Geology topics

Amy B. Zacheis

Publications and source records attributed to Amy B. Zacheis.

4 recordsLinked to original sources

USGS2016

Response of a subarctic salt marsh plant community to grubbing and grazing by captive lesser snow geese

F oraging intensity and faecal inputs are important determinants of plant community response to herbivory. We used captive adult lesser snow geese ( Anser caerulescens caerulescens ), which feed on both above- and below-ground plant tissues, to manipulate foraging intensity and faecal inputs to plots in a sedge meadow in spring, 1996. We measured plant and soil characteristics throughout the growing season of 1996 and in August 1997. We analysed three contrasts: grazed plots versus ungrazed controls, plots with a short period of feeding (3 goose-hours) versus plots with a long period of feeding (6 goose-hours), and grazed plots with faeces versus grazed plots without faeces. Although grazed plots had an order of magnitude higher foraging intensity than that imposed by wild geese in the marsh, there was no effect of feeding on biomass or nitrogen concentration in the dominant species, Carex ramenskii and Triglochin maritimum , after one and two growing seasons. The amount of forage removed by geese did not differ between plots grazed for long and short periods, indicating that geese were able to remove little additional biomass after 3 hours due to low availability. Therefore, the amount of biomass removed by geese was a better indicator of foraging intensity than the time geese fed on plots. The presence of faeces had no effect on biomass or nitrogen concentration in Carex ramenskii or Triglochin maritimum , or on rates of net nitrogen mineralization in soils. Thus, faeces did not appear to increase nitrogen availability for plants in this marsh, probably because faecal density was low.

Écoscience↗

USGS2002

Nitrogen dynamics in an Alaskan salt marsh following spring use by geese

Lesser snow geese ( Anser caerulescens caerulescens ) and Canada geese ( Branta canadensis ) use several salt marshes in Cook Inlet, Alaska, as stopover areas for brief periods during spring migration. We investigated the effects of geese on nitrogen cycling processes in Susitna Flats, one of the marshes. We compared net nitrogen mineralization, organic nitrogen pools and production in buried bags, nitrogen fixation by cyanobacteria, and soil and litter characteristics on grazed plots versus paired plots that had been exclosed from grazing for 3 years. Grazed areas had higher rates of net nitrogen mineralization in the spring and there was no effect of grazing on organic nitrogen availability. The increased mineralization rates in grazed plots could not be accounted for by alteration of litter quality, litter quantity, microclimate, or root biomass, which were not different between grazed and exclosed plots. In addition, fecal input was very slight in the year that we studied nitrogen cycling. We propose that trampling had two effects that could account for greater nitrogen availability in grazed areas: litter incorporation into soil, resulting in increased rates of decomposition and mineralization of litter material, and greater rates of nitrogen fixation by cyanobacteria on bare, trampled soils. A path analysis indicated that litter incorporation by trampling played a primary role in the nitrogen dynamics of the system, with nitrogen fixation secondary, and that fecal input was of little importance.

Alaska↗

USGS2001

Effects of migratory geese on plant communities of an Alaskan salt marsh

1. We studied the effects of lesser snow geese (Anser caerulescens caerulescens) and Canada geese (Branta canadensis) on two salt marsh plant communities in Cook Inlet, Alaska, a stopover area used during spring migration. From 1995 to 1997 we compared plant species composition and biomass on plots where geese were excluded from feeding with paired plots where foraging could occur. 2. Foraging intensity was low (650-1930 goose-days km-2) compared to other goose-grazing systems. 3. Canada geese fed mainly on above-ground shoots of Triglochin maritimum, Puccinellia spp. and Carex ramenskii, whereas the majority of the snow goose diet consisted of below-ground tissues of Plantago maritima and Triglochin maritimum. 4. Plant communities responded differently to goose herbivory. In the sedge meadow community, where feeding was primarily on above-ground shoots, there was no effect of grazing on the dominant species Carex ramenskii and Triglochin maritimum. In the herb meadow community, where snow geese fed on Plantago maritima roots and other below-ground tissues, there was a difference in the relative abundance of plant species between treatments. Biomass of Plantago maritima and Potentilla egedii was lower on grazed plots compared with exclosed, whereas biomass of Carex ramenskii was greater on grazed plots. There was no effect of herbivory on total standing crop biomass in either community. The variable effect of herbivory on Carex ramenskii between communities suggests that plant neighbours and competitive interactions are important factors in a species' response to herbivory. In addition, the type of herbivory (above- or below-ground) was important in determining plant community response to herbivory. 5. Litter accumulation was reduced in grazed areas compared with exclosed in both communities. Trampling of the previous year's litter into the soil surface by geese incorporated more litter into soils in grazed areas. 6. This study illustrates that even light herbivore pressure can alter plant communities and affect forage availability.

Journal of Ecology↗

USGS2001

Snow cover and snow goose Anser caerulescens caerulescens distribution during spring migration

Arctic geese often use spring migration stopover areas when feeding habitats are partially snow covered. Melting of snow during the stopover period causes spatial and temporal variability in distribution and abundance of feeding habitat. We recorded changes in snow cover and lesser snow goose Anser caerulescens caerulescens distribution on a spring migration stopover area in south-central Alaska during aerial surveys in 1993-1994. Our objectives were to determine whether geese selected among areas with different amounts of snow cover and to assess how temporal changes in snow cover affected goose distribution. We also measured temporal changes in chemical composition of forage species after snow melt. We divided an Arc/Info coverage of the approximately 210 km 2 coastal stopover area into 2-km 2 cells, and measured snow cover and snow goose use of cells. Cells that had 10-49.9% snow cover were selected by snow geese, whereas cells that lacked snow cover were avoided. In both years, snow cover diminished along the coast between mid-April and early May. Flock distribution changed as snow geese abandoned snow-free areas in favour of cells where snow patches were interspersed with bare ground. Snow-free areas may have been less attractive to geese because available forage had been quickly exploited as bare ground was exposed, and because soils became drier making extraction of underground forage more difficult. Fiber content of two forage species increased whereas non-structural carbohydrate concentrations of forage plants appeared to diminish after snow melt, but changes in nutrient concentrations likely occurred too slowly to account for abandonment of snow-free areas by snow geese.

Alaska↗