# How to address large sampling units but small sample sizes?

I've got data from eight one-hectare tropical forest plots, with all trees greater than a certain size measured and identified within them. These plots are different forest ages with two replicates per four age classes (e.g. 2 sites of forest which is 40 years old, 2 sites 60 years old etc.). Within these one-ha plots there are a total of ~17000 individual trees. I have several explanatory variables and wish to investigate the effect of age and these variables on species diversity. However, I'm not sure how to proceed with the sample size of 8 plots, and only 2 per age class, seeming incredibly low for any models - despite the large size of these sampling units.

Is there a way I could perhaps randomly subsample within the plots to increase my number of replicates (I would look into spatial autocorrelation) as the data does span a large area? Or would this be a form of pseudoreplication?

• It sounds like your 8 hectares are strata, not units. If you aggregate up all the data you collect within each hectare, it becomes an ecological study (a type of study looking at relationships between averages rather than average relationships). An ecological study would be a fairly deficient design for your hypotheses. Commented Sep 13, 2019 at 14:25
• I'm not entirely sure what you mean by strata, sorry! From what I've googled it looks like I've got 4 strata i.e. the 4 age categories, with 2 plots per stratum. It is an ecological study and the data had already been collected before I started looking into it, I'm trying to make the most of the plots and size of the plots that we have. Commented Sep 13, 2019 at 14:46
• Well that is the problem. You refer to "age" but one can only assume you mean age of trees. In what sense does a hectare of trees have an "age"? Commented Sep 13, 2019 at 14:48
• Ah sorry, maybe I wasn't clear - it's the forest age i.e. the amount of time since forest started growing on an area of land. That land could have previously been pasture/farmland etc. I'll edit the question to make that clear. Commented Sep 13, 2019 at 15:03
• @ A.Elsy, when @AdamO uses the term "ecological study", that does not mean a study having to do with ecology. This is a technical term used for a particular kind of observational study: en.wikipedia.org/wiki/Ecological_study. This is a little confusing in the context of your study of ecological processes.
– Jdub
Commented Sep 13, 2019 at 17:04