DATA:      Both et van Wirdum (1981), Farjon et Wiertz (1988)
DIRECTORY: \CANOCO\SAMPLES\UNIMODAL\VEGCHANG
PROBLEM:   What caused the vegetation change in a wetland subject to water
           extraction and acidification?
BOOKLET:   pp 189-200
ILLUSTRATION OF:
+ models with interaction effects
+ decomposition of variance in space and time components
+ grid permutation
+ environmental change inferred from vegetation change
_______________________________________________________________________________
FILE TYPE    |  FILE NAME    |         DESCRIPTION
-------------+---------------+-------------------------------------------------
 SPECIES     | grid_spe.dta  | 100 plant species in 20 plots arranged in a 
             |               |  5*4 grid, sampled in 1977 and 1988
ENVIRONMENT  | grid_env.dta  | plot, strip and year indicators, pH and water 
             |               |  depth
 PROJECTS    | dca.con       | DCA of the species data with environmental
             |               |  interpretation
             | pca.con       | PCA of the species data with environmental
             |               |  interpretation
             | rda0.con      | RDA of the species data with model "plot*year",
             |               |  equivalent with pca.con
             | fig2.con      | RDA with model "plot+year+strip.year" used to 
             |               |  produce fig.2 of the paper, which shows the
             |               |  spatial and temporal variation (pp 194)
             | fig2b.con     | As fig2.con, with less environmental variables, 
             |               |  to be able to use CanoDraw
             | fig3.con      | partial RDA focussing on how the change in time
             |               |  depends on space (strip; pp 196)
             | yeartest.con  | RDA with model "year" and covariables "plot") 
             |               |  to test the change in species composition 
             |               |  between 1977 and 1988 (pp 195)
             | waterxyr.con  | RDA with model "waterdepth88 . year" and 
             |               |  covariables "plot and year" to test the 
             |               |  interaction waterdepth.year, i.e. whether 
             |               |  the change was constant against the alternative
             |               |  hypothesis that it depended on water depth
             | watrxyr2.con  | RDA with model waterdepth * year and 
             |               |  covariables "plot and year"
             | stripxyr.con  | RDA to test the interaction strip.year
             | ph_water.con  | RDA to test the component "pH and water depth"
             | yr_water.con  | RDA on water depth and year to infer the change 
             |               |  in water depth (-pH=0)
             | yr_ph.con     | RDA on pH and year to infer the change in pH
             |               |  (-waterdepth =0)
             | yr_ph_wa.con  | RDA with model "year+pH+Waterdepth" to infer 
             |               |  the joint change (pp 196)
-------------+---------------+-------------------------------------------------

The data are described in ter Braak & Wiertz (1994), reproduced in 
Unimodal Models pp 190-191.
The 1997 and 1988 data are from Both & van Wirdum (1981) and Farjon & Wiertz (1988), respectively.

The area is known as Koolmansdijk near the village Lichtenvoorde.

References

Both, J.C. & Van Wirdum, G.(1981): Waterhuishouding, bodem en vegetatie
van enkele Gelderse natuurgebieden, RIN-report nr. 81/18
Rijksinstituut voor Natuurbeheer, Leersum. 

Farjon, A. & Wiertz, J.(1989): Milieu- en vegetatieveranderingen in
het schraalland Koolmansdijk (Lichtenvoorde) 1952-1988. Rin report
nr. 89/18. Rijksinstituut voor Natuurbeheer, Leersum. 

Ter Braak, C.J.F. & Wiertz, J.(1994): On the statistical analysis of
vegetation change: a wetland affected by water extraction and soil
acidification. Journal of Vegetation Science, 5: 361-372.


Details of grid_env.dta:

pH88  and Waterdepth en WA-peil are the means of the four corners of 
the gridcell.
Waterd88 = Waterdepth in 1988 in cm
Waterdep = Waterdepth in 1988 for 1988-samples and 
           Waterdepth in 1988 - 27 cm for 1977-samples