Spatial and temporal changes of vegetation cover in granite mountains in central Japan: a GIS-based approach

Degraded hillslope areas are widespread in the Tanakami area located in Shiga Prefecture of central Japan as a result of more than 1300 years of human impact. Consequently, accelerated erosion rates and high storm runoffs have been major environmental problems there. To attempt to stabilize hillslopes and to reduce sediment and water discharges, extensive reforestation projects have been conducted since the 1870s. The vegetation recovery in the Tanakami area over a 51-year period was assessed using a geographic information system-based approach. The results showed that, in the areas where only hillside planting work was conducted, the percentage of bare slope area increased mainly due to the destruction of the vegetation cover on the forested slopes with gradients exceeding 30 degrees, and/or on southwest and northwest slopes. Moreover, the destruction of vegetation cover on steep slopes was seen to be most prevalent where hillside planting work was conducted without slope terracing. In contrast, in the area where both hillside planting and tending works were implemented, the bare slope area tended to decrease through the study period. Consequently, in 1988, there were only 1 per cent of bare slopes in the area where both hillside planting and tending works were implemented; in contrast the bare slope areas where only hillside planting work was conducted still occupied 12–17 per cent. These results imply that the reforestation practices that include hillside planting and tending works, or at least slope terracing, are necessary to prevent the destruction of the vegetation cover on steep southwest and northwest slopes. Copyright © 2002 John Wiley & Sons, Ltd.     

Spatial patterns and temporal changes of heavy metal distributions in river sediments in a region with multiple pollution sources

Purpose

The main purpose of this study was to evaluate temporal and regional variability of contamination by heavy metals (HMs) in river sediments using their enrichment factors (EFs) and benchmarking according to sediment quality guidelines (SQGs). The Zlin region in the Czech Republic (Morava and Drevnice River basins) represents a model area where several regionally specific ecological risk assessment studies have recently been conducted with a focus on organic pollution, eco-toxicity, geological, and geochemical characteristics.

Materials and methods

Four consecutive sediment sampling campaigns were undertaken in spring and autumn 2005–2006. Aqua-regia leachable content of Cd, Co, Cr, Cu, Ni, Pb, Sb, V, and Zn in surface sediments from 14 sites was analyzed using ICP-MS, and Hg content was analyzed using AMA-254 analyzer. EFs were calculated to identify the human impact on pollution in the area. Comparisons to SGQs were conducted to identify the areas and HMs of greatest risk.

Results and discussion

Calculation of EFs contributed to the effective clustering of HMs. Median EFs of Co, Ni, and V ranged from 0.9 to 1.4 at all sites indicating concentrations very close to natural geological background levels. There was greater enrichment at locally polluted sites, the highest in the cases of Cd, Sb, Hg, and Cr. Widespread influence of diffuse HM sources (traffic, agriculture, and urban wastes) was apparent from elevated concentrations of Pb, Cu, and Zn at all sites. EF values also helped to identify the greatest temporal changes and shifts in HMs contamination between adjacent sites caused by 50-year recurrence interval floods in early spring 2006. The impact was most apparent in downstream sites; namely directly below the confluence of the two major rivers.

Conclusions

The overall contamination of HMs in the region was classified as low-to-moderate with significantly contaminated sub-areas. The study showed relatively stable spatial distributions of HMs, indicating potential sources of pollution. Cu was identified as the HM of greatest risk. The study emphasizes the necessity of considering both environmental circumstances and background HM occurrence to prevent misinterpretation of the pollution situation. The use of EFs which include grain size proxy normalization and HM background levels, along with the comparison of the detected concentrations to SQGs, proved an efficient way to identify hazardous contamination from anthropogenic sources.     

海南岛农业绿色发展指标时空变化特征

海南自建省以来农业生产规模、结构及生产方式均发生了很大改变,影响了其农业绿色发展程度。本文借助中国农业绿色发展指标体系,利用NUFER模型(NUtrientflowsinFoodchains,EnvironmentandResources use),选取并定量计算1988—2017年海南岛20项农业绿色发展指标,研究其时空变化特征,探究制约海南岛农业绿色发展的影响因素。研究表明:30年间海南省农业绿色发展水平总体呈下降趋势,较低级别(Ⅲ、Ⅳ级)指标数量由12个增加至15个,较高级别(Ⅰ、Ⅱ级)指标数量由8个减少至5个。随着蔬菜、水果等经济作物种植比例增加,畜禽养殖规模扩大与集约化程度提高,海南农业产值与社会发展水平不断升高,农业产值和农业机械化投入分别从0.62×104$·hm–2和3 kW·hm–2增加至16.1×104$·hm–2和13 kW·hm–2。30年来农业资源(氮素、磷素、农药和农膜)过量投入,其中农药和农膜的使用强度增幅最大,分别从8.0kg·hm–2和0kg·hm–2增加至41.9 kg·hm–2和34.7 kg·hm–2;由于生产力水平较低,导致养分(农田氮素盈余量、农田氮素径流量、农业源氨挥发等)环境排放量大幅增加,农业源氨挥发和单位播种面积农田氮素盈余增幅最大,分别从61.0 kg·hm–2和152.1 kg·hm–2增加至131.4 kg·hm–2和297.9 kg·hm–2。农业资源投入过量、农牧分离导致的环境污染是制约海南岛农业绿色发展的主要原因。在空间上,由于中部为山地林区,是国家重点生态功能保护区,开发力度较小,因此沿海平原的资源投入增长更快、养分环境损失量更多,经济增长、社会发展和农业生产3类指标提升更为迅速。今后海南岛应合理优化沿海地区种植结构,提高生产管理水平,加强农牧结合减少资源损失,实现海南岛农业绿色发展。     

Spatial and temporal patterns of vegetation recovery following sequences of forest fires in a Mediterranean landscape,Mt. Carmel Israel

The Mediterranean ecosystem of Mt. Carmel is subjected to increasing number of forest fires at various extents and severities due to increasing human activities. Accordingly, we tested whether in areas exposed to different fire histories vegetation regeneration is different in north versus south facing slopes, and the potential impact on erosion processes. Using remote sensing techniques we evaluated the Enhanced Vegetation Index (EVI) to monitor vegetation recovery following a single fire and three successive fires, using a series of Landsat images taken between 1985–2002. Following a single fire, vegetation cover reached pre-disturbance values within less than 5 years. Repeated fires caused further reduction of EVI values, especially at south facing slopes (SFS). The effects of three successive fires within 10 years, followed by a three year recovery period, however, are negligible when considering vegetation cover values. This was deduced as north facing slope EVI values returned to pre-disturbance conditions at the end of the 3 years and SFS EVI values to 80% of the pre-disturbance conditions. Our results indicate that Mediterranean eco-geomorphic systems are quite resilient, showing quick response, at least in terms of return to pre-disturbance states of vegetation cover, and hence of soil erosion rates. This is true not only in response to a disturbance caused by a single fire, but also for repetitive fire incidents.     

Spatial and temporal patterns of water-extractable organic carbon (WEOC) of surface mineral soil in a cool temperate forest ecosystem

Water-extractable organic carbon (WEOC) drives the C and N cycles in forest ecosystems via microbial activity. However, few studies have considered both then spatial and temporal patterns of WEOC in forest soils. We investigated the spatial and temporal variation in WEOC along a topographic sequence in a cool temperate deciduous forest. The concentrations of WEOC, carbohydrates, total phenols, and other organics were 126±51, 40±15, 1.5±0.5 and 85±43 mg C kg dry soil⁻¹, respectively. Carbohydrates and phenols accounted for 33±11 and 1.5±1.0% of WEOC, respectively. The effect of season on the WEOC concentration was stronger than that of slope position the growing season, although most of the soil properties varied markedly with slope position. The concentration of carbohydrates in WEOC showed similar seasonal patterns across slope positions. The carbohydrate concentration peaked in May and August. The results suggest that carbohydrates are controlled by the recent production of C, rather than by organic C that has accumulated in soil.     

Spatial distribution of spiders and epedaphic Collembola in an environmentally heterogeneous forest floor habitat

Describing the biotic and abiotic processes that are responsible for the formation of spatial patterns in predators and their prey is crucial for improving our understanding of food–web interactions. We studied the spatial distribution of four abundant spider species and three common groups of epedaphic Collembola prey in a beech-dominated (Fagus sylvatica) forest floor habitat and related the observed patterns to environmental heterogeneity, overall predator activity (all ground beetles and spiders) and prey availability (all Collembola) at the local scale. Spiders and epedaphic Collembola were sampled over 392 days in a spatially explicit design based on a regular grid of 25 pitfall traps (inter-trap distance 100 m). Environmental heterogeneity was characterized by cover of moss and litter as well as the amount of dead wood at each trap location. We first used the index of dispersion to characterize the spatial distribution of spider species and Collembola and then related the observed patterns to environmental heterogeneity, predator and prey availability while testing for spatial autocorrelation within the same models. All taxa were significantly more aggregated than expected from the assumption of random distribution. The distribution of spider species was positively (Coelotes terrestris) or negatively (Tenuiphantes zimmermanni and Tapinocyba insecta) related to the cover of moss and negatively related to litter cover (C. terrestris) or the local availability of prey (T. insecta). The distribution of Collembola was negatively related to local litter cover (Lepidocyrtus spp.) and positively related to the amount of medium deadwood pieces (all other Entomobryidae). Our study suggests that none of the spider species preferred areas of low overall predator activity density. Moreover, it does not indicate association of spider species to prey-rich areas at the analyzed scale of 100 m. It further highlights the importance of environmental heterogeneity, as different habitat properties differentially affected the local activity density of spiders and Collembola and thus considerably contributed to the understanding of distribution patterns.     

菜地土壤剖面上重金属元素含量随时间的变化规律研究

在宜城镇蔬菜基地内选择种植时间为1a、5a、10a、15a、20a、45a的菜地序列,并选择周围的水稻田作为对照地,研究了菜地土壤中Hg、Cu、Zn、Cr、Pb 5种元素含量随种植时间的变化趋势。结果表明,在菜地的种植过程中,土壤中Hg、Cu、Zn、Cr和Pb 5种微量元素的含量有不断累积的趋势,应引起足够重视。以上元素含量随菜地利用时间的增加而累积的原因与菜地中大量投入的无机肥料（尤其是磷肥）、动物粪肥以及农药有关。此外,该文提出的土壤元素含量变化速率的概念,可以直观反映土壤中某一元素浓度的增加或减少的快慢,对预测土壤中元素浓度的变化趋势有参考价值。     

Spatial and temporal controls of soil respiration rate in a high-elevation, subalpine forest

We examined soil respiration to determine what measurable environmental variables can be used to predict variation in soil respiration rates, spatially and temporally, at a high-elevation, mixed conifer, subalpine forest site at the Niwot Ridge Ameriflux Site in Colorado. For three summers, soil respiration rates were measured using soil collars and a portable gas-exchange system. Transects of the collars were established to ensure spatial characterization of the litter-repleted areas beneath tree crowns and the litter-depleted open spaces between tree crowns. Soil temperature and soil moisture were both identified as important drivers of soil respiration rate, but were found to confound each other and to function as primary controls at different scales. Soil temperature represents a primary control seasonally, and soil moisture represents a primary control interannually. Spatially, organic layer thickness, ammonium concentration, water content, and the microbial and soil soluble carbon pools were found to predict variation from point to point. Soil microbial biomass strongly correlated to soil respiration rate, whereas root biomass was identified as a weak predictor of respiration rate and only when controlling for other variables. Spatial variation in soil respiration rate is highly determined by the depth of the soil organic horizon, which in this ecosystem varies predictably according to distance from trees. The conclusions that can be drawn from the study provide the foundation for the development of future models of soil respiration driven by fundamental variables of the climate and soil microenvironment.     

1980 tephra from Mount St. Helens: Spatial and temporal variation beneath forest canopies

Summary Tephra and underlying litter and soil were sampled in 1980, 1982, and 1987 beneath subalpine forests where 4.5 and 15 cm of tephra fell during the 1980 eruption of Mount St. Helens, Washington State, USA. Coarse pumice had a higher initial pH and less total N, less exchangeable K, Ca, and Mg, and less extractable B and S than finer textured layers. Tephra pH and concentrations of cations and S decreased rapidly with time, especially during the first 2 years in the finer layers. Total N, Bray-Kurtz P, and organic C concentrations in the tephra increased with time. Changes within a site in total N, pH, organic C, P, Ca, Mg, and S from 1980 to 1987 exceeded the differences among sites at any one time. By 1987 a forest floor covered much of the tephra surface, and differences in Ca associated with site vegetation and seepage had developed in tephra layers of a similar depth. In 15 cm deep tephra at one site in 1987, the tephra crust beneath the forest canopy was thicker and had higher concentrations of coarse particles, organic C, total N, and cations than beneath forest openings. In concave microsites the crust was thicker, with higher pH, organic C, and total N but lower S than in adjacent convex microsites. Spatial and temporal chemical differences are sufficient to affect patterns of vegetation recovery.     

基于CMORPH CRT产品的太行山区降水时空格局

为有效利用太行山区降水资源,实现科学的水资源管理和生态建设,本研究利用1998—2017年CMORPHCRT卫星降水产品数据探究山区降水的时空格局和变化趋势,并通过18个地面雨量站的数据验证山区多年来降水趋势变化。结果表明:在年尺度上, 1998—2017年太行山区年均降水量和各季节降水量无明显变化趋势,太行山区南坡和东坡降水量高于北坡和西坡;在月尺度上,7月是全年降水的主要贡献时段,占全年总降水量的7.2%～32.4%,其次是8月和6月。太行山区南部和西北部降水呈现下降趋势,年均降水量减少2～6mm;山区西部和北部降水呈现增长趋势,年均增加量大于8mm;7月是山区降水趋势差异最大的月份,趋势变化范围在-8.6～8 mm·a~(-1)。根据地面实测数据验证降水变化趋势,在年尺度上,两者数据计算得到的降水趋势呈现极显著相关(P0.01);在季节尺度上,冬季(干季)和夏季(湿季)降水趋势变化与地面实测数据的降水趋势具有极显著相关性(R=0.902,P0.001;R=0.550,P=0.018),但在春季和秋季相关性不显著。根据1998—2017年降水趋势的空间分布栅格图,提取每一栅格的像元值,再将提取所得的降水趋势(PT)划分为6个区间(PT≤-5 mm·a~(-1)、-5 mm·a~(-1)PT≤0 mm·a~(-1)、0 mm·a~(-1)PT≤5 mm·a~(-1)、5 mm·a~(-1)PT≤10 mm·a~(-1)、10 mm·a~(-1)PT≤15mm·a~(-1)和PT15mm·a~(-1)),在不同的趋势区间探索20年来的降水趋势变化特征,研究发现在降水趋势5mm·a~(-1)的区间,降水量从1998年到2017年呈现显著增加的趋势。基于高分辨率卫星数据阐明太行山区降水时空格局和变化趋势,能够为该区域水资源合理利用和生态恢复提供建议和支持。     

Upscaling spatio‐temporal patterns of cation fluxes in acid forest soils

One main problem with current research on spatio‐temporal modeling of ion fluxes in forest soils is the separation of space and time effects in the soil‐monitoring concept. This article describes an approach to overcome this weakness. Time trends of point information on soil‐solution data (base‐cation concentrations and fluxes) are scaled by linking them to soil‐chemical data which is available in higher spatial resolution and can be upscaled to an area base. This approach is based on a combined evaluation of bulk soil and soil‐solution data using both statistical and process‐oriented methods. Multiple‐linear‐regression analyses coupled with geostatistics were developed to predict spatial patterns of exchangeable cation percentages. In a second step, empirical ion‐distribution coefficients were adapted according to Gapon using data of suction‐cup plots and bulk‐soil samples. Seasonally adjusted time‐series data of soil‐solution chemistry were then connected with the maps of the predicted exchangeable‐cation percentages by means of the Gapon equations. This evaluation step provided both time‐ and space‐dependent maps of cation concentrations in the soil solution. Finally, using the results of a water‐budget model it was possible to derive spatio‐temporal patterns of soil cation fluxes. Methodological limitations and the results of verification processes are discussed. The methods described can only be used in acidic soils and should not be used in soil layers rich in humus, since adsorption to C compounds differs from adsorption to clay minerals. The time increments of the models should be not shorter than yearly in order to suppress annual periodicity. Although the Gapon equations were not based on laboratory‐determined exchange solutions at quasi‐equilibrium, but rather on field data from the suction‐cup technique, the exchangeable‐cation percentages showed steady functions of selectivity coefficients. The methods tested at a watershed scale may be flexible enough to be applied at other scales as well.     

Forest clearcutting effects on trace metal concentrations: Spatial patterns in soil solutions and streams

Increased concentrations of solutes in drainage waters following forest clearcutting may affect downstream water quality. The objective of this study was to evaluate some of the processes regulating concentrations of trace metals and Fe in soil solutions and streamwater in a clearcut watershed by determining changes in metal release by soil horizon, stand vegetation and elevation. Commercial whole-tree harvesting of a watershed at the Hubbard Brook Experimental Forest, NH, U.S.A. resulted in increased loss of NO _inf3 ^sup? from the study watershed. This N0 _inf3 ^sup? loss resulted in acidification of soil solutions, which was associated with release of Mn and Zn from mineral soil to soil solutions and streamwater. Significant correlations of Pb and Fe with dissolved organic C (DOC) suggested that mobilization of these metals was linked to DOC transfer. However, there was little evidence of increased release of DOC, Fe, or Pb following the whole-tree harvest, except in a high elevation spruce-fir zone with shallow soils.     

Factors contributing to temporal stability in spatial patterns of water content in the tillage zone

The rates of many biological processes vary across an agricultural landscape in response to the spatial patterns of water content in the tillage zone. Although, water content varies temporally through the growing season, the combined effects of soil properties, landscape attributes, tillage or position relative to the crop row on the temporal variation in the spatial pattern in soil water content are not well understood. We measured the soil water content (0–0.20 m) regularly through three growing seasons at 32 positions along each of two transects in a side-by-side comparison of corn under conventional tillage (plowing and secondary tillage) and no till in order to identify factors with the strongest influence on the spatial patterns in water content. The tillage comparison traversed a landscape in which the clay content (cl) varied from 5.8 to 37.4% and the organic carbon content (OC) varied from 0.9 to 3.9%. The spatial pattern in water contents during wetting and drying events were temporally stable, as reflected in R²>0.7 of correlation analysis of water contents on successive measurement dates. Multiple regression analyses indicated that the water contents, averaged over all measurement dates, were positively correlated with cl and ln(OC) and were smaller in the row than the inter-row position. The reduction in water content due to conventional tillage was diminished with increasing OC. However, application of multiple regression analyses to each set of water contents measured on a given day for each year indicated that the impact of soil properties, tillage and position relative to the row varied within and among seasons.     

Trace element distribution within the tree phytomass and forest floor of a tolerant hardwood stand,Algoma, Ontario

An examination of tree phytomass and trace metal concentrations (w/w) and pools in the tree stratum and forest floor of a sugar maple-yellow birch forest was carried out at Turkey Lakes Watershed, Algoma District, Ontario. Estimated aboveground tree phytomass (167, 500 kg ha^?1) was dominated by stemwood, branches > 2 cm, and stem bark. Highest trace metal concentrations were found in foliage (Cu, Fe, Mn, Ni) and stem bark (Cd, Pb, Zn). Concentrations of essential trace metals found in all sugar maple components followed the expected sequence of Mn>Fe>Zn>Cu. Lead and Ni concentations were always higher than those of Cd. Concentrations of essential elements in foliage and other components were comparable to those reported in the literature for other localities in North America. There was no indication that availability of essential trace elements (e.g., Cu) to vegetation had been increased as a result of increased atmospheric deposition. Lead, Ni and Cd levels in vegetation and forest floor were lower than those reported for similar forested areas of the northeastern United States.     

城市典型植物群落温度效应的时空格局

以太原市城区典型绿地植物群落——杨树片林、禾本科草坪和灌木林为研究对象,对不同绿地周边温度的空间和时间变化进行测试,并对其降温能力进行了比较。结果表明：3种绿地的温度效应均表现为午后（14：00-15：30）最明显,上午（10：00-11：30）次之;而傍晚（17：00-18：30）杨树片林和灌林木呈与前两个时间段相反的变化趋势,草坪变化不明显。3种绿地对温度的影响均呈随与绿地距离增加而减弱的趋势。杨树片林对周边空气温度的影响强度为3．55℃,分别是灌木林的1．48倍、草坪的2．73倍。在影响范围上,杨树片林表现也比较突出,尤其是在14：00-15：30这一时段,杨树片林、灌木林和草坪的水平影响范围分别为14m、12m和8m,垂直影响范围分别为7．5m、3．5m和2．5m。     

Trends and patterns in lake acidification in the State of Vermont: Evidence from the Long-Term Monitoring Project

Twenty-four low acid neutralizing capacity (ANC) lakes in Vermont have been monitored since 1980 to characterize their chemical variability, and to determine if they exhibit temporal trends in acid/base chemistry. Many of the lakes exhibit significant decreasing trends in SO₄ ^2? and base cation (C_B) concentrations, but few exhibit significant changes in pH or ANC. An examination of all trend results (significant and insignificant) suggests a tendency for ANC and pH values in these lakes to be increasing, but either the changes are too small, or the number of observations too small, for these trends to be significant. Data from these lakes suggest that the primary responses of surface waters in this region to declining rates of SO₄ ^2? deposition are decreases in SO₄ ^2? concentrations and rates of cation leaching from watershed soils. Decreasing rates of c_b deposition may combine with lower rates of cation leaching to produce declines in c_B that are very similar to measured declines in SO₄ ^2? concentration. Vermont lakes exhibit their lowest ANC values in spring, attributable, for the most part, to dilution of c_B concentrations during spring snow melt. Concentrations of SO₄ ^2? are also more dilute in the spring, but c_B decreases are greater, and the net effect is a lowering of ANC. One quarter of the Vermont lakes monitored exhibit strong seasonality in NO₃ ^? concentrations, with peak concentrations near 70 Μeq L^?1. In these lakes, spring increases in NO₃ ^? concentrations are more important than C_B dilution in producing minimal spring ANC values.     

Spatial patterns of soil respiration in a spruce-fir valley forest,Northeast China

Purpose

The quantification of spatial patterns of soil respiration (R_S) is an important step in modelling soil carbon budgets. This study aims to characterise the spatial variability of R_S using traditional and geostatistical analyses in a mature temperate forest during the growing season, with emphases on temporal variation in the spatial patterns and soil properties and stand structural parameters driving the variability of R_S.

Materials and methods

R_S, soil temperature and soil water content were sampled at 780 positions in a 9.12-ha permanent plot in a spruce-fir valley forest in the spring, summer and autumn of 2015. Furthermore, edaphic properties were measured adjacent to each sampling point, and all trees with DBH (diameter at breast height of tree) greater than 1 cm were mapped in the plot.

Results and discussion

R_S showed strong spatial variation across the three measurement campaigns, with the autocorrelation length ranging from 10 to 17 m. The spatial variability of R_S in the spring period was relatively higher than that of summer and autumn. Soil water content was confirmed to be the primary factor driving spatial R_S, followed by soil temperature, soil organic carbon, total nitrogen, C:N, pH and the maximum DBH within radius of 4 m of sampling points. The multiple regression model fitted by soil properties and stand structural parameters could account for 11–32% of the spatial variation of R_S. However, the involved factors in the regression model varied with season, and soil temperature was more important in controlling the spatial variability of R_S in the spring period.

Conclusions

The study highlights that soil water content and soil temperature play the most important role in determining the spatial patterns of R_S across the growing season.

     

Trace metals in the forest floor at saddleback mountain,maine in relation to aspect,elevation, and cover type

The objectives of this study were to obtain information about trace metal levels in a montane ecosystem in western Maine, and to compare these results to levels of trace metals reported in the literature for other areas of New England. Forest floor samples were collected at Saddleback Mountain, Maine from sites along two elevational transects on the western and eastern slopes. Five sites were located on the western slope, each in a different vegetation zone, and three sites were selected on the eastern slope, each corresponding in elevation and vegetation type as closely as possible to three of the western sites. Forest floor samples were collected as 15 x 15 cm blocks to the surface of the underlying mineral soil and sectioned into 2 cm depth increments. Zinc and Cr concentrations in the forest floor were significantly greater on the western slope (118 and 3.7 mg kg^?1, respectively), whereas Pb concentration was greater on the eastern slope (80 mg kg^?1) Cadmium, Cr, Cu, Ni, V, and Zn contents were significantly greater on the western slope (45, 83, 79, 143, and 1432 mg in ^?2, respectively). Copper, Ni, Cd, and Zn concentrations and contents in the forest floor decreased with increasing elevation, and no trends of increasing trace metal contents with increasing elevation were evident. Trace metal concentrations and contents were always lower in the deepest increment of the forest floor as compared to the surface increment (except for Cr), but concentration and content trends with depth varied. Chromium tended to increase with depth where a depth trend was evident. Overall, forest floor trace metal levels were strongly related to forest stand type and forest floor properties.     

Influence of single trees on spatial and temporal patterns of belowground properties in native pine forest

Linkages between forest dynamics and ecosystem processes are poorly understood and this limits our ability to adequately estimate future changes in forest ecosystems due to human-induced global change. In particular at the single tree level, our understanding of temporal and spatial changes of belowground properties during forest succession is limited. Thus, our aim was to test whether we find a spatial and temporal gradient in nutrient availability and an associated shift in microbial community structure with increasing distance and age of single trees. We found that inorganic nitrogen was less available below the crown of single trees, while soluble organic carbon (DOC) was much more abundant, in particular in the inner zone of influence, i.e. close to the stem. The fungal:bacterial PLFA ratio was greater while microbial biomass carbon (MicC) was lower below the tree crown, indicating a strong influence of trees on spatial patterns of microbial biomass and community structure. Moreover, the positive correlation between MicC and total extractable N, and the negative correlation between fungal:bacterial biomass and δ¹⁵N, suggested that the microbial biomass was N limited below the tree crown and as a consequence nutrient cycling was presumably decelerated compared to open conditions. We also found a temporal pattern of increasing surface soil C and N content with increasing tree age (up to 250 years), underlining the significant role of single trees in creating spatial and temporal heterogeneity in forests.