<Emphasis Type="Italic">Melaleuca quinquenervia</Emphasis> dominated forests in Florida: analyses of natural-enemy impacts on stand dynamics

Melaleuca quinquenervia (melaleuca) is a native of Australia but has become an invasive plant in Florida, USA. We conducted a long-term demographic study of melaleuca in three sections (central, transitional, and peripheral) of monoculture stands located in Florida, and quantified absolute density, diameter at breast height and basal area of trees by section at three sites. Additionally, we monitored the impacts of natural enemy (insects and fungi) on melaleuca populations which became apparent after 2001. Both absolute density and basal area, from before (1997–2001) and after noticeable natural-enemy impact (2002–2005), were compared. Prior to the natural-enemy impact, absolute density of melaleuca trees declined primarily due to self-thinning and associated losses of small trees, but diameter at breast height increased, as did the basal area. Later during the period when natural enemies prevailed, absolute density declined at a significantly greater rate across all sections but was highest at the periphery. The decrease in mean absolute density and basal area/ha of melaleuca during the natural-enemy impacted period coincided with the increased incidence of the populations of plant-feeding insects and fungi. The mean diameter at breast height continued to increase in all sections of the stands throughout the study period. An increasing trend in basal area prior to natural-enemy impact was reversed after increase in natural-enemy abundance and noticeable impact in all three sections of the stands. These findings lend support to a growing body of literature that implicates natural enemies as increasingly important density-independent regulators of M. quinquenervia populations. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged     

Dormant Season Prescribed Fire as a Management Tool for the Control of <Emphasis Type="Italic">Salix caroliniana</Emphasis> Michx. in a Floodplain Marsh

Expansion of woody species into herbaceous wetlands is a serious concern in wetland management. Prescribed fire is often used as a tool to manage woody species, although many species resprout after fire making control problematic. In this study, we assessed the usefulness of repeated dormant season fires for controlling Salix caroliniana (Michx.) in a floodplain marsh in Florida. Salix is a common shrub in southeastern marshes that resprouts prolifically after fire. We compared stem basal area, stem density, and cover of Salix in three adjacent sites in a floodplain marsh in east central Florida. One site was burned once in February 1997, another site was burned in February 1997 and then again in March 1999 and one site was left unburned. At the unburned site, Salix stem basal area, stem density, and cover increased over the course of the study. In the two burned sites, the first fire destroyed large diameter stems and stimulated production of sprouts. As a result, stem basal area and cover decreased but stem density remained unchanged. The second fire caused a decline in stem density and a further decline in cover. Changes in understory species composition and cover could not be attributed to the fires. Our results suggest that dormant season fires are effective in reducing Salix cover and basal area, and that repeated fires have greater effects than a single fire.     

Species richness and evenness respond in a different manner to propagule density in developing prairie microcosm communities

Diversity has two basic components: richness, or number of species in a given area, and evenness, or how relative abundance or biomass is distributed among species. Previously, we found that richness and evenness can be negatively related across plant communities and that evenness can account for more variation in Shannon’s diversity index (H′) than richness, which suggests that relationships among diversity components can be complex. Non-positive relationships between evenness and richness could arise due to the effects of migration rate or local species interactions, and relationships could vary depending on how these two processes structure local communities. Here we test whether diversity components are equally or differentially affected over time by changes in seed density (and associated effects on established plant density and competition) in greenhouse communities during the very early stages of community establishment. In our greenhouse experiment, we seeded prairie microcosms filled with bare field soil at three densities with draws from a mix of 22 grass and forb species to test if increased competition intensity or seedling density would affect the relationships among diversity components during early community establishment. Increased seed density treatments caused diversity components to respond in a different manner and to have different relationships with time. Richness increased linearly with seed density early in the experiment when seedling emergence was high, but was unrelated to density later in the experiment. Evenness decreased log-linearly with seed densities on all sampling dates due to a greater dominance by Rudbeckia hirta with higher densities. Early in the experiment, diversity indices weakly reflected differences in richness, but later, after the competitive effects of Rudbeckia hirta became more intense, diversity indices more strongly reflected differences in evenness. This suggests that species evenness and diversity indices do not always positively covary with richness. Based on these results, we suggest that evenness and richness can be influenced by different processes, with richness being more influenced by the number of emerging seedlings and evenness more by species interactions like competition. These results suggest that both diversity components should be measured in plant diversity studies whenever it is possible.     

Phytoplankton succession and diversity in a warm monomictic,relatively shallow lake: Lake Volvi,Macedonia, Greece

In Lake Volvi, phytoplankton dominance was examined in relation to the main phases of the fluctuating physical state of the water column and nutrient levels. Four stages of algal succession were identified. The successional pattern was, in general, similar from year to year. External disturbances such as increased wind mixing and high floods had the effect of setting the succession back to an earlier stage.Nanoplanktic diatoms and flagellates dominated during the first stages of succession. The succession was running from r-selected species in early stages to K-strategists in summer and towards a mixed community in the terminal stage.Diversity was expressed by the indices of Gleason and Shannon (based on physical units and biomass). Interpretation of species diversity took into account the differential variations of its two components, the number of species and the evenness of their distribution. Diversity was more affected by evenness than by number of species.Diversity increased in late stages of succession corresponding to the complexity of the community (high number of species, high evenness). Physical disturbances influenced positively the diversity. The maximal diversity appeared in the transition periods between the compositional changes generated by disturbances and the true successional development. Disturbances may generate a more uniform distribution of diversity throughout the whole water column.The role of physical disturbances in increasing the phytoplankton diversity may be demonstrated from comparisons of diversity — evenness — species number of the same stages under different meteorological conditions.     

Response of grassland soil arthropod community to biological and conventional control of a native moth: using Beauveria bassiana and lambda-cyhalothrin for Dalaca pallens (Lepidoptera: Hepialidae) suppression

Conventional and biological control of a native moth, Dalaca pallens (Blanchard) (Lepidoptera: Hepialidae), were evaluated in Southern Chile in relation to changes on community metrics (diversity, species richness, evenness and dominance) of a soil-dwelling invertebrate assemblage. Two experiments were conducted (in winter and spring) to compare non-target effects of Beauveria bassiana (Balsamo) Vuillemin and lambda-cyhalothrin insecticide. The invertebrate community was sampled before and after spraying by extracting soil cores. Estimates of diversity (Shannon index), species richness, evenness (Hurlbert’s Probability of Interspecific Encounter) and dominance indicated that the invertebrate assemblage was strongly disturbed by lambda-cyhalothrin treatment but not by B. bassiana applied in winter, over the sampling period (40 days). Spring results revealed that diversity and evenness at control and at B. bassiana plots were similar between them and higher than at lambda-cyhalothrin plots, while there were no differences between sites 30 days after treatment in species richness. Inundative biological control using B. bassiana strain QU-B931 was considered to pose lower ecological risk than lambda-cyhalothrin, currently one of the most frequently used insecticides for D. pallens control.     

Trichomes: their Diversity,Distribution and Density in Acclimatization of Teak (Tectona grandis L.) Plants Grown in vitro

Diversity, distribution and density of trichomes were studied in relation to other morphological and physiological parameters of in vivo and in vitro teak (Tectona grandis L.) plants with the objective to understand their role in hardening and acclimatization of micropropagated plants. Less diversity and scanty distribution of trichomes of in vitro leaves in comparison to the in vivo ones were correlated with water loss of the former plants leading to low rate of survival after transplantation. The probable cause for absence of certain types of trichome in in vitro plants was also discussed.     

Effects of controlled livestock grazing and annual prescribed fire on epigeal termite mounds in a savannah woodland in Burkina Faso

The diversity and abundance of epigeal termite mounds were investigated in response to controlled livestock grazing and annual prescribed fire in a Sudanian savannah-woodland in Tiogo State Forest. Sampling of termite mounds was carried out in 4×4 subplots of 0.25 ha in a split-plot experimental design during the rainy season in 2002. There were two main plots of which one was fenced to exclude livestock grazing and the second exposed to grazing. Each of the main plots included 4 subplots with annual prescribed fire since 1992 and 4 subplots without fire. Data were collected on the number and characteristics of termite mounds. A mean density of 698 mounds ha⁻¹ was recorded. Mounds built by Trinervitermes spp. were the most abundant followed by Cubitermes spp., Macrotermes subhyalinus and M. bellicosus. The large mound-builders Macrotermes spp. dominated the community interms of basal area (96% of the total) and above-ground volume (99%). The diversity of mound types was notaffected by livestock grazing and annual early prescribed fire (P>0.05). There was no statistical effect of livestock grazing on mound density, whereas a strong depressive effect of annual fire was observed for Trinervitermes spp. mound density (P=0.012). In this ecosystem, annual prescribed fire appeared to be the major determinant for termite mound abundance. Received 2 February 2007; revised 23 October 2007 and 21 January 2008; accepted 22 Feburary 2008.     

Diversity measurements in shrubland communities of Galicia (NW Spain)

Diversity was studied in 10 communities, including the understory of native oak woodland, planted woodlands (pine and eucalypt), and shrublands in the strict sense (heathlands, broom shrublands, gorse shrublands).In each community, species richness, diversity, dominance and evenness were analysed. Differences were observed among communities with regard to species composition, richness in annual herbs, perennial herbs and shrubs, dominant plant families (Ericaceae, Papilionaceae) and diversification of shrub species.The possible relations between environmental stress and/or human influences on differences in diversity are discussed.     

Estimation of canopy density and irradiance in 20- to 40-year-old birch stands (Betula pubescens Ehrh. andBetula pendula Roth)

Three different experiments in birch (Betula pubescens Ehrh. andBetula pendula Roth) stands were conducted during summer 1991: an evaluation of the accuracy of the vertical tube method measuring crown free projection (CFP) in four birch stands; a study of relative irradiance (RI; photosynthetically active radiation, PAR), in birch stands differing in stem density and basal area; and an estimation of the CFP in different types of birch stands and the correlation between RI and CFP. The results indicate that the number of observation points well distributed over an area of 0.1 ha can vary between 50 and 200 to achieve sufficient accuracy. There were no significant differences in the CFP estimates made on the same plot by different observers including an untrained observer. CFP was related to basal area, stem number and diameter sum in a non-linear regression, CFP = A^*e^-BX. The correlations between RI and basal area, density and diameter sum, respectively, were 0.54, 0.57 and 0.67 for PAR. The coefficients of determination for RI (PAR) and CFP were high (0.86).     

Long-term species change in a Uruguayan grassland

Abstract. This paper reports on species changes which occurred in plots in a Uruguayan grassland after 55 yr of continuous grazing. The study was based on the pioneering work of B. Rosengurtt who sampled 10 plots in 1935; in 1990 we re-sampled five of them. Comparative studies were based on rank-frequency, diversity, evenness and multivariate analyses. Diversity was measured as species richness S, Shannon's index H and its exponential form N = e^H, evenness E = N/S and Gini's coefficient of hierarchy G. Species-richness of the plots increased significantly. Species which entered the sites are mostly weedy species, while those that have decreased are mostly palatable forage species. Evenness, however, remained constant. Floristic change was chiefly associated with time, and secondarily with plot soil-type. During the 55 yr that elapsed between both observation periods, a dramatic floristic change has occurred in this grassland site.     

不同刈割频度对大针茅草原群落特征及土壤元素含量的影响

在草原生态系统中,土壤是植物生长发育最重要的基质,对植物群落动态有显著的影响。刈割是内蒙古典型草原区除放牧外最重要的利用方式。研究不同刈割频度对典型草原区群落特征和若干土壤性质的影响及土壤因子与群落特征的相关性,旨在得出对群落多样性最有利并最适宜生产利用的刈割频度。研究区设置在内蒙古锡林浩特市东部以大针茅建群的典型草原;在2009—2013年进行不同频度的刈割处理,共设置处理,一年两次刈割、一年一次刈割、两年一次(割一年休一年)刈割、围封,在2013年8月采集测定土壤养分的样品。刈割对群落多样性影响显著,割一年休一年Shannon-Wiener多样性指数、Pielou均匀度指数、丰富度指数均高于其他刈割处理(P0.05);不同频度刈割下,一年两次刈割处理下土壤20—30cm和30—40cm的有机质含量显著高于其他处理(P0.05);不同频度刈割处理下土壤中的速效磷和速效氮的含量没有显著差异;一年两次处理的土壤全氮含量显著高于其他处理(P0.05)。Shannon-Wiener多样性指数与有机质含量、全氮含量呈显著负相关;Pielou均匀度指数与土壤元素间无显著相关关系;Richness指数与有机质含量呈显著负相关,与全氮含量为极显著负相关关系。割一年休一年刈割处理下土壤元素含量呈现更好的状态,结合群落物种多样性及生产利用的角度,割一年休一年为最合理的刈割频度。     

林分密度对新津文峰山马尾松人工林林下物种多样性和生物量的影响

以四川省新津文峰山马尾松(Pinus massoniana)人工林为研究对象,用典型抽样法探究5种林分密度(A:1000株/hm~2;B:1125株/hm~2;C:1250株/hm~2;D:1375株/hm~2;E:1500株/hm~2)对林下植被物种多样性和生物量的影响及林下植被物种多样性和生物量的相关性。结果显示:(1)共调查到植物124种,隶属于74科115属,灌木层物种少于草本层。(2)灌木或草本层在不同林分密度下的优势种都较一致。(3)灌木层物种丰富度指数D值、Shannon-Wiener多样性指数H值及草本层4个多样性指数均在密度B、E分别有最大和最小值;灌木层D值随密度增大而先增后减,其他3个指数变化规律不明显。灌、草层J_(sw)值较稳定。(4)灌木层生物量比草本层多。总体上灌、草层地上生物量大于地下生物量,都在密度B达最大;灌木地下生物量保持较稳定,而草本层变化幅度较大。(5)除灌木层J_(sw)值与该层各生物量呈负相关外,其余各指标均显示正相关。不同林分密度对马尾松林下植物多样性和生物量产生不同的影响,经综合研究分析认为,林分密度1125株/hm~2相对更利于该地马尾松人工林的可持续健康发展。     

豚草入侵对新疆伊犁河谷林下本地草本植物群落结构的影响

为探究外来入侵植物豚草（Ambrosia artemisiifolia）对本地植物群落结构的影响,结合区内林下草本植物调查和室内分析方法,分析了豚草不同入侵压力下（无入侵、轻度入侵、中度入侵、重度入侵）本地草本植物丰富度、盖度等特征,探讨了地形、气候、土壤、光照、人口密度等外部因素与豚草种群特征、本地植物群落结构之间的关系。结果表明：豚草种群盖度与其高度、密度、生物量显著正相关。与对照相比,轻度入侵下本土草本植物Shannon-Wiener多样性指数和Pielou均匀度指数显著增加,丰富度、盖度未出现显著差异。随着豚草入侵程度加剧,本地草本植物物种丰富度、盖度极显著降低,样方Shannon-Wiener多样性指数先升高再降低,本土草本植物Pielou均匀度指数差异不显著。冗余分析（RDA）表明,土壤全氮、与道路距离、土壤全磷、郁闭度对研究区植物群落结构影响最大,土壤全氮含量随豚草盖度和生物量增加而减少,距道路越近或光照越强,豚草盖度和生物量越高。增强伊犁河谷地区交通往来货物豚草检验检疫力度、增加林内植被郁闭度或是抑制区内豚草入侵的有效手段。     

三峡库区次生黄栌灌木林的群落特征及种间联结性

以三峡库区次生黄栌(Cotinus coggygria)灌木林群落为研究对象,基于样地调查,分析了生境特征和群落特征。结果显示:该群落共有植物30科37属56种,物种组成简单、多样性低,群落中以喜光、耐干旱瘠薄和碱性土壤的物种居多。海拔和土壤有效磷含量是生境差异的重要因素;海拔、坡度和坡向对物种分布的影响最大。海拔与物种密度极显著负相关,坡向与物种高度极显著正相关;土壤pH与物种多样性和均匀度显著负相关,速效钾含量与物种密度呈极显著正相关,有效磷含量与物种丰富度和多样性显著正相关,与盖度显著负相关。综上,海拔、坡度和坡向是影响物种分布的因素;土壤有效磷和pH是影响物种多样性的因素;海拔、坡向、坡度、土壤有效磷和速效钾是影响群落数量特征的因素。群落总体关联性和物种种间联结性均呈显著负相关,种间联结较松散,处于不稳定的灌草阶段,生态系统脆弱,对生境变化十分敏感。因此,在对三峡库区黄栌群落进行生态修复时,应以保护现有群落及其生境为前提,选择适生乡土植物进行合理配置,增加物种多样性,促进群落演替。     

Population dynamics of Panonychus osmanthi (Acari: Tetranychidae) on two Osmanthus species

Panonychus osmanthi is a non-diapausing species of spider mite that superficially resembles P. citri. It infests Osmanthus species, which are evergreen roadside and garden trees. The population dynamics of P. osmanthi were studied on Osmanthus aurantiacus and O.×fortunei during a three-year period. Seasonal changes in P. osmanthi populations were fundamentally the same in each year, although their density differed greatly from year to year. TheP. osmanthi population was bimodal, with one peak in spring (May–June) and another in winter (November–January). Populations abruptly declined after the spring peak. Predators showed a delayed density-dependent response to changes in spider mites from spring to summer, whereas in autumn and winter, predators were few because they had entered diapause. To determine the effect of predators on the rapid decline of spider mites just after the spring peak, the predators were removed by treating the trees with a synthetic pyrethroid. As a result, spider mite density did not decline after the spring peak and remained at a high level during the June-August period when spider mite density is usually very low. This suggests that predators play an important role in the drastic decline of P. osmanthi density just after the spring peak. This revised version was published online in July 2006 with corrections to the Cover Date.     

Response of shrubland birds to regenerating clearcut area and shape

Conservation of birds that breed in early-successional forests will require an understanding of their response to patch size and shape during the early seral stages following disturbance. We modeled the effects of patch area, patch shape, and time period following harvest on territory densities of 5 shrubland bird species and bird community composition in 36 clearcuts from 1997 to 2014 in the Missouri Ozarks, USA. Our best-supported models indicated that densities of indigo bunting (Passerina cyanea), yellow-breasted chat (Icteria virens), and prairie warbler (Setophaga discolor) declined from the early time period (1–7 years post-harvest) to the late time period (12–18 years post-harvest), regardless of clearcut area or shape. Yellow-breasted chat density and bird species richness were positively related to clearcut shape complexity. Bird species richness increased, and bird species density decreased with clearcut area during both time periods. Non-metric multidimensional scaling indicated that bird community composition was strongly related to time since harvest. Within the spatial scale of our study, successional stage is more influential than clearcut size and shape, and some bird species may benefit from relatively small or irregularly shaped clearcuts. © 2019 The Wildlife Society.     

目标树经营初期对柏木人工林土壤线虫群落的影响

为研究目标树经营初期对柏木人工林土壤线虫群落的影响,对遂宁市安居区处于竞争生长阶段的柏木林进行3种不同密度目标树经营,共计样地12个(目标树密度为6株/667 m~2、9株/667 m~2、12株/667 m~2以及对照各3个)。在目标树经营1年后,采集春、夏、秋、冬4个季节样品共252个,采用改进的Baermann湿漏斗法分离土壤线虫,共鉴定出土壤线虫59科143属。其中Prionchulus为优势属,食细菌性线虫38属,食真菌性线虫12属,植食性线虫36属,杂食/捕食性线虫57属。土壤线虫生活史策略以c-p 4类群为主,占总数的44.33%,其中目标树密度为9株/667 m~2整个样地(9N)的c-p 4占比最大。目标树经营增加了土壤线虫的数量,目标树密度为9株/667 m~2的目标树单株(9C)线虫密度达到最大;目标树经营处理中均以杂食/捕食性线虫数量最多,其中9C杂食/捕食性线虫数量均高于其他处理;目标树经营提高了多样性指数(H′)、均匀度指数(J)、线虫营养多样性指数(TD)、线虫成熟度指数(MI),目标树经营改善了土壤线虫群落结构,其中目标树密度为9株/667 m~2样地的土壤线虫群落结构最优。研究结果表明,采用目标树经营有利于提升土壤线虫群落多样性,使柏木人工林生态系统向更稳定的方向发展,其中目标树密度为9株/667 m~2的效果最为显著。     

高寒区青海云杉人工林密度与林下植物多样性的关系

为了研究青海云杉人工林密度对林下植物多样性的影响及二者的关系,探明维持植物多样性、人工林生态系统稳定性及其健康状况的合理林分密度,以青海大通宝库林区6种不同密度（3 400株/hm²、2 900株/hm²、2 600株/hm²、2 300株/hm²、2 150株/hm²、1 750株/hm²）25年生青海云杉人工林林下植物的重要值、丰富度指数、多样性指数、均匀度指数为指标,对林下植被多样性随林分密度的变化规律进行分析。结果表明:(1) 青海云杉人工林下共有维管束植物60种,非维管束植物1种,隶属于29科45属。（2）灌木层植被优势种受密度影响较大,草本层植被优势种受密度影响较小。（3）青海云杉密度分别与灌木层和草本层的S指数、H′指数、Ea指数均呈显著相关关系,且相关系数分别为0.688、0.937、0.762和 0.679、0.870、0.505。（4）随着青海云杉密度的增加,林下植被多样性呈先减少后增大再减少的变化规律,且密度为2 600株/hm²时,林下植物多样性综合得分最高。研究认为,青海云杉林下植被多样性对其密度响应具有非同步性;密度为2 600株/hm²时比较适合林下植被生长,并保持林下植物多样性水平。     

Mound building termites contribute to savanna vegetation heterogeneity

With biomass densities comparable to large ungulates and megaherbivores, termites play a key functional role in many tropical savanna ecosystems. This study focuses on vegetated termite mounds (termitaria) constructed by the Termitidae species Macrotermes herus. We studied how resource rich termitaria affect graminoid herbs (Poaceae and Cyperaceae), forbs and woody species composition and diversity. The density of termitaria explained 89% of the variation in dense thickets in the area. Fire tolerant Acacia species dominated the open savanna while fire sensitive species like Grewia spp. and the succulent Euphorbia candelabrum were restricted to termite mounds. Termitaria plots had four times the mean number of woody species and supported three times as many forb species as the adjacent savanna. For woody species, both the Shannon–Wiener index and the Shannon evenness index were higher on temitaria than on the savanna. There were no differences for graminoid herbs, except for the Shannon evenness index which was higher on termitaria. Our results indicate that graminoid herb richness peaks at lower productivity levels than trees and forbs in savanna ecosystems, as also recently found in temperate areas.     

Artichoke Leaf Morphology and Surface Features in Different Micropropagation Stages

Artichoke (Cynara scolymus L.) leaf size and shape, glandular and covering trichomes, stomatal density, stomata shape, pore area and epicuticular waxes during micropropagation stages were studied by scanning electron microscopy (SEM) and morphometric analysis with the aim to improve the survival rate after transfer to greenhouse conditions. Leaves from in vitro shoots at the proliferation stage showed a spatular shape, ring-shaped stomata, a large number of glandular trichomes and juvenile covering hairs, but failed to show any epicuticular waxes. Leaves from in vitro plants at the root elongation stage showed a lanceolated elliptic shape with a serrated border, elliptical stomata, decreased pore area percentage, stomatal density, and mature covering trichomes. One week after transfer to ex vitro conditions, epicuticular waxes appeared on the leaf surface and stomata and pore area were smaller as compared to in vitro plants. Artichoke acclimatization may be improved by hormonal stimulation of root development, since useful morphological changes on leaves occurred during root elongation.