wright, "Sex Ratios," pp. 87-88, and Wheelwright, "A
Hypothesis," pp. 281-283). In contrast, demographic
studies have been common at La Selva Biological
Station (Clark 1994) and Barro Colorado Island (Leigh
et al. 1982, D'Arcy and Correa 1985).
Observing that falling branches commonly break
up understory plants in the cloud forest and that these
broken sticks sometimes take root, Kinsman (1990)
tagged broken branches of 28 species of understory
cloud forest shrubs and treelets, left them on the for-
est floor, and censused them annually over a period
of five years to record their survival. Fourteen species
remained alive for five years and some became re-
productive. DNA screening techniques were used to
investigate the role of branch fragmentation on the
population structure of shrubs in the cloud forest (see
Bush, "Clonal Reproduction," p. 88). High genetic re-
latedness within the colonies of the understory shrub
Poikilacanthus macranthus indicated that in large
part they were clones formed by fragmentation. Ad-
aptations for regeneration by fragmentation in species
of Rubiaceae also suggest a possible scenario for these
plants to evolve into epiphytes (see Nepokropff and
Sytsma, "Evolution in Psychotria," pp. 75-78). In land-
slides in the elfin forest at Monteverde, the standing
crop of seeds in the soil was much greater than the
number of seeds falling into traps (Myster 1993). The
taxa that colonize landslides at Monteverde (Table
3.4) are closely related to those found on landslides
in Puerto Rican cloud forests.
3.4. Biogeography
The lower montane zone at Monteverde (the Tilaran
Mountain mass above 1200 m) supports 1708 species
(57% of the total flora of the study area), which is
approximately equal to the native flora of La Selva
Biological Station (Hartshorn and Hammel 1994), but
much higher than that of Santa Rosa National Park,
Barro Colorado Island (Panama), and the lowland
Amazonian forest sites in Manii National Park (Peru)
and Manaus (Brazil) (Croat 1978, Foster 1990, Gen-
try 1990, 1993; Table 3.8). Monteverde's high diver-
sity of epiphytes, especially the 419 species of or-
chids, contributes most to this difference, but the three
life zones above 1200 m also support a large num-
ber of trees (500 plus species). There are more species
Table 3.8. A comparison of the species richness of floras for several regions and research sites in the neotropics.
Site
Mexico
America north
of Mexico
Peru
Costa Rica
Texas
Monteverde area > 700 m
Manii National Park, Perub
Rio Manii, floodplain and
upland terrace
Monteverde area > 1200 m
La Selva Biological Station
Barro Colorado Island,
Panama
Adolpho Ducke Forest
Reserve, Manaus
Santa Rosa National Park
All Species
ca. 20,000
ca. 20,000b
17,143a
ca. 9000
ca. 5000
2985 d
2874
1856
1723 d
1678 d
1207 C
ca. 1030
603
Trees
NA
ca. 700
NA
>2000
NA
755
NA
NA
442
ca. 312
ca. 270
NA
NA
Ferns
NA
NA
NA
1058
NA
358
NA
NA
175
162
80
37
30
Orchids
NA
NA
1587
ca. 1500
NA
>500
NA
NA
291
114
78
24
11
Area (km^2 )
2,000,000
21,461,100
283,520
51,100
692,408
ca. 350
15,320
100
58
16
16
100
103
Source
Rzedowski 1978
Missouri Botanical
Garden (www.mobot.
org)
Brako and Zaruchi
1993
Mora-Retana and
Garcia 1992,
Dressier 1993, Atwood,
"Orchids," pp. 74-
75, INBIO (www.
inbio.ac.cr)
Rzedowski 1978,
B. Hammel (pers.
comm.)
Haber 1991 (Appendix 1)
Foster 1990
Foster 1990
Haber 1991 (Appendix 1)
Atwood 1988, Hartshorn
and Hammel 1994
Croat 1978, Hartshorn
and Hammel 1994
Prance 1990
Janzen and Liesner 1980
aDoes not include ferns.
IncludesG ferns and bryophytes.
Native and naturalized species; cultivated species are not included.
Includes pteridophytes.
67 Plants and Vegetation