Dear all:
I am working on analyzing the spatial structure of tree and environment data
as a preliminary step before doing further analysis. I was wondering which R
functions you recommend to assess the degree of spatial structure for tree
and habitat data given the following:
1. The locations of individual trees (> 1 cm DBH) were fully mapped in the
study area. The study area was one large plot that was divided into a grid
of contiguous squares for environmental (and other) data collection. The
environmental variables were mapped at a resolution of 5 x 5 m.
2. The final analysis - after checking for spatial structure of tree and
habitat data - will lump tree point data, i.e., use tree abundance data for
each 5 x 5 m square.
3. The data set with abundance for tree data per 5 x 5 m square has most
squares having zero abundance of a particular species.
4. Currently, I have identified that Ripleys K (and similar analyses) would
be a useful way to analyze fully mapped point data, e.g., analyzing the
degree of clumping of individual trees in the study area. However, given
that the abundance of trees in each grid square will be used later analysis,
perhaps for the spatial analysis a method besides Ripleys K (or similar
tests) should be used, e.g., a method that uses tree abundance data as part
of a lattice. What do you think?
5. My current plan is to analyze the environmental variables using a method
such as Morans I. I am currently deciding on what neighbor matrix to use
given that the data is in a grid. Do you know of a tutorial that compares
the functions that create nb (neighbor matrix) class objects? I would
like to create a graphic such as a correlogram (or alternatively a
variogram) that shows the spatial structure across distance classes. Which
graphic would you recommend for this type of initial check for spatial
autocorrelation?
6. I was also wondering about any suggestions of where to go to look for
ideas on analyzing large data sets, so as to not overload memory when using
R to conduct spatial analysis.
Please let me know if you have any suggestions. Thank you for your time and
consideration. I greatly appreciate any help you are willing to give.
Laura
--
" Genius is the summed production of the many with the names of the few
attached for easy recall, unfairly so to other scientists"
- E. O. Wilson (The Diversity of Life)
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