Do pigs kill trees

If European Wild Boar naturally live in the woods, then raising pigs in the woods sounds like the most natural way to raise pigs. I've heard two different things: pigs kill mature trees by destroying their feeder roots, and pigs benefit mature trees by aerating the soil. I'm guessing the difference between these two is rest period in between rooting, as well as amount of time spent in each paddock.

I've also heard that damage may not be evident for several years, because it may take years for a tree to die after the pigs have mortally wounded it in it's root system. Can anyone confirm this through long-term experience?

I have a small woodlot that I want to rotate pigs in, but not if the pigs will hurt the trees. I want to thin out most of the small trees, open the canopy up to 50% to allow forages to grow, coppice a part of it for firewood and tree hay (for goats), and give all the mature oaks and maples plenty of room to increase crown size for maximum maple syrup and acorn production.

Located in the Northwoods of Wisconsin. The woodlot is mostly hardwoods, previously managed for pulp and lumber. I want to manage it for food.

I know that rotating animals will hurt the regeneration of the woods, but I am ok with that for this particular woodlot. I plan to plant a few seedlings to control regeneration. I just don't want to hurt the mature trees. Any thoughts?

From a study in Minnesota:

The pigs do very little damage to orchard trees, Hoch said. “They usually don’t damage the trees very much, but they will turn over the soil. In some blocks… post-harvest, I’ve let them completely turn over the soil for us.”

This allows him to disk the field, quicker than mowing, and the orchard is smooth. The pigs are rotated into strawberries, brambles, plums, apricots and all the other fruits post-harvest, as well as through the apples.permanent fencing allows quicker movement of the pigs, preventing damage from rooting once the fallen fruits are consumed from the orchard floor.


https://countryfolks.com/agroforestry-pasturing-pigs-in-orchards/

With brambles, the pigs will graze the fruit off the ground post-harvest, as well as any remaining in the bushes. The concern is that the pigs will eat the raspberry roots, and they need to be rotated before doing so.

From a discussion:
Our saddlebacks uprooted and destroyed every bay tree we had in our copse, including mature ones, but they grow like weeds round here so not a big deal.   They also killed our two Robinia trees, but oddly enough, by eating the bark all round rather than uprooting them.   In the orchard they uprooted all the self seeded apple and plum saplings, but left the mature trees intact.  Ditto in the woodland - young trees with trunk diameters under 2 inches all went, older trees usually survived, presumably as their roots go much deeper.

Effects of rooting may take a while to show.  Rooting can partially sever tree roots and the effects won't show until a dry summer leaves the tree with inadequate water.

Thanks for the reply. I guess if disking doesn't hurt tree roots, then rooting probably doesn't have to hurt them either.

One more study:

Joseph Orefice, PhD, is an Assistant Professor of Forestry at Paul Smith’s College and he also owns/operates North Branch Farm in Saranac, NY where he raises heirloom figs, tomatoes, and beef in silvopastures.


"As a farmer, keeping pigs in forested areas does has its appeal. Pigs need shade during the summer and the diversity of insects, roots, nuts, and plants in wooded areas can be very appealing.  Pigs also require supplemental feed when pastured, a possible source of nutrients for the forest. However, the challenge is that when pigs are allowed to root they significantly damage soil structure leading to:

Loss of surface forages (which are less resilient under a tree canopy)
oss of the soil humus layer (habitat to multitudes of organisms and where over 90% of trees’ roots are located)
Significant soil compaction
Significant loss of soil structure and nutrients
   Increased surface runoff and soil erosion
   Destruction to the soil biotic community of a forest

When trees experience root damage their strategy is to live off stored energy reserves. It often takes years before these reserves run out and the tree starts showing signs of decline or mortality. Therefore, it is critical to maintain the integrity of tree roots and soil in silvopastures because a few weeks of soil disturbance can end decades of tree growth. Even more concerning is that it can take 5-10 years before this decline in tree health is evident."

Karina, in your second reply, do you know if the people were rotating them frequently, or just leaving them in with the trees?

Here is a link to the discussion

https://www.accidentalsmallholder.net/forum/pigs/pigs-to-keep-in-an-orchard/

One more study, in France, concluded:I have been thinking about this as well, so I have been digging 🙂


   choice of species is depending on the soil and desired added value for the pigs (fodder, shadow,…)
   protecting trees from rooting pigs is crucial
   Important to let trees grow strong before letting the pigs near them
   Rotation of the pigs within the system is recommended

Hey Y'all...

They will absolutely kill trees. Over the years and in many different situations I have witnessed it myself.
In most instances from eroding and the feeder roots described above. If they erode away the area around one that had enough ground around it but now has standing water around it, dead.
If you ring them so they don't root, you have to feed them lots more. If you don't, I've seen 100 year old Oaks with the bark eaten off 3 ft up the tree, dead as a door nail.
You could always cattle panel around the trees you want. I'd hot wire it too if they are say.. 200lbs plus.

Just to add my vote———— under some circumstances, they can kill trees.

I was amazed at the destruction one adult sow did to my farm. She was a pet and had run of the 20 acres, minus the 1 acre veggie garden I had at the time. Over to course of 2 years she…
… stripped the bark from a 50+ year old mango tree, killing it.
… killed several young guava saplings and a mulberry tree.
… she surface rooted here and there, especially around trees. I suppose she was harvesting the worms that inhabited the mulch. Initially I thought "how cool, she’s tilling in the mulch and compost". 5-7 years later I started seeing those trees starting to fade away. Now I have dozens of dead and dying trees.  
… she aggressively rooted on a hillside, resulting in significant erosion when we had a big storm. That hill required major repairs.

I still raise pigs, but now they are confined. They get to run free for about an hour about 4 times a week during guava season in order to eat the dropped guavas, but then I entice them back into their pens using tasty treats such as mangos, bread, cracked corn, spam slices. No more aggressive rooting.

Coming back to the orchard study, why does disking not hurt the roots of the apple trees? I did not realize that orchards got disked. Is it because the disker stays a certain distance from each tree, so only the edges of the root system are damaged? Then the root tips can grow back, kind of like "pruning" the roots? Analogous to pruning the branches?

Or is it only disked very shallowly, so the roots are BELOW the disturbed area? So that way the roots would not be disturbed at all?

I feel like I am missing something. I quote:

The key is to move them carefully,” Hoch said. “Time their moves so that they’ll just eat the dropped fruit and before they start rooting.”

The pigs do very little damage to orchard trees, Hoch said. “They usually don’t damage the trees very much, but they will turn over the soil. In some blocks… post-harvest, I’ve let them completely turn over the soil for us.”

Why let them completely turn over the soil if the key is to move them before they start rooting?

Su Ba, what a horrifying story! I'm glad I didn't start rotating them through my woods yet. I'm keeping them on my rough pasture for now. I am curious, did that sow return to root the same trees over and over, or did she take turns with different trees? Why do you suppose that some trees survived better than others? Do you think that all of your dead trees would have survived if they had only been rooted, say, once a year, so that the "pruned" roots would have enough time to regrow?

You could always cattle panel around the trees you want. I'd hot wire it too if they are say.. 200lbs plus.

Yeah, but I'd be guessing on how far away to put the fence to keep them out of that tree's roots.

1. Loss of surface forages (which are less resilient under a tree canopy)
2. Loss of the soil humus layer (habitat to multitudes of organisms and where over 90% of trees’ roots are located)
3. Significant soil compaction
4. Significant loss of soil structure and nutrients
5. Increased surface runoff and soil erosion
6. Destruction to the soil biotic community of a forest

Joseph Orefice's assessment of pigs rooting in a forest above.

1. I think surface forages would come back with sufficient rest between rotations, especially if a partially open canopy allows some grass to grow.
2. Does he mean from erosion and runoff? What if it's flat?
3. In a wet area of the woods, this would absolutely happen.
4. Isn't the pig adding nutrients?
5. Again, what if it's flat?
6. Again, I bet this depends on the amount of rest.

Kaarina, can you please link to that French study? The wild boar is native there, so they've been dealing with it forever and they may have a pretty good handle on it. I read the French Wikipedia article on the ecological role of the wild boar, but I think it raised more questions than it answered. If there is any kind of symbiotic relationship with trees, similar to cows pruning grass and building soil carbon to grow more grass and more cows, then it is not obvious to me at all.

Can anyone define the wild boar's ecological role? What is its "job"?

Sean Govan wrote:Coming back to the orchard study, why does disking not hurt the roots of the apple trees? I did not realize that orchards got disked. Is it because the disker stays a certain distance from each tree, so only the edges of the root system are damaged? Then the root tips can grow back, kind of like "pruning" the roots? Analogous to pruning the branches?

Yes, because they stay a safe distance away from the tree and they do prune the roots. Discing is an entirely different implement and practice.

Sean Govan wrote:Can anyone define the wild boar's ecological role? What is its "job"?

Here in the SE USA most consider them nothing but "Destroyers" crops, gardens, orchards, lawns.
Most farmers try to thin the #s to keep them at bay. Hold hunting party nights. and trap them all year round.

They used to root up my backyard so bad in FL I couldn't even mow it.
Now I'm in NW AL, the farmers here trap and eat the sows, bury the boars. When they get to great in #'s and start doing what they do best "destroy" everything.

It's job is exactly what it does everywhere in every environment, root, eat, poop & multiply. Ecologically, a top soil disturber. that capable of much more damage in the long run to everything it roots in on and around.

The problem arises when their #'s get to large and thus the land area they roam can't handle the pressure. Aka. penning them up, no matter the species. A lot of people who keep them decide on Kuni's or something like that, more of a compact variety.

Then we have 1 family sow pet that gives you the perfect idea of what they can do alone.

Link to the French study

https://i2connect-h2020.eu/casestudy/porchard-free-range-pigs-in-agroforestry/

Joel Salatin does some interesting things with pigs - much of it contained or quick rotation if I recall correctly. But I do remember he lets them free-range in the forest just in the fall when the chestnuts are dropping.

So I think a big chunk of this is only letting them in when there's lots of surface food, as was described in one of the articles. I've read a lot about the issues of wild boars damaging ecosystems - but the same is true of cattle if they aren't kept moving. Rotational grazing is Nature's Way!

One of the things that keeps animals moving is the presence of predators. That makes me wonder if there are any dogs that would be able to "herd" pigs?

This is the first time I have ever considered pruning a tree's roots, I didn't know that was a thing. A Google search of pruning roots yields some interesting results. I found this guideline for how much of a tree's surface roots can safely be pruned, at what distance from the tree, with how long of a rest period before pruning it again. This is bound to apply to pigs rooting as well.

Measure the diameter of your tree. Wrap a measuring tape around the tree, four feet from the tree’s base. Then, divide that number by 3.14. Generally, you can safely prune roots that are 5 times the diameter away from your tree. So, if your tree has a diameter of 3 feet, only cut tree roots 15 feet away from the tree.

https://blog.davey.com/removing-tree-roots-above-ground-will-it-harm-or-kill-the-tree/#:~:text=Generally%2C%20you%20can%20safely%20prune,until%20it%20is%20completely%20exposed.

Could selective pruning of roots by pigs stimulate productivity? Perhaps the pruned roots would grow back better in the disturbed soil?

There are many pros and cons about pigs in forests.

They DO damage if not managed throughout.

They DO GOOD if you fully understand and keep them in a holistic management system. (That needs of course space)

Dr Alan Savoy explains the how and why
Joel Salatin has paddock systems that works

...and there are many other Permaculture Farmers who use pigs as the ultimate machines in their fields.
Strict management is the key of it.

They start digging as soon the easy pickings of food are gone...
That is the management system you have to set up suitable for your turf..

Sean Govan wrote:This is the first time I have ever considered pruning a tree's roots, I didn't know that was a thing. A Google search of pruning roots yields some interesting results. I found this guideline for how much of a tree's surface roots can safely be pruned, at what distance from the tree, with how long of a rest period before pruning it again. This is bound to apply to pigs rooting as well.

Could selective pruning of roots by pigs stimulate productivity? Perhaps the pruned roots would grow back better in the disturbed soil?

No, It doesn't have to apply to pigs pruning.

When they prune the roots the roots stay below ground, are not subject to oxygen and drying out and it is a clean cut not being uprooted and the feeder roots eaten and/or the main root being gnawed on. Try to find a video of the process.

I strongly agree with See and Jay, it would take strict management, were talking a practically "eyes on" process if you don't protect your trees and their roots.

Sean, my sow had free run of 20 acres, so she had her favorite spots. Thus she tended to root up the soil around the same trees over and over again. Why did she choose those particular trees? She opted for those that had mulch and compost covering the ground around them. As I mentioned, I suspect she was hunting the worms. She rooted in plenty of other spots on the farm, but definitely favored wherever I had mulched the areas of my food forest/orchard. There were plenty of areas that were not being mulched and that she never touched, I assume because there was no food for her there.

If she had been rotated through pastures, never staying too long in one, I most likely wouldn’t have seen as much damage. Managed pastures also are seeded with forage, giving the pigs plenty of varied fresh grazing. This helps keep the pigs from damaging the land as badly. My 20 acres is not managed as livestock pasture.

See Hes wrote:There are many pros and cons about pigs in forests.

...and there are many other Permaculture Farmers who use pigs as the ultimate machines in their fields.

The problem with this is we see and hear of the success and the process usually while its happening or when it's successful after a few years.

I would beg to see those fields before and after 6-7-8- 10 yrs with before and after picture proof to see how the trees have faired.

Again I agree with Strict Management.

Su Ba wrote:Sean, my sow had free run of 20 acres, so she had her favorite spots. Thus she tended to root up the soil around the same trees over and over again. Why did she choose those particular trees? She opted for those that had mulch and compost covering the ground around them. As I mentioned, I suspect she was hunting the worms. She rooted in plenty of other spots on the farm, but definitely favored wherever I had mulched the areas of my food forest/orchard. There were plenty of areas that were not being mulched and that she never touched, I assume because there was no food for her there.

If she had been rotated through pastures, never staying too long in one, I most likely wouldn’t have seen as much damage. Managed pastures also are seeded with forage, giving the pigs plenty of varied fresh grazing. This helps keep the pigs from damaging the land as badly. My 20 acres is not managed as livestock pasture.

Agreed

Protecting the fruit trees is the option I would suggest the most. Then you can mulch and nurture the trees as well. Then you can have whatever animal you choose out there. You might have goats or something else one day. You could hand pick the fruit drop and feed the animals. You wouldn't have to worry about it near as much and everyone would win.

If anything take the time to figure out a good process, a well thought out plan is your best bet when combining the two.

When they prune the roots the roots stay below ground, are not subject to oxygen and drying out and it is a clean cut not being uprooted and the feeder roots eaten and/or the main root being gnawed on.

Will Witt, good point, but wouldn't a fence line be analogous to the "clean cut" of the human pruner? In other words, the part that gets uprooted and dries out, is like the part that a human pruner would completely cut off? Couldn't we use that formula to decide how far from the tree we can safely put the fence? I don't know, perhaps the dehydration of the exposed roots on the pig side would have a bad effect on the tree side. Whereas an actual clean cut would simply scar over and heal. In that case add some extra distance to the formula when fencing out the trees I guess.

I have my pigs under a popple and some birch now just to see what happens. There is a tremendous amount of rubbing on the bark, also rooting under the trees. Lots of root damage the very first day. If they can kill the trees I don't want, then I could have a lot of dry firewood standing in place in a few years.

See Hes, I will look up Dr. Alan Savoy, thanks for the tip.

The problem with this is we see and hear of the success and the process usually while its happening or when it's successful after a few years.

I would beg to see those fields before and after 6-7-8- 10 yrs with before and after picture proof to see how the trees have faired.

Me too. If the damage can take 10 years to kill the tree, then how do you know if you're adequately protecting the trees, until it's too late? Bye bye trees.

Joel Salatin video here.



His pigs plow everything up in between paddock moves, it looks like. It's a savannah-style landscape. He doesn't say they kill the trees, but he says they go in every seven years and "prune" the silvopasture, by removing "dead and diseased" trees. He also takes three pallets and makes a triangle around any small trees that sprout up that he wants to keep, for example persimmon, until they get big enough to not be killed by rubbing.

He moves them every 5-12 days, depending how big an impact they are having. He mentions that you can look at the previous paddocks and see a record of how wet it was while they were in there. No matter how wet it was when the pigs tilled it, the vegetation seems to come back nice. He says if you leave them too long, it comes back in weeds, and if too short, it comes back in brambles. His goal seems to be grass.

Any clue how long he's been doing this? "Every seven years" sounds like it's been a long time.

Perhaps the pigs aren't damaging most of the trees enough to kill them, but just damaging them enough that they need to put significant resources into regrowing their roots. That does not sound good for getting maximum acorn harvest in the fall. Even more so for maple syrup, which is already hard on the tree as it is. Sounds like I shouldn't put them near the trees at all, except for masting when there is mast, and I should move them at least once a day.

Generally, you can safely prune roots that are 5 times the diameter away from your tree.

I think the key word here is "safely." i.e. without killing the tree. I suspect that pruning 5 x the diameter away from your tree will still have an impact on tree health, mast and fruit production, and maple sap. Especially if it's all the way around the tree, rather than just on one side. Maybe 10x the diameter would result in a better balance between pork and production trees. Most of my "big" maples and oaks are only 12 to 18 inches thick. Of course, as the trees grow, the size of the pig free island has to grow, because the root zone has to grow.

The edges of the tree island would have access to nutrients and aerated soil from the pigs similar to discing in an orchard. The root tips.

Perhaps trees are more resilient to pigs in areas with extremely thick topsoil. The root zone would be deeper, leaving more margin of safety for the trees in between paddock moves. The "production tree" islands could be mulched every year to build topsoil more quickly.

A savannah style landscape probably helps as well, since there is plenty of grazing and they are not forced to root for fresh plant material. So reducing their need to root. And the grass covering of this landscape probably helps with erosion as well...the part that they root without grazing has plenty of dead plants on top to slow runoff, while the part that they graze without rooting shouldn't erode at all.

Opening up my thick woods into a savannah silvopasture will also provide lots of nutrients and opportunities for the trees that I keep. Less competition for light and nutrients, exclusive use of their own root space, lots of organic matter and decomposition from the dead roots of the trees I remove. Some of which were competing in its root zone.

Putting them on a flattish area is probably very important. Slopes sound bad for eroding the soil around the trees after rooting.

Time of year is a factor. Pigs root more in spring. Maybe because it's wet and soft, maybe because roots rhizomes and tubers have more starch in early spring, or maybe because they couldn't root much in winter and they need to get it out of their system. Perhaps more caution is called for in spring. Mine rooted and rerooted, 18 inches deep, it was spectacular. I had them till the garden after it dried out enough and they were very thorough.

Maybe cafeteria style mineral feeders would also reduce their need to root. Some rooting could be due to a mineral deficiency, which they try to fix by eating dirt.

Potential plan:

I am picturing a circle of polywire around each tree island, 8" high, connected to hot aerially and only when the pigs are being rotated through the area. Our ruminants could harvest the vegetation inside the tree island. They could be rotated through the area between pig rotations. That way the grass gets pruned at 12 to 18 inches every time (take half leave half) but the rooted area gets a longer rest from rooting. The grazed area probably needs a shorter rest than the rooted area.

The nutrient rich area just outside of the tree island, being constantly pruned by pigs, should develop huge amounts of small, tender feeder roots, which would perhaps be full of starch by late fall. Pigs it seems eat the bark off tree roots for the starch in areas of newly planted trees, I hear it's a huge problem in areas with feral hogs.

Herbivores prune and fertilize grass, causing more grass to grow so the herbivores have more food. Bees pollinate plants, causing seeds to be produced so that more flowers can grow next year so the bees can have more food. Perhaps pigs at the appropriate stocking density in the appropriate environment cause more vegetative tree roots to grow so the pigs can have more food. (I'm having trouble applying this analogy to mosquitos, unless mosquito bites make you more fertile or cause your blood to be more nutritious the next day, lol.)

I found a study from Hawaii that suggested pigs might be worm farmers. The researchers found that rooted areas had overall more earthworms than non-rooted areas. Other invertebrates decreased in the rooted areas, but the worms increased, causing overall biomass of invertebrates to be about the same per volume of soil in rooted versus non-rooted areas. This makes sense, since earthworms eat decaying plant matter, and lots of plants/plant parts die and are buried when pigs root them. Rooting also fluffs up the soil, perhaps facilitating earthworm movement and accelerating the decay of the dead plants due to more oxygen. This may explain why some people have observed feral pigs rooting the same area over and over.

Also some food plants are benefitted by soil disturbance, which sets back their competitors, opens paths for their roots, and spreads their tubers for reproduction. Sam Thayer planted two patches of Jerusalem artichokes near his cabin and regularly harvested from one of them. Within a couple of years, that patch had grown considerably and the other one was completely dead. Grass loves being grazed, but it doesn't like repeated digging. Jerusalem artichokes hate being grazed, but they love repeated digging.

Sus scrofa have always been a part of the European forest ecosystems. I figure that every part of an ecosystem must have some kind of benefit for the ecosystem as a whole. What that benefit might be for pigs in the woods, I am still trying to find out. Perhaps they don't directly benefit trees. Perhaps they somehow benefit other animals, or other plants. Who knows, maybe they benefit species who only live in dead trees, by making sure there's plenty of dead trees for them.

I keep hearing about oak savannahs, anyone ever hear of a maple savannah?

Here's another thought. Since I'm thinning out so many trees, I could pile brush really high and thick around the trees I want to keep. Eventually it would become a mulch and add nutrients to that tree's root zone.

Thinking more about those Jerusalem artichokes, maybe for pigs we should focus less on rotational grazing of grass, and more on rotational rooting of tubers, rhizomes, etc. The plants that love disturbance could have a symbiotic relationship with pigs.

And another thought on the hillside erosion: pigs naturally make a berm under their electric fence. So if strip grazing pigs on a gentle slope, the strips could be arranged on contour.

Sean Govan wrote:See Hes, I will look up Dr. Alan Savoy, thanks for the tip.

It is possible See Hes did a typo and meant Dr. Alan Savory, so if the first name doesn't work, try Savory: https://savory.global/our-mission/

Tree roots can have a very high starch content compared to grass roots. I imagine that they are also easier for adult pigs to grab than tiny grass roots and rhizomes. Maybe that is one reason why European Wild Boar prefers to live in the woods. According to this paper, healthy oak roots can have up to 30% starch, with 25% starch for maple roots: Estimating Starch Content in Roots of Deciduous Trees-A Visual Technique https://www.uvm.edu/femc/attachments/project/1138/Estimating_starch_content_in_roots_Wargo.pdf

The point of the paper was to find a quick visual technique to estimate starch levels in deciduous tree roots, to estimate their health and vigor. They cut cross sections of roots and stained them with an iodine solution to see starch reserves, which stain much darker than the surrounding tissue. This method could be used to determine if our pigs are impacting our silvopasture/woodlot too heavily year over year.

The paper points out that stressed trees draw on their starch reserves, resulting in lower starch content in the roots. In nature, I imagine that this makes those particular roots less attractive to pigs, causing them to move on or "rotate to their next paddock," thus giving those particular trees a break.

Here are some figures on grass for comparison.

Interesting quote from an article on the starch content of grass roots: "This starch may represent up to 10% of belowground dry weight in early winter, which, in Oklahoma grasslands, may be equivalent to approximately 300 pounds of starch per acre. The starch yield of potatoes can be more than 5,000 pounds per acre." Of course that is very dependent on the season.

A Swedish study in a 3 year old grass ley found starch content of roots varying from 1 to 8% and rhizomes varying from 20 to 40%.

I’m sorry I didn’t read all the other comments, but my brothers did gigs in a wooded area one year. I believe they were only on there a few months. Maybe if they’d had somewhere to rotate them frequently it would’ve been ok. But in their case, most of the trees died. The pigs just dug everything up and disturbed the roots too much.

I'm thrilled to see you're researching and planning.

Risk vs Reward vs Knowledge & Preparedness = Confidence & Success

Good Luck

Another tidbit from Joel Salatin on pigs' relationship with trees, around minute 30:15



Joel claims that American forests are suffering from a lack of disturbance or "ecological exercise," which he implies used to be accomplished by the Indians regularly clearing the forest floor with fire to create silvopastures and manage them for game.

So since pigs kill trees, maybe the role of the pig in nature is to create savannahs or silvopasture, by killing some of the trees but not all of them. Maybe some tree species are more resilient to root disturbance, and others less.

He says we are "stagnating our ecology in our state forests, which desperately need some disturbance."

"Virginia Tech Forestry Department will tell you that we are losing our oak trees because there is no disturbance anymore. Instead of fire, let's run some pigs through there to save the oak trees and turn acorns into pork." (Very close paraphrasing here.)

Any further comments? Is he wrong? He seems experienced and confident. I just learned that he wrote a book about the marvelous pigness of pigs, which I plan to get my hands on. So why all this discrepancy in what people are seeing? Is it really all just a question of rotation and stocking density? The folks in feral pig areas may not agree with his assessment that our forests need more disturbance--after all, a rooting pig is not the same as a brush-eating cow or herd of goats. You would think that browsing/grazing would be more similar to fire than rooting is.

I seem to remember that oak savannahs were maintained by fire and grazing.

On the other hand, his assessment that pigs can save oak trees supports the idea that each animal nurtures its own food source.

By the way, pigs aren't just a problem where they are an invasive species. They are also a problem in their historic native range in France, because their predators are gone and they are no longer hunted enough. Same problem as in America.

There's some interesting results when you Google "do forests need disturbance." The top result is the Wikipedia article on "Forest Dynamics." Quote:

"The sets and patterns of natural disturbances that characterize a particular area or ecosystem are referred to as the ecosystem's disturbance regime. A natural community is closely linked with its natural disturbance regime.[3] For example, temperate and boreal rainforests typically have a disturbance regime consisting of high-frequency but small-scale events, resulting in a highly complex forest dominated by very old trees.[4] In contrast, forests that have a disturbance regime consisting of high-severity stand-replacing events, such as frequent fires, tend to be more uniform in structure and have relatively young tree stands."

A low stocking density of pigs would cause "high-frequency but small-scale events."

Another great search result: https://treesforlife.org.uk/into-the-forest/habitats-and-ecology/ecology/natural-disturbance/

Quote: "Wild boar (Sus scrofa) formerly played a key role in the forest, as they still do elsewhere, in parts of mainland Europe. wild boar are omnivores, and their habit of rooting for food disturbs the soil, again creating a seed bed for trees, and reducing the dominance of bracken by breaking up its rhizomes." (I guess they don't have wild boar in the UK anymore?)

So there you go...they create the right conditions for more baby trees, whose roots happen to be one of their favorite meals. Another example of animals creating their own food source. They kill the mature tree, create a seedbed for baby trees, then come back and eat the baby trees' roots once they've sprouted.

Another quote: "It [tree-killing disturbance] also helps create an invaluable part of the forest ecosystem – dead wood. Shattered branch stumps, fallen branches and fallen trees support an incredibly rich array of highly specialised life-forms. Windblown trees also create habitats for organisms such as Agabus wasastjernae, a rare predatory diving beetle which lives in the pools of water that form in the hollows left by the upturned rootplates of Scots pines. The exposed, sometimes sandy, soil remaining in the rootplate often provides the ideal medium in which solitary bees and wasps can make their burrows, and it is not unusual for birds to make their nests among these raised roots." Again, when pigs kill trees they create habitat for more food species for themselves.

So I conclude: yes, pigs kill some trees. But, this is not necessarily a bad thing, as it creates habitat for more species, restarts forest succession, and creates more food for the pigs. Also, pigs are a forest animal, and in nature they need trees for shade if not food. Holistic management of pigs means you have to find the right stocking density for this to work. (By the way, I couldn't find any references to Alan Savory and pigs). So the only question when we want to keep pigs in a woodlot and protect certain trees, but not others, is how best to protect the ones we want. Maybe Joel's book will enlighten me.

This reminds me of something Joel keeps saying on the YouTube videos I listen to: "we need more trees and less forest." I don't understand that yet.

Baale laale wrote:Observational Monitoring: Long-term observation and monitoring are crucial to assess the impact of pigs on your specific woodlot. Document any changes in tree health, growth, or mortality over time. This will help you make informed decisions and adjust your management practices as necessary.

That's why I like the idea of taking a slice of a tree root to look at the starch storage. I tried to post the very impressive color photographs of the root slices, but it didn't work. Here is the link again: https://www.uvm.edu/femc/attachments/project/1138/Estimating_starch_content_in_roots_Wargo.pdf

I figure if the crowns look good, and a random sample of roots shows high starch levels, it's safe to assume that tree can share some starchy roots with a pig.

Penn State published a list of trees that tolerate some root disturbance and a list of trees that don't:

Trees Tolerant of Some Root Disturbance
American holly - (Ilex opaca)
crabapple - (Malus spp.)
eastern redbud - (Cercis canadensis)
hickory - (Carya spp.)
honeylocust - (Gleditsia triacanthos var. inermis)
hornbeam - (Carpinus spp.)
ironwood - (Ostrya virginiana)
Kentucky coffeetree - (Gymnocladus dioicus)
Norway spruce - (Picea abies)
red maple - (Acer rubrum)
river birch - (Betula nigra)
sycamore - (Platanus occidentalis)
Washington hawthorn - (Crataegus phaenopyrum)


Trees Sensitive to Root Disturbance
beech - (Fagus spp.)
buckeye - (Aesculus spp.)
cherry/plum - (Prunus spp.)
dogwood - (Cornus spp.)
hemlock - (Tsuga spp.)
larch - (Larix spp.)
linden - (Tilia spp.)
magnolia - (Magnolia spp.)
oak - (Quercus spp.)
pine - (Pinus spp.)
sugar maple - (Acer saccharum)

Source: Underplanting Trees - Respect the Roots - Penn State Extension https://extension.psu.edu/underplanting-trees-respect-the-roots

A good article on the arrangement of structural roots and feeder roots, and the impact of construction on mature trees: The Dangers of Root Disturbance | Arborilogical https://www.arborilogical.com/articles/all-articles/article-repository/2009/march/the-dangers-of-root-disturbance/