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| Titel |
Shrub patterns and surface hydrological fluxes in a semiarid hillslope |
| VerfasserIn |
Tal Svoray, Shai Sela, Shmuel Assouline |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033290
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| Zusammenfassung |
| Climate-vegetation interactions and feedbacks are the subject of many studies and recently,
the rainfall-plant-soil interplay in the hillslope scale is in the foci of ecohydrology. As most of
the models in this scale rely on synthetic environments, there is a need for studies that use
remotely sensed and in-situ data to examine the effect of hillslope hydrological processes on
ecosystem functioning and plant population spread in a more realistic manner. A major
problem is the difficulty encountered in simulating water budget and measuring
vegetation at the individual level. In this research, a typical hillslope was chosen offering
variations in slope decline and orientation, soil depth and vegetation cover, at the
LTER Lehavim site in the center of Israel (31020’ N, 34045’ E). The annual rainfall
is 290 mm, the soils are brown lithosols and arid brown loess and the dominant
rock formations are Eocenean limestone and chalk with patches of calcrete. The
vegetation is characterized by scattered dwarf shrubs (dominant species Sarcopoterium
spinosum) and patches of herbaceous vegetation, mostly annuals, are spread between
rocks and dwarf shrubs. Eight areal photographs of the slope, between the years
1978-2005, were acquired, georeferenced and shrub cover was estimated based on
supervised classification of the airphotos. An extensive spatial database of soil
hydraulic and environmental parameters (e.g. slope, radiation, bulk density, soil depth)
was measured in the field and interpolated to continuous maps using geostatistical
techniques and physically-based modeling. This spatio-temporal database was used to
characterize 1187 spatial cells serving as an input to a numeric hydrological model
(Hydrus 1D) solving the flow equations to predict soil water content at the single
storm and seasonal scales. The model was verified by sampling soil moisture at
63 random locations at the research site, during three consecutive storms in the
2008-09 rainy seasons. The results show that shrub-grass ratio (SGR) reached a
steady state phase with 20% cover in 1992 (after 14yr). This recovery rate is in
agreement with previous field studies. Quantification of the factors affecting shrub
establishment was done using stepwise regression, showing that slope decline,
radiation, soil texture, and rockiness are the leading physical factors. Furthermore, a
regression model that was applied between the integral of predicted soil moisture (based
on 30 years climate data record) and the shrub cover integral show that the soil
moisture model explained 31% of shrub cover variation during this period. The use of
Spatial Analysis by Distance Indices (SADIE) technique reveals that in areas of
higher vegetation cover there is strong and positive association between model
outputs (soil moisture predictions) and shrub cover while only weak association
was observed in regions of low vegetation cover. The results also show that this
relationship is not stationary throughout the slope and when the slope is divided
into discrete units, based on flowdirection analysis, the factors that affect shrub
establishment differ with additional effect of soil depth at the west facing slope. |
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