Survival of Perennial Grass Seedlings Under Intensive Grazing in Semi-Arid Rangelands

Salihi, D. O.; Norton, Brien E.

doi:10.2307/2403793

Cited by 49 publications

(30 citation statements)

References 7 publications

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“…These conditions are probably only episodically met, when cohorts of seedlings establish, with long periods of time when no/few seedlings establish. Severe trampling (cattle were particularly attracted to the irrigated plots during the warm dry months) likely further reduced tree seedling establishment, as was found for perennial grass seedlings (Salihi and Norton 1987) and woody seedlings (Pitt et al 1998;Kanz 2001). Acacia mellifera seedlings did not exhibit shade intolerance in our experiments.…”

Section: Discussionmentioning

confidence: 87%

Effects of rain, nitrogen, fire and grazing on tree recruitment and early survival in bush-encroached savanna, South Africa

2006

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Moisture, nutrients, fire and herbivory are the principal factors governing tree -grass cover ratios of savannas. We investigated tree (Acacia mellifera) recruitment after fire and under conditions of maximumrecorded rainfall, nitrogen addition and grazing in a completely-crossed field experiment. We employed a similar garden experiment with the exception of the fire treatment. Tree germination in the field was extremely low, probably due to below-average natural rainfall in plots that only received natural rain, and insufficient watering frequency in irrigated plots. Due to low germination in the field experiment, no treatment significantly affected tree recruitment. In the garden experiment, frequent watering, nutrient control (i.e. no nitrogen addition) and grazing enhanced tree recruitment with significant interactions between rain, nitrogen and grazing. We infer that above-average rainfall years with frequent rainfall events are required for mass tree recruitment. Grass defoliation makes space and resources available for tree seedlings. Nitrogen enrichment increases the competitive ability of fast-growing grasses more than that of the N 2 -fixing tree component. In contrast to conventional wisdom that grazing alone causes encroachment, we suggest that there are complex interactions between the above-mentioned factors and 'triggering' events such as unusually high rainfall.

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Section: Discussionmentioning

confidence: 87%

Effects of rain, nitrogen, fire and grazing on tree recruitment and early survival in bush-encroached savanna, South Africa

2006

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“…Although wind erosion was not measured in this study, it was confirmed by the characteristics in soil particle size distribution, with a lower content in fine size fractions (<0.1 mm) in the CG site (36%) than in the 5EX site (48%) and in the 10EX site (57%) ( increase in soil bulk density. The change of bulk density is considered as an important early indicator of ecosystem degradation (Rubio & Bochet 1998), because it leads to further alteration of soil properties related directly to plant growth, such as soil water infiltration and retention (Salihi & Norton 1987). Increased bulk density could feed back to other soilplant processes that continue to deteriorate the system (Manzano & Návar 2000).…”

Section: Discussionmentioning

confidence: 99%

Influences of grazing and exclosure on carbon sequestration in degraded sandy grassland, Inner Mongolia, north China

Zhao

Zhang

2003

New Zealand Journal of Agricultural Research

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Livestock grazing is recognised as one of the main causes of vegetation and soil degradation/desertification in the semi-arid Horqin sandy steppe of northern China. In this paper, soilplant system carbon (C) in a representative degraded sandy grassland in the Horqin sandy steppe (42°58' N, 120°42'E altitude c. 360 m a.s.l.) was measured. Three situations: long-term continuous grazing (CG), exclosure for 5 years (5EX), and exclosure for 10 years (10EX), were compared to assess the effect of grazing management on C sequestration. Ground cover increased from the CG (35%) to the 5EX (63%) and to the 10EX (81%), and accordingly soil organic C at 0-15 cm depth and total plant components C increased from the CG (492 and 98 g m -2 ) to the 5EX (524and 134 g m -2) and to the 10EX (584 and 317 g m -2 ). The results suggested that continuous grazing in the erosion-prone sandy grassland is very detrimental to vegetation and soil. Under exclosure conditions, vegetation restoration and litter accumulation significantly increased plantsoil system C storage, and thus sequestration of atmospheric C. It was concluded that the degraded sandy grassland could contribute to significant C sequestration with the implementation of protective practices.

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“…This technique does not have the shortcomings of other survival analysis techniques reviewed by Pyke & Thompson (1986). Maximum likelihood analysis based on the multinomial distribution was originally used to estimate survival in animal populations (Brownie et al 1978;White 1983) but has also been used successfully in plant populations (Gardiner 1986;Salihi & Norton 1987).…”

Section: Discussionmentioning

confidence: 99%

The impact of ?available area? onArtemisia tridentata seedling dynamics

Owens

Norton

1989

Vegetatio

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Seedling survival ofArtemisia tridentata ssp. tridentata (basin big sagebrush) was studied during 1984 and 1986 on a semi-arid rangeland in central Utah, USA. Seedlings were mapped in ungrazed pastures and observed on a 10 day interval for survival. Available resource area around individual seedlings was calculated using Theissen polygons. Over 90 ~ of the naturally-occurring seedlings occurred in polygons of 150 mm 2 or less. Seedlings with available areas greater than 300 mm 2 were more likely to survive than seedlings with less resource area. Differences in overall seedling survival in different study sites were noted. Survival was similar for all seedlings with less than 50 mm 2 available area. In 1986, precipitation and seedling survival were considerably lower than in 1984. Even in 1986, however, seedling survival in polygons greater than 300 mm 2 was always higher than for seedlings in smaller polygons. Survival patterns over each growing season closely followed the precipitation patterns.Mortality of first year Artemisia seedlings seemed to be density independent at the beginning of the growing season. Patterns of survival for seedlings in different available area classes were similar for the first 20 days after emergence. Survival rates were then consistently higher for seedlings with more than 300 mm 2 resource area. Changes in survival rates were linked to differences in pastures and the presence of nurse plants.

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Survival of Perennial Grass Seedlings Under Intensive Grazing in Semi-Arid Rangelands

Cited by 49 publications

References 7 publications

Effects of rain, nitrogen, fire and grazing on tree recruitment and early survival in bush-encroached savanna, South Africa

Effects of rain, nitrogen, fire and grazing on tree recruitment and early survival in bush-encroached savanna, South Africa

Influences of grazing and exclosure on carbon sequestration in degraded sandy grassland, Inner Mongolia, north China

The impact of ?available area? onArtemisia tridentata seedling dynamics

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