Forests and Their Management Dr. Ankur Awadhiya Department of Biotechnology Indian Institute of Technology, Kanpur Module - 12 Revision Lecture – 35 Revision (Part 2) (Refer Slide Time: 00:19) [FL] We move forward with our revision and today, we will start with module 5 forest surveying.(Refer Slide Time: 00:23) So, we saw that survey is the act of making measurement of the relative position of natural and man-made features on the earth surface and presentation of this information either graphically or numerically. (Refer Slide Time: 00:39) So, you take measurements, and you also have to present this data either graphically or numerically. There are three stages of surveying; taking a general view or the reconnaissance survey, observation and measurement, and presentation of data.(Refer Slide Time: 00:48) Then, we saw that there are two types of surveying. Plane surveying, when you take the surface of the earth to be a flat plane and this approximation is generally true, when you are surveying smaller areas less than 250 square kilometers in size. If you have larger areas, then you have to take care of the curvature of the earth; the true shape of the earth, which is a geode; and in this case, it is known as a geodetic surveying. (Refer Slide Time: 01:14)Now, surveying was generally done with classical tools such as chain and tape survey. Now, in the cases of chain and tape survey, you only take linear measurements; there are no angular measurements that are involved. Secondly, you have compass survey in which case you take angular measurements using compass, and linear measurement using a chain or a tape. Then, you have plane table surveys in which you take measurements and they, these are converted into drawings on a plane table. And typically, you only need to have two points; you know the distance between both of these points, they are in the straight line and for the rest of the points you only take the angular measurements. And, just by taking angular measurements you are able to plot them out on the sheet, where you have to measure the horizontal and the vertical angles both. (Refer Slide Time: 02:01) Now, measurements can be direct measurements; made using some measuring device or instrument, or indirect measurements that are made using an observable proportion or ratio such as the stake and shadow method.(Refer Slide Time: 02:14) Then, we defined error as the difference between a measured value and the true value. And, the properties are that there is no measurement that is exact; all measurements have some error, and because of this error, you can never know the true value of anything. Now, if you do not know the true value, you also cannot know the exact error; because your definition of error involves this true value. And, you cannot you can never measure the true value, because even if you are trying to measure the true value, there will be certain errors that will be involved. So, we try to take measurements in a way that the relative between the measurements cancel out the errors.(Refer Slide Time: 02:59) Next, we have the sources of errors; there are three main sources. Natural, due to variability in natural conditions such as temperature; or you have instrumental errors, if your instrument was not built properly or over time it has become worn out; or there are personal errors, when you are doing an error in the measurement, because you are not following the correct procedure. (Refer Slide Time: 03:21)Then, we looked at the difference between precision and accuracy. Precision is how close the measured values are to each other, and accuracy is how close the measured values are to the correct value. (Refer Slide Time: 03:32) And, we represented them in the form of these shots on a target board. And, here we said that these measurements are precise and accurate; these are precise, but not accurate; these on an average are accurate but not precise; and these are neither precise nor accurate. (Refer Slide Time: 03:53)Then, we defined bias as the difference between the mean of the measured values and the reference value. And, if the reference value is the true value, then bias is the error in management in measurement. (Refer Slide Time: 04:02) So, this is the bias; the shooter wanted to shoot at the bulls eye; so, the measurements are precise, but these are not at the bulls eye. (Refer Slide Time: 04:19) So, they are at a distance and this difference is the bias; and, biases can be removed by calibrating the instrument or the method of measurement.(Refer Slide Time: 04:24) (Refer Slide Time: 04:26) Next, we looked at basics of sampling. So, there is a difference between census and sampling. In the case of a census, you take or you measure everything. In the case of sampling, you would measure only a small portion of the whole population.(Refer Slide Time: 04:35) The objective of sampling is to secure a sample which will represent the population and reproduce the important characteristics of the population under study, as closely as possible. (Refer Slide Time: 04:46) Then, population is defined as the aggregate of units from which a sample is chosen.(Refer Slide Time: 04:51) And, sampling unit is defined as the subdivision of the population for the purpose of sampling. And, these can be administrative units or natural units, such as topographical sections, or sub compartments, or even artificial units like strips or plots and so on. (Refer Slide Time: 50:11) Now, a list of all the sampling units is called as the frame, and out of this frame you select a few of the samples.(Refer Slide Time: 05:15) So, one or more sampling units that are selected from a population according to some specified procedure will constitute a sample. (Refer Slide Time: 05:27) And, we also have the sampling intensity, which is the ratio of the number of units in the sample to the number of units in the population So, if you have more number of units in your sample, then your sampling intensity is more. So, say you have 100 individuals and if you are measuring 10 individuals, then you have a sampling intensity of 10 percent. If you are measuring 90 individuals, then you have a sampling intensity of 90 percent. (Refer Slide Time: 05:51) Now, we looked at the kinds of plots; you they can be circular, rectangular, strips, or they can even be topographical units, as are used in hills. (Refer Slide Time: 05:59)(Refer Slide Time: 06:02) Now, depending on the procedure, we defined simple random sampling, in which case, the each possible combination of sampling units out of the population has the same chance of being selected; such as a lottery. (Refer Slide Time: 06:12) Then, there is systematic sampling which uses a formula of selecting every kth unit starting with a number that is chosen at random.(Refer Slide Time: 06:22) Next, we have stratified sampling in which case you divide the heterogeneous population into sub populations known as strata; each of which is internally homogeneous in which case a precise estimate of any stratum mean can be obtained. (Refer Slide Time: 06:39) Next, we have multistage sampling, in which you first select the large scale the large size units. And, then you choose a specified number of sub-units from these selected large units.(Refer Slide Time: 06:51) And, then you have PPS sampling or the probability proportional to size sampling; in which case, when the units vary in their size and the variable under study is directly related to the size of the unit, such as the mass or the biomass the probabilities, may be assigned that are proportional to the size of the unit. So, in a PPS sampling the larger sized individuals are more are better represented. (Refer Slide Time: 07:18) Next, we looked at photogrammetry; photogrammetry is the science and technology of obtaining spatial measurements and other geometrically reliable derived products from photographs. So, you are obtaining spatial measurements and other geometrically reliable derived products. So, in this case, we are doing some sort of a survey that is being done using photographs. And, the survey is being done in such a manner that you are able to measure things out. It is a form of remote sensing; defined as the acquisition of information about an object or phenomenon without making a physical contact with the object. (Refer Slide Time: 07:50) Now, photogrammetry is based on the principle that, ‘triangulation permits depth perception.’ So, you have, for instance, you have two eyes and with both these eyes you are able to perceive the depth of different objects; depending on what is the angle that your eyes are subtending or what is the parallax error that you are seeing. So, in this method, you take photographs from at least two different locations; develop lines of sight from each camera to the points on the object. And then, mathematically intersect these lines of sight to get the 3-d coordinates of the point of interest.(Refer Slide Time: 08:23) So, this is the principle you are taking different photographs in a two-dimensional manner. And then, putting them through the mathematical computations of photogrammetry to get a 3D representation of what the actual object is. (Refer Slide Time: 08:38) So, the applications can be interpretive; to interpret the situation, or metric to measure something.(Refer Slide Time: 08:44) (Refer Slide Time: 08:45) Then, we looked at the use of drones. So, this is a satellite image; this is the drone image.(Refer Slide Time: 08:47) So, we can use it for interpretations such as, we saw that this building was not there in the satellite image, but it is there in the drone image. So, it was built after the satellite image was taken and before the drone image was taken. So, it can be used for such interpretations; you see difference in the land use. So, earlier these areas were plain like this; now, these areas are dotted, which means that there have there is a plantation that has come up in this area. (Refer Slide Time: 09:15)Next, we saw that, in the case of drones, you can fly them at a lower height, in which case you will start seeing the plants themselves. (Refer Slide Time: 09:20) So, these green spots are the plants. And, when you are seeing these plant,s you can even use this data for finding out the viability of different plants. (Refer Slide Time: 09:31) Then, we looked at how we can we can perform this computation in an automatic manner.(Refer Slide Time: 09:48) (Refer Slide Time: 09:49) So, there we started with this image of the pits that are dug, and the soil that is there along with the pits; we converted them into a black and white image a binary image.(Refer Slide Time: 09:51) And, with this binary image the computer was able to tell us what are what is the number of pits that are dug. (Refer Slide Time: 09:57)(Refer Slide Time: 09:58) What are the sizes of different pits? what is the average size of each pit? and so on. (Refer Slide Time: 10:01) And, in the case of photogrammetry, we typically use three different kinds of platforms. They can be ground-borne platforms, in which case, you are using cameras on the ground. And, the camera is horizontal or you can make use of space-borne platforms, in which case, you are using satellite data, and in this case the camera is vertical. The third option is that you can make use of air-borne platforms, in which case, you use an aircraft or a drone and in this case the camera may be at any angle.(Refer Slide Time: 10:32) Now, we defined spatial, temporal, spectral, and radiometric resolution. Spatial resolution is the ground size of a pixel in the image; essentially how many megapixels do you have in your camera. Temporal resolution is how frequently are you taking pictures or the frequency of flyovers. Spectral resolution is whether you are taking a black and white image or you are taking a colored image in three different bands or even more number of bands. So, it is the number of frequency bands that are recorded; it is just 1 band in the case of a black and white image, 3 bands in the case of an RGB image, and even more number of bands when you are also taking into account the infrared bands and the UV bands and so on. Next, you have the radiometric resolution which is the number of different intensities of radiation that the sensor is capable of distinguishing. So, essentially here, you are talking about what is the amount of information that is there in each band; what how many how many bits of information can be distinguished.(Refer Slide Time: 11:30) Next, we had a look at the parameters that define a good photograph. So, you have to look at the field of view; it depends on the focal length and the angle at that the camera is subtended to the object. Next is the focus, and we said that the depth of field depends on the f number. (Refer Slide Time: 12:23) So, if the f number is large, such as see f 11 or f 20 in that case, the aperture is very small in size and the depth of field is very large. On the other hand, if the f number is small; say f 2 in that case, you have a large sized aperture. And, in this case, you have a very small depth of field. Here, we defined far range photography or far-range photogrammetry where the focus is at infinity and close-range photogrammetry where the focus is at a finite distance. And, we saw that exposure depends on shutter speed, ISO, and the f number. Next, we talked about the orientation of the camera axis you have true vertical, near vertical and oblique axis or oblique orientation. In the case of true vertical, it is a hypothetical thing; the best you can get is a near vertical. And, in the case of oblique orientation, you have high oblique where the horizon is visible and a low oblique where the horizon is not visible. (Refer Slide Time: 12:45) Then, we looked at differences between vertical and oblique photographs. In the case of vertical photograph, it is a more uniform scale measurements are easier. In the case of oblique, there are differences as you move across the photograph and so on.(Refer Slide Time: 13:00) Now, in the case of air-borne for platforms, you need to ensure that there is a sufficient amount of overlap between different images. (Refer Slide Time: 13:09) And, there are certain corrections that need to be done, the if the altitudes varies during the flight the scale will vary. So, you try to fly your aircraft at the same altitude, and also you record the altitude. So, that if there are any changes to be made according to the altitude in the final image that can be made. The tilt; if it varies during the flight, then the scale will vary with the camera tilt across the photograph. Then, there are several distortions; the lens distortion, atmospheric distortion, and edge distortion. And, there is also a parallax shift with the altitude. (Refer Slide Time: 13:41) Now, in the case of measurements, you try to take a good overlap, so that you are able to have stereo viewing of the of these different locations, and you can make use of parallax shift to get a an idea of the altitude. (Refer Slide Time: 13:58)Now, in when you are using photographs to take measurements, it is good to use a metric camera, which is the stable; which has stable and precisely known internal geometries; low lens distortions; constant focal length of the lens. The image coordinate system is defined by four fiducial marks mounted on the cameras frame, and the aerial metric camera built into the airplanes look straight downwards. (Refer Slide Time: 14:22) If you want to take stereo measurements, you take a stereometric cameras; in which case, you have to metric cameras that are mounted at the ends of a precisely measured bar.(Refer Slide Time: 14:32) And, both of these have the same geometric properties. Now, applications of aerial photography; to make large scale plans, cadastral maps, land use maps, topography, hydrography and exploration and reconnaissance. (Refer Slide Time: 14:45) Products you can get; a digital elevation model, orthophotos, you can get thematic GIS data and other derived products and maps.(Refer Slide Time: 14:53) And, then we looked at how we make use of the of photogrammetric principles to get a 3D view. And here, we saw a 3D view of the Mudumalai Tiger Reserve, and we are also getting certain thematic information such as where the streams are located. (Refer Slide Time: 15:10) Next, we had a demonstration of this 3D video.(Refer Slide Time: 15:16) (Refer Slide Time: 15:19)(Refer Slide Time: 15:20) (Refer Slide Time: 15:20)(Refer Slide Time: 15:21) (Refer Slide Time: 15:21)(Refer Slide Time: 15:22) Then, we saw how we can use photogrammetry to discern water in a region taking the example of the Bhoj lake or the upper lake in Bhopal. (Refer Slide Time: 15:27) And, in the next lecture, we had to look at LiDAR which is Light Detection and Ranging. It is the word is made from a combination of laser and radar; where radar is radio detection and ranging.So, in this case, this is an active remote sensing technique, in because you are because, you require energy to illuminate the object using the lasers. It is an Air-borne Laser Scanning system or an ALS system, developed in 1960 by Hughes Aircraft. (Refer Slide Time: 15:51) We use laser, because it is a monochromatic beam; it is a directional beam; it retains its strength over long distances. (Refer Slide Time: 15:59)The concept is that you get position of the aircraft using differential GPS, in which case you have two stations. The ground station and also one station which is located in the aircraft. So, you use differential GPS and inertial measurement unit to get an idea of the acceleration and the orientation of the aircraft you. And, when you shine a laser beam, it goes interacts with the surface of the object and then it comes back. So, how much time does it take for the laser beam, to go from the aircraft and back, is then calculated. And, the distance to the surface is given by c into t by 2, where t is the time it takes for the laser beam to come back. And, by keeping track of angles, we can get a 3D, 3D scan. (Refer Slide Time: 16:42) The components are laser, there is scanner and optics, photo detector and receiver electronics, and positional and navigational systems.(Refer Slide Time: 16:50)D We saw that it works in two modes; LP mode which is the Last Pulse mode where the last return pulses are received. And, the FP mode which is the First Pulse mode where the first returned pulses are received. And, you can make use of LiDAR to get a DEM image, which is a Digital Elevation Model, which represents the elevation of the tallest surfaces at a point. And, a DTM model, which is a Digital Terrain Model representing the elevation of the ground. And, you can subtract DTM from DEM to get a DHCM which is a Digital Canopy Height Model.(Refer Slide Time: 17:24) (Refer Slide Time: 17:27) And so, now, in the case of scanning mechanisms, there are three typical scanning mechanisms that are used in oscillating mirror, which gives you a sawtooth pattern; a rotating polygon, which gives you parallel lines; and a notating mirror, which gives you elliptical shaped ground patterns.(Refer Slide Time: 17:41) Now, you can make use of a LiDAR in two families; you can make use of waveforms or you can make use of information in a discrete pattern. (Refer Slide Time: 17:48) (Refer Slide Time: 17:51)When talking about the wavelengths, you have the topographical LiDAR; in which gives near infrared light laser is used to map the land; or you can make use of bathymetric LiDAR; in which case our water penetrating green light is used, to measure the sea floor and the riverbed elevations. (Refer Slide Time: 18:10) In forestry, you can use LiDAR to get an idea of the DEM.(Refer Slide Time: 18:14) (Refer Slide Time: 18:18) Canopy structure; even the different cross sections of a tree.(Refer Slide Time: 18:19) (Refer Slide Time: 18:21)(Refer Slide Time: 18:23) Leaf area density, digital canopy height; you can measure carbon stocks; you can use a horizontal Lidar. (Refer Slide Time: 18:28)(Refer Slide Time: 18:29) And, get a better idea of the carbon stocks, or you can even study the plant growth and shape change. (Refer Slide Time: 18:32) As the plant grows, or you can use it to understand how your stand is behaving; do you have only young crops? do you have mature crops? do you have old crop? or do you have a mix? So, you can get a very good and a very fast idea in a very economical way.(Refer Slide Time: 18:50) Next, we looked at forest protection. (Refer Slide Time: 18:52) So, here, we started with the kinds of threats.(Refer Slide Time: 18:54) So, the you have natural threats and you have man-made threats. Natural threats are frost damage, wind throw, insects and pests, diseases, damaged by animals, invasive species, climate change, forest fires. (Refer Slide Time: 19:07) And man-made threats include illegal felling, illegal mining, illegal grazing, encroachment, degradation and pollution, poaching, invasive species, climate change and forest fires.And, we can emphasize that, in the case of invasive species, climate change, and forest fires, you can have both natural as well as man-made causes. (Refer Slide Time: 19:29) Then, we saw the impact of humans on the environment of forests is given by this equation I is equal to P into A into T, where I is the impact P is the population pressure A is the affluence or the per capita need for resources and T is the technology or the ability to extract these resources. So, if you have a large size population; everybody needs more resources and you have the technology to extract these resources; and that is the impact, will be very high.(Refer Slide Time: 19:57) Next, we saw how to estimate the rate of species loss using the island biogeography model; in which case,, S or the species richness is given by C, a constant of proportionality times A, or the size of island to the power of z, which is again another constant which. (Refer Slide Time: 20:17) And, this constant varies in different locations, and the way the values are typically between 0.15 and 0.35.(Refer Slide Time: 20:29) And, in this case, we saw that even if an area decreases by 90 percent, you still have a roughly 50 percent of the species richness that remains in that area. (Refer Slide Time: 20:39) So, there is ample scope for hope, but you cannot be extremely hopeful because then we calculated the rate of species loss. And, we saw that, in the case of tropical forests, we are losing as many as 27,000 species every year in a very conservative estimate.(Refer Slide Time: 20:55) Then, we say then we saw that all species are not equally susceptible to extinction. It depends on the rarity of species; if a species is rarer, then it has a greater chance to be extinct. (Refer Slide Time: 21:07) And, species some species are rarer because they are restricted to an uncommon habitat; they have a limited geographical range or they have low population densities.(Refer Slide Time: 21:16) . Then, we look at this acronym HIPPO, which which is a good mnemonic to remember the factors that are leading species towards extinction. So, H is habitat loss, I is invasive species, P is pollution, the other P is human overpopulation, and O is over harvesting of resources such as overfishing or over extraction of timber. (Refer Slide Time: 21:39) . Now, why does a population become extinct? You have two different kinds of factors; you have deterministic factors that act at large population sizes, such as birth rates and death rates. And, you have stochastic factors that act at small population sizes.(Refer Slide Time: 21:54) So, deterministic factors include birth rate, death rate, and the structure of the population; whether most of the individuals are young, most of the individuals are old, or most of the individuals are of a mature stage. (Refer Slide Time: 22:07) In the case of stochastic factors, you have demographic stochasticity which is the probabilities in reproduction, litter size, sex determination and death. So, it is just possible that most of the animals are having a very small litter size, just one progeny. And, if that happens; then the population is more pushed towards extinction, if the population size already is very small, or if all the progeny turn out to be males, or all of them turn out to be females. Then, we have environmental variation and fluctuations, catastrophes such as forest fires and diseases, genetic processes, deterministic processes such as density dependent mortality and migration among populations; and all of these are the stochastic factors. (Refer Slide Time: 22:51) Now, then next, we saw that the sensitivity of the species to human impacts is dependent upon the adaptability and resilience of the species, the amount of attention that humans are given to the to the species. So, charismatic species like tigers are more sensitive. Ecological overlap between humans and the species, and the home ranges requirements of the species; in which case, the species that require a larger home range size are more susceptible towards extinction; because if their home range reduces, then they are unable to cope with it. So, there is a need for protection.(Refer Slide Time: 23:23) (Refer Slide Time: 23:25) In the next lecture, we started with forest fires.(Refer Slide Time: 23:28) (Refer Slide Time: 23:29) This is an example of a forest fire, and the forest fire is defined as a generally uncontrolled fire in an area of combustible vegetation in the forest(Refer Slide Time: 23:36) And, we saw that a forest fire occurs when you have all the three vertices of the fire triangle. So, you need to have fuel, you need to have air, and you need to have heat; when all three of these are there together, then you have the forest fire. (Refer Slide Time: 23:51) There are certain natural causes of forest fire such as lightning, volcanic eruptions, rubbing of dry bamboo, friction of rolling stones.(Refer Slide Time: 24:00) you are maintaining your trees according to both shelter wood system and the selection system and so, with the forest is retained as an irregular stand.Now, the characteristics; it is a compromise between shelter wood system and selection system with regeneration fellings on the pattern of uniform shelter wood system or group shelter wood system, but with very long regeneration periods on the pattern of selection system, with the main objective of light increment resulting in irregular uneven-aged forests. (Refer Slide Time: 61:16) Advantages; there is adherence to natural system, more flexibility, more increment varied forests with bitter site utilization. (Refer Slide Time: 61:25)But the disadvantages are that there is very intensive felling, scattered fellings in a large area leads to a costly process, there is a regular damage to the young crop, requires skilled labor force, favors the shade the shade bearers, young crop remains under shade for a long time, and the trees make it branchy. Now, with a choice of all these different silvicultural systems, you can choose which one you want to use depending on which crop you are using; whether it is shade tolerant or light dependent, what is the kind of site that you are working with, and your silvicultural objectives. So, that is all for today. Thank you for your attention [FL].