Dear Friends,
I am performing na analysis and would like to hear your opinion about
it.
The System
A subtropical riparian forest
Dependent Variable: density of trees with diameter at 1.3 m height >= 5
cm
Management: most of the forest has been continuously exposed to cattle
grazing, but a small portion has been protected by fencing for the last 35
years.
Sampling design: 5 x 5 m plots
A variable number of 5 x 5 m plots was established in 5 distinct areas
of the forest: one area in the exclosure and four areas in the grazed part of
the forest. A larger number of areas could not be sampled in the exclosure due
to its restricted size. I know that this characterize pseudoreplication of the
excluded factor, but at the moment we have no alternatives, although we are
seeking them.
Areas A, B, C, D are grazed. Area E is the exclosure. RAIZNIND is
density per 5 x 5 plot.
Approaches to Analysis (using Systat)
ANOVA plus Planned Contrasts
Dep Var: RAIZNIND N: 198 Multiple R: 0.369 Squared multiple R: 0.136
Analysis of Variance
Source Sum-of-Squares df Mean-Square F-ratio P
Regression 9.177 4 2.294 7.614 0.000
Residual 58.149 193 0.301
-------------------------------------------------------------------------------
Durbin-Watson D Statistic 1.896
First Order Autocorrelation 0.041
Hypothesis Testing
Contrast between Areas A, B, C and D versus Areas E: 1 1 1 1 -4
Test for effect called: AREA$
A Matrix
1 2 3 4 5
0.000 5.000 5.000 5.000 5.000
Test of Hypothesis
Source SS df MS F P
Hypothesis 2.695 1 2.695 8.945 0.003
Error 58.149 193 0.301
According to this approach, the exclosures is different from the grazed areas
GLM with explanatory variables manajement (grazed x exclosure) and area
Categorical values encountered during processing are:
MANAGEMENT$ (2 levels)
GRAZED, PROTECTED
AREA$ (5 levels)
A, B, C, D, E
The following effects have lost degrees of freedom.
Initial Lost Final
Effect df df df
AREA$ 4 1 3
Dep Var: RAIZNIND N: 198 Multiple R: 0.369 Squared multiple R: 0.136
Analysis of Variance
Source Sum-of-Squares df Mean-Square F-ratio P
MANAGEMENT$ 0.802 1 0.802 2.663 0.104
AREA$ 6.917 3 2.306 7.653 0.000
Error 58.149 193 0.301
>From this, we conclude that there is no difference between the grazed and
>non-grazed areas, although there is considerable heterogeneity between the
>grazed areas.
I could not find help in Zar or Sokal and Rohlf, as well as in Systat's help.
What do you think about this?
Thanks in advance,
Alexandre
Dr. Alexandre F. Souza
Programa de Pós-Graduação em Biologia (Diversidade e Manejo da Vida Silvestre)
Universidade do Vale do Rio dos Sinos
Av. UNISINOS 950 - C.P. 275
São Leopoldo 93022-000
RS - Brasil
Telefone: (051)3590-8121 ramal 1263
[EMAIL PROTECTED]
http://www.unisinos.br/laboratorios/lecopop
