Small scale pH buffering in organic horizons of two boreal coniferous forest stands

Factors behind the small-scale variaton of pH were examined in O horizons (humus layers) developed under two stands of Picea abies (L.) Karst. (Site F and K) by combining data on the composition of the cation exchange complex with data from titrations of corresponding H⁺-saturated samples. Cations extractable in 0.5 M CuCl₂ (S=cmol_c kg^–1 [2Ca+2Mg+2Mn+K+Na]), aluminium extractable in 1.0 M KCl (Al_e=cmol_c kg^–1 [3Al]) and in 0.5 M CuCl₂ (Al_org=cmol_c kg^–1 [3Al]), as well as pH measured in 0.01 M CaCl₂ (pH_Ca) were analysed in one-cm-layers of 13 O horizon cores at each site. Composite samples representing each of the one-cm-layers at each site, as well as samples with two different levels of Al saturation at Site K, were H⁺ saturated and titrated with NaOH to chosen end points of pH_Ca=4.0 and 5.5 in a 0.01 M CaCl₂ ionic medium. The Acid Neutralisation Capacity (ANC) was estimated as the amount of base needed to increase pH_Ca of the composite H⁺-saturated samples to the mean pH_Ca of the corresponding natural samples. The ANC was found to be similar in magnitude or higher than the amount of sites binding S+Al_e, which suggests that 1.0 M KCl exchangeable Al ions are nonacidic in acid O horizons. The relative contribution from i) the capacity of acidic functional groups, ii) their acid strength and iii) their degree of neutralisation to differences in pH_Ca between sites, among cm-layers and between samples with different levels of Al saturation were estimated from titration curves adjusted to hold two out of three factors (i, ii and iii) to be constant. The degree of neutralisation explained most of the differences in pH_Ca between the two sites, as well as between samples with different levels of Al saturation at Site K. The pH_Ca decrease by depth at site F was, however, partly explained by an increasing acid strength. The study emphasizes the importance of examining not only changes in the degree of neutralisation, but also changes in the acid strength and the capacity of buffering functional groups before conclusions about causes behind acidification processes can be made. Difficulties of accurately estimating the degree of neutralisation (base saturation) of acidic functional groups from the composition of adsorbed cations, owing to the unknown acidity of adsorbed Al, was also demonstrated.     

Plant Recruitment in Early Development Stages on Rehabilitated Quarries in Hong Kong

To understand vegetation development during the ecological succession of rehabilitated quarries, floristic composition and structure were evaluated at different restoration phases on three quarries in Hong Kong that were planted with exotic woody species over the course of 2–14 years. A total of 113 species, of which 82 were woody species, were recorded. Exotic species dominated the overstory, and species number, richness, and diversity increased with age. Some light‐demanding early successional species were becoming dominant in the overstory vegetation at the older phases of revegetation. These species could be potential candidates for early enrichment planting with Acacia spp. Common secondary forest species occurred naturally in the understory vegetation, and were more abundant and dominant after 10 years of ecological development. The most successful restorations were on scree slopes using leguminous Acacia spp. as nurse species.     

兴安落叶松人工林腐殖质阴燃燃烧温度变化特征

森林地下火是发生在腐殖质层的一种缓慢、无焰、低温、持久的阴燃燃烧,整个燃烧过程都是靠自身所释放的热量所维持。所以地下火发生时产生的温度是研究其火行为特征的重要指标,更是森林地下火监测和扑救过程中的重要依据。以大兴安岭地区5种地类下人工种植的兴安落叶松林为研究对象,以室内控制点烧实验为基础,研究不同地类和腐殖质粒径阴燃燃烧的温度变化特征。结果表明：不同粒径的腐殖质阴燃燃烧最高温度之间不存在显著差异（P>0.05）,而不同地类和二者的交互作用对阴燃燃烧最高温度的影响则存在显著差异（P<0.05）;4种腐殖质粒径下不同地类之间的阴燃燃烧最高温度都存在显著差异（P<0.05）。任意一种腐殖质粒径下塔头甸子的阴燃燃烧温度都是最高的,最高可达897.53℃,其次是水湿地,有坡山地、无坡山地、农用地的腐殖质阴燃燃烧温度较低。不同地类的腐殖质燃烧地表温度较高,最高温度可达618.83℃;随着燃烧时间的增加,腐殖质燃烧的地表温度随之降低,二者之间关系可以用y=a×x^b方程拟合,并且拟合程度高（R²>0.9,P<0.01）。相关研究成果可以为该地区森林地下火监测扑救提供科学有效的理论依据。     

三种不同类型亚高山森林凋落物输入对土壤腐殖化的影响

森林凋落物既是土壤腐殖质的主要来源,也可以通过新鲜凋落物中易降解组分的输入激发土壤原有腐殖质的降解,导致其相互关系并不明确。以王朗国家级自然保护区内的典型亚高山针叶林、针阔混交林以及阔叶林为研究对象,开展土壤原位培养试验,设置允许凋落物正常输入和去除凋落物两种处理,分析2017年-2019年期间不同凋落物处理下森林土壤可提取腐殖物质的光密度特征,研究土壤腐殖化程度与凋落物的关系。结果表明,在2年的试验过程中,3种森林土壤的腐殖化程度整体表现为针叶林>混交林>阔叶林,均展现出在冬季降低,生长季增加的动态规律;凋落物对3个森林的土壤腐殖化程度均无显著影响,但凋落物输入明显改变了土壤腐殖化程度的季节性变化趋势,且在冬季的阔叶林和混交林中表现更为突出。冬季凋落物的输入使得阔叶林和混交林土壤的腐殖化程度明显降低,而生长季凋落物输入对3种森林土壤腐殖化程度无显著影响。这些结果表明气候变暖情景下冬季温度的上升可能导致土壤的腐殖化程度增加,但凋落物的存在可以减缓增加的趋势。这些结果对于具有明显季节性冻融且对气候变化敏感的亚高山森林土壤肥力管理及可持续经营具有一定的科学意义。     

Degree of Humification in Fresh Litter from a Subtropical Mixed Plantation Forest in Southwest China

The humification degree of fresh litter directly controls the accumulation of soil humus derived from plant litter, but very little information on this process is available. Planted forests are well known to restrict soil fertility, which is often indicated by the soil humus level. In this study, fresh litter was collected during different plant phenological stages during 2016 and 2017 in a mixed plantation in Southwest China. The values of hue coefficient ΔlogK (absorbance ratio of 400 nm and 600 nm on a logarithmic scale), optical density E4/E6 (absorbance ratio of 400 nm and 600 nm) and A600/C (absorbance at 600 mm per mg of carbon per ml of extraction) and the concentration of extractable humus carbon (HC) were determined in four litter components (foliar, twigs, reproductive organs and miscellaneous) of the dominant species (Pterocarya stenoptera, Quercus acutissima, Cunninghamia lanceolata and Toxicodendron vernicifluum). All of the litter components exhibited obvious humification characteristics, and showed the highest concentration of extractable HC during the leaf maturation period. The miscellaneous and foliar litters showed greater humification than the other litter types. The components of Pterocarya stenoptera litter exhibited greater degrees of humification than those of the other species, with lower ΔlogK and E4/E6 values and higher A600/C values. The litter from coniferous and evergreen species showed lower humification than that from broad-leaf and deciduous species regardless of the litter component examined. The present results provide new insights into the management of plantations and theoretical data to accurately improve the quality of plantations and maintain soil fertility under a global change.     

Characteristics of soil nitrogen mineralization in the rhizosphere of trees,shrubs, and herbs in subtropical forest plantations

为了探讨人工林内优势乔木和林下灌草根际土壤氮矿化特征, 明确乔灌草根际土壤氮转化差异, 该研究以江西泰和千烟洲站区典型人工杉木(Cunninghamia lanceolata)、马尾松(Pinus massoniana)和湿地松(Pinus elliottii)林为对象, 在植被生长季初期(4月)和旺盛期(7月)分析3种人工林内乔木、优势灌木(檵木(Loropetalum chinense)、杨桐(Adinandra millettii)、格药柃(Eurya muricata))和草本(狗脊蕨(Woodwardia japonica)、暗鳞鳞毛蕨(Dryopteris atrata))根际土壤的净氮矿化速率、土壤化学性质及土壤微生物特征。结果发现: 1)物种、林型和取样季节显著影响了根际土壤净氮矿化速率(N_min)、净铵化速率(N_amm)和净硝化速率(N_nit)。马尾松和湿地松林内林下灌草根际土壤净氮矿化的季节敏感性高于乔木: 4月乔木根际土壤N_min和N_amm显著高于大多数林下灌草, 而7月林下灌草根际土壤N_min和N_amm显著提高, 与乔木不再具有显著差异, 与主成分综合得分方差分析的结果一致。一般情况下, 杉木林N_min和N_nit显著高于马尾松林和湿地松林。7月净氮矿化显著高于4月。2)土壤铵态氮、硝态氮、全氮及土壤微生物量氮含量是影响根际土壤净氮矿化的主要因素。土壤化学性质对人工林根际土壤净氮矿化变异的贡献率为29.2%, 显著高于土壤微生物的解释率。充分考虑不同季节林下植被根际土壤的净氮矿化及其关键影响因素可为准确评估人工林生态系统养分循环状况提供重要支撑。     

Frass sampling and baiting indicate European earwig (Forficula auricularia) foraging in orchards

Abstract:  Earwigs are significant generalist predators of a range of orchard pests, but quantitative assessment of earwig density and beneficial impact is difficult. A sampling system was designed and tested, based on field placement of polycarbonate tubes in apple trees as scotophase arboreal refugia. Tubes containing artificial diet and provided with a black plastic sleeve had the highest earwig counts. Tubes with diet or the black sleeve alone were less preferred. Presence of distinctive frass was also evident in polycarbonate tubes containing artificial diet, and earwig frass was recorded at a higher frequency than earwig presence, indicating foraging and detection of the tubes at a higher rate than their use as shelters. At the tree level, there was a weak correlation between frass abundance and predation rates on leafroller egg batches placed as baits in the canopy, but not with earwig density measured by corrugated cardboard rolls or diet tubes. Diet tubes have the potential to offer new insights into earwig foraging behaviour in orchards.     

Damage to artificial seedlings across a disturbed Afromontane forest landscape

Seedling mortality is an important demographic bottleneck for forest regeneration, yet the factors influencing recruitment are often poorly characterized across space and time. In African highlands, where extensive patches of previously disturbed forests remain in persistent shrub‐dominated states, patterns of damage to seedlings have not been examined in detail. We used artificial seedlings to determine how (non‐herbivory‐related) damage varies across a fragmented forest landscape in the Bwindi Impenetrable National Park, Uganda. A total of 848 artificial seedlings were established in 106 plots, each with 8 seedlings, across a gradient of environmental factors, including habitat type, topographic position, distance to water, and distance to human activity. We divided damage into that due to vertebrates, plant debris, and unknown agents. From our 16,960 monthly stem assessments, 1,289 damage events were recorded. The mean “seedling” damage per year (± 1 SE) was 59.5 ± 2.3%. Damage was significantly more frequent in sites dominated by short herbs (66.1 ± 3.0) than in sites dominated by shrubs (60.1 ± 2.6) and ferns (47.9 ± 2.7). The mean percentage of damage by each class of agents was 45.8 ± 2.1% for vertebrates, 21.4 ± 2.1% for plant debris, and 3.8 ± 0.6% for unknown agents. These rates surpass those reported in other montane forests, likely reflecting the density of large vertebrates in our site. Our results indicate that most damage to artificial seedlings arises from larger vertebrates but that most spatial variation in this damage reflects the impacts of falling plant debris. These damage processes appear sufficient to constrain the regeneration of tree species in areas where forest cover is patchy and fragmented.     

Lowland tapirs facilitate seed dispersal in degraded Amazonian forests

The forests of southeastern Amazonia are highly threatened by disturbances such as fragmentation, understory fires, and extreme climatic events. Large‐bodied frugivores such as the lowland tapir (Tapirus terrestris) have the potential to offset this process, supporting natural forest regeneration by dispersing a variety of seeds over long distances to disturbed forests. However, we know little about their effectiveness as seed dispersers in degraded forest landscapes. Here, we investigate the seed dispersal function of lowland tapirs in Amazonian forests subject to a range of human (fire and fragmentation) and natural (extreme droughts and windstorms) disturbances, using a combination of field observations, camera traps, and light detection and ranging (LiDAR) data. Tapirs travel and defecate more often in degraded forests, dispersing much more seeds in these areas [9,822 seeds per ha/year (CI_95% = 9,106; 11,838)] than in undisturbed forests [2,950 seeds per ha/year (CI_95% = 2,961; 3,771)]. By effectively dispersing seeds across disturbed forests, tapirs may contribute to natural forest regeneration—the cheapest and usually the most feasible way to achieve large‐scale restoration of tropical forests. Through the dispersal of large‐seeded species that eventually become large trees, such frugivores also contribute indirectly to maintaining forest carbon stocks. These functions may be critical in helping tropical countries to achieve their goals to maintain and restore biodiversity and its ecosystem services. Ultimately, preserving these animals along with their habitats may help in the process of natural recovery of degraded forests throughout the tropics. Abstract in Portuguese is available with online material.