Relationships of Plant Parasitic Nematodes to Sites in Native Iowa Prairies

Soil samples were collected from three native Iowa prairies and analyzed for plant paiasitic nematodes and selected soil properties. Sites or nematodes were clustered with similarities related to habitat by a cluster analysis of site by nematode species and of nematodes by site. Some nematodes occurred in a wide range of prairie habitats, whereas others were more restricted. For example, greater numbers of Xiphinema americanum were in the low, well-drained sites than in the low wet sites or upland dry sites. Wet sites contained fewer nematodes than well-drained sites. Well-drained sites contained mainly Tylenchorhynchus maximus, Helicotylenchus pseudorobustus, and X. americanum. Wetter sites contained almost exclusively X. chambersi, H. hydrophilus, Telylenchus joctus, and an undescribed species of Tylenchorhynchus.     

Succession in sub‐boreal forests of West‐Central British Columbia

Abstract. Structural and compositional changes were analysed over the course of 400+ yr of post‐fire succession in the sub‐boreal forests of west‐central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approximately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca × engel‐mannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canopy structure became more complex as gap dynamics developed. Although these sub‐boreal forests contain few tree species, successional changes were pronounced, with structure changing more than composition across the chronosequence.     

Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland

Many early attempts at tallgrass prairie reconstruction failed to achieve the high species diversity of remnant prairies, and instead consist primarily of C₄ grasses. We hypothesized that frequent mowing of established prairie grasses could create sufficient gaps in the aboveground and belowground environment to allow for the establishment of native forbs from seed. We studied forb seedling establishment in a 25‐year‐old prairie planting in northern Iowa that was dominated by native warm‐season grasses. In winter 1999, 23 species of native forbs were broadcast into the recently burned sod at a rate of 350 viable seeds/m². Treatment plots were mowed weekly for either one or two growing seasons, and control plots were unmowed. Mowed plots had greater light availability than controls, especially when warm‐season grasses began to flower. Overwinter seedling mortality was 3% in mowed treatments compared to 29% in the controls. Forbs in mowed plots had significantly greater root and shoot mass than those in control plots in the first and second growing seasons but were not significantly more abundant. By the fourth growing season, however, forbs were twice as abundant in the mowed treatments. No lasting negative impacts of frequent mowing on the grass population were observed. Mowing a second year influenced species composition but did not change total seedling establishment. Experimental evidence is consistent with the idea that mowing reduced competition for light from large established grasses, allowing forb seedlings the opportunity to reach sufficient size to establish, survive, and flower in the second and subsequent years.     

封育对高寒草甸植物群落构成及生态位特征的影响

封育是天然草地管理的一种有效措施,利于草地生产力提高和退化草地恢复。该研究通过对青藏高原高寒草甸放牧和封育草地物种多样性、植被构成、植物种生态位特征、草地演替度等分析,解析高寒草甸植物种间关系及草地演替方向。结果表明:(1)封育显著降低了草地群落植物物种数以及α和β多样性指数,显著增加了草地1年生植物种数、地面芽植物种数和地上生物量。(2)放牧草地地上生物量以莎草科(59.7%)和禾本科(23.9%)为主,封育草地地上生物量以禾本科(85.0%)为主;放牧草地优势种为矮嵩草(Kobresia humilis)和线叶嵩草(K.capillifolia),封育草地优势种为垂穗披碱草(Elymus nutans)和早熟禾(Poasp.)。(3)放牧和封育草地的群落植物种重要值均与各自的生态位宽度变化规律一致。(4)草地植物种间竞争主要发生在不同科属植物种之间,封育增加了群落植物种整体生态位重叠值和植物种间竞争。(5)草地群落演替度为封育地放牧地,封育群落处于较稳定状态。研究认为,封育促进了高寒草甸由莎草+杂类草群落向禾草+杂类草群落演替。     

澳门黑沙水库植物群落与主要种类物候特征研究

为探讨澳门路环黑沙水库植物群落与物候特征,采用群落生态学的方法,研究了黑沙水库植物群落种类组成、空间结构、多样性及重点植物物候期。结果表明,在1200 m2样地中有维管植物88种,隶属于47科80属。乔灌层无明显优势树种,草本层中淡竹叶(Lophatherum gracile)具有较显著优势,各层植物分布均匀程度差异小。群落外貌终年常绿,大部分种类各物候期存在重叠现象,萌芽展叶期持续时间长,开花期集中在5-6月,果熟期10-12月最盛。根据乡土植物群落和物候特征,筛选并推荐在澳门及邻近区域可开发的景观植物,为构建生态价值高的植被景观或植被恢复提供参考。     

内蒙古草原退化群落恢复演替的研究—群落演替的数学模型

根据１９８３年至今１２年定位监测的结果,提出了一个描述典型草原在过大的牧压下退化和封育恢复演替的数学模型。建模的生态学公设是：１．植物群落占据的空间范围内环境因素视为均匀一致;２．退化和恢复演替进程中尚未发生植物种的消失和侵入;３．牲畜采食将增大牧草死亡率;４．草原群落内植物种群的竞争存在一个优胜顺序;５．植物种群增长遵循逻辑斯蒂克规律。对这一模型的稳定性分析说明：１．退化草原长期围封后可恢复到顶极状态;２．随着牧压的增强,草原群落将达到一个新的退化状态;３．退化过程和恢复过程的轨迹是不同的;４．草场改良措施改变了草原群落的演替轨迹和速率,使优质牧草在较大的种群尺度下向顶极状态演替。     

Plant Community Biomass Shifts in Response to Mowing and Fencing in Invaded Oak Meadows with Non‐Native Grasses and Abundant Ungulates

Many herbaceous meadows are dominated by competitive non‐native grasses and subject to ungulate herbivory, ecological processes that shift the proportional biomass of plant groups in the community. Predicting the outcome of restoration is complicated because herbivory and competition can interact. We examined the relationship between herbivory by native black‐tailed deer and domestic sheep and dominance of non‐native grasses in Garry oak meadows, one of North America's most endangered habitat types. A 3‐year factorial experiment tested the effects of mowing and fencing on plant community biomass, categorized into eight groups by geographic origin (native/non‐native), growth form (annual/perennial), and plant type (forb/grass). To test if the rarity of native plant groups was related to herbivory, we estimated ungulate foraging preferences for each plant group. Mowing and fencing treatments interacted for annual and perennial non‐native grasses. Dominance was shifted from non‐native to native grasses only when both mowing and fencing were applied. Fencing increased the total biomass, whereas mowing had no overall effect; however, fencing alone did not affect any individual plant group. Mowing shifted dominance from grasses to forbs, although both native and non‐native forbs benefited from the increased light availability. We also noted that herbivore fecal pellet densities were greatest in the spring, which coincided with the peak season of their preferred plant group, native perennial forbs. Overall, applying both mowing and fencing was the most effective restoration treatment to increase native plant groups and biomass.     

A Long‐Term Comparison of Hydrology and Plant Community Composition in Constructed Versus Naturally Occurring Vernal Pools

Successful restoration of ephemeral wetlands worldwide is particularly challenging, given the often‐precise relationship between hydrological features and plant community dynamics. Using a long‐term experiment in vernal pool restoration, we compare hydrological and vegetative characteristics of constructed pools with those of adjacent, naturally occurring reference pools. Although constructed and reference pools were similar in maximum water depth and duration of inundation at the beginning of our experiment in 2000, constructed pools were shallower and inundated for shorter periods by 2009. Native vernal pool species were able to establish populations in many constructed pools, and seeding sped their establishment. Comparing seeded plots in constructed pools with unseeded plots in reference pools, we found no significant difference in the cover of seeded species, native species, or exotic species in most years. In recent years, however, native species have declined in both constructed and reference pools. Finally, the cover of native vernal pool species was positively and non‐linearly associated with both water depth and seeding treatment. We conclude that the establishment of appropriate hydrological conditions was necessary, but not sufficient to promote successful performance of vernal pool species in constructed pools. Constructed pools with hydrologic conditions similar to those of reference pools were more likely to support populations of native vernal pool plant species, but only seeded pools were similar to reference pools in abundance of native cover. Most importantly, hydrological conditions in experimental pools have worsened since their construction, which may hamper persistence of native species in this restoration effort.     

Recovery of soil nitrogen pools in species‐rich grasslands after 12 years of simulated pollutant nitrogen deposition: a 6‐year experimental analysis

Nitrogen (N) deposition from anthropogenic sources is a global problem that can reduce biodiversity and impair ecosystem functioning through effects on soil eutrophication and acidification. While increasing controls on emissions of oxides of nitrogen (NO_x) have reduced European N deposition rates from their peak in the late 20th Century, little is known about the legacy effects of N deposition in soils or the reversibility of N‐induced shifts in ecosystem processes. We studied species‐rich limestone and acidic grasslands, located in a highly polluted region that received over 3000 kg N deposition ha^?1 throughout the 20th Century, followed by a decline of ～50% in NO_x deposition rate in the past two decades. We investigated the effects on seasonal and annual mean concentrations of soil mineral N in experimental plots established in 1990 receiving simulated enhanced N deposition (0–140 kg N ha^?1 yr^?1) until 2002, both in the final year of treatment, and the subsequent 5 years of ‘recovery’ following cessation of treatments. Winter–summer cycles of N mineralization–immobilization were strongly amplified by simulated N deposition rates through the final year of treatments and into the first year of recovery, with winter concentrations of ammonium‐N in the acidic grassland and nitrate in the limestone grassland enhanced by up to 360% and 450%, respectively. Both the magnitude of the seasonal variations and the residual effects of the treatments on soil mineral N concentrations decreased progressively in the first 5 years after treatments ceased, although dose‐dependent trends remained in the acidic grassland. This study establishes that reducing N deposition rates in species‐rich grasslands can reverse eutrophication, even in soils that have experienced prolonged high rates of deposition. It provides new insight into the rates of recovery following, and effects of, declining N deposition rates with implications for restoration of species‐rich grasslands.     

Vegetation Structure,Composition, and Species Richness Across a 56‐year Chronosequence of Dry Tropical Forest on Providencia Island,Colombia1

We compared vegetation structure and species richness across a 56‐yr chronosequence of six replicated age classes of dry tropical forest on the island of Providencia, Colombia, in the Southwest Caribbean. Stand age classes were determined using sequential, orthorectified panchromatic aerial photos acquired between 1944 and 1996 and Landsat 7 ETM + satellite imagery from 2000. Along the chronosequence we established 59 plots of 2 × 50 m (0.01 ha) to document changes in species richness, basal area, tree height, stem density, and sprouting ability. All woody trees and shrubs >2.5 cm diameter at breast height (DBH) were censused and measured. Although woody species density reached a peak in stands from 32 to 56 yr old, rarefaction analysis showed that species richness increased linearly with stand age and was highest in stands 56 yr old or greater. Nonparametric, abundance‐based estimators of species richness also showed positive and linear associations with age. Basal area and mean tree height were positively associated with age since abandonment, while sprouting ability showed a negative relationship. Our results indicate rapid recovery of woody species richness and structural characteristics along this tropical dry forest chronosequence.     

Leaf and Soil Nutrients in a Chronosequence of Second‐Growth Forest in Central Amazonia: Implications for Restoration of Abandoned Lands

Subsistence agriculture, cattle ranching, and periodical land abandonment are common land‐use practices in Amazonia. Because changes in land use affect biogeochemical cycles, secondary forests growing after land abandonment develop at varying speeds and spatial patterns, due in part to varying nutrient dynamics. Leaf and soil nutrient concentrations can provide useful information on nutrient cycling processes and strategies of nutrient use by trees that are suitable for introduction to abandoned areas. To understand nutrient dynamics in secondary forests from different regeneration stages, as well as the importance of pioneer species in the regeneration process, we measured the concentration of macronutrients in leaves of three pioneer tree species (Vismia cayennensis, Cecropia sciadophylla, and Bellucia dichotoma) in central Amazon secondary forests. We also measured macronutrients in the topsoil under the trees. We found that type of prior land use, time since abandonment, and number of fire events were significantly correlated with the concentrations of leaf and soil macronutrients, explaining between 10 and 38% of the variation in macronutrient concentrations. The observed patterns suggest that management practices affect the processes involved in N cycling and availability. Of the three pioneer species, C. sciadophylla showed the highest nutrient resorption efficiency and the highest leaf nutritional quality. We suggest that these two features determine a higher potential of C. sciadophylla for natural regeneration and restoration of abandoned lands.     

Fitness in Naturally Occurring and Restored Populations of a Grassland Plant Lychnis flos‐cuculi in a Swiss Agricultural Landscape

Wildflower seed mixtures are widely used for restoration of grasslands. However, the genetic and fitness consequences of using seed mixes have not been fully evaluated. Here, we studied the role of genetic diversity, origin (commercial regional seed mixtures, natural populations), and environmental conditions for the fitness of a grassland species Lychnis flos‐cuculi. First, we examined the relationship between genetic diversity, environmental parameters, and fitness in sown and natural populations of this species in a Swiss agricultural landscape. Second, we established an experiment in the study area and in an experimental garden to study the implications of local adaptation for plant fitness. Third, to examine the response of plants to different soil properties, we conducted an experiment in climate chambers, where we grew plants from sown and natural populations of L. flos‐cuculi as well as from seed suppliers on soils with different nutrient and moisture content. We detected no significant effect of genetic diversity on the fitness of sown and natural populations. There was no clear indication that plants from natural populations were better adapted to local environment than plants from sown populations or seed suppliers. However, plants of natural origin invested more into generative reproduction than plants from sown populations or seed suppliers. Furthermore, in the climate chamber, plants originating from natural populations tended to flower earlier. Our results indicate that using nonlocal seeds for habitat recreation may influence restoration success even if the seeds originate from the same seed zone as the restored site.     

An Investigation into the Effect of Soil and Vegetation on the Successful Creation of a Hay Meadow on a Clay‐Capped Landfill

This paper investigates the effect that manipulation of soil and vegetation conditions has on plant community development during attempts to create neutral hay meadow communities on a clay‐capped landfill in Somerset, United Kingdom. The objectives are (1) to determine the effect of manipulation of soil and vegetation on the development of the target plant community, (2) to identify whether these treatments had an effect on edaphic factors (physical and chemical properties, earthworm populations), and (3) to establish which, if any, of these edaphic parameters are underlying factors in determining the vascular plant community composition. In 2001 a commercial hay meadow seed mix was sown on three substrate treatments: (i) bare clay, (ii) a mixture of topsoil and compost ameliorant in equal proportions, and (iii) over naturally colonized vegetation. Plant community development and edaphic factors were monitored between 2001 and 2007. Although initially the presence of ameliorant promoted germination and growth of seeded species, after 2004 nonseeded competitive grasses dominated the sward. Where ameliorant was removed the target community continued to develop proving this to be the most successful treatment. This was found to be a due to suppression of competition from Elytrigia repens (Common couch), which grew most abundantly on soils with high organic matter and high soil water levels within the soil. Contrary to previous research, Trifolium repens (white clover) was not found to reduce forb diversity in this study. No evidence was found of earthworm abundance affecting plant community development.     

Effects of fire on ground‐dwelling arthropods in a shrub‐dominated grassland

Arthropods are abundant and diverse animals in many terrestrial food webs. In western Oklahoma, some shrublands are interspersed with discrete, dense thickets of tall, woody vegetation, known as mottes. Some of these shrublands are managed with prescribed burning. The goal of this study was to examine whether prescribed burning interacted with habitat type (i.e., shrubland versus mottes) to affect ground‐dwelling arthropod communities. Arthropods were collected in pitfall traps at four sampling locations in relation to mottes; in the center of mottes, and three plot location in shrublands; 1 m, 15 m, and 50 m away from the edge of the motte. There were three treatment levels for burning: one year postburn (burned in dormant months of 2017), two years postburn (burned in dormant months of 2016), and unburned (burned in dormant season of 2014 and prior). There were no significant interactions between prescribed burning and habitat type. Mottes had a different community of arthropods compared with the surrounding shrubland. Mottes also had lower overall abundance, but a higher diversity of arthropods. In terms of fires, arthropod communities one year after burning were different from those two or more years after burning. There was no effect of burning on overall arthropod abundance, but plots that were one year since burning had significantly lower diversity compared with plots that were two or more years postburn. The results of this study suggest that both fire and mottes can independently facilitate heterogeneity in arthropod communities, but they do not appear to interact with one another.     

Plant dispersal strategies and the colonization of Araucaria forest patches in a grassland‐forest mosaic

Questions: In a natural grassland‐forest mosaic: What is the influence of phylogeny and diaspore traits related to disperser attraction (DAT) on (1) seed size/number trade‐off (SSNT) in woody species colonizing forest patches; (2) on the frequency of the species? 3. What is the influence of forest patch area on mean seed size and number. 4. Do phylogeny and DAT expressed at the species level affect this relationship? Location: Campos grassland and Araucaria forest in São Francisco de Paula, RS, Brazil, at ca. 29°28’ S; 50° 13’ W. Methods: Forest patches of different sizes in a grassland site recovering for ten years since human disturbances were surveyed by the relative abundance of vertebrate‐dispersed woody saplings. We described colonizer species according to taxonomic phylogenetic relationships and diaspore type, size and color. We analyzed with a variation partitioning method their influence on SSNT and on species frequency in the patches. At the community level we regressed mean seed size and number on forest patch area and evaluated how these relationships were affected by phylogeny and DAT at the species level. Results: 1. Phylogeny and DAT mostly explained seed size and seed number per diaspore variation. 2. By controlling phylogeny and DAT influence the frequency of species in forest patches was positively associated with their seed number in the diaspores, and negatively associated with their seed size. 3. Mean seed size and seed number at the community level were positively associated with patch area. 4. When phylogeny and DAT influences on seed size were removed this relationship was stronger for seed size and weaker for seed number. Conclusions: 1. Energy allocation to dispersal in detriment of offspring survival increased the successful establishment of colonizer species in forest patches, despite phylogenetic relationships and DAT variation in their diaspores. 2. Although patch area exerted a selective pressure on seed size, habitat preferences of dispersers may also influence patch colonization.     

Succession in Bird and Plant Communities over a 24‐Year Chronosequence of Mine Rehabilitation in the Australian Monsoon Tropics

We compared the bird and woody plant communities of 2 to 24‐year‐old rehabilitation areas at Gove bauxite mine (20 km²) in the seasonal tropics of northern Australia, where Alcan has maintained a consistent rehabilitation program since it began operation in 1974. Birds were censused every second month over 2 years in 30 widely separated 0.25‐ha plots, representing five chronosequence stages. These were also compared with six (“off‐mine”) plots adjacent to the mine, which represented the annually burnt open forest typical of the region. Short‐lived Acacias dominated the early chronosequence stages, whereas eucalypts dominated in later stages. Mean avian species richness and abundance increased significantly along the chronosequence, with values for the oldest rehabilitation plots being very similar to those for the off‐mine plots. However, analyses of similarity revealed that the bird communities of the oldest rehabilitation plots were distinct from those of the off‐mine plots, indicating that succession in rehabilitation areas is not following a direct trajectory toward the native open forest surrounding the mine. Several hollow‐nesting bird species were scarce or absent in the rehabilitation areas, probably reflecting the absence of older hollow‐bearing trees. Many differences between the rehabilitation and the off‐mine areas in vegetation structure, woody flora, and avifauna appear to be related to the exclusion of fire from the minesite. We recommend the initiation of experiments designed to assess the effects of fire on the biota but caution against the use of fires for the majority of rehabilitation areas.     

Clear‐felling effects on colonization rates of shade‐tolerant forest herbs into a post‐agricultural forest adjacent to ancient forest

Question: Does clear‐felling influence forest herb colonization into post‐agricultural forest? Location: A stand of poplar cultivars with a dense understorey of Acer pseudoplatanus in Muizen forest (northern Belgium), planted in 1952 on farmland adjacent to ancient forest and clear‐felled in 1997. Methods: Shade‐tolerant forest herbs were surveyed in 112 grid‐based sample plots: just before clear‐felling, and 5 and 10 yr afterwards. Shade‐tolerant herbs were subdivided into ancient forest species (AFS) and other shade‐tolerant species (OSS). Effects of clear‐felling on species number per plot, total cover per plot and colonization rate of species groups were compared using non‐parametrical tests. Species number per plot was modelled by means of generalized linear mixed models (GLMMs), with inventory time, distance to the nearest parcel edge, and cover of light‐loving species (LS) as explanatory variables. The C‐S‐R signature (competitive, stress‐tolerant and ruderal strategies, respectively) shift of sample plots was calculated on the selected shade‐tolerant species. Results: Frequency of most species increased during the 10‐yr period. Number of OSS increased more and faster than that of AFS. OSS increased to the level of the adjacent forest, but was lower where LS cover remained high. There was a positive correlation between the change of the colonization rate and the competitive plant strategy. Conclusions: We assume that clear‐felling stimulated generative reproduction of shade‐tolerant herbs, whereas quickly emerging woody species controlled competitive exclusion by LS. Succession of dark and light phases, such as provided by an understorey managed as a coppice, could promote colonization of shade‐tolerant herbs into post‐agricultural forest.