DBH to Height

I’ve spent the last week making regressions for different data in R. Actually using R and manipulating data is quite easy. The hard part is trying to get good data. There are multiple years of data entered by multiple people at different times and in different ways. The result is a bit of a nightmare when it comes to using the data (and I have, in fact, had nightmares about it). There are some trees that have a diameter at breast height( DBH) but are only a foot high, there are some trees that have the same ID number as a different tree, and there are some trees that have simply gone missing. A big part of this summer will be finding if the funky data are from something being lost in conversion from PDF to Excel, or if there were errors recording data in the field.

One big issue with the data has been unique to me and the IPM I am building. Smaller trees are measured using height, and taller trees are generally measured using DBH. With matrix models this is not a problem, and is in fact a bit of a blessing, because there are different size classes and the cutoff for a size class can simply be where heights are no longer recorded and DBH is used instead. With an IPM, though, the data are continuous, and if the sizes of the trees are measured 2 different ways it is impossible to create a continuous set. I have been experimenting with different ways to deal with this. I could create two different kernels and two different populations, one with juvenile and one with adult trees, and have the two contribute to each other in different ways (like reproduction of adult trees adding to juvenile population), or I could try to convert the DBH measurements of adult trees to height and use a single kernel and population. After discussing with my professor it seems I will be attempting to convert DBH to height. I’ll see how well the two convert and hopefully the relationship between the two will be statistically significant, or else I’ll be making a much more complicated model than originally anticipated.

Comments

  1. melissahey says:

    How far back is the data that you are using to build this model/population? Is there any way you can use the pictures taken during the 2013 season for canopy to check and see if you are getting an accurate estimation of height based off of DBH? Or are you planning on measuring based off of angle when you go to Maine and Vermont this year to see if it is an appropriate estimation? Also, how do you think there was error in the conversion from PDF to Excel? Was it done manually or was there a method to transfer it directly to Excel? (I’m kind of guessing you are expecting human error considering the term funky data)