Monteverde : Ecology and Conservation of a Tropical Cloud Forest

relative to other tropical and temperate sites (Table
9.9), suggesting that emissions of NOX, NH 3 , and par-
ticles are high downwind from the sites. Because no
major urban areas exist, emissions likely originate
from forest and agricultural ecosystems. The burning
of vegetation typically results in considerable loss of
nitrogen and other ions from the site (Ewel et al. 1981,
Crutzen and Andreae 1990). Emissions of NO from
soils may also be stimulated following burning (Ander-
son et al. 1988). Other sources of NO include light-
ning discharges and downward transport of NOX from
the stratosphere (Logan 1983). Regional emission
inventories for the tropics are limited and still un-
certain (Crutzen and Andreae 1990). Because they
are projected to increase in the future, it is impor-
tant to understand the potential effects of increased
nitrogen deposition to tropical cloud forests such as
Monteverde.

Nutrient retention by the forest canopy. Net retention
of ions by the canopy is typically estimated by com-
paring measured or modeled estimates of total depo-
sition to fluxes in throughfall (TF) and stemflow (ST).
Canopy-atmosphere interactions are complex, but

clear patterns have emerged for individual ions. For

example, many canopies retain H+ and inorganic

nitrogen from atmospheric deposition, and net reten-

tion rates are positively correlated with deposition

rates, whereas potassium is leached from most cano-

pies (Parker 1983).

Fewer estimates exist for atmospheric deposition

and retention of ions by the canopy in tropical mon-

tane forests (Steinhardt and Fassbender 1979, Vene

klaas 1990). Their canopies are aerodynamically

rough due to high leaf areas and abundant epiphytes,

and therefore intercept wind-driven cloud water and

precipitation. Because many epiphytes are closely

linked to atmospheric sources of nutrients (Nadkarni

and Matelson 1991), estimates of atmospheric depo-

sition and net retention of ions by the canopy are

necessary to evaluate the potential effects of increased

H+ and nitrogen deposition on the canopy and the

ecosystem.

Our studies estimated net retention of deposited

ions by the canopy at the Monteverde leeward cloud

forest site (Clark et al. 1998). Throughfall was col-

lected in 20 plots distributed at random over 1 ha of

the primary forest study site adjacent to the meteoro-

Table 9.9. Cloud water chemistry (mean umol/liter) at montane forest sites in northern South,

Central, and North America.

Ion Concentration (umol/liter)

Location H+ NO,- NH 4 Na+ Mg^2

Temperate Sites

aGordon et al. 1994 (dry season samples collected at Pico del Avila and Altos de Pipe).

bWeathers et al. 1988, Ashbury et al. 1994.

GThis chapter.

dMohnen and Kadkecek, 1989 (5-year mean of summer values).

eMohnen and Vong 1993 (3-year mean of warm clouds).

fSigmon et al. 1989.

sSchaefer and Reiners 1990, Lovett et al. 1982.

hAneja etal., 1992.

Ca2+ K+

Tropical Sites

Caracas, Venezuela^3

Pico del Oeste, Puerto Ricob

Monteverde, Costa Ricac

23

9

20

28

132

94

31

60

64

103

177

80

32

32

149

64

62

650

397

365

9

8

85

44

63

29

10

63

31

35

9

5

25

13

31

Whiteface Mountain, New Yorkd

Shaver Hollow, Virginiaf

Mt. Moosilauke, New Hampshire^6 ^

Mt. Mitchell, North Carolina^6 -^11

122

274

171

205

263

270

288

335

398

62

115

94

155

132

180

195

130

174

74

124

93

84

107

102

108

175

184

3 3

— —

— —

13 2

— —

32 19

30 —

—

— —

11 3

— —

— —

5 3

— —

10 11

— 10

—

— —

325 Ecosystem Ecology and Forest Dynamics