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| RESEARCH SITE |
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Location and background
Yatir, a 28,000 ha afforestation system of mainly P. halepensis trees, located at the limit of the Mediterranean region and at the northern edge of the Israeli Negev desert
(31° 20’ N; 35° 3’ E), on undulated terrain at an elevation of 600 to 800 m above sea level. Most of the area was planted during the years 1965-69. The forest is distinct from the surroundings non-forested shrubland, as can be seen in the satellite image below. |
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Changes in greenhouse gases concentrations over the past decade. The concentrations of the main background atmospheric trace gases is determined on a weekly basis in our Negev sampling site, in the framework of the global NOAA-ESRL Cooperative Air Sampling Network (www.esrl.noaa.gov/gmd/ccgg/flask.html; see Figure below). The figure show the seasonal and long term trends in the concentrations of CO2, the carbon isotopic composition of the CO2
( 13C), methane (CH4), carbon monoxide (CO), Nitrous oxide (N2O) and the synthetic gas SF6. (ppm, ppb and ppt indicate concentrations as part per million, billion and trillion, respectively). |
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NOAA ESRL Carbon Cycle operates 4 measurement programs. Semi-continuous measurements are made at 4 baseline observatories and from tall towers. Discrete surface and aircraft samples are measured in Boulder, CO. Presently, atmospheric carbon dioxide, methane, carbon monoxide, hydrogen, nitrous oxide, sulfur hexafluoride, the stable isotopes of carbon dioxide and methane, and halocarbon and volatile organic compounds are measured. Contact: Dr. Pieter Tans, NOAA ESRL Carbon Cycle, Boulder, Colorado, (303) 497-6678, pieter.tans@noaa.gov, http://www.esrl.noaa.gov/gmd/ccgg/. |
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Meteorological characteristics
| Yatir site is a semi-arid forest, unique among the forest flux measurements sites in the global FluxNet system: It has annual mean global radiation of about 7.5 GJ m-2 y-1, annual rain-fall of 285 mm and annual mean temperature of 18.2 °C. The flux of latent heat of evaporation (LE) is limited, and compensated for by a massive sensible heat flux (H). |
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| Weekly mean values of climatic parameters in Yatir: (a) Soil water content (SWC) at depths 0-30 cm and 70 cm; (b) Air Temperature; (c) Vapor pressure deficit (VPD); (d) Photosynthetic active radiation (PAR). Note that panel b to d report daytime values only. |
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| Yatir energy budget: Multy-yearly averages of the sensible heat (H), latent heat (LE),
soil heat (G) and net radiation (Rn). |
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The ecosystem
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| The Yatir forest consists mainly Pinus halepensis trees (>90%), and after several thinning cycles the forest density today is ~ 300 trees/ha. The leaf area index (LAI) is about 1.7, with a range of about ±0.3 over the seasonal cycle and interannually; tree height is about 10 m, and mean stem diameter at breast height (DBH) of 17 cm. The main photosynthetic activity and stems incrementing period in the forest is from December to May; in contrast, buds-burst is in mid March and leaf development continues until October. Understory vegetation consists of dwarf shrubs, herbaceous species, biological crust and annuals, all of which constitute only a minor portion of the total ecosystem biomass. The forest is growing on about 0.20-1 m deep light Rendzina soil above chalk and limestone, with clay to sandy-clay-loam texture. |
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| Fluxes of CO2 in Yatir: Net ecosystem CO2 exchange (NEE); Gross primary production (GPP); Ecosystem respiration (Re). Note that negative values indicate uptake from the atmosphere into the forest biomass. Positive values indicate release of CO2 (for example by respiration) from the forest into the atmosphere. |
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| Variations in meteorological conditions, both at the seasonal and inter-annual time scales, have a significant effects on the forest functioning: Satellite vegetation index (Normalized Difference Vegetation Index; NDVI) during the rainy (January) and dry (May) seasons during wet year (1995) and drought year (2000) show mainly the dramatic changes in the level of forest photosynthetic activity. |
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