Authors:S. Aboling, M. Sternberg, A. Perevolotsky, and J. Kigel
The relationship between the soil seed bank at the onset of the growing season and the structure of the ensuing vegetation under grazing was investigated in an eastern Mediterranean grassland. Species responses to two contrasting cattle grazing regimes were studied through plant trait analyses. Traits included plant size, phenology, seed size and germination fraction. Changes in species composition of the soil seed bank and the vegetation were analyzed using a plant functional group approach. The results showed that seed bank and relative cover of tall annual and perennial grasses increased when grazed late in the growing season. The opposite was noted for short annual grasses, annual legumes, annual thistles, annual crucifers and other annual forbs. Grazing treatments little affected plant cover of herbaceous perennials. Tall annual and tall perennial grasses have large seeds and germination rates over 90%. Short annual grasses showed similarly high germination rates but with smaller seeds. Annual legumes were characterized by medium size seeds and lower germination fractions (<50%). Tall annual grasses showed high competition capabilities at late grazed paddocks due to a combination of regeneration traits that included: high germination fraction, larger seed and seedling size, and inflorescence with morphological defenses. It is proposed that in addition to plant size and palatability, regeneration traits such as seed dormancy, seed and seedling size play an important role in determining the vegetation structure under different grazing regimes, thus contributing to the high plant species diversity characteristic to Mediterranean grasslands.
Authors:Y. González, G. Aragón, A. Benítez, and M. Prieto
Altitudinal gradients involve macroclimatic changes that can affect the diversity of several organisms. We tested the effects of elevation and small-scale variables on the diversity and composition of terricolous communities (lichens and bryophytes) in five páramos in southern Ecuador. The altitudinal range considered (from 2700 to 4000 m a.s.l.) is associated with changes in rainfall, temperature and irradiance. At each páramo, forty 40 x 40 cm2 sample plots were randomly selected in similar areas of vegetation (grass páramo) and conservation status. The presence/absence and cover of lichens and bryophytes were recorded in 200 sample plots. A total of 90 species (46 lichens and 44 bryophytes) were identified. Our results showed that total species richness, lichen and bryophyte richness, Simpson’s inverse and Shannon’s index were related to elevation and slope. Nevertheless, the response to elevation was dependent on the organism considered. Thus, meanwhile lichens had their maximum richness at the highest elevation (3930 m a.s.l.), bryophytes had a maximum peak at middle elevation (3300 m a.s.l.). Species composition also differed significantly among the five páramos, especially in bryophytes. We conclude that differences in the elevation of these páramos and small-scale variables such as slope significantly affect the diversity and composition of terricolous communities.
To determine the effect of tree canopy composition on understory species abundance, three-hundred 2 m × 2-m quadrats from 30 high-latitude boreal forest stands were sampled. In addition, all trees within a 3mradius of each quadrat center and ≥1 m tall were also measured for height, basal diameter, and canopy width (n = 3130). Stands were 33–178 years old, with canopies of Populus tremuloides (trembling aspen) and Picea spp. (spruce) in varying proportions. Arctostaphylos uva-ursi, Calamagrostis purpurascens, Chamerion angustifolium, Shepherdia canadensis, and Hylocomium splendens were the most frequent understory species among quadrats. Scatterplots of P. tremuloides and individual vascular understory species cover values lacked bivariate trends, but the understory species had distinct maxima that ranged from 20 to 90%. A moderately strong correlation (r = 0.52, P <0.001) occurred between P. tremuloides canopy and total vascular understory plant covers, but weak individual species correlations (r = 0.22–0.35, P <0.001), suggested understory species variation was primarily determined by factors other than the amount of immediately overhead canopy cover. Canonical correlation analysis (R = 0.82, P <0.001) indicated that greater vascular understory plant cover occurred when forest stands consisted of P. tremuloides with large canopies and large basal diameters, and lacked Picea. Maximum cover for vascular understory species declined when Picea cover exceeded 7–10%. In combination, P. tremuloides stem densities or a metric based on summed canopy areas converted to a diameter value (canopy-area diameter), and the vertical silhouette area of Picea canopies (canopy profile area), as independent linear regression variables, explained ∼79% of the variance in total vascular understory plant cover. Several Picea basal areaderived metrics were strongly and positively associated with increasing H. splendens cover, but canopy profile area was more informative. Populus tremuloides canopy area and Picea canopy profile area, as indicators of shading, may be important determinants of vascular understory vegetation abundance in stands where solar radiation enters at angles of up to 52° during the summer.
A key structural component in peat bog formation is Sphagnum spp., which determines very specific associated environmental conditions. The aim of this study was to characterise some of the key factors affecting the diversity, species richness and abundance of sphagnum inhabiting ground beetles and to examine the maintenance of stable populations of cold adapted specialised peat bog species. A total of 52 carabid species were recorded by pitfall traps along six main habitats, such as the lagg zone, pine bog, hollows, hummock open bog and dome. The results are characterised by a low diversity, which vary significantly among habitat types, and include a high abundance of a few carabid species. Among the variables influencing carabid species richness and abundance were plant cover, pH and the conductivity of the Sphagnum mat water. Vascular plant cover was a key factor shaping carabid beetle assemblages in the slope and the dome, while electric conductivity affected carabid beetle assemblage in the lagg. Whereas, the water level was the most important factor for the hollows. At the same time, peat bog specialists showed low sensitivity to the gradient of the analysed variables. Most of the specialised species are protected boreal beetles in the temperate zone of Europe, and therefore Belarusian peat bogs are a significant repository of cold adapted specialised bog species and potentially represent a significant refugia for these species in the context of global warming.
Authors:A. Stanisci, D. Lavieri, A. Acosta, and C. Blasi
Structure and diversity trends (β-diversity and species richness) across the Fagus sylvatica timberline in the central Apennines were investigated. Twenty-three belt transects were laid out across the upper forest line in the Simbruini Mountains. Number of species, plant cover, and height of different layers were recorded in each quadrat. The moving split-window method was used to detect ecological discontinuities across beech timberlines. We show how β-diversity changes along timberlines and we put forward some hypotheses about the possible dynamics of these transitions. Fourmodels resulted from the analysis of β-diversity trends: two β-diversity peaks indicated a transition where shrubs, mainly Juniperus communis ssp. alpina, (two high peaks) or beech scrub (two small peaks) formed a mantle that could allow forest expansion. One high β-diversity peak referred to an anthropo-zoogenic boundary maintained by disturbance, without the presence of a mantle. A little peak indicated a gradual transition at the upper potential timberline limit where beech forest had lost its typical floristical composition and structural characteristics.
We study the structure of two contrasting alpine forest.pasture ecotones located in the Central Pyrenees (sites Ordesa and Tessó). We define ecotone structure as the spatial distribution of trees of different size classes and growth-forms, and the relationship between these aspects and the spatial distribution of understory vegetation and substrate. The studied ecotones are dominated by Pinus uncinata and have been little affected by recent anthropogenic disturbances (logging, grazing). One rectangular plot (30 x 140 m2) was located within each site encompassing treeline and timberline with its longest side parallel to the slope. The distribution of size and growth-form classes at Ordesa followed a clear sequence of increasing size downslope, from shrubby krummholz individuals to bigger arborescent trees. At Ordesa, regeneration was concentrated near the krummholz area and over rocky substrates. At Tessó, regeneration was abundant above the treeline, where the cover of the dominant understory shrub (Rhododendron ferrugineum) decreased. Detrended canonical correspondence analysis of tree and plant cover data, with respect to spatial location in the ecotone and substrate cover, demonstrated that elevation was an important factor controlling the distribution of trees and understory plants in both ecotones. Finally, k-means clustering with spatial constraint revealed abrupt spatial clusters along the slope at Ordesa. However, the ecotone at site Tessó was composed of elongated downslope spatial clusters suggesting greater spatial heterogeneity and subtle gradual changes due to other factors in addition to the altitudinal gradient (snow avalanches). These contrasting structures correspond well with the ecotone (sharp boundary, Ordesa) and ecocline (gradual transition, Tessó) concepts. This suggests the dominant role of different local environmental factors: wind at site Ordesa and avalanches at Tessó. Positive feedbacks, like facilitation among P. uncinata individuals (nurse effect), may maintain and intensify the sharpness of the ecotone at Ordesa.
Two introduced plant species, Cenchrus incertus and Ambrosia artemisiifolia were studied in a 0.5 km2 open sand area in the Kiskunság National Park. The site is covered by valuable semi-natural grassland and is bordered by dirt roads. The aim of the study was to assess the extent and pattern of the area occupied by the two species and to describe the composition of the vegetation invaded with more or less success. Populations of the two species were mapped. In each stand of Cenchrus, in fifty-three 4 m2 quadrats aboveground plant cover, slope and exposition were documented. Both species concentrated on the roads. They – especially Ambrosia – were rare inside the intact part of the site, and were absent on abandoned roads. Cenchrus was found also in small patches not related to roads, in sites grazed with sheep. No colonization was detected from the road populations into adjacent intact natural vegetation. The analysis of the quadrats showed that Cenchrus cover was low where perennial or annual open sand grassland specialists dominated, and cryptogam cover was high. Cenchrus dominated quadrats on road or non-road sites were not discriminated from each other by cluster analysis. In non-road quadrats Cenchrus cover positively correlated with slope. Ambrosia was only present in quadrats taken on or near the roads. Aware of the life history traits of the species and of the vegetation dynamics of the target community it can be concluded that propagule transport, soil perturbation and disturbance of the native vegetation together enhance colonization and persistence of both species.
The saline area of the Kiskunság region of Hungary has varied micro-topographic conditions with different plant communities. This study was performed in a dry sandy grassland community (
Potentillo arenariae-Festucetum pseudovinae
Soó (1938) 1940) and a neighbouring saline sandy grassland community (
Lepidio crassifolii-Puccinellietum limosae
Soó (1947) 1957). These are located at different elevations and have completely different floristic composition and physiognomy due to the soil characteristics and water availability. We assessed how the different environmental conditions during summer period might alter some physiological traits of two dominant xerophytes of sandy grassland (
Hack. ex Wiesb.) and two halophytes of saline grassland (
(W. et K.),
(Schur) Holmbg.). The relationship between soil water potential and water content showed lower water availability for plants in the saline habitat as the high water soluble sodium content (900–2000 ppm) of this soil type limits water absorption. Both halophyte species in this study exhibited lower K/Na ratio than xerophyte species. Between the two halophytes
can be described as a “leaf/shoot sodium accumulator” species while
as a “leaf sodium avoider” species. The four species differed in proline accumulation. The salt adapted species had multifold accumulation of proline as compared to species of dry sandy grassland. The three microhabitats differing in total plant cover offered different microenvironmental conditions for
. Proline content was twice higher in leaves of this species in the microhabitats with high soil Na
content than in the closed microhabitat. Every species showed a transient reversible decrease of potential photochemical efficiency of PSII (F
) at midday during the study period. In the saline habitat the midday depression of F
was much larger than in case of
which reflected its higher susceptibility to photoinhibition. In sandy grassland F
was smaller than that of
. Mesophyll succulence index (Sm) expressing the ratio of water content to chlorophyll content was the highest in
(1.6–2.2 g H
Chl). Sm was low in xerophyte species (0.5–1.1 g H
Chl), and the lowest value was found for the
(0.54 g H
2005–2010 között a Szent István Egyetem Növénytermesztési és Biomasszahasznosítási Bemutató Központjában Gödöllőn másodvetésű zöldtrágyázási kísérletekben vizsgáltuk különböző zöldtrágyanövények (facélia, mustár és olajretek) hatását a talajellenállásra, a talajnedvességre, illetve a gyökérfejlődését.
A 2009. száraz, és a 2010. nedves évek kivételével az átlagos évjáratokban minden zöldtrágyanövénynél szignifikánsan nagyobb talajellenállást mértünk, mint a kontrollnál. A zöldtrágyanövények gyökérzete a rövid vegetációs idő miatt csak a talaj felső rétegét hálózta be, ugyanakkor a különbség a gyökerezési mélység alatt, még a 40–50 cm-es talajrétegben is kimutatható volt.
A talajnedvesség-mérés egyik évben sem mutatott statisztikai különbséget a kezelések között.
Az őszi bedolgozás után tavasszal ismételten elvégzett mérések során sem a talajellenállás, sem a talajnedvesség esetében nem lehetett szignifikáns különbséget kimutatni a kezelések között.
A növényborítottság miatt fellépő nagyobb talajellenállás oka, hogy a gyökérzet oldalirányú növekedésével nyomást gyakorolt a talajra. A növények bedolgozását követően a zöld növényi gyökerek gyorsan elbomlottak, a helyükön kialakuló szerkezetes talaj ellenállása pedig tavaszra megegyezett a kontrolléval.
A kutatás több paraméterre kiterjedő eredményei alapján mindhárom növényfajt alkalmasnak találtuk zöldtrágyázásra, de talajba dolgozásukat csak későősszel javasoljuk, és lehetőség szerint csak tavaszi vetésű kultúra kövesse azokat.