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Transects

Page history last edited by Charles Forstbauer 10 years, 3 months ago

Totaled 6/8 DONE!

 

This video breaks down how line transecting is done and what kind of data can be taken from this procedure.

 

http://www.youtube.com/watch?v=aa4V9NbiphU&feature=related

 

A professor from SMU sumarizes in this article how transects can be used to not only measure changes but also estimate them using previous data.

http://people.smu.edu/scrain/LTcombs_ms3.pdf 

 

Transect : Transect is also a way of sampling populations. A transect line is used for measuring the changes between at least two areas, it can not measure the population, only the changes between two areas

 

This link describes why and how people would use transects to observe trees

http://www.chicagoriver.org/upload/Tree_Transect.pdf

 

A transect is a path along which one records and counts occurrences of the phenomena of study (e.g. plants noting each instance).

It requires an observer to move along a fixed path and to count occurrences along the path and, at the same time, obtain the distance of the object from the path. This results in an estimate of the area covered, an estimate of the way in which detectability increases from probability 0 to 1 as one approaches the path. Using these two figures one can arrive at an estimate of the actual density of objects.

 

Line transects are used when you wish to illustrate a particular gradient or linear pattern along which communities of plants and, or animals change. They provide a good way of being able to clearly visualize the changes taking place along the line.  Transect mapping is a tool used to describe the location and distribution of resources, the landscape and main land uses. It further allow participants to identify constraints and opportunities with specific reference to locations or particular ecosystems situated along the transect.

 

http://www.nzetc.org/tm/scholarly/tei-Bio21Tuat03-t1-body-d7.html

 This link provides a specific report on a transect taken in order to survey a ridge crest. You can see how data is collected from these procedures.

 

This link is an example of what a transect map might look like

http://sagehen.ucnrs.org/Photos/50th/dick_gard/slides/24-transect-map.html

 

Transect is also a way of sampling populations. A transect line is used for measuring the changes between at least two areas, it can not measure the population, only the changes between two areas. A transect line is useful for things like: A scientist wants to see the impact of urban cities on the average intelligence of the humans. Or: A scientist wants to know the impact of a nuclear power station to a city.

For a transect line, you need two areas, you connect them with a line and then you measure the population of the species you want to count (e.g.: intestinal bacteria). For counting them, you distribute quadrats in regular intervals on the transect line, and you count the species in those quadrants.


 

This video is an example of how transects are used by divers underwater

http://www.youtube.com/watch?v=5QknA9RRUh8

 

 

This video is another link showing how transects are used in a real life environment, counting butterfly populations

http://www.youtube.com/watch?v=-qrewFfvF3Y

 

Point transects are mostly used in avian surveys. They involve an observer standing at a given position and counting the number of objects seen, (n). This means there is no need to traverse difficult terrain as is required for line transects. Generally, all detections are recorded, regardless of distance from the point. Point counts to a fixed distance w are another form of quadrat sampling, these can be used if it can be assumed that all objects within a distance w of each point are detected.

In line transect sampling an observer counts the number n of objects seen while traversing a predetermined line of length L. The perpendicular distance of each object from the transect line is also recorded.

 

 

There are different types of transects, like belt transects, interrupted belt transects, line transects etc. Depending on what information one is desiring to recieve will depend on which transect is used. A belt transect is used to investigate the distribution of organisms. It records all of the species found between two lines and how far they are for a certain place or area and how many of them there are. Belt transects are also used to get more specific information than a regular transect line. An interrupted belt transect records all of the species found in square frames placed at certain intervals along a line. A line transect gives information simply on the presence or absence of a species while belt transects give abudance and more specific information desired.

 

This website informs you about line transects; http://www.countrysideinfo.co.uk/wetland_survey/line.htm

This website tells you about belt transects; http://www.tuhsd.k12.az.us/cds/departments/Science/belttransect.html

 

The following video is the beginning of nine that follows scientists through their sampling and study of tigers:

http://www.youtube.com/watch?v=aa4V9NbiphU&feature=related

 

The following link will also help to show all four different types of transects that there are (with photos and descriptions and graphs etc):
http://www.geography-fieldwork.org/ecologyfieldwork/sand_dunes/stage2.htm

 

some transects are done in order to sample an area specifically for climate changes (versus information on a species):

The International Geosphere-Biosphere Program has proposed a set of large-scale terrestrial transects to study the effects of changes in climate, land use, and atmospheric composition (ldquoglobal changerdquo) on biogeochemistry, surface-atmosphere exchange, and vegetation dynamics of terrestrial ecosystems. The transects (ap 1000 km) will be located along existing environmental and land use intensity gradients that span transitions between biomes in regions likely to be widely affected by forcing from components of global change or where the impacts of global change are likely to feed back to affect atmospheric, climatic, or hydrologic systems. Experimental studies on the transects will examine short-term changes in ecosystem function and biosphere-atmosphere interaction in response to variation in primary controlling variables. A hierarchy of modeling approaches will develop predictions of long-term changes in biome boundaries and vegetation distribution.

 

Showing the error that may come from using transects to sample (since they are so specific):

The line-point transect method has been used to estimate plant cover for about nine decades. In particular, the method is often used to determine baseline plant cover and monitor for changes in plant cover over time. In such cases, detection of change requires both the initial transect starting position and angle of orientation are exact in relocation without error. A study was conducted on influences of errors in basal cover estimates that resulted from inexact relocation and orientation of a resample transect. Simulation studies of actual field data showed that variation in plant cover estimates from relocated line-point transects increased with each source of error and combinations of these errors. Relocated transects resulted in unbiased estimates of total-plant cover only when means over all transects are used to detect changes over time. Substantial errors were observed when the mean cover of individually relocated transect was compared to its original transect

 

This clip shows how we ourselves can use transects to sample (just in our own backyards):

http://www.youtube.com/watch?v=JdtAExrzJtY

 

The following video shows an actual transect of the ocean done by some college students, college graudates and professors.

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http://warnercnr.colostate.edu/class_info/fw663/distance/index.html ---> This powerpoint goes into great detail describing transects and different methods of transect sampling. It shows the more mathematical side of sampling, and then goes into detail about what the data means scientifically.

Comments (2)

Jaime said

at 4:27 pm on Jun 3, 2010

There are different types of transects, like belt transects, interrupted belt transects, line transects etc. Depending on what information one is desiring to recieve will depend on which transect is used. A belt transect is used to investigate the distribution of organisms. It records all of the species found between two lines and how far they are for a certain place or area and how many of them there are. Belt transects are also used to get more specific information than a regular transect line. An interrupted belt transect records all of the species found in square frames placed at certain intervals along a line. A line transect gives information simply on the presence or absence of a species while belt transects give abudance and more specific information desired.

Jaime said

at 4:36 pm on Jun 3, 2010

The following link will also help to show all four different types of transects that there are (with photos and descriptions and graphs etc):
http://www.geography-fieldwork.org/ecologyfieldwork/sand_dunes/stage2.htm

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