3.3.2. Aboveground competition for light
Of all the major environmental factors that contribute to
reported multispecies system merits, the capture and use of
solar radiation is the one that has received the most attention
(Keating and Carberry, 1993). Overyielding by mixtures
has often been attributed to a more efficient use of light
by their canopies. Trenbath (1974) reported that an “ideal”
leaf arrangement could be approached by a mixture of a tall
erect-leaved genotype and a short, prostrate-leaved genotype.
Among aboveground factors, the factors that affect the light
regime of plant canopies are the amount of light and quality
of incident radiation, the canopy architecture and the optical
properties of the leaves and the soil (Sinoquet and Caldwell,
1995). In comparison with pure, uniform stands, light capture
depends on (i) the fraction of incident photosynthetically
active radiation (PAR) that is partitioned by heterogeneous
canopies and intercepted by each species, and (ii) the efficiency
with which intercepted radiation is converted by photosynthesis.
While direct measurement techniques have been
slow to develop, light modelling within multispecies systems
has quickly matured (Sinoquet and Caldwell, 1995). A number
of models are now available with different levels of complexity
for multispecies systems, but field applications face some
practical limitations. Compared with pure stands, multispecies
systems contain significant spatial variations in leaf area density
and leaf angle distribution that are difficult to simulate.