0198566123.pdf

●Type 5 eventsare those that destroy consumer
systems, by which is meant human systems,
possibly with subsequent repercussions for the
rest of the island’s ecology; examples again
include hurricanes and earthquakes. The eruptions
of Montserrat in 1995–1998 provide a classic
illustration of the extensive cross-cutting impact
that within-island volcanic action can have in
transforming the physiography, ecology and
human use of islands (Hilton et al. 2003; Le Friant
et al. 2004).

Magnitude and frequency

Between 1871 and 1964, an average of 4.6 hurri-
canes per year was recorded in the Caribbean,
resulting in, for example, a return time of 21 years
for the island of Puerto Rico (Walker et al. 1991a;
Fig. 2.21). With minimum wind speeds of
120 km/h and paths tens of kilometres wide, hur-
ricanes can have a profound impact, fundamental
to an understanding of the structure of natural
ecosystems in the region. Moreover, the Caribbean
by no means corners the market in tropical storms.
Hurricanes develop in all tropical oceanic areas
where sea surface temperatures exceed 27–28C,
although they are generally absent within
5 north and south of the equator, where persistent
high pressure tends to prevent their development
(Nunn 1994). Wind defoliation and large

blow-downs are important and frequent distur-

bances for forested tropical islands throughout the

hurricane belts, centred 10–20north and south of

the equator. They may have particularly destruc-

tive impacts on high islands, an example being the

devastation of large areas of forest on the Samoan

island of Upolu by tropical cyclones Ofa, Val, and

Lyn in 1990, 1991, and 1993, respectively (Elmqvist

et al. 1994). Although storm damage to lower

islands can also be severe, storms can be important

to island growth by throwing up rubble ramparts

(Stoddart and Walsh 1992). Thus some very small

islands, such as the so-called motu(sand islands),

may be in a kind of dynamic equilibrium with

both extreme and normal climatic phenomena

(Nunn 1994). A comprehensive analysis of distur-

bance regimes requires quantification of both

magnitude and frequency of events (Stoddart and

Walsh 1992). Lugo (1988) attempted this for a sub-

set of the Caribbean disturbance phenomena

given in Table 2.5. He concluded that, whereas

hurricanes have the highest frequency of recur-

rence among his major ‘stressors’, the susceptibil-

ity of Caribbean islands to hurricanes is

intermediate, partly because they do not change

the base energy signature over extensive periods.

Also, with the larger Caribbean islands, hurricane

damage is unlikely to impact catastrophically on

the entire island area. Given their recurrence

interval, these island ecosystems should be

40 ISLAND ENVIRONMENTS

1899

1928

1956

1893

1835

1825

1807 1837

1876

1932

1989

1766, 1772?

1867

1931

N

0 40 km

SAN JUAN

Luquillo

Forest

Figure 2.21Paths of hurricanes that have crossed Puerto Rico since AD1700. (Redrawn from Scatena and Larsen 1991, Fig. 1.)