Root distribution at various distances from clove trees growing in Indonesia

Efficient fertilizer application requires an understanding of the distribution of roots and soil nutrients in the soil profile. Cultural practices for clove trees in Indonesia has resulted in phosphorus (P) fertilizer being applied at the canopy edge; however, in these high P fixing soils efficient P fertilizer application should occur with the highest root densities. The objective of this study, therefore, was to determine the rooting distribution at various distances from the tree and soil depths for clove (Eugenia aromatica OK; variety Zanzibar) trees growing on an Andosol soil at Modoinding, Indonesia. Root distributions were determined to a 100-cm soil depth using soil cores at 0.5, 1.0 and 1.5 times the canopy radius for five 10-year-old clove trees grown on either level terrain or 23% slopes. Clove root length and weight densities decreased with soil depth and distance from the tree base. Fine clove roots (1 mm dia) comprised 72% of the total root length and was three to five times higher underneath the canopy than that outside the canopy. Roots were concentrated in the upper soil horizons; however, up to 36% of the total root length was found at a depth of 50–100 cm. Clove roots for trees growing at the level landscape position had the highest root length densities. Intercropped species root length densities were higher than clove root length densities at 1.5 times the canopy radius whereas intercropped root weight densities were higher than that for clove roots at both 1.5 and 1 times the canopy radius. Results suggest that fertilizer applications should be placed closer to the tree trunk rather than at the canopy edge to maximize P uptake by clove roots.     

Persistence of tree related patterns in soil nutrients following slash-and-burn disturbance in the tropics

Individual trees are known to influence soil chemical properties, creating spatial patterns that vary with distance from the stem. The influence of trees on soil chemical properties is commonly viewed as the agronomic basis for low-input agroforestry and shifting cultivation practices, and as an important source of spatial heterogeneity in forest soils. Few studies, however, have examined the persistence of the effects of trees on soil after the pathways responsible for the effects are removed. Here, we present evidence from a Mexican dry forest indicating that stem-related patterns of soil nutrients do persist following slash-and-burn removal of trees and two years of cropping. Pre-disturbance concentrations of resin extractable phosphorus (P), bicarbonate extractable P, NaOH extractable P, total P, total nitrogen (N) and carbon (C), KCl extractable nitrate (NO₃ ^-), and net N mineralization and nitrification rates were higher in stem than dripline soils under two canopy dominant species of large-stemmed trees with contrasting morphologies and phenologies (Caesalpinia eriostachys Benth. and Forchhammeria pallida Liebm.). These stem effects persisted through slash burning and a first growing season for labile inorganic and organic P, NaOH inorganic P, and plant-available P, and through a second growing season for labile organic P, NaOH organic P, and plant-available P. While stem effects for extractable NO₃ ^-, net nitrification rates, total N and C disappeared after felling and slash burning, these stem effects returned after the first growing season. These results support the view that tree-influenced patterns of soil nutrients do persist after tree death, and that trees contribute to the long-term spatial heterogeneity of forest soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Scattered trees as modifiers of agricultural landscapes: the role of waddeessa (Cordia africana Lam.) trees in Bako area, Oromia, Ethiopia

Scattered trees in general and scattered waddeessa (Cordia africana Lam.) trees in particular are very common across the agricultural landscapes in Oromia, Ethiopia. A study on this scattered waddeessa trees commonly growing on farmers' agricultural fields was conducted at Bako in western Oromia, Ethiopia with the objective of assessing their role in modifying the soil properties in the agricultural landscape. Soil samples from surface layers (0–10 cm) were taken at three concentric transects (0.5, 2 and 4 m) around the tree and compared with soil samples from the adjacent open areas (15 m distance from the tree), and then analysed following the standard procedures. Results showed that scattered waddeessa trees significantly modified the overall properties of the soil in the agricultural landscape of Bako area. But soil texture was not affected, indicating that it is more related to parent material than the tree influence. Hence, the soil patches observed under these waddeessa trees can be important local nutrient reserves that may influence the rural agricultural landscape. They also play an important role in generating local household income from the sale of products and conserving biodiversity by providing habitats and resources that are otherwise absent or scarce in agricultural landscape.     

Effects of tree clumps on soil characteristics in a humid savanna of West Africa (Lamto,Côte d'Ivoire)

The effect of tree clumps on soil characteristics was investigated in a humid savanna (Lamto, Côte d'Ivoire). Soil texture and field capacity were not significantly different under tree clumps compared to open grassland. On the other hand, bulk density was lower under tree clumps, likely due to a greater soil fauna activity under the trees. The pH, available phosphorus, cation exchange capacity, total carbon and total nitrogen contents were higher under tree clumps due to greater organic matter input beneath canopies. Potential soil respiration and mineral nitrogen accumulation were also enhanced, indicating a higher potential microbial activity under tree clumps. Soil water content was slightly lower beneath canopies (from July to November only between 0 and 10 cm depth) when soil moisture was above field capacity. During the other months, no significant difference was measured.     

云冷杉林林隙内倒木腐烂等级及其形成的微立地类型对土壤理化性质的影响

为揭示倒木腐烂等级及其形成的微立地类型对土壤理化性质的影响,分析了小兴安岭凉水国家级自然保护区谷地云冷杉林由倒木形成的林隙内不同腐烂等级倒木形成的3种微立地(丘顶、坑底和倒木下)的土壤理化性质(容重、毛管孔隙度、总孔隙度、毛管持水量、饱和持水量、土壤有机碳、全氮、全磷、有效磷、速效钾和pH值)和化学计量特征(C/N、N/P和C/P)的差异.结果表明: 倒木腐烂等级对土壤物理性质的影响不显著,而倒木形成的微立地类型对其影响显著.除土壤饱和持水量外,倒木下的其他土壤物理性质均最好,坑底最差;随着倒木腐烂等级的上升,除有效磷外的其他土壤养分含量呈显著上升趋势;3种微立地中,坑底土壤养分含量最低,pH最高;随倒木腐烂等级的上升,3种微立地浅层土壤C/N、N/P和C/P下降,而丘顶和坑底深层土壤C/N上升,N/P和C/P下降,C/P的变化趋势与土壤有效磷的一致.综上,随倒木腐烂等级的提高,土壤养分含量显著增加,且不同类型微立地之间差异明显,其中坑底始终最低.     

Hip holes: kangaroo (Macropus spp.) resting sites modify the physical and chemical environment of woodland soils

Abstract Hip holes are shallow, reniform‐shaped depressions found next to the trunks of many trees and shrubs in arid and semi‐arid Australia. They are constructed by kangaroos (Macropus spp.), who use them as diurnal resting sites, particularly during hot weather. Physical and chemical properties of soils in hip holes were compared with non‐hole microsites adjacent to the trunk (‘trunk’), microsites below the canopy (‘canopy’) and microsites out in the open (‘open’) under two trees (Eucalyptus intertexta, Alectryon oleifolius) and one shrub (Dodonaea viscosa) in a semi‐arid woodland in eastern Australia. Overall, there were few effects under D. viscosa apart from a greater (10‐fold) mass of litter in the hip holes compared with the trunk microsite. Hip holes under E. intertexta and A. oleifolius, however, contained six times more dung compared with the trunk microsite. For the two tree species, soils in the hip holes were significantly more erodible, as measured by aggregation levels, compared with the other microsites, but there were no significant differences in bulk density nor pH. Steady‐state infiltration rates at the hip hole and trunk microsites were significantly greater than those in the open, but there was no significant hip hole effect. Soils in the hip holes contained greater levels of exchangeable calcium and magnesium (E. intertexta) and greater exchangeable sodium (A. oleifolius) compared with trunk microsites. Hip holes under E. intertexta contained approximately 68% more organic carbon, total carbon and nitrogen, and 86% more sulfur compared with trunk microsites. Similarly, hip holes under A. oleifolius contained on average 38% more organic and total carbon, and 47% more nitrogen than trunk microsites. Given the density of hip holes and their impact on soil chemistry, kangaroos are considered to be important elements in the maintenance of heterogeneity in these woodlands.     

Unusual Fine Root Distributions of Two Deciduous Tree Species in Southern France: What Consequences for Modelling of Tree Root Dynamics?

The spatial distribution of fine roots of two deciduous tree species was investigated in contrasting growing conditions in southern France. Hybrid walnut trees (Juglans regia×nigra cv. NG23) and hybrid poplars (Populus euramericana cv. I214) were both cultivated with or without annual winter intercrops for 10 years on deep alluvial soils. Soil samples for measuring the fine root distribution of both trees and crops were obtained by soil coring down to 3-m depth at several distances and orientations from the tree trunk. The distribution of live fine roots from walnut and poplar trees was patchy and sometimes unexpected. In the tree-only stands, fine root profiles followed the expected pattern, as fine root density decreased with increasing depth and distance from the tree trunk. However, many fine root profiles under intercropped trees were uniform with depth, and some inverse profiles were observed. These distributions may result from a high degree of plasticity of tree root systems to sense and adapt to fluctuating and heterogeneous soil conditions. The distortion of the tree root system was more pronounced for the walnut trees that only partially explored the soil volume: in the tree-only stand, the walnut rooting pattern was very superficial, but in the intercropped stand walnut trees developed a deep and dense fine root network below the crop rooting zone. The larger poplars explored the whole available soil volume, but the intercrop significantly displaced the root density from the topsoil to layers below 1 m depth. Most tree root growth models assume a decreasing fine root density with depth and distance from the tree stem. These models would not predict correctly tree–tree and tree–understorey competition for water and nutrients in 3D heterogeneous soil conditions that prevail under low-density tree stands. To account for the integrated response of tree root systems to such transient gradients in soils, we need a dynamic model that would allow for both genotypic plasticity and transient environmental local soil conditions.     

Effect of annual variation in soil pH on available soil nutrients in pear orchards

Soil pH is an important factor affecting the availability of soil nutrients that impact plant growth. Given the susceptibility of soil pH to excessive fertilization and the widespread use of manures, it is essential to examine the influence of soil pH on the distribution and availability of soil nutrients. We sampled and analyzed brown soils from pear orchards in thirteen towns in Wendeng county. Samples were obtained from areas along or between rows of trees at specified distances and depths. The results showed that the soil pH fluctuated from 4.06 to 6.59 in October 2008 and from 4.24 to 7.57 in April 2009. The quantity of soil samples with pH below 5.50 increased by 34.6%. Analysis of the soil pH for samples obtained along the rows of trees showed that the pH decreased as the depth increased (except for the range 5.5 to 6.0); soil pH in the samples obtained between the rows of trees demonstrated different trends. The average organic matter (O.M.) content as well as the N (NH₄⁺) and available P, K, Cu, Zn, Fe, and Mn contents in the samples collected in October 2008 were higher than those observed in April 2009. Conversely, the values for other available nutrients were lower than those in the samples collected in April 2009. The available nutrients and organic matter (O.M.) content in different pH ranges varied. The soil pH was significantly or very significantly correlated with N (NH₄⁺ and NO₃^-), available K, Cu, Fe, and exchangeable Ca for the October 2008 samples, while a significant or very significant correlation existed between N (NH₄⁺), available P, Zn, exchangeable Ca, and exchangeable Mg for the April 2009 samples. The correlations between soil pH and the amounts of available nutrients and organic matter (O.M.) along the rows of trees in September 2009 were nearly consistent with those between the rows.     

Effect of annual variation in soil pH on available soil nutrients in pear orchards

Soil pH is an important factor affecting the availability of soil nutrients that impact plant growth. Given the susceptibility of soil pH to excessive fertilization and the widespread use of manures, it is essential to examine the influence of soil pH on the distribution and availability of soil nutrients. We sampled and analyzed brown soils from pear orchards in thirteen towns in Wendeng county. Samples were obtained from areas along or between rows of trees at specified distances and depths. The results showed that the soil pH fluctuated from 4.06 to 6.59 in October 2008 and from 4.24 to 7.57 in April 2009. The quantity of soil samples with pH below 5.50 increased by 34.6%. Analysis of the soil pH for samples obtained along the rows of trees showed that the pH decreased as the depth increased (except for the range 5.5 to 6.0); soil pH in the samples obtained between the rows of trees demonstrated different trends. The average organic matter (O.M.) content as well as the N (NH₄⁺) and available P, K, Cu, Zn, Fe, and Mn contents in the samples collected in October 2008 were higher than those observed in April 2009. Conversely, the values for other available nutrients were lower than those in the samples collected in April 2009. The available nutrients and organic matter (O.M.) content in different pH ranges varied. The soil pH was significantly or very significantly correlated with N (NH₄⁺ and NO₃^-), available K, Cu, Fe, and exchangeable Ca for the October 2008 samples, while a significant or very significant correlation existed between N (NH₄⁺), available P, Zn, exchangeable Ca, and exchangeable Mg for the April 2009 samples. The correlations between soil pH and the amounts of available nutrients and organic matter (O.M.) along the rows of trees in September 2009 were nearly consistent with those between the rows.     

Influence of scattered paddock trees on surface soil properties: A study of the Northern Tablelands of NSW

Summary Surface soil conditions were assessed under three tree species on a property near Armidale on the Northern Tablelands of NSW. In both a stocked and adjacent destocked paddock, five trees each of three eucalypt species: Eucalyptus melliodora, Eucalyptus blakelyi and Eucalyptus nova‐anglica, were selected. Soil samples were collected (depth 0–10 cm) along transects 20 m in length running from beneath the tree canopy progressively outwards into the open paddock. Six additional transects were also sampled outside the influence of the trees. Soil properties at a distance from the trees differed little between the stocked and destocked paddock with only a slight acidification in the stocked paddock. However, soil properties around the scattered trees showed considerable variation between stocked and destocked equivalents and most notably in a systematic pattern with distance from the trees themselves. For example, bulk density increased significantly, whereas soil pH, carbon, nitrogen and extractable phosphorus contents all decreased significantly with distance from the trees. However, stocking and camping had modified some of these soil properties. In the stocked paddock, the systematic change in nitrogen and phosphorus with distance from the trees was less clear and the degree of dispersion of the data was largest at the most heavily camped site. In this paddock, bulk density was also generally higher whereas pH, carbon and nitrogen contents were lower compared with the destocked equivalent. Extractable phosphorus content was also higher around the trees in the stocked paddock especially where camping activity was most intense. It is concluded that, although animal camping can modify their effects, scattered trees have a beneficial effect on soil properties and in this respect they have value in the grazing system from a soil conservation perspective.     

Litterfall and associated nutrient pools extend beyond the canopy of scattered eucalypt trees in temperate pastures

Scattered paddock trees are a keystone feature of temperate grazing landscapes of Australia. However, our understanding of their influence on their immediate environment, and specifically the spatial distribution and characteristics of litter, is still limited. Here, we quantified the spatial pattern of litter around 4 Eucalyptus species (Eucalyptus melliodora A. Cunn. Ex Schauer, E. viminalis Labill., E. blakelyi Maiden and E. michaeliana Blakely) in grazing landscapes on the Northern Tablelands of NSW, Australia. We examined the effect of species and soil parent material (basalt, granite and meta-sediments) on litter chemistry and chemical pools. Between 54–145 kg of litter was found around individual trees and litter density consistently declined with distance from the tree (330 g.m^?2 in the inner canopy to 4 g.m^?2 in the open paddock). However, an equivalent quantity of litter was found beneath and beyond the canopy indicating that a large quantity of the litter and nutrients fell beyond the edge of the canopy. Overall, leaf litter accounted for 23 to 34% of litterfall and had larger nutrient concentrations and pools than bark or stick litter. Most litter nutrients concentrations were independent of tree species or parent material but our results suggest that P, K and S were removed in foliage prior to abscission whilst Ca and Fe concentrations increased. The spatial patterns of litter distribution around scattered trees coincide with spatial patterns in soil properties that are frequently observed in these environments, and provide strong evidence of a significant link between these factors. Our results suggest that the removal of scattered trees from pastoral landscapes in this region of Australia will result in the loss of a significant litter input to the soil surface and will diminish this potentially important source of soil nutrients.     

Distribution of resting spores of the Lymantria dispar pathogen Entomophaga maimaiga in soil and on bark

Cadavers of late instar Lymantria dispar (gypsy moth) larvae killed by the fungal pathogen Entomophaga maimaiga predominantly contain resting spores (azygospores). These cadavers frequently remain attached to tree trunks for several weeks before they detach and fall to the ground. Density gradient centrifugation was used to quantify resting spores in the soil and on tree bark. Titers of resting spores were extremely high at 0–10 cm from the base of the tree and the number decreased with distance from the trunk of the tree. Titers were also highest in the organic layer of the soil with numbers decreasing precipitously with increasing depth in the soil. While resting spores were obtained from tree bark, densities per unit area were much lower than those found in the organic soil layer at the base of the tree. Field bioassays were conducted with caged L. dispar larvae to compare infection levels with distance from the tree trunk as well as on the trunk. Highest infection levels were found at 50cm from the tree base with lowest infection on the tree trunk at 0.5 m height, although we expected the highest infection levels among larvae caged at the bases of trees, where highest spore titers occurred. Laboratory experiments demonstrated that L. dispar larvae exposed to resting spore- bearing soil at the soil surface became infected while larvae exposed to soil with resting spores buried at least 1 cm below the surface did not become infected.     

Formation of nutrient‐poor soil patches in a semi‐arid woodland by the European rabbit (Oryctolagus cuniculus L.)

Abstract European rabbits (Oryctolagus cuniculus L.) occur over large areas of eastern Australia, where they disturb significant quantities of soil while constructing warrens. Although the effects of rabbits on vegetation are generally well understood, little is known about their effects on soil physical or chemical properties. We studied the effect of rabbit warrens on soil chemistry in a semi‐arid woodland supporting a high density of rabbit warrens. Within one large warren, we examined nutrient concentrations within three microsites (mound, inter‐mound and an intermediate disturbed area) representing a gradient of increasing rabbit disturbance, and supported this with a study of soil nutrients with depth within 1‐m‐deep trenches through five warrens. Landscape‐level changes in surface chemistry were also examined at an additional 23 warrens. At both patch and landscape scales, pH, electrical conductivity, soluble and exchangeable Ca²⁺ and K⁺, and total Al and Ca generally increased with increasing rabbit disturbance, while total C and S (LECO), total P and S (ICP), and soluble Na⁺ declined, and total N remained unchanged. Although chemical changes with depth were generally ill defined, surface soils tended to be more similar in their composition than deeper soils. Overall, our results reinforced the view that rabbits have a negative effect on surface soils in semi‐arid woodlands, and suggested that restoration of the original woodland vegetation may be hampered by changes in soil biogeochemistry associated with the warrens.     

西安附近苹果林地的土壤干层

根据西安附近苹果林下土壤含水量测定,研究了0~6m之间土壤含水量的变化与土壤干层问题。资料表明,西安附近15龄苹果林下2~3.5m深处土壤含水量为9.1%~9.2%,形成了发育弱的长期性土壤干层,10龄苹果林地2~4m深处也有干层发育,表明黄土高原的土壤干层分布已达黄土高原南部的关中地区;6龄苹果林下土壤有干化的显示,但无干层发育。分析得出,由降水少量决定的、埋藏深度小而厚度大的薄膜水带的存在是引起土壤干层发育的直接作用的因素。土壤干层的出现会引起土壤与植被的退化,应当避免严重的土壤干层出现。     

Savanna tree influence on understory vegetation and soil nutrients in northwestern Kenya

Abstract. Contrary to observations and models in which trees and herbaceous plants are viewed as competitors, we found that trees in an African savanna have positive impacts on herbaceous biomass production and composition, and on soil nutrient status. In the Turkana District of northwestern Kenya, we investigated vegetation and soil gradients along equi-angular transects radiating from the boles of individual Acacia tortilis trees. Total herbaceous biomass averaged 260 ± 17(se) g/m² at the bole and declined to 95 ± 8 g/m² in the tree interspaces. Soil organic carbon and total nitrogen concentrations were greatest (0.72 % and 0.083 %, respectively) in shallow soils near the bole and declined rapidly toward the interspaces and with increasing depth. Transects were also established between tree pairs to assess effects of differential canopy proximities. Grass production averaged 220 ± 21 g / m² below overlapping canopies, 150 ± 15 g / m² under individual canopies, and 95 ± 8 g / m² in interstitial areas. Detrended correspondence analysis revealed that shifts in species composition were correlated with distance from tree bole out to the edge of the canopy. Species response, in terms of relative cover, to increasing distance from the bole, seemed to fall into five general classes: 1) greatest at the bole, 2) increasing with distance from the bole, 3) greatest in the mid canopy zone, 4) least at the bole and 5) no response. Trees did not influence herbaceous compositionbeyondtree canopies. It is assumed that shade cast by the tree canopy with subsequent reductions of understory water stress and temperature and increased nutrient concentrations may be the most important factors affecting understory soil and vegetation.     

Accumulation of carbon and nitrogen by old arable land reverting to woodland

The accumulation of carbon (C) and nitrogen (N) was measured on two sites on Rothamsted Farm that had been fenced off some 120 years ago and allowed to revert naturally to woodland. The sites had previously been arable for centuries. One had been chalked and was still calcareous; the other had never been chalked and the pH fell from 7.1 in 1883 to 4.4 in 1999. The acidic site (Geescroft wilderness) is now a deciduous wood, dominated by oak (Quercus robor); the calcareous site (Broadbalk wilderness) is now dominated by ash (Fraxinus excelsior), with sycamore (Acer pseudoplatanus) and hawthorn (Craetagus monogyna) as major contributors. The acidic site gained 2.00 t C ha^?1 yr^?1 over the 118‐year period (0.38 t in litter and soil to a depth of 69 cm, plus an estimated 1.62 t in trees and their roots); the corresponding gains of N were 22.2 kg N ha^?1 year^?1 (15.2 kg in the soil, plus 6.9 kg in trees and their roots). The calcareous site gained 3.39 t C ha^?1 year^?1 over the 120‐year period (0.54 t in the soil, plus an estimated 2.85 t in trees and roots); for N the gains were 49.6 kg ha^?1 yr^?1 (36.8 kg in the soil, plus 12.8 kg in trees and roots). Trees have not been allowed to grow on an adjacent part of the calcareous site. There is now a little more C and N in the soil from this part than in the corresponding soil under woodland. We argue from our results that N was the primary factor limiting plant growth and hence accumulation of C during the early stages of regeneration in these woodlands. As soil organic N accumulates and the sites move towards N saturation, other factors become limiting. Per unit area of woodland, narrow strips; that is, wide hedges with trees, are the most efficient way of sequestering C – provided that they are not short of N.     

Invasion and persistence of bird-dispersed,subtropical thicket and forest species in fire-prone coastal fynbos

Abstract. Seedling abundance at four microsites (open fynbos, beneath emergent fynbos shrubs, beneath thicket, and beneath forest) was determined at three coastal dune landscapes, located along a gradient of increasing summer rainfall and where fire-dependent fynbos was the predominant vegetation. At all sites thicket seedlings were most common beneath emergent fynbos shrubs and under thicket clumps; seedlings of forest species were most abundant at forest microsites although some individuals were recorded beneath thicket. Very few thicket seedlings were observed in open fynbos. Birds play a keystone role in facilitating establishment of the fleshy fruit-bearing thicket flora. Seedling abundance at microsites of different thicket and forest species was generally unrelated to fruit abundance. Germination success of most species was highest under shaded conditions; soil organic content had no effect on germination. Removal of pulp and birdingestion enhanced the germination, relative to untreated controls, of two out of three species tested. A simple Markov model predicted a gradual increase in cover of the thicket and forest component and a gradual decline in fynbos under a ‘normal’ (20-yr interval) fire regime simulated over 10 cycles. Although inter-fire seedling establishment under emergent fynbos shrubs is important in the initial colonisation of fynbos by obligate resprouting thicket shrubs, these species persist and expand by vegetative recruitment after and between fires, respectively. In the prolonged absence of fire, the endemic-rich and fire-dependent fynbos flora would be replaced by species-poor forest and thicket.     

Spatial variability of soil nutrients and microbiological properties after the establishment of leguminous shrub Caragana microphylla Lam. plantation on sand dune in the Horqin Sandy Land of Northeast China

The objective of this study is to determine the spatial variability of nutrients, microbial biomass, and enzyme activities of soil due to the establishment of shrub plantation on moving sandy dunes, as part of an effort to understand the microenvironmental factors that control the soil microbiological properties. Caragana microphylla Lam., an indigenous leguminous shrub, is the dominant plant species used to control desertification in the semi-arid Horqin Sandy Land of Northeast China. In a 26-year-old C. microphylla plantation, soil samples were collected from three soil depths (0-5 cm, 5-10 cm, and 10-20 cm), three slope positions (windward slope, top slope, and leeward slope), and two microsites (under shrubs and between shrubs). The results showed significant differences in soil EC, nutrient content (except for total K), microbial biomass C and N, and the activities of dehydrogenase, urease, and protease at different slopes, soil depths, and microsites. Significant differences in pH at different microsites and slopes, soil moisture and polyphenol oxidase activity at different soil depths and slopes, and activities of phosphomonoesterase and nitrate reductase at different soil depths were also observed. The soil nutrient contents and microbiological activities were greater in the surface soil layer and decreased with the increase of soil depth. Soil organic C, total N, total P, available P and K, microbial biomass C and N, and the activities of enzymes tested (except for protease) under shrubs were higher than those in between shrubs. Furthermore, significant correlations among soil organic C, microbial biomass C and N, the activities of phosphomonoesterase, dehydrogenase, urease, protease, and nitrate reductase were observed, and correlations were also found among EC, total N, total P, available P and K, enzyme (except for polyphenol oxidase) activities, and microbial biomass C and N contents. These results suggest that microenvironmental factors (slope, soil depth and microsite) have significant influences on the spatial distribution of soil nutrients and microbiological properties when the C. microphylla sand-fixing plantation is established in the moving sand dunes in the Horqin Sandy Land.     

The Importance of Ficus (Moraceae) Trees for Tropical Forest Restoration

Forest restoration is an increasingly important tool to offset and indeed reverse global deforestation rates. One low cost strategy to accelerate forest recovery is conserving scattered native trees that persist across disturbed landscapes and which may act as seedling recruitment foci. Ficus trees, which are considered to be critically important components of tropical ecosystems, may be particularly attractive to seed dispersers in that they produce large and nutritionally rewarding fruit crops. Here, we evaluate the effectiveness of remnant Ficus trees in inducing forest recovery compared to other common trees. We studied the sapling communities growing under 207 scattered trees, and collected data on seed rain for 55 trees in a modified landscape in Assam, India. We found that Ficus trees have more sapling species around them (species richness = 140.1 ± 9.9) than non‐Ficus trees (79.5 ± 12.9), and significantly more saplings of shrub and large tree species. Sapling densities were twice as high under Ficus trees (median = 0.06/m²) compared to non‐Ficus (0.03/m²), and seed rain densities of non‐parent trees were significantly higher under Ficus trees (mean = 12.73 ± 3/m²/wk) than other fruit or non‐zoochorous trees (2.19 ± 0.97/m²/wk). However, our regression model found that canopy area, used as a proxy for tree size, was the primary predictor of sapling density, followed by remnant tree type. These results suggest that large trees, and in particular large Ficus trees, may be more effective forest restoration agents than other remnant trees in disturbed landscapes, and therefore the conservation of these trees should be prioritized.     

Seasonal soil‐surface carbon fluxes from the root systems of young Pinus radiata trees growing at ambient and elevated CO2 concentration

Elevated atmospheric CO₂ concentration may result in increased below‐ground carbon allocation by trees, thereby altering soil carbon cycling. Seasonal estimates of soil surface carbon flux were made to determine whether carbon losses from Pinus radiata trees growing at elevated CO₂ concentration were higher than those at ambient CO₂ concentration, and whether this was related to increased fine root growth. Monthly soil surface carbon flux density (f) measurements were made on plots with trees growing at ambient (350) and elevated (650 μmol mol^?1) CO₂ concentration in large open‐top chambers. Prior to planting the soil carbon concentration (0.1%) and f (0.28 μmol m^?2 s^?1 at 15 °C) were low. A function describing the radial pattern of f with distance from tree stems was used to estimate the annual carbon flux from tree plots. Seasonal estimates of fine root production were made from minirhizotrons and the radial distribution of roots compared with radial measurements of f. A one‐dimensional gas diffusion model was used to estimate f from soil CO₂ concentrations at four depths. For the second year of growth, the annual carbon flux from the plots was 1671 g y^?1 and 1895 g y^?1 at ambient and elevated CO₂ concentrations, respectively, although this was not a significant difference. Higher f at elevated CO₂ concentration was largely explained by increased fine root biomass. Fine root biomass and stem production were both positively related to f. Both root length density and f declined exponentially with distance from the stem, and had similar length scales. Diurnal changes in f were largely explained by changes in soil temperature at a depth of 0.05 m. Ignoring the change of f with increasing distance from tree stems when scaling to a unit ground area basis from measurements with individual trees could result in under‐ or overestimates of soil‐surface carbon fluxes, especially in young stands when fine roots are unevenly distributed.