Wednesday, August 29, 2012

On how I chose my samples - Part 2

So last I left off on the topic of choosing samples I was discussing how I realized that I really needed to have a good look around me and think about what I was trying to accomplish in order to help me come up with a sampling scheme.  And for the most part, that's just what I did.  During my field visits in the Summer and Fall of 2009, and even somewhat during field visits in 2010, I spent several hours standing in patches of Glossy Buckthorn thinking about how best to select plants to tag and follow.  Sometimes I would call my friend Adam (also studying plant ecology at the time) and bounce ideas off of him (or ask him to generate random numbers for me).  Sometimes I would call my wife and complain about the dense blackberry bushes, multi-flora rose, ticks, etc - ya know, sometimes you just need to whine a bit.

Here are a few of the standout observations that helped me develop my sampling scheme:

  • Glossy buckthorn patches vary in density and I wanted to avoid over-representing plants in areas of high density or under-representing plants in areas of low density
  • For the purposes of my study I want to follow individuals, therefore areas that are bare of Glossy buckthorn are not good places to look for plants to follow (yeah - this one is obvious)
  • Glossy buckthorn grows in varying ecological conditions (under story, gaps, riparian zones, uplands, etc.) and my samples should come from as many of these conditions as is feasible
  • The ecological conditions mentioned above are generally clumped. That is, the ecological conditions I'm interested in usually make up their own patch (e.g. a large patch of understory or wetland)
With these observations and thoughts in mind, I decide that the most important aspect of my sampling scheme should be that I select individual plants to follow across different plant densities and in different ecological conditions.  So here's the final sampling scheme I chose:
  • Ecological conditions - I selected a specific combination of ecological conditions (e.g. upland-understory forest) and using a GPS outlined the borders of a Glossy buckthorn infestation within the bounds of the borders of the ecological condition.
  • Individual plants - Once I had the border of an infestation, I selected 15 to 20 random points within these bounds where I set up 2x2m plots, or quadrats.  Within these plots, I tagged and measured all Glossy buckthorn plants that were taller than 10cm. Plants smaller than 10cm were considered saplings, which were sampled differently.
This type of sample scheme is essentially a stratified-random design, stratified across ecological condition and random within that condition.  So far I think it has worked out pretty well.

Random 2x2m plot in a large forest gap. Orange flags mark the corners of the quadrat.

Wednesday, August 15, 2012

Fieldwork, ESA, and Moving

The last few weeks have been filled with fieldwork in New Hampshire, travel to Portland, OR for the annual Ecological Society of America (ESA) meeting, and moving from our home out near Stony Brook to a new place in Nassau County (closer to NYC and to my wife's new job) - hence the lack of posts.  Here's a brief post concerning my experiences at the recent ESA meeting.

While in Portland I participated in some audiocasts with a group of friends and colleagues, during which we discussed some conference highlights.  At the end of each day (the meeting was four full days) we gathered and talked about one standout presentation we saw that day.  Give a listen to these audiocasts if you're curious a) what ecologists think and say about each others presentations, b) if you're curious what I thought were a few standout talks, and c) if you want a bit more than an hours worth of entertainment.  The audiocasts can be downloaded from my friend Gabe Yospin's website for our MondayWednesday, and (coming soon) Thursday sessions.  Gabe also did solo sessions on Sunday and Tuesday that are worth listening to.

This was my first ESA meeting and I must say, I was impressed.  ESA is a (relatively) large meeting, approximately 4,500 people this year.  There are more than twenty concurrent sessions at a time! Which means during any session there was usually more than one talk I wanted to see.  Also, the conference center was so large that if back-to-back sessions were on opposite ends of the center, it was almost impossible to see both talks in their entirety (had to leave one early and still showed up at the other late).    But these problems aside, I was definitely impressed and inspired by the science reported at this meeting.