Environmental Factors that Affect Primary Plant Succession Trajectories on Lahars(Popocatépetl Volcano,Mexico)

The earliest stages of plant succession on severely disturbed sites usually follow highly unpredictable trajectories. However, in the Popocatépetl volcano area(50 km SE of Mexico City),the development of physiognomically distinct primary plant communities suggests the occurrence of various successional trajectories only 10 years after the onset of colonization of a temperate forest on lahars. To characterize plant communities and determine the environmental factors that drive the differences observed between plant communities and their successional trajectories, we monitored 64 circular sample plots(3.14 m2) from 2002 to 2011. We examined the plant communities' composition and structure in terms of their species richness and abundance, plant cover, and maximum stem height,and recorded 13 environmental factors related to the volcanic deposit characteristics, microclimate, soil,flow dynamics and gravitational processes. A cluster analysis of the species abundance data showed that,by 2011, six plant community types(CT's) had established, including grasslands, and open, dense and very dense shrub lands. As these communities developed over the same period of time and within the same overall ecosystem, then these plant community types were interpreted as different stages of the same successional trajectory. Two sequential main stages that drive regeneration were identified from this successional trajectory: a) the first four years are characterized by a steady increase in species richness and physiognomic development(plant size and coverage), mostly dominated by Baccharis conferta, Eupatorium glabratum and Senecio barbajohannis; b) from the sixth year onwards, a continued increase in the abundance of those same species led to the development of the dense shrubland communities.Differences in the availability of soil resources and disturbances linked to recent lahar flows were the main factors accounting for such differences.

Changing assembly processes during a primary succession of plant communities on Mediterranean roadcuts

Aims Studying plant ecological succession provides insights into the spatiotemporal processes underlying community assembly and is of primary importance for restoration ecology.We investigate here colonization events and local community assembly over an original primary succession occurring on roadcuts after roadwork.For this,we addressed both the changes in species presence–absence(incidence data)to highlight pre-establishment filters and in species relative abundances to further assess the influence of local biotic processes.Methods We studied 43 limestone roadcuts in Mediterranean France,covering five age classes up to an age of 80 years,along with 13 natural cliffs as a reference,and we counted 14322 plant individuals on these sites.We applied a constrained nonsymmetric correspondence analysis of both the incidence(presence–absence)and abundance data to assess the variation of these data along the chronosequence.Important Findings Along the first 30 years,the initially abundant short-lived species declined both in terms of incidence and abundance and were replaced by longer lived herbaceous and woody species.This first phase was characterized by species that are widespread in the surrounding scrublands and was comparable to an early secondary succession there.After 30 years,there were continuing changes in incidence data with age,but no more significant change in species’abundances.This second phase was marked by the late colonization of specialists that did not become dominant.Although colonization and establishment limitation was thereby apparent for specialist species,a slow convergence of community composition toward the situation of natural cliffs could be detected in the older stages of the chronosequence.These findings convey insights into the natural dynamics of man-made outcrop plant communities and may be useful for the ecological management and restoration of such contexts.It also illustrates the interest of comparing incidence and abundance data to investigate the relative influence of ecological determinants on the assembly of plant communities.

Comparison of long-term results of trabeculectomy to treat pseudoexfoliative glaucoma and primary open angle glaucoma

AIM： To compare the long term outcome of trabeculectomy in patients with pseudoexfoliative glaucoma（PEG） and primary open angle glaucoma（POAG） in terms of surgical success. METHODS： The success of the trabeculectomy was evaluated by three criteria. Criterion A： intraocular pressure（IOP） ≤21 mm Hg and decrease in IOP ≥20%; Criterion B： IOP ≤18 mm Hg and decrease in IOP ≥30%; Criterion C： IOP ≤15 mm Hg and decrease in IOP ≥50%. Patients that met these criteria without medical treatment were considered to be completely successful, while those that met these criteria with medical treatment were considered partially successful. Significance levels of differences between the POAG and PEG groups in the Kaplan-Meier survival curves were calculated with the log-rank test. RESULTS： Sixty-four eyes from 64 patients with PEG and 51 eyes from 51 patients with POAG were evaluated. No significant differences were detected between the PEG and POAG groups according to full or partial success relative to each of the three criteria（A： P=0.73, 0.32; B： P=0.73, 0.31; C：P=0.90, 0.27）. CONCLUSION： There is no difference in the long-term success of trabeculectomy between PEG and POAG patients whose clinical characteristics are otherwise the same.

Glacial biodiversity of the southernmost glaciers of the European Alps(Clapier and Peirabroc,Italy)

We applied a multi-taxa approach integrating the co-occurrence of plants,ground beetles,spiders and springtails with soil parameters(temperatures and chemical characteristics)in order to describe the primary succession along two glacier forelands in the Maritime Alps(Italy),a hotspot of Mediterranean biodiversity.We compared these successions to those from Central Alps:Maritime glacier forelands markedly differ for their higher values of species richness and species turnover.Contrary to our expectation,Maritime glacier forelands follow a‘replacement change model’,like continental succession of Inner Alps and differently from other peripheral successions.We propose that the temperatures along these Mediterranean glacier forelands are warmer than those along other Alpine glacier forelands,which promote the faster species turnover.Furthermore,we found that early and mid successional stages of the investigated glaciers are richer in cold-adapted and endemic species than the later ones:we confirmed that the‘replacement change’model disadvantages pioneer,cold-adapted species.Given the overall correspondence among coldadapted and endemic species,the most threatened in this climate phase,our results raise new concerns about the extinction risk of these species.We also describe supraglacial habitat of Maritime glaciers demonstrating that supraglacial debris represents an environment decoupled from the regional climate and may have an important role as refugium for coldadapted and hygrophilous plant and animal species,whose survival can be threatened by climate change and by a rapid ecological succession in the adjacent forelands.

Conifer establishment after the eruption of the Paricutin volcano in central Mexico

Background:Volcanic eruptions have large effects on forest ecosystems and create new substrates,triggering primary succession processes.The Paricutín volcano,born in central-western Mexico,erupted between 1943 and 1952.After the cessation of the eruptive activity,plant colonization began on the lava flows and tephra deposits,including the conifer species that dominate the surrounding mature forests.This study aims to reconstruct the history of the establishment of conifer trees on the substrates created by the Paricutín eruption.Methods:16 sampling plots were established along three transects with northern,southern,and south-western aspects,located every 250 m from the preserved forest to the volcanic cone.Increment cores from 400 conifer trees were extracted and their age was determined by cross-dating annual tree rings.The order of the species colonization and the tree establishment,abundance,and dominance patterns were characterized.Also,the influence of the distance from the mature forests and the inter-annual climatic conditions on the temporal tree establishment pattern was evaluated.Results:Eight pine and one fir species have been established since 1970,only 18 years after the end of the eruptive period.However,tree establishment increased by 12.9%annually after 1995,with the youngest tree in our sample getting established in 2015.We did not find a well-defined temporal and spatial pattern of species arrival,which suggests that colonization occurred randomly,although the four pine species that were established early became the most abundant and dominant.Tree establishment was not influenced by the distance from the mature forest,and wet inter-annual conditions did not enhance pulses of tree recruitment,exhibiting a continuous tree establishment pattern.Conclusions:Conifer species have shown a great capacity for colonizing volcanic substrates created by the Paricutín eruption,which suggests that tropical montane conifers can regenerate rapidly under high-magnitude disturbances.These findings support the use of these forest species for ecological restoration.

Soil conditions and phylogenetic relatedness influence total community trait space during early plant succession

Aims the total space of traits covered by the members of plant com-munities is an important parameter of ecosystem functioning and complexity.We trace the variability of trait space during early plant succession and ask how trait space co-varies with phylogenetic community structure and soil conditions.Particularly,we are inter-ested in the small-scale variability in trait space and the influence of biotic and abiotic filters.Methods We use data on species richness and soil conditions from the first 7 years of initial succession of an artificial catchment in north-east-ern germany.total functional attribute diversity serves as a proxy to total trait space.Important Findingstotal trait space steadily increased during succession.We observed high small-scale variability in total trait space that was positively correlated with species richness and phylogenetic segregation and negatively correlated with total plant cover.trait space increased with soil carbonate content,while pH and the fraction of sandy material behaved indifferently.our results indicate that during early succession,habitat filtering processes gain importance leading to a lesser increase in trait space than expected from the increase in species richness alone.

Directional changes of species spatial dispersion and realized environmental niches drive plant community assembly during early plant succession

Aims Probabilistic models of species co-occurrences predict aggre-gated intraspecific spatial distributions that might decrease the degree of joint species occurrences and increase community rich-ness.Yet,little is known about the influence of intraspecific aggre-gation on the co-occurrence of species in natural,species-rich communities.Here,we focus on early plant succession and ask how changes in intraspecific aggregation of colonizing plant spe-cies influence the pattern of species co-existence,richness and turnover.Methods We studied the early vegetation succession in a six ha constructed catchment within the abandoned part of a lignite mine in NE Germany.At two spatial scales(1-and 25-m2 plots),we compared for each pair of species the intraspecific degree of aggregation and the pattern of co-occurrence and compared observed rela-tionships with temporal changes in important species functional traits.Important Findings The majority of species occurred in an aggregated manner,particu-larly in the first 2 years of succession.In pairwise comparisons,we found an excess of segregated species occurrences leading to a posi-tive link between intraspecific aggregation and pairwise species seg-regation as predicted by the aggregation hypothesis,particularly at the lower spatial resolution.The degree of intraspecific aggregation was negatively correlated with the community-wide level of species spatial turnover and with plot species richness.Our results are the first direct confirmation that increasing intraspecific aggregation and interspecific competitive interactions counteract in shaping plant community structure during succession.The respective effects of aggregation were strongest at intermediate states of early succession.

Successional trends and processes on a glacial foreland in Southern Iceland studied by repeated species counts

Introduction:Primary succession on glacial forelands is increasingly relevant as rapid glacial retreat is exposing growing land areas to plant colonization.We investigated temporal trends,controls,and outcomes in floral succession on a subarctic glacial foreland.Specifically,we examined changes in community composition(mosses,low shrubs,forbs,trees,and graminoids)over long-term(decadal)and short-term(<10 years)scales and attempted to identify the underlying processes responsible for the observed successional patterns.Methods:The study area was the foreland of the Skaftafellsjӧkull,located in Vatnajӧkull National Park near the south coast of Iceland.We established nine transect lines at varying distances from the ice front representing surfaces of age ranging from less than one decade to over 100 years.Each transect consisted of five measurement stations of 1 m2 where we measured vegetative cover(VC),species richness(SR),and species density(SD)and calculated species evenness(SE).Measurements were made initially in 2007 and repeated at the same geographic coordinates in 2014.Results:VC increased with distance from the ice front from 16%to over 90%.SR and SD increased from the youngest pioneer community through a mid-successional stage corresponding to an age of over 60 but less than 100 years.Increased VC but declining SR,SD,and SE characterized the oldest(over 100 years)bryophyte-dominated surfaces.Species turnover,which involved forbs almost exclusively,increased moderately from early through midsuccessional sites and declined on older sites.Comparison of the measurements made in 2014 to those made in 2007 demonstrates increased SR at mid-successional sites while SD remained relatively constant.Conclusion:At a small scale,colonization is controlled by local factors such as microtopography and aspect,particularly in proximity to the glacier.At the landscape level,changes in VC and community structure are controlled by time and nutrient availability.Low nutrient levels and limited site availability favor bryophyte dominance on the oldest surfaces.The greatest community-level changes observed over the 7-year interval were increases in surface cover by mosses and low shrubs,particularly in mid-successional and older sites.These changes suggest that the community on the oldest surfaces has not yet reached equilibrium.

Spatial and temporal dynamics of growth of woody plant species (birch and willows) on the foreland of a retreating glacier in southern Iceland

Background:The forelands of retreating glaciers are invaluable natural laboratories in which to explore the processes of primary succession.Numerous studies have been conducted on foreland chronosequences to identify temporal and spatial trends of the successional communities.This study focused on the spatio-temporal distribution of three woody plant species on the foreland of a retreating glacier in southern Iceland where historical observations provide precise age control of the moraines.To evaluate colonization and successional trends,we examined which species increase in abundance with time and tested the role of proximity to a seed source in colonization.Additionally,we quantified the rate at which biomass carbon is added to the landscape.Results:The density of stems of Betula pubescens increases with moraine age across the foreland chronosequence while the density of stems of both Salix lanata and Salix phylicifolia decreases.We found low statistical significance to the relationship between the density of B.pubescens and distance from a forested ridge nor did we find a relationship between the lengths of the stems and the moraine ages.Woody biomass increased fastest during early successional stages and reached a maximum of 28.5 g C m^(−2) on the oldest moraine.Conclusions:Early colonization of moraines was controlled by environmental filters which favored both Salix species.Colonization by B.pubescens followed as environmental factors,e.g.,favorable soil properties,improved.We found no conclusive evidence that proximity to a potential source of B.pubescens propagules was a significant factor in controlling colonization.The assumption that the abundance of individuals increased with time through later successional stages proved valid for B.pubescens,but not for either species of Salix.These findings are consistent with the classical spatial successional model of community homogenization.Thus,general successional processes at the landscape scale control the temporal dynamics of individual species.