gsi {dfoliatR}

Calculate the growth suppression index

Description

This function removes the nonhost growth signal from a host tree-ring series.

Usage

gsi(input_series)

Arguments

input_series

A dplr::rwl object with the host tree series as the first column and the non-host chronology as the second. Years should be the row names. This is specifically created by defoliate_trees() and passed to gsi().

Details

The growth suppression index (GSI) is referred to as the "corrected" series in OUTBREAK. It is calculated as:

GSI(i) = H(i) - (NH(i) - mean(NH)) sd(H)/sd(NH)

where H and NH are the host and nonhost tree-ring series as standardized index values; i is the year, and the functions mean() and sd() are applied to the common period.

gsi() will rarely be run directly by a user. It is called from defoliate_trees().

Value

A data frame with the two input columns (host and nonhost series) and 3 added columns:

1. The mean/sd adjusted non-host chronology,

2. The growth suppression index ("gsi") of the host series after subtraction of the adjusted nonhost chronology,

3. The normalized growth suppression index ("ngsi") generated by applying scale() to the gsi.