hey everybody it's mr. Smith's and today we'll be covering topic 5.2 which is clear-cutting as you can probably guess from the background here and the name clear-cutting is just cutting down all of the trees and we give an area at once usually to harvest them for lumber or to clear the land for some other use such as agriculture it's a really efficient way for clearing land or harvesting lumber so it tends to maximize economic profits in the short term but it has some serious consequences that we'll be exploring in today's video our objective for 5.2 today is to describe the effective clear cutting on forests the essential knowledge that we need in order to do this is that clear cutting is economically advantageous believes to soil erosion increased stream temperature and soil temperature and flooding we also need to know that trees in a forest absorb pollutants from the air and store or sequester carbon dioxide from the atmosphere which reduces the effects of climate change cutting trees down and burning them releases that carbon dioxide they store and contributes to climate change our suggested science skill for today is concept explanation so first we'll take a look at some of the direct short-term impacts of clear cutting on a forest and the first one and perhaps the most important is soil erosion so without the stabilizing effect of the trees roots in the soil anymore the topsoil which contains all the nutrients and the organic matter is much more prone to erosion it's easily blown away by the wind it's easily washed away by the rain and what's going to happen is we can see right here in the diagram there's gonna be channels carved into the side of slopes again the soil is just going to be washed away really easily by the rain and the wind and it gets deposited in nearby bodies of water so we can see in the second picture how muddy this stream is that increases its turbidity turbidity is a measure of the total suspended solids in a body of water and you can think of it as kind of how cloudy it is so this is a problem for fish it may make it harder for them to get oxygen from the water it may clog their gills it's also going to make it harder for plants that need sunlight to penetrate the water in order to photosynthesize we have another diagram here that shows the effect even of just leaving a strip of vegetation next to that stream so a lot of those trees there and the roots would absorb a lot of the sediments running down that if in the selective cutting an example but when it's clear-cut there's just no vegetation to stabilize the soil and as a result we get a really muddy stream and we get very turbid waters another important impact is the fact that this leads to increased soil and water temperatures so when we lose the shade that's offered by the leaves of the trees that's going to result in more sunlight hitting the soil and the soil is going to have a lower albedo meaning it's going to absorb more sunlight than the leaves of the trees did and so that's going to increase the temperature of the soil as well the loss of the shade on the river also warms the river and the fact that the river is now a muddy or darker color is also going to lead to the river absorbing more heat from the sun's rays this is a problem for microorganisms that live in the soil direct sunlight could kill them it also dries out the soil and it's going to make it even more prone to erosion and then finally we can even experience flooding and landslides when a forest is cut down and it's clear-cut so again without that stabilizing root structure in place the soil is far more prone to erosion another problem is that the logging machinery compacts the soil and the increased sunlight has dried it out so it's decreased the water holding capacity of the soil so now when it does rain that soil is going to hold a lot less water it's going to produce a lot more runoff and that's going to lead to landslides like we can see in this picture at the top of the screen it can also lead to flash floods because all of that excess rain is no longer able to be absorbed by the soil because it's not able to absorb water as well without the trees roots another consequence of clear-cutting is that it usually replaces mature forests like we see in the top picture here with tree plantations which we can see in the bottom picture so tree plantations are areas where generally just one species of fast-growing tree is replanted grown and then harvested the problem here is this greatly lowers biodiversity so because there are far fewer tree species there are far fewer habitats suitable for other organisms that may depend on those tree species with less biodiversity in both plants and animals we have lower ecosystem resilience so if there were to be some sort of natural faster or drought the tree plantation is far more vulnerable to total ecosystem collapse than this mature force which has such wide biodiversity it's also going to again allow for less habitats for a less diverse group of organisms and then we also have this fact that all of these trees are going to be the same age they're all planted at the same time they're all going to be about the same size and so this is not going to allow for dead trees to come into existence in this habitat which are needed by many organisms such as woodpeckers insects and other decomposers so we're not going to have the same succession in this ecosystem that we would in a mature forest where trees dying and falling down really is part of the ecosystems natural progression again it provides nutrients for decomposers and homes for many different organisms to understand some of the longer-term consequences of deforestation especially clear-cutting we need to look at some of the benefits that forests provide so we'll be discussing here how forests provide air filtration how they remove co2 from the atmosphere and then how they're a great reservoir for biodiversity so the stomata or the leaf pores of trees will oftentimes intake different air pollutants things like volatile organic compounds nitrogen dioxide and particulate matter and they'll actually store them in the tree so we can see in this diagram here these pollutants that are emitted by homes by factories by especially power plants are going to be taken right into the tree via these little leaf pores called stomata and then the tree will actually convert those into less harmful substances and they'll store them in the tree or store them in the soil and so they literally scrub the air clean of air pollutants another really important service that's provided by forests is the removal and storage of co2 from the atmosphere so we call this co2 sequestration or CS to store co2 storage so trees during photosynthesis taking carbon dioxide and they convert the carbon in carbon dioxide into sugars into tissues like the wood of the trunk and then they release oxygen which is needed by organisms like animals humans for respiration and then finally we know that they provide a really important habitat for tons of different organisms and this is a great reservoir for biodiversity it's going to lead to more ecosystem resilience and remember that humans have financial benefits from diverse ecosystems because they represent ecotourism so people will pay to come and view beautiful landscapes that have high biodiversity so given all those valuable services that forests provide we can look at some of these longer-term consequences of deforestation it's going to reduce the ability of forests to filter air pollutants and carbon dioxide from the atmosphere so cutting them down especially clear cutting them not only prevents them from continuing to take air pollutants out of the atmosphere and store co2 but it's going to actually release carbon dioxide back into the atmosphere when these leftover tree scraps like stumps or different branches when those decompose and break down they release their carbon dioxide back in the atmosphere so now we're actually contributing to climate change with deforestation another problem is that there's a method of agriculture called slash-and-burn which is exactly what it sounds like and this releases carbon dioxide stored in the trees in addition to nitrous oxide which is an incredibly potent greenhouse gas and water vapor which although it's a natural greenhouse gas can still disrupt the amount of moisture that's retained in an area and lead to a drying out so all of these effects contribute to climate changes were releasing greenhouse gases back into the atmosphere by cutting down trees and especially by burning them and preventing their future sequestration or storage of carbon dioxide our suggested science skill for practice of our q5 point to today is describing an environmental concept and so I want you to see if you can describe to ecosystem services provided by forests and then explain how clear-cutting that forest would affect each of those ecosystem services you describe alright everybody thanks for tuning in today don't forget to like this video if it was helpful subscribe for future apes video updates and check out other notes over here to the side and as always think like a mountain write like a scholar