Fertiliser response of vegetation on ultrabasic terraces on Rhum

Summary

The application of fertilisers to sparse vegetation on unstable ultrabasic soil on a ridge of extreme exposure on the Isle of Rhum, Inner Hebrides, resulted in a marked increase of vegetation cover and a change in species composition. On this site, nutrient deficiency appears to be a major factor limiting the development of closed plant communities.     

Soil acidity and nutrient deficiency in central Amazonian heath forest soils

Experiments were carried out to test the effects of liming and nutrient additions on plant growth and soil processes such as C and N mineralisation in three contrasting forest types in central Amazonia: the stunted facies of heath forest (SHF), the tall facies of heath forest (THF) and the surrounding lowland evergreen rain forest (LERF). Calcium-carbonate additions increased soil respiration in the field plots in the SHF; in laboratory incubations, soil respiration was higher in the SHF when soils were fertilised with N, and in THF and LERF after S additions. The addition of N alone or in different combinations generally induced a net immobilisation of soil N. Net nitrification increased during the incubation in SHF and THF soils fertilised with N+P, and in LERF soils fertilised with either N, or P, or CaCO₃. In a field experiment using ingrowth bags, a higher fine root production was observed in all forest types when bags were fertilised with CaCl₂ or CaCO₃, suggesting that Ca may be a limiting nutrient in these soils. Calcium-carbonate addition in a glasshouse bioassay experiment with rice showed an overall positive effect on the survival and growth of the seedlings. In other treatments where soil pH was not raised, the rice showed acute toxicity symptoms, poor root and shoot growth and high mortality. Similar results were yielded in a field experiment, using naturally established seedlings in the field plots in SHF, THF and LERF. It is concluded that the acute H⁺ ion toxicity is a major growth-limiting factor for non-adapted plants in heath forest soils in central Amazonia.     

The vegetation of ultrabasic soils on the Isle of Rhum II. The causes of the debris

Summary

The relationship between the Rhum ultrabasic skeletal soils and their debris vegetation was investigated by plant analyses and field and laboratory experiments. Samples of Agrostis vinealis, Arenaria norvegica ssp norvegica, Calluna vulgaris, Festuca vivipara, Plantago maritima and Racomitrium lanuginosum from these soils usually had low concentrations of potassium and calcium, and high concentrations of sodium, magnesium (and high Mg/Ca quotients), iron and nickel. There were instances of very high iron concentrations (up to 22.4mg g^?1 in Plantago maritima), very high Mg/Ca quotients (up to 27.8 in Arenaria novegica spp. norvegica) and high nickel concentrations (up to 0.48mg g^?1 in Plantago maritima). A nutrient addition experiment which was set up in 1965 on an exposed barren area had in 1982 over twice as many species as originally recorded and a nearly complete plant cover. Shorter-term work has confirmed that nutrient availability limits the ultrabasic vegetation. An experiment on Agrostis vinealis in simulated soil solutions showed that a gabbro (non-ultrabasic) clone had a higher R.G.R. (relative growth rate), even at the higher of two experimental Mg/Ca quotients, than two peridotite (ultrabasic) clones and was moreover not significantly affected by the higher nickel concentration used. It is concluded that the low vegetation cover on the skeletal soils is maintained by low soil nutrients which might interact with the coarsely sandy texture in exacerbating the effects of periodic drought and frost heaving. There is no unequivocal evidence for plant toxicities associated with high magnesium or nickel in the Rhum soils.     

Distribution and effects of tree leaf litter on vegetation composition and biomass in a forest-grassland ecotone

Aims After abandonment of grasslands, secondary succession leads to the invasion by woody species. This process begins with the accumulation of tree litter in the forest–grassland ecotone. Our objectives were to determine the relationships between litter amounts and vegetation composition and cover along natural forest–grassland ecotones and to experimentally study the initial effects of tree litter accumulation on grassland vegetation and on microsite conditions.Methods We established 11 transects varying from 12 to 15 m in length in different forest–grassland ecotones in the Lahn-Dill highlands, Germany, and measured the mass and cover of tree litter and the cover and composition of vegetation at five sequential positions along each transect by using 1 m 2 plots with five replications. In a field experiment, we established plots subjected to different litter amounts (0, 200 and 600g m ?2) and evaluated changes in grassland vegetation, soil temperature and soil nutrient availability below the litter layer.Important findings Tree litter amounts decrease from 650 to 65g m ?2 across the forest–grassland ecotone. Vegetation changed from shrubs and annual species (adapted to more stressful conditions) in the forests edge to grasses, rosettes and hemirosette species (with higher competitive abilities) in the grassland. These anthropogenic forest–grassland ecotones showed abrupt edges, and the two adjacent ecosystems were characterized by different species pools and functional groups. In the field experiment, the presence of a litter layer reduced vegetation biomass and cover; the species richness was only reduced in the treatment with high litter (600g m ?2). Additionally, adding litter on top of vegetation also reduced thermal amplitude and the number of frost days, while increasing the availability of some nutrients, such as nitrogen and aluminium, the latter being an indicator of soil acidification. Adding a tree litter layer of 600g m ?2 in grassland areas had strong effects on the composition and diversity of grassland vegetation by reducing the cover of several key grassland species. In, or near, forest edges, litter accumulation rapidly changes established vegetation, microsite conditions and soil nutrients.     

Long-term effects of climate and phosphorus fertilisation on serpentine vegetation

The long-term effects of phosphorus fertilisation and climate on serpentine plant communities in Tuscany, central Italy have been investigated by using data from a 12 year before-after control-impact (BACI) experiment. Using the point quadrat method, data on plant communities were collected in June of each year from 1994 to 2005 in eight 2 × 2 m plots, four fertilised with phosphorus and four used as controls. Climatic data were obtained from a nearby meteorological station and summarised in 24 variables. Phosphorus addition significantly affected vegetation cover of both vascular and cryptogamic vegetation but did not influence species richness. The effects on species composition were clear but not marked, and consisted in promoting the abundance of some species already present in the community but not leading to the colonisation of other species. Interannual climate differences affected vegetation cover in the fertilised plots but not in the control ones, while climate affected the species richness values of different/various life-forms in both groups of plots, with more evident effects in the fertilised one. The effects of climate on plant community composition were weak once both the variability among individual plots and the successional dynamics were subtracted from the variance in species composition.     

Can atmospheric input of nitrogen affect seed bank dynamics in habitats of conservation interest? The case of dune slacks

Questions: Does the increased atmospheric deposition of nitrogen, which can have major effects on the established vegetation of nutrient‐poor habitats, also impact germination from the soil seed bank? Location: Coastal dune slacks at Newborough Warren, Wales, UK. Methods: The effects of nitrogen addition (15 kg.ha^‐1.a^‐1) on seed germination from the soil seed bank were investigated using the seedling emergence method between September 2004 and February 2005. Results: More seedlings emerged from fertilised samples than unfertilised controls. Most species showed enhanced germination after fertilisation with nitrogen, with seedling numbers statistically significantly greater in nitrogen addition samples in a quarter of species abundant enough for analysis. Species that responded positively to fertilisation were species with low Ellenberg indicator values indicative of infertile sites. Conclusions: Most species showed increased germination after fertilisation with nitrogen, including early successional species normally growing in nutrient‐poor conditions. This suggests that the increased atmospheric deposition of nitrogen probably not only impacts on established vegetation, but also has the potential to alter seed bank dynamics.     

Spatial and temporal variation of soil moisture in dependence of multiple environmental parameters in semi-arid grasslands

Grazing of grasslands changes soil physical and chemical properties as well as vegetation characteristics, such as vegetation cover, species composition and biomass production. In consequence, nutrient allocation and water storage in the top soil are affected. Land use and management changes alter these processes. Knowledge on the impacts of grazing management on nutrient and water fluxes is necessary because of the global importance of grasslands for carbon sequestration. Soil water in semi-arid areas is a limiting factor for matter fluxes and the intrinsic interaction between soil, vegetation and atmosphere. It is therefore desirable to understand the effects of grazing management and stocking rate on the spatial and temporal distribution of soil moisture. In the present study, we address the question how spatio-temporal soil moisture distribution on grazed and ungrazed grassland sites is affected by soil and vegetation properties. The study took place in the Xilin river catchment in Inner Mongolia (PR China). It is a semi-arid steppe environment, which is characterized by still moderate grazing compared to other regions in central Inner Mongolia. However, stocking rates have locally increased and resulted in a degradation of soils and vegetation also in the upper Xilin River basin. We used a multivariate geostatistical approach to reveal spatial dependencies between soil moisture distribution and soil or vegetation parameters. Overall, 7 soil and vegetation parameters (bulk density, sand, silt and clay content, mean weight diameter, mean carbon content of the soil, vegetation cover) and 57 soil moisture data sets were recorded on 100 gridded points on four sites subject to different grazing intensities. Increasing stocking rates accelerated the influence of soil and vegetation parameters on soil moisture. However, the correlation was rather weak, except for a site with high stocking rate where higher correlations were found. Low nugget ratios indicate spatial dependency between soil or plant parameters and soil moisture on a long-term ungrazed site. However, the effect was not found for a second ungrazed site that had been excluded from grazing for a shorter period. Furthermore the most important soil and vegetation parameters for predicting soil moisture distribution varied between different grazing intensities. Therefore, predicting soil moisture by using secondary variables requires a careful selection of the soil or vegetation parameters.     

Distinguishing the effects of vegetation restoration on runoff and sediment generation on simulated rainfall on the hillslopes of the loess plateau of China

Aims

Since the 1970s, extensive croplands were converted to forest and pasture lands to control severe soil erosion on the Loess Plateau of China. We quantify the direct and indirect effects of vegetation restoration on runoff and sediment yield on hillslopes in the field to improve environmental governance.

Methods

An artificial rainfall experiment at a rainfall intensity of 120 mm h⁻¹ and a slope gradient of 22° were used to distinguish the effects of vegetation restoration on runoff and sediment yield.

Results

Compared to the farmland slopes, vegetation restoration directly prolonged the time-to-runoff by 140%, reduced the runoff rate by 20%, and increased the soil infiltration capacity by 15%. Vegetation restoration indirectly delayed the time-to-runoff by 120%, reduced the runoff rate and sediment yield rate by 50% and 94%, respectively, and increased the soil infiltration capacity by 58% on the hillslopes with vegetation restoration.

Conclusions

The direct effects of vegetation restoration on runoff and sediment yield were lower than its indirect impacts. Vegetation cover, decreases in soil bulk density, and increases in belowground root biomasses and > 0.25 mm aggregate stability were the primary causes of runoff and sediment yield reduction on the slopes with vegetation restoration.

     

Quantitative effects of vegetation cover on wind erosion and soil nutrient loss in a desert grassland of southern New Mexico,USA

Wind is a key abiotic factor that influences the dynamics of arid and semiarid systems. We investigated two basic relationships on vegetation manipulation (grass cover reduction) plots at the Jornada Experimental Range in southern New Mexico: (1) wind erosion rates (horizontal mass flux and dust emission) versus vegetative cover, and (2) nutrient loss versus vegetative cover. The results indicate that wind erosion rates and nutrient loss by dust emission are strongly affected by plant cover; however, the importance of shrubs and grasses in reducing dust flux may not be equal. The dramatic increase of wind erosion between 75% grass cover reduction and 100% grass cover reduction suggests that sparsely distributed mesquites are relatively ineffective at reducing wind erosion and nutrient loss compared to grasses. Comparisons of nutrients between surface soils and wind blown dust indicate that aeolian transport is a major cause for the loss of soil nutrients in susceptible environments. We found that increased aeolian flux over three windy seasons (March 2004–July 2006) removed up to 25% of total organic carbon (TOC) and total nitrogen (TN) from the top 5 cm of soil, and about 60% of TOC and TN loss occurred in the first windy season (March–July 2004). The balance between net loss of nutrients by aeolian processes and the addition of nutrients by biotic processes changed from negative (net loss) to positive (net accumulation) between 50% grass cover reduction and 25% grass cover reduction. The estimated lifetime of surface soil TOC and TN of about 10 years on the plot with 100% grass cover reduction indicates that impacts of wind erosion on soil resources can occur on very short timescales.     

Species diversity in plant communities on ultramafic soils in relation to pine afforestation

Abstract. The influence of pine afforestation on the species diversity of plant communities on ultramafic substrate was investigated in an area of Tuscany, central Italy, by means of species-area relationships, plant unit area, the Gini coefficient and the pattern of the index of Jaccard in relation to plot size. The species-area relationship was found to best fit the semilogarithmic model. Contrary to the available data for temperate ecosystems, tree canopy cover was found to increase the α-diversity of the understorey vegetation and its cover. The nutrient input due to the pine canopy caused an increase in the abundance of the grass Festuca inops — which was already present in the community — and subsequently the spread of several grassland species leading to a reduction in dominance concentration and to the formation of a species-rich grassland. The pine cover caused a decrease in floristic resemblance between plots, especially when the canopy cover is scattered. The increase in species richness found under the pine canopy, where the metal content in the soil is higher, suggests that potentially toxic metals are not the most limiting factor in Tuscan ultramafic soils. The typical poorness of vegetation on ultramafic soils should be first of all related to hydrological and nutritional stresses.     

Short‐Term and Long‐Term Effects of Soil Ripping,Seeding, and Fertilization on the Restoration of a Tropical Rangeland

Rangeland degradation is a serious problem in semiarid Africa. Extensive areas of bare, compacted, nutrient‐poor soils limit the productivity and biodiversity of many areas. We conducted a set of restoration experiments in which all eight combinations of soil tilling, fertilization, and seeding with native perennial grasses were carried out in replicated plots. After 6 months, little aboveground biomass was produced in plots without tilling, regardless of seeding or fertilization. Tilling alone tripled plant biomass, mostly of herbaceous forbs and annual grasses. Perennial grasses were essentially limited to plots that were both tilled and seeded. The addition of fertilizer had no significant additional effects. After 7 years, vegetation had declined, but there were still large differences among treatments. After 10 years, one tilled (and seeded) plot had reverted to bare ground, but the other tilled plots still had substantial vegetation. Only one seeded grass (Cenchrus ciliaris) was still a contributor to total cover after 10 years. We suggest that restoration efforts on these soils be directed first to breaking up the surface crust, and second to the addition of desirable seed. A simple ripping trial inspired by this experiment showed considerable promise as a low‐cost restoration technique.     

The consequences of multiple resource shifts on the productivity and composition of alpine tundra communities: inferences from a long-term snow and nutrient manipulation experiment

Background: Gradients in the amounts and duration of snowpack and resulting soil moisture gradients have been associated with different plant communities across alpine landscapes.

Aims: The extent to which snow additions could alter plant community structure, both alone and in combination with nitrogen (N) and phosphorus (P) additions, provided an empirical assessment of the strength of these variables on structuring the plant communities of the alpine tundra at Niwot Ridge, Colorado Front Range.

Methods: A long-term snow fence was used to study vegetation changes in responses to snowpack, both alone and in conjunction with nutrient amendments, in plots established in dry and moist meadow communities in the alpine belt. Species richness, diversity, evenness and dissimilarity were evaluated after 20 years of treatments.

Results: Snow additions, alone, reduced species richness and altered species composition in dry meadow plots, but not in moist meadow; more plant species were found in the snow-impacted areas than in nearby controls. Changes in plant community structure to N and N + P additions were influenced by snow additions. Above-ground plant productivity in plots not naturally affected by snow accumulation was not increased, and the positive responses of plant species to nutrient additions were reduced by snow addition. Plant species showed individualistic responses to changes in snow and nutrients, and indirect evidence suggested that competitive interactions mediated responses. A Permanova analysis demonstrated that community dissimilarity was affected by snow, N, and P additions, but with these responses differing by community type for snow and N. Snow influenced community patterns generated by N, and finally, the communities impacted by N + P were significantly different than those affected by the individual nutrients.

Conclusions: These results show that changes in snow cover over a 20-year interval produce measureable changes in community composition that concurrently influence and are influenced by soil nutrient availability. Dry meadow communities exhibit more sensitivity to increases in snow cover whereas moist meadow communities appear more sensitive to N enrichment. This study shows that the dynamics of multiple limiting resources influence both the productivity and composition of alpine plant communities, with, species, life form, and functional traits mediating these responses.     

Aeolian process effects on vegetation communities in an arid grassland ecosystem

Many arid grassland communities are changing from grass dominance to shrub dominance, but the mechanisms involved in this conversion process are not completely understood. Aeolian processes likely contribute to this conversion from grassland to shrubland. The purpose of this research is to provide information regarding how vegetation changes occur in an arid grassland as a result of aeolian sediment transport. The experimental design included three treatment blocks, each with a 25 × 50 m area where all grasses, semi-shrubs, and perennial forbs were hand removed, a 25 × 50 m control area with no manipulation of vegetation cover, and two 10 × 25 m plots immediately downwind of the grass-removal and control areas in the prevailing wind direction, 19° north of east, for measuring vegetation cover. Aeolian sediment flux, soil nutrients, and soil seed bank were monitored on each treatment area and downwind plot. Grass and shrub cover were measured on each grass-removal, control, and downwind plot along continuous line transects as well as on 5 × 10 m subplots within each downwind area over four years following grass removal. On grass-removal areas, sediment flux increased significantly, soil nutrients and seed bank were depleted, and Prosopis glandulosa shrub cover increased compared to controls. Additionally, differential changes for grass and shrub cover were observed for plots downwind of vegetation-removal and control areas. Grass cover on plots downwind of vegetation-removal areas decreased over time (2004-2007) despite above average rainfall throughout the period of observation, while grass cover increased downwind of control areas; P. glandulosa cover increased on plots downwind of vegetation-removal areas, while decreasing on plots downwind of control areas. The relationships between vegetation changes and aeolian sediment flux were significant and were best described by a logarithmic function, with decreases in grass cover and increases in shrub cover occurring with small increases in aeolian sediment flux.     

Effects of nutrient loading and extreme rainfall events on coastal tallgrass prairies: invasion intensity, vegetation responses, and carbon and nitrogen distribution

Soil fertility and precipitation are major factors regulating transitions from grasslands to forests. Biotic regulation may influence the effects of these abiotic drivers. In this study, we examined the effects of extreme rainfall events, anthropogenic nutrient loading and insect herbivory on the ability of Chinese tallow tree ( Sapium sebiferum ) to invade coastal prairie to determine how these factors may influence woody invasion of a grassland. We manipulated soil fertility (NPK addition) and simulated variation in frequency of extreme rainfall events in a three growing season, full factorial field experiment. Adding water to or pumping water out of plots simulated increased and decreased rainfall frequencies. We added Sapium seeds and seedlings to each plot and manipulated insect herbivory on transplanted Sapium seedlings with insecticide. We measured soil moisture, Sapium performance, vegetation mass, and carbon and nitrogen in vegetation and soils (0–10 cm deep, 10–20 cm deep). Fertilization increased Sapium invasion intensity by increasing seedling survival, height growth and biomass. Insect damage was low and insect suppression had little effect in all conditions. Recruitment of Sapium from seed was very low and independent of treatments. Vegetation mass was increased by fertilization in both rainfall treatments but not in the ambient moisture treatment. The amount of carbon and nitrogen in plants was increased by fertilization, especially in modified moisture plots. Soil carbon and nitrogen were independent of all treatments. These results suggest that coastal tallgrass prairies are more likely to be impacted by nutrient loading, in terms of invasion severity and nutrient cycling, than by changes in the frequency of extreme rainfall events.     

Long-term changes in vegetation and soil chemistry in a calcareous and sandy semi-natural grassland

Calcicole plant species are vulnerable to acidification and fertilization, caused by deposition and changes in land use, since they are adapted to nutrient-poor calcareous conditions. In this study we used vegetation data (vascular plants, bryophytes and lichens) from 1964 and 1985 and stored soil samples from 1966 to investigate long-term soil chemistry and vegetation changes in a semi-natural, sandy calcareous grassland in southern Sweden. In the re-investigation in 2008 we found that increased decalcification due to acidification could not be verified. The plant community had changed from stress-tolerant calcareous grassland towards a community promoted by higher nutrient availability. Furthermore, the cover of species indicating calcareous conditions had decreased. A decline in the cover of species adapted to alkaline, phosphorus-poor conditions may be due to increased nutrient availability, but there were also indications that the vegetation had changed due to overgrowth by woody plants. This long-term impoverishment of the plant community highlights the need for appropriate management of calcareous grasslands, in order to limit the nutrients available in the soil and prevent overgrowth by shrubs and trees.     

The effect of nutrient enriched sediment deposits on the vegetational traits of a patch-grazed semi-arid grassland

Permanent grazing exclosures were established in semi-arid grasslands to study long-term successional trends of vegetation in patches representing varying stages of vegetation retrogression. After an exceptionally heavy thunder-shower one research plot was flooded with run-off water from cultivated lands nearby, resulting in the deposition of nutrient enriched sediment in the research plot. The subsequent vegetational trends are compared to vegetational trends of similar patches in a control plot, in the same grazing camp, which was not flooded.Successional trends were accelerated in the sediment covered micro-plots due to the improvement of habitat conditions. Substantial basal cover increases, ranging from 30% to 124,5%, were recorded in flooded micro-plots. By comparison basal cover increases in the control plot varied from 1% to 45%. In both cases the basal cover changes were predominantly the result of basal cover increases of large, tufted, perennial grass species. Patches representing severe vegetation retrogression in the sediment covered research plot, in contrast to degraded patches in the control plot, showed the most significant increases in basal cover of large, tufted, perennial grass species. It is concluded that degraded grassland could be restored effectively through habitat improvements.Research conducted whilst employed by the Department of Plant Sciences, Potchefstroom University for Christian Higher Education, Potchefstroom, 2520, Republic of South Africa.     

Seven-Year Impact of Cover Crops on Soil Health When Corn Residue Is Removed

Removing plant residue from soil has been shown to have an adverse effect on soil health; however, the addition of cover crops may help mitigate these impacts. This study was conducted to assess the effect of incorporating cover crops on soil health with varying removal rates of corn (Zea mays L.) residues. Corn was grown in rotation with soybean (Glycine max) in a randomized, split-block design with three different corn residue removal levels (37, 55, and 98% of total above-ground C) as whole plot treatments and the presence or absence of cover crops as the split plot treatment. Soil samples were collected from both crop phases following 7 years of cover crop treatment and subjected to a suite of soil health measurements. In the soybean phase immediately following corn residue removal, there were significant (P?=?0.025) increases in the erodible fraction (EF) of soil aggregates and reductions in the stable, larger aggregate fractions. Cover crops mitigated these changes in aggregate distributions in the highest residue removal treatment. Residue removal resulted in a significant decrease in fPOM (P?=?0.03) while the addition of cover crops increased fPOM levels during the soybean phase (P?=?0.002). Residue removal significantly (P?=?0.017) decreased soil microbial enzyme activities while cover crops restored activities in the highest residue removal treatment (P?=?0.037). We also found higher fungal:bacterial ratios with cover cropping compared to no cover crops. We conclude that cover cropping continued over multiple years can partially mitigate negative effects of crop residue removal on soil health thus limiting soil erosion and maintaining nutrient cycling activities in the vulnerable period following residue removal.     

Effects of liming on forage availability and nutrient content in a forest impacted by acid rain

Acidic deposition and subsequent forest soil acidification and nutrient depletion can affect negatively the growth, health and nutrient content of vegetation, potentially limiting the availability and nutrient content of forage for white-tailed deer (Odocoileus virginianus) and other forest herbivores. Liming is a mitigation technique that can be used to restore forest health in acidified areas, but little is known about how it affects the growth or nutrient content of deer forage. We examined the effects of dolomitic limestone application on the growth and chemical composition of understory plants in an acidified forest in central Pennsylvania, with a focus on vegetative groups included as white-tailed deer forage. We used a Before-After-Control-Impact study design with observations 1 year before liming and up to 5 years post-liming on 2 treated and 2 untreated 100-ha sites. Before liming, forage availability and several nutrients were below levels considered optimal for white-tailed deer, and many vegetative characteristics were related to soil chemistry. We observed a positive effect of liming on forb biomass, with a 2.7 fold increase on limed sites, but no biomass response in other vegetation groups. We observed positive effects of liming on calcium and magnesium content and negative effects on aluminum and manganese content of several plant groups. Responses to liming by forbs and plant nutrients show promise for improving vegetation health and forage quality and quantity for deer.