rbar is typically calculated as 'the mean interseries correlation between all series from different trees' (Wigley et al. 1994). This can (and typically is) calculated over some common period that maximizes the number of years and series (e.g. the largest covering rectangle in a matrix of series (variables) and years (observations)). For use in deciding when there is sufficiently high, a running rbar can also be calculated for fixed windows of Y year overlapping by some number of years (e.g. 50 year windows lagged 25 years, or with 25 years of overlap; 100 year windows lagged 10 years at a time with 90 years of consecutive overlap, etc). dplR function is rwi.stats.running (https://github.com/cran/dplR/blob/master/R/rwi.stats.running.R)
Wigley1984.pdf
rbar is typically calculated as 'the mean interseries correlation between all series from different trees' (Wigley et al. 1994). This can (and typically is) calculated over some common period that maximizes the number of years and series (e.g. the largest covering rectangle in a matrix of series (variables) and years (observations)). For use in deciding when there is sufficiently high, a running rbar can also be calculated for fixed windows of Y year overlapping by some number of years (e.g. 50 year windows lagged 25 years, or with 25 years of overlap; 100 year windows lagged 10 years at a time with 90 years of consecutive overlap, etc). dplR function is rwi.stats.running (https://github.com/cran/dplR/blob/master/R/rwi.stats.running.R)
Wigley1984.pdf