In recent years, expansion of native and exotic evergreen shrubs into forest understories has been documented worldwide. Dense shrub thickets may interfere with tree establishment, suppress herbaceous cover, and contr...In recent years, expansion of native and exotic evergreen shrubs into forest understories has been documented worldwide. Dense shrub thickets may interfere with tree establishment, suppress herbaceous cover, and contribute substantially to total standing crop of leaf biomass. Expansion may occur because evergreen shrubs exploit seasonal variations in irradiance and temperature that are characteristic of temperate understory environments. We quantified leaf-level light environment and photosynthetic activity of three sympatric broadleaf evergreens (Ilex opaca, Kalmia latifolia, and Myrica cerifera) in a deciduous forest understory in Charles City County,Virginia,USAin order to understand seasonal intra- and interspecific ranges of broadleaf evergreen physiology. Two species (K. latifolia and M. cerifera) represent a diverse taxonomic range within broadleaf evergreens, and often form expansive thickets. We measured parameters related to canopy structure (e.g., bifurcation ratio, leaf angle) and photosynthetic performance (e.g., electron transport rate or ETR, chlorophyll content), to identify potential mechanisms facilitating expansion. ETR varied both seasonally and among species. In summer, M. cerifera ETR was nearly double that ofI. opaca or K. latifolia. Additionally, leaf temperature enhanced photosynthetic capacity of expansive species. Evergreen species, though capable of fixing carbon throughout the year, often exhibit slow growth rates and low physiological activity. Yet, we observed that the range of evergreen physiological activity may be broader than previously recognized. Furthermore, our results indicate potential for changes in composition and expansion of the evergreen shrub layer by species that exhibit structural and physiological mechanisms advantageous for future rises in temperature.展开更多
Natural selection processes are constantly influencing vegetation community composition. In the presence of anthropogenic contaminants additional forces act as filters controlling persistence of naturally occurring sp...Natural selection processes are constantly influencing vegetation community composition. In the presence of anthropogenic contaminants additional forces act as filters controlling persistence of naturally occurring species. Classical species diversity and richness metrics can miss subtle changes under disturbance regimes while species composition and functional characteristics may be able to detect them. Our study was designed to investigate legacy impacts of explosives contaminated soils in an experimental minefield on vegetative communities using ecological metrics. As hypothesized, species diversity and richness showed no change in the presence of explosive compounds while species composition provided clear separation of groups and functional trait dominance was also observed to change. Overall, presence of anthropogenic contaminates have led to community composition and functional shifts for vegetation after initial contamination. The responses in species composition and functional diversity/richness were a result of new tolerant species filling open niches in contaminated plots. More work is needed to confirm this in varied systems and in the presence of diverse contaminants.展开更多
文摘In recent years, expansion of native and exotic evergreen shrubs into forest understories has been documented worldwide. Dense shrub thickets may interfere with tree establishment, suppress herbaceous cover, and contribute substantially to total standing crop of leaf biomass. Expansion may occur because evergreen shrubs exploit seasonal variations in irradiance and temperature that are characteristic of temperate understory environments. We quantified leaf-level light environment and photosynthetic activity of three sympatric broadleaf evergreens (Ilex opaca, Kalmia latifolia, and Myrica cerifera) in a deciduous forest understory in Charles City County,Virginia,USAin order to understand seasonal intra- and interspecific ranges of broadleaf evergreen physiology. Two species (K. latifolia and M. cerifera) represent a diverse taxonomic range within broadleaf evergreens, and often form expansive thickets. We measured parameters related to canopy structure (e.g., bifurcation ratio, leaf angle) and photosynthetic performance (e.g., electron transport rate or ETR, chlorophyll content), to identify potential mechanisms facilitating expansion. ETR varied both seasonally and among species. In summer, M. cerifera ETR was nearly double that ofI. opaca or K. latifolia. Additionally, leaf temperature enhanced photosynthetic capacity of expansive species. Evergreen species, though capable of fixing carbon throughout the year, often exhibit slow growth rates and low physiological activity. Yet, we observed that the range of evergreen physiological activity may be broader than previously recognized. Furthermore, our results indicate potential for changes in composition and expansion of the evergreen shrub layer by species that exhibit structural and physiological mechanisms advantageous for future rises in temperature.
文摘Natural selection processes are constantly influencing vegetation community composition. In the presence of anthropogenic contaminants additional forces act as filters controlling persistence of naturally occurring species. Classical species diversity and richness metrics can miss subtle changes under disturbance regimes while species composition and functional characteristics may be able to detect them. Our study was designed to investigate legacy impacts of explosives contaminated soils in an experimental minefield on vegetative communities using ecological metrics. As hypothesized, species diversity and richness showed no change in the presence of explosive compounds while species composition provided clear separation of groups and functional trait dominance was also observed to change. Overall, presence of anthropogenic contaminates have led to community composition and functional shifts for vegetation after initial contamination. The responses in species composition and functional diversity/richness were a result of new tolerant species filling open niches in contaminated plots. More work is needed to confirm this in varied systems and in the presence of diverse contaminants.
