Germinable soil seed-bank of former grassland converted to coniferous plantation

The influence of afforestation with cedars on field layer vegetation and on the germinable soil seed-bank were investigated along a 60-m transect merging from open grassland to sparse and dense canopy cover. A total of 132 species were found, 76 in the seed-bank and 109 in the vegetation, with 53 species in common. Conifer cover was not found to be associated with a decrease in total number of species in the vegetation or seed-bank, but the mean number of species in the vegetation, total cover in field layer vegetation and mean number of individuals in the seed-bank decreased significantly from grassland to forest stands. The grassland seed-bank was dominated by Saxifraga tridactylites and Veronica agrestis; the seed-bank of plots of scattered cedars was dominated by Trifolium incarnatum ssp. molinerii; and that of dense cedar plantations was dominated by Campanula rapunculus. The number and cover of grassland species of field layer vegetation decreased in the forest, with respect to open grassland, and the same trend was found for density of individuals in the seed-bank. It is concluded that grassland restoration by cutting cedars cannot rely on the presence of grassland species in the soil seed-bank.     

Influence of colonizing shrubs on species-area relationships in alvar plant communities

Abstract. In herbaceous plant communities of Stora Alvaret (the Great Alvar), Öland, Sweden, we studied the dependence of species-area relationships on the canopy cover of the colonizing shrubs Juniperus communis and Potentilla fruticosa. A series of plots 0.25 - 256 m² in area were sampled in communities with varying canopy cover of Juniperus or Potentilla. Species number - log (area) regressions always fitted data better than log (species number) - log (area) regressions. The number of species declines more dramatically with increasing Potentilla cover than with increasing Juniperus cover. The total species number in large Juniperus plots follows a unimodal curve with a peak at about 75% shrub cover. The alvar (limestone grassland) species number in plots of all sizes declines monotonically with Juniperus cover following the regression equation S = 31.09 + 10.75 log A - 0.0025 P², where A is area and P is percentage Juniperus cover. There is a monotonic decline of species number with increasing shrub cover in Potentilla plots of all sizes. The species richness in plots with Potentilla was fitted by the regression equation S = 16.48+ 14.91 log A-0.131 P-0.00104 P² log A, where P is% Potentilla cover. A faster initial decline of species number with Potentilla colonization is apparently caused by its preferential establisment in species-rich, elevated microsites.     

Bryophyte colonisation in experimental microcosms: the role of nutrients, defoliation and vascular vegetation

A three-year multi-factorial microcosm experiment simulating fertilisation, defoliation and the composition of vascular vegetation in a dry grassland succession was used to test four hypotheses concerning the establishment and survival of bryophytes in grassland vegetation. H₁: bryophyte cover may be used to predict bryophyte species richness. H₂: bryophyte richness is suppressed at high nutrient levels and promoted by defoliation of vascular plants. H₃: species richness of bryophytes is influenced by the species composition of the vascular vegetation. H₄: bryophyte species richness is negatively correlated with vascular plant biomass.
The relationship between bryophyte richness and bryophyte cover was found to follow the classical species-area richness curve. Bryophyte species richness responded positively to defoliation and negatively to fertilisation. The species composition of vascular vegetation had no significant effect on bryophyte richness. Bryophyte species richness was lower at high vascular plant biomass and vascular plant dry weight above 400 g m⁻² appeared fatal to bryophytes. At high nutrient levels, defoliation increased bryophyte richness, but defoliation did not fully compensate for the negative effect of fertilisation. The study reinforces the concern for short lived shuttle bryophytes in the agricultural landscape.     

Changes in soil organic carbon and total nitrogen after 28 years grassland afforestation: effects of tree species, slope position, and soil order

The effect of conversion of grassland to woodland on organic carbon (OC) and total nitrogen (TN) has significance for global change, land resource use and ecosystem management. However, these effects are always variable. Here, we show results of a study in an arid area in China on profile distribution of OC and TN in soils covered by two different woody tree canopies and outer canopy space (grassland between woody plant canopies). The soils were at various slope positions (upper, middle and lower slopes) for Chinese pine (Pinus tabulaeformis) and Korshrinsk peashrub (Caragana korshinskii) lands, and of different soil orders (Castanozems, Skeletal, Loessial and Aeolian soils). The objectives were to relate the effects of land use change on OC and TN to slope position and soil order. Soil OC and TN were significantly larger at Korshrinsk peashrub slope locations than at Chinese pine slope locations. Soil OC and TN were small at the lower slope position for Korshrinsk peashrub, however, they were largest at the middle slope for Chinese pine. Korshrinsk peashrub always increased soil OC and TN under brush canopy at the three slope positions, while Chinese pine increased them at lower slopes and decreased them at upper slopes. For the soil types, OC and TN in Korshrinsk peashrub land were in the order of Castanozems > Skeletal > Loessial > Aeolian soils. Korshrinsk peashrub also increased OC and TN under brush canopy in the four soils. Our results indicated that soil OC and TN in canopy soils differed greatly from associated values in the outer canopy soils, and the effects of grassland afforestation varied significantly with tree species, slope position, and soil type. Therefore, we suggest that differentiating such factors can be an effective approach for explaining variances in OC and N changes caused by land use conversion.     

Methods of Measuring the Proportions of Plant-Species Present in Forest and Their Effect on Estimates of Bird Preferences for Plant-Species

Stem density, basal area, vegetation cover and vegetation surface area were compared as measures of the proportions of plant species present in North Okarito Forest, South Westland, for use in determining bird preferences for plant species. In general, stem density estimates of the proportions of canopy species were about 10 times lower than basal area estimates. The converse was true for estimates of the proportions of sub- canopy and understorey species. The proportions estimated from vegetation cover and vegetation surface area were similar for most species, and were intermediate between the proportions estimated from stem density and basal area. However, in the upper forest tiers, vegetation cover gave lower estimates for the proportions of canopy species and higher estimates for the proportions of sub-canopy species than given by vegetation surface area. These differences affect calculation of bird preferences for plant species. We recommend vegetation surface area as a measure of the proportional availability of plant species to birds because it is appropriate to most birds in New Zealand forests, is likely to be more accurate than visual estimates of vegetation cover, and can be measured on the same plots separately for trunks, branches, foliage, and fruit.     

Pine invasion impacts on plant diversity in Patagonia: invader size and invaded habitat matter

Conifers, which are widely planted as fast growing tree crops, are invading forested and treeless environments across the globe, causing important changes in biodiversity. However, how small-scale impacts on plant diversity differ according to pine size and habitat context remains unclear. We assessed the effects of different stages of pine invasion on plant communities in forest and steppe sites located in southern Chile. In each site, we sampled plant diversity under and outside the canopy of Pinus contorta individuals, using paired plots. We assessed the relative impact of pine invasion on plant species richness and cover. In both sites, richness and cover beneath pine canopy decreased with increasing pine size (i.e. height and canopy area). A significant negative impact of pines on species richness and plant cover was detected for pines over 4 m in height. The impact of pines on plant richness and cover depended on pine size (i.e. canopy area) and habitat type. Larger pines had more negative impacts than smaller pines in both sites, with a greater impact for a given pine size in the Patagonian steppe compared to the A. araucaria forest. Species composition changed between under and outside canopy plots when pines were 4 m or taller. Pine presence reduced cover of most species. The impacts of pine invasions are becoming evident in forested and treeless ecosystems of southern Chile. Our results suggest that the magnitude of pine invasion impacts could be related to how adapted the invaded community is to tree cover, with the treeless environment more impacted by the invasion.     

Stabililty and change in ultramafic fellfield vegatation at the Keen of Hamar,Shetland, Scotland

The paper reports 15 years' monitoring of erosion rates of drift soil deposits, fluctuations in vegetation cover, effects of nutrient addition and the population dynamics of rare species from the Keen of Hamar's fellfield habitat. Normal successional models do not apply on the fellfield since closed vegetation cover is restricted to soils on glacial deposits that once removed cannot be reconstituted from the underlying ultramafic parent material. The successional processes that occur are so slow and on so small a scale that it is concluded that the fellfield plant communities are stable. Eutrophication related to agricultural activity led to a temporary increase in plant cover and loss of habitat for the rare species. The numbers of individuals of the rare species have fluctuated locally from year to year but during the time of the observations the populations were relatively stable over the entire site. This means that the rarities have migrated within the site and this has important implications for their conservation. It is concluded that the Keen debris has retained more of its primeval appearance and vegetation than perhaps any other inland lowland area in the British Isles.     

Vegetation of tuscan ultramafic soils in relation to edaphic and physical factors

Vegetation and soil sampling were carried out in 80 plots located in five different ultramafic (serpentine) sites of Tuscany, central Italy. The physical and chemical features of each plot were determined and the species composition and cover recorded. The exchangeable fraction of soil metals was analysed because it gives a measure of their concentrations available to plants. The plots were classified by cluster analysis and ANOVA was used to compare the environmental variables of the groups of plots. Canonical correspondence analysis was used to detect the principal factors for gradients of species composition within the plant communities. A higher content of exchangeable metals was found under the more evolved and structured plant communities, suggesting that serpentine vegetation of Tuscany is not strongly limited by soil metals, such as chromium, cobalt, nickel and magnesium, typically associated with ultramafic soils. The low nutrient content of the soils and drought stress mainly due to topographical features, appear to have a more significant role in determining the typical scattered vegetation of the Tuscan ultramafics.     

The conservation ecology ofIris rossii Baker (Iridaceae), a threatened plant in rural Japan

Spatial distribution, size structure and reproductive activities of a population ofIris rossii were examined in managed secondary grassland with scattered pines and hardwoods. Size structure and fecundity patterns among individuals were different between the three sites, which were an open area, under pine canopy, and under hardwood canopy. Growth and reproductive parameters of the species were significantly different at each site. In the open area, mean shoot number of individuals was 9.17, and it was 6.37 under the pine canopy and 5.63 under the hardwood canopy. Fruit set ratio was 26.8% in the open area, 21.1% under the pine canopy and 12.1% under the hardwood canopy. Six seedlings were found in the open area and one under the pine canopy, while no seedlings occurred under hardwood canopy. Most of the individuals distributed in the sites where the height of herbaceous layer was low. These results suggest thatI. rossii can not grow in the closed, especially hardwood, canopies or tall herbaceous layer. Therefore, human interventions such as annual mowing for the restriction of the growth of dominant grasses and tree saplings are essential for the persistence of the population of the species.     

Feral horses dung piles as potential invasion windows for alien plant species in natural grasslands

Small scale disturbances could act as patches that provide sites for the colonization of competitively inferior species, promoting the establishment of non-native species in some cases. We analyzed the vegetation associated with feral horse dung piles in montane pampas grasslands in Mid-East Argentina and described the changes following their abandonment, evaluating whether dung piles act as invasion windows, allowing the entrance of alien plant species. We estimated the portion of the study area directly covered by horse manure and dung height was used to estimate the time elapsed after the abandonment of each pile. Vegetation replacement on dung piles of different ages was assessed and compared with grassland controls using discriminant analysis. We used regression analysis to look for changes in vegetation cover, species richness, species diversity and evenness in response to height (age) of the dung piles, and principal component analyses (PCA) to identify groups of plants associated with different successional stages. We compared cover of alien plant species on dung piles with grassland controls using one-way ANOVA. On average, 2.5% of the study area was covered by horse dung. Total vegetation cover, species richness, diversity and evenness increased after the piles were abandoned. Characteristic plant groups were associated with initial, middle and last phases of the studied succession. Vegetation on the dung piles significantly differed from that in grassland controls and two species were consistently associated with dung piles: the invasive Red Star Thistle, Centaurea calcitrapa, and a native grazing-intolerant grass, Nassella clarazii. Non-native species cover was also higher in dung piles than in control plots. Dung piles cover a significant portion of grassland area in our study site, produce significant changes in the vegetation and are associated with some invasive alien plants that could eventually colonize more pristine areas in the vicinity. On the other hand, they might represent refuges for palatable species, since horses seem to avoid them for grazing.     

小兴安岭阔叶红松林木本植物种-面积关系

种-面积关系研究是了解植物群落结构的重要途径,是群落生态学的基本问题。不同的研究方法对种-面积关系影响很大。利用黑龙江省小兴安岭两个10.4 hm2样地和5个1.0 hm2样地的调查数据,采用移动窗口法确定各样地的最小取样面积,避免了巢式取样法及随机样方法的不足。并采用4种种-面积关系模型进行拟合,评价各关系模型的适合度。在此基础上,基于最小面积进行模拟随机取样,探讨取样大小对物种数估计精度的影响。研究结果表明:由于拟合曲线模型的适用性及曲线外推可靠性问题的存在,采用拟合曲线的方法所估计的最小面积与实际值偏差较大。实际调查得到的各样地最小面积40 m×40 m—45 m×45 m,说明小兴安岭地区阔叶红松林群落所需的最小面积基本一致,但各样地群落结构的差异却在对取样数量的要求上体现出来。其中丰林与大亮子河样地物种数分布相对均匀,所需最小样方数量较少;而方正与胜山样地物种数分布异质性较大,差异的机理还有待于进一步研究。     

Changes in the plant community of a Brazilian grassland savannah after 22 years of invasion by Pinus elliottii Engelm

Abstract

Background: The invasion by Pinus elliottii is one of the most serious threats to the remaining native cerrado vegetation in São Paulo State, Brazil, causing biodiversity losses yet to be evaluated. We conducted a study in an area where P. elliottii began establishing in 1988.

Aims: To estimate diversity losses in the plant community and to understand the floristic and structural changes resulting from pine tree invasion of grassland savannah.

Methods: All plants taller than 50 cm were sampled in 35 plots (64 m² each) within an area densely invaded by P. elliottii and in 10 plots in non-invaded grassland savannah. Density, species richness, diversity, ground cover and spatial distribution were compared by Wilcoxon tests, non-metric multidimensional scaling and Payandeh indices.

Results: Twenty-two years after the arrival of the first invasive trees (founders), the grassland savannah has become a dense pine forest with 12,455 individuals ha^?1, a basal area of 26.44 m² ha^?1, a sparse native woody understory comprised of 16 species (H'?=?0.44), density of 1210 individuals ha^?1 and the herbaceous layer totally absent.

Conclusions: Invasion by Pinus elliottii has completely changed the structure of the grassland savannah and caused severe plant diversity losses. Native species surviving the invasion in the understory do not typically represent the previous composition and functional traits of the native vegetation.     

贺兰山地区植被冠层物候与树干形成层物候的关系

基于贺兰山地区98棵油松树轮样本的宽度数据、植被归一化指数(NDVI)数据以及土地覆被数据,采用VS-oscilloscope模型模拟的油松径向生长过程,研究植被冠层与树干形成层物候之间的联系。结果表明: 林地冠层与油松形成层生长结束期(EOS)显著相关,且高于草地与形成层之间的相关。油松生长开始期(SOS)和EOS分别与5—6月、8—9月的平均最低温度有关。5—6月的平均最低气温每升高1 ℃,SOS提前4.3 d;8—9月的平均最低气温每升高1 ℃,EOS推迟2.6 d。植被冠层物候与油松形成层物候的相关性受植被类型的影响;仅通过树轮生理模型模拟树木生长动态,结果可能存在偏差;利用遥感监测数据将冠层发育和形成层生长过程结合有助于更准确地了解树木生长动态。     

Establishment of

We compared establishment of Douglas fir (Pseudotsuga menziesii) and Corsican pine (Pinus nigra) seedlings in kanuka (Kunzea ericoides) and manuka (Leptospermum scoparium) shrubland to test the hypothesis that Douglas fir, because of its greater shade tolerance, is better able to establish in woody communities than pine species. Seed of the conifer species was sown under a range of canopy covers at six sites, the cover being low-statured vegetation in openings between stands, stand edges, and moderate and dense canopies. After three growing seasons, survival of Corsican pine seedlings was greatest in the open and declined progressively as canopy cover increased. This contrasted with Douglas fir, where survival was greatest at the canopy edge. Survival of Douglas fir seedlings significantly exceeded that of Corscican pine seedlings under dense canopy positions. Seedling numbers of both species declined significantly with increasing leaf area index of manuka, but not kanuka stands, where seedling numbers were lower. Leaf area index of manuka stands accounted for substantially greater variation in number and survival of Corsican pine than Douglas fir seedlings. It is concluded that Douglas fir is better able to establish in shaded environments in woody communities than Corsican pine; however, further monitoring is required to confirm the long-term survival of both species under the moderate and dense canopy positions in this trial.     

Restoring the Pygmy Pine Forests of New Jersey's Pine Barrens

The Pinelands National Reserve and UNESCO Biosphere encompass a large portion of southern New Jersey's Pine Barrens. Within the core preservation zone of these Reserves lies the Warren Grove Weapons Range, a military installation where exercises during the past 50 years have devastated portions of the indigenous pygmy pine-oak forest. In 1987, restoration efforts were initiated to identify materials and techniques that promote a diverse and productive native plant community atop drastically disturbed portions of the range. We used trial plantings to examine fertilizer and sewage compost fertility amendments, the effect of different native plant mixtures (including the dwarfed race of pitch pine, Pinus rigida), the influence of the ectomycorrhizal fungus Pisolithus tinctorius on the growth of pines and associated species, and mulch applications to conserve moisture and add organic matter. Following two growing seasons, test plantings exhibited 25% of the vegetation production found in the surrounding pine-oak community, 50% canopy closure, and levels of diversity comparable to the reference site. Maximum biomass and cover were achieved following the application of 16 Mg/ha compost and the establishment of pitch pine seedlings. Pitch pine was the dominant species in all plots where it was planted, with herbaceous species comprising the balance of the developing vegetation. Amendments of seeded grasses, P. tinctorius, and mulch influenced species composition but failed to enhance total plant production. We recommend restoring drastically disturbed sites in the pine plains with cultural input of compost to the spoils and planting of pitch pines and other woody species to accelerate the structural blending of reforested sites with the surrounding native vegetation.     

Influence of landscape and vegetation characteristics on herpetofaunal assemblages in Gulf Coastal Plain pine forests

Longleaf pine (Pinus palustris) savanna characterized by open-canopy, diverse herbaceous vegetation, and high amounts of bare soil once covered much of the southeastern United States Coastal Plain. The unique structural and vegetative conditions of this ecosystem support endemic reptiles and amphibians that have declined as longleaf pine forests have been lost or degraded. Private working pine (Pinus spp.) forests managed for timber production now occur throughout the southeastern United States and have replaced much of the historical longleaf pine savanna. The examination of herpetofaunal (reptile, amphibian) communities in private working loblolly pine (P. taeda) landscapes, particularly in the western Gulf Coastal Plain is lacking. Using repeated field surveys and hierarchical community occupancy models, we examined occupancy and species richness of herpetofauna across 81 sites spanning gradients of management practices, vegetative conditions, and soil composition in northwestern Louisiana, USA, 2017–2019. Young pine stands (<6 yr) exhibited structural characteristics most similar to mature longleaf pine reference sites (>30 yr), while mid-aged stands (13–26 yr) often featured closed canopy and dense midstory. Vegetation conditions varied widely depending on landscape characteristics and site-specific disturbance regimes. We documented 43 species of herpetofauna, including 9 open-pine-associated species. Occupancy of open-pine-associated herpetofauna was positively associated with open-canopy and understory conditions, and sandy soil area. Sites providing open-canopy conditions were often occupied by open-pine-associated species regardless of overstory type and disturbance method. Overall richness of herpetofauna was greatest at sites with moderate canopy cover outside of sandy soil regions. Working pine landscapes in the western Gulf Coastal Plain can support diverse herpetofaunal assemblages, including open-pine-associated species, when management practices maintain open-canopy conditions on sandy, upland soils. More broadly, our results provide insight into how forest management practices affect herpetofauna and may guide practices that can contribute to conservation value of working pine forests.     

Browsing‐mediated shrub canopy changes drive composition and species richness in forest‐tundra ecosystems

Changes in climate and in browsing pressure are expected to alter the abundance of tundra shrubs thereby influencing the composition and species richness of plant communities. We investigated the associations between browsing, tundra shrub canopies and their understory vegetation by utilizing a long‐term (10–13 seasons) experiment controlling reindeer and ptarmigan herbivory in the subarctic forest tundra ecotone in northwestern Fennoscandia. In this area, there has also been a consistent increase in the yearly thermal sum and precipitation during the study period. The cover of shrubs increased 2.8–7.8 fold in exclosures and these contrasted with browsed control areas creating a sharp gradient of canopy cover of tundra shrubs across a variety of vegetation types. Browsing exclusions caused significant shifts in more productive vegetation types, whereas little or no shift occurred in low‐productive tundra communities. The increased deciduous shrub cover was associated with significant losses of understory plant species and shifts in functional composition, the latter being clearest in the most productive plant community types. The total cover of understory vegetation decreased along with increasing shrub cover, while the cover of litter showed the opposite response. The cover of cryptogams decreased along with increasing shrub cover, while the cover of forbs was favoured by a shrub cover. Increasing shrub cover decreased species richness of understory vegetation, which was mainly due to the decrease in the cryptogam species. The effects were consistent across different types of forest tundra vegetation indicating that shrub increase may have broad impacts on arctic vegetation diversity. Deciduous shrub cover is strongly regulated by reindeer browsing pressure and altered browsing pressure may result in a profound shrub expansion over the next one or two decades. Results suggest that the impact of an increase in shrubs on tundra plant richness is strong and browsing pressure effectively counteracts the effects of climate warming‐driven shrub expansion and hence maintains species richness.     

Relationships of overstory to understory cover variables in a Ponderosa pine/Gambel oak ecosystem

Many studies have indicated relationships between individual species, but none have related combinations of overstory variables to understory herbaceous vegetation in a Ponderosa pine/Gambel oak ecosystem. Our objective was to determine not only the general relationships between the two sets of variables, but also identify the hyghest contributing variables. We used canonical correlation analysis to relate overstory variables (canopy cover, basal cover and density) to herbaceous vegetation cover variables. Canopy, basal, and ground cover were measured by the line intercept method using a 12.2 m tape as a sample unit. Tree density was measured by the Point-Center-Quarter method. The analysis was made with selected overstory variables and 5 understory herbaceous cover variables. This analysis revealed a significant canonical correlation between the two canonical variables (r=0.69). The analysis showed that among herbaceous cover variables, Oregon grape, Kentucky bluegrass, sedge, and foxtail barley; and among overstory variables, the density and the basal cover of Ponderosa pine indicated the highest positive contribution to the correlation of the two linear combinations while the density and canopy of Gambel oak negatively affected the canonical correlation.     

Grazing‐induced changes in plant–soil feedback alter plant biomass allocation

Large vertebrate herbivores, as well as plant–soil feedback interactions are important drivers of plant performance, plant community composition and vegetation dynamics in terrestrial ecosystems. However, it is poorly understood whether and how large vertebrate herbivores and plant–soil feedback effects interact. Here, we study the response of grassland plant species to grazing‐induced legacy effects in the soil and we explore whether these plant responses can help us to understand long‐term vegetation dynamics in the field. In a greenhouse experiment we tested the response of four grassland plant species, Agrostis capillaris, Festuca rubra, Holcus lanatus and Rumex acetosa, to field‐conditioned soils from grazed and ungrazed grassland. We relate these responses to long‐term vegetation data from a grassland exclosure experiment in the field. In the greenhouse experiment, we found that total biomass production and biomass allocation to roots was higher in soils from grazed than from ungrazed plots. There were only few relationships between plant production in the greenhouse and the abundance of conspecifics in the field. Spatiotemporal patterns in plant community composition were more stable in grazed than ungrazed grassland plots, but were not related to plant–soil feedbacks effects and biomass allocation patterns. We conclude that grazing‐induced soil legacy effects mainly influenced plant biomass allocation patterns, but could not explain altered vegetation dynamics in grazed grasslands. Consequently, the direct effects of grazing on plant community composition (e.g. through modifying light competition or differences in grazing tolerance) appear to overrule indirect effects through changes in plant–soil feedback.