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8What is the state of tropical montane
cloud forest restoration?
T. M. Aide and M. C. Ruiz-Jaen
University of Puerto Rico, San Juan, Puerto Rico, USA
H. R. Grau
Universidad Nacional de Tucuman, Tucuman, Argentina
ABSTRACT
The conversion of tropical montane cloud forest
(TMCF) to pastures and agricultural lands has been
an important activity in this life zone for many years.
Although forest clearing and grazing continues, in
some areas, changing political, economic, and social
drivers have led to the abandonment of marginal
areas. These dynamics provide an excellent
opportunity to study the rates of secondary
succession and test different restoration strategies.
The two major questions addressed in this review
are: “What factors control rates of TMCF recovery
once pastures or agricultural lands are abandoned?”,
and “What restoration strategies can be used to
overcome barriers to regeneration and accelerate
forest recovery?” To answer these questions a
literature review was carried out. Because few
restoration projects have been conducted in TMCF as
such, the conclusions are mainly based on studies in
tropical montane forests at large. Competition with
invasive grasses and ferns and poor seed dispersal
appear to be the most important factors limiting
natural forest recovery. To overcome these barriers,
one of the most cost-effective ways to accelerate
recovery is to promote the establishment of shrubs,
which help to shade out invasive grasses and ferns
and create more appropriate conditions for seedling
growth. Although this strategy can reduce
competition, planting will also be required to recover
a species composition similar to intact forest because
most forest species are rarely dispersed far from
forest stands.
INTRODUCTION
Tropical montane ecosystems have been transformed by
human use for hundreds of years. The most common causes
of forest transformation have been agriculture and grazing,
but timber harvesting has also contributed to forest degrad-
ation. Although clearing for illegal crops – e.g. poppy,
Papaver somniferum (Cavelier and Etter, 1995) or coca,
Erythroxylum coca (Bedoya, 1997) – continues to threaten
many areas of intact montane forest in Latin America, in
many other regions, agricultural and grazing lands are being
abandoned, often because of a loss of agricultural product-
ivity associated with accelerated erosion. Soil erosion can be
even worse where fire is part of the management practice
(Cavelier et al., 1998, 1999). For example, in the Sierra
Nevada de Santa Marta in Colombia, a long history of land
use, including fire, has resulted in the loss of >50 cm of soil,
which greatly limits agriculture and forest recovery (Aide
and Cavelier, 1994).
In recent years, rural to urban migration has been another
major factor influencing the abandonment of montane lands
(Aide and Grau, 2004). In some regions, armed conflicts have
stimulated rural–urban migration. For example, in Colombia,
approximately 2 million people have been displaced by civil
unrest, and the majority of these people have migrated out of
rural mountain regions (Chernick, 2000). Economic and social
changes have also stimulated rural–urban migration in areas
where small-scale agriculture on steep marginal lands cannot
compete with large-scale industrial agriculture and imported
products (Preston, 1996). In addition, many rural inhabitants,
especially young people, are attracted to cities because of greater
opportunities for education, social services, jobs, and an urban
lifestyle (Harden, 1996; cf. Grau et al., this volume).
Tropical Montane Cloud Forests: Science for Conservation and Management, eds. L. A. Bruijnzeel, F. N. Scatena, and L. S. Hamilton. Published by
Cambridge University Press. #Cambridge University Press 2010.
101
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Where rural–urban migration continues, the associated reduc-
tion in human pressure on the ecosystems could permit forest
recovery (Aide et al., 2000; Guariguata and Ostertag, 2001; Aide
and Grau, 2004). However, even when land is abandoned or
grazing intensity decreases, some forests may not recover
because the degraded system is “resilient.” Resilience of non-
forest vegetation is due to positive feedbacks that reinforce the
maintenance of the degraded state of the system (Hobbs and
Norton, 1996; Hartig and Beck, 2003; Suding et al., 2004). For
example, in many tropical areas, the grass Melinis minutiflora
invades after fires and its resinous leaves are highly flammable,
which promotes more fires and greatly inhibits forest regener-
ation (D’Antonio and Vitousek, 1992). In the South Ecuadorian
Andes, the bracken fern Pteridium arachnoideum dominates
degraded pastures and presents a major barrier to tree establish-
ment (Hartig and Beck, 2003; Gu
¨nter et al., 2009).
This review addresses the following questions:
Once pastures or agricultural lands are abandoned, what
factors control rates of tropical montane (cloud) forest
recovery?
When sites do not recover (i.e. they are in the resilient
degraded state), what restoration strategies can be used to
overcome barriers and accelerate forest recovery?
To answer these questions, a literature review was conducted
covering articles in Biological Abstracts (1997–2003), Web of
Science (1990–2004), Science Citation Index (1997–2002),
as well as The Scholarly Journal Archive (JSTOR), Springer,
and Organization for Tropical Studies databases. Initially, the
following key words were used: tropical, montane cloud forest,
restoration, reforestation, rehabilitation, and recovery. Given that
only a few articles were found with the explicit objective of active
restoration in TMCF (as defined in Hamilton et al., 1995), the
search was expanded using the following keywords: montane
forest, secondary succession, plantations, and afforestation. In
addition, references within articles identified in these databases
were used. Articles were evaluated to determine the major factors
controlling the rate of forest recovery and what management
activities were effective in accelerating forest recovery.
FACTORS CONTROLLING RATES OF
FOREST RECOVERY AND MANAGEMENT
SOLUTIONS
Studies of tropical montane (TMF) and tropical montane cloud
forest (TMCF) have identified soils, fire, seed dispersal, colon-
ization of pioneer species, and microhabitat conditions as the
major factors controlling forest recovery. Plantations were also
considered as a factor affecting forest recovery, but in other
studies plantations have been considered mainly as a management
tool (e.g. the first step in a reforestation project). The various
observations are summarized below by first discussing how each
factor affects rates of forest recovery and then presenting restor-
ation and management responses that could ameliorate the nega-
tive effects of each factor and accelerate forest recovery.
Soils
PROBLEMS
Although saturated anoxic soils (Silver et al., 1999), low nutrient
availability (Tanner et al., 1998; Stewart, 2000; Gu
¨nter et al.,
2009; cf. Benner et al., this volume; Roman et al., this volume),
compaction (Pedraza and Williams-Linera, 2003; Zimmermann
and Elsenbeer, 2008), or extensive erosion (Aide and Cavelier,
1994; Slocum et al., 2000) all can limit forest recovery, in the
present survey, few studies have identified soils as a major
limiting factor. In the context of TMCF, the prime soil charac-
teristic reported as limiting forest regeneration was soil compac-
tion associated with cattle grazing (Pedraza and Williams-Linera,
2003; cf. Zimmermann and Elsenbeer, 2008) or road construc-
tion (Olander et al., 1998). Compacted soils have been associated
with low sapling survivorship and growth (Pedraza and
Williams-Linera, 2003). In contrast, disturbed areas along tem-
porary roads or pipelines with low soil compaction had rapid
woody vegetation recovery (Malizia et al., 2004). An additional
problem of compacted soils is that they are often colonized by
grasses, which can increase susceptibility to fire, inhibit the
colonization of woody species, and make the system resistant
to forest recovery (Rosales et al., 1997; Olander et al., 1998; cf.
Hartig and Beck, 2003; Zimmermann and Elsenbeer, 2008).
MANAGEMENT SOLUTION
If soils are a limiting factor at a regional scale, this can be a
major challenge for restoration projects (Bradshaw, 1997).
Although areas can be fertilized, and soil material added, or
plowed in the case of compaction, these are expensive activities
if large areas are to be recovered (Bradshaw, 1997). At any scale,
an immediate management goal should be to reduce soil loss
(Calle, 2003). For example, a common practice is to plant or
leave strips of vegetation along the contours of a slope to reduce
soil erosion (Calle, 2003; Pedraza and Williams-Linera, 2003).
In relatively small areas, such as shallow landslips, fertilization
with nitrogen and potassium has facilitated the establishment of
tree species (Dalling and Tanner, 1995). At present, the most
widely used technique for improving degraded soils has been to
establish plantations because they increase soil nutrients and soil
organic matter, and protect the soil from erosion (Lugo, 1992;
Vanacker et al., 2007). For gullied areas, a number of mechan-
ical, but costly, techniques have been developed, but these
are beyond the scope of this review (see e.g. Blaisdell, 1981;
Hudson, 1995).
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Fire
PROBLEMS
In general, high rainfall and moisture in TMCF limit the number
and extent of fires. Fires can occur in TMCF during extended dry
periods (Asbjornsen et al., 2005; Hemp 2005; Asbjornsen and
Garnica Sanchez, this volume; Hemp, this volume #60), but they
appear to be more important in other high-elevation habitats (e.g.
paramo and dry shrub/pine forest) where there is less precipita-
tion (Hemp and Beck, 2001; Horn et al., 2001). Although this
may change in the future because of climatic drying (Hemp,
2005; Asbjornsen and Wickel, 2009; Foster, this volume), in
most TMCF settings, fire is associated with agricultural and
grazing activities (May, 1997; Scowcroft and Jeffery, 1999;
Kessler, 2000). As in other montane systems, if fires occur
frequently they can greatly reduce forest regeneration (Aide
and Cavelier, 1994; Cavelier et al., 1998; Ramirez-Marcial
et al., 2001; Duncan and Chapman, 2003a; Grau et al., this
volume) (Figure 8.1). In addition to the direct effect of killing
most woody species, fires can indirectly affect forest recovery by
increasing soil erosion and selecting for grasses and ferns. These
effects will negatively affect forest regeneration and could lead
to a resilient degraded state (Hartig and Beck, 2003; Suding
et al., 2004; Griscom et al., 2008).
MANAGEMENT SOLUTION
Fortunately, fires are still rare in undisturbed TMCF (cf. Wa
˚rd
et al., this volume), and given that agricultural activities are the
major source of fires, if a region is being abandoned, then the
frequency of fires should diminish. Where fires are a threat, they
can be controlled with firebreaks (Aide and Cavelier, 1995), fire
lookout and response teams, and education (Asbjornsen and
Garnica Sanchez, this volume). In some montane systems fire
may be used as a restoration tool. For example, in Thailand,
surface fires enhance seedling recruitment of deciduous diptero-
carp forest and pines by reducing grasses and woody lianas
(Werner and Santisuk, 1993). Similarly, in NW Argentina, fires
of intermediate frequencies can favor the expansion of Alnus
acuminata into montane grasslands by reducing competition
between tree seedlings and grasses (Grau and Veblen, 2000).
Seed dispersal
PROBLEMS
Many studies have investigated the importance of seed dispersal
as a limiting factor for natural regeneration (Aide and Cavelier,
1994; Holl et al., 2000; Oosterhoorn and Kappelle, 2000;
Zimmerman et al., 2000; Cubin
˜a
´and Aide, 2001; Gu
¨nter et al.,
2006). In virtually all studies, there is a rapid decrease in the
diversity of species and total number of seeds with distance
from the forest edge; seeds of most species are not detected
more than 20 m from the forest edge. Small wind-dispersed species
(often shrubs belonging to the Bignoniaceae and Asteraceae fam-
ilies) are an exception as their seeds can disperse further into the
abandoned lands. Contrary to this strong pattern of dispersal limi-
tation, recruitment patterns rarely show a clear procession from the
forest edge toward the center of the abandoned lands, suggesting
that seeding from adjacent forest is not always the limiting factor.
Aide et al. (2000) suggested that some species colonize pastures
when these are still actively used. If plants are capable of sprouting
after being cut or grazed, they may survive for extended periods,
and once the land is abandoned they can immediately dominate the
area. Regardless of the dispersal patterns or time of colonization,
the species that initially establish in these abandoned agricultural
lands make up a very limited sub-set of montane forest species,
suggesting that seed dispersal is a limiting factor for species
composition (Oosterhoorn and Kappelle, 2000).
MANAGEMENT SOLUTION
Different techniques have been used to increase seed dispersal
into abandoned lands. In many systems, remnant trees or shrubs
have played an important role in attracting dispersers and
accelerating regeneration (Slocum and Horwitz, 2000). Artifi-
cial perches also can attract birds and increase the seed rain
below the perch (Aide and Cavelier, 1994), but they rarely
increase seedling density (Holl et al., 2000; Shiels and
Figure 8.1. Remnant patches of montane forest in a matrix of degraded
grasslands maintained by frequent fires in the Sierra Nevada de Santa
Marta, Colombia.
WHAT IS THE STATE OF TMCF RESTORATION? 103
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Walker, 2003). A problem with artificial perches is that they do
not produce enough shade to reduce the grass cover, which can
limit the ability of seedlings to establish. Windbreaks (Harvey,
2000), fruit trees (Sarmiento, 1997a), and pioneer shrubs
(Posada et al., 2000) also attract bird dispersers and produce
more shade than artificial perches, thus making them good
candidates for increasing seed dispersal and seedling establish-
ment. For example, in NW Argentinean cloud forests, exotic
spiny shrubs (e.g. Crataegus oxyacantha) have facilitated the
establishment of native species by attracting bird dispersers
and protecting the new recruits from browsing by domestic
animals (Malizia and Greslebin, 2000). However, if the goal
of the project is to attain a species composition similar to intact
forest, seed collection, nursery activities, and planting will all
have to be major activities of a restoration project (Lamb and
Gilmour, 2004).
Colonization of pioneer species
PROBLEMS
Although seed dispersal can be a limiting factor in many sites,
grasses in abandoned pastures or early colonizers of abandoned
agricultural lands (e.g. ferns) can inhibit forest recovery. In some
cases, these species can even arrest succession. For example,
introduced African grasses (e.g. Melinis minutiflora, Pennisetum
clandestinum, Setaria sphacelata) often dominate montane pas-
tures, and once the pastures are abandoned these grasses grow
vigorously, impeding the establishment of woody species (e.g.
Colombia – Posada et al., 2000; Ecuador – Sarmiento, 1997a,b;
Zahawi and Augspurger, 1999; cf. Gu
¨nter et al., 2009; Costa
Rica – Holl, 1999; Hawai’i – D’Antonio and Vitousek, 1992)
(Figure 8.2). When the previous land use has been logging or
agricultural, ferns are often the first species to colonize the site.
In the Dominican Republic, native ferns that colonize landslides
have greatly expanded their local distribution by colonizing
abandoned agricultural lands (Garcia et al., 1994). These ferns
stabilize soils, reduce erosion, and increase soil organic matter,
but they can also inhibit the establishment of tree species
(Slocum et al., 2000). For example, Dicranopteris pectinata
has colonized and dominated abandoned agricultural fields for
>20 years because the fern produces a thick root mat on the soil
surface, which acts as a physical barrier and inhibits the estab-
lishment of other species (Figure 8.3; Slocum et al., 2000).
A similar case has been documented for the bracken fern Pteri-
dium arachnoideum in the South Ecuadorian Andes by Hartig
and Beck (2003). At other sites, exotic trees and shrubs (e.g.
Ligustrum spp. and Citrus spp.) have colonized abandoned agri-
cultural lands and areas with a history of intense grazing (e.g.
Grau and Aragon, 2000), and these species can also dominate a
site for many generations (Tecco and Rouges, 2000; Schulenberg
and Awbrey, 1997; Lichstein et al., 2004).
Figure 8.2. A three-year-old abandoned pasture dominated by
Pennisetum clandestinum in the Cordillera Central, Colombia.
Figure 8.3. Dicranopteris pectinata fernlands in the Cordillera Central,
Dominican Republic.
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MANAGEMENT SOLUTION
A diversity of approaches will be needed to eliminate or reduce
the densities of these grasses, ferns, and exotic trees and shrubs.
This constitutes a major challenge given that they often cover
extensive areas. In Colombia, a fast-growing tree, Montanoa
quadrangularis (Asteraceae), has been used to expand forest
cover into pastures by shading grasses and enhancing seedling
recruitment of forest species (Calle, 2003). Posada et al. (2000)
demonstrated that low-density grazing reduced the cover of
Melinis minutiflora and Pennisetum clandestinum in Colombia,
and permitted the colonization of wind-dispersed shrub species
that helped to shade out the grasses and create a microhabitat
appropriate for montane forest species (Figure 8.4). In the case of
the fern Dicranopteris pectinata in the Dominican Republic, fire
(May, 2000) and manual removal (including the root mat;
Slocum et al., 2004) were techniques that allowed many native
species to colonize. Surprisingly, the fern was slow in recover-
ing, and the shade produced by shrubs was already sufficient
to limit any future dominance, demonstrating that the fern-
dominated resilient state was easily shifted to a recovering state.
Eliminating invasive trees and shrubs will be much more difficult
and costly, however, and must be accompanied by extensive
planting of native species and long-term maintenance to avoid
the recolonization of the exotic species.
Microhabitat conditions
PROBLEMS
At a more local spatial scale, microhabitat conditions can influ-
ence colonization, growth, and survivorship and, in turn, the
composition of a recovering forest. Even if seeds disperse into
a site, to colonize, seeds must avoid predators. Few studies have
identified seed predation as a major limiting factor in montane
forest, but ant (Pedraza and Williams-Linera, 2003), cattle
(Alvarez-Aquino et al., 2004; Griscom et al., 2008), and rabbit
(Holl and Lulow, 1997) herbivory can affect plant growth and
survivorship in early stages of forest recovery. Other studies have
shown that poor mycorrhizae colonization of roots has limited
plant growth (Berish and Ewel, 1988; Rosales et al., 1997; Holl
et al., 2000). Mycorrhizal limitation is most common in soils that
are highly degraded (e.g. by mining; Miller and Jastrow, 1992).
Other factors that can reduce growth and survivorship include:
freezing at high elevation (Scowcroft et al., 2000; cf. Hemp,
this volume #12), low nutrient availability (Bruijnzeel and
Veneklaas, 1998; Gu
¨nter et al., 2009) and photo-inhibition (Loik
and Holl, 1999).
MANAGEMENT SOLUTION
The easiest way to avoid seed predators is to plant seedlings.
Seedlings will still be vulnerable to herbivores, but few studies
have identified herbivores as a limiting factor in abandoned
agricultural lands (see Holl and Lulow, 1997). Furthermore, if
seedlings are being produced for a restoration project they can be
inoculated with mycorrhizae to promote better growth and sur-
vivorship. Other studies have shown that nurse plants can modify
the microhabitat conditions and promote the establishment of
more sensitive species (Rhoades et al., 1998; Posada et al.,
2000; Scowcroft et al., 2000; Calle, 2003; Weber et al., 2008).
For example, in Colombia seedling density and richness were
higher below remnant trees in pastures in contrast to open areas
in pastures (Calle, 2003), whereas Posada et al. (2000) found
that low-density grazing promoted the establishment of wind-
dispersed shrubs, which shade out the grass. In Ecuador, small
nitrogen-fixing trees in pastures ameliorated microclimate con-
ditions and increased soil nitrogen levels, which, in turn, favored
the establishment and growth of montane species (Rhoades et al.
1998; cf. Weber et al., 2008; Gu
¨nter et al., 2009). On Hawai’i,
efforts to restore Metrosideros polymorpha and other native
species in exotic grasslands have been unsuccessful because
of high seedling mortality due to freezing. At this site, Acacia
koa survived better than other species, and once established,
it helped to reduce frost damage to seedlings planted below it
(Scowcroft et al., 2000).
Figure 8.4. A three-year-old abandoned pasture adjacent to the
site depicted in Figure 8.2 which had low-intensity grazing and was
dominated by Asteraceae shrubs.
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PLANTATIONS
In the literature, plantations have been treated as both a
factor limiting forest recovery and as a technique for acceler-
ating forest recovery. Plantations can help ameliorate all the
barriers discussed above. Plantations can improve soil condi-
tions by protecting soils from erosion (Wiersum, 1984;
Vanacker et al., 2007), and improving their nutrient content
by fixing nitrogen and adding organic matter (Lugo, 1992). In
montane ecosystems, a landscape that has increased forest
cover will be less vulnerable to fires than areas dominated
by grasslands and agricultural areas. In addition, plantations
can attract dispersers, which will increase plant diversity in the
understory community (Parrotta, 1992). Furthermore, planta-
tions will eliminate most grasses and ferns by producing
shade, and thus improve the microclimate conditions for many
forest species.
Although plantations can improve conditions for forest
regeneration, the long-term impact on forest recovery depends
on the species used, the management techniques, and the goals
of the project. In Uganda, forest regeneration in pine planta-
tions was faster than in grasslands, because recurrent fires set
back forest recovery in the grasslands (Zanne and Chapman,
2001). However, when these grasslands were protected from
fire, forest regeneration was similar to that within the planta-
tion (Duncan and Chapman, 2003a,b). In Colombia, although
plantations (e.g. Pinus,Cupressus,Eucalyptus,andAlnus)
helped improve soil characteristics and native tree species
established in the understorey, species diversity in secondary
forest of similar age was much higher compared with planta-
tions (Cavelier and Tobler, 1998; Cavelier and Santos, 1999;
Murcia, 1997; cf. Ho
¨lscher et al., this volume). These studies
suggest that, in the absence of fire, natural regeneration is a
better strategy for recovering biodiversity than establishing
plantations.
If the motive of a project is to restore natural vegetation,
are single-species plantations a useful restoration tool? The
answer is positive if soils are highly degraded and plantation
species can protect and improve soil conditions. Plantations
canalsobeincorporatedinalong-termrestorationplan,where
there is a need for short-term economic benefits (timber,
carbon credits), but after harvesting, native species in the
understory should be allowed to grow. Plantations may also
be useful for shading out grasses or ferns and attracting dis-
persers of native species, but if the final goal is a diverse
montane forest, plantation trees should not be established at
high densities. In many other cases, plantations do not seem
necessary or appropriate. Secondary forest of similar age will
support a (much) greater diversity of native species in
comparison with plantations, and at a much lower cost (cf.
Ho
¨lscher et al., this volume).
SYNTHESIS
Will tropical montane clould forest recover without intervention?
In many cases it appears that TMCF will recover, and studies have
estimated the recovery time to be between 65 and 200 years
(Weaver, 2000; Kappelle, 2001; Luna et al., 2001; Silver et al.,
2001). The recovery time will clearly depend on the kind, duration,
and intensity of previous land use, but it will also depend on what is
the measure of recovery. Although plant richness may recover in 65
years, it may take centuries to recover the species composition and
fauna similar to intact forest. As shown by Ko
¨hler et al.(this
volume), this is particularly true for the epiphyte layer in TMCF.
Ruiz-Jae
´n and Aide (2005) have shown that the majority of restor-
ation projects only measure a few structural variables and plant
richness, and few studies incorporate measures of the fauna or
ecosystems processes. As the field of restoration ecology matures,
it is necessary to incorporate more variables (e.g. fauna – Murcia
et al., 2001; Medina et al., 2002; Dunn, 2004; ecosystem process –
Ruiz-Jae
´n and Aide, 2005) as measures of recovery.
In other cases, aggressive pioneer species, fire, degraded soils,
or lack of seeds will produce feedbacks that can maintain the
system in a degraded state with no or very slow recovery. How
can the recovery process be accelerated and the shift from a
resilient degraded state to a state of recovery be facilitated?
The results of this review suggest that, in the majority of cases,
competition with grass and ferns is the major factor limiting the
initial stages of forest recovery in tropical montane systems, and
seed dispersal of mature forest species limits later stages of
recovery. To overcome the barrier of aggressive herbaceous
species, low-density grazing or manual removal is often suffi-
cient to initiate secondary succession. If native shrubs do not
establish rapidly, fast-growing trees, possibly plantation species,
can be used to shade out herbaceous species and attract dis-
persers. These strategies should produce a species-diverse sec-
ondary forest. If the goal of a project is to restore the species
composition of a mature montane forest, it is recommended to
establish a nursery of mature montane forest species and to plant
these into the site once the herbaceous cover has been reduced.
HOW CAN RESTORATION ECOLOGY
CONTRIBUTE TO THE FUTURE
OF TMCF?
In many regions, old threats to TMCF, such as clearing for
agriculture or grazing, or intensive logging continue (e.g.
Mosandl et al., 2008; cf. Mulligan, this volume). Although
economic development in the lowlands may reduce land use
intensity in many montane areas, development is also accompan-
ied by expanding infrastructure, which can impact TMCF forest
(e.g. in the form of wind turbines, communication towers,
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pipelines and roads; Young, 1994; Malizia et al., 2004).
A potentially much greater concern is the impact of global
climate change on TMCF (Pounds et al., 1999; Foster, 2001;
Lawton et al., 2001; Pounds and Puschendorf, 2004; Foster, this
volume; Nair et al., this volume). These impacts should be
mitigated, but our collective restoration experience in TMCF is
extremely limited. A recent review of tropical restoration showed
that the majority of projects are located in the lowland forest
zone, with only 13% conducted in TMCF (Meli, 2003).
On the other hand, if the trend of rural–urban migration con-
tinues in Latin America, large areas of marginal pastures and
agricultural lands will be abandoned, and much of this area will
be in TMCF. Puerto Rico is a dramatic example of rural–urban
migration, agriculture abandonment, and forest recovery. Forest
cover increased from <10% in the late 1940s to >40% at
present, following socio-economic changes associated with eco-
nomic globalization (Rudel et al., 2000; Grau et al., 2003).
Although Puerto Rico is an extreme example, a similar process
is occurring in other areas of Latin America (Zweifler et al.,
1994; Preston et al., 1997; Southworth and Tucker, 2001; Rudel,
2002). How should these abandoned lands in the TMCF zone be
managed? Most of these areas will be left to natural regeneration,
if only due to financial limitations. In many cases, this will be an
appropriate “management” strategy, particularly given the low
cost. In other areas where aggressive herbaceous species have
arrested or greatly slowed succession (i.e. resilient degraded
sites), or areas of special conservation importance, active restor-
ation could help to accelerate the recovery process.
As restoration projects expand forest cover, positive feedbacks
should reinforce regeneration processes. For example, as forest
cover and connectivity increase, fire frequency will decrease, and
seed dispersal and animal populations should increase. Understand-
ing the dynamics of these feedbacks, and developing dynamic
models should be part of future restoration projects and be incorpor-
ated into the international research agenda, such as the Forest
Landscape Restoration project (Maginnis and Jackson, 2005;
www.unep-wcmc.org/forest/restoration/globalpartnership/index.
htm). To meet these present and future restoration/management
challenges, it is important to get beyond talking about restoration
or applying results from other lifezones, and begin a coordinated
effort to understand how TMCF can be restored. Payment for
environmental services is a possible approach to stimulate future
restoration efforts (e.g. Costa Rica – Rodriguez Zun
˜iga, 2003;
cf. Tognetti et al., this volume; Calvo-Alvarado et al., this volume).
ACKNOWLEDGEMENTS
During the preparation of the manuscript the authors received
support from the NASA-IRA program and the Dean of Graduate
Studies and Investigation (DEGI) of the University of Puerto
Rico. The International Institute of Tropical Forestry of the
U.S. Forest Service assisted with the literature search and travel
expenses. The comments of Becky Ostertag, Zoraida Calle,
Sampurno Bruijnzeel, and Larry Hamilton improved the
manuscript.
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