Microbial activity in Arctic tundra ecosystems continues through the winter and is an important component of the annual C budget. This activity is sensitive to climatic variation, particularly snow depth because that regulates soil temperature. The influence of winter conditions on soil N cycling is poorly understood. In this study, we used intact core incubations sampled periodically through the winter and following growing season to measure net N mineralization and nitrification in dry heath and in moist tussock tundra under ambient and experimentally increased snow depths (by use of a snowfence). In dry heath, we sampled soils under Dryas octopetela or Arctostaphylos alpine, while in tussock tundra, we sampled Eriophorum vaginatum tussocks and Sphagnum dominated areas between tussocks. Our objectives were to: (1) examine how different winter snow regimes influenced year-round N dynamics in the two tundra types, and (2) evaluate how these responses are affected by dominant species present in each system. In tussock tundra, soils with increased winter snow cover had high net N mineralization rates during the fall and winter, followed by immobilization during thaw. In contrast, N mineralization only occurred during the autumn in soils with ambient snow cover. During the growing season when N immobilization dominated in areas with ambient snow cover, soils with increased winter snow cover had positive net mineralization and nitrification rates. In dry heath tundra, soils with increased snow depth had high late winter net N mineralization rates, but these rates were: (a) comparable to early winter rates in soils under Arctostaphylos plants with ambient snow cover; (b) greater in soils under Arctostaphylos plants than in soils under Dryas plants; and (c) less than the rates found in tussock tundra. Our findings suggest under ambient snow conditions, low soil temperatures limit soil N mineralization, but that deeper snow conditions with the associated warmer winter soil temperatures dramatically increase over-winter N mineralization and thereby alter the amount and timing of plant-available N in tundra ecosystems. (C) 2003 Elsevier Ltd. All rights reserved.

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Increased snow depth affects microbial activity and nitrogen mineralization in two Arctic tundra communities - eScholarship

 Image 1 outlines the different ‘strata’ or pastures proportions referred to in the descriptions of PUP grazing management.  Making an informed decision about pasture allocation is centred around quantifying what is on offer both in terms of quantity and quality.  The amount of kikuyu consumed by a milking cow is primarily dictated by the quantity on offer. However, pasture factors that also influence intake are: o the height of the pasture o the amount of previous faecal and urine residual contamination o the quality of the pasture consumed Grazing Kikuyu using PUP

방목 초지관리 ( Grazing Management )

Analysis of trends and agricultural drivers of farmland bird declines in North America: A review

Year-round horse grazing supports typical vascular plant species, orchids and rare bird communities in a dry calcareous grassland

This document has been prepared at the request of the Secretariat of the FAO Commission on Genetic Resources for Food and Agriculture, and in close collaboration with the FAO Animal Production and Health Division, to facilitate the Commission’s deliberations when it will review key issues in ecosystem services provided by livestock species and breeds at its Fifteenth Regular Session.

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Ecosystem services provided by livestock species and breeds, with special consideration to the contributions of small-scale livestock keepers and pastoralists

Effects of grazing on grassland birds are generally thought to be indirect, through alteration of vegetation structure; however, livestock can also affect nest survival directly through trampling and other disturbances (e.g., livestock-induced abandonment). We extracted data on nest fates from 18 grazing studies conducted in Canada. We used these data to assess rates of nest destruction by cattle among 9 ecoregions and between seasonal and rotational grazing systems. Overall, few nests were destroyed by cattle (average 1.5% of 9132 nests). Nest destruction was positively correlated with grazing pressure (i.e., stocking rate or grazing intensity), but nest survival was higher in more heavily grazed areas for some species. Because rates of destruction of grassland bird nests by cattle are low in Canada, management efforts to reduce such destruction may not be of ecological or economic value in Canada.

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Direct Effects of Cattle on Grassland Birds in Canada

The western prairie fringed-orchid is a rare North American orchid restricted to a few remnants of wet to mesic tallgrass prairie. It is federally listed in both Canada and the United States and both countries have developed a recovery plan for the species. Two key management objectives are to monitor population trends and identify beneficial management practices. We used 21 y of data from the Manitoba metapopulation to assess effects of weather and land management on this species. Our results suggest the metapopulation in Manitoba is relatively stable. Western prairie fringed-orchids appear to benefit most from a combination of warm temperatures in the previous growing season followed by cool snowy but short winters and wet springs. Periodic burning (e.g., every 2–3 y) may benefit fringed-orchids, whereas grazing may be detrimental. This was not a controlled experiment, however, and gaps in the data may have influenced our results. Prescribed burning is a viable management tool for curtailing wo...

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Effects of Weather and Land Management on the Western Prairie Fringed-orchid (Platanthera praeclara) at the Northern Limit of its Range in Manitoba, Canada

The xeric hypothesis is that bees are more abundant pollinators than anthophilous flies in dry, temperate biomes, and the habitat filtering hypothesis is that differences in the proportions will im...

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Habitat filtering influences plant–pollinator interactions in prairie ecosystems

The small white lady's-slipper, Cypripedium candidum, is a rare perennial orchid with a limited distribution in Canada, occurring as isolated populations in remnant tallgrass prairie in southern Manitoba and Ontario. The species is listed as endangered in both provinces and as threatened federally. Despite its status, information on how environmental conditions and land management affect population size and persistence of this species is limited. We used 20 y of monitoring data collected for a subset of the largest population in Canada to evaluate the response of small white lady's-slipper to land management and weather. Long-term monitoring suggests the population is in decline and may not persist under the current climate and management regime. Temperature appears to regulate vegetative growth and flowering proximately. Warm temperatures early in the spring, when shoots are emerging, appear favored, but high temperatures during anthesis appear detrimental, reducing both vegetative growth and flowering. In contrast, precipitation appears to have a lag effect on growth and flowering. However, snow depth was identified as a positive influence on vegetative growth, suggesting precipitation in early spring, when shoots are emerging, is also important for above-ground growth. Some grazing appears to benefit the species presumably by reducing competition and shading, but frequent grazing may increase the risk of direct damage to individuals from cattle consumption and trampling and does not provide sufficient time for individuals to recover following grazing events. Our findings add to the knowledge of orchid conservation and management, highlighting the importance of long-term monitoring in detecting population trends in species with erratic life cycles and fluctuating populations, such as the small white lady's-slipper.

Barbara I. Bleho

Papers

Direct Effects of Cattle on Grassland Birds in Canada

Effects of Weather and Land Management on the Western Prairie Fringed-orchid (Platanthera praeclara) at the Northern Limit of its Range in Manitoba, Canada

Habitat filtering influences plant–pollinator interactions in prairie ecosystems

A 20 y Analysis of Weather and Management Effects on a Small White Lady's-slipper (Cypripedium candidum) Population in Manitoba