Relative abundance of invasive plants more effectively explains the response of wetland communities to different invasion degrees than phylogenetic evenness

Native plant communities are commonly invaded by invasive plants to different degrees.However,the relative contribution of the invasive plant abundance vs.phylogenetic evenness to the responses of wetland communities to different degrees of invasion is still unclear.In addition,whether such contribution varies with environmental conditions such as flooding is also unclear.To address these questions,we chose Alternanthera philoxeroides as the invasive plant,and set up four invasive degrees by changing the community species composition under both flooding and non-flooding conditions.The relative abundance of A.philoxeroides and phylogenetic evenness changed simultaneously with the change in the community invasion degree.The invasion degree significantly affected the individual biomass of A.philoxeroides and some native species.Variation partitioning showed that the relative abundance of A.philoxeroides contributed more to variation in community indicators than phylogenetic evenness,regardless of flooding.Spearman rank correlation test showed that the relative abundance of A.philoxeroides was negatively correlated with the individual biomass of A.philoxeroides and some native species,while the phylogenetic evenness was positively correlated with only a few native species.And their correlation strength and significance were all affected by specific species and flooded environment.In conclusion,our results suggest that the relative abundance of A.philoxeroides can more effectively explain the wetland community response to different invasion degrees than phylogenetic evenness,regardless of flooding.

Are some communities of the coastal dune zonation more susceptible to alien plant invasion?

Aims Coastal areas,and in particular coastal dunes,are ecosystems strongly affected by the invasion of alien plants.However,few attempts have ever been made to quantify alien species incidence in different communities along the coastal zonation.This work aims to analyze the distribution of alien plants along the coastal zonation of sandy shores on the Tyrrhenian coast,addressing specifically differences among plant communities in abundance of alien plants.Methods The study was performed on recent dunes(Holocene)of the central western coast of Italy.We selected dune landscapes where invasion processes were particularly evident.Vegetation plots were randomly sampled and through cluster analysis,we identified six plant communities corresponding to the typical zonation described for the Tyrrhenian sandy coast of Central Italy.We evaluated and compared frequency and abundance of invasion in these different communities.Further,we investigated how propagule pressure(measured using as proxy human structures)contributed to the observed invasion patterns.Important Findings We found a relatively low total number of aliens but also a differential distribution pattern and strong abundance of some of the aliens in specific sectors of the vegetation zonation.The perennial community of transition dunes appears most affected by invasion processes,related almost exclusively to the frequent and widespread Carpobrotus aff.acinaciformis.This alien species reaches high cover values,apparently lowering cover of native species of transition dune plant communities.Higher levels of invasion in the transition dune can be partially explained because of greater propagule pressure in this section of the dune profile.Our findings thus have important conservation and management implications since transition dune communities with Crucianella maritima are rare and protected(sensu Habitat 92/43/EEC Directive)along the entire Italian coast.

Effect of Senna obtusifolia(L.)invasion on herbaceous vegetation and soil properties of rangelands in the western Tigray,northern Ethiopia

Introduction:Invasion of exotic plant species is a well-known threat to native ecosystems since it directly affects native plant communities by altering their composition and diversity.Moreover,exotic plant species displace native species through competition,changes in ecosystem processes,or allelopathic effects.Senna obtusifolia(L.)invasion has affected the growth and productivity of herbaceous vegetation in semi-arid regions of northern Ethiopia.Here,we investigated the species composition,species diversity,aboveground biomass,and basal cover of herbaceous vegetation,as well as soil properties of rangelands along three S.obtusifolia invasion levels.Methods:Herbaceous vegetation and soil properties were studied at two locations,Kafta Humera and Tsegede districts,in the western Tigray region of northern Ethiopia under three levels of S.obtusifolia invasion,i.e.,non-invaded,lightly invaded,and heavily invaded.Herbaceous plant species composition and their abundance were assessed using a 1-m^(2) quadrat during the flowering stage of most herbaceous species from mid-August to September 2015.Native species were classified into different functional groups and palatability classes,which can be useful in understanding mechanisms underlying the differential responses of native plants to invasion.The percentage of basal cover for S.obtusifolia and native species and that of bare ground were estimated in each quadrat.Similar to sampling of the herbaceous species,soil samples at a depth of 0–20 cm were taken for analyzing soil physical and chemical properties.Results:Highly palatable grasses and legumes based on the frequency of occurrence were 1.9 and 3.8 times higher in non-invaded sites than in lightly and heavily invaded sites,respectively.Furthermore,unpalatable plant species were 4.0 times higher in the heavily invaded sites than in the lightly invaded sites.Aboveground biomass,basal cover,and species diversity of the herbaceous vegetation were significantly(P<0.01)lower in the heavily invaded sites compared to the non-invaded sites.However,most soil properties were not affected by S.obtusifolia invasion compared with non-invaded sites in our study.Conclusions:Our findings contribute towards better understanding of how S.obtusifolia invasion affects the community structure and composition of native herbaceous vegetation in semi-arid rangelands in northern Ethiopia.Further long-term studies are required to understand the mechanisms of how S.obtusifolia invasion influences soil properties for better control and eradication of its invasion in the semi-arid rangelands of northern Ethiopia.

Studying the patterns of alien and native floras of some habitats in Srinagar city, Kashmir, India

Introduction:Urban flora is an important component of human-dominated ecosystems that links urban dwellers with nature.This study aims at compiling and analysing the alien and native vascular plant species of some selected habitats in the Srinagar city,Kashmir,India.Methods:Bi-seasonal sampling was employed and each habitat type(viz.,graveyards,grasslands,orchards and wastelands)was sampled at seven different sites.Results:The number of species recorded from graveyards was 96;from grasslands 112;141 from orchards and 110 from wastelands.The level of invasion among habitats varied from 67.27%to 68.75%,with a mean value of 67.86%;out of clubbed species list,64.84%were alien.Asteraceae,Poaceae,Brassicaceae and Fabaceae were the biggest families in all four habitat types.Conclusions:Our research shows that across habitats,alien plant species are the predominant part of their floras.