Seasonal variation of energy and water vapor exchange rates above and below a boreal jack pine forest canopy

Baldocchi, Dennis; Vogel, Christoph; Hall, B. D.

doi:10.1029/96jd03325

Cited by 237 publications

(183 citation statements)

References 56 publications

(55 reference statements)

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“…The values of λE/λE eq , when soil moisture at the grassland site was ample, agree with measured and modeled evaporation rates from well-watered canopies of native vegetation (McNaughton and Spriggs, 1986;Baldocchi et al, 1997) and with data from another California annual grassland (Valentini et al, 1995). In contrast, Wever et al (2002) reported that λE/λE eq of a Canadian perennial grassland was lower, ranging between 0.8 and 1.0 under ideal plant and soil conditions.…”

Section: Evaporation and Soil Moisturesupporting

confidence: 54%

How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland

Baldocchi

Kiang

2004

Agricultural and Forest Meteorology

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Savannas and open grasslands often co-exist in semi-arid regions. Questions that remain unanswered and are of interest to biometeorologists include: how do these contrasting landscapes affect the exchanges of energy on seasonal and annual time scales; and, do biophysical constraints imposed by water supply and water demand affect whether the land is occupied by open grasslands or savanna? To address these questions, and others, we examine how a number of abiotic, biotic and edaphic factors modulate water and energy flux densities over an oak-grass savanna and an annual grassland that coexist in the same climate but on soils with different hydraulic properties.The net radiation balance was greater over the oak woodland than the grassland, despite the fact that both canopies received similar sums of incoming short and long wave radiation. The lower albedo and lower radiative surface temperature of the transpiring woodland caused it to intercept and retain more long and shortwave energy over the course of the year, and particularly during the summer dry period.The partitioning of available energy into sensible and latent heat exchanged over the two canopies differed markedly. The annual sum of sensible heat exchange over the woodland was 40% greater than that over the grassland (2.05 GJ m −2 per year versus 1.46 GJ m −2 per year). With regards to evaporation, the oak woodland evaporated about 380 mm of water per year and the grassland evaporated about 300 mm per year. Differences in available energy, canopy roughness, the timing of physiological functioning, water holding capacity of the soil and rooting depth of the vegetation explained the observed differences in sensible and latent heat exchange of the contrasting vegetation surfaces.The response of canopy evaporation to diminishing soil moisture was quantified by comparing normalized evaporation rates (in terms of equilibrium evaporation) with soil water potential and volumetric water content measurements. When soil moisture was ample normalized values of latent heat flux density were greater for the grassland (1.1-1.2) than for the oak savanna (0.7-0.8) and independent of moisture content. Normalized rates of evaporation over the grassland declined as volumetric water content dropped below 0.15 m 3 m −3 , which corresponded with a soil water potential of −1.5 MPa. The grassland senesced and quit transpiring when the volumetric water content of the soil dropped below −2.0 MPa. The oak trees, on the other hand, were able to transpire, albeit at low rates, under very dry soil conditions (soil water potentials below −4.0 MPa). The trees were able to endure such low water potentials and maintain basal levels of metabolism because * Corresponding author. Baldocchi et al. / Agricultural and Forest Meteorology 123 (2004) ecological forcings kept the tree density and leaf area index of the woodland low, physiological factors forced the stomata to close progressively and the trees were able to tap deeper water sources (below 0.6 m) than the grasses.

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Section: Evaporation and Soil Moisturesupporting

confidence: 54%

How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland

Baldocchi

Kiang

2004

Agricultural and Forest Meteorology

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521

411

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“…ments reported for other boreal forest sites (Perttu et al, 1980;Amiro and Wuschke, 1987;den Hartog et al, 1994;Fitzjarrald and Moore, 1994;Baldocchi and Vogel, 1997;Jarvis et al, 1997;Constantin et al, 1999;Goldstein et al, 2000). Considering the low leaf area index at this site, the relatively small differences in net radiation absorption compared with other sites suggest that the combination of day length (over 14 h on most summer days), sky conditions, and canopy reflectivity (with a mean short-wave albedo of 0.132 in this stand) is attributable more to total radiation absorption in the boreal forests than to the actual leaf area index.…”

Section: Net Radiation Absorptionmentioning

confidence: 99%

“…The amount of energy absorbed by a forest ecosystem and the amount converted for heating the air and soil and evaporating water is governed by the biophysical properties of the forest canopy and soil surfaces and the driving potentials established by the temperature and humidity gradients between the surface and the atmosphere (Raupach, 1995;Baldocchi and Vogel, 1997;. Consequently, the seasonal patterns of surface energy fluxes and their partitioning will be modulated by a concurrent seasonality in biotic factors such as stand structure, foliage development and stomatal conductance and abiotic variables such as solar radiation, temperature, wind and precipitation.…”

Section: Introductionmentioning

confidence: 99%

Seasonal variation in energy and water fluxes in a pine forest: an analysis based on eddy covariance and an integrated model

Wang¹,

Kellomäki²,

Zha³

et al. 2004

Ecological Modelling

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“…The OJP canopy is 14 m in height with a projected leaf area index of 1.79 (Chen et al, 1997), and is situated on a coarse sandy soil. The understorey is very sparse, with some alder (Alnus crispa), bearberry (Arctostaphylos uvaursi), bog cranberry (Vaccinium vitisideae) and lichens (Cladina spp) (Baldocchi et al, 1997). The OBS stand is 12 m tall and consists mainly of black spruce (Picea mariana, (Mill.)…”

Section: Study Sites and Measurementsmentioning

confidence: 99%

Modified snow algorithms in the Canadian land surface scheme: Model runs and sensitivity analysis at three boreal forest stands

Bartlett¹,

2006

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Seasonal variation of energy and water vapor exchange rates above and below a boreal jack pine forest canopy

Cited by 237 publications

References 56 publications

How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland

How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland

Seasonal variation in energy and water fluxes in a pine forest: an analysis based on eddy covariance and an integrated model

Modified snow algorithms in the Canadian land surface scheme: Model runs and sensitivity analysis at three boreal forest stands

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