Mayfly bioindicator thresholds for several anthropogenic disturbances in neotropical savanna streams

Anthropogenic disturbances are widely recognized as major threats to terrestrial and aquatic biodiversity worldwide, including areas located in non-forest ecosystems. Headwater streams in the neotropical savanna are severely threatened by large-scale landscape changes that degrade local habitat characteristics and lead to biodiversity loss. The objective of our study was to evaluate Ephemeroptera assemblages as bioindicators of catchment land use and cover, local streambed and riparian vegetation conditions, and instream water quality. To do so, we sampled mayfly nymphs in 184 stream sites across a broad disturbance gradient in four hydrologic units of the Brazilian neotropical savanna. We selected seven metrics without significant co-variation with natural variability: % catchment urban, riparian vegetation condition index (RCOND), human disturbances of the stream channel and riparian zone (W1_HALL), substrate mean embeddedness (XEMBED), dissolved oxygen (mg L⁻¹), pH, and total phosphorus (mg L⁻¹). We ran threshold indicator taxa analysis (TITAN) for each disturbance metric to detect change points in mayfly genera responses (whether sensitive or tolerant) and assemblage turnover pattern. TITAN showed that 20 of the 39 genera found were robust bioindicators (based on purity and reliability values >0.95), sixteen of them being sensitive to increased disturbance. The most sensitive genera were Tricorythopsis (Leptohyphidae) and Camelobaetidius (Baetidae), showing decreased abundance to most disturbance metrics. We found a turnover pattern of mayfly genera in response to W1_HALL in a narrow variation range. For total phosphorus, the benchmark value defined in Brazilian Federal Legislation is higher than the turnover threshold of several mayfly genera. This indicates that we will lose many sensitive genera even within the limits imposed by national environmental legislation. The indicator taxa approach, based on multiple taxa rather than univariate metrics or single indicator species, demonstrates the value of quantitative ecological information for conserving and managing freshwater ecosystems globally.     

科尔沁沙地典型固沙人工林地土壤水分时空特征及其对环境因子的响应

土壤水分时空动态特征对于干旱地区人工林的可持续经营与管理起着至关重要的作用。以位于科尔沁沙地南缘的樟子松和柠条固沙人工林为对象，于2018年11月-2019年11月连续观测了林地0-200 cm土壤剖面的含水量、温度及微气象因子，系统分析了土壤水分的时空变化特征及其对环境因子的响应。研究期内，两种林地土壤水分的季节变化可分为冻结期、补充期、消耗期和稳定期；依据土壤剖面的水分特征可分为易变层、活跃层和稳定层，但两种林地的分层深度有一定差异。在生长季内（5-10月），土壤含水量对大气降雨的响应随着土层深度的增加而减弱；降雨对樟子松人工林0-20 cm层土壤水分的影响极显著（P<0.01），对柠条人工林0-10 cm层的影响极显著（P<0.01）、20-60 cm层显著（P<0.05）。在土壤冻融周期内（2018年11月-2019年4月），两种林地的土壤均表现为"单向冻结"和"双向融化"的特点；土壤温度是影响冻融期内土壤含水量的关键因素，两者呈极显著的指数函数关系；樟子松和柠条人工林土壤的最大冻结深度分别为170 cm和190 cm，前者10 cm土层解冻时间要比后者晚11 d，可能与乔木树冠的遮阴作用有关。潜在蒸散与柠条林0-60 cm层、樟子松林0-20 cm和200 cm层的土壤水分呈极显著相关（P<0.01），而与樟子松林60 cm和160 cm层呈显著相关（P<0.05），这与树木蒸腾和土壤蒸发等综合作用有关。研究表明，由于两种人工林的树种组成、树冠大小、郁闭程度和根系分布等结构特征不同会导致林地土壤水分时空特征的异质性及其对环境因素响应的差异。     

Ecological and environmental effects of land use change in rapid urbanization: The case of hangzhou,China

Land use changes sharply under rapid urbanization, yet its ecological and environmental effects are often neglected in land use decisions. Using the case of Hangzhou, China, we analyze the ecological and environmental effects of land use changes, including ecosystem services value (ESV) and carbon emissions, based on Landsat TM images from 1995, 2000, 2005, 2010, and 2014. We found significant ecological and environmental effects of land use changes under rapid urbanization. The value of ecosystem services in Hangzhou decreased from 546.7 million USD in 1995 to 448.97 million USD in 2014, and the ratio of ESV to GDP decreased from 5.8% to 0.6%. The net carbon emissions associated with land use changes increased from 4.26 million tons in 1995 to 15.10 million tons in 2014, mainly due to the increase of built-up land carbon emissions and the decrease of forest land carbon sink. The ESV is unevenly distributed spatially and low ESV spread from the central to the peripheral area. We use scenario analysis to illustrate that economic growth and environmental protection could be coordinated by bringing ecological and environmental effects into land use decisions.     

樟子松人工林原产地与不同自然降水梯度引种地土壤和植物叶片生态化学计量特征

降水格局是影响陆地生态系统结构和过程的重要环境要素,尤其对于干旱/半干旱地区,降水变化是植物生长驱动的关键生态因子。目前,针对降水变化对陆地生态系统C、N、P等元素生物地球化学循环过程影响开展了大量研究。然而,关于沙地樟子松重要引种地科尔沁沙地自然降水梯度下沙地樟子松人工林土壤、植物生态化学计量特征的研究未见报道。因此,本研究以樟子松原产地红花尔基和引种地科尔沁沙地自然降水梯度下4个典型沙地樟子松人工林为对象,研究樟子松引种地降水变化对土壤(0—10,10—20 cm和20—40 cm)和植物(1年和2年生叶)生态化学计量特征的影响。研究结果发现:(1)与红花尔基原产地樟子松人工林相比,科尔沁沙地引种的樟子松人工林土壤C、N、P元素含量显著降低;(2)科尔沁沙地自西向东,随降水量增加,沙地樟子松人工林土壤C、N、P含量以及C∶P和N∶P表现为逐渐增加趋势,而土壤C∶N呈减少趋势;(3)随着降水量增加,樟子松叶C含量呈下降趋势,叶N含量和N∶P比值呈增加趋势,植物叶P含量无一致性规律;(4)樟子松叶片P含量与土壤C、N、P含量呈极显著正相关关系,而叶片C和N含量与土壤C、N、P含量无显著相关性。研究表明,沙地樟子松引种地科尔沁沙地土壤C、N、P养分比较缺乏,且随着降水增加土壤N养分限制降低,而土壤P养分限制增加。本研究从生态化学计量特征角度,为今后开展科尔沁沙地不同降水梯度条件下引种樟子松人工林提供理论依据。     

Long‐term trends in restoration and associated land treatments in the southwestern United States

Restoration treatments, such as revegetation with seeding or invasive species removal, have been applied on U.S. public lands for decades. Temporal trends in these management actions have not been extensively summarized previously, particularly in the southwestern United States where invasive plant species, drought, and fire have altered dryland ecosystems. We assessed long‐term (1940–2010) trends in restoration using approximately 4,000 vegetation treatments conducted on Bureau of Land Management lands across the southwestern United States. We found that since 1940, the proportions of seeding and vegetation/soil manipulation (e.g. vegetation removal or plowing) treatments have declined, while the proportions of prescribed burn and invasive species treatments have increased. Treatments in pinyon‐juniper and big sagebrush communities declined in comparison to treatments in desert scrub, creosote bush, and riparian woodland communities. Restoration‐focused treatment objectives increased relative to resource extraction objectives. Species richness and proportion of native species used in seeding treatments also increased. Inflation‐adjusted costs per area rose 750% for vegetation/soil manipulation, 600% for seeding, and 400% for prescribed burn treatments in the decades from 1981 to 2010. Seeding treatments were implemented in warmer and drier years when compared to the climate conditions of the entire study period and warmer and wetter years relative to several years before and after the treatment. These results suggest that treatments over a 70‐year period on public lands in the southwestern United States are shifting toward restoration practices that are increasingly large, expensive, and related to fire and invasive species control.     

How disturbance,competition, and dispersal interact to prevent tree range boundaries from keeping pace with climate change

Climate change is expected to cause geographic shifts in tree species' ranges, but such shifts may not keep pace with climate changes because seed dispersal distances are often limited and competition‐induced changes in community composition can be relatively slow. Disturbances may speed changes in community composition, but the interactions among climate change, disturbance and competitive interactions to produce range shifts are poorly understood. We used a physiologically based mechanistic landscape model to study these interactions in the northeastern United States. We designed a series of disturbance scenarios to represent varied disturbance regimes in terms of both disturbance extent and intensity. We simulated forest succession by incorporating climate change under a high‐emissions future, disturbances, seed dispersal, and competition using the landscape model parameterized with forest inventory data. Tree species range boundary shifts in the next century were quantified as the change in the location of the 5th (the trailing edge) and 95th (the leading edge) percentiles of the spatial distribution of simulated species. Simulated tree species range boundary shifts in New England over the next century were far below (usually <20 km) that required to track the velocity of temperature change (usually more than 110 km over 100 years) under a high‐emissions scenario. Simulated species` ranges shifted northward at both the leading edge (northern boundary) and trailing edge (southern boundary). Disturbances may expedite species' recruitment into new sites, but they had little effect on the velocity of simulated range boundary shifts. Range shifts at the trailing edge tended to be associated with photosynthetic capacity, competitive ability for light and seed dispersal ability, whereas shifts at the leading edge were associated only with photosynthetic capacity and competition for light. This study underscores the importance of understanding the role of interspecific competition and disturbance when studying tree range shifts.     

沈阳市东部土地利用格局变化

以沈阳市东部１９７６～１９８９年的历史航空像片为基础,以地理信息系统（ＧＩＳ）技 术为手段,分析土地利用的空间格局及其变化．结果表明,针叶林、水田平均嵌块体大小增 加,旱地、落叶林、灌丛平均嵌块体大小减少;分数维值略有增加．预示嵌块体形状逐步复 杂化;多样性指数、均匀性指数增加．优势度和蔓延度指数由原来的１．６３２７和８９．２０２２分 别减少到１．３２２６和８８．２７４４,说明景观嵌块体的空间分布趋于均匀,嵌块体的聚集分布状 况将随时间的推移逐步分散化．此外．本文对沈阳东部土地利用格局变化的原因进行了剖 析．     

The role of landscape history and persistent biogeographical patterns in shaping the responses of Mediterranean land snail communities to recent fire disturbances

Aims To assess the impact of various fire regimes over the past 30 years on land snail communities and to analyse the role of recent landscape history and the influence of biogeography in shaping the response patterns of gastropod communities following disturbances by fire. Location South-eastern France (Provence) and Mediterranean region. Methods Stratified sampling within 12 sites was undertaken with regard to fire regime (i.e. number of fires, fire intervals and age of the last fire) occurring over the past 30 years. The study was complemented by a historical analysis using aerial photographs, old maps of vegetation cover and an analysis of the biogeographical composition of malacofaunas. Data were investigated using Correspondence Analysis and Sørensen coefficient of similarity. Results When a disturbance regime (land use or fire disturbances) has been maintained over decades or centuries, land snail communities appear highly modified and tend to be composed of only Mediterranean and xerophilous species. However, low fire regimes, since the 1970s, do not seem to greatly affect the composition of gastropod communities. Indeed, shade-loving, mesophilous and European range species persist even after successive fires within some sites. In addition, the malacofaunas have a higher component of European range species with increasing distance from the Mediterranean sea. Main conclusions Analysis of the response patterns of gastropod communities to fire shows a response to numerous different factors. The composition of current land snail communities is not only the result of (more or less) recent patterns of fire regimes but also of anthropogenic disturbances, of landscape changes over the last centuries and of subsequent structure of the pre-fire habitat, as well as of the influence of a biogeographical gradient. However, the response patterns observed and the persistence of pre-fire communities imply the presence of cryptic refuges located within burned areas.     

PHYLOGENY OF THE GENUS COLEOCHAETE (COLEOCHAETALES,CHAROPHYTA) AND RELATED TAXA INFERRED BY ANALYSIS OF THE CHLOROPLAST GENE rbcL1

The genus Coleochaete Bréb. is considered to be a key taxon in the evolution of green algae and embryophytes (land plants), but only a few of the approximately 15 species have been studied with molecular phylogenetic methods. We report here the sequences of the gene rbcL from six new cultures of Coleochaete and two of Chaetosphaeridium Klebahn. These sequences were combined with 32 additional sequences, and phylogenetic analyses were performed with maximum likelihood, distance optimality, and parsimony methods. Important subgroups within Coleochaete include two primary lineages, one marked by fully corticated zygotes and the other by naked or weakly corticated zygotes. In the first lineage there is a subclade with tightly joined filaments and distinctive (“T‐shaped”) cell division, an assemblage of strains that resembles the endophytic species Coleochaete nitellarum Jost, and a clade with loosely joined filaments and “Y‐shaped” cell divisions. Consistent with recent multigene phylogenies, these analyses support the monophyly of the Coleochaetales, place the Charales as the sister taxon to land plants, and indicate that Chaetosphaeridium is far more closely related to Coleochaete than to Mesostigma Lauterborn.     

Diversity of plants in cocoa agroforests in the humid forest zone of Southern Cameroon

In the humid forest zone of Southern Cameroon, farmers generally associate cocoa with native and exotic trees in complex agroforestry systems. Despite the socio-economic and ecological importance of these systems, few studies have investigated their plant composition. We investigated tree composition of cocoa agroforests along a gradient of market access, population density and resource use intensity in the humid forest zone of southern Cameroon, comprising (i) the sub-region of Yaoundé, (ii) the sub-region of Mbalmayo, and (iii) the sub-region of Ebolowa. Market access, population density and resource use intensity all decreased from the first to the third sub-region. We quantified the diversity of tree species associated with cocoa within individual agroforests, among agroforests in the same region, and among the three sub-regions, and classified the tree species according to their main uses. A total of 9.1 ha belonging to 60 cocoa agroforests were inventoried in 12 villages. We encountered a total of 206 tree species with an average of 21 tree species per agroforest. In the more urbanized area around Yaoundé, agroforests were less diverse than in the other sub-regions. In all of the agroforests, food producing tree species tended to be more frequent than other species. Two thirds of the food trees were native forest species and one third was introduced. From Ebolowa to Yaoundé, the density of food producing trees doubled and the density of exotic food-producing species increased relative to native species. Some local species producing high-value non-timber forest products were found in the agroforests, but their density was far lower than that of exotic tree species. The agroforests also provide medicine, charcoal and other products for household consumption and sale. We conclude that unless there are specific efforts to promote local forest tree species in cocoa agroforests, these will progressively lose importance with increasing market access, population pressure and land use intensity.