Agriculture Reference
In-Depth Information
Fig. 9.3
Schematic representations to show photosynthetic production under favorable periods
of different lengths. (
a
) Evergreen species have an advantage because of the low maintenance
costs during a short unfavorable period. (
b
) Shedding leaves during the unfavorable period is
advantageous in the longer favorable period. (
c
) Paying back construction costs within one short
favorable period. Solid increasing line indicates net gain during favorable periods. Broken
decreasing lines are maintenance costs during unfavorable periods. Broken increasing line from
the origin touches the curve at the point where the marginal gain is maximum
shorter than 1 year, the deciduous habit will appear. The percentages of deciduous
species increase and evergreen species decrease with the shortening of favorable
period. The percentage of evergreen species reached a minimum value at an inter-
mediate length of
f
(at around
f
= 0.5). When the favorable period length becomes
still shorter, the percentage of evergreen species increases again.
Various observations are consistent with this sort of interplay between the length
of the favorable period and the balance between evergreen and deciduous foliar
habits. Some tree species, such as
Mallotus japonicus
and
Alnus japonica
, are
deciduous in central Japan but are evergreen on Okinawa in southern Japan. Some
evergreen trees in Singapore such as
Trema orientalis
,
Ficus elastica
, and
Duabanga
sonneratioides
become deciduous north along the Malay Peninsula (Koriba
1948a,b). Almost all the trees in a riparian forest in Costa Rica were evergreen
compared to only about half in nearby upland forests (Frankie et al. 1974; Opler
et al. 1980). Similarly, Condit et al. (2000) reported that the percentage of the
deciduous tree species across the Isthmus of Panama increased from 14% on the
Atlantic Ocean side (annual precipitation, 2,839 mm) to 28% on Barro Colorado
Island (2,570 mm) and 41% on the Pacific Ocean side (2,060 mm). When the favor-
able period length becomes still shorter, the percentage of evergreen species
increases again. Such shifts in the balance of deciduous and evergreen species can
occur even in the restricted growing season of arctic regions. Of 18 plant species
