Effects of Jack Pine Plantation Management on Barrens Flora and Potential Kirtland's Warbler Nest Habitat

Jack pine barrens, once common in northern lower Michigan, mostly have been converted to managed jack pine plantations. Management of the disturbances associated with logging provides the opportunity to maintain the unique plant assemblages of jack pine barrens and nest habitat of the federally endangered Kirtland's warbler. Studies indicate that Carex pensylvanica can develop into dense mats and strongly compete with other barrens species such as Vaccinium angustifolium, which seem to be important species for Kirtland's warbler nest locations. According to forest managers, the most important factors facilitating high cover of V. angustifolium and reducing cover of C. pensylvanica are the amount of shade produced by tree crowns before harvest (pre‐harvest shade), the length of time between harvest and planting (planting delay), and fire. We found that high or low levels of pre‐harvest shade had no effect on cover of either V. angustifolium or C. pensylvanica. Planting delays of at least three years following prescribed burns generally increased cover of V. angustifolium in forest plots, which are important for warbler nesting. Analysis of community composition in openings indicated that burning enhanced the growth of barrens species. We found only weak evidence for a negative correlation between the cover of V. angustifolium and C. pensylvanica on our study sites. The openings created in the jack pine plantation are important refugia for barrens flora that would likely be lost under forests managed strictly for jack pine. Maintenance of jack pine barrens flora and Kirtland's warbler nest habitat is possible within the context of a heavily managed forest plantation system.     

Spatial patterns of ectomycorrhizal fungal inoculum in arbuscular mycorrhizal barrens communities: implications for controlling invasion by <Emphasis Type="Italic">Pinus virginiana</Emphasis>

Invasion of globally threatened ecosystems dominated by arbuscular mycorrhizal plants, such as the alkaline prairies and serpentine barrens of eastern North America, by species of ectomycorrhizal (ECM) pine (Pinus) seriously threatens the persistence, conservation, and ongoing restoration of these rare plant communities. Using Maryland serpentine barrens and an Ohio alkaline prairie complex as model systems, we tested the hypothesis that the invasiveness of Virginia pine (Pinus virginiana L.) into such communities is regulated by the spatial pattern of ECM fungal inoculum in the soil. ECM colonization of pine seedlings can occur by (1) hyphae growing from the roots of mature ECM pines colonizing nearby seedlings (contagion model), (2) pine seedlings being infected after germinating in open areas where spores are concentrated in feces of animals that have consumed sporocarps (centers of infection model), and (3) colonization from spores that are wind-dispersed across the landscape (background model). To test these models of dispersal of ECM fungal inoculum into these barrens, we used autocorrelation and spatially explicit mapping techniques (semivariance analysis and kriging) to characterize the distribution and abundance of ECM inoculum in soil. Our results strongly suggest that ECM fungi most often disperse into open barrens by contagion, thereby facilitating rapid pine colonization in an advancing front from mature pine forests bordering the barrens. Spatial patterns consistent with the centers of infection model were present but less common. Thus, current management techniques that rely on cutting and fire to reverse pine invasion may be ineffective because they do not kill or disrupt hyphal mats attached to mature roots of neighboring pines. Management alternatives are discussed.     

长白山典型林区森林资源景观格局变化分析

利用研究区1985年及1999年遥感影像作为数据源,在GIS支持下并结合地面资料对森林资源景观格局及其变化进行研究．从两期地物斑块面积标准偏差来看,成熟针叶林(1985年为279．3,1999年为98．64)、成熟阔叶林(1985年为162．94,1999年为68．54)、中龄阔叶林(1985年为113．14)、中龄针叶林(1999年为160．71)斑块面积分布均匀程度均较同期其它地物类型小,这也说明这些地物组成中景观类型多样性及物种多样性．从景观相似性指数分析来看,中龄阔叶林(1985年为0．118,1999年为0．116)、中龄针叶林(1985年为0．07,1999年为0．336)、成熟阔叶林(1985年为0．312,1999年为0．228)、成熟针叶林(1985年为0．237,1999年为0．174)4类植被在15年间较同期其它地物类型稳定,是研究区景观的主要组成部分．湿地在两期的孔隙度都较大,湿地的均质化程度很小,形成了更多的斑块镶嵌体,湿地破碎化程度较高．     

Accelerated soil CO<Subscript>2</Subscript> efflux after conversion from secondary oak forest to pine plantation in southeastern China

Soil respiration (R _s) is an important component of the carbon cycle in terrestrial ecosystems, and changes in soil respiration with land cover alteration can have important implications for regional carbon balances. In southeastern China (Xiashu Experimental Forest, Jiangsu Province), we used an automated LI-8100 soil CO₂ flux system to quantify diurnal variation of soil respiration in a secondary oak forest and a pine plantation. We found that soil respiration in the pine plantation was significantly higher than that in the secondary oak forest. There were similar patterns of soil respiration throughout the day in both the secondary oak forest and the pine plantation during our 7-month study (March–September 2005). The maximum of R _s occurred between 4:00 pm and 7:00 pm. The diurnal variations of R _s were usually out of phase with soil surface (0.5 cm) temperature (T _g). However, annual variation in R _s correlated with surface soil temperature. Soil respiration reached to a maximum in June, and decreased thereafter. The Q₁₀ of R _s in the secondary oak forest was significantly higher than that in the pine plantation. The higher Q₁₀ value in the secondary oak forest implied that it might release more CO₂ than the pine plantation under a global-warming scenario. Our results indicated that land-use change from secondary forest to plantation may cause a significant increase in CO₂ emission, and reduce the temperature sensitivity of soil respiration in southeastern China.     

Why Pine Barrens Restoration Should Favor Barrens Over Pine

Pine barrens include an assortment of pyrogenic plant communities occurring on glacial outwash or rocky outcrops scattered along the Atlantic coastal plain from New Jersey to Maine, and inward across New England, New York, Pennsylvania, and the northern Great Lakes region. At least historically, pine barrens provided some of the highest quality terrestrial shrublands and young forests in the eastern North American sub‐boreal and northern temperate region. However, the mosaic open‐canopy, sparse‐shrub, and grassland early successional state is generally lacking in contemporary pine barrens. Many sites in the northeastern United States have converted to overgrown scrub oak (Quercus ilicifolia, Quercus prinoides) thickets and closed canopied pitch pine (Pinus rigida)‐dominated forests. Thinning pitch pine is a contentious issue for the imperiled pitch pine‐scrub oak barrens community type (G2 Global Rarity Rank, 6–20 occurrences). Here we provide a historical, ecological, and resource management rationale for thinning pitch pine forest to restore savanna‐like open barrens with a mosaic of scrub oaks, heath shrubs, and prairie‐like vegetation. We postulate that the contemporary dominance of pitch pine forest is largely of recent anthropogenic origin, limits habitat opportunities for at‐risk shrubland fauna, and poses a serious wildfire hazard. We suggest maintaining pitch pine‐scrub oak barrens at 10–30% average pitch pine cover to simultaneously promote shrubland biodiversity and minimize fire danger.     

Response of soil respiration to temperature and soil moisture: Effects of different vegetation types on a small scale in the eastern Loess Plateau of China

Soil respiration is affected by vegetation and environmental conditions. The purpose of this study was to investigate the effect of vegetation type on soil respiration, temperature and water content, and their correlations on a small scale. We measured soil respiration rate (R_s) over a 3-year period at biweekly intervals in three plots in the eastern Loess Plateau of China, with the same soil texture but different vegetation types: pine forest, grassland, and shrub land. Simultaneously, soil temperature (T_s) at 10 cm depth and soil water content (W_s) within 10 cm depth were measured. The seasonal course of R_s and T_s showed a similar temporal variation in the three plots, with higher values in summer and autumn and lower values in winter and spring. No significant differences (P>0.05) were found between plots, except for W_s. The mean cumulative release of CO₂ efflux from March to December was 962.5, 1027.5, and 1166.5 g C m^? 2 a^? 1 for plots 1, 2, and 3, respectively, with no significant difference between plots. The fitted exponential equations of R_s versus T_s from the 3-year data-set were significant (P < 0.05) with an R² of 0.72, 0.64, and 0.72 for plots 1, 2, and 3, respectively. The calculated Q₁₀ from the parameters of the fitted equation was 3.57, 3.52, and 3.61, and the R₁₀ was 2.36, 2.03, and 2.37 μmol CO₂ m^? 2 s^? 1 for plots 1, 2, and 3, respectively. Compared with the T_s, the correlations between R_s and W_s were not significant for the three plots. However, if the T_s was above 10°C, then their correlation was significant, and W_s had an impact on R_s. Four combined regression equations including two variables of T_s and W_s could be well established to model correlations between R_s and both T_s and W_s. Our study demonstrated that the exponential and power model fitted best and no significant different correlations of combined equations existed between the three plots. These results show that vegetation type had little impact on R_s, T_s, W_s, and their correlations, as well as on related parameters such as Q₁₀ and R₁₀. Therefore, while doing R_s research in a horizontal patchy vegetation conditions on a small area, the sampling location of measurements should focus on vertical dominant vegetation and ignore patch vegetation so as to reduce field work load.     

Effects of Forest Age on Soil Autotrophic and Heterotrophic Respiration Differ between Evergreen and Deciduous Forests

We examined the effects of forest stand age on soil respiration (SR) including the heterotrophic respiration (HR) and autotrophic respiration (AR) of two forest types. We measured soil respiration and partitioned the HR and AR components across three age classes ∼15, ∼25, and ∼35-year-old Pinus sylvestris var. mongolica (Mongolia pine) and Larix principis-rupprechtii (larch) in a forest-steppe ecotone, northern China (June 2006 to October 2009). We analyzed the relationship between seasonal dynamics of SR, HR, AR and soil temperature (ST), soil water content (SWC) and normalized difference vegetation index (NDVI, a plant greenness and net primary productivity indicator). Our results showed that ST and SWC were driving factors for the seasonal dynamics of SR rather than plant greenness, irrespective of stand age and forest type. For ∼15-year-old stands, the seasonal dynamics of both AR and HR were dependent on ST. Higher Q₁₀ of HR compared with AR occurred in larch. However, in Mongolia pine a similar Q₁₀ occurred between HR and AR. With stand age, Q₁₀ of both HR and AR increased in larch. For Mongolia pine, Q₁₀ of HR increased with stand age, but AR showed no significant relationship with ST. As stand age increased, HR was correlated with SWC in Mongolia pine, but for larch AR correlated with SWC. The dependence of AR on NDVI occurred in ∼35-year-old Mongolia pine. Our study demonstrated the importance of separating autotrophic and heterotrophic respiration components of SR when stimulating the response of soil carbon efflux to environmental changes. When estimating the response of autotrophic and heterotrophic respiration to environmental changes, the effect of forest type on age-related trends is required.     

Vegetation responses to landscape structure at multiple scales across a Northern Wisconsin,USA, pine barrens landscape

Increasing awareness of the importance of scale and landscape structure to landscape processes and concern about loss of biodiversity has resulted in efforts to understand patterns of biodiversity across multiple scales. We examined plant species distributions and their relationships to landscape structure at varying spatial scales across a pine barrens landscape in northern Wisconsin, U.S.A. We recorded plant species cover in 1×1 m plots every 5 m along a 3575 m transect, along with variables describing macro- and micro-landscape structure. A total of 139 understory plant species were recorded. The distributions of many species appeared to be strongly associated with landscape structural features, such as distinct management patches and roads. TWINSPAN and detrended correspondence analysis (DCA) identified three groups of species that overlapped extensively in the ordination, possibly reflecting the relatively homogeneous nature of disturbance in the pine barrens landscape. Distribution of understory plants did not reflect all of the patch types we identified along the transect; plot ordination and classification resulted in three to five plot groups that differed in niche breadth. Wavelet transforms showed varying relationships between landscape features and plant diversity indices (Shannon–Weiner, Simpson's Dominance) at different resolutions. Wavelet variances indicated that patterns of Shannon diversity were dominated by coarse resolutions ranging from 900–1500 m, which may have been related to topography. Patterns of Simpson's Dominance were dominated by 700 m resolution, possibly associated with canopy cover. However, a strong correspondence between overstory patch type and diversity was found for several patch types at ranges of scales that varied by patch type. Effects of linear features such as roads were apparent in the wavelet transforms at resolutions of about 5–1000 m, suggesting roads may have an important impact on plant diversity at landscape scales. At broad scales, landscape context appeared more important to diversity than individual patches, suggesting that changes in structure at fine resolutions could alter overall diversity characteristics of the landscape. Therefore, a hierarchical perspective is necessary to recognize potential large-scale change resulting from small-scale activities.     

Understanding the key characteristics and challenges of pine barrens restoration: insights from a Delphi survey of forest land managers and researchers

Pine barrens are open‐canopy ecological communities once prevalent on sandy soils across the northern Great Lakes Region of the United States and Canada, though fire suppression and plantation forestry have now reduced them to a few isolated areas. Efforts to restore pine barrens are underway on some public lands, but lack of knowledge on the social and ecological issues and challenges that affect these projects impedes fuller progress. As a precursor to designing a public preference survey for pine barrens restoration, we sought input from those with expert knowledge about pine barrens. Using a three‐round modified Delphi survey, forest land managers and researchers identified the key characteristics of pine barrens and important current and future management challenges. Key characteristics were related to fire, landscape structure, plant and animal species, soils, and social themes. Current and future challenges were related to landscape, invasive species, social, economic, climate change, and science themes. Four social issues (education, fire acceptance, fire risk, aesthetics) were rated among the top current challenges but none of them maintained prominence as future challenges. Potential explanations for this shift are that the experts felt these social concerns would be resolved in time or that other issues, such as development pressures and budgets for carrying out restoration, would become greater future challenges. Our approach can be used by managers and researchers to better understand the ecosystems they seek to restore and to communicate with public stakeholders about restoration efforts.     

重庆缙云山两种林分土壤呼吸对模拟氮沉降的季节响应差异性

氮沉降对土壤呼吸的影响仍然存在着争论,需要进一步研究。选择重庆缙云山的马尾松林和柑橘林开展了氮添加实验,分别设置3个氮添加水平(低氮T_5:20 g N m~(-2)a~(-1),中氮T_(10):40 g N m~(-2)a~(-1)和高氮T_(15):60 g N m~(-2)a~(-1))和对照(T_0:0 g N m~(-2)a~(-1))共4个水平的处理,各林分每个处理各9次重复,每个处理量分4次,在每个季度开始各施1次。采用ACE(Automated Soil CO_2 Exchange Station,UK)自动土壤呼吸监测系统测定两林分土壤表层(0—10 cm)的呼吸、温度和湿度,分别在当年的7月、9月、11月、第2年的1月、2月、3月、5月、6月各连续测定4d,每天(8:00—18:00)4次,以揭示两种林分土壤呼吸对模拟氮沉降的季节动态响应及其差异性。结果表明:(1)柑橘林与马尾松林林下土壤表层呼吸表现出一致的季节变化动态趋势:夏季春季秋季冬季,但柑橘林土壤呼吸显著高于马尾松林(P0.05)。(2)总体上氮沉降抑制了2种林分土壤表层呼吸,而N沉降量大抑制程度越高。只在冬季土壤湿度低的马尾松林下氮沉降促进了土壤呼吸。(3)土壤温度与土壤呼吸有极显著的正相关指数关系(P0.01),而土壤水分与土壤呼吸有显著的二次模型拟合关系,但均受到氮沉降量处理的影响。综合分析表明,在亚热带山区2类森林下的典型案例结果支持氮沉降抑制土壤呼吸的认识。     

天山中段北坡森林土壤有机碳库稳定性组分沿海拔的分异规律

在高纬度高海拔区域气温增幅更大的背景下,高山亚高山森林土壤有机碳稳定性组分分配比关系以及由于此差异导致对增温的反馈效应均有待深入阐释。天山森林是以雪岭云杉(Picea Schrenkiana)为单优树种的温带针叶林,在天山北坡中山带(海拔约1760—2800 m)呈垂直落差超过1000 m的带状斑块分布,便于排除混交树种的影响,而量化土壤有机碳库稳定性组分分配比关系沿海拔的分异规律,及其对气候变化的响应情况。沿海拔梯度设置森林样地并分层采集土样,研究各土层土壤总有机碳库(C_SOC)、活性碳库(C_a)、缓效性碳库(C_s)、惰性碳库(C_p)、微生物量碳(MBC)在海拔梯度上的变化特征,通过碳库活度(A)、碳库活度指数(AI)、碳库指数(CPI)、土壤碳密度(SOCD),探讨天山森林土壤有机碳稳定性组分沿海拔的分异特征。结果表明：(1)随着海拔的升高,天山中段北坡云杉森林土壤C_a占比逐步升高,C_s和C_p占比逐步降低,这意味着天山中段北坡云杉...     

内蒙古农牧交错区不同土地利用方式下土壤呼吸速率及其温度敏感性变化

2009年8-10月, 采用动态气室法观测了内蒙古农牧交错区多伦县农田、弃耕和围封3种土地利用方式下, 土壤呼吸速率从6:00到18:00的变化规律, 分析了不同深度的土壤温度与土壤含水量对土壤呼吸速率的控制作用。结果表明, 空间尺度上, 不同土地利用方式的土壤呼吸速率由高到低依次为: 农田>弃耕>围封; 时间尺度上, 土壤呼吸速率在6:00-18:00的变化趋势为单峰曲线, 在12:00-15:00达到峰值, 随后降低, 在18:00基本恢复到6:00左右的呼吸水平, 同时, 土壤呼吸速率在9、10月显著降低。利用Van’t Hoff指数模型研究不同深度土壤温度对土壤呼吸速率的影响发现, 10-15 cm深度的土壤温度对土壤呼吸速率的影响最为显著, 其中, 土壤呼吸温度敏感性由高到低分别为: 农田>围封>弃耕。相反, 由于8-10月土壤含水量变化较小, 故土壤含水量与土壤呼吸速率间的相关性不显著, 土壤含水量不能解释该时段土壤呼吸速率的变化。     

Phenophases alter the soil respiration–temperature relationship in an oak-dominated forest

Soil respiration (SR) represents a major component of forest ecosystem respiration and is influenced seasonally by environmental factors such as temperature, soil moisture, root respiration, and litter fall. Changes in these environmental factors correspond with shifts in plant phenology. In this study, we examined the relationship between canopy phenophases (pre-growth, growth, pre-dormancy, and dormancy) and SR sensitivity to changes in soil temperature (T_S). SR was measured 53 times over 550 days within an oak forest in northwest Ohio, USA. Annual estimates of SR were calculated with a Q₁₀ model based on T_S on a phenological (PT), or annual timescale (AT), or T_S and soil volumetric water content (VWC) on a phenological (PTM) or annual (ATM) timescale. We found significant (p<0.01) difference in apparent Q₁₀ from year 2004 (1.23) and year 2005 (2.76) during the growth phenophase. Accounting for moisture-sensitivity increased model performance compared to temperature-only models: the error was −17% for the ATM model and −6% for the PTM model. The annual models consistently underestimated SR in summer and overestimated it in winter. These biases were reduced by delineating SR by tree phenophases and accounting for variation in soil moisture. Even though the bias of annual models in winter SR was small in absolute scale, the relative error was about 91%, and may thus have significant implications for regional and continental C balance estimates.     

Long-term patterns of fruit production in five forest types of the South Carolina upper coastal plain

Fleshy fruit is a key food resource for many vertebrates and may be particularly important energy source to birds during fall migration and winter. Hence, land managers should know how fruit availability varies among forest types, seasons, and years. We quantified fleshy fruit abundance monthly for 9 years (1995–2003) in 56 0.1-ha plots in 5 forest types of South Carolina's upper Coastal Plain, USA. Forest types were mature upland hardwood and bottomland hardwood forest, mature closed-canopy loblolly (Pinus taeda) and longleaf pine (P. palustris) plantation, and recent clearcut regeneration harvests planted with longleaf pine seedlings. Mean annual number of fruits and dry fruit pulp mass were highest in regeneration harvests (264,592 ± 37,444 fruits; 12,009 ± 2,392 g/ha), upland hardwoods (60,769 ± 7,667 fruits; 5,079 ± 529 g/ha), and bottomland hardwoods (65,614 ± 8,351 fruits; 4,621 ± 677 g/ha), and lowest in longleaf pine (44,104 ± 8,301 fruits; 4,102 ± 877 g/ha) and loblolly (39,532 ± 5,034 fruits; 3,261 ± 492 g/ha) plantations. Fruit production was initially high in regeneration harvests and declined with stand development and canopy closure (1995–2003). Fruit availability was highest June–September and lowest in April. More species of fruit-producing plants occurred in upland hardwoods, bottomland hardwoods, and regeneration harvests than in loblolly and longleaf pine plantations. Several species produced fruit only in 1 or 2 forest types. In sum, fruit availability varied temporally and spatially because of differences in species composition among forest types and age classes, patchy distributions of fruiting plants both within and among forest types, fruiting phenology, high inter-annual variation in fruit crop size by some dominant fruit-producing species, and the dynamic process of disturbance-adapted species colonization and decline, or recovery in recently harvested stands. Land managers could enhance fruit availability for wildlife by creating and maintaining diverse forest types and age classes. © 2012 The Wildlife Society.     

Density and habitat associations of Henslow's Sparrows wintering in saline soil barrens in southern Arkansas

ABSTRACT Although the habitat requirements of breeding populations of Henslow's Sparrow (Ammodramus henslowii) have been examined, less is known about their habitat requirements and ecology during the nonbreeding season. We estimated population densities and quantified habitat associations of Henslow's Sparrows wintering in saline soil barrens in southern Arkansas. Densities of Henslow's Sparrows in the saline soil barrens were similar to those in the Longleaf Pine (Pinus palustris) Ecosystem of the southeastern United States, considered by many to be their primary wintering habitat. Henslow's Sparrows were closely associated with open areas with greater cover of Aristida spp. and globe beaksedge (Rhynchospora globularis), greater stem density at 11–20 cm above ground, more lichens, more herbaceous cover, more bare ground, greater occurrence of little bluestem (Schizacyrium scoparium) as the tallest vegetation, less moss, and less shrub cover than randomly selected sites. In contrast to the results of studies conducted in the Longleaf Pine Ecosystem, the presence of Henslow's Sparrows in our study was not correlated with the height of the tallest vegetation. Our results indicate that saline soil barrens of southern Arkansas support a high density of wintering Henslow's Sparrows and do so for longer postdisturbance periods than longleaf pine savanna. We also found that stem density near the ground was similar to that reported from longleaf pine savanna, but only about half that observed on their breeding grounds. Areas used by Henslow's Sparrows had more lichen and less moss cover, suggesting that those areas were drier than random sites within the barrens. Further research is needed to determine if large populations of Henslow's Sparrows winter in other saline soil barrens and if fire influences habitat associations and densities in the barrens.     

Soil respiration in a Mediterranean oak forest at different developmental stages after coppicing

To assess the variation of soil respiration at different forest stages we measured it in a coppiced oak (Quercus cerris L.) chronosequence in central Italy during two campaigns, spanning 2 successive years, in four stands at different stages of the rotation: 1 year (S1), 5 years (S5), 10 years (S10) and 17 years (S17) after coppicing. The contribution of the different components of soil respiration flux (aboveground litter, belowground decomposition soil organic matter and root respiration) was estimated by a paired comparison of manipulative experiments between the recently coppiced stand (S1) and mature stand (S17). Ninety percent of soil respiration values were between 1.7 and 7.8 μmol m^?2 s^?1, with an overall mean (±SD) of 4.0±2.7 μmol m^?2 s^?1. Spatial variation of soil respiration was high (CV=44.9%), with a mean range (i.e. patch size) of 4.8±2.7 m, as estimated from a semivariance analysis. In the absence of limitation by soil moisture, soil respiration was related to soil temperature with the exponential Q₁₀ model (average Q₁₀=2.25). During summer, soil moisture constrained soil respiration and masked its dependence on soil temperature. Soil respiration declined over the years after coppicing. Assuming a linear decline with stand age, we estimated a reduction of 24% over a 20‐year‐rotation cycle. The response of soil respiration to temperature also changed with age of the stands: the Q₁₀ was estimated to decrease from 2.90 in S1 to 2.42 in S17, suggesting that different components or processes may be involved at different developmental stages. The contribution of heterotrophic respiration to total soil respiration flux was relatively larger in the young S1 stand than in the mature S17 stand.     

Annual variation in soil respiration and its components in a coppice oak forest in Central Italy

In order to investigate the annual variation of soil respiration and its components in relation to seasonal changes in soil temperature and soil moisture in a Mediterranean mixed oak forest ecosystem, we set up a series of experimental treatments in May 1999 where litter (no litter), roots (no roots, by trenching) or both were excluded from plots of 4 m². Subsequently, we measured soil respiration, soil temperature and soil moisture in each plot over a year after the forest was coppiced. The treatments did not significantly affect soil temperature or soil moisture measured over 0–10 cm depth. Soil respiration varied markedly during the year with high rates in spring and autumn and low rates in summer, coinciding with summer drought, and in winter, with the lowest temperatures. Very high respiration rates, however, were observed during the summer immediately after rainfall events. The mean annual rate of soil respiration was 2.9 µ mol m^?2 s^?1, ranging from 1.35 to 7.03 µmol m^?2 s^?1. Soil respiration was highly correlated with temperature during winter and during spring and autumn whenever volumetric soil water content was above 20%. Below this threshold value, there was no correlation between soil respiration and soil temperature, but soil moisture was a good predictor of soil respiration. A simple empirical model that predicted soil respiration during the year, using both soil temperature and soil moisture accounted for more than 91% of the observed annual variation in soil respiration. All the components of soil respiration followed a similar seasonal trend and were affected by summer drought. The Q₁₀ value for soil respiration was 2.32, which is in agreement with other studies in forest ecosystems. However, we found a Q₁₀ value for root respiration of 2.20, which is lower than recent values reported for forest sites. The fact that the seasonal variation in root growth with temperature in Mediterranean ecosystems differs from that in temperate regions may explain this difference. In temperate regions, increases in size of root populations during the growing season, coinciding with high temperatures, may yield higher apparent Q₁₀ values than in Mediterranean regions where root growth is suppressed by summer drought. The decomposition of organic matter and belowground litter were the major components of soil respiration, accounting for almost 55% of the total soil respiration flux. This proportion is higher than has been reported for mature boreal and temperate forest and is probably the result of a short‐term C loss following recent logging at the site. The relationship proposed for soil respiration with soil temperature and soil moisture is useful for understanding and predicting potential changes in Mediterranean forest ecosystems in response to forest management and climate change.     

汉江流域景观格局变化对土壤侵蚀的影响

在流域尺度上,景观格局变化是决定土壤侵蚀程度的重要因素。以汉江流域为研究区域,基于2000—2015年四期土地利用类型数据及环境气象数据,运用中国土壤流失方程和逐步回归法,探究景观格局变化对土壤侵蚀的影响。结果表明:(1)在2000—2015年间,汉江流域土壤侵蚀量下降,高值区分布在流域中部草地区,低值区分布在流域东西两侧的林地和耕地区。不同坡度下各等级土壤侵蚀量不同,侵蚀量最大值出现在10—30°的坡度范围内。(2)研究期间,汉江流域的景观破碎化程度加强,斑块形状趋于简单,各斑块自身连通性增强,景观类型空间分布均匀。(3)汉江流域土壤侵蚀量与斑块密度和平均邻接度指数呈正相关,与蔓延度指数和香农均匀度指数呈负相关,即景观破碎度越高、连通性越差,土壤越容易遭受侵蚀,反之则不易受到侵蚀;研究表明景观格局变化对土壤侵蚀有显著影响,结果可为流域尺度景观管理与水土保持研究提供参考。     

Vegetation composition,structure and soil properties across coastal forest–barren ecotones

Coastal barrens support rare plant species but may be threatened by forest encroachment. We determined whether trees spread into coastal barren habitat from forest patches and assessed plant species composition and soil properties across the forest–barren ecotone. We quantified tree age and height, soil properties, and vascular plant, bryophyte and lichen species composition along transects perpendicular to the edges of tree patches within the forest–barren ecotone in coastal Nova Scotia. Randomization tests assessed whether the vegetation and environmental characteristics were significantly different in the transition zone compared to one or both adjoining ecosystems. We used ordination to examine trends in species composition across the ecotone and the relationship to environmental variables. Tree age and height decreased continuously from the forest towards the edge of the forest patches. There were also trends in vegetation composition and structure from the forest into the open barrens. Many species were most abundant within the transition zone, although not always significantly. Soil properties were relatively uniform across the ecotone. The structure and vegetation of the forest–barren ecotone suggests that forest patches act as nuclei for forest expansion on barrens with a typical successional pathway where coastal barren vegetation is gradually replaced by forest species. This encroachment may pose a threat to rare barrens communities. While landscape factors such as salt spray and wind exposure may determine the general locations where forest can establish, biotic processes of growth and dispersal appear to govern the fine-scale expansion of tree patches.