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Extending the baseline of tropical dry forest loss in Ghana (1984–2015) reveals drivers of major deforestation inside a protected area

  • CSIR-Forestry Research Institute of Ghana

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Tropical dry forests experience the highest deforestation rates on Earth, with major implications for the biodiversity of these ecosystems, as well as for its human occupants. Global remote sensing based forest cover data (2000 − 2012) point to the rapid loss of tropical dry forest in South America and Africa, also, if not foremost, inside formally protected areas. Here, we significantly extend the baseline of tropical dry forest loss inside a protected area in Ghana using a generalizable change detection technique. The forest cover change detection is based on the normalized difference vegetation index (NDVI) derived from historical Landsat data (1984–2015). Field measurements were carried out in dry semi-deciduous forest and in the adjacent savanna and woodland. Estimates of the canopy area index and above ground woody biomass were related to NDVI derived from Landsat 8 data. The change detection indicated significant NDVI decrease in a large area initially covered by tropical dry forest, associated with deforestation. The peak in deforestation was found to have occurred between 1990 and 2002, hereafter, the conservation status of the area was improved. A combination of remote sensing data corroborated by secondary data sources provides evidence for the almost complete clearance of a tropical dry forest inside a strictly protected area, attributable to logging and land clearing for arable farming. The NDVI change detection also revealed NDVI increase in the adjacent woodlands from 2002 to 2015, demonstrating woody encroachment. Historical fire data from the MODIS burned area product indicate that the deforested area experienced a high frequency of anthropogenic burning since 2004, which may have caused further degradation and largely prevents forest regeneration. The results show the ongoing destruction of tropical ecosystems even within ostensibly protected areas and ask for the revision of protection and management strategies of such areas.
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Biological Conservation
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Extending the baseline of tropical dry forest loss in Ghana (19842015)
reveals drivers of major deforestation inside a protected area
Thomas A.J. Janssen
, George K.D. Ametsitsi
, Murray Collins
, Stephen Adu-Bredu
Imma Oliveras
, Edward T.A. Mitchard
, Elmar M. Veenendaal
School of GeoSciences, University of Edinburgh, Crew Building, The King's Buildings, EH9 3JN Edinburgh, United Kingdom
Plant Ecology and Nature Conservation Group, Wageningen University, Droevendaalsesteeg 3a, 6708 PB, Wageningen, The Netherlands
Department of Earth Sciences, VU Amsterdam, Boelelaan 1085,, 1081 HV Amsterdam, The Netherlands
Forestry Research Institute of Ghana, UPO 63, KNUST, Kumasi, Ghana
Environmental Change Institute, School of Geography and the Environment, University of Oxford, South Parks Road, OX1 3QY Oxford, United Kingdom
Tropical dry forests experience the highest deforestation rates on Earth, with major implications for the biodi-
versity of these ecosystems, as well as for its human occupants. Global remote sensing based forest cover data
(20002012) point to the rapid loss of tropical dry forest in South America and Africa, also, if not foremost,
inside formally protected areas. Here, we signicantly extend the baseline of tropical dry forest loss inside a
protected area in Ghana using a generalizable change detection technique. The forest cover change detection is
based on the normalized dierence vegetation index (NDVI) derived from historical Landsat data (19842015).
Field measurements were carried out in dry semi-deciduous forest and in the adjacent savanna and woodland.
Estimates of the canopy area index and above ground woody biomass were related to NDVI derived from Landsat
8 data. The change detection indicated signicant NDVI decrease in a large area initially covered by tropical dry
forest, associated with deforestation. The peak in deforestation was found to have occurred between 1990 and
2002, hereafter, the conservation status of the area was improved. A combination of remote sensing data cor-
roborated by secondary data sources provides evidence for the almost complete clearance of a tropical dry forest
inside a strictly protected area, attributable to logging and land clearing for arable farming. The NDVI change
detection also revealed NDVI increase in the adjacent woodlands from 2002 to 2015, demonstrating woody
encroachment. Historical re data from the MODIS burned area product indicate that the deforested area ex-
perienced a high frequency of anthropogenic burning since 2004, which may have caused further degradation
and largely prevents forest regeneration. The results show the ongoing destruction of tropical ecosystems even
within ostensibly protected areas and ask for the revision of protection and management strategies of such areas.
1. Introduction
Deforestation and forest degradation (DD) represent a global pro-
blem (e.g. Hansen et al., 2013). West Africa is no exception where DD
has occurred for millennia, principally due to logging, charcoal pro-
duction and slash and burn agriculture (Hawthorne and Abu-Juam,
1995; Lupo et al., 2015). However, agricultural expansion and in-
creasing levels of illegal logging and re disturbance have dramatically
increased DD since the end of the 19th century (Hansen and Treue,
2008; Hawthorne and Abu-Juam, 1995; Hosonuma et al., 2012; Wardell
et al., 2003). Since 1990, the forest area in Ghana has decreased on
average by 2% every year (FRA, 2010). As a result, timber exports have
dropped markedly over the past decade: from 2008 to 2013 the total
volume of Ghana's timber exports declined by ~50% following decades
of unsustainable exploitation (Hoare and Wellesley, 2014). The loss of
natural forest in Ghana has signicant socio-economic and ecological
implications as these forests provide important ecosystem services and
represent hotspots of biodiversity (Brooks et al., 2002; Norris et al.,
In the forest savanna transition zone of West Africa, savanna and
tropical dry forest occur in close proximity under similar climatic
conditions. Tropical dry forests are particularly vulnerable to anthro-
pogenic disturbances and experience high deforestation rates (Hansen
et al., 2013). In contrast, woody encroachment of open ecosystems and
Received 4 May 2017; Received in revised form 16 October 2017; Accepted 3 December 2017
Corresponding author at: Department of Earth Sciences, Earth and Climate Cluster, Vrije Universiteit Amsterdam, Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.
Present address.
E-mail address: (T.A.J. Janssen).
Biological Conservation 218 (2018) 163–172
0006-3207/ © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (
in particular the savanna and woodlands in large areas across sub-Sa-
haran Africa is being reported (Eldridge et al., 2011; Mitchard and
Flintrop, 2013). Rising atmospheric carbon dioxide and relief from
anthropogenic pressure are cited as possible drivers of such encroach-
ment (Lambin et al., 2001; Lloyd et al., 2008; Mitchard et al., 2009;
Mitchard and Flintrop, 2013). In the forest-savanna transition zone,
deforestation and woody encroachment can occur simultaneously due
to the action of multiple anthropogenic and biophysical drivers. Dry
forest and transitional forests harbour crucial resources of genetic di-
versity, increasingly important for climate change adaptation in the
context of the predicted warming and drying trend for West Africa
(Boko et al., 2007; Millar et al., 2007).
The Forestry Department of Ghana (FDG) formally recognised the
importance of tropical dry forests in 1962 and established multi-func-
tion barrierreserves in the transitional zone between the Guinea sa-
vanna and the fringing dry semi-deciduous forest (Hagan, 1998; Hall
and Swain, 1981; Hawthorne and Abu-Juam, 1995; Swaine, 1992). The
aim was to maintain a high forest cover in order to protect natural
water sources, to provide shelter to agricultural crops from dry season
winds and to provide forest products for the surrounding human po-
pulation (Hagan, 1998). Furthermore, the FDG aimed to preserve a dry
forest belt as a re break, to prevent the increasingly severe bushres
from northern Ghana spreading southward (Hagan, 1998). Yet due to
illegal logging and the extreme El Niño drought of 1983, most of these
barrier reserves were degraded by the mid-1990s and needed urgent
protection (Hawthorne and Abu-Juam, 1995).
This paper focuses on one of these barrier reserves, the Kogyae Strict
Nature Reserve (Figs. 1 & 2). Kogyae is the only designated strict nature
reserve in Ghana, being devoted solely to scientic researchwith
entry by humans for tourism or other uses prohibited (Hagan, 1998).
The dry forest and savanna woodlands of Kogyae have received parti-
cular scientic interest recently, in the study of vegetation structure,
re ecology, plant physiology and carbon dynamics in the forest-sa-
vanna transition zone (Cardoso et al., 2016; Domingues et al., 2010;
Moore et al., 2017; Torello-Raventos et al., 2013; Veenendaal et al.,
2015). Kogyae is classied as category Ia protected area by the Inter-
national Union for the Conservation of Nature (Ofori et al., 2014). The
literature suggests that from 1984 to 1998 the population of commu-
nities inside and surrounding Kogyae tripled, mainly as a result of the
new road access opened in 1984 (Awuku-bor, 1999; Hagan, 1998). In
this period, illegal logging, agricultural expansion, charcoal production
and widespread re contributed to DD inside Kogyae (Awuku-bor,
1999; Hagan, 1998; Wildlife Department, 1994). According to a recent
survey conducted by the authors among park rangers and local people,
the local communities were removed from Kogyae by the Wildlife De-
partment in 2002. While logging and farming have been limited since
2002, res are now lit every year, both illegally by poachers as well as
by wildlife ocers to provide fresh grass for grazing wildlife (Ayivor
and Ntiamoa-Baidu, 2015). The current reserve management may thus
be in direct contradiction with the original aim, the conservation of
tropical dry forest, for which the reserve was set up.
We assess the changes woody cover that has occurred inside Kogyae
in the past three decades using Landsat-derived NDVI in a multi-decadal
change analysis. Thereby, we add quantitative spatiotemporal data to
the existing, mostly anecdotal, history of Kogyae from 1986 to 2015. In
addition, the climate and re record are used to provide insights into
these drivers of woody cover change. We aim to answer the following
research questions:
- What woody cover changes are observed and what was the extent of
- How did the drivers of woody cover change develop over time?
- How did the legal protection status of Kogyae and management
eorts contribute to the conservation of dry forest?
We use insights from the case study to understand the processes
driving woody cover changes in the Zones of Transition in Africa and to
evaluate conservation eorts in the past decades.
Table 1
Description of the Landsat images used in the NDVI change detection.
Year Date Sensor Cross-calibration formula
1984 21st of
= 1.268(NDVI
1990 22nd of
= 1.073(NDVI
) + 0.118
2002 15th of
= 1.158(NDVI
2015 27th of
Fig. 1. The location of the Kogyae Strict Nature Reserve within the dierent vegetation zones of Africa and Ghana. Vegetation zonation of Africa and Ghana adapted from Aubreville et al.
(1958) and Yengoh et al. (2010), respectively. The vegetation zonation within Kogyae is adapted from a vegetation map in the Kogyae Management Plan (Wildlife Department, 1994),
which is based on in situ observations by Schmitt and Adu-Nsiah in AprilJune 1993 (K. Schmitt, pers. com. 27 August 2015).
T.A.J. Janssen et al. Biological Conservation 218 (2018) 163–172
2. Materials and methods
2.1. Study area
The Kogyae Strict Nature Reserve (7° 1552N, 1° 0447W) is a
330 km
protected area located in the north-eastern part of the Ashanti
region in central Ghana. Kogyae experiences a bimodal annual rainfall
distribution with high precipitation from March to July and from
September to October corresponding to the passage of the Inter-
Tropical Conversion Zone across the region (McSweeney et al., 2010).
December and January are dry with 25.2 mm and 16.9 mm average
accumulated precipitation respectively. The pronounced dry season
from December to March is caused by prevailing dry and dusty Har-
mattanwinds from the north east (McSweeney et al., 2010). The mean
annual rainfall is approximately 1350 mm and mean annual tempera-
ture is 28 °C with minimum variation in temperature over the year
(McSweeney et al., 2010; Wildlife Department, 1994).
2.2. Woody cover change
2.2.1. Field data
Field estimates of aboveground woody biomass (AGB) and canopy
area index (CAI) were used to evaluate the suitability of Landsat de-
rived NDVI to detect changes in vegetation cover in the study area.
Thirty nine rectangular vegetation plots of 20 × 20 m were established
in the north-western corner of Kogyae in October 2014. The aim was to
include the entire range of woody cover present in the study area, in
order to evaluate the suitability of the NDVI in detecting gradual
changes in woody cover. The eld plots were located in vegetation
types that are dierent in both their structural characteristics and
oristic composition (Table S1), ranging from open, treeless grassland
to tall forest with a high canopy cover and biomass (Torello-Raventos
et al., 2013; Veenendaal et al., 2015). All trees with a diameter at breast
height (DBH) of > 2.5 cm were tagged, measured and identied at
species level. Tree height was estimated with a laser rangender
(TruPulse®200, Laser Technology Inc.). The projected crown dimen-
sion was estimated by measuring the diameter of the crown on two
perpendicular axes with a measuring tape. The edge of the crown was
visually determined by looking up at an angle of 180°. Geographic
coordinates were determined at the centre of each plot using a hand
held GPS device (Etrex Lengend HCx, Garmin Ltd., U.S.). For each plot
the CAI (m
canopy area/m
ground area) was calculated as the sum of
all crown dimensions divided by the plot area (400 m
). AGB was cal-
culated using the general dry forest equation from Chave et al. (2005).
Tree DBH, tree height and species specic wood density retrieved from
the Global wood density database (Chave et al., 2009; Zanne et al.,
2009) were used to calculate the AGB of the individual trees.
2.2.2. Landsat based change detection
We chose to use the Normalized Dierence Vegetation Index (NDVI)
derived from images acquired by three Landsat satellites to detect
changes in woody vegetation cover. Landsat satellites have con-
tinuously acquired multispectral images with a 30 m horizontal re-
solution since 1972. The NDVI was selected as it is a widely used and
validated index of vegetation greenness. NDVI has been used to sepa-
rate woody and grass vegetation in savannas (Archibald and Scholes,
2007) and to monitor woody vegetation changes in the Sahel (Horion
et al., 2014) and in the forest savanna transition zone of Cameroon
(Mitchard et al., 2009). Timing of image capture was chosen to max-
imise the contribution of woody vegetation to the NDVI signal and to
omit the contribution of grasses. In a similar environment in Cameroon,
Mitchard et al. (2009) found that the NDVI from images captured in the
early dry season was most sensitive to woody vegetation greenness. We
conrm this from regular in situ observations in Kogyae, as in the early
dry season (mid-November) all tree species are still in full leaf while
grasses have senesced. Unfortunately, cloud-free historical images from
mid-November covering the study area are rare in the Landsat archive,
making an annual assessment of changes in NDVI impossible. There-
fore, we selected four usable (> 70% cloud-free) images for the change
analysis that would approximate three periods in the recent manage-
ment history of Kogyae: the pre-disturbance (19841990), the dis-
turbance (19902002) and the recovery period (20022015).
Remaining clouds and cloud shadows were masked from the NDVI
images using the Fmask automated cloud detection algorithm version
3.3 using default settings (Zhu et al., 2015; Zhu and Woodcock, 2012).
The NDVI was calculated using the Landsat 8 image and values were
extracted to derive plot averaged NDVI. To evaluate the suitability of
NDVI to assess changes in woody vegetation cover in this environment,
we performed an asymptotic regression to link plot-averaged NDVI to
eld estimates of CAI and AGB. Plots 32 and 34 were excluded as they
Fig. 2. A Corona satellite photograph captured in January 1966 (A) and a Landsat 5 NDVI image from November 1984 (B) provide an indication of the initial vegetation cover inside
Kogyae. The dry semi-deciduous forest in Fig. 1 is visible as darker colours in the Corona photograph and as high NDVI (> 0.6) in the Landsat image. The bight white areas in the south
west of the reserve (NDVI < 0.5) are sparsely vegetated rocky outcrops, known as Boval vegetation. The Guinea savanna is visible as greyish colours in the Corona photograph (NDVI
0.50.6). The boundary between the forest and savanna is abrupt, accentuated by annual res that generally extinguish at the forest edge (Swaine, 1992).
T.A.J. Janssen et al. Biological Conservation 218 (2018) 163–172
were dominated by a few large trees resulting in unrealistically high
AGB values for this environment of > 700 Mg ha
(see Table S1).
The dierent Landsat sensors exhibit dierences in sensitivity and
spectral band designation that can provide errors in the change detec-
tion. To minimize these errors we use a cross-calibration method to
calibrate the three historical NDVI images to the NDVI image of
November 2015 (Mitchard et al., 2009). For the cross-calibration pro-
cedure, 100 points were selected to represent pseudo-invariant target
areas in undisturbed tropical forest fragments, on roads and rocky
outcrops. A linear regression was then applied to obtain the calibration
equation for the 1984, 1990 and 2002 images (Fig. 3). The calibrated
NDVI images were compared pairwise (i.e. 19841990, 19902002,
20022015) to calculate the relative change in NDVI (ΔNDVI) in every
time period, using the following equation:
The magnitude and direction of change was established by scaling
ΔNDVI in terms of standard deviations (SDs) away from no change
(ΔNDVI = 0). We use the average SD (0.048) of change in the three
examined periods obtained within the borders of the reserve. For more
details about the change detection method, see Mitchard et al. (2009).
To examine how ΔNDVI diered between the initial land cover
types in our study area, principally savanna and dry forest, we used the
earliest Landsat image available from November 1984 to derive a land
cover map. We used all seven spectral bands of the image in a random
forest supervised classication (Breiman, 2001) with 50 randomly
sampled training samples (100100 m). Because there is no eld data
available from 1984 to train the classication, we visually assigned the
training samples to either forest, savanna or boval vegetation using the
vegetation map and Corona satellite image in Fig. 1 and 2, respectively,
as a reference.
2.3. Precipitation and re
Monthly accumulated precipitation from January 2000 to January
2016 was retrieved from the tropical rainfall measuring mission
(TRMM) (GIOVANNI, 2015). The monthly precipitation data was area
averaged for a rectangular area around Kogyae (NE = 7° 43,0° 83;
SW = 7° 0,1° 24). Fire data was collected from the Moderate Re-
solution Imaging Spectroradiometer (MODIS) Burned Area product
(MCD45A1) which contains date of detected burning at a 500 m hor-
izontal resolution. The data is acquired since the year 2000 by the
MODIS sensor on-board the Terra and Aqua satellites. The separate
monthly tiles were merged to derive one raster with the day of burning
in the dry season (October March) of every year. This resulted in 14
raster datasets containing the day of detected burning, from the dry
season 20012002 to the dry season of 20142015. From these datasets
the total area burned in every month of the dry season from 2000 to
2015 was calculated.
3. Results
3.1. Linking eld data to the NDVI
Field estimated AGB was strongly related to eld estimated CAI
= 0.75, p < 0.0001, n = 37, Fig. 4). AGB increased linearly with
CAI, roughly 100 Mg ha
with every unit of CAI. Plot averaged NDVI
was related to both eld estimated CAI (R
= 0.66, p < 0.0001,
n = 37) and AGB (R
= 0.62, p < 0.0001, n = 37, Fig. 5).
Fig. 3. The cross-calibration regression of 100 pseudo-invariant targets that expectedly did not change in vegetation cover between 1984 and 2015. From left to right: the regression of
November 1984 NDVI against November 2015 NDVI (R
= 0.94, p < 0.0001), November 1990 against November 2015 (R
= 0.97, p < 0.0001, n = 100) and November 2002 against
November 2015 (R
= 0.94, p < 0.0001). The cross-calibration equations are provided in Table 1.
Fig. 4. Field estimated AGB regressed against the eld estimated CAI. The correlation is
particularly strong in open ecosystems with low AGB and CAI.
T.A.J. Janssen et al. Biological Conservation 218 (2018) 163–172
3.2. Changes in NDVI
The change detection procedure showed both NDVI increase and
decrease between 1984 and 2015 (Fig. 6, Table S2). The detected de-
crease in NDVI occurred almost exclusively in areas that were covered
by dry forest in 1984. Between 1984 and 1990, 10.2% of this forest area
experienced a detectable decrease in NDVI. More than half of this area
(64.7%) decreased in NDVI between 1990 and 2002. In the period
20022015 there was a loss of NDVI in 28.3% of the dry forest area.
NDVI increase occurred mainly in the savanna, with 4.4%, 4.8% and
37.6% of this area showing detectable increases in NDVI in the periods
19841990, 19902002 and 20022015, respectively.
The rate of signicant NDVI loss in the area covered by dry forest
increased from 1.7% yr.
in the rst 6 years (19841990) to 5.4%
in the following 12 years (19902002). Hereafter, from 2002 to
2015, the rate of NDVI loss in the forest area decreased again to
2.2 yr.
, cancelled out by a detectable increase of 2.4% yr.
. Based
on the observation that the decrease in NDVI occurred almost ex-
clusively in the central dry forest belt (Figs. 6 & 7) we can conclude that
this NDVI decrease is indicating DD inside Kogyae. The NDVI increase
from 2002 to 2015 in the area initially covered by forest points to a
possible post-disturbance recovery of the vegetation. The area covered
by savanna showed a 2.9% yr.
increase of NDVI in the period
20022015. Branching patterns of positive NDVI change were visible in
the NDVI change map of 20022015 that closely match the branching
patterns of small streams that ow to the north into the Sene river
(Fig. 7). This suggests that water availability is possibly driving the rate
of woody encroachment in the savanna of Kogyae.
3.3. Interactions of re and climate
The MODIS burned area product showed that res were very fre-
quent inside Kogyae (Fig. 7). In 52.3% of the reserves surface area
(180.7 km
)are was recorded every 1 to 2 years, while in another
24.1% of the area (83.3 km
)are was recorded at an interval of 2 to
3 years. The remaining 23.6% of the area (81.8 km
) experienced a re
return interval of 3 to 14 years. The area inside the reserve that burned
annually varied signicantly over the years (Fig. 8). The rst four years
of the record show relatively small burned areas. However, in the dry
season of 20042005, 56.3% of the reserve area (194.6 km
) burned.
Thereafter, the area that burned annually remained large, with the
exception of 20102011 (51.2 km
) and 20132014 (35.2 km
). There
was a signicant linear correlation between the extent of area burned in
January and February and the accumulated precipitation in January
= 0.45, p < 0.001, n = 14).
4. Discussion
We observed a number of changes in the study area that are im-
portant for the long term resource exploitation and future management
of the area and oer insights into long term dynamics of protected
areas. The NDVI change detection procedure reveals the previously
unidentied and complete clearance of a dry forest inside Ghana's IUCN
Category Ia Kogyae Strict Nature Reserve between 1984 and 2015. The
Landsat archive oered us the possibility to detect woody cover
changes in three time periods that correspond to changes in land use,
resource management and human pressure inside the reserve (Fig. 9).
The estimated rate of deforestation more than doubled from 1.7% yr
in the pre-disturbance period to 5.4% yr
in the disturbance period
(19902002). From 2002 to 2015, referred to as the recovery period,
the deforestation rate declined again to 2.2% yr
, somewhat higher
than the national deforestation rate of 2% yr
in Ghana in the same
period (FRA, 2010).
Three dierent procedures were performed to reduce uncertainties
and prevent errors of commission in the NDVI change detection ana-
lysis. First, by selecting images captured on similar times in the dif-
ferent years intra-annual or seasonal variation in NDVI is largely ex-
cluded from the NDVI change detection. Secondly, the cross-calibration
of the NDVI images from the dierent years ensures that distortions due
to sensor dierences are excluded while the cross-calibration procedure
also reduces some of the remaining seasonal variation. Finally, by
measuring NDVI change in terms of standard deviations of change
within Kogyae, only areas that show a signicant magnitude of change
are detected. The observed changes in tree cover were found to coincide
with a number of historical events in the region. (Fig. 9). The opening of
road access in 1984 contributed to the inux of migrant farmers into
Kogyae, engaged in arable farming (Mertens and Lambin, 2000;
Wildlife Department, 1994). Low initial population density and land
Fig. 5. Landsat 8 NDVI captured on the 27th of November 2015 regressed against eld estimated CAI (A) and AGB (B). CAI and AGB showed an asymptotic relationship with NDVI with
the response of NDVI to woody cover saturating around CAI = 2 m
and around AGB = 200 Mg ha
T.A.J. Janssen et al. Biological Conservation 218 (2018) 163–172
availability in protected areas have been found to act as pull factors to
migrants in Ghana and elsewhere in Africa (Awuku-bor, 1999; Hartter
et al., 2014; Zommers and Macdonald, 2012). The rate of forest clearing
for arable farming accelerated in the early 1990s (Fig. 9)(Awuku-bor,
1999; Hagan, 1998; Wildlife Department, 1994).
Two factors have been contributed to the failing of the reserve
management in protecting the dry forest of Kogyae. First, a lack of
denite policies and management guidelines led to a situation in which
the local wildlife ocers were responsible for setting out their own
management priorities (Wildlife Department, 1994). Secondly, the
community of settlers used to see the reserve as potential farmland that
was to be released to them and therefore they did not recognise the
status of Kogyae as a protected area (Awuku-bor, 1999; Hagan, 1998;
Wildlife Department, 1994). The history of Kogyae provides a textbook
example of how imposing protected areas on local communities without
strong enforcement rarely leads to successful conservation (e.g. Ineld,
2001). The extensive deforestation observed is in line with the general
trend of DD in Ghana's barrier reserves in the 1990s. Another docu-
mented example is the Tain II tributaries barrier reserve (Hawthorne
and Abu-Juam, 1995; Kyereh et al., 2007). Kogyae's watershed pro-
tection function is now lost with the eects felt by local communities.
Streams dry up completely during the dry season (Hagan, 1998) and the
water supply from boreholes is reduced, resulting in water shortages
(Ofori et al., 2014). Furthermore, dry forest tree species constitute an
essential part of rural livelihoods as many species are used for charcoal
and household fuel, fodder, construction wood, medicine and food
(Paré, 2008). The eects of DD on biodiversity inside the reserve are
expected to be substantial (Barlow et al., 2007; Green et al., 2013; Koh
and Sodhi, 2010; Norris et al., 2010).
Some of the larger mammal species previously common inside the
reserve, for example Elephant (Loxodonta africana) and Black-and-
white Colobus (Colobus polykomos) have become locally rare or extinct
(Ayivor and Ntiamoa-Baidu, 2015). Tree species that occur in the dry
semi-deciduous forest inside Kogyae are growing at the very limit of
their ecological distribution. Economically important transitional tree
species in Kogyae include Afzelia africana and Khaya senegalensis, both
classied as vulnerable in The IUCN Red List of Threatened Species.
Genotypes found in these populations are expected to represent
Fig. 6. Map showing the 1984 land cover in Kogyae derived from the random forest classication (top left). Major rivers and streams in the study area are depicted in blue: the Afram
river tributaries in the south-west and the Sene river tributaries in the north-east. Negative change in NDVI occurred mainly in the dry forest belt in the centre of the reserve, particularly
in 19902002. Large areas of the savanna in the north-east of the reserve show a signicant increase in NDVI in 20022015 associated with woody encroachment. The increase of NDVI in
this period shows branching patterns, following the course of multiple streams that intersect the savanna. Clouds were masked and shown in white. (For interpretation of the references to
colour in this gure legend, the reader is referred to the web version of this article.)
T.A.J. Janssen et al. Biological Conservation 218 (2018) 163–172
valuable genetic resources, especially in the context of climate change
adaptation (Gonzalez, 2001; Millar et al., 2007). It would be a tre-
mendous loss for the biodiversity, rural livelihoods and the forestry
sector of Ghana if these genotypes would disappear completely.
A recent survey among (retired) wildlife ocers and people from
local communities (results not shown) conrmed that in 2002, all the
farming communities residing within the reserve were expelled by the
Wildlife Department. This is conrmed by the interpretation of aerial
images (Google Earth), as the area that was deforested within the
reserve is presently not cultivated and has been clearly abandoned. The
decline of forest loss observed after 2002 (Fig. 6) can therefore be at-
tributed with condence to a tighter control on arable farming within
Fig. 7. Fire return interval from 2000 to 2015 derived from
the MODIS burned area product. The deforested area shows
frequent burning as this area experiences at least one re
every two years. Also the savanna in the north experiences
a high re frequency. Areas in the south-west are char-
acterised by a longer re return interval of 3 to 5 years.
Note that the re return interval inside Kogyae is sig-
nicantly shorter compared to the re return interval in the
direct surroundings.
Fig. 8. The extent of area burned in the three dry season months (above) and the accumulated precipitation in January (below). Associations are observable between the detected burned
area and January precipitation. In 2004, 2006 and 2014 the accumulated precipitation in January peaks above 35 mm. In these years the recorded burned area in the dry season was also
relatively low. From 2007 to 2010, January was dry and these years also show a large area burned in January.
T.A.J. Janssen et al. Biological Conservation 218 (2018) 163–172
Kogyae by the reserve management. Yet the rate of woody cover loss in
the north of the reserve remained high until 2015 (Fig. 6). This can be
attributed to the damage caused by recurrent annual res, as re is
known to accelerate forest degradation in areas where forest cover has
been previously reduced and a high re frequency is maintained
(Hawthorne, 1994; Hosonuma et al., 2012; Swaine, 1992).
While res are lit every dry season at the edges of the reserve
(Ayivor and Ntiamoa-Baidu, 2015), the re record shows that a rela-
tively high precipitation in January (> 35 mm) can prevent the res
from burning a large area of the reserve (Fig. 8). This eect of dry
season precipitation via fuel moisture on the annual variability of re
extent is well described on larger spatial scales for the African continent
(Andela and van der Werf, 2014), Amazonia (Aragão et al., 2008) and
equatorial Asia (van der Werf et al., 2008). The MODIS re record
suggests that the area burned inside the reserve has increased since
2004, this is conrmed by observations by the reserve management
(Ayivor and Ntiamoa-Baidu, 2015). The fragmentation of dry forest, the
opened canopy and the increase of savanna grasses in open areas have
increased re fuel loads with poaching and park management sus-
taining a high re frequency. Logged and burned forests are found to be
susceptible to renewed burning due to a substantial and dry fuel load
(Kyereh et al., 2007) and a similar eect is found when analysing long
term re experiments(Veenendaal et al., in press). Eventually, much of
the original forest changed into the treeless tall grasslands and Chro-
molaena odorata thickets existing there today. The annual early
burning management likely prevents or slows down the return of tro-
pical dry forest previously present.
NDVI increase was widespread in the savanna and woodland inside
Kogyae from 2002 to 2015. Our results suggest that regular res were
not able to prevent woody encroachment in the savanna as the NDVI
increase occurred in the north eastern savanna zone that experienced a
relatively short re return time of 1 to 2 years in the period 20002015
(Fig. 7). Finding woody encroachment along streams and in the savanna
ads to the increasing amount of evidence reporting woody encroach-
ment in the woodlands and savanna of sub-Saharan Africa (Mitchard
and Flintrop, 2013) and in the western Sahel (Horion et al., 2014).
Deforestation of tropical dry forests is a major global issue. From
2000 to 2012 tropical dry forests in Latin America, Africa and Eurasia
experienced the highest deforestation rates of all forest ecosystems
(Hansen et al., 2013). Forest clearing for agriculture is recognised as the
main driver of DD in the tropics (Hosonuma et al., 2012). We show how
dry forests are extremely susceptible to DD even if they are located in a
protected area in the strictest sense. Formal de jure protection can be
totally disconnected from de facto status, leading to creation of so-
called paper parks(Figueiredo, 2007; Joppa et al., 2008). Dry forest
patches are still present in Kogyae and the areas surrounding these
patches are showing signs of forest recovery. However, annual res are
hindering forest recovery. This suggests that Kogyae's management
should re-assess the current practice of deliberate burning. Interna-
tional mechanisms that will provide funding for reforestation activities
in the context of climate change (REDD+), and biodiversity con-
servation schemes may provide an avenue for the restoration of Ko-
gyae's forest. Most broadly, this study contributes to the ongoing debate
about the eectiveness of protected areas (Di Minin and Toivonen,
2015; Joppa et al., 2008; Symes et al., 2016). We have demonstrated
the application of remote sensing techniques to provide robust change
detection using freely-available data, and have revealed a hitherto
undocumented and near-complete loss of Ghana's most strictly pro-
tected forest.
We would like to thank the Wildlife Division of the Forestry
Commission of Ghana for granting us research permission to work in
the Kogyae Strict Nature Reserve (KSNR). Our appreciation also goes to
the Park Manager, Mr. Dwoben Nyantakyi, and his staat Dome Camp
for providing security and technical assistance in the eld, particularly
Isaac Sarpong, Kwaku Yinye and Yaw Agyeman, who in addition or-
ganized various scattered settler communities in KSNR to participate in
interviews to verify our ndings. Finally, we would like to thank the
three anonymous reviewers for their comments and suggestions. EM
was funded by a research fellowship from NERC (grant ref.: NE/
I021217/1). TJ was partly funded by the Netherlands Earth System
Science Centre (NESSC), a program of the Ministry of Education,
Culture and Science (OCW) of the Netherlands. EV and GA were funded
by the EU FP7 GEOCARBON project (grant agreement no. 283080) in
Appendix A. Supplementary data
Supplementary data associated with this article can be found in the
online version, at doi:
Fig. 9. History of Kogyae, as described in the literature (Awuku-bor, 1999; Hagan, 1998; Ofori et al., 2014; Wildlife Department, 1994) and from the interpretation of the NDVI change
detection and MODIS re record results.
T.A.J. Janssen et al. Biological Conservation 218 (2018) 163–172
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... Moreover, the result of the forest change analysis implies that forest loss is about twice the gains (net loss), and this suggests that the rate at which the TOFR is losing its forest cover is higher than the rate at which it is gaining forest cover. This outcome of our study is consistent with that of a study from the Kogya forest reserve in Ashanti Ghana, where there is a significant net loss in the forest cover (Janssen et al., 2018). Also, our findings are consistent with the findings by Hansen et al. (2013) who measured more forest losses than gains in the global forest cover, with the tropical areas experiencing the most substantial quantity of forest losses. ...
... Nonetheless, the forest change pattern in the TOFR is different because agricultural activities and the expansion in the developed land inside the reserve are the major proximate factors contributing to forest change. Similar to our findings, Janssen et al. (2018) have found that arable farming is the main contributing factor for forest loss in the Kogya forest reserve area. In the Brong Ahafo and Western Regions of Ghana, forest loss is mostly attributed to human settlement development (Benefoh et al., 2018). ...
... This concern could be due to the alarming rate at which these anthropogenic activities are degrading the forests. However, the differences between the land change pattern in the TOFR and other locations such as southern Ghana (see Benefoh et al., 2018;Janssen et al., 2018;Alo and Pontius, 2008) show there is a need to consider several proximate factors when designing a forest policy. ...
Forest cover change is a major contributing factor to global environmental change. Whereas several studies have focused on the general land use and land cover dynamics, we focus on analysing forest cover change patterns in a protected landscape taking into consideration how other land categories are increasing at the expense of the forest. In this study, we analyse forest cover change patterns and associated proximate land use factors between 1987 and 2017 using Landsat images from the Tano-Offin Forest Reserve (TOFR) in Ghana. Using the Random Forest machine learning algorithm, we classified the images into forest, developed land, and agricultural land. The study finds that forest cover losses are 1.9 and 1.4 times the amount of forest cover gains in 1987-2002 and 2002-2017, respectively. We find that even though the forest cover is more likely to recover from the agricultural land, land developers mostly targeted the agricultural land. The focus of Ghana's Forest and Wildlife Policy and the underlying process of forest cover change in the TOFR suggest that a country's forest policy should focus on a combination of diverse and spatially explicit proximate factors that are likely to threaten the integrity of forests.
... Classified images were validated using Google earth image and field verification. Several research works are found to have different types of vegetation indices (NDVI, SAVI, etc.) for assessing the health of vegetation, vegetation cover, etc. (Labib et al. 2020a, b;Janssen et al. 2018;Kriegler et al. 1969;Rouse et al. 1974;Huete 1988;Huang et al. 2021). This study has adopted two indices, e.g., NDVI and SAVI, for measuring forest resources. ...
... NDVI is widely recognized in measuring forest health, greenness, the productivity of the forest, and forest cover change (Meneses-Tovar 2011; Gandhi et al. 2015). Many studies have been conducted based on NDVI to monitor the forest resources, landscape changes (Janssen et al. 2018), forest degradation (Meneses-Tovar 2011), etc. In this study area, NDVI value varies from À0.416 to 0.5539 in the year 1991 and from À0.758 to 0.482 in 2021. ...
... Most land surrounding PAs has been converted for agricultural use [13], and the principal driver in southwestern parts is cocoa farming. The complete clearance of tropical dry forests inside Kogyae (Category Ia) was due to arable farming and logging [54]. Some PAs have been able to mitigate threats; Bui NP has maintained its lion populations despite being in a highly agricultural area and Nini-Suhien NP remains unlogged [49]. ...
... In both countries, all PA categories were exposed to anthropogenic modification, even Category Ia, which explicitly aims to limit human impacts and maintain a high degree of naturalness [3]. This observation is in line with the complete clearance of forests recorded inside Ghana's Kogyae Strict Nature Reserve [54]. Bui NP contains areas with no recorded human modification, supporting other findings that Category II, which has the lowest levels of HMc in both countries here, may be better at mitigating threats [70,71]. ...
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This study assesses the representation of defined ecoregions, slope profiles, and species richness of threatened mammals in the International Union for Conservation of Nature (IUCN)-listed protected areas in Ghana and Côte d’Ivoire. It also evaluates the exposure of protected area categories to the cumulative degree of human modification and their vulnerability to future agricultural expansion. Spatial gap and statistical analyses were performed using quantitative data from publicly available online global databases. Analyses indicated key conservation priorities for both countries: (1) to increase the protection of the Guinean forest–savanna mosaic, West Sudanian savanna, and Eastern Guinean forests, especially of the Eastern Guinean forests’ ecoregion associated with the Guinean forests of the West Africa biodiversity hotspot; (2) to increase the protected area coverage of flat lands and low slopes; and (3) to enhance the size and connectivity of existing protected areas, including restoring degraded habitats. The study emphasizes that improving the ability of tropical protected areas to conserve nature and mitigate anthropogenic threats should be a global conservation priority. Improving the data quality and detail within the World Database on Protected Areas and ground-truthing them are recommended urgently to support accurate and informative assessments.
... This implies that bush fire, if not controlled could worsen the state of the forest, increasing water shortages, destroying organic matters in the soils and increasing erosion and droughts. There are evidences of fire occurrence in the Northern regions of Ghana(Dwomoh et al. 2019;Janssen et al. 2018;Addo-Fordjour and Ankomah 2017). In 2016, fires were widespread, with an estimated 2137 km 2 of forest reserve area got burned, particularly within the moistFig. ...
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Understanding vulnerability to climate change (CC) is necessary to inform policy makers about appropriate strategies for mitigating and adapting to CC impact. However, research suggests that Ghana is more prone to the impact of CC, affecting vulnerable sectors and might not be able to achieve sustainable development goal (SDG) 11: sustainable cities and communities by 2030. This study synthesises scholarly literature and aims to examine the vulnerability to climate change, mitigation and adaptation practices focusing on agriculture, water and sanitation, forestry, and cities and infrastructure to proffer solutions to enhancing the sustainability of social–ecological systems in Ghana. The study has found that climate-sensitive sectors in Ghana remain vulnerable to climate change with limited adaptive capacity, for example, limited access to technologies and poor knowledge about CC in the agricultural sector; poor quality of water and sanitation services and infrastructural development; illegal logging and a lack of forest conservation practices; and poor maintenance of green and socio-economic infrastructure in the urban and rural areas. Further, the study highlights considerable variation by sectors, particularly with regard to agricultural sector. The study indicates that communicating mitigation and adaptation raises public awareness of the opportunity and threats brought about climate change. The study concludes by calling for the formulation and implementation of National Climate Change Communication Strategy (NCCCS) to govern the communication of climate adaptation plans in Ghana. Specific recommendations for the climate-sensitive sectors are presented in this study.
... Based on the selection of indicators, research results in the literature on deforestation, and the data availability of its drivers (Rudel et al., 2009;Houghton, 2012;Schultz et al., 2016;Dezécache et al., 2017;Curtis et al., 2018;Felipe-Lucia et al., 2018;Janssen et al., 2018;Twongyirwe et al., 2018; Amaral e Silva et al., 2020;Bos et al., 2020;Hamunyela et al., 2020;Nansikombi et al., 2020;Rhyme et al., 2020;Trigueiro et al., 2020;Khalatbari et al., 2021), a total of seven indicators of potential drivers were selected to construct a potential deforestation area risk index (Table 1). ...
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Forests are important for the global carbon cycle, hydrothermal balance, and climate change. Human activities can exert a significant impact on forest ecosystems, thereby having the potential to alter their physical and chemical properties and thus affecting carbon, water, and heat budgets, and climate change. The historical reconstruction of the disturbance of global forests can help us understand the processes and patterns of human activities and global change. In this paper, we construct a deforestation prediction model using a Spearman correlation coefficient and implement the XGBoost method, using Python 3.6, for the reconstruction of deforestation intensity data from 2000 to 2019. Secondly, the selection of the driver indicators is done by using extreme difference regularization to unify the magnitude, and the potential deforestation area risk index is calculated in the form of equal weights. Finally, the actual deforestation data were used for optimization and validation. The model shows that the deforestation hotspots are mainly concentrated in the southern and southeastern regions of China and that there are large differences in deforestation in different provinces. In the future, the fine spatial and temporal patterns of deforestation in China during the historical period can be quantitatively reconstructed, which can provide some reference information for forest disaster prevention and forest management in China.
This chapter explores how natural and invaded ecosystem provide habitat and energy supply for the entire soil food web, how biological invasion changes habitat of the soil organisms, and two study cases considering invasive plant species (Cryptostegia madagascariensis and Prosopis juliflora) from tropical zones. Natural ecosystem is defined as a community of biotic and abiotic entities that naturally occurs in a specific range, while biological invasion defines the spread and dominance of any organisms in a new range. These two concepts are strongly linked to each other in moist and dry tropical ecosystems, and in some cases, they create a war condition (by antagonism) that affects the entire soil food web. Natural ecosystem can provide a wide range of physical, chemical, and biological processes that promotes the entire soil food web, while invasive organisms just change the habitat for their own benefit.
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We applied a participatory mapping approach supported by very high-resolution satellite imagery to reconstruct spatially explicit, year-to-year land use transitions in two highly biodiverse, data-scarce forest frontier landscapes in northeastern Madagascar. We explored these transitions in the light of major continuous trends and discrete events highlighted by local farmers as influencing their land use decisions. Our results suggest that the process of establishing protected areas first reinforced ongoing deforestation, but later led to a significant reduction of forest loss rates. Recent cash crop booms appear to have induced agricultural intensification processes in our study landscapes, while also putting additional pressure on forests, as people may be encouraged to clear forest for cash crop cultivation. These findings are crucial to understanding rapid land use change processes in forest frontier contexts in the humid tropics, and especially to informing natural resource governance and development initiatives in complex mosaic landscapes. ARTICLE HISTORY
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A study was conducted in Thuma area in central Malawi to quantify contemporary land cover and to explore the degree of land use change in the Thuma forest reserve area of Malawi by analysing and comparing satellite-derived land cover maps from 1997, 2007 and 2017. The study was carried out using Remote Sensing and Geographic Information System (GIS), focusing on analysis of Landsat 5 ETM and Landsat 8 ORI/TIRS satellite images. The classification was conducted for the following distinct classes; closed forest, open forest, shrubland, savanna grassland, agriculture fields, and water. The analysis revealed that closed forest diminished from 19% in 1997 to 10% in 2007 to 6% in 2017. Open forest reduced from 30% to 21% from 1997 to 2007 but increased to 22% in 2017. Agriculture area almost doubled from 37 % in 1997 to 64 % in 2017. Actual area from 1997 to 2017, shows that closed forest has reduced from 7,000 ha to 3,000 ha while open forest from 12,900 ha to 7800 ha. Savanna grassland has doubled from 5,900 ha to 13,000 ha. However, future studies should use modern satellites such as Sentinel and Landsat 9 for improved quantification of changes. The findings show that even the protected forest reserve (previously dominated by closed forest) is not fully protected from deforestation by local communities. Government and other stakeholders should devise measures to meet the needs of the surrounding communities and the ecological/biophysical needs of the reserves. Based on this study, issues of re-demarcation of the forest reserve and accessed area should also be explored. This study serves as a reference for the management of Thuma Forest Reserve as a refuge for natural tree species, rivers that harbour endemic fish species ( Opsaridium microlepis and Opsaridium microcephalis ) and the sustainable management of endangered elephants in the reserve.
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Nos últimos anos a redução da cobertura vegetal das caatingas vem chamando atenção e incentivando estudos que buscam entender a dinâmica de retração de suas coberturas vegetais. Nesse sentido, o objetivo desse estudo é analisar a estrutura da cobertura vegetal em diferentes áreas das caatingas nas últimas três décadas, e investigar os fatores que possam influenciar o comportamento da distribuição da cobertura vegetal em duas áreas de monitoramento nos estados de Pernambuco e Bahia. Para isso, foram utilizadas imagens de satélite obtidas a partir dos sensores TM e OLI, acoplados ao satélite Landsat 5 e 8, respectivamente, as quais foram submetidas a calibração radiométrica, extração do Índice de Vegetação Ajustada ao Solo (IVAS) e a classificação supervisionada. O estudo mostrou que ao longo dos aproximados 30 anos de estudo, houve grande variabilidade da dinâmica de mudanças áreas de caatingas, porém prevalecendo uma tendência de diminuição da Caatinga Fechada sendo substituída pelas caatingas Semiaberta e Caatinga Aberta. Verificou-se, também, que principalmente nos últimos 11 anos ocorreu aumento das áreas de agricultura / pastagem / caatinga Gramíneo Lenhosa. Essas mudanças são impulsionadas por alterações antrópicas, principalmente a o crescimento de áreas de pastagens e pela diminuição dos totais pluviométricos nos últimos anos.
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Unlabelled: Forest encroachment into savanna is occurring at an unprecedented rate across tropical Africa, leading to a loss of valuable savanna habitat. One of the first stages of forest encroachment is the establishment of tree seedlings at the forest-savanna transition. This study examines the demographic bottleneck in the seedlings of five species of tropical forest pioneer trees in a forest-savanna transition zone in West Africa. Five species of tropical pioneer forest tree seedlings were planted in savanna, mixed/transition, and forest vegetation types and grown for 12 months, during which time fire occurred in the area. We examined seedling survival rates, height, and stem diameter before and after fire; and seedling biomass and starch allocation patterns after fire. Seedling survival rates were significantly affected by fire, drought, and vegetation type. Seedlings that preferentially allocated more resources to increasing root and leaf starch (starch storage helps recovery from fire) survived better in savanna environments (frequently burnt), while seedlings that allocated more resources to growth and resource-capture traits (height, the number of leaves, stem diameter, specific leaf area, specific root length, root-to-shoot ratio) survived better in mixed/transition and forest environments. Larger (taller with a greater stem diameter) seedlings survived burning better than smaller seedlings. However, larger seedlings survived better than smaller ones even in the absence of fire. Bombax buonopozense was the forest species that survived best in the savanna environment, likely as a result of increased access to light allowing greater investment in belowground starch storage capacity and therefore a greater ability to cope with fire. Synthesis: Forest pioneer tree species survived best through fire and drought in the savanna compared to the other two vegetation types. This was likely a result of the open-canopied savanna providing greater access to light, thereby releasing seedlings from light limitation and enabling them to make and store more starch. Fire can be used as a management tool for controlling forest encroachment into savanna as it significantly affects seedling survival. However, if rainfall increases as a result of global change factors, encroachment may be more difficult to control as seedling survival ostensibly increases when the pressure of drought is lifted. We propose B. buonopozense as an indicator species for forest encroachment into savanna in West African forest-savanna transitions.
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The paper assessed the integrity of Kogyae, Ghana’s only Strict Nature Reserve, as a Category Ia protected area, against the backdrop of pressures and threats posed by anthropogenic drivers. Primary data were derived from a combination of approaches namely, Rapid Assessment and Prioritization of Protected Areas Management Methodology, participatory appraisal approach and institutional data gathering. The results identified adjacent landuse, poverty in nearby communities, and high population density as the underlying threats facing the reserve. These had fuelled proximate threats including bush fires, logging and poaching. The study revealed also that the recent re-zoning of the reserve by extending its boundaries to enhance its ecological viability has not only strained the relationship between local people and officials of the Wildlife Division officials, but become the root cause of most of the underlying threats. Considering the pressure and threats of Kogyae, the study proposes two options for resolving the situation: granting the communities’ request to engage in ecologically friendly activities in the ‘Special Use Zone’ by re-categorizing the zone appropriately according to IUCN definition, or resettlement of the communities elsewhere to free the reserve from human activities
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Protected areas (PAs) are an essential tool for the conservation of biodiversity globally. Previous studies have focussed on the effectiveness of PAs and the design of optimal PA networks. However, not all PAs remain intact permanently; many PAs undergo downgrading, downsizing and/or degazettement (PADDD), a fact largely ignored until recently. The drivers of enacted PADDD events and the factors influencing its spatial occurrence are poorly understood, potentially undermining the efficacy of PAs and PA networks. Here we examine the spatial relationship between PADDD and economic, demographic, and structural variables, using a 110 year dataset of 342 enacted PADDD events across 44 countries in the tropics and sub tropics. We find that the probability of an enacted PADDD event increases with the size of the PA and through a synergistic interaction between PA size and local population densities. Our results are robust to the under-reporting of enacted PADDD events that occur among smaller PAs and in regions with lower population density. We find an economic motive for PADDD events, given that the opportunity costs associated with larger PAs are higher, on average, than smaller PAs. Our findings suggest a need for conservation practitioners to better consider PA characteristics, as well as the social, economic, and political context in which PAs are situated, to aid the creation of more efficient and sustainable PA networks. In particular, the dynamics of enacted PADDD events highlight the need to explicitly consider PA robustness as a core component of systematic conservation planning for PA networks.This article is protected by copyright. All rights reserved.
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Through interpretations of remote-sensing data and/or theoretical propositions, the idea that forest and savanna represent "alternative stable states" is gaining increasing acceptance. Filling an observational gap, we present detailed stratified floristic and structural analyses for forest and savanna stands located mostly within zones of transition (where both vegetation types occur in close proximity) in Africa, South America and Australia. Woody plant leaf area index variation was related to tree canopy cover in a similar way for both savanna and forest with substantial overlap between the two vegetation types. As total woody plant canopy cover increased, so did the relative contribution of middle and lower strata of woody vegetation. Herbaceous layer cover declined as woody cover increased. This pattern of understorey grasses and herbs progressively replaced by shrubs as the canopy closes over was found for both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are taken into account, a less marked transition in woody plant cover across the savanna–forest-species discontinuum is observed compared to that inferred when trees of a basal diameter > 0.1 m are considered in isolation. This is especially the case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total subordinate cover is also observed as savanna stand canopy closure occurs. Despite similarities in canopy-cover characteristics, woody vegetation in Africa and Australia attained greater heights and stored a greater amount of above-ground biomass than in South America. Up to three times as much above-ground biomass is stored in forests compared to savannas under equivalent climatic conditions. Savanna–forest transition zones were also found to typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, consistent across all three continents coexistence was found to be confined to a well-defined edaphic–climate envelope with soil and climate the key determinants of the relative location of forest and savanna stands. Moreover, when considered in conjunction with the appropriate water availability metrics, it emerges that soil exchangeable cations exert considerable control on woody canopy-cover extent as measured in our pan-continental (forest + savanna) data set. Taken together these observations do not lend support to the notion of alternate stable states mediated through fire feedbacks as the prime force shaping the distribution of the two dominant vegetation types of the tropical lands.
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An ongoing question in paleoenvironmental reconstructions of the central African rainforest concerns the role that prehistoric metallurgy played in shaping forest vegetation. Here we report evidence of intensive iron-ore mining and smelting in forested regions of the northern Congo Basin dating to the late Holocene. Volumetric estimates on extracted iron-ore and associated slag mounds from prehistoric sites in the southern Central African Republic suggest large-scale iron production on par with other archaeological and historically-known iron fabrication areas. These data document the first evidence of intensive iron mining and production spanning approximately 90 years prior to colonial occupation (circa AD 1889) and during an interval of time that is poorly represented in the archaeological record. Additional site areas pre-dating these remains by 3-4 centuries reflect an earlier period of iron production on a smaller scale. Microbotanical evidence from a sediment core collected from an adjacent riparian trap shows a reduction in shade-demanding trees in concert with an increase in light-demanding species spanning the time interval associated with iron intensification. This shift occurs during the same time interval when many portions of the Central African witnessed forest transgressions associated with a return to moister and more humid conditions beginning 500-100 years ago. Although data presented here do not demonstrate that iron smelting activities caused widespread vegetation change in Central Africa, we argue that intense mining and smelting can have localized and potentially regional impacts on vegetation communities. These data further demonstrate the high value of pairing archeological and paleoenvironmental analyses to reconstruct regional-scale forest histories.
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Aichi target 11 of the Convention of Biological Diversity promotes the expansion of the global protected area network to cover 17 percent of all terrestrial land and ­10 percent of coastal and marine areas by 2020 ( At the recent World Parks Congress, organized by the International Union for Conservation of Nature (IUCN) in Sydney, Australia, 12 innovative approaches were promoted as part of the “Promise of Sydney” to help transform decisionmaking, policy, capacity, and financing for protected areas in the next decade ( The first of such approaches includes a list of 20 important recommendations to help reach conservation goals. Many of these ­recommendations are provided for ­single countries to take action individually. In addition, the final recommendation advocates that a more ambitious target of protection (50 percent global protection) should be promoted to more adequately conserve biodiversity. Both points are problematic: recent research shows that facilitating international collaboration among countries is crucial to identifying and implementing a well-connected system of protected areas that can better represent threatened biodiversity, and setting unrealistic and politically challenging global protection targets is unneeded. This Viewpoint presents three main themes of the recommendations that would benefit from greater emphasis and the promotion of the importance of international collaborations.
We assessed data from 11 experiments examining the effects of the timing and/or frequency of fire on tropical forest and/or savanna vegetation structure over one decade or more. The initial ‘control treatment’ in many such cases consisted of previously cleared land. This is as opposed to natural vegetation subject to some sort of endogenous fire regime before the imposition of fire treatments. Effects of fire on fractional foliar cover are up to 10-fold greater when clearing pre-treatments are imposed. Moreover, because many of the ‘classic’ fire trials were initialised with applied management questions in mind, most have also used burning regimes much more frequent and/or severe than those occurring in the absence of human activity. Once these factors are taken into account, our modelling analysis shows that nonanthropogenic fire regimes serve to reduce canopy vegetative cover to a much lower extent than has previously been argued to be the case. These results call into question the notion that fire effects on tropical vegetation can be of a sufficient magnitude to maintain open-type savanna ecosystems under climatic/soil regimes otherwise sufficient to give rise to a more luxurious forest-type vegetation cover.
Net primary productivity (NPP) is one of the most important parameters in describing the functioning of any ecosystem and yet it arguably remains a poorly quantified and understood component of carbon cycling in tropical forests, especially outside of the Americas. We provide the first comprehensive analysis of NPP and its carbon allocation to woody, canopy and root growth components at contrasting lowland West African forests spanning a rainfall gradient. Using a standardised methodology to study evergreen (EF), semi-deciduous (SDF), dry forests (DF) and woody savanna (WS), we find that (i) climate is more closely related with above and belowground C stocks than with NPP (ii) total NPP is highest in the SDF site, then the EF followed by the DF and WS and that (iii) different forest types have distinct carbon allocation patterns whereby SDF allocate in excess of 50% to canopy production and the DF and WS sites allocate 40-50% to woody production. Furthermore, we find that (iv) compared with canopy and root growth rates the woody growth rate of these forests is a poor proxy for their overall productivity and that (v) residence time is the primary driver in the productivity-allocation-turnover chain for the observed spatial differences in woody, leaf and root biomass across the rainfall gradient. Through a systematic assessment of forest productivity we demonstrate the importance of directly measuring the main components of above and belowground NPP and encourage the establishment of more permanent carbon intensive monitoring plots across the tropics.
Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and