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African Studies Quarterly | Volume 17, Issue 2 |June 2017
Hannah V. Herrero is a University of Florida Geography Ph.D. candidate studying long-term vegetation health and
land cover change of savanna landscapes in and around protected areas in southern Africa. She wishes to pursue a
career combining research and application to ecosystem management.
Jane Southworth is Professor and Chair, Department of Geography, University of Florida with research interests
based on the study of human-environment interactions within the field of Land Change Science. Her particular focus
is on remote sensing of vegetation dynamics and savanna systems.
Erin Bunting received her Ph.D. from the University of Florida and is currently a geographer with the United States
Geological Survey. In late 2017, she will become Director of Remote Sensing & GIS Research and Outreach Services at
Michigan State University. Her research focuses on remote sensing of landscape change across global drylands.
Brian Child is Associate Professor, Department of Geography and Center for African Studies, University of Florida
with a research focus on community-based conservation, parks management, and environmental / resource
economics conducted throughout much of East and Southern Africa.
http://www.africa.ufl.edu/asq/v17/v17i2a4.pdf
© University of Florida Board of Trustees, a public corporation of the State of Florida; permission is hereby granted for individuals
to download articles for their own personal use. Published by the Center for African Studies, University of Florida.
ISSN: 2152-2448
Using Repeat Photography to Observe Vegetation Change Over
Time in Gorongosa National Park
HANNAH V. HERRERO, JANE SOUTHWORTH, ERIN BUNTING,
and BRIAN CHILD
Abstract: Protected areas are important conservation tools, as they can be managed to
preserve baseline ecosystem health, including that of vegetation dynamics.
Understanding long-term ecosystem dynamics within a protected area enables one to
understand how this static park landscape responds to outside pressure and changing
drivers. In this study, a repeat photography analysis was used to analyze changes in the
vegetation pattern and abundance at Gorongosa National Park in Mozambique across
seventy-two years of the parks history. Archival photographs dating as far back as 1940
were selected for sites that could be relocated in a subsequent field visit in 2012.
Qualitative and quantitative analysis on vegetation abundance by structural group was
undertaken using Edwards’ Tabular Key. Results when comparing the photographic
pairs show that, in general, tree cover has increased on average from 25 percent to 40
percent over the last seventy-two years. This 15 percent increase may be in response to
environmental drivers such as human management, herbivory, fire, and precipitation.
Contrary to many recent studies on shrub encroachment in southern Africa, this study
finds an increase in tree cover. Such analysis and results are valuable in that they
demonstrate long-term ecological change within a managed protected area.
Introduction
Dryland ecosystems, defined as water limited systems, cover more land globally than any other
ecosystem type and range from desert to savanna landscapes in their structure. Globally,
dryland ecosystems are projected to experience broad scale change in composition and
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productivity related to global environmental change, specifically climate change. Dryland
expansion has been noted globally and caused by a net reduction in soil available moisture due
to changes in precipitation regimes. This global expansion of drylands has resulted in savanna
like composition in new and ever expanding areas.
1
Savannas, such as those that dominate
Gorongosa National Park (GNP) sustain up to one-third of the world’s human population and
13.6 percent of global Net Primary Productivity.
2
Savannas are a globally distributed ecosystem
that can be defined as grassland with scattered trees or shrubs. Across southern Africa upwards
of 54 percent of the landscape is deemed savanna and these areas are highly heterogeneous in
composition.
3
The primary drivers of savanna pattern and process that produce differential
responses of vegetation cover are fire, grazing, climate variability and agriculture.
4
Monitoring land-cover changes in savanna ecosystems can be difficult because of their
highly heterogeneous composition.
5
However, monitoring these system changes is important to
ecosystem function and diversity. Therefore, it is critical to monitor land-cover changes across
these sensitive savanna regions as events such as shrub encroachment and landscape
degradation have been noted in the literature.
6
Up to 31 percent of southern Africa’s savannas
may be considered degraded.
7
Landscape degradation in this context is defined as a decrease in
vegetation cover (or even a complete loss), a shift in species towards annual plants, shrub
encroachment (vegetation densification), long-term overgrazing, weakening perennial grasses,
and/or a decrease in biodiversity.
8
Shrub encroachment is an ecological process observed across
Southern Africa, including South Africa and Botswana.
9
However, a literature review shows
that across Mozambique, particularly in and around GNP, studies on and quantification of
shrub encroachment have not taken place. The present study aims to remedy this. Shrub
encroachment is of particular concern to ecologists because of the transformation of habitats,
that is to say, the loss of one habitat and the gain of a fundamentally different, and often less
desirable, type.
10
Potential impacts of shrub encroachment are biogeochemical and biophysical
changes. Factors that catalyze shrub encroachment are the exclusive use of moisture by the
encroaching shrub species, high amounts of soil nutrients, low fire frequency, and high cattle
selectivity.
11
Remote measurements of past landscapes can be used to study change over time. One way
this can be done is via the use of traditional photography, specifically a process called repeat
photography. Repeat photography is the practice of taking a photograph from the same
physical perspective at different points in time. This is a technique that was first developed in
Europe in the 1880s to evaluate landscape change with glaciers.
12
It has since expanded across
all ecosystems types globally.
13
Repeat photography is a valuable tool because it gives us a
much longer time-series of data than satellite remote sensing alone, which only goes back to the
mid-1970s, and in terms of more useful spatial and temporal analysis, the mid-1980s. We also
have a much higher spatial resolution with ground-point photography.
14
Gorongosa National Park (GNP), where this research was undertaken, is a mid-latitude
highly heterogeneous savanna landscape, which has undergone significant human influence
across the last 70 years.
15
The goal of this study is to assess vegetation change, in particular
related to tree and shrub covers using repeat photography with two related research questions.
This research therefore asks: (1) has there been a change in tree cover? (2) has there been a
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change in shrub cover to indicate any potential shrub encroachment as has happened across
many other savanna park landscapes?
Study Area
Gorongosa National Park, whose area is around 4000 km2, is located at approximately 18.2°S
and 34.0°E (Figure 1). The average temperature in the park fluctuates between 15°C and 30°C
with mean annual precipitation (MAP) from 1981 to 2016 of ~1000 mm (Figure 2), but it has
slightly decreased over time. The minimum total annual precipitation was ~650 mm in 1992 and
the maximum total annual precipitation was ~1625 mm in 2001. In GNP, the wet season lasts
from November to March, which is driven by the migration of the Intertropical Convergence
Zone. The park is located south of the Zambezi River, north of the Pungwe River, west of the
Indian Ocean, and east of Mount Gorongosa. The elevation of the park ranges from around
fifteen meters in the lowlands to 1800 meters on the mountaintop. The Gorongosa ecosystem is
very complex and contains multiple types of habitats including savanna, miombo, and montane
forest, but the main focus of this project is on the savannas.
Figure 1. Study Area Map of GNP and its Location within Africa
Sample sites 1-6 are marked for the repeat photography locations.
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In 1920, during the time of the Portuguese colonization of Mozambique, Gorongosa was set
up as a Game Reserve. Gorongosa was established as a national park by the Portuguese
government in 1960. However, shortly thereafter, in 1964, the war for independence from
Portugal began and lasted until 1974, when Mozambique was declared independent. Based on
aerial surveys at the end of the 1960’s and early 1970’s an estimated 2,200 elephant, 14,000
buffalo, 5,500 wildebeest, 3,000 zebra, 3,500 waterbuck, 2,000 impala, 3,500 hippo, and herds of
eland, sable, and hartebeest were all found within GNP.
16
These surveys provide the “baseline”
for current conservation in the park. In 1977, a civil war broke out and lasted for fifteen years.
At various points during the war, the headquarters for each side was within GNP and many
battles took place inside the park and at nearby Mount Gorongosa.
17
These wars resulted in
GNP losing from 90 percent to 99 percent of its large animal populations.
18
In addition to this,
during the period from 1993 to 1996 a variety of illegal hunting ventures existed within GNP
and killed even more of the already devastated wildlife populations. This extreme loss of
wildlife diverges from natural systems processes, and these population numbers in Gorongosa
are opposite of what was observed in most of southern Africa’s protected areas during this
period (1970-2005).
19
Figure 2. Total Annual Precipitation Amounts Interpolated Over the Park 1981-2016
Source: Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS)
In 2004, the Gorongosa Restoration Project began as a partnership between the Carr
Foundation and the Mozambican government. Gorongosa has adopted a management and
development model that balances conservation with the needs of the people surrounding the
park by increasing tourism, science, and community investment in the park.
20
As part of the
conservation effort, park managers have been conducting baseline ecosystem monitoring,
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which is why managers are interested in determining how vegetation is changing within the
park. In 2010, three years into the Gorongosa Restoration Project, an aerial survey was
conducted and found that wildlife within the park had increased by about 40 percent since the
beginning of the restoration project.
21
Methods
This study analyzed ground based photographs from at least two dates, one from the 1900s and
the second from 2012, to describe the vegetation change in GNP, which has a large digital
archive with several hundred landscape photos and many hours of video. After sorting through
the photographs and videos, nineteen photographs or still captures of the video from six sites
around GNP were selected as these were deemed useable, meaning the location was identifiable
and the photos could be repeated today.
During the 1930s several structures were built inside the park, some of which at least still
partially stand today. The majority of the photographic evidence presented here focuses on the
area around these structures because these were the most accurately identifiable. One of the
best examples of this is the “Lion House” on the edge of the floodplain. Many of the
photographs are focused around the Lion House because this was one of the main areas tourists
would visit within the park. When these structures were built, the area directly under them was
cleared, and therefore the vegetation was altered. The structures and roads then fell into
disarray with the political turmoil and fighting.
There are seventy-two years of data presented in this study, though not at a consistent time
interval. The earliest photograph analyzed was from 1940, and the dates then range through the
early 1970s (see tables for the exact year of each photograph). Each of the sites of the earlier
images was located in July 2012 (during the dry season) and a “repeat” photograph was taken.
To insure as much compatibility as possible these “repeat” photographs were taken from a
similar vantage point and distance as the original photograph, and a similar focal length and
angle was also used. In the historical archive, the exact camera and lens were not recorded.
Therefore, a basic 18-55 mm lens was used, unless otherwise specified. In certain cases that were
further away a longer lens of 70-300 mm was used. Seasonality was accounted for because the
park is closed during the rainy season, so all comparison photographs were from the dry season
in the past. Using shadows, the time of day was matched between the historical photographs
and the shots taken in 2012. At each of the sites a GPS location was also recorded. Vegetation
plot analysis and qualitative field notes, including dominant vegetation types, and overall
landscape type were also recorded (Table 1) for the current analysis.
The changes in the photographs were quantified by using Edwards tabular key to structural
groups and formation classes to determine what habitat cover was present at each of the dates
(Table 1).
22
This key includes Dominant Height Class, Total Plant Cover >0.1 percent, and Total
Plant Cover <0.1 percent (bare ground) to distinguish between Woodland (tree dominated),
Bushland (tree and shrub dominated), Shrubland (shrub dominated), Grassland (grass
dominated), and Herbland (herb dominated) in southern Africa. The same research method was
implemented by the first author throughout the analysis to ensure consistency, and the process
was as follows: historical and July 2012 photographs were placed side-by-side and broken into
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Table 1. Edwards Tabular Key for Vegetation Structure used for the Vegetation Samples
Taken at Each Repeat Photography Site.
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four quadrants with a grid overlay. Then percentages of each type of vegetation were estimated
in each quadrant by visual quantification, summed, and recorded. The percentage change over
time was then calculated using the formula:
Results
The data from the estimates of vegetation cover show that overall tree cover has increased from
1940 to 2012 (Figure 3). The historic photographs have an average of 25 percent tree cover,
whereas the new photographs show an average of 40 percent tree cover. This is an average
increase of 15 percent through time. The exception to this is in the second of the three
photographs 15 Chitengo (Site 4, the base camp of the park) and the photographs taken at the
location named the Hippo House (Site 6) where there was a loss of vegetation cover.
Table 2. Repeat Photographic Sites
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Note: Sites, with name, year taken, photographs analyzed, percent tree cover recorded
in historic photography and 2012 photograph and percent change, and a 2012 Google
Earth Image of each site, with the star representing where the site is. (For details of
where the site is spatially within the park, see Figure 1.)
The photographs at Site 1 were taken on the edge of floodplain, where the “Lion House”
still stands and four cabins used to stand (Table 2). At site 1 in a 1960 photograph, the majority
of the shot is low closed grassland and behind that is short closed woodland. This area may
have been cleared previously to allow construction of these structures. From this perspective in
2012, tree growth is prominent. This area is now classified as closed short woodland. The
dominating genus is Vachellia (previously Acacia), and the dominant species is Vachellia
xanthophloea (fever tree). These trees have grown in closer to the site of the original structures,
though only the foundations remain today. The grass composition has remained similar.
The photograph taken at Site 2 was just outside the National Park gate (Table 2). In a 1957
photograph, there was a much lower density of trees in the background with a significantly
taller bare tree rising up above the canopy in the background. From this perspective in 2012,
there are several larger branches in the foreground, and there are more trees and scrub on either
side of the road just inside the gate. While both of these photographs would have vegetation
classified as tall closed woodland, the tree cover has greatly increased in density in the recent
image.
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Figure 3. Percent of Tree Cover in GNP, at the six selected sites
Note: Percent of tree cover determined from 19 photographic sample pairs, beginning in 1940 to
2012 (For order of site dates, see table 2 above).
The photograph taken at Site 3 was at the old Pungwe River crossing just outside the park
gates (Table 2). In a 1957 photograph, the site contained some bare ground with tall closed
shrubland with short closed woodland behind that. This area was previously cleared in order to
make a roadway to the original entrance into the park before the current paved road was
created. From this perspective in 2012, grass growth is prominent, and this area is now
classified as tall closed grassland with tall open woodland behind it. The grass composition was
fairly homogenous in 2012. The area around the old river crossing is now used for agricultural
production.
The photograph from Site 4 is of Chitengo, which is the center of human activity in the park
(Table 2). In a 1967 photograph, there are several large trees in both the left and right of the
frame. A photograph taken from the same perspective in 2012 shows that the tree closest to the
concrete on the left hand side is missing. However, when we look at the next image comparison,
we can see that there are overall more trees in 2012, and the trees that are there are larger and
denser.
The photograph from Site 5 is an area that contains the Vunduzi River in the foreground
with the Bunga Inselbergs and Mount Gorongosa in the background (Table 2). At site 5, in a
1965 photograph, there was open short grassland a few hundred meters on either side of the
Vunduzi River. This grassland was bordered by short closed woodland. When this shot was
retaken in 2012, riparian vegetation has filled in the area around the Vunduzi River. Further out
from the river vegetation density and coverage increased into a short bushland, which is a
result of shrub encroachment. Some of the taller trees have been replaced with shorter bushes.
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The photograph taken at Site 6 was at the Hippo House, alongside Lake Urema (Table 2). In
a 1970 photograph, the site contained many tall trees, and was classified as tall open woodland.
At the time this area was used as a lunch spot for tourists in the park. In 2012, all of the trees
have disappeared. Even the scrub palms have largely been eliminated. Left now is ground with
very short grass cover, and a few taller patches of grass.
Discussion and Conclusion
Until recently, we were limited to ground-point and aerial photographs for spatial-temporal
studies of landscape change across GNP. However, this research is unique in that it provides a
much longer timeframe and finer spatial resolution than most imagery-based studies can. It
does however find similar trends to recent studies, such as Daskin et al. (2015) who also found
increased tree cover throughout the park landscape. Unlike other parks in the region, we see an
increase in tree cover and not shrub encroachment. As mentioned earlier, shrub encroachment
has a variety of negative impacts on ecosystems, so this increase in tree cover may indicate that
GNP vegetation is healthier relative to other parks in the region, as a result of the unique
situation of removal or herbivory in their park during the wars. As such, this provided an
unbelievable natural experimental situation for herbivory removal impacts and also highlights
the importance of such tools as repeat photography which provides a much longer time frame
for study. This also provides an excellent basis for park management, as clearly for tourism
parks need to maintain wildlife numbers but also ensure maintenance of the larger ecosystem
health. This longer-term study provides an exciting and underutilized approach on which
management and future plans can be based. Repeat photography approaches should be used
across a suite of park landscapes where historical photographic datasets exist in order to add a
different “on the ground” perspective, get longer-term data (pre-dating satellites), and finer
temporal resolution going forward, as well as much finer spatial resolution. Utilizing this
technique can also target specific areas of interest. Given the new digital age and the progress of
tourism in this park, many photographs are now being taken and stored for potential future
use.
As already noted, this study shows, via a comparison of historic photographs to ones taken
in 2012, that tree cover has increased on average from 25 percent to 40 percent (15 percent
overall) over the last seventy-two years across Gorongosa National Park. However, this study
did not capture specific evidence of shrub encroachment; rather, the growth of the tree cover
was quite clear overall.
23
Even though there are similar savanna landscapes throughout the
lower part of the park, we cannot make blanket statements about the entire park. The individual
areas studied do offer great insight into general conservation patterns and can assist managers
in making decisions. Aside from providing ecological baselines, managers are also interested,
from a historical perspective, in seeing how the park has changed over the last seventy-two
years. There are some areas in the park that demonstrated extensive growth of vegetation, like
the Lion House with trees, the Pungwe River crossing with trees, and the Bunga Inselburgs with
riparian trees and also shrubs. Hippo House looked very different in that there was almost a
complete loss of tree cover.
Multiple factors may contribute to changing vegetation structure. One factor is
management. For example, in the repeat photography of the Lion House, it may be the case that
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Vachellia were present until humans built infrastructure. The National Park gate and Chitengo
are also managed areas that have been maintained in a similar way throughout history,
especially given that the Restoration Project has reinstated tourism in the park. At the Bue
Maria River crossing, what was once a maintained road has been abandoned, but part of the
area is now devoted to agriculture as well. Other factors may be more natural. In the repeat
photograph of Mount Gorongosa with the Vunduzi River and Bunga Inselbergs, we saw a great
deal of change over time (Table 2). The source of this river is radial flow from Mount
Gorongosa.
24
As evidenced in the photograph, the river has meandered further to the south (to
the left in the photo in Table 2) since 1965. This may suggest a change in the flood regime of this
river from the mountain, which in turn affects the distribution of rich soil and riparian and
floodplain associated vegetation around the river.
25
The repeat photograph of the Hippo House
showed that there has been tree cover loss. Given the history of this area, it is unclear whether
this area was cleared during the war by military forces to better use this house on stilts as a
watchtower, or if excessive flooding from the Lake is responsible for this loss of trees.
26
Regardless of the reason, the area has not returned to tree cover and so is more likely a natural
change and highlights one of the few areas of tree decline, which is mostly likely due to water.
The landscape of GNP is sculpted by numerous drivers of spatial heterogeneity including:
herbivory, climate variability, and fire.
27
Large animals, such as elephants, are at least partially
responsible for the management of Vachellia seedlings through browsing and trampling.
28
In a
study in Tanzania, it was found that decreasing the number of herbivores (due to poaching) led
to an increase in shrub and tree vegetation.
29
During the War for Independence and civil wars,
90-99 percent of all the large mammals in Gorongosa were extirpated.
30
Managers have been
implementing a plan to increase the number of megafauna (mostly herbivores, such as
elephants, hippos, buffalo, and eland) to maintain vegetation and overall health of the
ecosystem. As of 2015, the number of herbivores from the beginning of the project in 2007 has
increased by 40 percent.
31
Therefore, it will be critical to continue to monitor this landscape as
wildlife numbers are increased in an attempt to return the park to its earlier floral and faunal
state, which is one of the primary goals of the GNP management team.
Another one of the main drivers in these savanna systems is climate, including
precipitation and temperature.
32
Changes in precipitation can contribute to changes in land
cover type.
33
In this park, there is a mean annual precipitation of ~1,000 mm from 1981 to 2016
(Figure 2), (with a minimum total annual precipitation of ~650 mm in 1992 and ~1625 mm in
2001). Given the slight decrease in total annual precipitation through time, this park may be
susceptible to some land cover change. However, research has shown that the main climate
driver in landscapes below 700mm mean annual precipitation (MAP) is precipitation.
34
In these
lower precipitation zones, there is a strong linear relationship between metrics of biomass (for
example, spectral-based indices such as NDVI) and precipitation.
35
In the transition zone of 700-
950mm MAP both precipitation and temperature co-dominate the vegetation cover. Though
above 950mm MAP, temperature and fire dominates the landscape pattern. Precipitation in
Gorongosa National Park fluctuates near these MAP boundaries, so each of this climate factors
(precipitation, temperature, and fire) may play a role in land cover change. Under climate
change, these factors should be monitored further.
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Fire frequency has shown conflicting impacts of sprouting of vegetation. In general, where
fires are more frequent, grass is promoted, and where fires are less frequent, trees are
promoted.
36
The dominant tree genus that has increased in the documented sites is Vachellia (see
Site 1 photos in Table 2). In other studies, Vachellia was also found to be one of the primary
increasing tree genera and pioneers in Africa.
37
After reconstructing the fire history of GNP over
the last half of the 20th century, Daskin et al. 2015 found that fire frequency has not significantly
decreased over time.
38
No single driver is responsible for the vegetation mosaic across GNP,
but with significant herbivory change, some climate changes, and slightly differing fire regimes,
we are potentially seeing a broad scale alteration of the resultant vegetated landscape.
Future research would continue with the utilization of satellite imagery, beginning in the
1980s, in order to extend the spatial extent. Time series metrics and further discrete data
classification of imagery would be ideal to evaluate moderate-term (over the last 30 years)
vegetation change and the changing pattern of cover across the entire landscape.
Acknowledgements
The lead author would like to thank the Gorongosa Restoration Project, Carr Foundation, and
Gorongosa National Park for the generous opportunity to study in Mozambique.
Notes
1
Chapin 2002; Monserud et al. 1993.
2
Feng and Fu 2013; Ciais 2009.
3
Chapin, 2002
4
Andela et al.,2013; Campo-Bescos et al. 2013; Archer et al. 1995; Van Auken 2000;
Bond et al. 2003; Asner et al. 2004.
5
Skarpe 1992.
6
Campbell and Child 1971; Ringrose et al. 2008.
7
Vogel and Strohbach 2009.
8
Ibid.
9
Campbell and Child 1971; Grossman and Gandar 1989.
10
Walker et al. 2004.
11
Moleele 2002.
12
Webb, 2010.
13
Byers 1987; Crimmins and Crimmins 2008.
14
Hottman and O’Connor 1999.
15
Ringrose et al. 2008.
16
Tinley 1977.
17
Parque Nacional Da Gorongosa Website 2015; Stalmans 2012.
18
Stalmans 2012.
19
Craigie et al. 2010.
20
Roe 2004.
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21
Parque Nacional Da Gorongosa Website 2015.
22
Edwards 1983.
23
Daskin et al. 2015.
24
Tinley 1977.
25
Richter and Richter, 2000.
26
Stalmans 2012.
27
Moleele et al., 2002.
28
Cumming and Cumming, 2003.
29
Prins and van der Jeugd 1993.
30
Stalmans 2012.
31
Parque Nacional Da Gorongosa Website 2015.
32
Andela et al. 2013; Campo-Bescós et al. 2013.
33
Andela et al. 2013; Campo-Bescós et al. 2013; Moleele et al. 2002.
34
Campo-Bescos et al. 2013.
35
Bunting et al. 2017.
35
Bond et al. 2003.
35
Hottman and O’Connor 1999.
36
Bunting et al. 2017.
36
Daskin et al. 2015
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