Canopy gap size influences niche partitioning of the ground-layer plant community in a northern temperate forest

Aims The Gap Partitioning Hypothesis(GPH)posits that gaps create heterogeneity in resources crucial for tree regeneration in closed-canopy forests,allowing trees with contrasting strategies to coexist along resource gradients.Few studies have examined gap partitioning of temperate,ground-layer vascular plants.We used a ground-layer plant community of a temperate deciduous forest in northern Wisconsin,USA,as a model system to test whether the GPH extends to the relatively species-rich ground layer.Methods We used a well-replicated experimental approach that included a gap opening gradient(five gap sizes,6,10,20,30 and 46 m diameter,and undisturbed reference areas),a within-gap location gradient(gap edge to center),and a temporal gradient(0,2,6 and 13 years after gap creation).The data were observations of ground-layer plant abundance,published plant traits,and a modeled index of understory light environments.We ordinated the plant abundance data and evaluated the relationships of composition,traits and light environment by gap size,location along the forest-gap transect and time,with several approaches such as correlations,descriptive statistics,non-parametric tests of group differences and indicator species importance values.Important Findings Ground-layer plant composition and traits differed across gap sizes,within-gap locations and over time.Gaps of all sizes differed in composition from undisturbed areas,and all pair-wise combinations of gap size also differed in composition,except the 6 m from the 10-m gaps.Large gaps(46 m)also displayed within-gap compositional gradients from gap edge to center locations.Compositional differences in gap size were evident 2 years after gap creation and,contrary to our hypotheses,remained different over the 13-year period,even in gaps with crown closure.In contrast to the neutral theory,species functional traits and microenvironmental conditions were related to variation in ground-layer composition.Species with smaller seeds,lower shade tolerance,later bloom times,shorter stature and longer leaves were associated with higher light,more central gap locations,larger gap sizes and greater time since gap creation.The correlation between gap size and ground-layer plant composition and traits provides evidence for gap partitioning by the diverse ground-layer community in this temperate deciduous forest community.

Effect of rangeland rehabilitation on the herbaceous species composition and diversity in Suswa catchment,Narok County,Kenya

Introduction:Land degradation is a serious environmental problem of our time.In Kenya,it is estimated that 30%of the total land mass is severely degraded.Suswa catchment within Narok County is a good example with gullies of over 25 m deep and 30 m wide.In response to the increasing land degradation in the area,the Sustainable Land Management(SLM)project rehabilitated the catchment through establishment of soil and water conservation structures such as cutoff drains,semicircular bunds,and water retention ditches.Despite the various rehabilitation approaches carried out,little research has been done to ascertain their effect on successful vegetation recovery.This coupled with the fact that many restoration approaches have failed in East Africa and Kenya in particular gave drive to the study.The objective of this study was to determine the effects of rangeland rehabilitation on herbaceous species composition and diversity in a severely degraded rangeland.Methods:To assess the diversity of aboveground herbaceous layer in the rehabilitated and degraded areas along a slope(upper,middle,and lower),line transect and quadrat count methods were used.Within each slope position,three 100-m-long transects were placed across the hill parallel to one another 30 m apart using a tape.The species hit,the closest species to the hit,and hits on bare ground were recorded.Along the same transects,1-m2 quadrats were placed 25 m apart and aboveground biomass determined by the use of the destructive method.In the determination of species richness,diversity,relative abundance,percentage cover,and species composition,the Shannon-Wiener diversity index was used.Data collected on vegetation attributes was subjected to analysis of variance(ANOVA)using Genstat and Tukey’s HSD post hoc used in means separation where F values were significant.Results:The results showed that percent cover(74.67%),aboveground biomass(1459 kg/ha),relative abundance,richness,composition,and diversity of perennial grasses significantly(P≤0.05)increased downslope and were higher in the rehabilitated area than in the degraded area.On the contrary,forbs and annual grasses were significantly(P≤0.05)higher within the degraded area compared to the rehabilitated area and increased upslope.Conclusions:In general,herbaceous species diversity,species richness,relative abundance,percentcomposition,biomass production,and percent cover of perennial grasses significantly increased downslopeand were higher in the rehabilitated area compared to the degraded area.On the contrary,the sameattributes for forbs and annual grasses were higher in the degraded area and increased upslope.The studyconcluded that effective rangeland rehabilitation has the potential to enhance vegetation regeneration andhence forage productivity.Conclusions:ln general,herbaceous species diversity,species richness,relative abundance,percent composition,biomass production,and percent cover of perennial grasses significantly increased downslopeand were higher in the rehabilitated area compared to the degraded area On the contrary,the same attributes for forbs and annual grasses were higher in the degraded area and increased upslope.The studyconduded that effective rangeland rehabilitation has the potential to enhance vegetation regeneration andhence forage productivity.

Tree species determine soil seed bank composition and its similarity with understory vegetation in a semi-arid African savanna

Introduction:The presence of larger trees in semi-arid African savannas creates sub-habitats,which influences on herbaceous plant communities grown under their canopies differently from opened areas.Knowledge of seed banks accumulated in the soils over time beneath larger trees could facilitate the recovery of plant communities that might disappear due to sustained heavy grazing,prolonged fire,or other anthropogenic factors in semi-arid African savannas.However,the impact of larger trees on soil seed bank composition and its similarity with plant communities grown under their canopies are less understood in semi-arid African savannas.Therefore,we studied the effect of leguminous and non-leguminous tree species and their canopies on soil seed bank(SSB)composition and its similarity with understory vegetation(USV)in a semi-arid savanna of Ethiopia.Methods:We selected 20 matured trees from 3 dominant tree species,representing one leguminous(Acacia robusta Burch)and 2 non-leguminous tree species(Ziziphus spina-Christi and Balanites aegyptiaca(L.)Del),found in isolation,a total of 60 trees for this study.Under each selected individual tree,the species composition of USV were recorded using 1-m2 quadrat in four directions(north,south,east,and west)under the inside and outside tree canopies during the flowering stage.Similarly,soil samples in a 1-m2 quadrat were also collected under the inside tree canopies and their corresponding outside canopies,in each individual tree,for the determination of SSB composition,using a seed emergence method.Then,the soil was thoroughly mixed after removal of all roots and plant fragments,and spread over sand in plastic pots to a depth of 20 mm.The pots were placed at random in a glasshouse,examined every 3 days,for the first 2 months,and thereafter weekly for 6 months.A total of 960 soil samples were used for the determination of SSB composition during this study.Results:A total of 64 species were emerged from the SSB samples,of which 27 were grasses(19 annual and 8 perennial grasses),35 annual forbs and 2 woody species.Acacia robusta had a higher seedling density in the SSB compared to other tree species,whereas Z.spina-Christi had higher species diversity in the SSB than other tree species.Moreover,seedling density and species diversity were higher under the inside canopies than outside tree canopies.The mean similarity in species composition between the SSB and USV was low.However,it was higher under the leguminous trees than non-leguminous trees,and under the inside tree canopies than outside canopies.Conclusions:We found that mature tree species maintained a higher SSB species diversity and abundance under their canopies than the surrounding opened areas.Therefore,conservation of mature dominant tree species is of paramount importance for ecological stability and possible restoration of degraded semi-arid savannas under the changing climate and global warming.