Succession and management - Ecological Applications: Toward a Sustainable World - page 217

(a) 125-year-old

lava flow N

37-year-old
lava flow

16-year-old
lava flow

700
600
500
400
300
200
100

2 km

(b)

0-
year-
old

16-
year-
old

37-
year-
old

125-
year-
old

800-
year-
old

Bare
land

Alnus
shrub

Machilus and
Prunus forest

Castanopsis
forest

Fig. 8.1 (a) Locations of sampling sites on 16-, 37- and 125-year-old lava fl ows on Miyake-
jima Island, Japan. Sites outside these fl ows are at least 800 years old. Altitudinal contours
are shown in meters. (b) In the earliest stage of succession, soil was sparse and lacking in
nitrogen, an essential plant resource: the only vegetation consisted of a few small alder trees
( Alnus sieboldiana ). In the older plots (37-800 years old), 113 species were recorded,
including ferns, herbs, lianas and trees. This primary succession consisted of: (i) coloniza-
tion of the bare lava by the nitrogen-fi xing alder; (ii) facilitation (through improved nitrogen
availability) of mid-successional Prunus speciosa and the late-successional evergreen tree
Machilus thunbergii ; (iii) establishment of a mixed forest in which Alnus and Prunus were
shaded out (i.e. outcompeted); and (iv) competitive replacement of Machilus by the longer
lived Castanopsis sieboldii . (After Kamijo et al., 2002.)

et al., 2001). In addition, some early species change the abiotic environment in ways (e.g. by pro-
viding shade or improving soil quality) that make it easier for later species to establish and thrive
- this is known as facilitation. A fi nal species interaction may also play an important role in deter-
mining the course of succession. Predation, whether of seeds or mature vegetation, can slow or
stop a successional sequence in its tracks. Thus, apart from competition-colonization trade-off,
successional niche and facilitation, we have to add a fourth mechanism - interactions with enemies
- to fully understand ecological succession.

The concept of the successional mosaic and the central role of disturbance
Some disturbances are on a very large scale. Thus, thousands of hectares of forest may be simul-
taneously destroyed by a fi re caused by lightning or by a careless camper. The subsequent suc-
cessional sequence starts at the same time over this large area and proceeds more or less in
synchrony. However, a forest that appears to have reached a stable community structure when
studied on a large scale will always be a mosaic of miniature successions. And the same is true
for a grassland or rocky shore community. Every time a tree falls, a grass tussock dies or a boulder
is turned over, an opening is created in which a new mini-succession starts. The resulting spatio-
temporal pattern is called a successional mosaic.
The frequency with which disturbance occurs infl uences the patchy nature of the successional
mosaic. But it also helps determine the total number of species in the area. Where disturbances