Animal Impact on Biodiversity

Since I read Alan Savory's "Holistic Management" last year, I've been considering how wild animal impact figures into natural ecosystems. I live in Southern Missouri, and have lived in other places in midwest and east. In most places in the eastern half of the country, deer are the only wild ungulates remaining. Alan Savory didn't describe much about these types of ecosystems, but I mention him because it's what got me on this train of thought. I now believe that extirpation of large ungulates and their predators has had a much more profound impact on forests east of the plains than most people realize, and also set in motion much of the invasive exotic problems that get so much attention now, and the ecosystems could actually sustainably support significantly higher animal biomass than now as long as it was composed of diverse species, with many of them being migratory. However, this is just my theory that I've put together, so I wanted to throw it out to this forum to see what people have to say.

A couple hundred years ago, elk also ranged over practically all of the eastern half of the country, and bison over most of it too. Bison were most numerous on the plains, but they also ranged east into places like Pennsylvania and North Carolina, although not as far as New England. Both of these animals live in herds that range over much larger areas than deer, as well as having different food preferences.

In most of the eastern half of the country, deer populations are much higher than historical norms. I have seen extreme cases where the only things growing below deer browse height are plants that deer don't like. Most places are not that extreme, but overpopulation of deer still causes a lack of diversity in the forest. This is the case where I live, not only do gardens and fruit trees definitely need to be fenced off, but there's a lot of effect on the woods, for example we have a number of larger serviceberries but no smaller ones because of too much deer browse, while some other places in the same county with fewer deer have plenty of young serviceberries. A decent amount of oak and hickory seedlings manage to make it past deer browse if they're in a good site, which shows the deer population isn't as extreme as some places, but it's pretty obvious the forest is moving toward a lower diversity dominated by plants deer don't like as much, such as cedar, carolina buckthorn, persimmon, buckberry, pawpaw, and spicebush, as well as grasses where there's enough light. I've only lived here for a few years, but I know someone who lived here 20 years ago and says there used to be some patches of rare medicinals that aren't here anymore. They didn't disappear overnight, but clearly the amount of deer we have leads to lower diversity.

Deer overpopulation is something many know about, but for years something struck me as not right. The historical deer density prior to European settlement is most commonly said to be around 8-10 per square mile, although it would have varied with the habitat. I believe that, as my observations are that current populations well above that are detrimental to the ecosystems over time. However, considering the sheer biomass of animals supported in parts of the world such as Africa, how could our ecosystems sustainably support so few.

I believe the key is diversity. The woods I live in still has tons of plant growth, just more and more of it is less palatable to deer. How many people have considered how unprecedented it is for an ecosystem on the North American continent to not have any large grazers that eat lots of grass. Deer are browsers and don't eat grass to any significant extent. For many millions of years there were herds of various grazers and browsers with their different diets all over the continent. Also it's unprecedented for many millions of years to not have animals that roam over wide areas in large herds. Deer typically have a home range of a square mile or less. Wide-ranging Herds have a much different impact on the landscape than deer. They affect one area severely but then move on, so they won't just keep nibbling on their favorite plants as soon as they try to regrow.

The impact of the soil of natural herding behavior has been proved by Alan Savory (as long as the animals don't stay in the same place too long). He focused on the brittle landscapes where the land can actually desertify over time without herding animal impact, but even in more wet and humid landscapes that behavior surely has ecological fuctions. These principles are applied in rotational grazing of domesticates, but I haven't heard anyone apply them to the forest of the eastern half of the US.

Most recently has been the loss of the bison and the elk, but the book "The Ghosts of Evolution" by Connie Barlow awakened me to how the loss of all the megafauna at the end of the ice age still has many ripples on today's ecology. She focused on seeds that are best dispersed by megafauna and some other things like thorns that are best suited to defend against larger animals than have been seen since the ice age, but didn't go into more general ecological effects, probably because they're harder to prove. However I can only imagine in the days of the megafauna the landscapes of North America could have sustainable supported much more animal biomass because of all the different species with their different niches.

So in conclusion, my thinking is that the land is better off with deer densities closer to the historical average (a lot lower than most place today), but the land could support more wild animals if the diversity of animal species was higher and many of them were ones that behaved in wider-ranging large herds, as well as their predators. Unfortunately those are the types of animals that are some of the most in conflict with the dominant human culture here.

I agree with what you've said.  We have a whole lot of deer here, including exotic deer and even African antelope (haven't seen any on our place yet) but people are trapping for coyote and mountain lion.  It's ridiculous. 

All these grazers and browsers, including sheep, goats, and cattle, do reduce the plant diversity a lot. 

The behavior of the animals is very important too, the same grazers and browsers that reduce diversity under improper human management can increase it under conditions of natural herding behavior caused by their predators in the case of wild animals, and also can be mimicked in small, frequently rotated grazing paddocks on farms and ranches.

I realized I mentioned the animal connection to invasive exotics in my first post but forgot to elaborate on it. It's from my observations that in areas where the browsing pressure is mostly from deer, that most of the problem exotic invasives are plants that the deer don't eat. In my area, there aren't that many exotics in the woods, but as I mentioned before they are still shifting more and more toward the natives that the deer don't like. If the animal pressure was from more diverse species, I suspect many of the invasives wouldn't be the same issue. Of course there are many other factors involved, but I'm convinced that invasive species are more of a symptom than a root cause.

One interesting tidbit, here in Missouri two of the most common plants that do well in heavily deer-browsed areas are carolina buckthorn (frangula caroliniana) and buckbrush (Symphoricarpos orbiculatus). The name buckbrush suggests that deer like it, but I don't see browse on it even when other plants right nearby are heavily browsed. They are natives but will form dense thickets especially in areas with lots of deer. When I lived in southern Minnesota, two of the worst invasives were european buckthorn (Rhamnus cathartica) and tatarian honeysuckle (Lonicera tatarica). Although those exotics formed even more dense thickets than our Missouri natives do, possibly because of fewer natural enemies, it is interesting that the natives that are increasing their coverage in Missouri are related to and have similar roles as the exotics that are taking over in southern MInnesota. The two buckthorns are obviously in the same genus, and buckbruseh is in the honeysuckle family and has many similarities in form and niche as tatarian honeysuckle, although it's a bit shorter. This points out to me that it's human alterations to the environment that are behind these specis changes, rather than the plants being so evil.

hi Castanea,

it's hard to determine what the East was like. I guess it depends upon when you check
1. Before whites when the native american population was high
2. after the whites when the native american population was low but before whites moved west
3. as the trappers moved west
4. as the pioneer hunters moved west
5. as the farmers moved west

each stage changed the prior one
6. here in Pa, all the forest ( except a few selected protected areas) have been cut down 3-4 times since the whites came. most of the state was farmland in the late 1800's
7. the native deer population was wiped out by the Civil War.
8. Deer were reintroduced from Michigan and Kentucky in the early 1900's
9. deer populations peaked about 10 years ago. it was not unusual, and expected by some, to see 100 deer when out hunting in the northern counties.
10. changes in the hunting season and bag limits have reduced the populations to protect the forest but not without the complaints of hunters



http://www.permacultureactivist.net/articles/Beavers.htm
Learning from the Ecological Engineers:
Watershed Wisdom of the Beaver


Before Europeans arrived, there were an estimated 100 to 400 million beaver in North America. Today there are roughly 9 million, with their numbers having rebounded from an even lower nadir at about 1900. Early records show that beaver lived in nearly every body of water in New England.
    The first white settlement in New England began with the arrival of the Mayflower in 1620, and in the decade following, 100,000 beaver were skinned in Massachusetts and Connecticut. Having quickly depleted the coastal stocks, trappers moved west into New York and killed another 800,000 beaver from 1630 to 1640. In 1638 England’s Charles II declared beaver fur to be mandatory in the manufacture of hats, to the animal’s further misfortune.

      As the slaughter spread westward, the numbers increased: The French port of Rochelle received 127,080 beaver pelts in 1743 alone (beaver were not the sole target—1267 wolves and a staggering 16,512 bears were also shipped to Rochelle that year). By 1850, beaver were nearly extinct from the Atlantic to the Oregon Territory. Entire deciduous riparian forests disappeared from the west coast. Without the beaver’s omnipresent influence, streams in every watershed eroded into the deep channels we know today, and soil washed to the sea.



http://heritagebooks.com/mm5/merchant.mvc?Screen=PROD&Store_Code=HBI&Product_Code=H1526&Category_Code=

The Hunting Pioneers, 1720-1840: Ultimate Backwoodsmen on the Early American Frontier


The Hunting Pioneers, 1720-1840: Ultimate Backwoodsmen on the Early American Frontier - Robert John Holden with Donna Jean Holden. This book is the first comprehensive account of the ultimate wilderness archetypes - the hunting pioneer families in the deep woods. These hunting pioneers had a totally different perspective on the wilderness than did the farming pioneers who far outnumbered them. The hunting pioneers continually sought out remote forests where the game animals roamed, while the farming pioneers followed close behind, methodically destroying those wilds with their axes and plows. A dynamic force from the early 1700's to the mid-1800s, the hunting pioneers originated in the Delaware River colony of New Sweden. The Swede-Finns lived there in the forests where their way of life was greatly influenced by the local Indians. Over the years, these Swede-Finns were joined by English, German, and Scotch-Irish immigrants who also adopted the hunting pioneer lifestyle. Together they led the frontier advance through the backcountry of Pennsylvania, Maryland, Virginia, the Carolinas, and Georgia, all the way to the edge of the treeless Great Plains


this book tells of accounts of the pioneer hunters shooting eastern buffulo roaming in herds of hundreds of animals

Thanks for mentioning the beaver, Duane. They are certainly a keystone species too, and more evidence of the importance of animals in shaping ecosystems.

Reading this thread reminds me of how real wealth this country has squandered. We have a long way to go. Good points, Castanea.