Preparing to Head North

My model is progressing nicely. I’ve made a few alterations to fix things, and hit a few snags that need to be worked out. But the main thing I’ll be doing this week is preparing for the trip to Vermont and Maine. All the datasheets that we need to fill out need to be organized and include all sorts of data from previous years, such as what tree number is in which plot and how high or how wide each tree was. The trees need to be organized so we can walk the plots in order and not have to rustle through the sheets to find the right paper every time we reach a new plot. We also need to determine exactly what data we need to be collecting. There really is no limit to what we want, we are only limited by what we have time to collect! Departure is in less than a week, so I’ll be very busy.


I finally got the model working! The kernel looks good and its graph is pretty (below). I’ve used some iterative code to find the model’s stable population growth rate, stable stage distribution, and reproductive value vector. I have not used a very large matrix due to the computing limitations of my laptop, but I can easily transfer my code to a more powerful computer when it becomes necessary.

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I’ve created a regression for converting dbh to height and it’s working pretty well. One issue with it is that when I combine the data for young trees (which were measured in height) and bigger trees (which I converted), there is very little variance among the heights of larger trees; the conversion has served as a smoother of the data. This makes a regression for growth fit much more nicely, but unfortunately also creates an uneven distribution of residuals. I have attached a variance to the conversion to add some variance among its outputs, but there is still a skew in the residuals. I am currently looking into implications this may have.

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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.

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Some Direction

I was a little hazy on what I’d actually be doing this summer. Would I be helping someone else with her research? Would I be using data that was already collected? Or would I be messing around until I had the opportunity to head to Maine and Vermont to collect new data? It turns out I’m doing a little bit of each. There is an incredible amount of data being used for a matrix model that has been in the works longer than I’ve been at W&M, and I am helping sort through it, picking out funky pieces of data and marking them so they can be checked with the real trees when we take the trip to Maine. I am also using the current data to practice my modeling skills. One goal for the summer is having a functional model for the Maine data. I am using a statistical program, R, that is very different than Python ( the language I’ve used so far in my CS classes), and I spend a significant amount of time just trying to find proper syntax and functions for the things I want to do. Once more data is collected, there will be two years of data collected from the Vermont site, and I spend time this fall building a new model for a new set of data.

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