CHAPTER FOUR
Forested Watersheds, Water
Resources, and Ecosystem
Services, with Examples from
the United States, Panama, and
Puerto Rico
M.C. Larsen
Smithsonian Tropical Research Institute, Balboa, Republic of Panama
1. INTRODUCTION
Forested watersheds offer access to vital natural resources, i.e., water
supply for drinking, agriculture and industry, transport routes, and hydro-
electric energy. Ecosystem services provided by these watersheds are
numerous and, in addition to good quality water, include reduced peak river
flow during storms; increased availability of groundwater and base flow in
streams during seasonal dry periods and droughts; reduced soil erosion and
landslide probability; enhanced resilience to wildfire, pathogens, and inva-
sive species; biodiversity; genetic resources; and recreation [1e3].
These resource and esthetic benefits come with risks associated with
floods, landslides, and wildfires, which are episodic natural disturbances in
these settings. Furthermore, these disturbances compromise the provision of
the ecosystem services listed previously. Nonetheless, natural landscape distur-
bance by floods has well-known benefits, i.e., delivery of nutrients to flood
plains; landslides open forest gaps that create small-scale opportunities for
successional vegetation growth, while hurricanes and wildfires similarly serve
as large-scale mechanisms for resetting landscapes and creating new habitats.
More than half of the world population now lives in urban areas, which
are expected to absorb all the population growth expected over the next
four decades, mostly in the cities and towns of the less developed regions.
The United Nations [4,5] has defined 23 megacities with at least 10 million
inhabitants; all but 6 of these are in the developing world. These populations
place large stresses on water and other resources.
Chemistry and Water
ISBN 978-0-12-809330-6
http://dx.doi.org/10.1016/B978-0-12-809330-6.00004-0
© 2017 Elsevier Inc.
All rights reserved. 161 j
Societies that derive ecosystem services from forested watersheds face
multiple challenges. Loss of forest cover during the 20th century has been
well described [1,6]. This loss continues in the 21st century, and work by
Hansen et al. [7] and Kim et al. [8] shows that forest cover in tropical Amer-
ica is in decline. For example, from 1990 to 2010 in Panama, forest cover
decreased from 4.6 to 4.01 M ha [8]. Land cover change during this period
is more complex in Puerto Rico, where, according to Gould et al. [9], forest
increased in the eastern part of the island, regenerating on abandoned lands,
while urbanization intensified in areas surrounding the Luquillo Experi-
mental Forest (LEF; also located in eastern Puerto Rico). The reduction
and fragmentation of forest cover compromises virtually all ecosystem ser-
vices: water availability and quality, hydroelectric energy, wood products,
carbon sequestration, maintenance of biodiversity, and reduction of natural
hazard and vulnerability. Moreover, changing climate is already reducing the
capacity for some forested watersheds to provide important services, as
described in the following.
Societal use of forested watersheds and ecosystem services in the Amer-
icas, as elsewhere in the world, has increased substantially as global popula-
tion has grown to the current level of 7.3 billion. The intensity of this use
puts all ecosystem services at risk and requires attention at multiple societal
and governmental levels so that these services are not severely compromised.
This paper describes ecosystem services derived from new-world tropical
and temperate forested watersheds and provides first-order examples of
the value placed on these services.
In the US and other countries, public and private sector policies are
increasingly placing values, often monetized, on ecosystem services so that
these services can be better understood, and management decisions,
including trade-offs, can be made collaboratively and transparently [10].
As these valuation and management approaches become more sophisticated,
there is a concurrent need for more advanced and comprehensive moni-
toring and accounting systems, requiring investment from public and private
entities. Some general US and Caribbean region examples are described in
the following, with discussion of water resources and other ecosystem
services. For Panama, the Panama Canal watershed is the focus, and in
Puerto Rico, examples are drawn from the Luquillo Mountains.
2. CLIMATE CHANGE
Climate change is well documented and poses a number of direct chal-
lenges for our ability to continue to extract benefits from forested watersheds.
162 M.C. Larsen
Additionally, population growth will require more arable land for agriculture,
pushing managed forests onto areas of degraded and lower-quality soils [11].
One example of an observed change in climate is from long-term stream flow
data in the northwestern US. According to Stewart et al. [12], peak snowmelt
runoff is now approximately 2 weeks earlier than observed during the period
from 1948 to 2000 in many western rivers and is predicted to be 30e40 days
earlier as the 21st century progresses. Missouri River stream flow has also
changed during the period from 1960 to 2011, with changes in climate
and land use practices, according to a US Geological Survey (USGS) analysis
of data at 227 streamgages?? [13]. Some regions (Kansas and southern
Nebraska) of that watershed have reduced flows, while some northern tribu-
taries, mainly in North and South Dakota, show increases in flow.
Water resource management challenges are likely to intensify over most
land areas in the 21st century with the increases in the frequency, intensity,
and/or amount of heavy precipitation that are expected as a result of a
warmer atmosphere [14]. At the same time, warmer air temperatures and
increases in intensity and duration of drought and heat stress are likely
over many land areas [14,15], contributing to greater likelihood of major
droughts, water stress, disease, and wildfires. Additionally, droughts and
warmer temperatures stress forests, making them more susceptible to
insect-borne diseases [15,16] (Fig. 4.1). Fluctuations between these
Figure 4.1 View of lodgepole pine forest in the northern Williams Range Mountains,
Colorado, US. Pine bark beetles have killed more than 80% of the mature trees in
this forest; mortality is visible in the red (dark gray in print versions)ebrown (darker
gray in print versions) color of the dead or dying trees. Photo source: USGS, http://
minerals.cr.usgs.gov/projects/colorado_assessment/.
Forested Watersheds, Water Resources, and Ecosystem Services 163
extremes of drought and heavy precipitation are likely to occur in spatial
and temporal patterns that do not conform to past weather and climate
patterns [17].
What have we already observed? Globally averaged air temperatures over
land and ocean warmed by 0.85C from 1880 to 2012. Moreover, the
period from 1983 to 2012 was the warmest 30 years of the last 1400 years
in the northern hemisphere [14]. Since 1901, an increase in average midlat-
itude northern hemisphere land area precipitation has been observed. From
1901 to 2010, global mean sea level rose by 0.19 m, and from 1979 to 2012,
annual mean Arctic sea ice extent decreased 3.5e4.1% per decade [14]. For
example, Arctic sea ice extent in January 2016 was the lowest January extent
in the satellite record and was below the previous record January low in
2011 (Fig. 4.2). This is particularly relevant to Panama, as the Arctic Ocean
is predicted to transition to a seasonally ice-free state during the middle of
the 21st century [18]. The revenues derived from shipping through the Pan-
ama Canal are a major part of the economy of the nation. As navigational
(bathymetric data are sparse) and security systems (coast guard resources in
the region are limited) are developed, this will provide potential Arctic ship-
ping routes as cost-effective alternatives to the Panama (and Suez) Canal
because of distance reductions of 35e60%.
Figure 4.2 Winter Arctic sea ice cover for the period November through March. Image
courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder, https://
nsidc.org/arcticseaicenews/.
164 M.C. Larsen
Temporal and spatial patterns of precipitation distribution continue to
change in North America and elsewhere, challenging water resource man-
agers in their already difficult decision-making for allocation of water
supplies. For example, water from the Lake Mead Reservoir is used for
public supply and irrigation in Arizona, Nevada, California, and northern
Mexico. The Las Vegas Valley is particularly dependent on the reservoir for
its water supply. Barnett and Pierce [19] have estimated that there is a 50%
chance that Lake Mead, a key source of water for the southwestern US,
will be dry by 2021 if the climate warms as predicted and if regional water
consumption is not reduced. There is evidence that we are seeing this
change now. USGS and NASA Landsat satellite imagery from 2000 to
2015 shows that the lake, located at the Nevada/Arizona border, has
been losing water volume for most of that period of record [20]
(Fig. 4.3). The Southern Nevada Water Authority has been responding
to this challenge by proactively implementing a wide range of water
conservation strategies, such as lawn and golf course watering restrictions
and incentives that include a rebate to customers of $2 per square foot
($0.19 per m2) of grass removed and replaced with desert landscaping up
to the first 5000 square feet (465 m2) converted per property. In addition,
the Authority has extensive water reuse requirements and practices in place
in public use areas.
Mean Annual Lake Elevation at Hoover Dam (ft)
1,080
1,150
1,220
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
Figure 4.3 Landsat 7 and Landsat 8 images comparing Lake Mead areal extent in 2000
and 2014. Note substantial shrinkage. The mean annual lake elevation plot shows that
water storage in the lake is in a multiyear decline. Images from USGS/NASA, http://
earthobservatory.nasa.gov/IOTD/view.php?id¼86426.
Forested Watersheds, Water Resources, and Ecosystem Services 165
3. ECOSYSTEM SERVICES AND VALUATION
The Millennium Ecosystem Assessment established a benchmark for
ecosystem services based on a 4-year United Nations assessment of the condi-
tion and trends of the world’s ecosystems and the services we draw from them
[21]. They further broadly defined ecosystem services as provisioning services,
regulating, cultural, and supporting [22]. Although the term “ecosystem
services” has become widely used and discussed, the concept is not new
[23]; for example, von Th€unen [24] discussed land use and landscape-
derived services needed to sustain an agrarian-based self-sufficient state.
A regulating ecosystem service is easily understood, for example, as the
improvement in water quality that is gained by protecting a watershed to
enable the ecosystem to provide this service instead of depending on the
construction and operation of water treatment facilities [21]. This difference
has been described as green versus gray infrastructure.
Water sustains life on earth and is critical to nearly all other ecosystem ser-
vices. Global estimates of ecosystem service values are provided by Coates
et al. [25] and van der Ploeg et al. [26] in US dollars per hectare as $452 for
water supply; $1966 for a set of regulatory services, which includes water
flow regulation, waste treatment, and water purification; mitigation of
extreme events (floods, droughts) and other regulatory services (air quality,
climate regulation, erosion prevention, pollination, and biological control);
and $398 for cultural services.
As has been stated by many, “you can’t manage what you don’t measure.”
Measuring the effects ecosystem services valuation policies is complex
because of the many forces involved, including climatic, local- to global-
scale markets, and various intersecting, sometimes conflicting policies. In
addition, long-term monitoring of forest cover, land use change, streamflow,
agricultural practices, etc., is costly and in many cases not sustained by
governmental agencies. For example, Sanchez-Azofeifa et al. [27] evaluated
a payment for ecosystem services (PES) program that was implemented in
Costa Rica in the 1990s to reduce deforestation. The authors did not observe
significant effects of the PES program, but state that other policies, such as the
creation of national parks and biological reserves, had already lowered defor-
estation rates and may have reduced the PES impact on land use practices.
3.1 United States: Ecosystem Service Payment Programs
PES is not new to the US. Starting in the 1980s, the US Conservation
Reserve Program, which is administered by the US Department of
166 M.C. Larsen
Agriculture, initiated payments to farmers to refrain from planting crops in
environmentally sensitive areas. Wilson and Carpenter [28] synthesized the
results of 30 different US studies from the period of 1971 to 1997 to describe
the state of knowledge and gaps in understanding for the valuation of water
resource ecosystem services. They stated that these valuation estimates tend
to be specific to particular ecosystems and socioeconomic settings, and posit
that physical and social scientists need to collaborate more effectively to
improve future management and research.
TheObama administration, concerned over the impacts of climate change
on the US private and public sector, has directed federal agencies with natural
resource missions to develop ecosystem services assessment methods and ap-
proaches to devise innovative payment methods for ecosystem services. These
approaches are designed to improve the management of these services [29].
According to Schaefer et al. [10], the federal agencies’ ecosystem services ap-
proaches are grouped into enhancing investment in conservation and natural
resource management, improving the cost-effectiveness of programs, making
trade-offs transparent and avoiding unintended negative consequences of pol-
icy actions on ecosystems, enhancing resilience, and supporting public partic-
ipation in the planning process. The agencies collaborated with the Duke
University Nicholas Institute for Environmental Policy Solutions to produce
a guidebook that describes and provides case study examples of ecosystem ser-
vices approaches [30]. Because the guidebook was produced in 2014, it is not
yet known how effective this strategy will be.
Carbon sequestration, water quality regulation, and biodiversity habitat
protection, as well as suites of services such as wetland mitigation and
conservation easements, have been assigned economic values in a number
of states in the US [31]. Mercer et al. [31] describe three types of payments
to landowners: payments directly from the government; voluntary payments
from businesses, individuals, and nongovernmental organizations; and
payments made to comply with government regulations, such as the Clean
Water Act or the Endangered Species Act. The revenues for governmental
and private sector PES derived from forested watersheds in the US were esti-
mated at $1.9 billion in 2007 by Mercer et al. [31]. They note that because
they lacked data on payments for some services, $1.9 billion is a conservative
estimate. Their estimate includes $365 million from government sources
(19%) and $1.5 billion (81%) from nongovernmental sources, including
payments for wetland mitigation, conservation easements, and carbon
offsets. Nongovernment payments come from conservation organizations
such as the Nature Conservancy, the Trust for Public Land, the
Forested Watersheds, Water Resources, and Ecosystem Services 167
Conservation Fund, and Ducks Unlimited, who provide funds to conserve
land for ecosystem services such as water quality protection and biodiversity.
In another estimate of economic value obtained from an ecosystem,
Batker et al. [32] estimated that the value of the natural infrastructure
provided by the Mississippi River Delta ecosystem would be $330 billion
to $1.3 trillion for a combination of hurricane and flood protection, water
supply, water quality, recreation, and fisheries.
In a detailed report describing US federal and other programs that
provide incentives for maintaining or enhancing ecosystem services, Scarlett
and Boyd [33] include brief descriptions of various payment schemes from
around the country:
• Florida pays farmers to maintain wetlands with a goal of improving water
storage.
• In Seattle, new efforts to maintain natural landscapes have reduced storm
water runoff at a cost that is 25% lower than traditional engineering
solutions.
• Farmers in the Tualatin Basin, Oregon, were paid $6 million by water
managers to plant trees along streams to meet water temperature re-
quirements. The resulting shade along riparian corridors reduces water
temperatures in the river channel and along the near-channel banks and
floodplains. This allowed the water agencies to avoid a $60 million cost
for refrigeration systems to cool wastewater effluent and storm water
runoff. Riparian forests provide additional ecosystem benefits because
they enhance bird and other wildlife habitats.
• New York City spent over $1.5 billion to protect and restore watersheds
in the Catskill Mountains to maintain good water quality for the city.
This avoided a $9 billion cost to construct and maintain water filtration
and treatment facilities.
• The US Fish and Wildlife Service initiated a terrestrial carbon sequestra-
tion program to restore areas of the Lower Mississippi River Valley. They
collaborated with a number of private and nonprivate entities, including
energy companies and nonprofit organizations, to add 16,200 ha of
restored habitat to their system of refuges and restored 32,400 ha to
native habitats. In addition, they planted 22 million trees that, in the
coming century, are estimated to sequester 33 million tons of carbon.
This is roughly equivalent to the annual emissions from 5.5 million cars
in the US.
• The state of Ohio started a Water Resource Restoration Sponsorship
Program to provide loan rate reductions for wastewater treatment
168 M.C. Larsen
projects in cases where the loan recipient commits to use a portion of
their cost savings to protect watersheds and restore a land trust, park
district, or other watershed protection project.
Avoiding hazardous areas such as floodplains reduces exposure for people
and infrastructure. Many communities in the US use land management
strategies, such as defining and zoning areas for conservation lands in flood-
plains, and other hazards, such as steep hillslopes. As discussed previously,
this practice reduces exposure, thereby minimizing disaster costs associated
with floods and landslides.
Kousky et al. [34] estimated benefits provided by floodplain conservation
lands in an 11,330-ha area along theMeramec River, Missouri. In their anal-
ysis, approximately $13 million per year of flood damages were avoided by
preventing development in the 500-year floodplain of the study area. They
further estimated that this was a 38% reduction from average damages
expected if these lands were not in a conservation area. In their simple
benefitecost analysis, they note that when considering this potential damage
savings along with the recreational and esthetic benefits obtained, these
conservation lands yield benefits for the region that exceed the opportunity
costs of development.
It is widely recognized that vegetation, particularly forest, can stabilize
steep slopes. Although not a US example, a study by Rickli and Graf [35]
examined the effect of forest on shallow landslides. The authors showed
that landslides were less frequent in forested terrain than in open land in
six study areas in Switzerland. Their data also show that landslides mapped
in forests occurred on steeper slopes than landslides mapped in open land.
Landslide losses are increasing in the US (and around the world) in asso-
ciation with growing population and development. Spiker and Gori [36]
maintain that this trend will continue because of development in hazardous
areas, expansion of transportation infrastructure, deforestation of landslide-
prone areas, and climate change. These authors outlined a national landslide
hazards mitigation strategy that would reduce the cost of landslide hazards
and would require new partnerships between government, academia, and
the private sector to sustain and expand a range of approaches, including
research and development of mapping and other mitigation tools.
3.2 Ecosystem Services Obtained From
the Panama Canal Watershed
The 3313 km2 Panama Canal watershed is located at 9 north latitude with
elevations that are generally 300 m or less above sea level, although several
Forested Watersheds, Water Resources, and Ecosystem Services 169
peaks reach 1000 m elevation [37,2]. Annual rainfall is variable across the
watershed, from a low on the Pacific side of the isthmus of 1600 mm to
more than 3000 mm on the Caribbean/Atlantic side. Approximately half
of the watershed is in forest, mostly evergreen canopy, defined as tropical
moist forest; however, forests near the Pacific coast are about 25% decidu-
ous, while the wetter region near the Atlantic has few deciduous trees and
includes wet forest and submontane?/forest [37,38].
Ecosystem services derived from the Panama Canal watershed provide a
robust example of multiple high-value services with national, regional, and
global significance [11]. Water is the most important control on virtually all
canal watershed ecosystem services [39]. Annual precipitation in the canal
watershed is reported as a volume of 8.9 km3 for the period from 1993 to
2004 [40]. This translates to an annual stream flow volume of 4.4 km3,
with 2.6 km3 (59%) used for lockages of vessels transiting the canal,
1.2 km3 (27%) for hydroelectric power generation, and 0.27 km3 (6%) for
drinking water supply, according to an average canal watershed water
budget published by Stallard et al. [2]. The balance, 7%, is mainly evapora-
tion and groundwater infiltration [40].
Most of the nation’s population of close to four million resides in or near
the canal watershed, mainly along the canal route. Financial income is a major
ecosystem service of the canal. A total of $1.91 billion in tolls were collected
in 2014 for ships using the canal. About half of this is used for operations, and
the balance goes into the general fund for the Republic of Panama. The
Panama Canal Authority (ACP) has 9000 employees, but activities directly
or indirectly related to canal operations generate some 200,000 jobs [41].
Shipping companies pay to use the canal because of major fuel and time
savings, which prevents substantial burning of fossil fuel and consequent
emission of greenhouse gases. For example, a ship traveling between New
York and San Francisco saves about 13,000 km by using the Panama Canal
instead of going around Cape Horn. About 14,000 ships use the canal every
year [42]. Most of these are from the US, followed by those from China,
Chile, Japan, Colombia, and South Korea. As such, the fuel savings and
greenhouse gas emissions reductions achieved by the shipping companies
from these countries (and others) are a valuable ecosystem service provided
by the canal watershed but used globally. For example, shipping cargo from
Shanghai to New York through the Suez Canal takes about 77 days for a
round trip, but only 56 days per trip through the Panama Canal. When
the Panama Canal starts use of its expanded set of locks in June 2016, which
will allow greater capacity vessels to transit the system, it is expected that
170 M.C. Larsen
total reduced fuel consumption will decrease CO2 emissions by an estimated
160 million tons in the first 10 years of operation.
Approximately 197,000 m3 of water has been used for each vessel to
transit the canal on average in recent years [43]. That totals 2.76 km3 of
water per year for shipping purposes, which, using the $1.91 billion in tolls,
equals a value of 1.4 m3 of water per dollar, or conversely, a value of $0.69
per m3 of water. Using the 3313 km2 area of the Panama Canal watershed,
the annual shipping value per hectare of land is $5765. These are overly
simplistic valuations of water and land, but provide a gauge of the value of
the land used to support this particular water use in Panama. The approximate
value does not include the important hydroelectric, esthetic, recreational,
carbon sequestration, biodiversity maintenance, or overall ecosystem habitat
values that are also provided by this water.
An additional complication of placing a specific economic value on
water in the Panama Canal watershed is that each cubic meter of this water
gains more importance during shortage periods. Average annual rainfall is
2659 mm at the Smithsonian Tropical Research Institute, administered
Barro Colorado Island Nature Monument, located within the Panama
Canal watershed (Fig. 4.4). Rainfall totals have a large interannual variation
in accumulation, with a low of 1699 mm in 1997 and a high of 4487 mm in
1981. During drought years, the ACP has sometimes had to require that
Figure 4.4 Annual rainfall totals, 1925 to 2015, Smithsonian Tropical Research Institute,
Barro Colorado Island, Panama. Average for the period is 2659 mm. Note large interan-
nual variation in accumulation. Data source: Steven Paton, Smithsonian Tropical Research
Institute, http://biogeodb.stri.si.edu/physical_monitoring/research/barrocolorado.
Forested Watersheds, Water Resources, and Ecosystem Services 171
vessels transiting the canal do so with reduced draft, which means that the
fees paid by the shipping companies are also reduced.
Drinking water and energy production are the other major economically
quantified ecosystem services of this watershed. Drinking water for more
than half of the nation’s population is obtained from the watershed; energy
production for more than half of Panama’s electrical energy supply is hydro-
electric from dams in the canal watershed. In 2014, the canal generated
$246 million in revenue from the sale of electric power and $29.4 million
from the sale of potable water [43]. The Panama water authority (the Insti-
tuto de Acueductos y Alcantarillados Nacional) charges approximately $0.26
per m3 to the consumer for potable water [44].
As noted previously, recreation, tourism, carbon sequestration, and
maintenance of biodiversity are other important ecosystem services derived
from the Panama Canal watershed. Total annual tourism revenue for the
nation in 2015 from an estimated two million visitors was approximately
$4 billion. Because data are limited, estimating economic values for carbon
sequestration and maintenance of biodiversity is beyond the scope of this
paper (see Ref. [11] for discussion of these services).
At 9 north latitude, Panama has the good fortune to be located just
south of the AtlanticeCaribbean and Pacific hurricane zones. In the past
150 years of tracking of hurricanes, none have directly impacted the coun-
try. Nonetheless, floods caused by other weather systems, often convective
disturbances associated with the location of the intertropical convergence
zone (a dynamic band of convective moisture associated with the conver-
gence of near-equatorial easterly trade winds from the northern and south-
ern hemispheres), are not uncommon, and flood risk is the principal natural
hazard faced by Panama, where many people live along or near riparian
corridors. Storms with significant flooding in the canal watershed tend to
occur at the end of the rainy season, for example: October 1923, November
1931, November 1932, November 1966, December 1985, December 2000,
November 2004, and December 2010 [45]. A notable example of a major
storm on this list with associated significant flooding is the event of
December 2010. This storm, known as La Purisima, serves as a good illus-
tration of flood and landslide hazard mitigation as an ecosystem service in
the Panama Canal watershed [46]. The storm also illustrates what happens
when hazard-related ecosystem services are at or beyond their limits when
a rare, large-magnitude storm affects hillslopes and riparian corridors.
La Purisima, described as the largest 3-day storm in the Canal watershed’s
100-year recorded history, was associated with the interaction of a frontal
172 M.C. Larsen
system and the intertropical convergence zone, and produced 760 mm of
rainfall in 24 h. Mean stream flow for the principal canal watershed fluvial
system, the Chagres River, was 908 m3 per second, and a 3-day total steam
flow volume of 235 million m3 was calculated. This volume has a recurrence
interval of approximately 300 years and was the largest flow recorded in the
78 years since recordkeeping began [46]. In a rare mitigation step, the ACP
was forced to open the canal locks to discharge water, halting ship transit
through the Canal for 17 h [46]. Additionally, the rainfall caused more
than 500 landslides and temporarily closed the two roads that connect the
two major cities of the country, Panama City and Colon. The landslides
also introduced a massive pulse of sediment into river channels, raising water
turbidity at a key public supply intake to 600 nephelometric turbidity units,
closing water supply facilities and leaving parts of Panama City without
normal water supply for 50 days. These aspects of the environmental
response to this rare storm illustrate what happens when ecosystem services
are fully or partially overwhelmed by the magnitude of the event.
About half of the canal watershed has been deforested, and the official
policy in the canal watershed (Law 21) is to reforest in anticipation of regain-
ing ecosystem services [2]. Canal watershed locks and dams were at their
design limits during this flood, meaning that if there was much more stream
flow, which would have been the case if more of the watershed had been
deforested, the dam and the locks could have failed, a major disaster for
Panama and world shipping. This averted disaster shows the high ecosystem
service value of the forested areas of the Panama Canal watershed. Important
services, including canal operations, were temporarily compromised, but
canal infrastructure held up. Furthermore, an essential measure of the value
of an ecosystem service with regard to hazard mitigation is loss of life. In spite
of the large magnitude of this storm, few casualties were reported. The great
importance of maintaining forest in this watershed, with extensive high-
value infrastructure downstream, as well as critically important public water
supplies, cannot be overemphasized. The environmental response provides a
good example of when green (forested land) and gray (dams, locks) infra-
structure is overwhelmed. The dams and locks (gray infrastructure) reached
their design limits, and the green “infrastructure” (forests) was at capacity for
mitigation.
With respect to ongoing management of flood hazard as an ecosystem
service, the ACP has a flood control program that identifies, mitigates,
and responds to conditions that pose a danger to communities and property
located along riparian corridors (and on key ACP reservoirs and canal
Forested Watersheds, Water Resources, and Ecosystem Services 173
infrastructure) that could potentially interrupt canal operations [45]. The
ACP, like many agencies that manage multiuse reservoirs (i.e., reservoirs
used for a combination of flood control, hydroelectric energy production,
drinking water supply, irrigation, and recreation) uses a complex set of
metrics to control canal watershed reservoir levels to ensure water availabil-
ity for human consumption, ship transit, and hydropower generation. One
of the annual challenges faced by the ACP is associated with the timing and
amount of rainfall delivered to the canal watershed by storms at the end of
the wet season in December. The largest storms are often at the very end of
the season, when reservoirs may be at, or close to, their maximum volume.
4. ECOSYSTEM SERVICES OBTAINED FROM THE
LUQUILLO MOUNTAINS, PUERTO RICO
Puerto Rico, the smallest island (9000 km2) of the Greater Antilles, is
located in the northeastern Caribbean at 18 north latitude, about 1700 km
southeast of Miami, US. It is an island of high relief with a maximum eleva-
tion in the central eastewest trending mountain range of 1338 m. The recti-
linear island measures 65 km northesouth and 180 km eastewest. Gradual
forest removal began in the 1600s as land was cleared for agriculture by
European settlers. After three centuries of extensive subsistence and planta-
tion agricultural land use, most (94%) of Puerto Rico had been deforested by
the late 1940s [9]. A shift away from agriculture toward industry began in the
1950s and resulted in much abandoned pasture and farmland that are now in
secondary forest [9].
Topography in the Luquillo Mountains is rugged, stream channels are
deeply incised, and annual rainfall averages more than 4000 mm in the upper
elevations [47]. The mountains are largely within the boundaries of the El
Yunque National Forest (EYNF), also known as the LEF, an intensely stud-
ied 11,300-ha preserve that is completely forested and under the administra-
tion of the US Forest Service. Because of the 1000-m elevational,
temperature, and precipitation gradient, multiple forest types are present
in the LEF, including subtropical moist forest and subtropical wet forest,
with subtropical rainforest, lower montane wet forest, and lower montane
rainforest at high elevations [9,48].
Prior to the 1898 US invasion, the Luquillo Mountains had been afforded
some degree of forest protection during the 19th century by the Spanish crown
because of the value of the hardwood there for shipbuilding and other pur-
poses. This, along with localized cutting of wood to make charcoal, was one
174 M.C. Larsen
of the first described ecosystem services derived from the forest. During the
20th century, the mountains gained new uses as they were managed by the
USForest Service as a recreational area and as thePuertoRicoWaterAuthority
(PRASA) began to use high-quality streamflow for drinking water supply in
the region [49]. A first approximation of the value of public supply water
from the LEF was estimated by Crook et al. [49] using stream flow from
the nine rivers that drain the mountains. These rivers have modest water
extraction sites, operated by PRASA, which is required to limit extraction
in order to maintain minimum stream flow so as to sustain ecological function
of the streams [50]. Water is extracted from 34 locations along these rivers,
and on a typical day, 70% of stream flow from within the forest is diverted
before reaching the ocean (Fig. 4.5). Two intakes draw particularly large
amounts of water: the intake at Río Mameyes, which is permitted to extract
18,940 m3/day, and the intake at Río Fajardo, permitted to extract
45,460 m3/day [49].
In 2004, an approximate total of 0.252 million m3/day of water was
withdrawn from streams draining the LEF. PRASA charges $1.06 per m3
for average residential customers. Using this price to the consumer for
potable water in Puerto Rico, the daily volume of potable water withdrawn
from the LEF has a total maximum possible value of approximately $267,000.
Figure 4.5 Map of public supply water intakes on streams draining the Luquillo Exper-
imental Forest, eastern Puerto Rico. Forest boundary shown in white orthogonal lines;
watershed boundaries are nonrectilinear white lines. Intakes shown with circles in
which diameter is proportional to the intake withdrawal capacity, ranging from less
than 10 m3 per day to more than 10,000 m3 per day. Figure simplified from Crook KE,
Scatena FN, Pringle CM. Water withdrawn from the Luquillo experimental forest, 2004. U.S.
Department of Agriculture, Forest Service, General Technical Report GTR-IITF 34; 2007. 26 p.
Forested Watersheds, Water Resources, and Ecosystem Services 175
Hydropower represents only 1% of total electric energy for Puerto
Rico, most of which (69%) is generated by oil-burning power plants
[51]. Hydropower generation is severely limited because the 224 rivers in
Puerto Rico are relatively short in length (a few tens of km), with only
modest catchment size. This small watershed size, in combination with
episodic droughts, makes hydroelectric energy unreliable [52]. A small
hydroelectric facility on the south side of the Luquillo Mountains, on the
Río Blanco, has a capacity to generate 5 MW, according to Liu et al.
[51]. This is 12% of the 41.8 MW capacity from a total of 21 hydroelectric
units on six rivers around the island. Puerto Rico’s electricity costs are about
27 cents per kilowatt hour, approximately twice what they are in the US
[53]. One megawatt equals 1000 kW, so at $0.27 per kilowatt, if the Río
Blanco facility was operating at full 24 h/day capacity (it is reportedly not
doing so), it would be producing electricity valued at $32,400 per day
($11.8 million/year).
The US Forest Service describes a “site visit” as the entry of one person
to a national forest site or area to participate in recreational activities for an
unspecified period of time. A “national forest visit” can be composed of
multiple “site visits.” In 2006, there were 1.336 million site visits to the
EYNF, and in 2011, there were 1.123 million (written communication,
Jose Ortega, Recreational Program Leader, EYNF, Puerto Rico, US Forest
Service, September 8, 2015). The American Sportfishing Association [54]
quantifies the economic value of visits to US Forest Service managed lands
that are made for hunting, fishing, and wildlife viewing activities. Hunting
and fishing are not permitted within the EYNF boundaries, so information
for Puerto Rico was restricted to wildlife viewing activities. Bird watching is
one the principal wildlife viewing activities as Puerto Rico, in combination
with the US Virgin Islands, has approximately 270 species of birds [55].
Additionally, there is great interest in the dwindling populations of the
once widely distributed Puerto Rican parrot. Between 2000 and 2003, an
estimated annual average of $3.2 million was spent in Puerto Rico for
wildlife viewing associated with the EYNF [54]. As the number of visitors
to the forest has increased since 2003, it is likely that the economic contri-
bution of wildlife viewing associated with the EYNF has also increased. US
Forest Service data show an EYNF recreational visitor rate in excess of
1,000,000 per year.
Carbon sequestration and maintenance of biodiversity are other impor-
tant services derived from the Luquillo Mountains and the forested
11,300 ha of the LEF, but these are beyond the scope of this paper.
176 M.C. Larsen
Mitigation of flood and landslide hazards that not only threaten people
and infrastructure, but compromise ecosystem services, is achieved largely
through the practices of strong governance. An important part of the gover-
nance is minimization of forest removal in steeply sloping regions and
zoning to prevent housing or other construction on or near the base of steep
hillslopes [56]. Forested hillslopes provide a landslide hazard mitigation
ecosystem service that also applies to flood hazard mitigation for people
and structures located along riparian corridors. The presence of forest
reduces storm runoff volume and reduces storm runoff peak stream flow
in rivers, spreading the runoff volume over a larger time step than would
occur if no forest were present [3].
In its recorded history, floods have caused the largest loss of life in Puerto
Rico, which is the case for most countries around the world. Major floods
during the 19th and 20th centuries were associated with rainfall delivered by
tropical disturbances (depression, storms, hurricanes), and killed thousands
[57]. Most of these flood deaths were prior to 1940 when zoning for housing
location and construction standards were not well defined or regulated.
Improved governance, including planning and zoning, has greatly reduced
loss of life from flooding across the island. Effective governance is also
evident in Puerto Rico, where a well-coordinated response system of
governmental agencies is initiated each time that a tropical disturbance
or other heavy rain threatens the island. Additionally, general education
of the public for hazard preparation and a well-informed, decentralized civil
defense network have combined to reduce loss of life to near zero during
large storms.
CONCLUSIONS
The US, Panama, and Puerto Rico provide examples of a variety of
payment programs for ecosystem services and for the services derived
from forested watersheds, and offer insights into how we consider and
take advantage of these services. The examples show the benefits and limi-
tations of the ecosystem services provided by forested watersheds and how
some of the services are valued. The examples also illustrate the importance
of the maintenance and expansion of watershed forest cover as well as strong
governance, which includes well-informed science- and engineering-based
infrastructure zoning, planning, and design. Not surprisingly, because of its
geographic size, large economy, and well-established natural resource regu-
latory policies, the US has the most developed set of PES.
Forested Watersheds, Water Resources, and Ecosystem Services 177
In most countries, PES from forested watersheds is indirect. It is a value
that is most commonly extracted for hydroelectric energy, water supply, and
recreation through governmental or private sector charges to deliver these
commodities to users. As the brief examples listed above demonstrate,
most US programs that offer payments for ecosystem services don’t focus
on a single service. The programs are meant to incentivize general conser-
vation practices, which support a range of benefits obtained from forested
watersheds and other environments.
In spite of the numerous large investments made by federal, state, and
local governments, as well as those made by nongovernmental organiza-
tions, many landowners do not participate in these PES programs. See
Mercer et al. [31] for a discussion of data and statistics on this topic. Mercer
et al. [31] further state that “the economic and social forces that have led to forest
fragmentation and loss in the US are so strong that PES payments have so far not
had a significant impact on forest land use at the regional or national level” and
that “changes in government and corporate policy will be critical for PES to result
in large enough financial returns to effectively compete with development and other
economic drivers of land use in the US in order to have a significant impact on the
provision of forest-based ecosystem services.”
To best manage water resources and other ecosystem services, there is an
increasing need for local land management actions and adaptation, which
includes sustaining diverse forest cover, minimizing soil erosion and degra-
dation, and assuring that road networks and essential infrastructure are well
planned [58] and not built in areas subject to flood, landslide, and other
hazards [59,60]. These actions assure that both the natural and built environ-
ments (green and gray infrastructure) are managed in coordination,
improving and enhancing the benefits derived from each [61,62].
Additionally, mountains and rivers are often transboundary, crossing
political and cultural divisions. As such, effective management of ecosystem
services is highly dependent, not just on local strong governance, but also on
the cooperation of local stakeholders, regional and national institutions, and
in many cases, international institutions [63]. Additionally, timely access to
governmental communication of accurate information associated with
hazards, i.e., precipitation, streamflow, estimated fire probability, flood
and landslide warnings, is key to effective response of at-risk communities
so that loss of life is minimized.
Lastly, with changing climate, water resources management and flood
(and landslide) hazard mitigation challenges are now increasing because
the long-standing approach for estimating streamflow and flood probability
178 M.C. Larsen
is based on the principal of stationarity, which means that the present likeli-
hood of streamflow and floods in a watershed can be well determined by
examining the past 30 or more years of stream flow record. This approach
has been weakened by changing rainfall and stream flow patterns observed
in recent decades [17,64]. The intergovernmental panel on climate change
(IPCC) [14] Fifth Assessment Report concluded that climate change has
begun to affect the frequency, intensity, and length of many extreme events,
thus increasing the need for additional timely and effective adaptation.
ACKNOWLEDGMENTS
Funding support for work on this paper was derived through the budget of the Smithsonian
Institution. This paper was improved by comments from anonymous reviewers.
REFERENCES
[1] Noble IR, Dirzo R. Forests as human-dominated ecosystems. Science 1997;277:
p.522e525.
[2] Stallard RF, Ogden FL, Elsenbeer H, Hall J. Panama canal watershed experiment:
Agua Salud project. Water Resour Impact 2010;12(4):17e20.
[3] Ogden FL, Crouch TD, Stallard RF, Hall JS. Effect of land cover and use on dry season
river runoff, runoff efficiency, and peak storm runoff in the seasonal tropics of Central
Panama. Water Resour Res 2013;49(12):8443e62.
[4] United Nations. World urbanization prospects, the 2011 revision. UN Department of
Economic and Social Affairs/Population Division; 2011. 318 p.
[5] United Nations, Department of economic and social affairs, population division.
World Urbanization Prospects: The 2014 Revision, Highlights 2014 (ST/ESA/
SER.A/352).
[6] Food and Agriculture Organization. State of the World’s forests, FAO. Rome (Italy):
United Nations; 1997.
[7] Hansen MC, Potapov PV, Moore R, Hancher M, Turubanova SA, Tyukavina A,
Thau D, Stehman SV, Goetz SJ, Loveland TR, Kommareddy A, Egorov A,
Chini L, Justice CO, Townshend JRG. High-resolution global maps of 21st-century
forest cover change. Science 2013;342:850e3.
[8] Kim DH, Sexton JO, Townshend JR. Accelerated deforestation in the humid tropics
from the 1990s to the 2000s. Geophys Res Lett 2015;42. http://dx.doi.org/10.1002/
2014GL062777.
[9] Gould WA, Martinuzzi S, Parés-Ramos IK. Land use, population dynamics, and
land-cover change in eastern Puerto Rico, Ch. B. In: Murphy SF, Stallard RF, editors.
Water quality and landscape processes of four watersheds in eastern Puerto Rico. U.S.
Geological Survey Professional Paper 1789; 2012. p. 25e42.
[10] Schaefer M, Goldman E, Bartuska AM, Sutton-Grier A, Lubchenco J. Nature as cap-
ital: advancing and incorporating ecosystem services in United States federal policies
and programs. Proc Natl Acad Sci USA 2015;112(24):7383e9. http://dx.doi.org/
10.1073/pnas.1420500112.
[11] Hall JS, Kirn V, Yanguas Fernandez E, editors. Managing watersheds for ecosystem
services in the steepland neotropics. Inter-American Development Bank. IDB
Monograph, 340; 2015. 186 p.
[12] Stewart I, Cayan DR, Dettinger MD. Changes in snowmelt runoff timing in western
North America under a ‘business as usual’ climate change scenario. Clim Change 2004;
62:217e32.
Forested Watersheds, Water Resources, and Ecosystem Services 179
[13] Norton PA, Anderson MT, Stamm JF. Trends in annual, seasonal, and monthly
streamflow characteristics at 227 streamgages in the Missouri river watershed, water
years 1960e2011. U.S. Geological Survey Scientific Investigations Report
2014e5053. 2014. 128 p., http://dx.doi.org/10.3133/sir20145053.
[14] IPCC. Climate Change. In: Core Writing Team, Pachauri RK, Meyer LA, editors.
Synthesis report. Contribution of Working Groups I, II and III to the fifth assessment
report of the Intergovernmental Panel on climate change. Geneva (Switzerland):
IPCC; 2014. 151 pp.
[15] Bentz BJ, Régniere J, Fettig CJ, Hansen EM, Hayes JL, Hicke JA, Kelsey RG,
Negron JF, Seybold SJ. Climate change and bark beetles of the western United States
and Canada: direct and indirect effects. BioScience 2010;60:602e13.
[16] Clark JS, Iverson L, Woodall CW, Allen CD, Bell DM, Bragg DC, D’Amato AW,
Davis FW, Hersh MH, Ibanez I, Jackson ST, Matthews S, Pederson N, Peters M,
Schwartz MW, Waring KM, Zimmermann NE. The impacts of increasing drought
on forest dynamics, structure, and biodiversity in the United States. Glob Change
Biol 2016. http://dx.doi.org/10.1111/gcb.13160.
[17] Milly PCD, Betancourt J, Falkenmark M, Hirsch RM, Kundzewicz ZW,
Lettenmaier DP, Stouffer RJ. Stationarity is dead: whither water management. Science
2008;319:573e4.
[18] Stephenson SR, Smith LC. Influence of climate model variability on projected Arctic
shipping futures. Earth’s Future 2015;3. http://dx.doi.org/10.1002/2015EF000317.
[19] Barnett TP, Pierce DW. When will Lake Mead go dry? Water Resour Res 2008;44:
W03201. http://dx.doi.org/10.1029/2007WR006704.
[20] U.S. Department of the Interior, Bureau of Reclamation. Lake Mead at Hoover Dam,
elevation. 2015. http://www.usbr.gov/lc/region/g4000/hourly/mead-elv.html.
[21] MEA. Millennium Ecosystem Assessment. Ecosystems and human well-being: a
framework for assessment. Washington (DC): Island Press; 2003. 266 p. http://
www.maweb.org.
[22] MEA. Millennium Ecosystem Assessment. Ecosystems and human well-being: synthe-
sis. A report of the millennium ecosystem assessment. Washington (DC): World
Resources Institute and Island Press; 2005. www.maweb.org/documents/document.
356.aspx.pdf.
[23] SCEP, Study of Critical Environmental Problems. Man’s impact on the global envi-
ronment - assessment and recommendations for action. Cambridge (Massachusetts):
The MIT Press; 1970. 319 p.
[24] von Th€unen JH. Der isolierte Staat in Beziehung auf landwirtschaft und
National€okonomie. 3rd ed. 1842. Berlin (Rostock).
[25] Coates D, Pert PL, Barron J, Muthuri C, Nguyen-Khoa S, Boelee E, Jarvis DI. Water-
related ecosystem services and food security. In: Boelee E, editor. Managing water and
agroecosystems for food security; 2013. p. 29e41.
[26] van der Ploeg S, de Groot RS,Wang Y. The TEEB valuation database: overview of struc-
ture, data and results. Foundation for sustainable development. Wageningen Neth 2010.
[27] Sanchez-Azofeifa GA, Pfaff A, Robalino JA, Boomhower JP. Costa Rica’s payment for
environmental services program: intention, implementation, and impact. Conserv Biol
2007;21:1165e73.
[28] Wilson MA, Carpenter SR. Economic valuation of freshwater ecosystem services in
the United States: 1971e1997. Ecol Appl 1999;9(3):772e83.
[29] Executive Office of the President. Priority agenda for enhancing the climate resilience
of America’s natural resources (Executive Office of the President, Washington, DC).
2014. https://www.whitehouse.gov/sites/default/files/docs/enhancing_climate_
resilience_of_americas_natural_resources.pdf.
180 M.C. Larsen
[30] National Ecosystem Services Partnership. Federal resource management and ecosystem
services guidebook (National Ecosystem Services Partnership, Duke University,
Durham, NC). 2014. https://nespguidebook.com/.
[31] Mercer DE, Cooley D, Hamilton K. Taking stock: payments for forest ecosystem
services in the United States; 2011.
[32] Batker D, de la Torre I, Costanza R, Swedeen P, Day J, Boumans R, Bagstad K.
Gaining ground. Wetlands, hurricanes and the economy: the value of restoring the
Mississippi River Delta. Tacoma (Washington): Earth Economics; 2010. http://
www.eartheconomics.org/FileLibrary/file/Reports/Louisiana/Earth_Economics_Report_
on_the_Mississippi_River_Delta_compressed.pdf.
[33] Scarlett L, Boyd J. Ecosystem services: quantification, policy applications, and current
federal capabilities. Resources for the Future Discussion Paper No. 11e13. 2011. 78 p.
[34] Kousky C, Walls M, Chu Z. Measuring resilience to climate change: the benefits of
forest conservation in the floodplain, p. 345e360. In: Sample VA, Bixler RP, editors.
Forest conservation and management in the Anthropocene: conference proceedings.
RMRS-P-71. Fort Collins, CO. US Department of Agriculture, Forest Service.
Rocky Mountain Research Station; 2014. 494 p.
[35] Rickli C, Graf F. Effects of forests on shallow landslides e case studies in Switzerland.
Snow Landsc Res 2009;82(1):33e44.
[36] Spiker EC, Gori PI. National landslide hazards mitigation strategy: a framework for loss
reduction U.S. Geological Survey Open-file Report 00-450, 2000. 49 p.
[37] Condit RS, Robinson DW, Ibanez R, Aguilar S, Sanjur A, Martinez R, Stallard RF,
Garcia T, Angehr GR, Petit LJ, Wright SJ, Robinson TR, Heckadon-Moreno S. The
status of the Panama canal watershed and its biodiversity at the beginning of the 21st
century. Bioscience 2001;51(5):135e44.
[38] Iba~nez R, Condit RS, Angehr GR, Aguilar S, Garcia T, Martinez R, Sanjur A,
Stallard RF, Wright SJ, Rand AS, Heckadon-Moreno S. An ecosystem report on
the Panama canal: monitoring the Status of the forest communities and the watershed.
Environmental Monitoring and Assessment 1. 2002. p. 65e95.
[39] Stallard RF. Understanding natural capital, part a: geophysical context. In: Hall JS,
Kirn V, Yanguas Fernandez E, editors. Managing watersheds for ecosystem services
in the steepland neotropics. Inter-american development bank. IDB Monograph,
340; 2015. p. 20e34.
[40] IDB. Panama canal expansion program. Inter-American Development Bank Environ-
mental and Social Management Report PN-l1032. 2012. 38 p.
[41] Panama Canal Annual Report, 120 p., http://www.pancanal.com/eng/general/
reporte-anual/index.html; 2014.
[42] Smith R. A hundred years old today, the Panama canal is about to get a lot bigger. Natl
Geogr 2014. http://news.nationalgeographic.com/news/2014/08/140815-panama-
canal-culebra-cut-lake-gatun-focus/?rptregcta¼reg_free_np&rptregcampaign¼2015
012_invitation_ro_all#.
[43] Panama Canal, http://www.pancanal.com/eng/general/canal-faqs/physical.html; 2015.
[44] IDAAN, Instituto de Acueductos y Alcantarillados Nacional. http://www.idaan.gob.
pa/; 2015.
[45] Cuevas JA. The Panama canal Authority’s flood control program. In: Building knowl-
edge bridges for a sustainable water future, proceedings of the second international
symposium on building knowledge bridges for a sustainable water future, Panama, Re-
public of Panama, 21e24 November, 2011. Published by the Panama Canal Authority
(ACP) and UNESCO; 2011.
[46] Espinosa JA. Water management in the Panama Canal during the December 2010
extreme flood. In: Tarte A, et al., editors. Second international symposium on building
knowledge bridges for a sustainable water future, Panama, republic of Panama41e45.
Panama (Republic of Panama): Panama Canal Authority and UNESCO; 2011. 301 p.
Forested Watersheds, Water Resources, and Ecosystem Services 181
[47] Larsen MC. Landslides and sediment budgets in four watersheds in eastern Puerto
Rico, Ch. F. In: Murphy SF, Stallard RF, editors. Water quality and landscape
processes of four watersheds in eastern Puerto Rico; 2012. p. 153e78. U.S. Geological
Survey Professional Paper 1789.
[48] Harris NL, Lugo AE, Brown S, Heartsill Scalley T, editors. Luquillo experimental for-
est: research history and opportunities. EFR-1. Washington (DC): U.S. Department of
Agriculture; 2012. 152 p.
[49] Crook KE, Scatena FN, Pringle CM. Water withdrawn from the Luquillo experi-
mental forest, 2004. U.S. Department of Agriculture, Forest Service, General Tech-
nical Report GTR-IITF 34. 2007. 26 p.
[50] PRASA. Puerto Rico Aqueduct and Sewer Authority Report. 500 p., http://www.
gdb-pur.com/investors_resources/documents/praqueductsewerauth02a-fin-295mm.
pdf; 2012.
[51] Liu H, Masera D, Esser L, editors. World small hydropower development report 2013.
United Nations Industrial Development Organization; 2013. International Center on
Small Hydro Power, www.smallhydroworld.org.
[52] Larsen MC. Analysis of 20th century rainfall and streamflow to characterize drought
and water resources in Puerto Rico. Phys Geogr 2000;21:494e521.
[53] Gross D. Why is Puerto Rico burning oil to generate electricity? Slate. 2014. http://
www.slate.com/articles/business/the_juice/2014/05/puerto_rico_is_burning_oil_
to_generate_electricity_it_s_completely_insane.html.
[54] American Sportfishing Association (ASA). State and national economic effects of fish-
ing, hunting and wildlife-related recreation on U.S. Forest Service-Managed ands.
2007. Report prepared for the Wildlife, Fish and Rare Plants U.S. Forest Service
U.S. Department of Agriculture. 11.15.13, http://www.fs.fed.us/biology/resources/
pubs/wildlife/usfs_wildlife_based_recreation_economic_contributions_1_03_07.pdf.
[55] Raffaele HA. A guide to the birds of Puerto Rico and the Virgin Islands. Princeton
(New Jersey): Princeton University Press; 1989.
[56] Keefer DK, Larsen MC. Assessing landslide hazards. Science 2007;316:1136e8.
[57] Ramos-Ginés O. Estimation of magnitude and frequency of floods for streams in
Puerto Rico: new empirical models. U.S. Geological Survey Water-Resources Inves-
tigations Report 99-4142, 1999. 41 p.
[58] Larsen MC, Parks JE. How wide is a road? The association of roads and mass-wasting
disturbance in a forested montane environment. Earth Surf Process Landforms 1997;
22:835e48.
[59] Larsen MC, Torres Sanchez AJ. The frequency and distribution of recent landslides in
three montane tropical regions of Puerto Rico. Geomorphology 1998;24:309e31.
[60] Larsen MC, Wieczorek GF. Geomorphic effects of large debris flows and flash floods,
northern Venezuela, 1999. In: Latrubesse E, editor. Tropical geomorphology with
special reference to South America. Zeitschrift f€ur Geomorphologie Suppl, vol. 145;
2006. p. 147e75.
[61] Green PA, V€or€osmarty CJ, Harrison I, Farrell T, Saenz L, Feketea BM. Freshwater
ecosystem services supporting humans: pivoting from water crisis to water solutions.
Glob Environ Change September 2015;34:p.108e118.
[62] Saenz L, Mulligan M, Arjonac F, Gutierrez T. The role of cloud forest restoration on
energy security. Ecosyst Serv 2014;9:180e90.
[63] ISDR. Hyogo framework for action 2005e2015: building the resilience of nations and
communities to disasters. World Conference on disaster reduction 18e22 January
2005, Kobe, Hyogo, Japan. International strategy for disaster reduction. 2005. Extract
from the final report (A/CONF.206/6), www.unisdr.org/wcdr. 25 p.
[64] Larsen MC. Global change and water resources, where are we headed? Water Resour
Impact Am Water Resour Assoc 2012;14(5):3e7.
182 M.C. Larsen