scholarly journals Evaluation of a Factor Exclusion Experiment Designed to Assist in Elucidating the Etiology of Citrus Blight

2002 ◽  
Vol 15 (15) ◽  
Author(s):  
L. J. Marais ◽  
J. H. J. Breytenbach ◽  
K. S. Derrick
Keyword(s):  
Exclusion Experiment ◽  
Citrus Blight

scholarly journals Effects of Grazer Exclusion on Carbon Cycling in Created Freshwater Wetlands

Land ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 805
Author(s):  
Delanie M. Spangler ◽  
Anna Christina Tyler ◽  
Carmody K. McCalley
Keyword(s):  
Soil Carbon ◽  
Carbon Cycling ◽  
Belowground Biomass ◽  
Freshwater Wetlands ◽  
Wetland Creation ◽  
Free Access ◽  
Exclusion Experiment ◽  
Herbivore Exclusion ◽  
Sequestration Potential ◽  
Natural Wetlands

Wetland ecosystems play a significant role in the global carbon cycle, and yet are increasingly threatened by human development and climate change. The continued loss of intact freshwater wetlands heightens the need for effective wetland creation and restoration. However, wetland structure and function are controlled by interacting abiotic and biotic factors, complicating efforts to replace ecosystem services associated with natural wetlands and making ecologically-driven management imperative. Increasing waterfowl populations pose a threat to the development and persistence of created wetlands, largely through intensive grazing that can shift vegetation community structure or limit desired plant establishment. This study capitalized on a long-term herbivore exclusion experiment to evaluate how herbivore management impacts carbon cycling and storage in a created wetland in Western New York, USA. Vegetation, above- and belowground biomass, soil carbon, carbon gas fluxes and decomposition rates were evaluated in control plots with free access by large grazers and in plots where grazers had been excluded for four years. Waterfowl were the dominant herbivore at the site. Grazing reduced peak growing season aboveground biomass by over 55%, and during the summer, gross primary productivity doubled in grazer exclusion plots. The shift in plant productivity led to a 34% increase in soil carbon after exclusion of grazers for five growing seasons, but no change in belowground biomass. Our results suggest that grazers may inhibit the development of soil carbon pools during the first decade following wetland creation, reducing the carbon sequestration potential and precluding functional equivalence with natural wetlands.

scholarly journals Grazing by wild red deer maintains characteristic vegetation of semi‐natural open habitats: Evidence from a three‐year exclusion experiment

2020 ◽  
Vol 23 (4) ◽  
pp. 522-538 ◽  
Author(s):  
Friederike Riesch ◽  
Bettina Tonn ◽  
Hans Georg Stroh ◽  
Marcus Meißner ◽  
Niko Balkenhol ◽  
...  
Keyword(s):  
Red Deer ◽  
Exclusion Experiment

Assessing the role of generalist predators in the biological control of alfalfa weevil (Coleoptera: Curculionidae)

2017 ◽  
Vol 149 (4) ◽  
pp. 525-533 ◽  
Author(s):  
Tatyana A. Rand
Keyword(s):  
United States ◽  
Biological Control ◽  
Experimental Work ◽  
United States Of America ◽  
Acyrthosiphon Pisum ◽  
The United States ◽  
Generalist Predators ◽  
Alfalfa Weevil ◽  
Exclusion Experiment ◽  
Predator Exclusion

AbstractAlfalfa weevil (Coleoptera:Curculionidae) is a major pest of alfalfa throughout the United States of America. Biological control research has disproportionately focussed on introduced parasitoids. Generalist predators may also be important, but experimental work evaluating their impacts is lacking. I combined a cross-site survey with a predator exclusion experiment to identify key predators, and test for impacts on weevil survival and plant defoliation levels in Montana and North Dakota, United States of America. Spiders (Araneae) dominated the complex, followed by Nabidae (Hemiptera) and Coccinellidae (Coleoptera). None of the dominant predators showed aggregative responses to weevil (Hypera postica (Gyllenhal); Coleoptera: Curculionidae) or pea aphid (Acyrthosiphon pisum (Harris); Hemiptera: Aphididae) densities across 10 sites surveyed. However, weevil densities were positively correlated with both coccinellid and nabid densities across transects at the experimental site. Thus, predator groups traditionally associated with aphids can show strong aggregative numerical responses to alfalfa weevil larvae at smaller scales. Predator exclusion revealed no significant predator effects on larval survival or alfalfa damage. However, final densities of pea aphids were significantly higher in exclusion treatments relative to controls. The results suggest that even under conditions where predators exert significant pressure on aphids, they may still have minimal impacts on weevils. Additional experimental work is necessary to determine the broader potential of generalist predators as alfalfa weevil control agents.

scholarly journals Effects of Drought on the Phenology, Growth, and Morphological Development of Three Urban Tree Species and Cultivars

2019 ◽  
Vol 11 (18) ◽  
pp. 5117 ◽  
Author(s):  
Stratópoulos ◽  
Zhang ◽  
Häberle ◽  
Pauleit ◽  
Duthweiler ◽  
...  
Keyword(s):  
Water Supply ◽  
Tree Species ◽  
Urban Areas ◽  
Selection Criterion ◽  
Root Systems ◽  
Urban Trees ◽  
Morphological Development ◽  
Root:Shoot Ratio ◽  
Exclusion Experiment ◽  
Mitigation And Adaptation

: Under changing climatic conditions, drought may become a critical constraint for trees in urban areas, particularly at roadsides and highly paved squares. As healthy urban trees have proven to be an important mitigation and adaptation tool for climate change as well as a significant provider of ecosystem services, there is a need for planting species and cultivars capable of coping with the limited water supply. However, data on species’ and cultivars’ response to drought, particularly their water supplying root systems remains rare. To consider the whole plant responses to drought situations, we studied the growth and phenology of three frequently planted tree species and cultivars with a diameter of 5–6 cm during a one-year rainfall exclusion experiment conducted in a nursery field as well as the dry biomass of the compartments branch, stem, and root after excavation. Our results revealed that species’ and cultivars’ performance were linked to their within-plant carbon partitioning. A high tolerance to drought was noted for Acer campestre, with a particularly high ratio of root:shoot ratio, which made it presumably less susceptible to droughts. Tilia cordata ‘Greenspire’ was highly affected by the reduced water availability visible through prematurely leaf senescence, while Carpinus betulus ‘Fastigiata’ suffered from losing a considerable part of its root biomass, which resulted in the lowest root:shoot ratio of all species and cultivars. This study demonstrated the need for investigating the reaction patterns of species and cultivars by considering both the above-and the below-ground plant parts. We recommend that, for future tree plantings at harsh and challenging urban sites, an important selection criterion should be species’ and cultivars’ capability to develop and retain strong and dense root systems even under limited water supply, as that is believed to be an important trait for drought tolerance.

The impact of root exclusion on duff moisture and fire danger

2015 ◽  
Vol 45 (8) ◽  
pp. 978-986 ◽  
Author(s):  
Dan K. Thompson ◽  
John Studens ◽  
Chelene Krezek-Hanes ◽  
B. Mike Wotton
Keyword(s):  
Water Content ◽  
Mineral Soil ◽  
Root Water Uptake ◽  
Volumetric Water Content ◽  
Exclusion Experiment ◽  
Stand Type ◽  
Low Levels ◽  
The Impact ◽  
Soil Interface ◽  
Root Exclusion

The impact of root water uptake on duff (both fibric and humic horizons) moisture was investigated at deciduous, mixedwood, and conifer stands in Ontario, Canada. Roots were actively excluded from the duff layer using geotextiles inserted at the duff–mineral soil interface and along the plot edges; liquid and vapour water flow was otherwise not affected by the geotextiles. Root exclusion caused little difference in duff moisture content prior to early June, after which the root exclusion plots remained at 15%–20% volumetric water content, whereas root-intact plots declined to as low as 5% volumetric water content during rain-free periods. Only in the root-intact plots did the duff water content reach sufficiently low levels that duff evaporation was limited by low water content. The net effect of root exclusion was to reduce the cumulative growing season water loss in the duff by 19%–31%, depending on the stand type. Root exclusion also decreased the number of days with a high probability of duff smouldering from as many as 72 days·year−1 to as few as 0 days·year−1. This root exclusion experiment provides a model for short-term duff moisture transitions under thinned forests such as those forests under community wildfire protection.

RAIN Project: Results after 8 Years of Experimentally Reduced Acid Deposition to a Whole Catchment

1993 ◽  
Vol 50 (2) ◽  
pp. 258-268 ◽  
Author(s):  
Richard F. Wright ◽  
Erik Lotse ◽  
Arne Semb
Keyword(s):  
Acid Deposition ◽  
Soil Chemistry ◽  
Nitrogen Saturation ◽  
Base Cations ◽  
Strong Acid ◽  
Catchment Scale ◽  
Exclusion Experiment ◽  
Surface Water Chemistry ◽  
Southern Norway

At Risdalsheia (southern Norway), an ongoing catchment-scale acid-exclusion experiment has been conducted since 1984 as part of the RAIN project (Reversing Acidification In Norway). Acid precipitation is collected on a 1200-m2 transparent roof, treated by ion exchange, sea salts readded, and reapplied as clean rain beneath the roof Up to 1990 annual surveys of soil chemistry have revealed no significant trends. The chemical composition of runoff has changed: sulfate decreased from about 111 μeq/L in 1984 to 38 μeq/L in 1992 and nitrate from about 33 to 5 μeq/L. Base cations decreased and alkalinity increased over the 8-yr period from −88 to −29 μeq/L to compensate for this change in strong acid anions. Much of the alkalinity change is due to the increased role of organic anions. The results fit an empirical nomograph relating alkalinity, base cations, and strong acid anions and a new empirical nomograph relating alkalinity, H+, and total organic carbon. The acid-exclusion experiment provides the first catchment-scale evidence for the reversibility of nitrogen saturation; RAIN results corroborate field observations of changes in surface water chemistry in response to reduced acid deposition as well as process-oriented, conceptual acidification models.

scholarly journals Herbivory modulates soil CO2 fluxes after windthrow: a case study in temperate mountain forests

2019 ◽  
Vol 139 (3) ◽  
pp. 383-391 ◽  
Author(s):  
Mathias Mayer ◽  
David Keßler ◽  
Klaus Katzensteiner
Keyword(s):  
Soil Carbon ◽  
Plant Community ◽  
Plant Communities ◽  
Soil Conditions ◽  
Negative Consequences ◽  
Mountain Forests ◽  
Exclusion Experiment ◽  
Vegetation Shifts ◽  
Ungulate Herbivory ◽  
Carbon Losses

AbstractUngulate herbivory can alter functional plant communities of early-successional forest ecosystems. The consequences of such vegetation changes on soil carbon cycling are still not fully understood. Here, we used an ungulate exclusion experiment to investigate how different levels of herbivory and associated changes in vegetation succession modulate soil CO2 efflux and its heterotrophic and autotrophic sources following windthrow in temperate mountain forests. Our results indicate that only high levels of ungulate herbivory and associated vegetation shifts from tree to rather grass dominated plant communities affect soil CO2 fluxes. We did not find evidence that a moderate herbivory level and accompanied smaller shifts in the functional plant community affect soil CO2 fluxes. A greater soil CO2 efflux under the influence of high herbivory pressure was primarily attributed to accelerated heterotrophic respiration, likely due to warmer soil conditions. Moreover, autotrophic respiration from grass roots and associated microbial communities is suggested to contribute to higher soil CO2 fluxes. We conclude that intense herbivory and accompanied successional changes in the functional plant community enhance soil carbon losses following forest windthrow. This might have negative consequences for the soil carbon stocks and for the climate system.

Soil acidity and citrus blight

1997 ◽  
Vol 28 (6-8) ◽  
pp. 603-612
Author(s):  
Heinz K. Wutscher
Keyword(s):  
Soil Acidity ◽  
Citrus Blight
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