By Bianca T. Esposito, NWNL Research Intern
(Edited by Alison M. Jones, NWNL Director)
NWNL research intern Bianca T. Esposito is a Syracuse University senior studying Biology and Economics. Her summer research was on the nexus of biodiversity and water resources. She already has 3 NWNL blogs on African and N American watershed species: Wild v Hatchery Salmon; Buffalo & Bison; & Papyrus & Pragmites.
African Elephant, Mara Conservancy, Kenya
This blog compares Africa’s savannah elephant (Loxodonta africana) to the N. America’s white-tailed deer (Odocoileus virginianus) in North America’s eastern United States. They present unlikely, but strikingly interesting comparative behaviors and impacts within their watersheds.
In the Pliocene Era, elephants roamed and trumpeted their presence across the planet. Today they are a keystone species in African watersheds, including the Nile, Mara and Omo River Basins. Yet these giants are increasingly vulnerable to human poaching, hunting and destruction of habitat and migratory corridors. As a result, African savannah elephants are categorized as a “vulnerable” species.
In North America, white-tailed deer (also called Virginia deer) are present across the continent from the Atlantic Coast’s Raritan River Basin to the Pacific Coast’s Columbia River Basin. These nimble jumpers probably came to N America in the Miocene Era as browsers competing for their niche with American rhinos. As they wheeze, grunt and bleat their presence today, they have few natural predators remaining, other than car collisions. Deer in the eastern US are a “Least Threatened” species – while Columbian white-tailed deer in Oregon’s Lower Columbia River Basin are “Near Threatened”.
White-Tailed Deer , Upper Raritan River Basin, New Jersey
North American male deer stand at 6-7 feet and weigh 100-275 pounds (¼ of a ton, the weight of a baby elephant). In contrast, full-grown elephants stand at 11 feet (twice as tall as deer) and weigh up to 13,000 lbs (6.5 tons). Yet despite these huge size differences, these 2 species impacts on watershed forests are quite similar. As herbivores, both threaten and alter their habitats’ vegetative diversity, growth and regeneration.
VEGETATION & FOREST INTERFACE
Elephants alter their watersheds by converting woodland to shrubland. Elephants consume large amounts of vegetation allowing growth of plants previously blocked from the sun. However the benefit of increasing plant diversity is countered by the destruction elephants cause while browsing their way through watersheds. They remove trees, trample grasses and compact the soil. This limits forest regeneration since seedlings cannot grow and their trails cause soil erosion.
Similarly, deer today are increasingly damaging forest vegetation due to their soaring populations. In the Raritan River Basin, impacts of high deer populations have resulted in habitat loss for birds and other animals that rely on vegetation for protection. Thus, native species are decreasing and could eventually disappear locally.
Another similarity both species face is that of negative interactions with humans. Elephant and deer both damage farmers’ crops. Elephant contact with humans continues to increase as they lose their traditional habitats due to human infringement and development. Increased development has also led farmers to further transgress into what was elephant rangeland or migratory corridors. In following and browsing along their ancient pathways and territories today, elephants can trample crops and even kill people. Those elephants are often killed in retaliation. In Tanzania’s Serengeti District, the effect of elephants raiding crops means a bag of maize can be locally more valuable than the cost of building a classroom or tarmac road.
In America, deer find an ideal environment in urban and suburban areas with their mix of ornamental shrubs, lawns and trees. Since deep forest vegetation is too high for them, deer browse along the “edge habitat” which also provides easy access to suburban yards.
White-tailed deer crossing a road (Creative Commons)
With the loss of wolves, bears and cougars, deer have had a lack of predators, causing their populations to soar. Now their biggest predators are human hunters and car accidents which cause deer and human fatalities. As well, human health impacted by deer that browse in the woods, meadows or dunes with ticks carrying Lyme disease (Lyme borreliosis). Lyme disease can be lethal, or at the least debilitating, for humans, livestock and pets.
For elephant and deer, interaction with humans is not beneficial for either species. Sadly, given less space for the exploding human race, these fateful interactions will only increase.
The spread of human settlements, agriculture and livestock farming have replaced elephants’ natural habitats. Clearing of those traditional lands disturbs and decreases water volume in their rivers and lakes. Yet, when elephants were there, they created water holes which increased water availability for themselves and other species. Simultaneously, humans are increasing their consumption of today’s decreasing water and other natural resources.
This scenario is dramatically playing out in Kenya’s Mara River Basin. In the Mau Forest highlands, human deforestation has depleted flows of source tributaries of the Mara River, a lifeline to the Maasai Mara National Reserve and Tanzania’s Serengeti National Park. In turn, lowered water levels downstream have increased temperatures and disrupted local rainfall patterns. Thus the human takeover of the Mau Forest has chased out the elephant and disturbed downstream ecosystems, which in turn will contributed to decreases in wildlife populations and thus park revenues from tourism.
Elephants have direct impacts on water sources and availability since they are a “water-dependent species.” When water is scarce, they dig in dry river beds to provide water for themselves, other animals, and humans. Additionally, elephants migrate to find water – even if only via artificial, supplementary water points. More research is needed, but water availability may become a useful tool for regulating elephant distribution and managing ecological heterogeneity. Yet an abundance of artificial water should be avoided in conservation areas where the presence of elephant would cause vegetation degradation.
African Elephants crossing the Mara River, Mara Conservancy, Kenya
Deer, unlike elephants, have a more indirect impact to water resources. Their impacts are more about quality of water than its availability. The nutrients and pathogens excreted by white-tailed deer become water pollutants in nearby streams and groundwater, especially during in storm runoffs. Deer waste dropped in and along streams in the Raritan River Basin produces greater pathogenic contamination than cattle manure deposited away from streams.
HUNTING AS A WAY TO REDUCE HUMAN-WILDLIFE CONFLICTS
Hunting is a controversial solution to controlling these species’ threats of ecosystem degradation and human conflict. Hunting elephant to counter their negative impacts has much greater negative consequences than hunting deer. Elephant poaching for lucrative ivory profits became such a serious threat that elephants became listed as an Endangered Species. While a 1989 ban on international ivory trade allowed some populations to recover, illegal ivory trade still occurs and threatens elephant populations. Thus, shooting elephants marauding crops and killing farmers is not an option – thus the search for other means to controlling elephant degradation.
After elephants devour all vegetation in an area or during droughts, they migrate. However, that puts them face to face with today’s man-made fences and trenches built to stop elephants, as well as with new communities and farms. Thus Kenyan conservancies, International Fund for Animal Welfare, Addo Elephant NP, Sangare Conservancy and other groups began creating “protected elephant corridors.” Such corridors provide elephants safe migratory paths where they don’t disturb humans.
Ranger at the entrance gate to Sangare Conservancy, Kenya
Deer hunting however is viewed by many as a positive means to control over-abundant deer populations destroying gardens and forests. In rural regions, deer are still hunted for food and sport which helps save forest saplings from deer browse. But that removes only a limited number, and there have been traditional limits on deer hunting. Along Mississippi’s Big Black River, the state still restricts killing year-old bucks and any deer hunting during floods. Many such restrictions are being loosened today to help counter the rapid growth of deer populations. As well, to reduce deer browse and car collisions, some suburbs hold carefully-organized, targeted hunts by licensed “sharp-shooters,” and the venison is harvested for homeless shelters. Suburban methods to combat deer intrusions also often include installing 8-foot tall fences to protect gardens, landscaping and critical ecosystems.
Fence of the Sangare Conservancy, Kenya
Elephants’ foraging creates open habitats for other species. However, browsing of resulting mid-successional species by elephants and other species can stop regrowth of trees and forest. “As go the elephants, so go the trees.” This issue is similar to deer browsing on soft-leaved saplings in N. American forests that preventing the growth of future forests.
Yet elephants compensate for their heavy vegetative consumption. More than a dozen tree species depend on forest elephants for to spread their seeds. This type of seed dispersal occurs via each elephant’s daily 200-lb. dung droppings, thus ensuring survival of vegetation. Another benefit of creating open spaces by altering and removing trees is the opportunity for greater faunal diversity. Elephants uproot and fell trees and strip bark; but in this process, they break down branches which provides access to food for smaller wildlife.
Herd of African elephants with newborn, Lake Manyara National Park, Tanzania
All this change created by elephants creates “a cyclical vegetational seesaw of woodland to grassland and back to woodland.” As debris of trees felled by elephants shields pioneer grasses and shrubs from trampling, deep-rooted perennial grasses can grow. These grasses attract grazers to the area, while the browsers leave. When the woodlands regenerate, elephant number will return, followed by browsers.
Deer, unlike elephants, are non-migratory however, and thus they don’t spur cycles of regeneration. Therefore, watersheds with deer-infested forests face ongoing degradation. Today’s soaring numbers of deer prevent any chance of forest recovery from their constant browsing. Deer also displace native wildlife, which furthers the cascade of ecosystem degradation. When a forest loses trees, there is less water recycling since trees produce and move rain downwind to other terrestrial surfaces. Water retention in a forest is also related to presence of ground cover – also eaten by deer – which decreases stormwater runoff and downstream erosion in floodplains or wetlands. A lack of ground cover causes inland forests and downstream areas to become arid and potentially a waste land. The deer do not produce compensatory benefits that elephant produce.
White-tailed deer Upper Raritan River Basin, New Jersey
Elephant and deer each have increasingly negative impacts on watershed vegetation and human communities. However a big difference exists in effective stewardship for controlling these species. In Africa, elephant numbers (2007-2014) have dropped by nearly a third, representing a loss of 144,000 elephants. Begun in 2014, the Great Elephant Census (GEC) accounted for over 350,000 savannah elephant across 18 African countries and states the current yearly loss at 8 per cent. Tanzania, having one of the highest declines, and Mozambique have lost 73,000 elephants due to poaching in just five years.
However deer populations have exploded. In 2014, US deer populations across the United States were estimated at over 15 million. In New Jersey, there are approximately 76-100 deer per square mile; yet a healthy ecosystem can support only 10 deer per square mile. These high densities of deer are decimating US forests.
Making elephant poaching illegal and banning ivory trade has saved elephant populations in Africa. But in N America further controls of the growing population of deer is badly needed. The most obvious step towards this goal would be to remove deer hunting restrictions – the very opposite of Africa’s stopping the hunting and poaching of elephants.
On both continents, immediate solutions are critical if we are to protect our forests and water supplies – critical natural resources of our watersheds – from degradation being increasingly incurred by both species. Elephants consume vegetation and degrade areas of abundant water; while tick-carrying deer contaminate water with their excrement and threaten the future of our forests. One could summarize the consequence of too many deer as “No Forests – No Water” – and the consequence of losing elephant as “No Elephants – No Water.”
All photos © Alison M. Jones unless otherwise noted.