Oil and Gas Pipeline Construction-Induced Forest Fragmentation and Biodiversity Loss in the Niger Delta, Nigeria ()
1. Introduction
The Niger Delta covers an area of approximately
50,000 km
2 between Latitudes 4˚0'0''N and 8˚0'0''N, and Longitudes 5˚0'0''E and 7˚0'0''E [1] (Figure 1). It is within two meters above sea level [2] and extends over four ecological zones: coastal barrier islands, brackish/saline water mangrove swamps, freshwater swamp forests (permanent and seasonal), and dry upper plain lowland rain forests [3] . The hydrological boundaries between these ecological zones are imperceptible; so also are some of the forest zones particularly the fringing of the mangrove forest and freshwater swamp forest. It is also the largest wetland in Africa with rich biological diversity [1] [4] -[8] . Its mangrove forest is the largest in Africa (
11,134 km
2) and the fourth largest in the world [9] .
Across the different ecological zones, the Niger Delta is home to diverse assemblages of Not Evaluated (NE), Data Deficient (DD), Least Concern (LC), Near Threatened (NT), Vulnerable (VU), Endangered (EN) and Critically Endangered (CR) wildlife species. Some of the threatened species, which have been previously reported in IUCN red list are the pygmy hippopotamus (Choeropsis liberiensis), manatees (Trichechus senegalensis), maritime hippopotamus (Hippopotamus amphibious), Nile crocodile (Crocodylus niloticus), slender nosed crocodile (Crocodylus cataphractus) and dwarf crocodile (Osteolaemus tetraspis) [3] [4] . Ohimain [5] also reported that such wildlife species as the Cape clawless otter (Aonyx capensis), African palm nut vulture (Gypohierax angolensis), fire-footed squirrel (Funisciurus pyrropus), Hammerkop (Scopus umbretta), African fish eagle (Haliaeetus vocifer), Sclater’s guenon (Cercopithecus sclateri), sitatunga (Tragelaphus spekei), white throated monkey (Cercopithecus erythrogaster), which occurred in the area required conservation.
However, the Niger Delta is known and recognized globally not for the rich biological diversity but for its non-renewable oil and gas resources. The region is home to the hydrocarbon exploration and production activities in Nigeria where proceeds from this singular industry (i.e., oil and gas) accounts for over 90% of the nation’s total export earnings [1] . With proven crude oil reserve of 37.2 billion barrels, 165 trillion standard cubic feet (scf) of natural gas, 75.4 trillion scf of non associated gas and average of 2.28 million barrels of crude oil production per day, Nigeria is Africa’s largest crude oil producer, the world’s 11th largest producer as well as 8th largest exporter 2011 [10] . Nigeria has been exporting crude oil from this region since 1958. Effective oil and gas exploration and production has therefore taken place in this region described as environmentally sensitive
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Figure 1. Map showing the Niger Delta of Nigeria.
and fragile [1] [3] , with brackish and fresh water swamps cris-crossed by anastomosing network of rivers, creeks and distributaries/tidal channels [7] for more than fifty years. This will likely continue for the next fifty years or more.
The completion of every successful oil and gas exploration and production activity is to hook up the producing well to a gathering facility through a flowline. The gathering facility may be a flow station or Floating Production Storage and Offloading (FPSO) system (strictly offshore). These products are transported from the gathering facility to a refinery or outright selling point (terminals) through pipelines. In the Niger Delta the flowlines and pipelines range from diameter of six inches (6") to thirty six inches (36") with Right of Way (RoW) of
15 m
to
30 m
in width. Their construction involves acquisition and clearing the RoW of all vegetation and wildlife, and excavation by the open-cut method (thrust boring at major road and river crossings). The open cut method requires deployment of excavators and other earth-moving equipment: the depth of excavation ranging from
3 m
to
15 m
. Backfilling after pipe laying is mostly haphazard resulting in blockage of natural drainages and eventual flooding [6] [7] . At present, there are 23 export terminals, 112 flow stations and over
20,000 km
of flowline/pipeline infrastructure concentrated within this
50,000 km
2 area.
Studies and reports implicating different oil and gas exploration and production activities in the Niger Delta to forest fragmentation and overall biodiversity depletion abound [1] [3] -[7] [11] -[18] . Empirical investigations into flowline/pipeline construction activities and their operation vis-à-vis their impacts on this ecologically and biologically diverse but fragile and sensitive region are lacking. This study investigates and quantifies the impact of flowline/pipeline construction activities in the Niger Delta and proffers remedial measures to mitigate and restore adversely impacted areas.
2. Materials and Methods
2.1. Study Area and Rationale
The field studies were conducted between 2009 and
2012 in
Rivers and Bayelsa States within latitudes 4˚0'0''N and 6˚0'0''N, and longitudes 5˚0'0''E and 7˚0'0''E (Figure 1). The studies were tailored to capture two broad categories of oil and gas pipeline impacts on biodiversity (i.e., plants and wildlife) viz: (i) impacts associated with pipeline construction and (ii) impacts associated with the operational phase of pipeline facilities. To achieve these objectives, two different pipeline RoWs at different stages of existence were chosen.
1) A
45 km
pipeline project under construction (Figure 2(A)). This is within lowland and freshwater swamp forests. RoW clearing and excavation/trenching activities were observed vis-à-vis impacts on biodiversity.
2) A
120 km
long pipeline (Figures 2(B)-(D)), which has been in existence for upwards of twenty five (25) years. The pipeline originated in a lowland rainforest, crossed seasonal and permanent freshwater swamp forests, mangrove forests and terminated in a barrier island. During the study, a section of this pipeline within the mangrove forest section was being replaced. This replacement activity increased the opportunity to document construction impact on the mangrove forest area.
Study methodology included inventory/sampling of plant and animal species, observations and use of still life photographs and interview/discussions with locals; comparison with forest climaxes in contiguous areas and by copious reference to existing information [9] . For vegetation and wildlife assessments, the pipeline RoWs provided continuous linear transect.
2.2. Vegetation Sampling and Assessment
At each sampling point along the transect, a tape measure was used to mark out
100 m
×
100 m
plot. Each
100 m
×
100 m
plot was further demarcated into four random blocks of
20 m
×
20 m
. This was to ease sampling and increase the opportunity of encountering all plant species during inventory. Within each chosen block, vegetation assessment was made through copious visual observations of the status of the flora. On-site identification as well as inventory of all plant species within each sample station was carried out. Data obtained was further used for determining the density, relative distribution and frequency of occurrence of major plant species. The structure and physiognomy of the vegetation of the area [height, crown diameter and crown depth of all woody stems
3 m
or more in height or over
10cm
in diameter at breast height (
1.3 m
)] were estimated in the field and ratified with reference to
Richards
[19] . Trees were identified to species level using Flora of Tropical West Africa [20] -[22] and Trees of Nigeria [23] .
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Figure 2. (A) Section of the
45 km
pipeline under construction in moist lowland rainforest section. Notice the different earth moving equipment, excavated earth, pipes; (B)-(D) Different segments of the
120 km
existing pipeline RoW ((B) is along lowland rainforest area, (C) is across freshwater swamp forest area, and (D) is through mangrove swamp forest i.e., brackish water area).
2.3. Wildlife Survey and Assessment
The wildlife assessment involved a survey of amphibians, reptiles, birds, and mammals in the study areas using the existing RoW as linear transects. For the census of the birds, reptiles and other animals, which readily offered themselves for observation, the direct count method was adopted using a pair of binoculars. By probing such humid habitats as logs, heaps of dry or decaying leaves, ponds, forest undergrowth and burrows, the presence of some animals like amphibians, reptiles and small mammals were revealed. All captured, dislodged or sighted animals were identified, often on the spot, to possible taxonomic levels using field guides and keys [24] -[28] . For species which do not offer themselves readily for observation, the indirect method, which makes use of evidence of animal’s presence [29] , was used. Such signs of animal occupation as burrows, faecal pellets (droppings), hairs, foot prints or tracks, sloughed skin, devoured food (cassava, yam tubers, oil-palm fruits, other fruits), as well as vocalization, skeleton/carcass and trampled grass were of immense use in the course of the investigation. Further information on the wildlife diversity, abundance and use in the areas were obtained through inspecting series of traps and snares set by hunters and interviewing them. Wildlife species displayed for sale around villages close to the RoWs were noted.
3. Results
3.1. Status of the Forest and Vegetation of the Area
The
165 km
study area comprises
133 km
of moist lowland/freshwater swamp and
32 km
of mangrove swamp forests. Typically, the pipeline RoWs have width of
30
m. Thus, approximately
4,950,000 m
2
(equivalent of 495 hectares) area of moist lowland/freshwater swamp forest (
3,990,000 m
2
≈ 399 hectares from
133 km
long RoW) and mangrove swamp forest (
960,000 m
2
≈ 96 hectares for
32 km
) was cleared to realize the pipelines. Observations and results from the study show that the area has different forest ecosystems, which are rich in biological diversity. A total of 219 species (
192 in
moist lowland rainforest,
113 in
freshwater swamp forest and
8 in
mangrove swamp forest) of plants from 66 different families were recorded (Table 1). The family Leguminosae
*Lowland = Moist Lowland Rainforest; **Freshwater = both seasonal and permanent freshwater swamp forest; NA = not applicable i.e., no common name; + = present; − = not present.
Wildlife inventory (invertebrates not included) in the area revealed considerable diversity of wildlife species in 4 broad groups. This comprised 125 different fauna species from 64 families (Table 2-5). Mammals from 22 families (Table 2) accounted for 44 (35.2% of total number of species) of the species described (Figure 4). 20 of these mammals including the Pan troglodytes-chimpanzee (EN), Cercopithecus erythrogaster-white throated
![]()
(a)![]()
(b)
Figure 3. (a) Species composition of the most dominant plant families in the study areas; (b) Percentage contribution of different plant families (based on plant habit) to the vegetation of the study area.
![]()
Figure 4. Percentage contribution of different wildlife groups in the study areas.
guenon (VU), Trichechus senegalensis-African civet (VU) and Panthera pardus-leopard (VU) are threatened or near threatened according to IUCN and Nigerian Conservation status. Other taxa represented in the records are 10 species of amphibians from 5 families (Table 3), 20 species of reptiles from 13 families (Table 4), and 51 species of birds from 24 families (Table 5). Birds accounted for 40.8% of the total faunal species in the area (Figure 4). 7 of the 51 species of birds, which includes grey parrot (VU), Anambra waxbill (VU) and hooded vulture (EN), are threatened. The goliath frog (an amphibian) and river turtle (reptile) are endangered, while the West African dwarf crocodile, another reptile, is vulnerable. These are threatened in line with IUCN and Nigerian Conservation status. Though the birds showed more species diversity, the amphibians were more abundant in population and Bufo regularis (the common African toad), was the most dominant amphibian. This species occurred in all the ecological zones. Three totems (Table 6), Kinixys erosa (serrated hinge-backed tortoise), Python sebae (Rock python), and Python regius (Royal python) were recorded.
3.3. Critical Impacts on Biodiversity of the Area
The impacts observed and recorded during the study include colossal destruction of plants and dislodgement of animals from their habitat (Figures 2(A)-(D), Figure 5(A) and Figure 5(B)), creation of multiple accesses into hitherto un-accessed forests resulting in increased logging/hunting of wildlife (Figures 2(A)-(D)). Within the lowland tropical rainforest, the RoW has converted to derived savanna (forest fragmentation) dominated by grasses, sedges and amphibians (Figure 2(B)). In the freshwater swamp areas, the same RoW was observed to be route for migration of invasive alien species like water hyacinth (Figure 5(C)). Other terrible impacts recorded are pipeline rupture leading to spillage into water bodies and farmland, loss of aquatic flora and fauna, fire incidents, destruction of forest biodiversity, and death of humans (Figures 5(A)-(F)), heightened flooding and erosion due to removal of vegetal cover and disruption of hydrologic patterns, and distortion of the ecotone zone of the freshwater swamp and mangrove forests.
4. Discussion
Results obtained from this study agree with the fact that diverse ecological zones translate to diversity in species; a scenario easily adducible for the Niger Delta from information presented in Tables 1-5. That the Niger Delta is replete with species of plants and animals including endemic species is well documented [1] [3] [6] [31] [32] . With 219 species of plants in 66 families, and 125 different fauna species from 64 families (excluding invertebrates) from the study area, this study lays credence and strongly supports previous reports that the Niger Delta is ecologically diverse in species.
Forests in the Niger Delta are productive and sensitive ecosystems dominated by rainforest and mangrove
![]()
Figure 5. (A)-(F) Different impacts from the operational phase of the
120 km
pipeline observed during the study: (A) Large scale destruction of mangroves resulting from fire incidence, which occurred after oil spillage from the pipeline; (B) Colossal kill of freshwater swamp forest and forest resources after an oil spill and fire incidence along the freshwater swamp section of the same pipeline. Notice crude oil streaming along the RoW. The RoW provides access for the streaming crude oil to freely move into water bodies, ponds, and farmlands along the course; (C) Water hyacinth (Eichhornia crassipes), an invasive alien species, along the RoW; (D) Stilt roots of Rhizophora sp. heavily covered with crude oil resulting from spillage along the mangrove section of the pipeline RoW; (E) Another section of
5A
at low tide. Arrow points to pool of crude oil persisting in the mangrove “chikoko” soil two years after the spillage; (F) Farmland along the RoW, which was impacted by oil spill from the pipeline. Crops planted in the farm include cassava, yam and cocoyam. Communities along the drier section of the
120km
RoW are allowed to farm beside the RoW.
![]()
![]()
Table 2. Fauna of the Study Area (Mammals).
![]()
Table 3. Fauna of the Study Area (Amphibians).
trees [3] . They are of considerable ecological importance not only because of their use as spawning and feeding grounds for many varieties of fish and shrimps but also of economic importance because forests are sources of timber, poles, fire wood, palm oil and other local food crops and medicinals. The forests support diverse wildlife species including totems as demonstrated by the results of this study. However, oil and gas exploration and production activities have over the years impacted negatively (directly and indirectly) on the biological diversity of this region resulting in increasing rate of threat to species and extinction of others (Tables 1-5). Opening up of landlocked rich forest ecosystems during such activities as pipeline construction encourage unsustainable forest exploitation, environmental degradation and biodiversity loss in the area. These activities accentuate flooding and flooding impacts, and the operational consequences of these pipelines, which include vandalization and oil spillage, exacerbate greenhouse gas emission and global warming. Oil spillage from oil and gas facilities and their impacts on biodiversity, soil, water, agricultural lands and humans in the Niger Delta is widely reported [33] -[38] , and are confirmed by this study. That the construction and laying of flowlines/pipelines leading to the clearing of vegetation and excavation of earth has caused destruction and loss of forests and biodiversity thereby changing the landscape of the Niger Delta is not questionable. With an estimated whooping 8,778,000 stands of lowland rainforest/freshwater swamp forest trees and 864,000 stands of mangroves that were destroyed with construction and laying of pipeline along the studied
165 km
stretch, the impact of the over
2000 km
network of oil and gas pipelines in the Niger Delta can be imagined. This makes forest trees and plants the most affected
![]()
Table 4. Fauna of the Study Area (Reptiles).
biodiversity of the area. It must be stated that the removal of these trees has direct negative consequences on the wildlife, which co-habit with them; hence the number of fauna threatened with extinction in Tables 2-5. These fauna were automatically dislodged and or destroyed.
At present only less than 4% of Nigeria’s rainforest cover is left. More frightening is the fact that the loss is still continuing at the rate of 3.5% annually [39] . This implies colossal loss of biodiversity. This study has identified oil and gas pipeline construction as major culprit in moist lowland/freshwater swamp and mangrove swamp forests destruction in the Niger Delta.
5. Conclusion
It is noteworthy that in Nigeria, oil and gas exploration and production is sine qua non for government earnings and therefore tied to national development. However, it has caused unimaginable destruction to biodiversity and humans, and affected means of rural livelihood. Every caution must therefore be taken to apply best practice in the business of oil and gas exploration and production as applicable in other countries. Pragmatic efforts and policies geared towards reducing land-take for pipeline construction by using existing RoW for new flowlines/pipelines must be pursued and encouraged by the appropriate government arms. The RoW width of
30 m
utilized for construction of most pipelines should be reduced to between
15 m
and
20 m
as one of the mitigations for impacts associated with vegetation clearing and biodiversity loss. There is also need to enforce restrain on construction of pipelines across identified local biodiversity hotspots in the region. At the moment, surveillance against pipeline rupture, failure and vandalism seems to be reactionary as against realistic pragmatism. Government must therefore liaise with concerned companies to evolve functional RoW surveillance methods, which
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Table 5. Fauna of the Study Area (Birds).
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Table 6. Wildlife Species Considered totem, or associated with taboos in the study area.
EN = Endangered, VU = Vulnerable, LR/NT = Lower Risk/Near Threatened, LR/CD = Lower Risk/Conservation-Dependent, LC = Least Concern, DD = Data Deficient.
will completely eliminate pipeline vandalisation and its attendant consequences. This should as much as possible include robust education and awareness campaigns on the impacts of pipeline vandalization on biodiversity and humans. Where possible, the use of RoW for farming should be encouraged with extreme caution and supervision.
NOTES
*Corresponding author.