Resource assessment exercises: introduction to response designs
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{{info|message=What the function <code>tapply()</code> does|text=The function <code>tapply(x, group, function)</code> applies a <code>function</code> to values in a group. In the last code example we looked at the variable <code>ba</code> of <code>trees</code>. The grouping variable is <code>stratum</code>. For all values <code>ba</code> in each group (i.e., stratum) we apply a function. The argument <code>x</code> in <code>function(x)</code> stands for the values in group $i$. The sum is taken for all the values in the group and then divided by 25. <code>tapply(trees$dbh,trees$stratum, mean)</code>| would give us the mean of <code>dbh</code> in each stratum.}} | {{info|message=What the function <code>tapply()</code> does|text=The function <code>tapply(x, group, function)</code> applies a <code>function</code> to values in a group. In the last code example we looked at the variable <code>ba</code> of <code>trees</code>. The grouping variable is <code>stratum</code>. For all values <code>ba</code> in each group (i.e., stratum) we apply a function. The argument <code>x</code> in <code>function(x)</code> stands for the values in group $i$. The sum is taken for all the values in the group and then divided by 25. <code>tapply(trees$dbh,trees$stratum, mean)</code>| would give us the mean of <code>dbh</code> in each stratum.}} | ||
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| + | ==Related pages== | ||
| + | * Previous page: [[Resource assessment exercises: resource assessment basics additional exercises|Resource assessment basics additional exercises]] | ||
| + | * Next page: [[Resource assessment exercises: fixed area plots|Fixed area plots]] | ||
==References== | ==References== | ||
<references/> | <references/> | ||
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| + | [[category:Response designs in resource assessment (2014)|Introduction to response designs]] | ||
Revision as of 15:59, 23 June 2014
In the introduction we mentioned that in forest inventories we usually do not sample individual trees. In this section we will have a look at different response designs. These include fixed area, nested fixed area plots, and plots of variable size. For other types of observation units see, e.g. Gregoire & Valentine (2008)[1], and Kleinn (2013) [2].
Our target parameter will be the basal area (BA) ha\(^{-1}\). The BA in square meters (m\(^{2}\)) of a single tree, i.e., the cross-section of a tree trunk, is defined as,
| $\text{BA}=\frac{\pi\times(\text{DBH}/2)^2}{10000}$ | 1 |
Here, the DBH is given in centimeters, and we, therefore, have to divide by 10,000. The BA ha\(^{-1}\) for the simulated forest is
trees$ba <- (pi * (trees$dbh/2)^2)/10000 sum(trees$ba)/50 # the area of the forest is 50 hectares ## [1] 28.66 tapply(trees$ba, trees$stratum, function(x) sum(x)/25) # per stratum ## 1 2 ## 13.95 43.36
What the function sum()does- the function
sum(x)simply takes the sum ofx. To get the sums of columns and rows usecolSums()androwSums(), respectively.
- What the function
tapply()does - The function
tapply(x, group, function)applies afunctionto values in a group. In the last code example we looked at the variablebaoftrees. The grouping variable isstratum. For all valuesbain each group (i.e., stratum) we apply a function. The argumentxinfunction(x)stands for the values in group $i$. The sum is taken for all the values in the group and then divided by 25.tapply(trees$dbh,trees$stratum, mean)
Related pages
- Previous page: Resource assessment basics additional exercises
- Next page: Fixed area plots
