| Autor: |
W.A. Dugas, Carl C. Daamen, K.G. McNaughton, P.T. Prendergast, M.J. Judd |
| Rok vydání: |
1999 |
| Předmět: |
|
| Zdroj: |
Agricultural and Forest Meteorology. 93:171-183 |
| ISSN: |
0168-1923 |
| Popis: |
Orchards and many other land surface types have vegetation that does not completely cover the underlying ground surface. For these land surfaces there are at least two distinct and interacting surface components, the overstorey/canopy and the understorey/ground. Independent measurement of energy fluxes from each component is an important step toward understanding the factors controlling the resultant overhead flux. In this study, we evaluated flux measurement methods in a sheltered lemon orchard where the canopy of the lemon trees covered 39% of the orchard floor. Lemon tree transpiration was measured using the stem heat balance method with branch measurements scaled up to canopy level. These measurements compared well with Penman–Monteith transpiration. For the understorey, the sum of latent and sensible heat fluxes measured by eddy correlation was equal to available energy. Eddy correlation and Bowen ratio methods of flux measurement also compared well in the understorey. However, at the height of the shelters above the orchard we observed an inconsistency between eddy correlation and Bowen ratio methods which suggested that the latter method is unreliable at this location. Flux measurement and interpretation in an orchard can be complicated by the presence of windbreaks or shelters. In particular, the source area for fluxes above a sheltered orchard may include the shelter trees and adjacent orchard blocks. Our orchard block (42 m × 124 m) was surrounded by shelter trees 8 m high and differed from the surrounding blocks in that the understorey was bare rather than covered in grass. This difference enabled us to examine the likely source area contributing to our measurements. Good agreement was found between eddy fluxes measured at 8 m (above the orchard) and the sum of the component fluxes from within the orchard block. Our analysis indicated that the source area for fluxes measured at 8 m is largely within the orchard block studied. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect