So we're here at the UBC farm. Why did you choose this site? Well, I chose this site because it does have a lot of deciduous trees and we wanted to show the influence of these deciduous trees on the forest floor. And we have bigleaf maple and a lot of alder. And why do we have deciduous trees here?
Well, as it turns out, it's the disturbance history of the area in that it had been cleared about maybe 60 years ago, 50, 60 years ago, and the first trees to come in were the deciduous trees. So we've dug down to the B horizon and we can see how the forest floor is sitting on top of the mineral soil. Why are these organic horizons important? Well, to begin with, I wanted to point out that we have organic horizons.
makes this soil very different from an agricultural soil because an agricultural soil is just mineral soil and with no organic horizons on it. So here in the forest soil we have the organic horizon and so it's having an influence. on everything from above that doesn't happen in agriculture.
So it has an influence on the availability of nutrients on this site because a lot of the nutrients are held within this organic matter that's here. And as the organic matter decomposes, the nutrients become available. It has an influence on the physical properties of this site, so the moisture holding capability. So this organic material is really good at holding the nutrients.
holding on to moisture and keeping this site moist even when it gets quite dry. And then also it influences temperature. It has a buffering influence with temperature so that we don't get huge temperature extremes down in the mineral soil.
In relation to, you probably are thinking about climate change, how forest floors perhaps could relate to climate change. Well this is an area where there's a lot of carbon in the forest floor and so the carbon in that soil that could be either carbon sink or it could be a carbon source. if it decomposes.
So it's important in terms of global climate change as well. So you mentioned the deciduous trees here. We have maple and alder.
How is the litter from those trees affecting the forest floor properties here? Well this litter is falling from the trees, the alder and the big leaf maple and black cottonwood to the surface and this litter is quite fertile, has a lot of nutrients in it, particular nitrogen. from the alder, but other nutrients as well.
And this means that the organisms here have access to carbon and to the nutrients, and they use that as a food source and they mix the organic material into the soil, so we end up with this AH down here. So the forest floor above with the organisms in it that's formed from the leaves mixing into the AH below. Now I should mention that we don't have much L here.
and that's because we're shooting in the summertime and so it's decomposed, that material has. But if we came back in the fall we'd have much more litter because it would have freshly fallen. How is measuring the depth of forest floor horizons different than measuring mineral horizons?
Well the mineral horizons we measure from the mineral organic interface down. So here we have a B and then we have an AH. and the forest floor starts up here.
So if we were measuring the mineral soil, we would go find that interface right about there and take our measuring tape and measure from that point and down. So for our AH, what would you say in centimeters we have in terms of depth? About 15? Yeah, roughly about 15 centimeters.
and then we're into the B. For the organic horizons or the forest floor we measure from mineral organic interface and up and so we're going to put it here and measure up in this direction so the total depth is about about, what do you see there? Maybe 5 centimeters? Okay, 5-6 centimeters, that's our total forest floor.
And so we'd go zero and up to 7 centimeters or 5 centimeters and that would be how we'd measure the organic horizons. In this section of the UBC farm, the trees are a little different. What can you tell me about the trees we're seeing here? Well, the trees we see here are trees we typically find in this area. And so we have Douglas fir and we have some hemlock as well.
And we typically find them in a mix in this kind of coniferous forest. Can we go take a look at the forest floor? Sure, let's go. I've noticed here we have a bit more of a litter layer.
Why are these coniferous needles not decomposing as much as the deciduous leaves? Well, they're here and fairly thick because they have a poor quality for decomposition, and that quality relates to the characteristics of the coniferous needles. Coniferous needles have more carbon, less nitrogen, so they have a higher CN ratio.
And they also have more lignin here. There's twigs here, you can see the twigs, and they've got high lignin content, and so they don't decompose as rapidly. So that's why we end up with a fairly thick-ish L horizon. Okay, and also I noticed we have a fairly thick AH, and it doesn't seem like we have much of a F horizon.
Why is that? Well, typically we would expect an F horizon under these conifers and we don't have that here. And that's most likely due to this organism here, the earthworm. And I'm pulling one up from below, but we saw others while we were digging here. And these earthworms are active because they're in this area.
We're at UBC Farm and there are plenty of earthworms around the area and they've migrated into here. And they've been quite active in eating up. forest floor and mixing it into that mineral soil thus forming that deepish AH.