P.I.(s): Hank A. Margolis -- Universit`eacute Laval
Collaborators: Geoffrey Edwards, Keith Thomson, Alain Viau -- Universit`eacute Laval
Objectives: This project will examine the relationship between net photosynthetic (net Ps) capacity, N concentration and percent photosynthetically active radiation (%PAR) of three major boreal forest cover types (jack pine, black spruce and aspen) as well as their link to remotely-sensed and land-based measures of reflected and absorbed radiation. We will attempt to establish general relationships which can be used to predict the vertical distribution of the net Ps capacity for these cover types, including their understories, when neither water nor temperature is greatly limiting. We will also determine how these relationships will vary over the growing season and among six different stand conditions at the Northern Study Area (NSA). Furthermore, the photosynthetic response surface of foliage from the three main cover types with respect to light, temperature, vapor pressure deficit and internal CO2 will be determined during each IFC using a laboratory-based photosynthetic system with cut branches. The effects of in situ frost exposures on the photosynthetic characteristics of the three main cover types as well as their patterns of recovery will be determined in order to introduce more realistic algorithms of the effects of frost on carbon flux. PAR measurements taken within the the canopy will be supplemented with geometry measurements of the different canopy constituents and the spatial variability of these measurements within the stand will be examined. Additionally, the BRDF of soil and understory components, the spatial variability of the spectral signatures of soil and understory components, and the spectral distribution of hemispherical downwelling radiation will be characterized in order to drive and validate a forest canopy reflectance model (TRELITE). This model will be used to estimate PAR levels within the various forest canopies and these estimates will then be used as input to the photosynthetic model. Depending on the availability of additional resources, canopy biochemistry (lignin, cellulose, starch, sugars, chlorophyll and terpenes) will be followed over the growing season for six stands.
Objectives:
There are five main components to this study:
Data Collection and Equipment:
Measurement Sites and Periods:
Known Problems and Caveats:
Measurements of angular and nadir reflectance of the understory, the solar plane orientation was generally random in respect to the angular plane but was known in most cases. Some of the data were normalized to the white reference panel when the panel was in shade.
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Last Updated: October 29, 1997