Agriculture Reference
In-Depth Information
pollutants, and attack by herbivores or pathogens each impose qualitatively different
challenges to leaf function (Kozlowski and Pallardy 2002), which we also address
in this chapter.
Box 8.1
Succession
Vegetation is inherently dynamic: plants grow and interact with one another
while responding to changing environmental conditions. Occasionally these
dynamics in a plant community are punctuated by more disruptive events that
destroy some part of the plant community. Succession refers to the sequence
in which plants colonize and develop in an area after such a disturbance. A
successional sequence can be initiated by disturbances at large spatial scales
such as volcanic eruption, windstorms, fire, flooding, and landslides or at
small spatial scales by simply the death of a single tree. In the case of a big
volcanic eruption such as that of Krakatau in 1883, all the vegetation on this
isolated oceanic island was killed by a thick layer of ash and the succession
began on barren land. Even in this extreme case plants and animals dispersed
to the island within several decades, and more than 200 species were recorded
on Krakatau only 50 years after the eruption. Succession typically is initiated
less dramatically and involves colonization from nearby undisturbed areas.
Because stochastic factors play a large role in dispersal and colonization, we
cannot forecast precisely the course of succession, but we can recognize spe-
cies that during early versus late stages of succession have characteristic suites
of features. Early successional plant species produce abundant small seeds,
have a high growth rate with low stem density, high maximum photosynthetic
rates, and short leaf longevity. Late successional plant species produce fewer
but large seeds, have low growth rates with high stem density, low maximum
photosynthetic rates, and long leaf longevity.
Insolation and Leaf Longevity
Diverse lines of evidence among and within species support the generalization
that leaf longevity is relatively short in sunny compared to shaded environments.
Early successional species are widely observed to have shorter leaf longevity
than late successional species (Kikuzawa 1978, 1982, 1983, 1988; Koike 1988),
which is consistent with the greater insolation typical of sites after disturbance.
Similarly, in the understory of both tropical forests (Reich et al. 1991, 2004) and
mature temperate forests (Kikuzawa 1984, 1988, 1989; Lei and Koike 1998),
species typically have long-lived leaves, some surviving more than a single sea-
son. If a species occurs in both sun and shade, leaf longevity is long in the
shaded environment (Kikuzawa 1989; Sterck 1999; Reich et al. 2004).
For example, in a Southeast Asian tropical forest, leaf survivorship of the
