I'm working on long-term vegetation development on lava flows. I'm
interested in the relationship between various ecological and environmental
response variables (e.g. days of snow cover, soil temperature, foliar
nutrient concentrations) and two fixed
factors: microtopographic position ('Topo', with two levels: 'hillock' and
'hollow') and lava flow age ('Age', with three levels: '26_years',
'161_years' and '848_years').
Three lava flows of different ages were selected for the study. Sampling
was carried out at three locations on each flow; each location comprised
paired 'hillock' and 'hollow' plots (below).
Flow ? ? ? ? ? ?Location ? ? ? ?Topo
26_years ? ? ? ?1 ? ? ? ? ? ? ? Hillock
26_years ? ? ? ?1 ? ? ? ? ? ? ? Hollow
26_years ? ? ? ?2 ? ? ? ? ? ? ? Hillock
26_years ? ? ? ?2 ? ? ? ? ? ? ? Hollow
26_years ? ? ? ?3 ? ? ? ? ? ? ? Hillock
26_years ? ? ? ?3 ? ? ? ? ? ? ? Hollow
161_years ? ? ? 4 ? ? ? ? ? ? ? Hillock
161_years ? ? ? 4 ? ? ? ? ? ? ? Hollow
161_years ? ? ? 5 ? ? ? ? ? ? ? Hillock
161_years ? ? ? 5 ? ? ? ? ? ? ? Hollow
161_years ? ? ? 6 ? ? ? ? ? ? ? Hillock
161_years ? ? ? 6 ? ? ? ? ? ? ? Hollow
848_years ? ? ? 7 ? ? ? ? ? ? ? Hillock
848_years ? ? ? 7 ? ? ? ? ? ? ? Hollow
848_years ? ? ? 8 ? ? ? ? ? ? ? Hillock
848_years ? ? ? 8 ? ? ? ? ? ? ? Hollow
848_years ? ? ? 9 ? ? ? ? ? ? ? Hillock
848_years ? ? ? 9 ? ? ? ? ? ? ? Hollow
Generally, there was only one observation per cell. In this design, there
are replicate observations of hillocks/hollows on each flow, but these
observations are paired (a bit like a split plot design, or what Quinn &
Keogh call a partly-nested ANOVA).
I would like to analyze the effect of Age and Topo on the response variables
(taking each variable individually). My initial thought was to use aov with
Age and Topo as fixed effects, and Location (a blocking factor) as a random
effect. But I am not sure how to specify the error term to account for the
blocking. Would lme be more appropriate in this case?
Can anyone help with the model specification?
Nick
--
Dr Nick Cutler
Postdoctoral Research Assistant
School of Geography and the Environment
Oxford University Centre for the Environment
Dyson Perrins Building
South Parks Road
Oxford OX1 3QY
UK
Tel.: +44 1865 275 860