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Bendix, J.; Silva, B.; Roos, K.; G&ouml;ttlicher, D.; Rollenbeck, R.; Nauss, T. &amp; Beck, E. (2009): <b>Model parameterization to simulate and compare the PAR absorption potential of two competing plant species</b>. <i>International Journal of Biometeorology</i> <b>OnlineFirs</b>, xx-xx.

Resource Description

Title: Model parameterization to simulate and compare the PAR absorption potential of two competing plant species
Short Name: Model parameterization
FOR816dw ID: 687
Publication Date: 2009-10-08
License and Usage Rights:
Resource Owner(s):
Individual: Jörg Bendix
Contact:
Individual: Brenner Silva
Contact:
Individual: Kristin Roos
Contact:
Individual: Dietrich Göttlicher
Contact:
Individual: Ruetger Rollenbeck
Contact:
Individual: Thomas Nauss
Contact:
Individual: Erwin Beck
Contact:
Abstract:
Abstract Mountain pastures dominated by the pasture grass Setaria sphacelata in the Andes <br/> of southern Ecuador are heavily infested by southern bracken (Pteridium arachnoideum), a major <br/> problem for pasture management. Field observations suggest that bracken might outcompete the grass <br/> due to its competitive strength with regard to the absorption of photosynthetically active radiation <br/> (PAR). To understand the PAR absorption potential of both species, the main aim of the current paper <br/> is to (i) parameterize a radiation scheme of a two-big leaf model by deriving structural (LAI, leaf angle <br/> parameter) and optical(leaf albedo, transmittance) plant traits for average individuals from field <br/> surveys, (ii) to initialise the properly parameterized radiation scheme with realistic global irradiation <br/> conditions of the Rio San Francisco Valley in the Andes of southern Ecuador, and (iii) to compare the <br/> PAR absorption capabilities of both species under typical local weather conditions. Field data show <br/> that bracken reveals a slightly higher average leaf area index (LAI) and more horizontally oriented <br/> leaves in comparison to Setaria. Spectrometer measurements reveal that bracken and Setaria are <br/> characterised by a similar average leaf absorptance. Simulations with the average diurnal course of <br/> incoming solar radiation (1998-2005) and the mean leaf-sun geometry reveal that PAR absorption is <br/> fairly equal for both species. However, the comparison of typical clear and overcast days show that two <br/> parameters, (i) the relation of incoming diffuse and direct irradiance, and (ii) the leaf-sun geometry <br/> play a major role for PAR absorption in the two-big leaf approach: Under cloudy sky conditions (mainly <br/> diffuse irradiance), PAR absorption is slightly higher for Setaria while under clear sky conditions <br/> (mainly direct irradiance), the average bracken individual is characterized by a higher PAR absorption <br/> potential. (~74 MJ m-2 a-1) . The latter situation which occurs if the maximum daily irradiance exceeds <br/> 615 W m-2 is mainly due to the nearly orthogonal incidence of the direct solar beam onto the <br/> horizontally oriented frond area which implies a high amount of direct PAR absorption during the <br/> noon maximum of direct irradiance. Such situations of solar irradiance favouring a higher PAR <br/> absorptance of bracken occur in ~36% of the observation period (1998-2005). By considering the <br/> annual course of PAR irradiance in the San Francisco Valley, the clear advantage of bracken on clear <br/> days (36% of all days) is completely compensated by the slight but more frequent advantage of Setaria <br/> under overcast conditions (64% of all days). This means that neither bracken nor Setaria show a <br/> distinct advantage in PAR absorption capability under the current climatic conditions of the study area.
Literature type specific fields:
ARTICLE
Journal: International Journal of Biometeorology
Volume: OnlineFirs
Page Range: xx-xx
Metadata Provider:
Individual: Maik Dobbermann
Contact:
Online Distribution:
Download File: http://www.tropicalmountainforest.org/publications.do?citid=687


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