#6 Thinning to grow fat trees fast(er)

Thinning may be the most controversial and poorly understood aspect of growing trees. Whether for conservation, timber or both, competition between trees may be slowing their growth and reducing the quality of your forest. 

In this podcast Rowan explains how managing the 'personal space' around each tree can help create a more valuable forest.  He also touches on the risk of believing in a commercial thinning option and why the expectation of a market for small diameter trees has undermined the development of high value forests on farms around the world. 

Photo: thinning our 22-yr-old English Oak plantation in 2017

Links:  

Our website: https://www.agroforestry.net.au/

Rowan's papers on thinning and pruning:

https://agroforestry.net.au/edit/pdfs/pruning%20paper%20afg%20mag.pdf

https://agroforestry.net.au/edit/pdfs/blackwood%20conference%20paper.pdf

Our YouTube channel: https://www.youtube.com/@bambraagroforestryfarm4008

Music by Mountain Grey.

Transcript

SPEAKER_00 0:15

Well, welcome back to another podcast. This one's going to be about thinning trees out, giving them more space and and letting them grow. It's funnily enough, it's probably the most controversial issue in tree growing for timber, certainly around the world, but increasingly also to do with biodiversity. I drive around the landscape, I see a lot of plantings done for conservation. They fill it up with trees when they're young, but those trees, as they develop, begin to compete. And that's what we want to talk about today. How there's a shift in a forest from particularly a planted one or a naturally regenerated forest. Initially, when the trees are very small, they benefit from being close to their neighbors. I call it mutual shelter. But as they develop, the increasing competition for light, largely, but also moisture and to lesser extent nutrients, I guess, means that their growth is affected. Now, there's a lot of discussion in the popular media about uh happy trees, caring trees, talking to each other, and that has driven a lot of people to think for conservation you should never touch a forest, that uh we just let nature take its course. I think I've probably said before nature has no course. It's a response to a range of uh natural processes. But what we do in this podcast is talk about how particularly farmers, but anyone dealing with tree growing, can manage a forest or a planting over time and therefore direct its growth to achieve the outcomes they want. And they may be conservation outcomes. So I've got no problem with that. We do a lot of planting that has that purpose in mind as well, but there could be aesthetics or timber production and others. Now, whatever you're planting trees for, you have the opportunity to tap its growth and direct it in a certain way. And I'm not going to say there is a right way or a wrong way. My interest is getting back to the fundamentals and saying this is how trees grow. And if you understand that, maybe you've got some choices you can make about which way you want to grow it. Nature and growth will take a forest, and if it's suited to the environment and doesn't suffer extreme drought or fire, it will grow. But where it grows to is not predetermined. The potential we have as managers is to direct that growth. Joskin Tibbetts came on and we talked about pruning, which is one intervention. But thinning is probably the critical and most important one. Managing the competition in a forest. And in order to do that, I've got to go back to the real fundamentals. And today we're just talking about thinning or controlling how much personal space each tree has. Maybe that's a good way to look at it, the personal space available to each tree and the nature of that space. What impact do other trees in the landscape have, both smaller, larger, same species or whatever, what impact do they have on the nature of that personal space around a particular tree, and how does that environment created by that space affect tree growth? I'm going to use that as a starting point. First of all, we need to understand how a tree grows. There are two growing points in the above-ground part of the tree. It's height growth, which is occurring at the tip of the tree and the tip of the branches, elongation, and there's thickening, thickening of the branches, thickening of the stem. And largely today we're talking about that thickening. It's the growth that occurs from the cambium just below the bark, all over the tree, that produces wood cells on the inside and bark cells on the outside. So when you go and see a tree and hug a tree, for example, you're feeling that diameter, the distance around the tree or through the tree, and all that growth has occurred over the top of a few cells that were created as the tree grew past that point in height. Now, one thing we do know is that for many, many different reasons, fatter trees, larger trees, are often the aim, often the purpose, often the reason we're growing it, whether it's for biodiversity, aesthetics, ability to withstand a bushfire, or just for timber production, fatter trees tend to be of greater value. It's certainly what we've produced on the farm. Fat trees, they look great. And when we do harvest some of those fat trees, they're really good for sawmilling. They produce better quality timber, wider boards, every aspect of it becomes more profitable and higher value, which is my interest in managing the personal space around these trees because it does have an impact on how the trees grow in diameter. So, what happens when a tree grows in diameter? Probably the easiest way to think of it, and I know it's not the case for all trees, but you've probably seen growth rings in trees. The growth ring of a species that's deciduous or one in a temperate area, there tends to be one growth ring per year, annual growth rings. So if we open up a tree, a teacup in Darwin or an oak in the temperate region, or even a eucalypt growing in a cold area, we can actually see how much it grew each year by looking at the cross section of this tree. So if we look at that increase in diameter growth, the distance between the ring, it tells us a lot about the environment of that personal space in which that tree was growing. Because in order to grow wood, there has to be a canopy that's active, exposed to sunlight. If that canopy is large enough, it will maintain a supply of sugars down the stem, feeding the cambium, which put the growth on. How much growth you get seems to be dictated by how active that canopy is and how big it is. Of course, it needs water supply and sunlight, and these might vary to some extent over the seasons, but you can expect on a normal year, an average year, you get a certain amount of growth per tree. I was trying to think of a way of describing this, and let's um let's imagine you plant a tree in a big well or a pipe. It's two meters in diameter, and you plant the tree in the middle of this dark pipe, and the only light that's coming is directly from above into this pipe. And you plant a very small seedling there, and it probably loves the environment. It's beautiful and sheltered, there's plenty of light coming down, it can grow a canopy, and in those first initial years of growth, it may, for example, put on one centimeter growth all the way around. So the growth rings are one centimeter apart, and if you measure the tree one year, the next year it would be two centimeters bigger because there's one centimeter extra growth all the way around the tree. As the canopy tries to get larger, and this is the key about personal space: in order to maintain that one centimeter wide growth ring, it has to have a larger canopy next year than it had this year. And that's because that one centimeter growth of wood is going to be on a larger circumference of tree. So there's going to be, I could work it out, 10-15% more wood required in terms of cell growth than there was the previous year in order to maintain a one centimeter wide growth ring for that particular year. So you can imagine in order to achieve that or maintain that growth rate, the canopy has to be larger than it was the year before, and therefore it expands. Now, canopies can be deeper, but in most cases it is the width of the canopy which determines how much light it gets, not how deep it is, because the lower branches, the ones in the shade, aren't going to be very productive. To capture more sunlight, the canopy has to be wider. So imagine our tree growing in our two-meter-wide pipe and it's starting to approach the edges, it can't expand anymore, and what you find is the canopy then is fixed. There's only so much light available that canopy. So last year it put on one centimeter of diameter, same amount of canopy, it's not going to do that. Maybe 0.75 of a centimeter between each growth ring. And the year after it's got to try and grow on top of that maybe half a centimeter and then a bit smaller. And what we find is if the canopy's not expanding because it's been restricted by something, and you know I'm going to talk about restricted by other trees in the forest, but let's just stick to the pipe example for a moment. Each subsequent year the growth ring will be smaller in width than it was the previous year because the canopy can't expand, and eventually it'll get to a point where there is only millimeters of growth per year. And at this point, it's really tricky. Some trees shut down their growth and become stagnant, actually just stop growing, hold their space. This is actually quite common in rainforests, even where trees under the canopy shut down and wait. They're waiting for a storm event or or dare I say, someone to cut down the tree next to it and create a more sunlight and then they can start growing. But in many forests or most forests, the trees can't wait that long. And they slow down to the point where they can't produce enough energy from that canopy to maintain the growth that they did before, particularly if the trees around it are growing taller and the shade is increasing. So that's when we have the trees dying, the ones, the losers, the ones that are left behind, the ones that are feeling the pressure from the other trees around it. And in a native forest environment, most native forests and many plantations, planted trees in conservation areas, the trees are allowed to grow until they reach that point of very intense competition, and you find that some trees start to die. It's called self-thinning, and funnily enough, there is a very strong mathematical relationship, how many trees can actually survive that process. And this has been studied for decades. Self-thinning is not new science. About a hundred years ago, people in America really studied the mathematics of this and helped us understand how we can appreciate how much space we need for a tree to maintain growth rates and what impact does that increase in competition have on whether they actually survive in that forest. Let's consider what we're doing with many of our tree planting projects. We plant trees in a block when they're young, they're like that little tree in the well. It grows very well. They actually benefit from the mutual shelter provided by their neighbors, particularly shelter from the wind. The wind can have a damaging effect on height growth and branch development. So having mutual shelter, as I call it, is a great advantage. And then things start to tip over. The personal space around the tree becomes restricted, it starts getting more competition, less mutual benefit, and eventually to the point where the tree has to slow its growth down because it hasn't got the canopy to maintain its growth rate. And as I said, most native forests and conservation plantings are at that point. If you go into a native forest or even just go to look at the timber in your house that came from native forest, you'll notice that the growth rings are often millimeters apart. That is not a reflection of the potential of the tree to grow, it's a reflection of how that species was grown. We can grow trees faster, we can maintain their diameter increment if we control the personal space around the trees. So the other way to think of it, let's think about free growth. We call that when a tree is not exposed to any competition. It's growing in full sunlight out in the middle of a paddock. Now we start thinking, well, there's no mutual shelter there. Although this tree has got ample access to light and moisture, because there's no competing trees around it, it is exposed to the elements. So there is a sweet spot there between having enough trees on your in your forest to provide the mutual shelter, which may include, you know, suppressing the undergrowth, improving the hydrology and the climate in amongst the trees, maybe increasing the fertility or the presence of mycorrhizal fungi, all these things might occur. But if you have more trees than that, you're going to find your trees are growing slowly. So it's about looking at the forest, and we can do a lot of data analysis to help this, but essentially you just look at the forest and you can think about are these trees benefiting from the mutual shelter from the other trees around them, or are they beginning to suffer? Um, that's just an objective assessment. Whether or not you act on that depends on whether you think you'd prefer if there was a different environment around that. So we're looking at that sweet spot in many of our forests. And I would argue that most of our native forest and most of the plantations around the world, particularly those I've worked in on farms in Southeast Asia and America and others, they're crying out for a thinning. And they're crying out for a thinning because the trees have been let to grow, they're too close together. The objectives of the landholder is to try and produce larger trees, but their trees aren't growing because there's too many. And they feel caught in a bind as landholders because they say, Well, I planted all these trees, I want to get a return for every tree that I planted. And as a result of that, they're asking around and begging people to try and find a market or buy their small diameter trees, and the buyers are saying, Well, I can't make any money out of that small diameter tree. Small diameter trees are the most expensive tree wood to harvest. You cut a tree down, whether it's a chainsaw or a machine, you've got to cut down many trees to make a cubic meter of wood. And then you've got all these small trees with lots of bark on them. The wood may be lower quality because it's juvenile wood, it's early, it uh doesn't has a wide sap wood, hasn't you know, hasn't had time to grow over the pruning wounds. So many factors mean that this wood, this small diameter wood, which is choking up our forests and our plantations, is actually the most expensive, lowest quality wood to try and find a market for. I appreciate right around the world, everyone's desperately looking for a market for this timber. It's the holy grail of forestry, really. Everywhere I go in the world, people are desperately saying we need more research to find a profitable use for these small diameter trees so that we can go into our forests and harvest them and make money out of these trees that we planted. Maybe it's a reflection of my time, my 40 years in forestry. It's not going to happen. Whether it's LVLs or biochar or even firewood, if we do find that these small diameter trees are worth growing and harvesting, people aren't going to harvest them by taking out individual trees out of a mixed species forest or a small planting on a farm, because it's just going to be too expensive. They're going to grow those logs or get them from plantations on flatland, large monocultures, probably going to clear fill the whole plantation to get it because the economies mean because the timber is so expensive and low value that to make the whole process viable, those trees almost have to be free. And that's the situation we are caught up in Australia at the moment. There are hundreds of thousands of hectares of unthinned, heavily stocked plantation eucalypse, and people are saying we need a market for this. And I'm saying, well, yeah, you might find a market for that, but it's not going to encourage anyone to plant more trees, particularly to grow trees on farms for high value products. And what we really need, if I'm going to get distracted and talk about the research needs, we need more research on the quality and the value of the products that we can produce if you manage the plantation intensively, thinning and pruning it, because we know it's possible. You don't have to believe me, but we do need some research on the quality of particularly fast-grown eucalypts, uh, large size timber harvested from very large ones, not those small diameter trees. Anyway, that's a little bit off the track. So when we talk about thinning, we're talking about managing the personal space around a tree to maintain or maximize the growth rate of those trees in diameter, and in doing so achieve the outcomes that we want. Well, large trees for biodiversity, uh, large trees for more resilience from bushfire, or large trees because they're more attractive or higher value for timber. The other point is we talked about pruning in a previous podcast. We prune our trees because it has a dramatic effect on wood quality. By removing the knots, we get clean timber, and that allows us to do lots of things at a lower cost. It reduces the cost of harvesting and processing because you're not discarding or managing or chopping off branches, and it also increases the recovery of higher value products through the process. But if you're going to prune trees, pruning is a cost per tree. So every time you go into a forest and prune a tree, say I've got a beautiful tree in front of me, I'm going to prune it, climb it, or use a pole pruners or whatever I do, I'm going to invest some money into this individual tree. And then I go to the next tree. If the next tree is only three meters away and I invest the same amount of time and money into that tree, those two trees we know are going to start competing for light and they're both going to grow slower. If they grow slower, I've spent twice, I've spent more time pruning, but I get slower growth on the trees that I prune. So rather than walk three meters to the next tree, I like to walk six or eight meters to the next tree and then prune that one because I'm putting the same amount of work per tree in, but every tree has more personal space, more light, more access to moisture and nutrients, and in response will grow faster, therefore giving me a greater return for that pruning time. And that becomes a big factor. If you don't prune, and this is what a lot of conventional forestry around the world has got itself in such a bind, because they don't prune, they need to maintain a high stocking rate of trees in the first 10 to 15 to 20 or 30 years, depending on how fast the trees grow, to suppress the branches on the trees so that they're small and in some cases those branches die and fall off, because we know that those branches, particularly if they get large, make that timber unsuitable for structural purposes or furniture and other uses. So they use competition. To avoid pruning, but by doing so mean that their trees grow slower and it takes longer. And it also means that they get to a point where the trees are stop growing. And unless they take about half the trees out of the site, their best trees are gonna suffer. So they're desperately looking for a commercial thinning operation. It's the trees are so big then that the cost of going in there and just felling them and leaving on the ground to rot is too high. They're desperate for people to come in with heavy logging equipment, thin it all. So if you're on a steep site or in a irregular planting on a farm, you're not going to get these machinery coming in, which is why a lot of farmers in our area. We prune our trees and we thin very early trees that we don't want there for biodiversity, shelter, aesthetics. We take them out early when they're small so that they don't start competing with our timber trees. The reason we plant, we still plant more than we hope to harvest is because you need a selection ratio. Let's say you take a hundred people, line them up from the smallest to the tallest, and then you're picking a basketball team and you pick the tallest 10. If you only have 10 to choose from, you haven't got the ability to pick the best trees. And as a result, you still want some sort of selection ratio, as well as that early mutual shelter. On a very windy site, you still need to achieve that mutual shelter, and you might do that by planting a few more, or maybe planting fast-growing understory around your trees, but you don't need to crowd the trees. There is a common saying amongst even experienced tree growers, which surprises me. They say you plant the trees close together, so you force the tree up to the light. It's entirely wrong. But then people will show you. Look at this tree growing in this light well in the forest. It's being forced up, it's tall and skinny. And I said, Well, the reason it's tall is it's had beautiful shelter, and the growing tip has grown to its potential given the site conditions. It's grown quite well. But the reason it's skinny is because all the other branches have been suppressed and there's very little canopy on that tree, so you end up with a very tall, skinny tree. Compared to the tree growing out in the middle of a paddock that's had full sunlight, that's been exposed to the elements, and the growing tip has been affected by exposure to wind or drying effects or other things, and you end up with an apple-shaped tree. So that's a fallacy. We need enough shelter for that particular site so that the growing tip can grow to its potential, but that doesn't mean you want to shade the side branches in order to grow the tree straighter. That's not required. We know that shading the side branches, killing them off because of shade, is just reducing diameter increment. Well, you'll just say, well, I've you've been pruning the branches off. Yes, pruning does slow diameter growth, but only for a short period of time. What we find is that uh pruning actually improves the form of a tree, because a young tree tends to be very conical in shape, the main stem or the trunk. So as you go up the trunk, it gets smaller in diameter because there's active branches all the way down the stem. But if you take the lower branches off and lift the active canopy higher, you actually find that the lower stem becomes more cylindrical. I've got off the track again, talking again about pruning. Today's focus is on the thinning aspects of the tree. So we've talked about the personal space and the dilemma that many growers find themselves in, and the fact that for many farmers, particularly, inexperienced tree growers, they've spent 10 to 15 years caring for these trees, and then someone like me comes in and says, Well, you said you wanted to grow large trees, these trees are all competing. You've probably got too many trees, and you probably have to get rid of them. And because they're small, no one's going to give you any money for them. If you can use them yourself for firewood or posts, that's fantastic. But you'll probably only get a return equivalent to the labor you put in. The actual tree standing in the forest is not going to be worth anything. In fact, you might see it as a cost to get that tree out. So managing trees in a forest is about balancing mutual shelter with competition for light to achieve the outcomes you want. One way to think about this competition or this personal space in a forest is to think about leaf area. For each species, there seems to be a certain carrying capacity in leaf in that environment. Now, during the period of a season, this varies. So if you if you're in amongst a eucalypt forest, for example, you'll know in the in the heat of summer, when moisture competition in the temperate regions is severe, the canopy starts dropping leaves, reducing its leaf area. But over the course of the year, let's just talk about spring when a lot of the growth is actually occurring, there's ample water, ample nutrients. There'll be a maximum leaf area for eucalypt leaves in that forest. And same for a pine forest or same for an oak forest. They're all the same. Now, because they're different types of leaves, different genetics background, they do vary in their leaf carrying capacity, and they also differ in their productivity, the amount of sugar that they can produce from the same amount of leaf. So we find that between species there is quite big differences in the carrying capacity of a forest. The amount of leaf for a particular species does govern how much sugar is produced and flows down the stem. But if we think about stocking rate, how many trees there are per hectare, if there is a fixed amount of leaf area, if we halve the number of trees in the forest and they're still well spread through the area, and we allow the trees to respond, the ones that we leave behind, they will put on pretty close to the same leaf area that was on the twice the number of trees before. So each tree in that forest, on average, will have twice the amount of leaf. So it will produce twice the amount of sugars that will flow down the stem, and you'll probably find twice the amount of wood growth occurring on that stem compared to the forest that wasn't thinned. And really, that should be fairly clear, obvious to many people, and we have an option then about how many trees we spread spread that available or potential leaf area over. I guess I like to concentrate them on less trees because if you get more leaf on an interval tree, you don't only get better growth in diameter, you also potentially get a much healthier tree. So I guess the question many landholders have is say, do my trees need thinning? Or how do I know when to thin and how hard to thin? It is possible to do some measurements and compare them with what's occurring in natural forest or plantation data that we have and get a feel for how much you need to thin. But the starting point is, I think for most landholders, is to just look at the trees and look at their history. If you're able to read the growth rings and their annual growth rings in that tree, cut a few trees down, or if one is damaged but a good sized tree, take it down, study the growth rings and see whether or not growth is starting to slow in diameter or has done over the recent years, and can that be explained by competition with other trees? The other way is to look at the canopies of the trees. If we, as we said, the canopy has to be larger every year in order to maintain growth rate, we can just look up at the canopy and ask the question: is there space for this tree to expand its canopy next year? If there is very little light or space between the canopies, we can assume that it's like growing in that deep well, it's been confined by the sizes, and the canopy won't be able to grow anymore. We could ask the question: are the trees next to our tree overtopping it and shading it directly in some way? And if that's the case, we expect the tree that's been overtopped will be in the shade, not full sunlight, and will grow slowly for the same amount of canopy. If we start looking at the canopies like that and saying, well, if I want a tree that I'm standing beside to grow well and expand next year, which of the trees around it should I remove to provide a nice balanced area for that canopy to expand into? We often use a paint tin. We walk through and select the best trees in our forest. Well, what we do is we grade them one, two, and three. And you might say, I'm gonna walk in the forest and I'm gonna put a nice green mark on all the number one trees, the best trees, the straight trees, the healthy trees, the ones of the species that I want to keep. And then I'm gonna go through the forest again with a red paint tin. And I'm gonna mark all the trees that are no good for my intended use, whether that's timber production or otherwise, and saying, Well, that tree is crooked, it's a wrong species, or it's had insect attack, or it's rot, or the bark's damaged, or it's leaning over, and you might say, They're all my red trees. Then you look at the ones that haven't been marked, they're all your number twos. We'll just leave them aside at this stage. Then look at the forest and say, if I cut down all the trees that I've marked with red paint, all the number threes, will that release a lot of growing space for all the remaining trees in the forest? Well, it's certainly going to release some, if it's 20-30% of the number of trees in the forest, there's going to be a lot of extra space. Maybe that's the first thing you do. But I'm also going to say you might keep a few of those number threes if they don't have some good trees in the vicinity, but you still want tree cover on that site for biodiversity or shade or something else. So we're talking about removing the number threes that are in the vicinity of other trees. And you might find that's all you need to do to kick start the growth of that forest. Now, are you going to get much product from those number three trees? They're the crooked, skinny, bent, um haven't grown very well trees. Some of them might be quite large, heavy branches, lost their tops, uh, but all they're going to probably have in them is firewood. And because you've got on a farm, possibly not a lot of volume of that, I suspect you're not going to find a commercial market for it. And that's okay because the reason for doing it is in order to drive the growth towards the best trees in the forest. Now, if you come back at the following year and you've taken out all the worst trees, or a few years later, you've taken all the worst trees out, and you think, well, all the trees are pretty good now. There's no really bad ones, but the competition is starting to build again. I can see the lower branches are getting affected and the upper canopies. They still haven't got room to expand into. Maybe we should move it, remove a few more. You might do the same thing, but this time when you're picking number three trees, you're being much more ruthless. You're saying they've got to be perfectly straight or they've got to be perfectly this, or you might start saying, These are two good trees, but they're too close together. Now, how close is too close together in an open forest? Well, I suspect you can have a couple of trees three, four, five meters apart. They will be touching canopies on one side, but as long as there's plenty of open space around it and most of the light is coming from above rather than the side, I think you're probably going to be fine. So I'd concentrate on removing the poorly formed trees. And it may be that you get to the point where rather than take out the trees that are performing badly, you're starting to get a few trees which are big and you want to take them out for a building project or for sale or something, and then you start taking the biggest trees out, and that'll start moving your forest forward as you release larger and larger gaps. How do you actually do it? Well, this is a tricky situation for a for a manual operation where you're using a chainsaw and felling trees. If your forest has become quite dense, it can be very tricky to harvest individual trees. And you'll see that in the big industrial commercial plantations where they use machines, they go through and they take out every third or fifth row and some of the trees between those rows with the machine, and they can get them on the ground quite well by doing that. They can get access. But if you're going through a forest and just trying to cut down some big big trees that are close to others, you may find it's hard to get them on the ground. We use a logging winch to help us directionally forward, but the key is we do a lot of that thinning to waste very early so that we create a parkland, and a parkland is easy to move through and easy to get trees on the ground. The other option, which you can do at any stage, is you might look at ring barking or stem injecting the trees. This is often done in native forests, for example, which come up very thick, regrowth, a couple of thousand regrowth stems, 10 to 15 centimeters in diameter in the forest. Very labor-intensive or tricky operation to cut those trees down, and even if you do cut them, they'll sprout again from the base and then crowd out your forests. So they do a lot of stem injection. They inject a herbicide into the stem, into the sapwood, it flows up the trunk and kills the canopy. And when the canopy dies, the root system dies, so you rarely have a problem of a flush of growth coming from that tree. The other option is ring barking. You actually remove the bark from the tree, just the bark, down to the wood, but you have to remove it all the way around, and you've got to do it so there's a significant gap. So you might remove five centimeters of bark in a strip right around the tree. This is the easiest time of year to do this, is in spring when the tree's actively growing. I sometimes do this for demonstration using a handsaw or a small chainsaw, walk around the tree very quickly, just nicking it down to the wood, and then using a hammer or the back of an axe, knocking that bark off. What you're doing then is you're not actually killing the canopy of the tree because water can still travel up through the sapwood. You are potentially killing the root system because sugars flow down the inner bark, they can't get past the point where you've ring barked the tree and the root system will die. Having said that, I have had farmers ring me up saying, I've ring barked all my trees, but some of them died and many didn't. What's going on? And what's happening there is the plantation was probably getting to an age where there was quite a significant amount of root grafting between the trees, and that root grafting meant that a tree could actually survive, its canopy was getting water from the root system, its root system was getting fed sugars from another stem next to it, and it sounds perverse, but you can actually have a ring-bark tree that stays alive as long as the root system is being supplies. And that raises the other issue where we we know there may be the potential for root grafting between trees, and this is very common in eucalypts. I've seen it in pines and oak, it's many, many species. Over time, the roots cross over and they just graft together, and then the flow of water up the stems can cross that graft, and the flow of sugars down through the trunk can cross that graft and feed the alternative root system. And as a result of that, if you cut the trees and put a herbicide on the stump, which is quite a common practice to try and kill trees, that herbicide could be drawn down into the root system across the root graft, and then up the tree beside it and kill the tree that you're actually trying to help by doing the thinning. And we call that flashback. I won't touch that method, it's too risky. But if you put the herbicide into the sapwood, it will flow up to where the active canopy is, and in response to that, you'll find that you very rarely get a flashback if the tree is still standing and you've put the herbicide into the into the main stem. So that's uh a couple of options on thinning. Again, the larger the trees, the more expensive and labor-intensive a thinning is. So the key is, and the difficult thing for so many landholders, is to do it before the competition starts, when the trees are quite small, and once you just got enough mutual shelter. So I wouldn't go into a plantation on an exposed hillside when they're only three or four years old and cut half the trees down because those trees are probably just starting to shelter each other because it's an exposed site. So on an exposed site, you might just leave the trees there for a little bit longer, but then watch how they grow. And when you think the competition's becoming too severe, then you can start reducing that. And again, I mean, I could go through lots of graphs and details and stocking and talk about basal area and leaf area indexes and various other things, but the key is watch your trees, measure them if you can. If you've got a tree that does not shed its bark every year, and that might be an oak or a pine or a blackwood or or even some of the iron barks and other eucalypts that hold their bark, you could actually just walk through your forest one day with a diameter tape, measure the trees, and paint the number on the stem. Pick all the nice trees, the best ones, and then next year come through and do it again and write down how much it actually grew, and then go back a third year and do it again. We're exploring how we can do this on digital tagging and other methods, but whatever you can do to record the annual growth of some of your best trees, and then you go back and look at those and say, Well, this tree is slowing down. Look around, look at its canopy and say, I can see why it's slowing down. I'm gonna have to thin this forest. So that's really the key. Grow your trees as well as you can. How big do you want them to get before they start becoming commercial? Well, that really depends on the species. Uh, is the sapwood millable or saleable? Uh, do you get a premium for the heartwood? Uh, what effect did the pruning history have? It's difficult to tell. But on our farm, I'm finding with my own sawmill and logging equipment, it is not worth milling a eucalypt if it's not over 40 or 45 centimeters in diameter. And as a result of that, I've now got a guide in my mind about how much I could thin to waste early and still not miss out on the opportunity to start harvesting some commercial logs. I'm not going to fuss around with trying to find products for 10, 15, 20, 25 centimeter diameter trees. That wood is low density, it's because it's juvenile wood, the knotty core is huge, the bark is difficult to remove, it's not going to be viable to do. You don't have to make money out of every tree in order to create a profitable forest. In fact, a profitable forest is one that's producing high value material as quickly as possible, and you can do that by spacing the trees earlier, ensuring that they are growing in a sheltered environment to their potential, and that the growth that is possible for that site, the leaf area, is going on the trees that have been well managed or are straight or are of the species you want. And none of what I've said contradicts the potential to. Get biodiversity, ecology, and aesthetic outcomes from your forest as well as timber. Because so often having large trees adds to the aesthetic and the biodiversity and the ecological values of your forest. Having them further apart allows you to do things, grazing, understory, walk amongst your trees. It actually adds value to all the other aspects of it. A dense dark forest is often one that creates stress for the landholder. It doesn't produce value. Trees take much, much longer before they reach a commercial size. It has fewer ecological, environmental, or aesthetic values associated with our forests. It's probably not somewhere you want to go. Certainly not somewhere you want to go and have a picnic compared to a well-managed open parkland of trees that are providing a spectrum of values. So I see no conflicts between managing our forest thinning and pruning in order to get quality timber. I find a very good match between those actions or those management options and all the other reasons that we want to grow trees on our farm. And that mix is probably not what we're seeing in conventional forestry, or where farmers grow the forests that they're told are the best for timber production. Or effectively, they're copying the production models used by large forest growers who, admittedly, may have vertically integrated operations, have access to the machinery and the processing to get a product out of a small diameter tree. But I dare say they're not paying themselves for that small diameter tree. They're just trying to generate a create a business. If you approach those companies and say, Oh, I can see you're harvesting uh 20 centimeter diameter trees or 15 centimeter diameter pine trees, I've got lots of those. Come and buy mine. Like I know we've got plenty of those, and they're not worth anything. Despite the fact that they're producing a valuable product, because the product they're producing, for it to be viable depends on having a low-cost resource. And that's really the trap we're getting into with all this enthusiasm for uh research and development to into small diameter trees, is that it's might be able to use the low-cost, low-value resource that we currently have in the landscape, but it is not going to encourage better management of the forests that we need in the future. It may just lead to a bit of clear felling and conversion of unmanaged forests back to agriculture. But it's not going to suddenly be a story down at the local uh community dinner where they say I made millions of dollars out of my 15 centimeter eucalyp in a thinning operation. It's probably not going to happen. And as we've seen with pulpwood, for that to be commercially viable, it is scale, uniformity, flat land, monocultures, rapid growth rates in high rainfall areas. I'm not sure that type of forestry is actually going to meet the needs of a farming community that's spread across a broad landscape, low, medium, and high rainfall, and even in the high rainfall areas, the farmers are looking to options to plant trees that support agriculture, diversify their farming operation, utilize land that's too steep or rocky or wet or dry for conventional agriculture, and that's not the sites that we're going to be growing these industrial type plantations on them. But with thinning, you may be able to produce high-value timber that is worth harvesting. For this morning, for example, I took out a just a single pine tree that we'd pruned out of our plantation. I just want some more pine timber available for renovations and jobs around the farm. So I'll be milling it into two-inch material, then packing, drying it, and just having it available when I need it. But I chose a tree that was only a few meters away from a good straight tree. So by taking out the tree that I took, which was slightly bent, I'll be releasing the growing space and improving the growth of the other ones. It was easy to fill because it was growing in a parkland. It was over 65-70 centimetres in diameter, I should go and measure it, and it was pruned to six and a half meters. So I've got a good log out of that. So I'll get a good recovery. Probably produce in the order of two-thirds of a cubic meter of useful timber out of that. It was well worth harvesting. It was well worth harvesting with a chainsaw and tractor. It was an easy operation. Knock it off before morning tea, half a day on the mill now. I'll have the product. I could sell that product directly to wood users or I could utilize it myself. If the tree was small in diameter, none of that would be viable. If I'd done a conventional forest on that site, I would have been desperately looking for a commercial thinning operation from that forest, and it wouldn't have happened because the forest is small in area and there's plenty of unthinned pine plantations. Why would anyone come to our place to buy small diameter pine? There's acres and acres and hectares and hectares of it in the country. And that's what I'm hearing in America and Europe, just the same thing. Plantations are not being thinned because the farmers were under the impression that they would get a commercial thinning, but the markets have evaporated, or the cost of the machinery and the labor have now become so high that you can't get a value for it. Or it's simply too far away from the markets. So the forestry that we saw in the 60s and 70s, which did require these commercial thinnings of small diameter material in order to keep the forest growing, in a first world country, it just doesn't seem to be practical or possible in the future. And I might be proved wrong, but as I said, if they do find some magic holy grail market for these small diameter trees, all you're going to see is small diameter forests. And uh we're not going to have the multi-purpose mature forests that so many of us talk about wanting for all their values, but also are going to produce these high-value solid wood products of the future. So that's a um a discussion about thinning. It's probably uh to some extent demonstrates a concern about some of the development approaches to forestry that have occurred in the last few decades. For farmers, we have alternatives. We don't have to participate in the programs that conventional forestry is able to apparently make work because of their scale and uniformity. But there are other options. As I said, I don't want to tell farmers why to grow trees, but if you want to grow trees of size, you have the opportunity to do that. And thinning or spacing, well, let's get back to that term I use, giving each tree sufficient personal space to grow to its potential is the key to produce high value forests for a whole range of reasons. So thanks very much for that, and we'll catch up again with another podcast in the future. Regards.