Small-scale resource heterogeneity in semi-arid landscapes

1994 ◽  
Vol 1 (3) ◽  
pp. 201 ◽  
Author(s):  
David J. Tongway ◽  
John A. Ludwig
Keyword(s):  
Grazing Pressure ◽  
Arid Ecosystems ◽  
Small Scale ◽  
Patchy Distribution ◽  
Landscape Degradation ◽  
Term Change ◽  
Regulation Mechanisms ◽  
Acacia Aneura ◽  
Semi Arid

Patchy distribution of plant populations is a hallmark of arid and semi-arid ecosystems. This has been attributed to the patchy distribution of scarce or limiting resources across the landscape and within the soil itself. Behind these descriptive properties are a range of processes which are the causal mechanisms of resource allocation, conservation and utilization within the landscape. Terrain-controlled mechanisms have been previously described in respect of groved mulga (Acacia aneura) communities. This paper describes a set of resource regulation mechanisms which are largely controlled by plants and plant communities and which are effective at fine scales. The actual mechanisms are inferred from field observations, and validated by looking for the net effects of defined processes acting over time. Plant-mediated resource control is inherently more sensitive to grazing pressure than terrain-controlled processes, because herbivores are able to quickly and drastically alter the density and basal cover of plants, and so change the effectiveness of the control processes. This may lead to a long-term change in system function. This paper examines the generality of these propositions in a series of contrasting landscape types, and proposes a framework by which landscape degradation can be assessed by examining the modes of basic resource regulation.

Species Responses to Grazing and Environmental-Factors in an Arid Halophytic Shrubland Community

1987 ◽  
Vol 35 (2) ◽  
pp. 135 ◽  
Author(s):  
RB Hacker
Keyword(s):  
Environmental Factors ◽  
Soil Salinity ◽  
Large Scale ◽  
Chemical Properties ◽  
Grazing Pressure ◽  
Aerial Photographs ◽  
Small Scale ◽  
Factors Affecting ◽  
Species Responses

Species responses to grazing and environmental factors were studied in an arid halophytic shrubland community in Western Australia. The grazing responses of major shrub species were defined by using reciprocal averaging ordination of botanical data, interpreted in conjunction with a similar ordination of soil chemical properties and measures of soil erosion derived from large-scale aerial photographs. An apparent small-scale interaction between grazing and soil salinity was also defined. Long-term grazing pressure is apparently reduced on localised areas of high salinity. Environmental factors affecting species distribution are complex and appear to include soil salinity, soil cationic balance, geomorphological variation and the influence of cryptogamic crusts on seedling establishment.

scholarly journals Crossing Boundaries–Tactical Urbanism Practices in Guangzhou City

2019 ◽  
Author(s):  
Fanying Jiang ◽  
SueAnne Ware ◽  
Wei Gao
Keyword(s):  
Local Community ◽  
Small Scale ◽  
Urban Context ◽  
Guangzhou City ◽  
Term Change ◽  
Tactical Urbanism ◽  
Spatial Appropriation ◽  
Community Spaces ◽  
Textile Factory

Tactical Urbanism is a growing movement across the world in which individuals, communities, and municipalities are improving their cities by using short-term, lowcost, and small-scale interventions and policies to catalyze long term change. The aim of this paper is to test the principle sand the approach of tactical urbanism to solve Guangzhou’slocalpublicspacesproblemsbyshowcasingtwotacticalurbanismprojects which have been completed in the Guangzhou urban context. These two cases reveal the opportunities that bottom-up approaches like tactical urbanism can build a bridge to conjunct with long term planning efforts and complete the top-down mechanisms. IntheZhusigangcommunitycase,we examine the spontaneous unplanned practices in the local community,which resemble“Tacticalurbanism” principles,and their spatial appropriation and utilization of marginalized community spaces. We assess how and where daily activities are happening and what other amenities could be provide by temporarily introducing these activities into a local gallery space. In the former textile factory case, we present examples that make the case for temporary, flexible and experimental responses to urban vacant land, then conclude by outlining the potential benefits and drawbacks of this temporary use model. This paper explores the existing practices of appropriation and the potential of temporary occupation in the city and concludes with thoughts on how tactical urbanism, an international movement, might gain a foothold in the context of local Chinese communities

Small-scale spatial patterns of two soil lichens in semi-arid Mediterranean steppe

2003 ◽  
Vol 35 (1) ◽  
pp. 71-81 ◽  
Author(s):  
Fernando T. Maestre
Keyword(s):  
Spatial Distribution ◽  
Correlation Analysis ◽  
Spatial Pattern ◽  
Soil Surface ◽  
Arid Ecosystems ◽  
Small Scale ◽  
Significant Relationships ◽  
Arid Steppe ◽  
The Individual ◽  
Semi Arid

AbstractBiological crusts are a common feature of the soil surface in arid and semi-arid ecosystems, where they play a major role in ecosystem functioning. In recent years, there has been an increasing interest in the ecophysiology, floristics, and dynamics of crust-forming lichens but little is known about the effect of vascular plants on their small-scale spatial distribution. To increase our understanding about the interactions between crust-forming lichens and vegetation in semi-arid areas, the spatial pattern and interaction of two soil lichens, Cladonia convoluta and Squamarina cartilaginea, at two microsites in semi-arid Stipa tenacissima steppe of south-eastern Spain are evaluated. The aim of this study was to determine if the microsite provided by Stipa tussocks promoted changes in the individual patterns and in the spatial covariation of these soil lichens. Spatial analysis by distance index (SADIE) coupled with correlation analysis was used to explore the individual patterns and the spatial relationships between the two species. SADIE detected a significant clumped pattern in the spatial distribution of both species, but Stipa tussocks promoted changes only in the spatial pattern of Cladonia. Correlation analysis revealed the presence of significant relationships between the two species, particularly close to Stipa tussocks. The results show that the microenvironment provided by Stipa is able to modify the small-scale spatial pattern of soil lichens in semi-arid steppe, and suggest the presence of facilitation between Stipa and Cladonia.

scholarly journals Drought dominates the interannual variability in global terrestrial net primary production by controlling semi-arid ecosystems

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Ling Huang ◽  
Bin He ◽  
Aifang Chen ◽  
Haiyan Wang ◽  
Junjie Liu ◽  
...  
Keyword(s):  
Primary Production ◽  
Interannual Variability ◽  
Southern Hemisphere ◽  
Interannual Variation ◽  
Net Primary Production ◽  
Arid Ecosystems ◽  
Leading Role ◽  
Main Driver ◽  
Semi Arid

Abstract Drought is a main driver of interannual variation in global terrestrial net primary production. However, how and to what extent drought impacts global NPP variability is unclear. Based on the multi-timescale drought index SPEI and a satellite-based annual global terrestrial NPP dataset, we observed a robust relationship between drought and NPP in both hemispheres. In the Northern Hemisphere, the annual NPP trend is driven by 19-month drought variation, whereas that in the Southern Hemisphere is driven by 16-month drought variation. Drought-dominated NPP, which mainly occurs in semi-arid ecosystems, explains 29% of the interannual variation in global NPP, despite its 16% contribution to total global NPP. More surprisingly, drought prone ecosystems in the Southern Hemisphere, which only account for 7% of the total global NPP, contribute to 33% of the interannual variation in global NPP. Our observations support the leading role of semi-arid ecosystems in interannual variability in global NPP and highlight the great impacts of long-term drought on the global carbon cycle.

scholarly journals Altered phenology and temperature sensitivity of invasive annual grasses and forbs changes autotrophic and heterotrophic respiration rates in a semi-arid shrub community

2013 ◽  
Vol 10 (4) ◽  
pp. 6335-6375 ◽  
Author(s):  
M. Mauritz ◽  
D. L. Lipson
Keyword(s):  
Soil Respiration ◽  
High Temperatures ◽  
Temperature Sensitivity ◽  
Seasonal Pattern ◽  
Arid Ecosystems ◽  
Small Scale ◽  
C Storage ◽  
Annual Grasses ◽  
Semi Arid ◽  
Invasive Annuals

Abstract. Many invasions, like the wide-spread establishment of annual grasses and forbs in semi-arid shrublands, are associated with climate change. In order to predict ecosystem carbon (C) storage it is critical that we understand how invasion affects soil respiration (Rt). Because plants and microbes have different seasonal dynamics, determining the relative contribution of autotrophic (Ra) and heterotrophic (Rh) respiration provides critical insight into soil C processes. Using automated soil respiration measurements and root exclusion cores we evaluated the moisture and temperature sensitivity of Rt and Rh and calculated the contribution of Ra in native shrub and invaded areas. Invasion increased cumulative Rt by 40% from 695 (±51) g C m−2 under shrubs to 1050 g C m−2 (±44) in invaded areas. Cumulative Rh did not change but invasion altered the seasonal pattern of Rh. Throughout the season Rt and Rh responded positively to temperature increases when soils were wet and negatively when soils were dry. Invasion increased temperature sensitivity of Rt and Rh in wet soils and decreased temperature sensitivity in dry soils. The altered temperature sensitivity of invasives was attributed largely to differences in phenology. Early phenology of invasive grasses caused rapid Ra increases early in the season; late phenology of invasive forbs resulted in the surprising maintenance of diurnal Ra and Rh signals despite high temperatures and low soil moisture. Invasion extended the respiration season of the system. Ability of the invasive community to withstand high temperatures and drought could confer greater resilience if temperature and precipitation patterns in the region change. The high contribution of Ra by invasive annuals means ecosystem C storage will depend heavily on seasonal rainfall dynamics and productivity of invasive annuals. In semi-arid ecosystems even small scale changes in plant community composition alter Rt, Ra and Rh and should be considered when attempting to predict Rt.

Soil physicochemical and microbiological indicators of short, medium and long term post-fire recovery in semi-arid ecosystems

2016 ◽  
Vol 63 ◽  
pp. 14-22 ◽  
Author(s):  
Miriam Muñoz-Rojas ◽  
Todd E. Erickson ◽  
Dylan Martini ◽  
Kingsley W. Dixon ◽  
David J. Merritt
Keyword(s):  
Arid Ecosystems ◽  
Microbiological Indicators ◽  
Semi Arid

Long-term changes in vegetation, gradual and episodic, on the TGB Osborn Vegetation Reserve, Koonamore, South Australia (1926 - 2002)

2005 ◽  
Vol 53 (4) ◽  
pp. 283 ◽  
Author(s):  
Russell Sinclair
Keyword(s):  
Gradual Increase ◽  
South Australia ◽  
Gradual Change ◽  
Sheep Grazing ◽  
Rainfall Events ◽  
Show Evidence ◽  
Acacia Aneura ◽  
Permanent Quadrats ◽  
Semi Arid

The TGB Osborn Vegetation Reserve at Koonamore, South Australia, is a 390-ha exclosure in semi-arid chenopod shrubland. The area was heavily overgrazed in 1925 when it was fenced to exclude sheep. Permanent quadrats and photopoints have been maintained to the present. Feral rabbits were sometimes numerous until the mid-1970s but have since been controlled. The records represent 50 years without sheep grazing, followed by 26 years without either sheep or rabbits. Dramatic seedling establishment events have occurred since 1978 for the following species: Acacia aneura Benth., Myoporum platycarpum R.Br., Senna artemesioides subsp. coriacea Randell, S. artemesioides subsp. petiolaris Randell, Acacia burkittii Benth., Dodonaea attenuata A.Cunn., Eremophila longifolia (R.Br.) F.Muell., E. sturtii R.Br. and Maireana pyramidata (Benth.) Paul G.Wilson. However, the chenopod shrubs Atriplex vesicaria Benth. and A. stipitata Benth. increased earlier and did not respond in the same way to episodic rainfall events or rabbit control. Numbers of Alectryon oleifolius (Desf.) S.T.Reynolds and Casuarina pauper F.Muell. ex L.A.S.Johnson have remained almost unchanged, whereas Maireana sedifolia (F.Muell.) Paul G.Wilson and M. astrotricha (L.Johnson) Paul G.Wilson have shown a very gradual increase over time. The data show evidence for both episodic and gradual change among different species.

scholarly journals Predicted land use and land cover outlook for semi-arid Lokere and Lokok catchments in Karamoja region, Uganda

2020 ◽  
Vol 28 (4) ◽  
pp. 595-616
Author(s):  
R. Osaliya ◽  
O.V. Wasonga ◽  
J-G. Majaliwa Mwanjalolo ◽  
L. MacOpiyo ◽  
G. Kironchi ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Small Scale ◽  
Multi Criteria Evaluation ◽  
Evaluation Strategies ◽  
Business As Usual ◽  
Policy Shifts ◽  
Karamoja Region ◽  
Semi Arid

The semi-arid Lokere and Lokok catchments in northeastern Uganda are experiencing land use and land cover (LULC) change driven by policies and actions aimed at pastoralist sedentarisation. While these efforts present a trajectory of a landscape dominated by farming, livestock herding or grazing persists. The objective of this study was to project medium, and long-term LULC for Lokere and Lokok catchments in Karamoja, Uganda. We applied automatic multi-perceptron neural network, built on Markov chain modeling method, along with multi-criteria evaluation strategies; all embedded in the IDRISI Land Change Modeler (LCM) to project the catchments’ LULC to the year 2030 and 2050. The model was trained using 1994 and 2003 LULC, and validated with 2013 LULC. Results of three modelled policy scenarios; business as usual (BAU), pro-livestock and pro-farming; to the years 2030 and 2050 showed that small scale farming (SSF) would increase in all scenarios, even if policy shifts to promote livestock rearing. Pro-farming policies would, in both 2030 and 2050, result in reduction of grassland as SSF increases; doubling the 2003 land area by 2050. The results of this study facilitate assessment of potential impacts of the future LULC and policy evaluation in the catchments.

Grass-mediated Capture of Resource Flows and the Maintenance of Banded Mulga in a Semi-arid Woodland

1997 ◽  
Vol 45 (2) ◽  
pp. 331 ◽  
Author(s):  
Val Jo Anderson ◽  
Ken C. Hodgkinson
Keyword(s):  
Soil Water ◽  
Isotope Composition ◽  
Life Forms ◽  
Grazing Pressure ◽  
Perennial Grasses ◽  
Xylem Water Potential ◽  
Scarce Resources ◽  
Landscape Processes ◽  
Acacia Aneura ◽  
Semi Arid

It has been proposed for semi-arid and arid regions that the scarce resources of water and nutrients normally limiting plant growth are distributed patchily in the landscape in order to maintain both stability and productivity (Tongway 1990). ‘Fertile patches’ are maintained by the concentration of resources during flows and when resource control is weakened their persistence is threatened. This proposition was tested by comparing water relations of perennial life-forms in the nutrient and water rich ‘island-bands’ of mulga (Acacia aneura F.Muell. ex Benth.) shrubs, with and without perennial grasses. Dawn xylem water potential (dawn ψx) and stable hydrogen isotope composition data showed that A. aneura and companion grasses competed for soil water, whereas the poplar box (Eucalyptus populnea F.Muell.) trees accessed additional sub-soil water. During a drying cycle, dawn ψx of A. aneura on the upslope portion of ‘island-bands’ was –2 MPa where grass was abundant, and –4.8 MPa where grasses were killed by heavy grazing. On the downslope portions, dawn ψx of A. aneura was similar at –4.2 MPa. Recruitment of A. aneura was occurring in the upslope portion, but was less where there were no grasses. There were more dead A. aneura shrubs on the downslope portion and in grass-free ‘island-bands’. The results suggest that removal of perennial grasses by grazing shortens the period of water supply to A. aneura shrubs in ‘island-bands’ and they prematurely die during low rainfall periods. Furthermore, continued grazing pressure from domestic and non-domestic herbivores will prevent restoration of landscape processes necessary for the survival of these shrubs and associated flora.

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