[R-sig-eco] community similarities in time

[sebastiankr]

Hi all

I apologize in advance if this is not the right place for my questions.

I am looking at a forest succesion based on a long term monitoring program.
The area consists of 350 ha of heath divided in 33 quadrats. Among other
things I am interested in determining succession pathways, rates and
trajectories (convergence, divergence, etc). For that I will calculate
simmilarities/distances between the different quadrats and determine
temporal and spatial effects. 
However there are several problems I need to overcome:

1. Different sample size. Quadrats differ in area and samling intensity has
changed over the years (first 8 suveys were complete census, while last two
were sampling plots within each quadrat). Does it make sense to extrapolate
the smaller sample areas and then standardize so that maximum abundance = 1
?

2. Is it valid to extract the distances/simmilarities between two
consecutive years obtained either directly or from an ordination space and
then use this in a regression type analysis to determine if there is a trend
(community becoming more stable). 

3. Different time intervals. Given that the intervals between surveys differ
(min = 5 years, max = 21) and if the above is valid is it possible to
transfrom this distance measure into something like distance per year
instead?

thanks for your help

Sebastian Kepfer

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