Competitive Grass Species Research Articles

Exploring the drivers of vascular plant richness at very fine spatial scale in sub-Mediterranean limestone grasslands (Central Apennines, Italy)

Secondary dry grasslands in Europe can host high levels of vascular plant richness at small spatial scales. However, in Southern Europe their biodiversity patterns are largely unexplored. In this work, we aim at: (i) estimating plant species richness patterns at very fine scales in montane dry grasslands, on limestone bedrock, in Abruzzo Lazio and Molise National Park (Central Apennines, Italy); (ii) assessing the most important physical and edaphic drivers of biodiversity patterns at multiple plot sizes. We used randomly placed nested-plot series where we measured alpha-diversity at three different plot sizes (1 m2, 0.1 m2 and 0.01 m2) and within-plot beta-diversity (as expressed by the slope of the species-area curve across plot sizes). Variable selection was performed by means of Random Forests. Relationships between selected variables and diversity measures were then assessed using Regression Trees, Linear and Generalized Linear Models. Overall, results pointed to topographically-controlled edaphic factors (soil pH and silt fraction) as the main drivers positively influencing alpha-diversity at all spatial scales, with a positive effect of rock cover and slope inclination at smaller spatial grains. Beta-diversity was positively influenced by rock cover. We suggest that high-pH, steep and/or rocky sites feature higher species richness because they lack competitive grass species. Our results are in agreement with previous works underlining the importance of less productive habitats for the conservation of secondary grassland biodiversity.

Long‐term influence of sod cutting depth on the restoration of degraded wet heaths

AbstractTemperate heaths have an unfavorable conservation status in most European biogeographical regions. Increasing nitrogen levels promote competitive grass species such asMolinia caerulea, which is a main threat to heathland conservation in Europe. This article investigates the long‐term influence of sod cutting and the resulting changes in soil properties on the heath composition, integrity, and structure. In 15 nature reserves across the northern half of Belgium, we used (1) a large number of plots (203); (2) a broad range of sod cut depths (2–40 cm), and (3) a temporal dimension that describes how long the effects of sod cutting persist (census up to 19 years after sod cutting). Multivariate analyses were used in order to explore the influence of sod cut depth and time after sod cutting on the soil and vegetation properties. There was a positive relationship between sod cut depth and soilpHand water level, and a negative relationship with Al3+,NH4+, and total organic matter (TOM). However, only a limited number of typical (target) species appeared after sod cutting, and then only weakly. Most of the time they remained a minor component of the restored vegetation. Moreover,M. caeruleareappeared and its cover significantly increased during the years following sod cutting. Although we were able to show that sod cut depth has a differential effect on soil properties and vegetation recovery, it also appeared that sod cutting does not restore wet heaths in the long term when applied in regions with high nitrogen deposition.

Post-Soviet recovery of grassland vegetation on abandoned fields in the forest steppe zone of Western Siberia

Following the collapse of the Soviet Union in 1991 around 45 million hectares of arable land became abandoned across Russia. Our study focused on the recovery potential and conservation value of grassland vegetation on ex-arable land in the Tyumen region of the Western Siberian grain belt. We compared ex-arable grasslands of different successional stages with ancient grasslands as reference for the final stage of succession along a climatic gradient from the pre-taiga to the forest steppe zone. Plant community composition and species richness of ex-arable land clearly developed towards reference sites over time, but even after 24 years of abandonment, the grassland vegetation had not totally recovered. The γ-diversity of vascular plants was slightly higher on ex-arable land than in ancient grasslands but the mean α-diversity was still moderately lower. A significant proportion of the vegetation of ex-arable land still consisted of ruderal and mesic grassland species and the number and cover of meadow-steppe species was significantly lower than in ancient grasslands. Grazing and time since abandonment positively affected the reestablishment of target grassland species, whereas it was negatively affected by the cover of grasses. In contrast to ex-arable land, the conservation value of arable land is only modest. Therefore, future intensification of land use is most likely less harmful if directed to existing arable land. Re-cultivation of ex-arable land and grassland improvement operations such as seeding of competitive grass species are major threats for the biodiversity of secondary grasslands on ex-arable land in the forest steppe zone of Western Siberia.

Do soil nutrients mediate competition between grasses and Acacia saplings?

AbstractThe structure and composition of savanna vegetation is influenced by resource availability and disturbance. Grasses, a major component of savanna systems, influence the tree‐grass balance by competing with trees for light, water and soil nutrients as well as providing fuel for fires. Overgrazing, and the ensuing decreased grass competition and fire effects resulting from diminished grass vigor and cover, are thought to be major drivers of bush encroachment. To investigate impacts of competition from grass on saplings of Acacia karroo Hayne. and Acacia nilotica (L.). Willd. ex. Del. under high and low soil fertility, six grass species, Aristida junciformis (Trin & Rupr.), Eragrostis capensis (Thunb.) Trin., Hyparrhenia hirta Stapf., Panicum maximum Jacq., Sporobolus africanus (Poir.) Robyns & Tournay and Themeda triandra Forssk., were planted in pots with a tree sapling as the central test species. The major competitive effects experienced by tree saplings were dependent on nutrient level and the identity of the competing grass species (P < 0.001). Aboveground A. karroo was more strongly affected by grass competition under high nutrient conditions, whereas an increase in nutrient level had little effect on the competition between A. nilotica and the grasses (P < 0.001). Acacia karroo was also strongly affected by grass competition belowground; however, the opposite trend was observed for A. nilotica (P < 0.001). Eragrostis capensis was one of the most competitive grass species, reducing sapling aboveground biomass by 85% and 65% under high and low nutrient conditions, respectively, and sapling belowground biomass by 71% on average. Increasing nutrient availability resulted in an increase in competition exerted on A. karroo by all grasses but little to no change for A. nilotica. Changes in savanna composition and structure are thus likely to be influenced by grass species composition and soil nutrient status.

Native and Exotic Grass Competition with Invasive Hoary Cress (Cardaria draba)

AbstractThe Eurasian perennial mustard, hoary cress,Cardaria draba(Brassicaceae), is an invasive weed in western North America that can displace native plants and other desirable forage species in pastures and rangelands. This study investigated the competitive ability of 11 grasses representing nine species in the generaFestucaandPoafrom either North America (NA) or Europe (EU) against hoary cress. Hoary cress was grown alone and with four different grass densities under controlled conditions with ample water and nutrient supply, typical for riparian and disturbed habitats, in which hoary cress infestations are commonly found. Of the fiveFestucagrasses tested, onlySchedonorus phoenix(=F. arundinacea) decreased hoary cress biomass. Four of the sixPoagrasses tested decreased hoary cress biomass and were ranked by decreasing competitive effects as follows:P. annua>P. compressa(EU) >P. pratensis(EU) >P. compressa(NA). The most competitive grass species also experienced higher intraspecific competition. Within both grass genera, Eurasian species were more competitive against hoary cress than their North American congeners, which suggests that hoary cress establishment may be facilitated by lower biotic resistance in the invaded range. Regardless of origin, sod-formingPoaspecies were competitive at low densities, whileFestucaspecies only had significant effects at high densities if at all. Based on our results we recommend the use ofPoaspecies for restoration of riparian and disturbed sites following the control of hoary cress infestations to restrict recolonization.

Management to enhance pollen and nectar resources for bumblebees and butterflies within intensively farmed landscapes

There have been serious global declines in diversity of bumblebees, butterflies and other pollinating insects. The most effective means of increasing abundance and diversity of bumblebees on farmland is to sow simple, low cost mixtures of dicotyledons rich in pollen and nectar, as prescribed under the UK agri-environment schemes. The potential benefits of this management prescription for butterflies are unknown. Similarly, more information is needed on how to manage this habitat to maximise the provision of pollen and nectar resources whilst protecting breeding habitat for butterflies. This study aimed to devise mixtures and cutting management regimes which address these issues. We found significant effects of seed mixture, timing and frequency of cutting, and removal of cut material on vegetation composition, flower resource availability and pollinators (the abundance, species richness and temporal distribution of butterflies and bumblebees, including males and queens, attracted to the mixtures). We recommend that nectar flower mixtures are refined by the inclusion of the best performing species to provide mid- and late-season forage resources (Trifolium spp., Lotus corniculatus and Centaurea nigra), and the removal of competitive grass species. Summer cutting in May or early June, with removal of herbage where possible, should be applied to half the patch to extend the flowering season, and minimise damage to butterfly breeding habitat. This should be accompanied by the typical autumn cut to the whole patch. Even with best management practice, such nectar flower mixtures are only effective for 3–4 years and this should be recognised in policies aimed at enhancing pollinator populations in agricultural landscapes.

Restoring grassland biodiversity: Sowing low-diversity seed mixtures can lead to rapid favourable changes

We studied the effect of sowing low-diversity seed mixtures (containing 2–3 competitive grass species) on the regeneration of vegetation on croplands previously used as alfalfa fields. In four permanent plots in 10 restored fields (four with alkali and six with loess seed mixture) the cover of flowering plants was recorded and phytomass was measured between 2006 and 2008. We asked three questions: (i) How fast will weedy, short-lived species decrease in abundance during secondary succession enhanced by sowing low-diversity seed mixtures? (ii) Can weeds be suppressed by sowing competitive native grasses, followed up by management by mowing? (iii) Can succession towards the target native grasslands be accelerated by sowing only low-diversity seed mixtures compared to set-aside old field succession? Our results showed that in just two years a vegetation dominated by perennial grasses has developed, which successfully prevented the establishment of weed species. These results suggested that sowing seeds of two or three competitive grass species is an effective tool to eliminate weed domination and to lead towards the restoration of species poor grasslands with grass domination such as alkali grasslands. However, the developed dense perennial grass cover and the accumulated litter may hamper the immigration of specialist species characteristic to reference grasslands. Therefore, the restoration of species-rich grasslands requires the facilitation of the immigration of grassland specialist species by further management (grazing, mowing and/or hay-transport).

The effect of restoration techniques on non‐target species: case studies in moorland ecosystems

AbstractQuestions: What is the impact on non‐target species of restoration methods to establish Calluna vulgaris on grass‐dominated moorlands?Location: A Nardus stricta‐dominated moorland in Wales and a Molinia caerulea‐dominated moorland in Northern England, UK.Methods: Two replicated experiments were established on grass‐dominated moorlands. The treatments comprised disturbance (rotavation and trampling by animals), addition of Calluna seed, and three different grazing regimes, together with a no grazing control.Results: The creation of bare ground and addition of seed increased the establishment of the desired dominant shrub, Calluna vulgaris. In the Nardus sward, rotavation and trampling were equally successful in establishing Calluna, but rotavation was more successful in the Molinia sward. Rotavation inhibited the growth of competitive grass species better than trampling. However, the disturbance techniques were detrimental to other components of the plant community, causing a decline in the cover of desirable species such as Vaccinium myrtillus and other dwarf shrub species and a small increase in the occurrence of undesirable species such as Juncus effusus. Grazing also controlled competitive grass species: Festuca ovina decreased in cover at a grazing intensity of 1.5 ewes/ha; Molinia caerulea and Agrostis spp. declined when cattle were included in the grazing regime, but increased in cover when ungrazed or when grazed at 1.5 ewes/ha.Conclusions: When restoration concentrates on the establishment of one or a few species, it is important to monitor how the techniques used affect the rest of the plant community – particularly with regard to losses of desirable species or increases in undesirable species.

Differential herbivory tolerance of dominant and subordinate plant species along gradients of nutrient availability and competition

We tested whether differences in the herbivory tolerance of plant species is related to their abundance in grassland communities and how herbivory and nutrient availability affect competitive balances among plant species through changes in their tolerance. The experimental approach involved a simulated grazing treatment (clipping) of two competitive grass species (Arrhenatherum elatius and Holcus lanatus) and two subordinate forb species (Prunella vulgaris and Lotus corniculatus) along a gradient of nutrient availability and under conditions of competition. Total standing, aboveground, root, and regrowth biomass were evaluated at the end of the experiment as an estimate of the capacity to compensate for twice removing aboveground biomass at different nutrient levels (NPK). Although clipping had a more pronounced negative effect on dominant plant species (Arrhenatherum and Holcus) than on subordinate species, the negative effects on dominant species were offset by the application of fertilizer. The combined effect of fertilizer and competition had more negative effects on the performance of Lotus and Prunella than on the dominant species. In terms of competition, the regrowth ability of Arrhenatherum and Holcus increased with the application of fertilizer, while the opposite pattern was observed for Lotus and Prunella. The addition of fertilizer has a positive effect on both grass species in terms of growth in clipped pots and competition, while subordinate species did not respond to the addition of fertilizer to the clipped pots and were negatively affected by competition with both grass species. The results suggest (1) that species replacement towards subordinate species as a function of herbivory is partially dependent on the herbivory tolerance of that species, (2) competitive relations between competitive grass species and subordinate forb species change under different environmental conditions, and (3) although grazing disturbance significantly influences competitive relations in favor of less competitive species, increasing nutrient levels counteract the negative effect of grazing on dominant competitive plant species.

Influence of slope and aspect on long‐term vegetation change in British chalk grasslands

1 The species composition of fragmented semi-natural grasslands may change over time due to stochastic local extinction and colonization events, successional change and/or as a response to changing management or abiotic conditions. The resistance of vegetation to change may be mediated through the effects of topography (slope and aspect) on soils and microclimate. 2 To assess long-term vegetation change in British chalk grasslands, 92 plots first surveyed by F. H. Perring in 1952–53, and distributed across four climatic regions, were re-surveyed during 2001–03. Changes in vegetation since the original survey were assessed by comparing local colonization and extinction rates at the plot scale, and changes in species frequency at the subplot scale. Vegetation change was quantified using indirect ordination (Detrended Correspondence Analysis; DCA) and Ellenberg indicator values. 3 Across all four regions, there was a significant decrease in species number and a marked decline in stress-tolerant species typical of species-rich calcareous grasslands, both in terms of decreased plot occupancy and decreased frequency within occupied plots. More competitive species typical of mesotrophic grasslands had colonized plots they had not previously occupied, but had not increased significantly in frequency within occupied plots. 4 A significant increase in Ellenberg fertility values, which was highly correlated with the first DCA axis, was found across all regions. The magnitude of change of fertility and moisture values was found to decrease with angle of slope and with a topographic solar radiation index derived from slope and aspect. 5 The observed shift from calcareous grassland towards more mesotrophic grassland communities is consistent with the predicted effects of both habitat fragmentation and nutrient enrichment. It is hypothesized that chalk grassland swards on steeply sloping ground are more resistant to invasion by competitive grass species than those on flatter sites due to phosphorus limitation in shallow minerogenic rendzina soils, and that those with a southerly aspect are more resistant due to increased magnitude and frequency of drought events.

Root interactions between young Eucalyptus deglupta trees and competitive grass species in contour strips

To reduce soil erosion on sloping fields grass strips are commonly planted on the contours. The integration of timber trees into such strips can be economically beneficial and at the same time increase the anti-erosion effect of the strips. Root competition between grasses and trees within such strips may affect tree development, but might also reduce root competition between the trees and adjacent field crops if the grass strips restrict the lateral development of the tree root systems. The present experiment, carried out on a fertile site (Aquandic Dystrudept) in a high-rainfall region in Costa Rica (2700 mm per year), was designed to evaluate whether the lateral extension of the root system of Eucalyptus deglupta could be restricted by strips of the grasses Panicum maximum, Brachiaria brizantha or Saccharum officinarum, planted either in single, double- or triple-rows on both sides of rows of the trees. E. deglupta growth was significantly reduced in the association with P. maximum, the most competitive grass species, and to a lesser extent, by the double- and triple-row B. brizantha strips. In these treatments, the total number of lateral tree roots, as evaluated in profile walls, was reduced by up to 40% compared to the no-grass control. Furthermore, the lateral restriction of the tree root systems led to an increased density of tree roots between the grass strips. S. officinarum did not reduce the total number of tree roots and only slightly restricted lateral tree root extension. Grass strips composed of multiple grass rows appeared to restrict lateral tree root development more than strips with single grass rows but this effect was not statistically significant. None of the grasses forced the tree root systems to develop at a greater depth; on the contrary, tree roots were more superficial in the profiles beyond as well as between the grass strips in comparison to the no-grass control. There was some evidence of an increased root barrier effect of the grass strips in areas with a compacted topsoil. The barrier effect tended to decrease with increasing age of the trees. These results suggest that strips of competitive grasses can reduce the lateral root development, especially of young trees, when planted in contour strips, and this may reduce and/or delay root competition with neighboring field crops. The observed trends are likely to change as trees grow older and longer-term studies are needed.

Effects of reclamation measures on plant colonization on lignite waste in the eastern Pyrenees, Spain

Abstract. This paper deals with vegetation establishment on waste dumps in the montane and submontane belts of the eastern Pyrenees, where submediterranean Quercus humilis forests, Pinus sylvestris forests and mesoxerophilous pastures make up most of the landscape; these are considered as target communities for reclamation. The waste consists of marl and lime regolith, very poor in nutrients and structure (Poch et al. 1989). The dumps were terraced in 1985–1986; some were left for spontaneous re‐colonization and others were reclaimed in various ways. In 1992 we took 36 vegetation samples on the dumps, based on the point quadrat procedure, to evaluate the colonization status and the differences between reclamation techniques. The samples were analysed on the basis of their species composition (ecological groups and multivariate analysis) and structural aspects (coverage, diversity, etc.). Reclamation treatment results varied widely, most of the dumps showing a low degree of naturalness. Colonizing vegetation ranged from a mixture of opportunist and stress‐resistant taxa, forming poorly covered surfaces on the dumps where colonization has been poor, to dense grasslands dominated by one (or a few) introduced competitive grass species, where reclamation procedures had been intensive. Sowing treatments, where pasture species were sown onto dumps, produced intermediate results, as resulting vegetation cover was similar to control plots and naturalness was low, but in a few cases they yielded more interesting swards, fairly dense and diverse, and including high numbers of spontaneous species. Choice of sown species and proximity to undisturbed vegetation accelerate succession.

PERFORMANCE OF SOME GRASS–ALFALFA MIXTURES IN SOUTHWESTERN SASKATCHEWAN DURING DROUGHT YEARS

Six perennial grass–alfalfa mixtures were studied at three locations in the Brown soil zone of Saskatchewan during successive drought years 1956 to 1962. Account was taken of comparative yields, persistence, drought tolerance, and component compatibility. Differences in competition and suppression are discussed. Crested wheatgrass or intermediate wheatgrass with alfalfa gave highest yields. Russian wild ryegrass was the most competitive grass species. Russian wild ryegrass and bromegrass were the two grasses which reduced the alfalfa component the most, resulting in lower yields of the mixtures.