Section 17: Site Preparation

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Scooter
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Section 17: Site Preparation

Post by Scooter » Fri Feb 13, 2015 4:11 pm

When a block is site prepped, or scarified, it means that after the logging activities are finished, there is some sort of additional mechanical or chemical activity done to prepare the site for seedlings to be planted. The main reason that blocks are site prepped is to enhance the likelihood of survival of seedlings, and to attempt to optimize their long-term growth. A by-product of this activity is that it often makes it easier for planters to plant the trees, although in some cases, site prepping a block can actually make planting more difficult, depending on the planting specs.


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There are a lot of different types of site prep, such as mounding, trenching, windrows, and drag scarification. Most of these broad categories have several varieties of treatment that planters may eventually encounter.

Incidentally, when a planter screefs a spot for a tree, this is basically a type of localized site preparation. Some foresters refer to screefing as hand scarification or manual scarification.


Untreated Ground

Ground that has not had any site preparation work done can be referred to by quite a few different terms: untreated, unprepared, unprepped, unscarified, raw, or plant-as-is. Foresters tend to use the term untreated, while planters tend to say unprepped or raw. Occasionally, planters will see disturbances on the ground that were made by the tracks of skidders or other logging machinery. This can be confusing, but it isn’t actually an official type of site preparation.

If a section of a block has been treated, it’s usually fairly obvious, and easy to differentiate from raw ground. However, there are exceptions, which we’ll see in a few minutes.

Stump side processing happens when cut trees are processed where they are cut, which leaves slash widely dispersed around the block. Roadside processing means that trees are dragged to the roads before being processed. Slash along the roads is then piled and burned. Roadside processing usually results in cleaner blocks than stump side processing.


Trenching

If you’re trying to envision a trench, don’t think of large trenches that soldiers could hide in. Think of small ditches. A very close analogy would be the furrows that a farmer might dig to grow vegetables. In fact, trenches are sometimes called furrows. There are also other names for trenching, such as disc-trenching, or rips. Each name generally refers to a slightly different type of trenching. Although the term trenching is used more commonly than furrowing, it would be more accurate to refer to most trenches as furrows.

For disc-trenching, a rotating disc with tines or blades is used to rip up dirt and throw it off to the side, creating a one-sided trench. New planters will be given some training in assessing which side of the trench is the “cut” side, and which is the “flip” side. The difference is not always obvious, but it’s usually important for a planter to be able to assess which side of the trench is which. Most of the time, trenching machinery will have two discs on the back, and they each flip dirt to the “outside” as they drive across a block, so you’ll see the flip side of the trench alternating in every second trench. However, it’s possible to have machinery which creates three trenches with each pass, so sometimes you’ll see a 2-and-1 pattern in the flip side, or even all flips on the same side. This is further complicated by the direction that the trencher was driving at the time.

If trenches are well done, you may see that the sod and grass roots that were flipped off to the side will have mineral soil at the top, but as you dig down into it, you’ll run into the upside-down sod laying on the surface. The depth of this layer of dirt in the flipped-over part of the trench is quite important to some foresters.

Ripper plows are another type of trenching. Rips are usually made by a large sharp metal tooth digging down into the ground, and cutting a groove through the surface of the ground. The size of that tooth can vary. Ripper plowing is generally advantageous on very wet sites that require winter harvesting of frozen ground. When the ground freezes, some types of machinery and scarification implements become unusable because they cannot penetrate the frozen ground. A ripper plow is usually attached to a heavy bulldozer which can press the tooth into the frozen ground. It’s also possible to have a triangular blade, which throws the dirt better than a tooth does. Such a plow is very similar in appearance to disc-trenching, although the trenches will have symmetrical flips on both sides.

Don’t get caught up too much into worrying about memorizing the various types of trenching. I’ve seen both one-sided and two-sided trenches that were anywhere from a few inches deep and a foot wide, to giant trenches that were more than four feet deep and four feet wide. The main thing is to understand where the forester wants the trees to be planted. This isn’t consistent either.

Some foresters will ask for trees to be planted on the absolute tops of the trenches, no matter how much or how little dirt there is compared to organics and litter. Some foresters will ask for trees to be planted on the highest point of the trench where the plug is still able to be planted firmly in moist and squeezable dirt and decayed organics. Some foresters will ask for trees to be planted at the “hinge,” which is the point between the cut-out part of the trench, and the flipped over sod. In this case, the forester probably wants the plug to be in 100% dirt. Finally, some foresters will ask for the trees to be planted in the bottom of the trench. Foresters will almost never want you to plant trees on the cut side of the trench, because then you wouldn’t be taking advantage of the dirt that has been flipped over or exposed.

Why do foresters have so many different opinions on the best place to put the trees? It relates to the characteristics of the region and of the block itself. If a forester wants the trees planted high, he or she is probably trying to let the seedlings get a few degrees of extra warmth from the soil in a colder site, or to provide better drainage for the roots in a wet site. If the forester is aiming for trees planted on the hinge, he or she is probably focusing on eliminating the need for the planters to screef down to mineral soil. If the forester is asking for trees in the bottoms of the trenches, it’s probably either because the site is really dry and they’re trying to maximize moisture for the roots, or because there are cattle at large on the site and they’re trying to protect the trees from getting walked on. Cattle usually don’t walk in the bottoms of trenches.

Trenches are fairly common thoroughout some parts of British Columbia, although the machines generally can’t work on anything other than flat ground or minor slopes. Unless your block is almost completely flat, expect there to be patches of unprepped ground on hillsides and in gullies. Trenched blocks are usually priced pretty low, because they can be quite easy to plant in.

Hopefully, the site prep operator created the trenches running in lines perpendicularly away from the roadways through the block, rather than parallel to the roads. As a planter, you’ll want to be able to plant up and down the lengths of the trenches, rather than having to plant across them. Piece management is very important in trenched areas, to minimize the time spent crossing trenches. When you get to your first trenched section, ask your foreman or trainer for guidance on the best way to work your piece. You may find in areas where trees are planted in the bottoms or on the hinges that it can be difficult to follow trees properly, since they’re somewhat hidden from view.

When you get to a new trenched block, it’s pretty important to clarify with your crew boss what the specs are, so the forester doesn’t fault you for putting the trees in the wrong place.


Mounding

Mounds are created when a machine scoops some dirt out of the ground and makes a pile beside the hole. When this is done, the dirt coming out of the hole is almost always flipped upside down into a pile, just like the side of a trench is flipped upside down and outward. Therefore, most mounds are not completely made up of mineral soil. If you dig down into them, you eventually find an upside-down layer of sod resting on another layer of sod. Remember that for every mound on a block, there will be a corresponding hole.

As with trenching, there are a lot of different terms for mounding, and several of these types are distinct varieties of mounds. Some examples would be Bräcke, excavator, donaren, and hoe mounds.

Excavator mounds are created by an excavator. Hoe mounds are the same thing. These mounds are not created in any sort of grid-like or regular pattern; they’re just a random jumble of holes and mounds. Excavator mounds vary in size, but most are at least three feet across and a foot high, and I’ve occasionally seen much larger mounds which were six feet across and three feet high. Usually, when an excavator is making these mounds, it will park in one spot and make six or eight mounds in a semi-circle around itself, then move over about twenty feet to make the next set.

Donaren mounds are usually made by a machine such as a skidder, or by a tracked machine like a bulldozer or something similar. They’re very similar to disc-trenches in that they usually run in straight lines, and two rows of small mounds are made with each pass of the machine. Donaren mounds are usually only around two feet wide, and a foot high. These mounds look very consistent and their layout is much more patterned than excavator mounds, since they’re made in straight rows. Donaren mounds are sometimes referred to as mini mounds.

Bräcke mounds are very rare in BC nowadays. They’re like huge donaren mounds. They were moderately common in the 1990’s, but foresters ran into a lot of frost heaving issues due to large clay caps. They were usually about four times the size of a donaren mound, and they ran in straight lines. These mounds are still common in other parts of Canada.

Most foresters want you to plant your seedlings on the very top center of the mound, or the highest point of the mound. This maximizes soil temperature, and if the mounds were created to help with soil drainage, planting the tree on the top is the best way to keep the plugs from being over-saturated. However, in some areas, you might occasionally have a forester who asks you to plant the trees on the edges of the mounds, perhaps because the tops of the mounds get too dry, cracked, or crumbly in the late summer and fall. Planting on the top is better if a goal is to keep the seedling away from competing vegetation.

Mounds are less common than trenches throughout BC, mostly due to financial considerations, and it’s quite rare to see an entire block that has been mounded. Usually, a forester will make mounds in isolated swampy or wet sections within a block, where the soils are normally too wet for the trees to survive. You’re more likely to encounter a lot of water in a mounded area than in a trenched area.

Mounded areas are usually a bit faster to plant than unprepped ground, but definitely not as fast as good trenching. If your piece is full of donaren mounds, it might be advantageous to think about your piece management the same way that you’d approach trenches, although it’s a lot easier to “cross rows” of donaren mounds efficiently than it is to cross trenches. It’s also easier to follow trees on mounds because they’re more visible.


Scrapes

Scrapes are also made by excavators. The machine usually just uses the tip of its bucket, or an attachment that looks similar to a rake, to pull back the sod and expose a rectangle of dirt that isn’t dug into the ground. This is intended to avoid issues with water pooling in the scrapes, or frost pockets. The planter is usually expected to either plant one tree in the middle of each scrape, or two trees at opposite corners of a scape.

Scrapes don’t seem to be a very cost-effective type of site prep. If the main point of the scrape is simply to expose mineral soil for the planter, it would be cheaper to use a trencher, which costs far less to operate and which is much faster than an excavator. However, the advantage of using an excavator to make scrapes is that an excavator can work on steeper slopes than a trencher can, and for small and extremely steep hillsides, the arm of the excavator can even reach up or down to make the prep without the machine having to park on the steepest part of the slope.

Scrapes aren’t very common in BC. Scrapes can also sometimes be mistaken for small mounds, if the scrapes get dug out too deeply and the resulting pile of sod and litter and dirt increases in size. Make sure that your foreman or trainer explains to you exactly where the forester wants the trees within the scrape.


Windrows

Windrows are basically long rows of slash and other logging debris, like an elongated slash pile. A block may have dozens of windrows, each of which is almost the length of the block. Typically, these are created when a bulldozer goes through a block and pushes all of the slash up into long rows, so the area between the windrows is much cleaner. This process of pushing the slash into piles is sometimes referred to as blading. Blading helps to temporarily remove competing vegetation from planting spots. It also exposes soil to natural seed release, and increases the soil temperature by exposing the soil to more sunlight.

In some areas, the windrows are eventually burned, but in other areas, they are simply left to decay and rot over time. Blocks with windrows are usually relatively easy to plant on, since most of the slash has been moved out of the way of the planters. However, windrows can be awkward. Proper piece management is necessary, so you aren’t forced to climb over a windrow to get into the next section of plantable ground. Climbing over a windrow would be a potential safety hazard, and it’s also not very efficient.


Drag Scarification

Dragging is usually accomplished by having machines drag large metal cylinders around a block. These cylinders can be a couple feet wide, eight or ten feet long, and quite heavy. Quite often, they’re also covered with a bunch of steel teeth, which are sometimes referred to as shark fins. When a skidder or dozer drags these around the block, they break up quite a bit of the slash on the block, flattening it and making it easier for planters to walk around. Dragging can also be accomplished with blankets of heavy steel chains.

Breaking up the slash is helpful because it allows the slash to decompose more quickly over time. However, the primary reason for dragging is to spread the cones across the block more evenly, and to break them open to release seeds for natural regeneration. It is common for foresters to prescribe lower planting densities on ground that has been dragged than on nearby unprepped ground, under the presumption that natural regen will augment the density of the planted trees.

Sometimes, dragging is accomplished by simply having a bulldozer driving around a block, crushing slash with its weight, and sometimes dragging a single tooth along behind it. This is called “drag tooth scarification” and results in dragged areas with occasional small tooth marks cut through them. The groove from the tooth might look like a very tiny trench, only a couple inches wide.

It can sometimes be hard to tell that a block has been dragged, until you get out and start walking around it. At that point, you may notice that the slash is fairly low to the ground and is much more broken up than usual. Planters will often mistake dragged ground for unprepped ground, even though dragged ground is usually slightly easier to plant than raw ground.


Chemical Scarification

Insecticides and pesticides are often applied to seedlings being grown in nurseries. However, herbicides are sometimes applied directly to blocks. These herbicides are designed to target certain species of plants that may cause competition for the planted seedlings and naturals. Herbicides may target grasses, brush, and other broad-leaf vegetation, but don’t necessarily harm the coniferous trees if applied in the proper concentrations. Herbicides can be applied manually, by workers walking through the blocks and hand spraying from backpacks, or can be applied by aerial means, such as bush planes or helicopters.

Herbicides are sometimes applied before a block is planted, and sometimes after planting is complete. Herbicides are more common on blocks where large amounts of grass and vegetation are present. If a block is herbicided before planting commences, the planters will probably notice large areas of dead grass and vegetation, which makes the planting easier.

It is common on herbicided blocks for planters to encounter green strips where no herbicide was applied. This often happens along the edge of the blocks, because the herbicide applicators don’t want to accidentally herbicide outside the block boundaries. It’s also common for strips along creeks and ephemeral streams not to be herbicided, to prevent the herbicide from going directly into the water. Of course, chemicals always get washed off the blocks and into streams eventually, but most herbicides are designed to do their work in the first couple hours and then become chemically inert.

If you’re planting on a block that needed to be herbicided before it was planted, you can probably assume that it was rather nasty to start off, and may still have some ugly, grassy, and green strips to deal with.


Prescribed Burning

Broadcast burning is another way of treating a block, although it is done through oxidation rather than chemical burning. Intentional broadcast burns are almost non-existent nowadays, although they were common in the 1980’s. When burning was popular, foresters would light a block on fire after logging was done, to attempt to burn off most of the dried slash, and to make it easier for planters to get at the soil. However, the industry has recognized that creating air pollution and releasing carbon is not an environmentally sound approach to forestry, and also that decaying slash is beneficial for a block in the long term. Planters rarely work on burns anymore, unless they were created naturally by wildfires, or inadvertently due to man-made causes such as an escape burn while burning piles in the fall.


Selective Harvesting

Selective harvesting refers to logging that doesn’t remove all of the trees in an area, which means that the block is not a clear-cut. Sometimes, machines will remove perhaps half of the trees in an area, and leave the rest in an even pattern of distribution. Sometimes, long corridors will be cut through an area, to provide alternating strips of open ground and mature wood. It’s also possible for coniferous trees to be harvested but deciduous trees to be left standing in some mixed-wood stands, so planters may end up doing an under-plant below mature aspen trees. Finally, it’s important to know that selective harvesting isn’t always done with machines. It’s possible for people to go in and do hand-falling of trees, and to pull the timber out with horses, to minimize damage to the remaining standing timber.


Assessing a Block

When looking at a block and deciding how easy it will be to plant, there are a surprising number of characteristics that can differentiate it from other blocks, such as the geography, slash, and soils.

In terms of geography, important things to consider include the elevation, the slope (how level it is), and the topography (whether it is a rolling or flat surface). If the block is sloped, the aspect affects how soon the snow will melt off in the spring, because south-facing aspects lose their snow fastest. The ratio of block size to the length of roads, and also the placement of those roads, are important. The road network on a block usually determines where caches will be placed, and how easy it will be for planters to access all parts of the block.

In terms of the surface, the amount and average size/length of the slash is particularly important, as is the height of this slash above the ground. Are the woody debris coarse or fine? How green is the block, and what types of grass, brush, and vegetation are present? Different types of vegetation cause variations in difficulty of planting. The time of year that the block was harvested can also affect the planting. If the block was harvested in the winter, the vegetation might have been somewhat protected by the snow, and thus might be more resilient.

In terms of soils, the biggest question is whether or not there is a lot of rock in the ground. If so, what kind is it: cobble, regular stones, slate, or gravel? Is there a lot of soil, or is it mostly black organics? If soil is present, is it red/brown mineral soil, or powdery grey, or heavy in clay content? Is there any sand? Is the soil well-drained, or will it hold a lot of moisture?

We’ve already touched on a number of these characteristics previously, but the lesson here is that during your planting career, you’ll eventually learn to recognize a tremendous amount of variation between the blocks that you work on, and even throughout your piece on any given block.

Here is a link to a page (focusing on Manitoba) which reinforces some of the above, and also shows that there can be significant variation between provinces:

https://www.gov.mb.ca/conservation/fore ... eprep.html



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