The role of light, soil and human factors on the probability of occurrence of an invasive and three native plant species in coastal transitions of coastal mississippi, USA

Aims understanding relationships between the distributions of species and their surrounding environment provides a basis for forecasting how species will respond to future environmental changes.In this study,we examined the effects of environmental factors and human devel-opmental features associated with disturbances on probability of occurrence of juveniles of invasive Triadica sebifera and three native plant species,Baccharis halimifolia,Ilex vomitoria and Morella cer-ifera within a typical coastal transition in coastal mississippi,USA.Methods We recorded presence of juveniles of focal species and measured environmental factors(soil salinity,canopy openness,soil texture and soil carbon to nitrogen ratio)along an 11.3 km transect located at grand bay National Estuarine research reserve.Further,we doc-umented anthropogenic features and associated activities as a proxy for human disturbance.Important Findings With the exception of I.vomitoria,all other species occurrences were significantly influenced by an interaction between soil salinity and canopy openness.The occurrence of I.vomitoria sharply decreased with salinity.B.halimifolia occurrence peaked at moderate levels of salinity and low to moderate levels of canopy openness.occurrences of M.cerifera and the invasive T.sebifera were highest at low levels of salinity and canopy openness.These results indicate that salinity is a strong driver that limits distribution of juvenile native and invasive species in coastal transitions.logistic regression confirmed the positive effects of anthropogenic disturbances on T.sebifera and I.vomitoria occurrence.It appears that while soil salinity is likely to drive retreat of the seaward boundaries of woody plant species distributions,increased human developments along the coast likely enhance the inland spread of species,in particular the invasive T.sebifera by increasing distur-bances and facilitating dispersal.results from this study can offer insight for the development of T.sebifera management and preventive meas-ures for further spread along coastal areas of the southeastern USA.

Mowing and fertilizer effects on seedling establishment in a successional old field

Aims We used a 10-year field experiment that consisted of mowing and fertilizer treatments to evaluate the role of niche limitation in seedling establishment of species from different functional groups and of varying local abundance in an old field undergoing succession.Methods Seedlings of nine different species were planted into a successional field subjected to mowing and fertilizer treatments for 10 years that resulted in different plant communities and resource availability.Species representative of the factorial combination of three functional groups(C4 grasses,C3 grasses and legumes)and three abundance categories(abundant,present,or absent in the old field)were planted in four treatments resulting from the factorial combination of annual spring mowing(mowed and unmowed)and fertilizer application(annually fertilized and unfertilized).Survivorship,relative growth rate(RGR)and biomass were measured to determine the role of niche limitation on recruitment and growth.Important Findings Mowing increased the establishment success of seedlings.Fertilization had little influence on seedling performance and survivorship.C3 grasses had the highest survivorship,while C4 grasses and legumes had equivalent RGRs,but higher than C3 grasses.By contrast,survivorship of legumes was unrelated to mowing or fertilizer,suggesting that establishment of this functional group was dependent on other,unmeasured conditions or processes.Species already present,but at low abundance,performed better than locally abundant or absent species.Propagule limitation may restrict the arrival of a species.However,recruitment and establishment was subject to niche limitation,which varied among species,functional groups and whether a species is already resident at the site and its abundance.Thus,species interactions restrict establishment during old-field succession,supporting the niche limitation hypothesis.