ABSTRACT
Northeastern U.S. farms are often situated adjacent to forestland due to the heterogeneous nature of the landscape. We investigated how forested areas influence Carabidae diversity within nearby crop fields by establishing transects of pitfall traps. Trapping extended across a forest-agriculture ecotone consisting of maize, an intermediate mowed grass margin, and a forest edge. Carabidae diversity was compared among the three habitats, and community and population dynamics were assessed along the transect. We used a principal response curve to examine and visualize community change across a spatial gradient. The highest levels of richness and evenness were observed in the forest community, and carabid assemblages shifted significantly across the ecotone, especially at the forest-grass interface. Despite strong ecotone effects, population distributions showed that some species were found in all three habitats and seemed to thrive at the ecotone. Based on similarity indices, carabid assemblages collected in maize adjacent to forest differed from carabid assemblages in maize not adjacent to forest. We conclude that forest carabid assemblages exhibit high degrees of dissimilarity with those found in agricultural fields and forested areas should thus be retained in agricultural landscapes to increase biodiversity at the landscape scale. However, ecotone species found at forest edges can still noticeably influence carabid community composition within neighboring agricultural fields. Further studies should determine how these shifts in carabid assemblages influence agroecosystem services in relation to ecosystem services observed in fields embedded in an agricultural matrix.
Subject(s)
Coleoptera , Ecosystem , Animals , Pennsylvania , Poaceae , Zea maysABSTRACT
Natural cores of vegetation and soils of arctic tundra were collected in frozen condition in winter near Barrow, Alaska (71°20'N). These cores were used as microcosms in a phytotron experiment to measure the interactions, if any, between increasing atmospheric CO2 concentration and fertilization by ammonium nitrate on net ecosystem CO2 exchange and net yield of tundra vegetation. Increased soil N significantly enhanced net ecosystem CO2 uptake. The effect of increased CO2 concentration had little or no effect on mean net ecosystem carbon balance of the tundra microcosms. Added N significantly increased leaf area and phytomass of vascular plants in the microcosms while increased atmospheric CO2 had no effect on these parameters. We conclude that atmospheric CO2 is not now limiting net ecosystem production in the tundra and that its direct effects will be slight even at double the present concentration. the most probable effects of carbon dioxide in the coastal tundra will be through its indirect effects on temperature, water table, peat decomposition, and the availability of soil nutrients.
ABSTRACT
Cores of wet coastal tundra collected in frozen condition in winter were used as microcosms in a phytotron experiment that assessed the effects of doubling the present atmospheric CO2 concentration, increasing temperature, and depressed water table on net ecosystem CO2 exchange. Doubling atmospheric CO2 had less significance in regard to net carbon capture or loss in this ecosystem as compared to the significant effects of increased temperature and lowered water table level. Both of the latter are to be expected as atmospheric CO2 increases in the Arctic.
ABSTRACT
Intact cores from the wet coastal arctic tundra at Barrow, Alaska, were used as microcosms in the measurement of CO2 fluxes between peat, vegetation, and atmosphere under controlled conditions. Net ecosystem CO2 uptake was almost twice as high at present summer temperatures (4° C) than at 8°. Lowering the water table from the soil surface to -5 cm also had a pronounced effect in decreasing net ecosystem carbon storage. Warming of the tundra climate could change this ecosystem from a sink for atmospheric CO2 to a source.