highly correlated with nearby shaded surface temperature, and individual grasshoppers enclosed on the two slopes had significantly higher relative growth rates on the warmer east slope. Temperature effects were manifest at the population level as well. A. clavatus was significantly more abundant on the east-facing than on the west-facing slope, despite similar vegetation in both areas. This study contributes to our understanding of the myriad of factors governing insect distribution and abundance by attempting to integrate the physiological and ecological, abiotic and biotic, influences on both individuals and populations.     

Canopy damage to native vegetation on the central coast of New South Wales: Current status and detection of future changes

Abstract Canopy damage to coastal native vegetation was surveyed at Norah, Wybung and Wamberal Heads and at Little Beach on the central New South Wales coast in 1987. This preceded the commissioning of an ocean sewerage outfall at Norah Head in 1988, but postdated the commissioning of other outfalls in the region. Damage to the canopy of shrub species was assessed at the whole-plant level using a visual score. The method of scoring for canopy damage was tested for repeatability between observers; the average deviation between means was 5%, and the maximum deviation was 10% of the value of the mean. Mean per cent canopy damage scored for shrubs of various species at these sites ranged from negligible to very heavy. Comparison between sites and aspects was limited to Banksia integrifolia. Stands of this species on the southern side of Norah and Wybung Heads had approximately double the canopy damage of those on the northern side; this difference was significant. To confirm the patterns of damage seen at the whole-canopy level, the fate of tagged shoots of B. integrifolia was followed for 4 months. These shoots were also more damaged on the southern side than on the northern side of the two headlands. Analysis of wind speed and direction at Norah Head showed that the southern side of the headland received substantially more strong winds (>21 km h^?1) than the northern side. Airborne salt spray is known to be carried mainly in winds above this speed. In cases where 20 or more individuals of a species were found at a site, mathematical models relating the canopy damage of each plant to wind exposure, distance from the sea, and slope were investigated. Of 15 such cases, 13 significant models were found, with exposure being the major significant factor in accounting for variation in the data. Distance from the sea was only significant twice, and slope not at all. The pattern of damage, and its relationship to wind speed, direction, and exposure, are consistent with salt-spray being the major cause of leaf and shoot death at these sites. The sample sizes necessary to detect future changes of given magnitude to canopy damage were calculated.     

Plant neighbours mediate bird predation effects on arthropod abundance and herbivory

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Drought-resistant physiological characteristics of four shrub species in arid valley of Minjiang River, China

The formation of 161 km-long arid valley (170 km²) of Mingjiang River is attributed to the effect of foehn. The arid valley presents harsh conditions for the growth of vegetation, which include higher annual evaporation and transpiration rate (1400–2000 mm), lower annual precipitation rate (400–700 mm), steep slope, and infertile soils. Although the vegetation is dominated by xerophilous bushes and grasses, it plays a significant role in soil and water conservation in watershed and provides important references in the arid valley as it is very difficult to grow trees. Drought-resistant physiological characteristics of four native species, i.e., Sophora davidiana, Bauhinia faberi var. microphylla, Convolvulus tragacanthoides, and Artemisia gmelinii, have been measured. It was found that the content of chlorophyll, free proline and soluble sugars showed an increase, whereas evaporation ratio, WSD, RWC and cytolemma osmosis showed a decrease under drought stress. Integrated assessment of the four species indicated that the integrated drought resistance index was the highest in July (0.507), followed by September, August and June, whereas it was the lowest in May (0.442). The result provided a basis for vegetation restoration, especially it improved survival of planted species in May and June when plant species exhibit the weakest drought resistance.     

立地类型对张广才岭天然白桦林生态系统碳储量的影响

运用相对生长方程与碳/氮分析方法,测定了我国温带张广才岭7种立地类型(阳坡上、中、下坡位和阴坡上、中、下坡位及谷地)天然白桦林的生态系统碳储量(植被与土壤)及植被净初级生产力与年净固碳量,揭示立地类型对温带天然白桦林生态系统碳库及其固碳能力的影响规律。结果表明:1白桦林植被碳储量((76.28±18.11)—(115.57±5.59)t C/hm~2)在阴、阳坡的上坡位和下坡位显著高于谷地35.1%—51.5%(P0.05),阴、阳坡中坡位高于谷地但差异性不显著(32.5%—33.6%,P0.05);2其土壤碳储量((81.53±6.15)—(181.90±21.62)t C/hm~2)在阳坡各坡位显著高于阴坡中、下部与谷地24.0%—123.1%(P0.05),阴坡上、中部显著高于阴坡下部和谷地36.0%—81.2%(P0.05);3其生态系统碳储量((174.57±20.27)—(282.96±17.92)t C/hm~2)在阳坡各坡位显著高于阴坡中、下坡位与谷地14.1%—62.1%(P0.05),阴坡上、中坡位显著高于阴坡下坡位与谷地19.5%—48.1%(P0.05);4其植被净初级生产力((6.98±1.60)—(9.59±0.69)t hm~(-2)a~(-1))在阴、阳坡上坡位显著高于阴坡中坡位34.2%—37.4%(P0.05),其他4个立地类型高于阴坡中坡位但差异性不显著(8.5%—20.6%,P0.05);5其年净固碳量((3.26±0.74)—(4.56±0.36)t C hm~(-2)a~(-1))在阳坡上坡位显著高于阴坡中坡位39.9%(P0.05),其他5个立地类型高于阴坡中坡位但差异性不显著(9.2%—30.4%,P0.05)。因此,张广才岭天然白桦林的生态系统碳储量及其固碳能力均存在着明显的立地分异规律性,故在评价与管理我国温带白桦林碳汇时应考虑立地类型影响。     

Mountains and their ecotones increase landscape heterogeneity and maintain a unique assemblage of grasshoppers in the southern Kalahari

1. South Africa is a megadiverse country. Here, natural communities are unevenly distributed across, and within, seven distinct biomes. In such heterogeneous landscapes, understanding spatial patterns of biodiversity is essential for planning and implementing efficient conservation measures.
2. The southern Kalahari, forming part of South Africa's savanna biome, is an arid region of peculiarly high diversity and endemism. The responses of orthopteran assemblages to changing environmental conditions across the Kalahari were investigated by comparing alpha and beta diversity levels across discrete vegetation types in the Tswalu Kalahari Reserve. The degree of association between species and specific vegetation types were also studied and how a key life history trait - dispersal ability – influences community composition was determined.
3. This study identified 46 grasshopper species within the reserve, which compares well with richness levels in other more productive habitats of the country. Local (alpha) diversity was higher in mountain and mountain-ecotone sites versus vegetation types on the plains, and species turnover was also exceptionally high – approaching 100% - across these two groups. The few (3) dispersal limited species recovered were associated only with the mountain-ecotone group, with emergent dominance patterns suggesting that competitive rather than dispersal abilities determine the species composition of unique assemblages in the landscape.
4. Topology plays a key role in maintaining spatial diversity across the southern Kalahari landscape. Mountains, and their ecotones, promote not only species turnover, but also richness and functional diversity. These can be viewed as islands of diversity, and should be targeted priority areas for conservation beyond the boundaries of protected areas.

     

The relationships between vegetation type and topography in Lassen Volcanic National Park

The relationships between topographic features and the relative abundances of vegetation types were analyzed for the mid-montane conifer forests, the upper montane conifer forests and the alpine areas of Lassen Volcanic National Park in the Cascade Range of northern California using Landsat Thematic Mapper data. Vegetation types were identified from Landsat Thematic Mapper data and included pine, fir, montane chaparral, willow/alder and herbaceous communities. Topographic features including aspect, slope steepness, slope configuration (i.e., convex, straight or concave) and slope position (i.e., ridge top to valley bottom) were computed from USGS Digital Elevation Models. The distribution of montane chaparral was consistent with its dependency on fire with chaparral communities being more abundant on more xeric aspects and on steeper and more xeric slope configurations. Slope position was important in determining the distribution of willow/alder communities which were more abundant in valley bottom locations. Both slope steepness and slope position affected the abundance of herbaceous communities. Herbaceous communities were: (1) more prevalent on steeper slopes due to the distribution of dicotyledonous forb species; and (2) more abundant in valley bottoms due to the distribution of monocotyledonous species in wet meadows. Pines and firs were separated along a gradient of slope steepness with the firs being more abundant on steep slopes and the pines being more abundant on shallow slopes. In the alpine areas above 2350 m, the abundance of most vegetation types declined with increasingly mesic aspects. This decline may be related to the prolonged persistence of snow in areas of less intense solar radiation.     

Plant-parasitic Nematodes in Loess Toposequences Planted with Corn

Populations of plant-parasitic nematodes in an Iowa cornfield were studied along north- and west-facing toposequences. Samples were collected monthly during the growing season. The greatest biomass for Xiphinema americanum occurred at the footslope on the north face. Paratylenchus microdorus had its greatest biomass at the summit position, generally more in the west- than in the north-facing slope. Pratylenchus spp. in the roots peaked at the toeslope in the north-facing slope, but at the footslope in the west-facing slope. Helicotylenchus pseudorobustus peaked at the backslope and the toeslope along the north- and west-facing slopes, respectively. Diversity, as computed for each plot by the Shannon-Weiner diversity index, was highest at the backslope in both toposequences.     

Oviposition site preference of Barbitistes vicetinus (Orthoptera,Tettigoniidae) during outbreaks

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Seasonal variation in the rate of evaporative water loss in the kangaroo rat,Dipodomys panamintinus

• 1.1. Evaporative water loss was measured as a function of temperature, season and grouping in the kangaroo rat, Dipodomys panamintinus for a one year period.
• 2.2. Three groups of Panamint kangaroo rats were set up and studied during the various changes in season. The three groups were designated as field, exposed and control. These groups revealed the effects of acclimatization, captive acclimatization and laboratory acclimatization respectively.
• 3.3. There is a highly significant difference in the rate of evaporative water loss in the Field Panamint kangaroo rats during the Fall, Winter and Spring.
• 4.4. In general, the quantity of water loss via evaporation was higher in the female Panamint kangaroo rats.
• 5.5. Water loss via evaporation in the control and exposed groups was least affected by seasonal change.
• 6.6. In comparison to the other two groups, the field male and female Panimint kangaroo rats possessed the highest slope (rate) and mean (quantity) for all seasons.
• 7.7. The combined effect of both grouping and season affects both the rate and quantity of evaporative water loss in the Panamint kangaroo rat.

     

Oceanic thermal structure mediates dive sequences in a foraging seabird

1. Changes in marine ecosystems are easier to detect in upper‐level predators, like seabirds, which integrate trophic interactions throughout the food web.
2. Here, we examined whether diving parameters and complexity in the temporal organization of diving behavior of little penguins (Eudyptula minor) are influenced by sea surface temperature (SST), water stratification, and wind speed—three oceanographic features influencing prey abundance and distribution in the water column.
3. Using fractal time series analysis, we found that foraging complexity, expressed as the degree of long‐range correlations or memory in the dive series, was associated with SST and water stratification throughout the breeding season, but not with wind speed. Little penguins foraging in warmer/more‐stratified waters exhibited greater determinism (memory) in foraging sequences, likely as a response to prey aggregations near the thermocline. They also showed higher foraging efficiency, performed more dives and dove to shallower depths than those foraging in colder/less‐stratified waters.
4. Reductions in the long‐term memory of dive sequences, or in other words increases in behavioral stochasticity, may suggest different strategies concerning the exploration–exploitation trade‐off under contrasting environmental conditions.

     

Dust accumulation due to anthropogenic impact induces anatomical and photochemical changes in leaves of Centranthus ruber growing on the slope of the Vesuvius volcano

• In Mediterranean ecosystems, some natural areas are exposed to severe anthropogenic impact. Especially in summer, the considerable number of tourists visiting such areas, often with vehicles, causes deposition of dust over the vegetation due to formation of powder clouds, also favoured by wind erosion, high temperature, low precipitation and incoherent soil structure. The main aim of this study was to analyse whether the deposition of dust can induce changes in leaf anatomical functional traits and in the efficiency of photosynthetic apparatus in Centranthus ruber, a species widespread in Mediterranean ecosystems.
• Leaf morpho‐functional traits were quantified in plants growing at sites characterised by high (HD) and low (LD) dust deposition, in periods with high anthropogenic impact. Analyses included quantification of chlorophyll fluorescence emission parameters, photosynthetic pigment concentration as well as stomatal size and frequency, leaf lamina thickness, quantification of intercellular spaces and phenolics in the mesophyll through microscopy.
• The overall analysis suggested that the different conditions of dust deposition induced different adjustment of morpho‐functional traits in leaves of C. ruber. High dust deposition shielded the leaf lamina, protecting the photosynthetic apparatus from excess light and favoured plant photochemical efficiency. Leaves exposed to low dust deposition showed higher accumulation of phenolic compounds, protecting chloroplast membranes and characterised by high thermal dissipation of excess light.
• Such adaptive phenomena can affect vegetation dynamics due to possible different species‐specific plant responses, resulting in different plant competitiveness under the limiting conditions of Mediterranean environments.

     

Effects of NaCl stress on seed germination and seedling development of Brassica insularis Moris (Brassicaceae)

• Brassica insularis is a protected plant that grows on both coastal and inland cliffs in the western Mediterranean Basin. The objective of this study was to test if any variability exists in the salt stress response during seed germination and seedling development in this species relative to its provenance habitat.
• Variability among three populations in the salt stress effects on seed germination and recovery under different temperatures was evaluated. The effect of nebulisation of a salt solution on seedling development was evaluated between populations growing at different distances from the sea.
• Seeds of B. insularis could germinate at NaCl concentrations up to 200 mm . Seed viability was negatively affected by salt, and recovery ability decreased with increasing temperature or salinity. Inter‐population variability was detected in salt response during the seed germination phase, as well as in seedling salt spray tolerance. The inland population seedlings had drastically decreased survival and life span and failed to survive to the end of the experiment. In contrast, at least 90% of the coastal seedlings survived, even when sprayed at the highest frequency with salt solution.
• This study allowed investigation of two natural factors, soil salinity and marine aerosols, widely present in the B. insularis habitat, and provided the first insights into ecology of this protected species and its distribution in the Mediterranean. These results might be useful in understanding the actual distributions of other species with the same ecology that experience these same abiotic parameters.

     

Coexistence mechanisms of evergreen,deciduous and coniferous trees in a mid-montane mixed forest on Mt. Emei,Sichuan, China

Structure and regeneration of a mid-montane (2200 m a.s.l.)mixed forest codominated by evergreen (Lithocarpuscleistocarpus), deciduous (Acer flabellatum)andconiferous (Tsuga chinensis, Abies fabri, andTaxus chinensis) trees were analyzed in a 40m× 60 m plot on Mt. Emei, Sichuan, China. Plant communitystructure and composition varied depending on topographic micro-habitat withinthe plot. Four topographic communities (topo-communities) were distinguishedwith dominant species corresponding to topography: (1)Abies – valley bank, (2) Acer– lower steep slope, (3) Lithocarpus – uppergentle slope, and (4) Tsuga – ridge. The coexistencemechanisms of the evergreen, deciduous, and coniferous trees were determined byidentifying the regeneration process characteristic of each dominant species,asrepresented by their seedling dispersion patterns and seedling establishmentalong the topographic gradients. The saplings and seedlings of the dominantswere distributed differently according to the topography:Lithocarpus under the canopy of parent trees and in gapsofthe upper gentle slope and ridge, Acer mainly in bothwell-lit and shady sites on the lower steep slope and on fallen logs,Abies on the valley bank but only in well-lit sites,Tsuga on the ridge, Taxus mostly onrock and well-lit sites on the slopes. Distribution of surviving saplings andseedlings was also related to the species of nearby canopy trees. We suggestthat Lithocarpus, Tsuga and Acer tendto be self-replacing in their own topographic habitats, andAbies survives as a fugitive by occupying occasionalsuitable gaps. The variation in soil conditions, particularly nutrients, withtopography affected seedling establishment and the growth of trees. Thesuccessional change of quantitative species composition, as predicted by theMarkovian model, shows the mixed forest to be in a sustained climax stage.