Litter Removed Research Articles

Tree roots exert greater impacts on phosphorus fractions than aboveground litter in mineral soils under a Pinus sylvestris var. mongolica plantation

Detritus inputs from aboveground litter and belowground roots, as well as roots exudates sustain soil phosphorus (P) supply in forests, but how the aboveground litter and roots differentially and interactively drive soil P transformations and availability is poorly understood. We experimentally removed aboveground litter, and then excluded roots in litter intact/removed plots in a nutrient-poor Mongolian pine (Pinus sylvestris var. mongolica) plantation in northern China. Phosphorus fractions with different bioavailability (labile P, moderately labile P, stable P, and occluded P), P adsorption characteristics and related biochemical properties in mineral soils were examined five years after the establishment of the experiment. Root exclusion significantly reduced labile organic P by 56%, and did not affect other recalcitrant organic P fractions and total organic P in both the litter intact and removed plots. Root exclusion significantly elevated all inorganic P fractions by 21%–26% in the litter removed plots, but not in the litter intact plots. Litter removal alone did not change soil P fractions except that it slightly increased labile organic and stable inorganic P concentrations. Maximum P adsorption capacity was improved by litter removal, but maximum P buffer capacity was neither affected by litter removal nor by root exclusion. Soil organic P fractions were correlated closely with soil microbial biomass, acid phosphatase activities and soil organic carbon, while inorganic P fractions were correlated significantly with exchangeable Ca2+ concentration and pH. The results revealed the predominant role of roots in driving the mobilization of inorganic, as well as mineralization-immobilization of organic P in this Mongolian pine plantation, and highlighted the facilitation of aboveground litter on root driving mobilization of soil inorganic P.

Increasing Levels of Physical Disturbance Affect Soil Nematode Community Composition in a Previously Undisturbed Ecosystem.

Soil is essential for the sustenance of life. Diverse soil organisms support several biological processes such as organic matter decomposition, mineralization, nutrient cycling, and controlling pests and diseases. Among multicellular soil organisms, nematodes are ubiquitous, functionally diverse, and abundant. Notably, agricultural practices have diverse impacts on plants, soils, and soil organisms. Tillage affects nematodes directly by altering pore size and disrupting the continuity of water films and indirectly by affecting the lower trophic groups such as bacteria and fungi. The primary goal of this study was to examine the effect of increasing levels of physical disturbance on nematode communities in an undisturbed forest ecosystem. The experiment included four treatments: control with no disturbance, surface litter removed with no litter and no vegetation, tilling the soil with a rototiller every 2 mon, and every 2 wk. Tillage significantly reduced the overall abundance and overall richness of nematode communities over time. Among nematode trophic groups, tillage significantly reduced the abundance and richness of bacterial feeders, predators, and omnivores over time. The abundance and richness of c-p 2, c-p 4, and c-p 5 class nematodes were significantly decreased by tillage. Unlike tillage, minimal disturbance such as removal of surface litter resulted in a significant decrease in the abundance of only three genera: Acrobeles, Aporcelaimellus, and Boleodorus. Nonmetric multidimensional scaling analysis revealed that nematodes of higher c-p classes such as Dorylaimida, Aporcelaimellus, Alaimus, Clarkus, and Tripyla were sensitive to physical disturbances. Bacterial feeders belonging to the c-p 2 class such as Tylocephalus, Acrobeles, Ceratoplectus, Plectus, and Pseudacrobeles were significantly reduced by tillage. Moreover, tillage significantly reduced the functional metabolic footprint of nematodes, which indicates decreased metabolic activity, reduced C inflow, and poorly structured soil food webs. Previous studies conducted in agricultural ecosystems determined that Clarkus, Filenchus, and Plectus were tolerant to tillage; however, they were found sensitive to tillage in our study. Overall, our study suggests that increasing levels of physical disturbance are detrimental to nematode community abundance and diversity that could affect soil ecosystem stability and sustainability.

How Do Ground Litter and Canopy Regulate Surface Runoff?—A Paired-Plot Investigation after 80 Years of Broadleaf Forest Regeneration

Relatively minimal attention has been given to the hydrology of natural broadleaf forests compared to conifer plantations in Japan. We investigated the impacts of ground litter removal and forest clearing on surface runoff using the paired runoff plot approach. Plot A (7.4 m2) was maintained as a control while plot B (8.1 m2) was manipulated. Surface runoff was measured by a tipping-bucket recorder, and rainfall by a tipping-bucket rain gauge. From May 2016 to July 2019, 20, 54, and 42 runoff events were recorded in the no-treatment (NT), litter removed before clearcutting (LRBC), and after clearcutting (AC) phases, respectively. Surface runoff increased 4× when moving from the NT to LRBC phase, and 4.4× when moving from the LRBC to AC phase. Antecedent precipitation index (API11) had a significant influence on surface runoff in the LRBC phase but not in the NT and AC phases. Surface runoff in the AC phase was high regardless of API11. The rainfall required for initiating surface runoff is 38% and 56% less when moving from the NT to LRBC, and LRBC to AC phases, respectively. Ground litter and canopy function to reduce surface runoff in regenerated broadleaf forests.

Litter removal enhances soil N2O emissions: Implications for management of leaf-harvesting Cinnamomum camphora plantations

Nitrous oxide (N2O) and carbon dioxide (CO2) contribute substantially to global climate. Understanding N2O and CO2 emission intensity from forest soil is important for greenhouse gas (GHG) budget and climate change mitigation. Litter decomposition and nitrogen (N) addition are two crucial factors impacting soil GHG production, but magnitude depends on litter characteristics. Cinnamomum camphora is used for leaf-harvesting for essential oil extractions, which may disturb litter input and hence soil GHG emissions. We conducted an in situ study over fourteen months in C. camphora plantations to compare litter removal to litter control, combined with N addition, quantify production of N2O and CO2 in full-factorial complete-randomized design. Soil N2O emission rates were significantly influenced by litter and N treatment, while CO2 emissions were only impacted by interactions between litter and N treatment. Specifically, soil N2O emission rates were increased by 681%, while copy number of five functional microbial genes associated with N2O productions were increased by 2.8 to 71.4 times following litter removal. C. camphora litter might have released chemicals associated with inhibition of related microbial activities. Soil CO2 emission rates were 25% higher with litter removed and 34% lower with litter when N was added, further indicating inhibition effects of C. camphora litter on microbial activities. In future management of C. camphora plantations with intensive defoliation management and fertilization practice, litter regimes with more litter input should be considered in mitigation of soil GHG emissions, and hence global climate change.

氮肥添加对高寒藏嵩草(Kobresia tibetica)沼泽化草甸和土壤微生物群落的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 氮肥添加对高寒藏嵩草(Kobresia tibetica)沼泽化草甸和土壤微生物群落的影响 DOI: 10.5846/stxb201508041642 作者: 作者单位: 西南民族大学生命科学与技术学院;中国科学院水利部成都山地灾害与环境研究所;中国科学院成都生物所,中国科学院水利部成都山地灾害与环境研究所,中国科学院成都生物所,西南民族大学生命科学与技术学院,西南民族大学生命科学与技术学院,西南民族大学生命科学与技术学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划（973计划）（2013CBA01807）；国家自然科学基金项目（31370542）；中央高校基本科研业务费优秀科研团队及重大孵化项目（2014NZYTDO1） Effects of N addition on the plant and soil microbial community in alpine Kobresia tibetica meadow of Qinghai-Tibet Plateau Author: Affiliation: College of Life Science and Technology,Southwest University for Nationalities,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以藏嵩草沼泽化草甸为研究对象，利用磷脂脂肪酸（PLFA）技术，研究连续6年N素添加对地上植被群落数量特征、土壤微生物群落结构的影响。结果表明：①藏嵩草沼泽化草甸群落生物量、枯枝落叶对施肥处理无明显响应，且莎草科植物对土壤氮素的吸收和利用率较低。②施肥增加了0-10 cm土壤微生物类群PLFAs丰富度，尤其细菌和革兰氏阳性菌PLFAs，降低了10-20 cm PLFAs丰富度；③磷脂脂肪酸饱和脂肪酸/单烯不饱和脂肪酸、细菌PLFAs/真菌PLFAs的比值随土壤层次增加而增加；④ 0-10 cm土层，革兰氏阳性菌、真菌PLFAs含量与pH、土壤速效磷、速效氮、土壤有机质显著正相关（P < 0.05或P < 0.01）；10-20 cm土层，细菌、革兰氏阳性菌、真菌和总PLFAs含量与土壤有机质含量显著正相关（P < 0.05或P < 0.01）。表明藏嵩草沼泽化草甸微生物PLFAs含量和丰富度对施肥的响应存在明显的土层梯度效应，土壤微生物PLFAs含量和丰富度主要受表层土壤初始养分含量的影响。 Abstract:Effects of continuous six-year N addition on the quantitative properties of plant and soil microbial communities in alpine Kobresia tibetica meadows were investigated experimentally by using field surveys and phospholipid fatty acid (PLFA) analyses. The experiment included four manipulative treatments involving both N and litter:added N (+N) with the litter removed (LR), +N with the litter left intact (LI), LI without N addition (-N), and LR with -N. Soil samples were collected at the depths of 0-10 and 10-20 cm. Aboveground biomass (AGB), litter biomass, microbial community composition, and nutrient content were measured. The results showed that (1) fertilization did not have significant effects on AGB and litter biomass. (2) N addition significantly increased the abundance of the microbial group PLFAs at the soil depth of 0-10 cm, particularly the abundance of the bacterial PLFAs (B PLFAs) and gram-positive bacterial PLFAs (G+ PLFAs), but decreased microbial abundances at the soil depth of 10-20 cm. (3) The ratio of the normal saturated fatty acids/monounsaturated fatty acids and B PLFAs/fungal PLFAs (F PLFAs) increased with the increase in the soil depth. (4) G+ PLFA and F PLFA contents were significantly and positively correlated to pH, available phosphorus, available nitrogen, and soil organic matter contents at 0-10 cm soil depth. The contents and abundance of fatty acids were mainly regulated and affected by initial nutrient level in the topsoil after short-term N addition. These results indicate that microbial communities in this alpine tundra are sensitive to both litter and N inputs, and that the vertical structures of these communities are particularly vulnerable. 参考文献 相似文献 引证文献

Consequence of litter removal on pedogenesis: A case study in Bachs and Irchel (Switzerland)

In forests, soils contain at least twice as much carbon than plants that mostly grow in the upper layers. Litter at the interface between soils and the atmosphere regulates a variety of biogeochemical cycles, which are important for both plants and soils and have possible implications for other environmental components. We have compared leachates collected during an incubation experiment on: a) two deciduous leaves; b) organic and mineral horizons; c) treated with litter removal (and untreated) plots, to assess the changes in the chemical composition of the litter layers and leachates during weathering and their influence on the underlying horizons. Two different types of broadleaves – beech and oak – become indistinguishable when they experience weathering. As a litter horizon is altered, it becomes more stable and loses fewer elements, both in gaseous and liquid forms. The annual removal of litter represents a net loss of biomass from the system. Nevertheless, the effect on soil in the medium term is not significant. Leaves and litter horizons were incubated in micro-lysimeters, leached, and characterised by different analytical approaches, from elementary analyses (dissolved organic carbon, CO2 production, nitrogen forms, UV absorptivity) to solid state NMR spectroscopy. The results reveal that the removal of the litter does not degrade the underlying soils, in direct contrast to what was thought to be the case previously. Moreover, it extends previous knowledge that litter removal promotes an increase in fulvic acid activity in underlying horizons. The results demonstrate how this human disturbance, if not combined with other degradation factors, could promote podzolisation. In a wider outlook, if managed properly (for example, by burying litter removed after its use in animal husbandry), even the repeated removal of forest biomass contribute not negatively to the genesis of these soils.

The role of resource limitation in restoration of sagebrush ecosystems dominated by cheatgrass (Bromus tectorum)

Success of invasive annual grasses is often linked to increases in resources, and restoration ecologists have suggested that decreasing nitrogen (N) availability and restoring more conservative N cycles with lower N turnover should decrease the competitive advantage of these invaders and facilitate establishment of native perennials. We developed a multivariate conceptual model of the likely effects of environmental factors (precipitation and temperature) and potential management treatments (repeated burning, litter manipulation, and seeding an annual competitor) on soil N availability and success of cheatgrass, the most widespread invader in the western United States. We examined effects of the treatments in a five year field study in a cold desert shrubland. We used generalized linear mixed‐effects models to examine differences among treatments over time, and structural equation modeling (SEM) to evaluate component hypotheses of the conceptual model. We hypothesized that burning would result in a pulse in soil available N due to heat‐induced soil organic matter denaturation, but that subsequent fires would volatilize soil and biomass N resulting in progressive N deficiency. However, soil available N in burned plots was never lower than pre‐burn levels, likely because burn temperatures were too cool to volatilize N from soils or aboveground biomass. Repeated burning decreased litter biomass, but there were generally no differences in soil available N between litter intact and litter removed plots. Litter removal had a negative effect on cheatgrass success likely due to effects on seed entrapment and plant establishment rather than N mineralization. Plots seeded with wheat generally had the lowest cheatgrass success, but available N was similar to other treatments, and decreased cheatgrass success was likely due to competition for other soil nutrients or water and reduced litter. In this semi‐arid shrubland, long‐term trends in available soil N and cheatgrass success were most strongly associated with precipitation and winter minimum temperatures. Treatments did not result in longer‐term decreases in soil N, but indicated that integrated restoration approaches that reduce litter and seed banks and increase competitive interactions may be effective at reducing cheatgrass success and facilitating establishment of natives.

Urea addition and litter manipulation alter plant community and soil microbial community composition in a Kobresia humilis meadow

Overgrazing and climate change strongly affect alpine meadows by decreasing the plant community biomass and deteriorating the soil environment. To understand how the plant community and soil microbial community structure respond to grazing and N deposition, we conducted an experiment to remove or maintain the plant litter under the chronic addition of N in the Haibei Alpine Meadow in 2005. The experiment included four treatments: added N (+N, 20 g m−2) with the litter removed (LR), +N with the litter left intact (LI), LI without N addition (−N), and LR with −N. Soil samples were collected at depths of 0–10 and 10–20 cm, and the following parameters were measured: 1) aboveground biomass (AGB) and litter biomass and 2) microbial community composition and content. Overall, the AGB and litter biomass significantly increased by 45.85% and 50.42% in response to N addition, whereas litter removal increased the AGB by 52.96%. The addition of urea N significantly decreased the PLFA content of the bacterial, gram-positive (G+), gram-negative (G−) at a soil of 0–10 cm in the LI and LR treatments by 64.87%, 61.82%, 76.07% and 64.86%, 53.02%, 51.44%, respectively. However, the PLFA content of the bacterial increased from 37.09 to 53.54 nmol g−1 and from 37.09 to 62.05 nmol g−1 at a depth of 10–20 cm for the +N + LI and +N + LR treatments compare to the LR+(−)N treatment, respectively. In addition, the total PLFAs in the LR+(−)N treatment significantly increased by 50.61% at a depth of 0–10 cm but decreased from 121.62 to 42.31 nmol g−1 at a depth of 10–20 cm relative to the LI+(−)N treatment. Using PLFA as a biomarker, we detected that G− bacteria and total PLFA generally increased with increasing soil depth in the +N plots. However, the content of G− was the highest at a depth of 0–10 cm and the lowest at a depth of 10–20 cm in the LR plots. The modification of soil microbial biomass at a depth of 0–10 cm was induced by the bottom-up effect of changes in soil nutrient contents and using ability, which were driven by N addition and litter manipulation. Thus, different soil depths with different soil nutrient conditions resulted in a strong microbial community composition gradient.

红树林湿地相手蟹科动物摄食生态研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 红树林湿地相手蟹科动物摄食生态研究进展 DOI: 10.5846/stxb201301160110 作者: 作者单位: 国家海洋局第三海洋研究所,国家海洋局第三海洋研究所,国家海洋局第三海洋研究所,厦门大学,国家海洋局第三海洋研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41206108，41076049）；福建省自然科学基金项目（2011J05111）；海洋公益性行业科研专项项目（201205008） Feeding ecology of sesarmid crabs in mangroves Author: Affiliation: Third Institute of Oceanography, State Oceanic Administration,Third Institute of Oceanography, State Oceanic Administration,Third Institute of Oceanography, State Oceanic Administration,Xiamen University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:相手蟹科物种是红树林湿地的主要底栖动物类群，在生态系统中起着重要的作用。我国大陆地区目前已记录的相手蟹科物种数量为12种，低于其它红树林地区（国内常用的采样方法会造成螃蟹物种数量和密度的低估），其中褶痕相手蟹（Sesarma plicata）、无齿相手蟹（S. deaani）和双齿相手蟹（S. bidens）等是常见种。红树植物叶片是相手蟹科动物的主要食物来源，相手蟹科动物通过地表摄食和洞穴贮存的形为消耗了大量的红树植物凋落叶，使这些凋落叶的有机质和营养元素得以保留在生态系统内，在凋落叶的周转和物质归还方面起到重要的作用。它们同时也摄食红树植物的繁殖体并且对不同物种的繁殖体具有摄食偏好，这可能对一些红树物种的植被更新能力和红树植被群落结构产生影响。相手蟹科动物对不同物种和不同状态的红树叶片也存在摄食偏好，通常对腐烂的叶片摄食偏好较强；螃蟹的摄食偏好与叶片的营养成份、粗纤维和单宁含量以及C/N比等性质有关；但在恶劣的野外环境下，螃蟹则会表现出随机性摄食。目前关于相手蟹科动物生态学作用的认识仍不充分，例如它们的种群大小和对凋落物的转化作用等，有待于进一步研究。 Abstract:Sesarmid crabs, common macro invertebrates in mangrove ecosystems, influence the structure and function of mangrove habitats through their burrowing activities and processing of leaf litter. A total of 12 sesarmid species have been recorded in mainland China, which may be an underestimate since more sesarmid species have been reported in Hong Kong and other tropical mangrove regions. (The reason for this underestimation could be due to the method commonly used to locate the crabs within mainland China. The most common method used is to place plot frame on the soil surface and simply dig to about 20-30 cm, and sift through the soil to locate crabs which could allow sesarmid crabs to escape deeper into the soil during the digging.) The most common sesarmid species in China are Sesarma plicata, S. deaani and S. bidens, while Neosarmatium meinerti is widely recorded in tropical areas of Australia and Kenya. Mangrove plant tissues, mainly leaves, are the main food source of sesarmid crabs, but crabs also feed on sediment detritus and faunal tissue to supplement the nutrient limited mangrove leaves. Some dietary specializations among different mangrove crabs have been recognized. Some crabs feed on only live leaves obtained by climbing into trees, while some species feed only on dead leaves on the mangrove floor. Crabs also have frequently been observed burying fallen mangrove leaves, to enhance leaf nutrition quality, prevent leaf litter from being removed by tidal flushing and avoid competition and predation when food or time available for collecting food is limited, and predator abundance is high. The feeding preference of sesarmid crabs for mangrove leaves with different conditions or from different mangrove species also has been reported from the laboratory and the field research. For example, sesarmid crabs in China prefer leaves of Kandelia candel over those of Bruguiera gymnorrhiza and Aegiceras corniculatum. Leaf characteristics such as C/N ratio, tannin, water and crude fiber contents determine the feeding preferences. Generally, sesarmid crabs prefer decomposed leaves, ascribed to the decreased tannin content and C/N ratio, and increases in water during leaf decomposition. It also has been suggested that crabs need to consume more decomposed leaves to obtain adequate C and N since they have lower C and N assimilation rates from those leaves. Feeding preferences have been more often demonstrated in laboratory studies while some field studies have revealed a lack of selective feeding of different mangrove species. This is probably due to the environmental stresses in field like predation, limited feeding time, and limited food availability. The ability of sesarmid crabs to remove leaf litter has been studied frequently in the past decades, and crabs have been shown to consume a large proportion of annual leaf fall production, far in excess of the local production in some mangrove forests. The ability of crabs to remove litter seems to be stronger in tropical areas than in subtropical or warm temperate areas. In subtropical areas like China, removal of leaf litter is affected by temperature and showed significant seasonal variation. Not only sesarmid crabs but some snails (e.g. Terebralia palustris) and ocypodoid/grapsid crabs (e.g. Helograpsus haswellianus and Ucides cordatus) also have been reported to consume mangrove leaves. Direct grazing of leaf litter by crabs accounts for a small proportion of leaf litter removed from mangrove floor in China, while the stocking of leaves in crab burrows for later consumption is the key way by which leaf litter is retained in the ecosystem, preventing tidal export. Through shredding and grazing of leaf litter, crabs also initiate and enhance the breakdown of mangrove detritus and recycling of nutrients. Sesarmid crabs also have been found to graze mangrove propagules and seeds, thus play a critical role in determining seedling recruitment and vegetation regeneration. It also has been suggested that the predation preference on some non-dominant mangrove species regulates their distribution with the vegetation community. The feeding ecology of sesarmid crabs and its involvement of in mangrove restoration, their retention of C and nutrients in mangrove soils and predation of seeds/propagulse are worthy further studies. 参考文献 相似文献 引证文献

Susceptibility of eastern US habitats to invasion of Celastrus orbiculatus (oriental bittersweet) following fire

Fire effects on invasive species are an important land management issue in areas subjected to prescribed fires as well as wildfires. These effects on invasive species can be manifested across life stages. The liana Celastrus orbiculatus (oriental bittersweet) is a widespread invader of eastern US habitats including those where fire management is in practice. This study examined if prescribed fire makes these habitats more susceptible to invasion of C. orbiculatus by seed at Indiana Dunes National Lakeshore. Four treatments (control, litter removed, high and low intensity fire) were applied in six habitat types (sand savanna/woodland, sand prairie, moraine prairie, sand oak forest, beech-maple forest, and oak-hickory forest) and germinating seedlings were tracked over two growing seasons. Treatment did not have a significant effect on the germination, survival, or biomass of C. orbiculatus. However, habitat type did influence these responses mostly in the first growing season. Moraine prairie, beech-maple forest, and oak-hickory forests had the greatest peak percentage of germinants. Moraine prairie had significantly greater survival than oak forest and savanna habitats. Control plots with intact litter, and the moraine prairie habitat had the tallest seedlings at germination, while tallest final heights and greatest aboveground biomass were highest in oak forest. Thus, fire and litter removal did not increase the susceptibility of these habitats to germination and survival of C. orbiculatus. These results indicate that most eastern US habitats are vulnerable to invasion by this species via seed regardless of the level or type of disturbance to the litter layer.

Tree seedling recruitment in Amazon secondary forest: Importance of topography and gap micro-site conditions

Deforested lands in Amazonia are usually converted into pastures and maintained through annual prescribed burning which depletes the soil seed bank. Here, we assess the effect of topography and micro-site conditions on the seed bank and recruitment success of tree species in 20-year old secondary forests developing on abandoned pastures in Central Amazonia, Brazil. Seedling emergence, mortality, and growth were monitored in four 1×1-m sub-plots located systematically in the center of 21 10×10-m artificial canopy gaps, seven each on three different topographic positions – plateau, slope, and bottomland. The 84 seedling sub-plots were assigned to four different treatments generated by the combination of two litter treatments, litter intact and litter removed, and two soil treatments, soil turned and soil unturned. Sixteen soil samples were collected from the four corners of each sub-plot for analysis of the seed bank. There was no significant effect of topography on the number of seeds, although on the average, densities on the plateaus and the bottomlands were more than double that on the slopes. Seedling emergence increased 200% with litter removal and 50% with soil turning relative to respective controls. Seedling emergence was significantly higher in bottomlands than in slopes, and seedling growth was significantly higher in bottomlands and slopes than in plateaus, indicating that water availability may be the limiting factor for the recruitment success on the higher parts of relief. There were no effects of topography and litter removal on seedling mortality. Management tools that can accelerate succession on intensively used land offer options for fostering reforestation. Based on this study, manipulating litter and soil micro-environment provide viable methodological tools.

Seasonal variability of leaf litter removal by crabs in a Kandelia candel mangrove forest in Jiulongjiang Estuary, China

The seasonal variability of leaf litter removal by crabs was observed from May 2006 to April 2007 in a Kandelia candel mangrove forest in Jiulongjiang Estuary, China. Daily average quantities of leaf fall ranged 0.85–3.86 gDW m −2 d −1, with high values in May, August, October and November. The whole-year's leaf fall was 6.48 t ha −1 yr −1 (1.81 gDW m −2 d −1). The standing stock of leaf litter on the forest floor was 7.78 gDW m −2 averaged from the whole year's data, with the lowest value in December (1.23 gDW m −2) and the highest in April (16.18 gDW m −2). Annually averaged removal (consumption on mangrove floor + burial in burrows) rate of leaf litter by crabs was 0.59 gDW m −2 d −1. High seasonal variability was observed in the removal rates of leaf litter by crabs. Removal rates in the winter months (December, January and February) were 0.07–0.09 gDW m −2 d −1, much lower than those in other months with values of 0.59–1.18 gDW m −2 d −1. Annually averaged percentage of leaf fall removed by crabs was 33%, with the highest values in September (reached 76%) and the lowest values in winter months. Of leaf litter removed by crabs, a large proportion was buried by crabs, and only 12% was consumed by crabs on the forest floor. Leaf litter removal rate, consumption rate on the forest floor, percentages of leaf fall and standing stock removed on the forest floor were significantly positively correlated with air temperature, indicating that leaf removal ability by crabs was higher in warm months than in cold months.

Effect of Standing Litter on Rough Fescue Utilization by Cattle

Fescue grasslands are well suited to dormant-season grazing, whereas spring defoliation is detrimental to rough fescue ( Festuca campestris Rydb.). Dormant-season grazing may also condition fescue plants for subsequent selection in spring by removing standing litter (i.e., senesced biomass). This relationship must be understood in order to manage grazing and conserve rough fescue. This study determined the effects of standing litter on plant selection and utilization by cattle in spring. Forty dormant rough fescue plants were conditioned in fall by removing standing litter in a 4 (treatments) × 10 (blocks) randomized complete block design. This design was repeated with the use of 2 separately grazed paddocks. Treatments were a control (no litter removal) and standing litter removed at 14-, 7-, and 2.5-cm stubble height. Nonparametric plant selection data were analyzed with the use of χ 2 methods. Spring biomass utilization was estimated nondestructively through height–weight modeling techniques, and data were analyzed with the use of analysis-of-variance procedures. The stubble height of standing litter affected ( P < 0.05) plant selection by cattle in the first 2 days of the trial when grazing pressure was light. By the end of the 6-d grazing period 96% of fescue plants were selected at least once. Additionally, 18% of plants were regrazed at least once after 3 days, and 48% after 6 days. Thus, the protective barrier effect of standing litter had limited effect on plant selection by cattle except when grazing pressure was light. However, the degree of spring biomass utilization increased with shorter stubble heights. After 6 days of grazing, the current growth of plants with standing litter removed at 2.5 cm was utilized at 64%, and control plants were utilized 9%. Therefore, at high grazing pressure the mass of standing litter influenced the degree of utilization, suggesting litter retention is important in limiting grazing impacts on rough fescue. Los pastizales de “Fescue” están bien adaptados al apacentamiento en la época de dormancia, mientras que la defoliación en primavera es perjudicial para el “Rough fescue” ( Festuca campestris Rydb.). El apacentamiento en durante la dormancia también puede acondicionar las plantas para la selección subsecuente en primavera al remover el mantillo en pie (i.e., la biomasa senescente); esta relación debe ser entendida para manejar el apacentamiento y conservar el “Rough fescue.” Este estudio determinó los efectos del matillo en pie en la selección y utilización de las plantas por el ganado en la primavera. Cuarenta plantas de “Rough fescue” fueron acondicionadas en otoño removiendo el mantillo en pie de ellas y se asignaron a 4 tratamientos en 10 bloques bajo un diseño de bloques completos al azar. Los tratamientos fueron: control (sin remoción del mantillo) y remoción del mantillo en pie a 14, 7 y 2.5 cm de altura del rastrojo remanente, este diseño se repitió usando separadamente dos potreros apacentados. Los datos noparamétricos de la selección de plantas se analizaron con métodos de χ 2 . La utilización de la biomasa en primavera fue estimada por métodos no destructivos mediante técnicas de modelado de altura-peso y los datos fueron analizados usando procedimientos de análisis de varianza. En los primeros 2 días del ensayo, cuando la presión de apacentamiento fue ligera, la altura del rastrojo del mantillo en pie afectó ( P < 0.05) la selección de plantas por el ganado. Al final del periodo de apacentamiento de 6 días, 96% de las plantas de “Rough fescue” fueron seleccionadas al menos una vez. Adicionalmente, 18% de las plantas fueron re- apacentadas al menos una vez después de 3 días y 48% después de 6 días. Así, el efecto de barrera protectora del mantillo en pie fue limitado sobre la selección de las plantas por el ganado, excepto cuando la presión de apacentamiento fue ligera. Sin embargo, el grado de utilización de la biomasa en primavera aumentó en las alturas de rastrojo más cortas. Después de 6 días de apacentamiento, el crecimiento de las plantas con remoción de mantillo en pie a 2.5-cm de altura del rastrojo fue utilizado al 64% mientras que las plantas control se utilizaron 9%. Por lo tanto, con una presión de apacentamiento alta la masa de mantillo en pie influenció el grado de utilización, sugiriendo que la retención de mantillo en pie es importante para limitar los impactos del apacentamiento sobre el “Rough fescue.”.

Responses of desert grassland vegetation to mesquite removal and regrowth

The purpose of this study was to determine the long-term response of understory vegetation in the desert grassland of southeastern Arizona, USA, to removal and regrowth of mesquite Prosopis juliflora (Swartz) DC. var. velutina (Wooton) Sarg. trees. The study involved 3 treatments applied to mesquite in 1966; mesquite left intact (MI), mesquite removed (MR), and mesquite removed, sprouted, and regrown (MRS). Vegetation responses to 2 litter treatments, litter intact (LI) and litter removed (LR), also were examined. Cover of understory vegetation and juvenile mesquite (< 1.5 m height) were measured in canopy and open (intercanopy) locations. Major changes between 1967 and 1991 were increased cover of juvenile mesquite, shrubs, halfshrubs, bush muhly Muhlenbergia porteri Scribn., and Lehmann lovegrass Eragrostis lehmanniana Nees., and a decline in cover of Arizona cottontop Digitaria californica (Benth.) Chase, and plains bristlegrass Setaria macrostachya H.B.K. Arizona cottontop, plains bristlegrass, and bush muhly were more abundant in canopy locations; black grama Bouteloua eriopoda Torr. and Lehmann lovegrass were more abundant in open locations. Lehmann lovegrass cover was lowest in canopy locations of the mesquite intact treatment. Combination of the mesquite removed and sprouted and litter intact treatments favored increased cover development of native perennial grasses. Litter removal enhanced cover development of Lehmann lovegrass, most likely through increased amount of red light and increased soil temperature fluctuations. Low levels of understory cover (22% average) probably facilitated recruitment of mesquite and other woody plants. Our observation that the greatest cover of Arizona cottontop, plains bristlegrass, and bush muhly occurred in the canopy location of the mesquite intact treatment suggests a potential strategy for maintaining diversity of native perennial grasses. Mature mesquite should be examined as a refuge for native species.

Responses of desert grassland vegetation to mesquite removal and regrowth

The purpose of this study was to determine the long-term response of understory vegetation in the desert grassland of southeastern Arizona, USA, to removal and regrowth of mesquite Prosopis juliflora (Swartz) DC. var. velutina (Wooton) Sarg. trees. The study involved 3 treatments applied to mesquite in 1966; mesquite left intact (MI), mesquite removed (MR), and mesquite removed, sprouted, and regrown (MRS). Vegetation responses to 2 litter treatments, litter intact (LI) and litter removed (LR), also were examined. Cover of understory vegetation and juvenile mesquite ( 1.5 m height) were measured in canopy and open (intercanopy) locations. Major changes between 1967 and 1991 were increased cover of juvenile mesquite, shrubs, halfshrubs, bush muhly Muhlenbergia porteri Scribn., and Lehmann lovegrass Eragrostis lehmanniana Nees., and a decline in cover of Arizona cottontop Digitaria californica (Benth.) Chase, and plains bristlegrass Setaria macrostachya H.B.K. Arizona cottontop, plains bristlegrass, and bush muhly were more abundant in canopy locations; black grama Bouteloua eriopoda Torr. and Lehmann lovegrass were more abundant in open locations. Lehmann lovegrass cover was lowest in canopy locations of the mesquite intact treatment. Combination of the mesquite removed and sprouted and litter intact treatments favored increased cover development of native perennial grasses. Litter removal enhanced cover development of Lehmann lovegrass, most likely through increased amount of red light and increased soil temperature fluctuations. Low levels of understory cover (22% average) probably facilitated recruitment of mesquite and other woody plants. Our observation that the greatest cover of Arizona cottontop, plains bristlegrass, and bush muhly occurred in the canopy location of the mesquite intact treatment suggests a potential strategy for maintaining diversity of native perennial grasses. Mature mesquite should be examined as a refuge for native species.

Responses of desert grassland vegetation to mesquite removal and regrowth

Abstract The purpose of this study was to determine the long-term response of understory vegetation in the desert grassland of southeastern Arizona, USA, to removal and regrowth of mesquite Prosopis juliflora (Swartz) DC. var. velutina (Wooton) Sarg. trees. The study involved 3 treatments applied to mesquite in 1966; mesquite left intact (MI), mesquite removed (MR), and mesquite removed, sprouted, and regrown (MRS). Vegetation responses to 2 litter treatments, litter intact (LI) and litter removed (LR), also were examined. Cover of understory vegetation and juvenile mesquite (< 1.5 m height) were measured in canopy and open (intercanopy) locations. Major changes between 1967 and 1991 were increased cover of juvenile mesquite, shrubs, halfshrubs, bush muhly Muhlenbergia porteri Scribn., and Lehmann lovegrass Eragrostis lehmanniana Nees., and a decline in cover of Arizona cottontop Digitaria californica (Benth.) Chase, and plains bristlegrass Setaria macrostachya H.B.K. Arizona cottontop, plains bristlegras...

Central dieback of the dryland bunchgrass Eragrostis curvula (weeping lovegrass) re-examined: The experimental clearance of tussock centres

Experiments were conducted to investigate: (1) tiller recruitment within the interior of Eragrostis curvula tussocks, with and without litter removal; and (2) effects of moderate defoliation on tiller recruitment within the interior of the clump. Tiller recruitment within the interior of non-defoliated plants was significantly (p<0·01) increased by litter removal. When field-grown plants were defoliated, the tillering rate was greater (p<0·01) in plants with litter retained than those with litter removed 91 days after defoliation. When the greenhouse-grown plants were defoliated, tiller recruitment was greater (p<0·05) in plants with litter retained than those with litter removed during the first 13 weeks after defoliation. Tillering in the non-defoliated plants was less (p<0·05) than in defoliated plants with litter retained. Litter removal or moderate defoliation stimulated basal tillering by opening up the canopy and providing more light available to the basal buds. Therefore, the central dieback is not simply a natural consequence of tillering pattern; resource depletion within the interior may be a contributing factor to this phenomenon.

Effects of stand age and litter removal on the regeneration of Populus tremuloides

Abstract. The objective of this study was to demonstrate the regeneration by root suckering of Populus tremuloides (quaking aspen) along a successional sere at Lake Duparquet in NW Québec with six sites of different ages ‐ 46, 74, 120, 143, 167 and 230 yr since last fire. In 1990, in each of the sites, one 20 m x 20 m plot was cut. In each plot, 4‐m2 plots were selected, both control and with litter removed. The number of suckers and their height were estimated for each plot in 1991, 1992 and 1993. Results showed that sucker production was not related to the number of P. tremuloides before the clearcut, but it was related to litter whereby increasing cover lowered the production. The number of suckers produced in the control plots did not show any significant difference along the successional sere for any of the three years. Scarified plots had more suckers than control plots, and this increase was more pronounced and significantly different for the younger stage. Regression analysis for the 1991 and 1992 data showed that sucker number in scarified plots decreased with increasing seral stage age. Mortality, after three growing seasons, was about 60% for all plots and was not affected by seral stage and treatment. We suggest that removal of litter in scarified plots exposed the roots to higher temperatures and caused wounds, both of which may have stimulated the production of suckers in young seral stages.

Effect of forest floor disturbance on seedling establishment of Chamaecyparislawsoniana

Native seeds of Chamaecyparislawsoniana (A. Murr.) Parl. (Port-Orford-cedar) were sown on treated 1-m2 plots in four natural stands in southwestern Oregon, U.S.A. Treatments, replicated four times per stand, were (1) control, with natural litter undis-turbed, (2) litter removed, (3) litter removed and burned with ash replaced on plot, and (4) spaded after litter removal. Eighty-nine percent of germination occurred in early to mid-June. The spading treatment had the most germinants and the most survivors. Litter removal and burning treatments supported many fewer germinants, had the smallest seedlings, and had no survival after two growing seasons. Percentage survival of the few germinants in the control was as good as for the spading treatment, 5–6% after three summers. Although much natural seedling establishment may occur on natural litter, soil disturbance appears to greatly increase the rate of establishment. Litter removal alone does not increase establishment.

Cycling of nitrogen by surface-casting earthworms in a pasture ecosystem

Production of surface casts and the removal of plant litter from the soil surface by earth-worms had similar seasonal variations, with maximum values in May and minimum values occurring in July and August. Seasonal variations in the total nitrogen (TN) and oxidizable carbon contents of casts were closely related to variations in litter production. The C:N ratio of casts (10.7) was consistently smaller than that of underlying soil material (15.0 and 14.2 for the 0–5 and 18–22 cm depths, respectively), which is probably due to the mineralization of plant-derived organic material during passage through earthworms and utilization of low C:N ratio litter. Seasonal changes in the amounts of inorganic N forms in casts showed a build-up of NH 4 +N in the cooler winter months (July and August), attaining a maximum of 112 μg.g −1. with a decrease in autumn (April and May) and early spring (September and October), reaching a minimum of 54 μg.g −1. The opposite trend existed for seasonal variations in the NO 3 −-N content of the casts. Because only minor fluctuations in the amounts of N forms were obtained for underlying soil material during the casting period, the more dramatic changes observed in the casts could not be explained by soil variations. Seasonal variations in urease enzyme activity, associated with fluctuations in organic matter content, were more important than the effect of temperature on enzyme activity in accounting for seasonal variations in the NH 4 +-N content of casts. It was calculated that 73% of the TN content of litter removed from the surface by earthworms was accumulated in casts, indicating both the importance of earthworms in incorporating litter N with soil material and the inefficiency of N digestion by earthworms.