[R-sig-eco] error strata in R

[Nick Cutler]

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