.. only:: html
|LS| Updating Forest Stands
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Now that you have digitized the information from the old inventory maps and
added the corresponding information to the forest stands, the next step would
be to create the inventory of the current state of the forest.
You will digitize new forest stands from scratch following an aerial photo from
that forest area. The forestry map you digitized in the previous lesson was
created from an aerial Color Infrared (CIR) photograph. This type of imagery,
where the infrared light is recorded instead of the blue light, are widely used
to study vegetated areas. You will also use a CIR photograph in this lesson.
After digitizing the forest stands, you will add information such as new
constraints given by conservation regulations.
**The goal for this lesson:** To digitize a new set of forest stands from
CIR aerial photographs and add information from other data-sets.
|basic| Comparing the Old Forest Stands to Current Aerial Photographs
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The National Land Survey of Finland has an open data policy that allows you
downloading a variety of geographical data like aerial imagery, traditional
topographic maps, DEM, LiDAR data, etc. The service can be accessed also in
English `here `_.
The aerial image used in this exercise has been created from two orthorectified
CIR images downloaded from that service (M4134F_21062012 and M4143E_21062012).
* Open QGIS and set the project's CRS to :guilabel:`ETRS89 / ETRS-TM35FIN` in
:menuselection:`Project --> Properties... --> CRS`.
* Make sure that :guilabel:`Enable 'on the fly' CRS transformation` is checked.
* From the :file:`exercise_data\\forestry\\` folder, add the CIR image
:file:`rautjarvi_aerial.tif` that is containing the digitized lakes.
* Then save the QGIS project as :file:`digitizing_2012.qgs`.
The CIR images are from 2012. You can compare the stands that were created
in 1994 with the situation almost 20 years later.
* Add your :kbd:`forest_stands_1994.shp` layer.
* Set its styling so that you can see through your polygons.
* Review how the old forest stands follow (or not) what you might visually
interpret as an homogeneous forest.
Zoom and pan around the area. You probably will notice that some of the old
forest stands might be still corresponding with the image but others are not.
This is a normal situation, as some 20 years have passed by and different
forest operations have been done (harvesting, thinning...). It is also
possible that the forest stands looked homogeneous back in 1992 to the person
who digitized them but as time has passed some forest has developed in different
ways. Or simply the priorities for the forest inventory were different that they
are today.
Next, you will create new forest stands for this image without using the old
ones. Later you can compare them to see the differences.
|basic| Interpreting the CIR Image
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Let's digitize the same area that was covered by the old inventory, limited by
the roads and the lake. You don't have to digitize the whole area, as in the
previous exercise you can start with a vector file that already contains most
of the forest stands.
* Remove the :kbd:`forest_stands_1994.shp` layer.
* Add the :kbd:`forest_stands_2012.shp` layer, located in the :kbd:`exercise_data\\forestry\\` folder.
* Set the styling of this layer so that the polygons have no fill and the borders are visible.
.. image:: img/stands_2012_1.png
:align: center
You can see that a region to the North of the inventory area is still missing.
That will be your task, digitizing the missing forest stands.
But before you start, spend some time reviewing the forest stands already
digitized and the corresponding forest in the image. Try to get an idea about
how the stands borders are decided, it helps if you have some forestry knowledge.
Some ideas about what you could identify from the images:
* What forests are deciduous species (in Finland mostly birch forests) and
which ones are conifers (in this region pine or spruce). In CIR images,
deciduous species will often come as bright red color whereas conifers
present dark green colors.
* When a forest stand age changes, by looking at the sizes of the tree crowns
that can be identified in the imagery.
* The different forest stands' densities, for example forest stand were a
thinning operation has recently been done would clearly show spaces between
the tree crowns and should be easy to differentiate from other forest stands
around it.
* Blueish areas indicate barren terrain, roads and urban areas, crops that have
not started to grow etc.
* Don't use zooms too close to the image when trying to identify forest stands.
A scale between 1:3 000 and 1: 5 000 should be enough for this imagery.
See the image below (1:4000 scale):
.. image:: img/zoom_to_CIR_1-4000.png
:align: center
|basic| |TY| Digitizing Forest Stands from CIR Imagery
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When digitizing the forest stands, you should try to get forest areas that are
as homogeneous as possible in terms of tree species, forest age, stand density...
Don't be too detailed though, or you will end up making hundreds of small forest
stands that would not be useful at all. You should try to get stands that are
meaningful in the context of forestry, not too small (at least 0.5 ha) but not
too big either (no more than 3 ha).
With this indications in mind, you can now digitize the missing forest stands.
* Enable editing for :kbd:`forest_stands_2012.shp`.
* Set up the snapping and topology options as in the image.
* Remember to click :guilabel:`Apply` or :guilabel:`OK`.
.. image:: img/snapping_2012.png
:align: center
Start digitizing as you did in the previous lesson, with the only difference
that you don't have any point layer that you are snapping to. For this area you
should get around 14 new forest stands. While digitizing, fill in the
:kbd:`Stand_id` field with numbers starting at :kbd:`901`.
When you are finished your layer should look something like:
.. image:: img/new_stands_ready.png
:align: center
Now you have a new set of polygons defining the different forest stands for
the current situation as can interpreted from the CIR images. But you are
obviously still missing the forest inventory data, right? For that you will
still need to visit the forest and get some sample data that you will use to
estimate the forest attributes for each of the forest stands. You will see how
to do that in the next lesson.
For the moment, you still can improve your vector layer with some extra
information that you have about conservation regulation that should be taken
into account for this area.
|basic| |FA| Updating Forest Stands with Conservation Information
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For the area you are working with, it has been researched that the following
conservation regulations must be taken into account while doing the forest planning:
* Two locations of a protected species of Siberian flying squirrel (Pteromys volans)
have been identified. According to the regulation, an area of 15 meters around
the spots must be left untouched.
* A riparian forest of special interest growing along a stream in the area must
be protected. In a visit to the field, it was found that 20 meters to both
sides of the stream must be protected.
You have one vector file containing the information about the squirrel locations
and another containing the digitized stream running in the North area towards
the lake. From the :kbd:`exercise_data\\forestry\\` folder, add the vector files
:kbd:`squirrel.shp` and :kbd:`stream.shp`.
For the protection of the squirrels locations, you are going to add a new
attribute (column) to your new forest stands that will contain information
about point locations that have to be protected. That information will later be
available whenever a forest operation is planned, and the field team will be
able to mark the area that has to be left untouched before the work starts.
* Open the attribute table for the :kbd:`squirrel` layer.
* You can see that there are two locations that are defined as Siberian flying
squirrel, and that the area to be protected is indicated by a distance of
15 meters from the locations.
To join the information about the squirrels to your forest stands, you can use
the :guilabel:`Join attributes by location`:
* Open :menuselection:`Vector --> Data Management Tools --> Join attributes by location`.
* Set the :kbd:`forest_stands_2012.shp` layer as the :guilabel:`Target vector layer`.
* As :guilabel:`Join vector layer` select the :kbd:`squirrel.shp` point layer.
* Name the output file as :kbd:`stands_squirrel.shp`.
* In :guilabel:`Output table` select :guilabel:`Keep all records (including
non-matching target records)`. So that you keep all the forest stands in the
layer instead of only keeping those that are spatially related to the squirrel
locations.
* Click :guilabel:`OK`.
* Select :guilabel:`Yes` when prompted to add the layer to the TOC.
* Close the dialogue box.
.. image:: img/join_squirrel_point.png
:align: center
Now you have a new forest stands layer, :kbd:`stands_squirrel` where there are
new attributes corresponding to the protection information related to the
Siberian flying squirrel.
Open the table of the new layer and order it so that the forest stands with
information for the :guilabel:`Protection` attribute are on top. You should
have now two forest stands where the squirrel has been located:
.. image:: img/joined_squirrel_point.png
:align: center
Although this information might be enough, look at what areas related to the
squirrels should be protected. You know that you have to leave a buffer of
15 meters around the squirrels location:
* Open :menuselection:`Vector --> Geoprocessing Tools --> Buffer`.
* Make a buffer of 15 meters for the :kbd:`squirrel` layer.
* Name the result :kbd:`squirrel_15m.shp`.
.. image:: img/squirrel_15m.png
:align: center
You will notice that if you zoom in to the location in the Northern part of the
area, the buffer area extends to the neighbouring stand as well. This means that
whenever a forest operation would take place in that stand, the protected
location should also be taken into account.
.. image:: img/north_squirrel_buffer.png
:align: center
From your previous analysis, you did not get that stand to register information
about the protection status. To solve this problem:
* Run the :guilabel:`Join attributes by location` tool again.
* But this time use the :kbd:`squirrel_15m` layer as join layer.
* Name the output file as :kbd:`stands_squirrel_15m.shp`.
.. image:: img/joined_squirrel_buffer.png
:align: center
Open the attribute table for the this new layer and note that now you have
three forest stands that have the information about the protection locations.
The information in the forest stands data will indicate to the forest manager
that there are protection considerations to be taken into account. Then he or
she can get the location from the :kbd:`squirrel` dataset, and visit the area
to mark the corresponding buffer around the location so that the operators in
the field can avoid disturbing the squirrels environment.
|basic| |TY| Updating Forest Stands with Distance to the Stream
-------------------------------------------------------------------------------
Following the same approach as indicated for the protected squirrel locations
you can now update your forest stands with protection information related to
the stream identified in the field:
* Remember that the buffer in this case is 20 meters around it.
* You want to have all the protection information in the same vector file,
so use the :kbd:`stands_squirrel_15m` layer as the target.
* Name your output as :kbd:`forest_stands_2012_protect.shp`.
Open the attributes table for the new vector layer and confirm that you now have
all the protection information for the stands that are affected by the protection
measures to protect the riparian forest associated with the stream.
Save your QGIS project.
|IC|
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You have seen how to interpret CIR images to digitize forest stands. Of course
it would take some practice to make more accurate stands and usually using other
information like soil maps would give better results, but you know now the basis
for this type of task. And adding information from other datasets resulted to
be quite a trivial task.
|WN|
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The forest stands you digitized will be used for planning forestry operations
in the future, but you still need to get more information about the forest.
In the next lesson, you will see how to plan a set of sampling plots to
inventory the forest area you just digitized, and get the overall estimate
of forest parameters.
.. Substitutions definitions - AVOID EDITING PAST THIS LINE
This will be automatically updated by the find_set_subst.py script.
If you need to create a new substitution manually,
please add it also to the substitutions.txt file in the
source folder.
.. |FA| replace:: Follow Along:
.. |IC| replace:: In Conclusion
.. |LS| replace:: Lesson:
.. |TY| replace:: Try Yourself
.. |WN| replace:: What's Next?
.. |basic| image:: /static/global/basic.png