Felling trees, furthering malaria: links
between deforestation and disease in developing nations
First online: 9 May 2019
Kelly
F. Austin
Kelly
F. Austin is an Associate Professor of Sociology and Director of the Global
Studies program at Lehigh University. Her research focuses on examining trends
in health and environmental outcomes across developing nations. Austin conducts
cross-national, quantitative research, as well as fieldwork on malaria, coffee
production, and other health and environmental inequalities in rural Uganda.
–––––––––––––––––––––––––––––––––––––––––––
DOI: 10.3197/jps.2019.3.2.13
Licensing: This article is Open Access (CC BY 4.0).
How to Cite:
Austin, K.F. 2016. 'Felling trees, furthering malaria: links between deforestation and disease in developing nations'. The Journal of Population and Sustainability 3(2): 13–32.
https://doi.org/10.3197/jps.2019.3.2.13
–––––––––––––––––––––––––––––––––––––––––––
Malaria
represents a leading illness and cause of death throughout areas of the Global
South. Since malaria is transmitted through the bite of the Anopheles mosquito,
environmental conditions are paramount in understanding malaria
vulnerabilities. A burgeoning area of research connects anthropogenic
deforestation and subsequent land-use changes to the expansion of mosquito
habitats and malaria outbreaks. This paper explores those literatures, and also
examines the drivers of deforestation in the Global South to demonstrate how
population pressures, agricultural production, and rural migration patterns
underlie motivations for deforestation and land transformation in poorer
countries.
Keywords:
Malaria; deforestation; land-use change; rural migration; population growth.
Introduction
Malaria
is a parasitic disease that has plagued human societies throughout history, and
continues to represent a major threat to health and well-being today. In 2017,
there were over 219 million cases of malaria, including nearly 500,000 deaths
(WHO, 2019). The majority of deaths from malaria are among infants, children,
and pregnant women. In fact, malaria claims the life of a child under the age
of 5 years every two minutes (WHO, 2019). The continued impact of malaria is
somewhat of a conundrum, as malaria represents a preventable and curable
infection. However, new trends in antibiotic resistance may threaten this
claim. As the female Anophelesmosquito
transmits malaria to humans, changes to the environment are also paramount in
facilitating new and continued vulnerabilities (e.g. Yasuoka and Levins, 2007).
Nearly
half of the world’s population is at risk of malaria (WHO, 2019). Most malaria
cases and deaths occur in Sub-Saharan Africa, but regions of Latin America,
South-East Asia, the Eastern Mediterranean, and the Western Pacific also
represent malaria hotspots. Ninety countries currently have ongoing malaria
transmission (WHO, 2019). Although recent decades have wrought significant
gains in controlling malaria and preventing deaths, there are clear signs that
these trends are reversing. While malaria rates declined from 2000 to 2015, in
the most recent years, rates of incidence have increased. According to the latest
World Malaria Report, released in November 2018, there were 219 million cases
of malaria in 2017, up from 217 million cases in 2016 (WHO, 2019). The
re-emergence of malaria is likely tied to many different factors, such as
persistent poverty, insecticide resistance, and perhaps, most notably,
anthropogenic environmental change (e.g. Pattanayak et al., 2006).
As
mosquitoes represent the disease vector for malaria, malaria vulnerabilities
are deeply connected to environmental conditions. Even seemingly minor changes
to the environment and local ecologies can have profound impacts on mosquito
habitats, breeding cycles, biting rates, and other factors that affect malaria
transmission. Over the last two decades in particular, a wealth of research
from the fields of public health, epidemiology, and entomology focused on
deforestation and land-use change in explaining heightened malaria
susceptibilities for rural populations. This article will explore this vein of
research highlighting the factors and diverse processes that link forest loss
to malaria. These factors include alterations to landscapes and local
ecologies, changes to the availability or composition of water at breeding
sites, and influxes of migrant labor. Furthermore, a focus on the causes of deforestation
in developing nations illuminates how population pressures and rural migration
patterns spur forest loss and heighten vulnerabilities to malaria for
marginalized rural populations. Although growing urban populations and export
agriculture operations are often implicated as key drivers of forest loss in
the Global South, closer examination reveals these as distal causes that shape
rural migration to forest frontier zones. The populations most at risk for
frontier migration are also among the most vulnerable to malaria due to their
poor socio-economic status and lack of access to healthcare.
Malaria: A parasitic and
pervasive disease
Malaria
is caused by Plasmodium parasites. There are five parasite
species that cause malaria in humans, with Plasmodium falciparum and Plasmodiumvivax representing
the most common parasite strains (WHO, 2019). These species of parasites have
distinct regional zones, as P. falciparum is responsible for the overwhelming
majority of malaria cases in Sub-Saharan Africa and South-East Asia, and P. vivax is
most common in the Americas (WHO, 2019). Plasmodium parasites
rely on two hosts throughout their lifecycle: a mosquito and a human (or another
mammal) (Mayxay et al., 2004). Only around 30 of the 400 different species of Anopheles mosquito
can act as vectors for the parasite, and only the bite of a female Anophelesmosquito spreads the parasite from one
person to another (Mayxay et al., 2004; Neafsey et al., 2015; WHO, 2019). The
different types of malaria parasites cause different variations of the disease
in humans, with some forms being milder than other strains. Just as the type of
parasite species varies by region, different types of Anopheles mosquitoes
tend to transmit the parasites on different continents. For example, Anopheles gambiae is the main vector for malaria in Africa,
while Anopheles darlingi is
the key mosquito associated with malaria transmission in the Americas (WHO,
2019).
The
key malaria vector mosquito species tend to be most active between dusk and
dawn. Anopheles mosquitoes lay their eggs in still or
slow-moving water bodies. Eggs become larvae and eventually transform into
adult mosquitoes. While male mosquitoes are essentially pollinators that feed
solely on plant matter, the female mosquitoes also need blood to nurture and
feed their eggs (Mayxay et al., 2004; Neafsey et al., 2015; WHO, 2019).
Rainfall patterns, temperature, and humidity also impact the number, survival
rates, and breeding activity of mosquitoes (e.g. Norris, 2004); transmission
generally accelerates in warm, wet places where the mosquito lifespan is
longer.
Human
immunity represents another important factor affecting whether or not malaria
is acquired, and, if so, the severity of the illness. Individuals that have
been exposed to malaria several times throughout their life can acquire partial
immunity that reduces the chance of severe disease and death (WHO, 2019). For
this reason, most malaria deaths occur in young children and among populations
that have not been previously exposed to the disease.
Malaria
causes fever and flu-like symptoms, including chills, nausea, vomiting, and
aches or joint pains (CDC, 2019; WHO, 2019). Symptoms manifest around one to
two weeks after the infected mosquito bite. During this incubation time, an Anopheles mosquito
can bite an infected human and transmit the parasite to another. Especially
among youth and non-immune groups, malaria can quickly lead to death. For
example, in infants, some deaths have been recorded just 18 hours after initial
symptoms appeared. If untreated, malaria leads to severe anemia, respiratory
distress in relation to metabolic acidosis, and cerebral malaria, where there
is inadequate blood flow to the brain and other vital organs, leading to
permanent disability, even if the malaria is eventually able to be treated
effectively (CDC, 2019; WHO, 2019).
Early
diagnosis of malaria is essential for management of the disease and prevention
of death (CDC, 2019; Stratton et al., 2008; WHO, 2019). Microscopy and rapid
diagnostic tests are the most common and effective ways of diagnosing the
disease (WHO, 2019). However, these methods may be inadequate, especially in
poor areas that often lack sufficient expertise, health personnel, and
diagnostic equipment (e.g. Bates et al., 2004). Currently, there are many drugs
available to combat the infectious parasite, but reduced effectiveness and
antibiotic resistance represent major limitations. The most effective and
popular drug consists of artemisinin combination treatments (ACTs) (WHO, 2019).
Other drug treatments, including quinine and chloroquine, are now largely
ineffective at treating malaria due to the development of resistance. In
addition, recent studies document increased tolerance to ACTs in many regions,
leading to concerns over the potentials of widespread antibiotic resistance
(e.g. Hastings and Ward, 2005; WHO, 2019).
Both
the malaria parasites and the Anopheles mosquitoes that carry them are highly adaptable
and resilient species. Their resilience in part explains why malaria has been a
leading cause of death among humans for centuries, if not millennia. In fact,
the first evidence of malaria parasites was found in mosquitoes preserved in
amber from the Paleogene period approximately 30 million years ago. While
malaria is an “old” disease, current transformations to the environment may be
producing “new” vulnerabilities, including expanding mosquito habitats,
intensifying biting rates, and exposing fresh populations that lack immunity
and appropriate access to primary health care.
Links between deforestation and
malaria
Human
transformations to the environment have become so immense that the current
geological age is now denoted the “Anthropocene”. Forest loss represents one of
the most significant global environmental problems, as new estimates now assert
that since humans started cutting down forests, around 50% of all trees have
been felled (National Geographic, 2018). Global tree cover loss reached a
record 29.7 million hectares (or 73.4 million acres) in 2016. The loss is 51%
higher than the previous year, totaling an area about the size of New Zealand
(Weisse and Goldman, 2017). Deforestation contributes to other environmental
concerns, including global climate change and biodiversity loss. Additionally,
the felling of trees impacts human well-being, especially as deforestation is
linked to furthering malaria vulnerabilities in a wide range of studies (e.g.
Norris, 2004; Lima et al., 2017; Yasuoka and Levins, 2007; Vittor et al., 2006,
2009).
Clearing
forests alters local ecosystems in a variety of ways, including changing local
temperatures, soil conditions, water resources, and the ecology of flora and
fauna. These modifications can have a notable impact on mosquito habitats,
lifecycles, and behaviors. Additionally, deforestation predominantly involves
the conversion of forest land to agriculture and livestock grazing areas (FAO,
2018), and these activities also influence the mosquito disease vector in a
variety of ways. While the number of studies exploring such links have
burgeoned over the last few decades, the observed connection between forest
loss and mosquitoes was articulated over 50 years ago; Livingstone (1958: 554)
comments that “it is only when man cuts down the forest that breeding places
for A[nopheles] gambiaebecome almost infinite.” Other researchers also illustrate links
between land cover change and malaria outbreaks at much earlier points in human
history, such as in Ancient Rome (e.g. O’Sullivan et al., 2008).
Current
studies examining the links between forest loss and mosquitos generally utilize
a mix of satellite or remote sensing data to ascertain forest loss. This
typically is combined with entomology data that measure mosquito larvae, the
presence of parasites, or biting rates, as well as epidemiological data or
secondary data on malaria cases, often gathered from local health centers or
through direct malaria microscopy testing. Much of this research is conducted
in areas of the Brazilian or Peruvian Amazon (e.g. Barros et al., 2015; Hahn et
al., 2014; Vittor et al., 2006, 2009; Yanoviak et al., 2006), as well as other
areas in South America, Sub-Saharan Africa, and South East Asia (e.g. Afrane et
al., 2008; Basurko et al., 2013; Bonneaud et al., 2008; Himeidan et al., 2012;
Kweka et al, 2016; Nath et al., 2012; Saxena et al., 2014; Vanwambeke et al,
2007). While these types of studies are typically concentrated in isolated
areas within specific countries or regions, the consistencies of the findings
across geographic zones speak to the existence of larger-scale patterns. A few
cross-national studies linking deforestation rates to malaria incidence support
this claim (e.g. Austin, 2013; Austin et al., 2017); however more
cross-regional studies of forest loss and the incidence of mosquitoes or
malaria would greatly contribute to the generalizability of these findings.
The
processes linking forest loss to malaria vulnerabilities are diverse but,
fundamentally, many studies find that there are more malaria parasites or
mosquito larvae in deforested areas or areas on the forest fringe (the edge of
deforested areas) in comparison to areas of intact forest (e.g. Barros et al.,
2015; Bonneaud et al., 2008; Caldas de Castro et al., 2006; Nath et al., 2012;
Olson et al., 2010; Saxena et al., 2014; Vanwambeke et al, 2007; Wayant et al.,
2010). Deforestation’s impact on local temperatures is a subject of detailed
examination in current research. As forest cover is lost, temperatures
increase, and generally, the incubation period of malaria parasites and the
speed of larval development is inversely correlated with temperature (Afrane et
al., 2008, 2012; Kweka et al, 2016; Himeidan et al., 2012; Nath et al., 2012;
Patz et al, 2006). Amazingly, a mere half-degree centigrade increase in
temperature can translate into a 30% to 100% increase in mosquito abundance
(Pascaul et al., 2006). For example, Afrane and colleagues (2008) find that the
overall parasite infection rate of mosquitoes in deforested sites is greatly
increased compared with that in forested sites. Overall, due to changes in
temperature and humidity, vectorial capacity in the Kenyan highlands is
estimated to be 77.7% higher in the deforested sites than in the forested sites
(Afrane et al., 2008).
Other
studies have found that indoor temperatures increase in dwellings located in
deforested and frontier zones (e.g. Afrane et al., 2012; Himeidan et al., 2012;
Kweka et al, 2016). A rise in indoor temperatures attracts more mosquitos into
dwellings at night during prime biting hours, and can also increase the biting
rates of mosquitoes (Afrane et al., 2012; Kweka et al., 2016). An increase in
biting frequency means that mosquitoes feed more frequently on humans and,
thereby, enhance rates of malaria transmission, potentially exponentially.
Vittor
and colleagues (2006) arrive at a similar conclusion in their research
conducted in the Peruvian Amazon. They tested fifty-six sites with varying
degrees of deforestation over several weeks and found that Anophelesdarlingi was
captured in the greatest quantities at sites with little remaining forest.
Furthermore, deforested sites had biting rates that were more than 278 times
greater than in areas that were predominantly forested (Vittor et al., 2006).
In
addition to a rise in outdoor and indoor temperatures, researchers highlight
other processes connecting deforestation to malaria risk. Many emphasize that
water mediates the relationship between deforestation and malaria, and that
felling trees greatly impacts aquatic environments that promote mosquito
development (e.g. Barros et al., 2015). For example, puddles, ponds, and
slow-moving streams that exist under thick forest canopy are too heavily shaded
for mosquitos and tend to be highly acidic, as much organic debris, such as
falling leaves, lands in such pools. But water pools in deforested areas and
frontier zones have greater exposure to sunlight and a lower level of acidity,
raising numbers of mosquito eggs and larvae (e.g. Norris, 2004). While
completely sun-exposed ponds are generally not preferred by mosquitoes,
researchers have found that semi-shaded ponds in frontier zones or on forest
fringes have elevated levels of mosquito larvae (e.g. Barros et al., 2015).
Micro dams, that slow or stop water flow, are also created when fallen trees
obstruct streams and rivers, and represent prime mosquito habitats (e.g. Barros
et al., 2015). Thus, felling trees can expose ponds and streams to the correct
amount of sunlight and potentially expand mosquito habitats (e.g. Norris,
2004).
It is
important to emphasize that deforestation simply represents the first step in a
series of land-use changes, and that population growth and expansions in
agriculture represent the prime motivation for deforestation in most areas
(e.g. Confalonieri et al., 2014; FAO, 2018; Hahn et al., 2014; Norris, 2004;
Pattanayak et al., 2006; Saxena et al., 2014). The secondary growth that is
created by crops and plantations often affords mosquitos habitats with the
right level of shade and protection, and many studies have found an abundance
of mosquito larvae in recently deforested agricultural areas (e.g. Basurko, et
al., 2013; Yanoviak 2006; Vittor et al., 2006, 2009). Additionally,
agricultural production leads to the creation of dams, irrigation systems,
ditches, and roads, all of which greatly expand the availability of standing
water, thereby proliferating mosquito breeding sites, with a resultant rise in
malaria rates (e.g. Basurko, et al., 2013; Bauch et al., 2015; Confalonieri et
al., 2014; Hahn et al., 2014; Silva-Nunesa et la., 2012; Yanoviak et al.,
2006). Selective logging also provides the right mix of sun and shade that
mosquitoes prefer, leading to significant increases in malaria incidence in
nearby populations (e.g. Hahn et al., 2014). Remarkably, mosquito eggs and
larvae can develop in just a few millimeters of water, thus fallen plant parts,
tree-holes (left-behind rotted out stumps), and even the hoof-prints of cattle
can quickly become prime mosquito environments (e.g. Norris, 2004; Yanoviak et
al., 2006).
Certainly,
the proximity of humans and human residences in relation to mosquito habitats
shape malaria vulnerabilities (e.g. Vanwambeke et al, 2007). Malaria epidemics
can occur when environmental conditions suddenly favor habitat proliferation
and hence transmission (WHO, 2019). They also can occur when people with low
immunity move into areas with intense malaria transmission, for instance to
work on agricultural plantations or cattle ranches. Many studies illustrate the
link between deforestation and malaria incidence as facilitated by the migrant
workforce, who often come from other rural areas or urban centers, and thus
have limited or no immunity to malaria (e.g. Barbieri et al., 2005; Basurko, et
al., 2013; Bauch et al., 2015; Pattanayak et al., 2006). For example, Barbieri
and colleagues (2005) find that malaria cases in Brazil are often concentrated
among work-age males, defying traditional trends in this disease where infants,
children, and pregnant women typically are most vulnerable. Indeed, rates of
malaria in the Amazon are often highest among migrant workers, and the high
mobility of migrant workers also increases the potential spread of malaria to
additional populations. They argue that rural settlement areas are susceptible
to the outbreak of malaria in their initial stages due to the intense contact
between settlers and mosquitoes, especially during land clearance activities
(Barbieri et al., 2005).
Migrant
agricultural workers also face other sources of susceptibility. They tend to
live in poorly constructed or temporary dwellings that do not provide barriers
to mosquitoes at night (Barbieri et al., 2005; Basurko, et al., 2013). They are
often without mosquito nets, the main form of malaria prevention during
nighttime hours (Basurko, et al., 2013). Similarly, many migrant settlements
have outdoor kitchens and living spaces, where workers gather at dusk and after
dark when Anopheles mosquitoes are most active. Furthermore,
non-immune migrant workers typically work in remote areas that lack health
centers and basic public health infrastructure. Thus, there can be significant
delays between contracting malaria and getting adequate medical intervention,
which only increases the possibilities of transmitting the disease to others
when mosquitoes bite those with active symptoms (Barbieri et al., 2005; Bauch
et al., 2015).
Humans
can also affect malaria vulnerabilities in newly established agricultural areas
and frontier zones in other ways. For example, many note the importance of fish
ponds in facilitating close human-mosquito interactions; studies in areas of
the Brazilian Amazon link environmental changes wrought by the emerging local
aquaculture industry to increased malaria risk (e.g. Olson et al., 2010; Lima
et al., 2017). Farmers and local populations often establish water collection
sites and fish ponds in semi-shaded areas very near settlements for
convenience, but this creates mosquito breeding sites very close to where
humans reside (e.g. Bauch et al., 2015). Indeed, some primary deforestation is
done specifically to create areas for fish ponds and wells (e.g. Olson et al.,
2010; Lima et al., 2017). Although fish can eat mosquito larvae, these studies
clearly document that fish pools tend to have very large populations of larvae,
and that the fish are not effective in quelling mosquito populations. For
example, Olson and colleagues (2010) find that ponds, wells, and fish farms
larger than 50 meters in circumference have a significant abundance of Anopheles darlingilarvae.
Similarly, Vittor and colleagues (2006) find that large ponds and fish farms
surrounded by some secondary vegetation were the most common A. darlingi breeding sites, and also that mosquito
biting rates are especially high in the deforested zones near established fish
ponds.
Some
researchers carefully point out that during and in the immediate years after
deforestation, mosquito larva numbers, parasite levels, or malaria cases tend
to be very high, but can then fall off after a site has been completely cleared
for many years (e.g. Barros et al., 2015; Caldas de Castro et al., 2006;
Guerra, Snow, and Hay, 2006; Olson et al., 2010). For example, Caldas de Castro
and colleagues (2006) argue that rates of malaria begin to decline and remain
low about 10 years after complete forest removal. Indeed, the bulk of this
research emphasizes that “frontier” zones on the edge of deforested areas or
forest “fragments” pose the highest risk (e.g. Lima et al., 2017). As mentioned
briefly earlier, this is due to the fact that mosquito larvae do not prefer
fully exposed sun-lit areas (e.g. Barros et al., 2015). However, it is
important to stress that most areas that are deforested are subsequently used
for agriculture and ranching, which do tend to create prime mosquito habitats
and introduce non-immune populations. Furthermore, areas that are deforested
and left fallow eventually become areas of secondary re-growth, fostering
additional mosquito breeding sites, given the shrub and semi-shade conditions
that eventually emerge (e.g. Barros et al., 2015; Nath et al., 2012; Vittor et
al., 2009).
It
should also be acknowledged that not all studies find a link between land cover
change and malaria, as some demonstrate no link or point out that deforestation
may decrease malaria rates over the long-term, as explained above.
Inconsistencies in the literature may be due to differences in research methods,
land change definitions, study approach or design, scale, or locational focus
(Lima et al., 2017). However, the body of research that asserts clear links
between deforestation and malaria is large and growing, and far exceeds the
limited number of studies that find no demonstrable link (e.g. Lima et al.,
2017).
Trends and causes of
deforestation in developing nations
Zones
where malaria is endemic are also areas that face some of the highest rates of
deforestation, including tropical and sub-tropical regions of Sub-Saharan
Africa, Central and South America, and South East Asia (e.g. FAO, 2018).
Deforestation is not a natural phenomenon, but rather results predominantly
from human activities. The main causes of deforestation in developing nations
include expansion in agriculture, fuel wood consumption, livestock ranching,
logging, and infrastructure, such as road creation (e.g. FAO, 2018; Population
Action International, 2011). It is important to note that these proximate
causes tend to vary across regions. For example, logging is very prominent in
S.E. Asia, while cattle ranching characterizes many areas of South America, and
fuel wood consumption is highest in Sub-Saharan Africa, particularly East
Africa (e.g. Carr, Suter and Barbieri, 2005; FAO, 2018; Rudel, 2005). However,
agricultural development characterizes each of these areas and is often
emphasized as the main driver of forest loss globally (e.g. FAO, 2018;
Population Action International, 2011). Certainly, overpopulation and
population growth underlie each of these causes. Population pressures on
forests in rural areas can manifest in both direct and indirect ways, as will
be explained below (e.g. Carr et al., 2005; Rudel, 2005).
The
total world population is expected to increase from 7.6 billion to 10 billion
by 2050 and global demand for food is also expected to increase by 50% during
this period (FAO, 2018). The nations with the highest rates of forest loss tend
to have large populations and high population growth rates, such as in Brazil,
Indonesia, DR Congo, and Nigeria (FAO, 2018). Fertility rates remain high among
many poor nations, especially for rural residents that live on forest
frontiers; for example, family sizes in rural areas of the Global South
commonly exceed 7 children (Carr et al., 2005; Clark, 2012). Also, many
Sub-Saharan African nations in particular have an extreme “youth bulge” where
over 50% of the population is under the age of 18. Such demographic patterns
will increase the momentum of population pressures on forests.
Small
frontier farmers who live on the edges of forested expanses drive the bulk of
deforestation in less-developed nations for settlement and food production
(Carr et al., 2005; Lopez-Carr and Burgdorfer, 2013). Subsistence farmers have
big families, and large household sizes put immediate pressure on forests
(Dolisca et al., 2007; Rudel, 2005). Indeed, many researchers point out that
despite increases in commercialized agriculture in developing nations, it is
small-scale and subsistence farmers that are responsible for the bulk of direct
forest felling (Carr, 2009; Lopez-Carr and Burgdorfer, 2013). While rural to
urban migration and upwards trends in urbanization are significant, as will be
discussed in more detail below, there is a notable and often overlooked level
of rural-to-rural migration which puts extreme burdens on forests (e.g. Carr
2009; Rudel, 2005).
Indeed,
the highest rates of fertility and household-level population growth will
continue to occur among rural people living in or on the edges of forests.
Rural or subsistence farmers in less-developed nations are typically poor and
rely on cleared land for household food production (e.g. Dolisca et al., 2007;
Rudel, 2005). Their agricultural production is expansive rather than intensive,
due to a lack of money to afford fertilizers or farm machinery and the ample
availability of household labor (Lopez-Carr and Burgdorfer, 2013). As household
size continues to increase and soils slowly become depleted over time, these
rural families move or expand farm areas, deforesting in order to maintain and
expand yields (Clark, 2012; Dolisca et al., 2007; Kong et al., 2019; Lopez-Carr
and Burgdorfer, 2013).
These
populations are often termed “frontier migrants”, and although logging
industries or commercial agriculture firms are most often implicated as the
main culprits in global forest loss, it is these small-scale farmers that are
directly responsible for the highest levels of actual felling, especially in
tropical and old-growth forests (e.g. Carr, 2009; Lopez-Carr and Burgdorfer,
2013; Kong et al., 2019). As children mature in frontier households, they
follow the examples of their parents and expand to new areas to support their
growing families (e.g. Carr et al., 2005). Rural frontier migrants tend to be
poor, have low levels of education, and have very limited wage labor prospects,
thus they aim to establish new farmlands as a source of household security and
resource provision (Carr, 2009; Kong et al., 2019; Rudel, 2005). Indeed, the
most pressure is put on forests when rural population growth is high and
households are poor (Jha and Bawa, 2005).
Although
rural population growth overall has declined over the years, largely due to
migration to urban areas within developing nations, deforestation rates have
remained steady or even increased in most developing nations. In fact, the
World Resources Institute reports that 2017 was the second-worst year on record
for tropical forest loss (Weisse and Goldman 2018). These trends suggest that
even amid declining rural population levels, the rate of forest-clearing per
farmer has increased (Lopez-Carr and Burgdorfer, 2013). This is likely due to
increased land fragmentation, land consolidation, and heightened soil
depletion, facilitating rural-to-rural migration to new areas by established
households or second-generation households (e.g. Carr, 2009; Kong et al., 2019’
Lopez-Carr and Burgdorfer, 2013; Rudel, 2005).
Many
researchers also note the importance of land tenure insecurity in promoting
deforestation among rural farmers (e.g. Dolisca et al., 2007; Lopez-Carr and
Burgdorfer, 2013; Rudel, 2005). Frontier migrants moving to new areas deforest
in order to make claim to land in regions where there are no formal regulations
or land titles, or in areas where land ownership is loosely regulated. Those
without land titles are thus pressured to convert forested land to agriculture
as fast as possible, leading to rapid felling. Rural people without land titles
are more likely to migrate to new areas on the forest frontier in comparison to
rural subsistence farmers with land titles (Carr, 2009).
Urbanization
and agricultural commercialization or agricultural exports are also recognized
as key drivers of deforestation in developing nations, albeit indirectly.
Indeed, consumption levels of forest products, such as food and timber, are
growing globally, and most of this consumption takes place in urban centers or
developed nations far from the sites of forest loss in rural areas of the
Global South (e.g. Carr et al., 2005; DeFries et al., 2010). However, this
remote demand remains significant. Growing urban populations may be less
dependent on solid fuels, but still demand food, and the diets of urban
residents are increasingly reliant on meat, which creates elevated forest
resource pressures (Carr et al., 2005; DeFries et al., 2010). Researchers
emphasize that large-scale cattle ranchers and commercialized agricultural
firms may not be responsible for as much primary deforestation as it seems, but
rather, are significant in pushing out small-scale rural peasants who have
already deforested (e.g. Carr, 2009; Carr et al., 2005; Lopez-Carr and
Burgdorfer, 2013). As lands become consolidated and sold off to large-holders,
this indirectly motivates deforestation by pushing frontier farmers into new
unclaimed areas where they initiate primary forest loss to re-establish
production and gain tenure to land (e.g. Carr et al., 2005; Lopez-Carr and
Burgdorfer, 2013). In this way, political-economic or core-periphery
relationships, related to the acquisition of environmental space in poorer
nations to support consumption levels in more affluent areas globally, do play
an important role in promoting deforestation in less-developed nations, though
this is hard to quantify or measure directly.
Conclusion
The
World Health Organization (2016) estimates that nearly a quarter of all deaths
worldwide are due to environmental causes. As rates of environmental
degradation and transformation continue to grow in scale and scope, this impact
is only likely to intensify. Zoonotic diseases, or diseases that affect both
humans and insects or other animals, will likely be of growing concern in the
coming decades as population growth, increased food consumption levels, and
resulting environmental degradation expand human interactions with potential
disease pathogens. Malaria, often a disease that is “forgotten” among affluent
populations, is experiencing a resurgence, in part due to human impacts on the
natural environment that expand potential mosquito habitats and influence
biting behaviors.
This
paper brings to light a large and growing body of research that links
deforestation to malaria epidemics in poor nations. Research has demonstrated
that forest loss can lead to heightened malaria vulnerabilities through a
number of mechanisms, such as raising indoor and outdoor temperatures,
increasing the availability of mosquito breeding sites, and introducing migrant
worker populations that lack malaria immunity into endemic regions. Many of
these mechanisms necessarily concern establishing water or altering current
water sources in ways that proliferate mosquito larvae, such as creating standing
water through micro dams, irrigation ditches, road building, crop residues,
tree holes, or wells and fish ponds. Overall, this research finds that
“frontier zones” located on the edge of deforestation sites, agricultural
sites, areas of secondary re-growth, and selective logging in particular offer
the right mix of sun, shade, still water sources, and nearby human settlements
necessary to increase malaria parasite levels and disease transmission (e.g.
Lima et al., 2017).
Deforestation
is caused by population pressures by people both near and far from forested
areas in malaria-endemic nations (e.g. FAO, 2018). A number of studies
emphasize that it is poor, rural frontier migrants that are most directly
responsible for felling trees and living on forest fringes (e.g. Carr, 2009;
Kong et al., 2019; Lopez-Carr and Burgdorfer, 2013). It should be emphasized
that these marginalized populations are among the least educated, have the
highest fertility rates, and are likely to have very limited access to basic health
resources. Thus, rural people that live nearest to deforestation sites where
malaria vulnerabilities are highest due to entomological and ecological factors
are also those that face the highest demographic and socio-economic
vulnerabilities to the disease. While commercial agricultural producers and
ranchers are likely contributing to forest loss indirectly by displacing rural
families, these large farms are also often located on forest fringes, can
encourage mosquitoes in other ways (e.g. irrigation, road building), and bring
in migrant workers who lack immunity to malaria or proper access to healthcare.
Thus, it is important to emphasize that patterns in deforestation and land use
in developing nations serve to not only further mosquito habitats, but also
invite populations who are most at risk of acquiring and succumbing to malaria.
Despite
significant improvements in malaria prevention, diagnosis, and treatment over
the last several decades, global malaria rates are now rising and this disease
remains a leading cause of death in many areas of the Global South (WHO, 2019).
In addition to deforestation, many scholars note potential influences of
climate change in spreading mosquito habitats (e.g. Pattanayak et al., 2006).
Heightened environmental change and population dynamics in rural areas, coupled
with increasing insecticide and antibiotic resistance, likely mean that
concerns over malaria and other mosquito-borne diseases are only going to
magnify in the coming decades. Undoubtedly, understanding and mitigating the
underlying anthropogenic causes of malaria transmission deserves vigilant
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