worts) contributes substantially to total litterfall in-
puts to the forest floor (Nadkarni and Matelson 1992).
Due to the high concentrations of polyphenols and
aliphatic hydrocarbons in bryophytes, the decompo-
sition rate of bryophyte litter is approximately half
that of vascular plant foliage (Clark et al. 1998a). As a
result, the large amounts of organic matter in the soils
of tropical montane forests typically represent the
most significant pools of carbon and nitrogen in the
ecosystem (Grieve et al. 1990, Tanner 1977, Marrs et al.
1988, Vance and Nadkarni 1990, Kitayama 1993).
Our understanding of the soils of Monteverde
would greatly benefit from a general soil survey. A
positive correlation between climate and organic
matter exists in soils along altitudinal transects (e.g.,
Marrs et al. 1988, Grieve et al. 1990, Kitayama 1993).
To what extent is this pattern also controlled by parent
material and litter quality? How does microclimate,
specifically exposure to wind-driven cloudwater and
precipitation, interact with other factors in soil for-
mation at Monteverde?
Other questions concern the occurrence of short-
statured vegetation, or dwarf forests, in tropical mon-
tane sites, which has been attributed to small amounts
of available nutrients in soils, particularly nitrogen
and phosphorus. To what extent do soil physical
properties (e.g., porosity, bulk density, clay content)
control soil stability, contribute to mass wasting pro-
cesses, and control vegetation stature? Although the
interaction of factors such as microclimate, soil physi-
cal factors, soil nutrient supply, disturbance, and site
hydrology is known to influence vegetation stature,
explanations for the occurrence of dwarf forests elude
ecologists (Grubb 1977, Bruijnzeel and Proctor 1993).
Changes in land use in Monteverde have contrib-
uted to changes in carbon and nitrogen storage in
soils. The cutting of forests for pastures and other
agricultural uses typically involves the removal of the
forest floor, but the extent to which organic matter in
the A and B horizons is affected has not been stud-
ied in Monteverde. How do these practices affect the
long-term carbon and nitrogen levels in soil, and how
quickly does reforestation restore them?
2.6. Hydrology of MonteverdeThe movement and storage of water above, on, and
below the earth's surface is called the hydrologic
cycle. It forms a key link between the physical envi-
ronment and living organisms. Given the importance
of understanding the movement and storage of water
in montane regions, there are astonishingly few data
to describe the hydrologic cycle in the Cordillera de
Tilaran. Although precipitation records for Monte-verde extend to 1956, measurements of other elements
of the hydrologic cycle are almost entirely lacking.
This discussion thus relies on qualitative observations
and studies from other areas of the humid tropics.
For a given drainage basin, the hydrologic cycle
can be viewed as a system where inputs equal outputs,
plus or minus changes in storage. Precipitation and
cloud water are the primary inputs; the most signifi-
cant outputs are evapotranspiration (ET) and stream-
flow (surface runoff that moves in a definite channel).
Evapotranspiration refers to the three major processes
that return moisture to the atmosphere in vegetated
areas: (1) evaporation of precipitation intercepted by
plant surfaces ("interception loss"), (2) transpiration
of water through stomata on leaf surfaces, and (3)
evaporation of moisture from the soil or open water
surfaces. Because it is difficult to separate these path-
ways, they are commonly treated together as ET (War-
ing and Schlesinger 1985, Manning 1992).
In the humid tropics, the output from ET and
streamflow is nearly continuous. In contrast, precipi-
tation and cloud water events are discrete and may
be separated by dry periods of up to several weeks or
months. The relationship between precipitation and
stream discharge follows a predictable pattern, where
discharge is the volume of water moving past a point
along a stream over a specific time interval (typically
m^3 /s; Fig. 2.10). In humid areas such as Monteverde,
relatively short periods of higher discharge are asso-
ciated with precipitation events, followed by longer
periods where water is released from storage. StoredFigure 2.10. Hydrograph of streamflow in response to a
rainstorm from a 100-km^2 basin.29 The Physical Environment