# pointer.rgc: Calculate pointer years using the relative growth change... In pointRes: Analyzing Pointer Years and Components of Resilience

 pointer.rgc R Documentation

## Calculate pointer years using the relative growth change method

### Description

The function calculates event and pointer years on a `data.frame` with tree-ring series using the relative growth change method, described as abrupt growth change method in Schweingruber et al. (1990). This method relates tree growth in year `i` to the average growth of `n` preceding years. Thresholds for event- and pointer-year calculations can be adjusted.

### Usage

``````pointer.rgc(data, period = NULL, nb.yrs = 4, rgc.thresh.pos = 60, rgc.thresh.neg = 40,
series.thresh = 75, make.plot = FALSE)
``````

### Arguments

 `data` a `data.frame` with tree-ring series (raw or detrended) as columns and years as rows (e.g., output of `read.rwl` or `detrend` of package dplR). `period` a `vector` specifying the start and end year of the analysis. Defaults to the full period covered by the data. `nb.yrs` an `integer` specifying the number of preceding years to be used in calculating relative growth changes. Defaults to 4. `rgc.thresh.pos` a `numeric` specifying the threshold above which a relative growth change (in percentage) for a specific tree and year is considered a positive event year. Defaults to 60. `rgc.thresh.neg` a `numeric` specifying the threshold below which a relative growth change (in percentage) for a specific tree and year is considered a negative event year. Defaults to 40. `series.thresh` a `numeric` specifying the minimum percentage of trees that should display a positive (or negative) event year for that year to be considered as positive (or negative) pointer year. Defaults to 75. `make.plot` a `logical` specifying whether a bar plot, showing mean relative growth changes, should be created. Pointer years are indicated with dark-gray bars. Defaults to FALSE.

### Details

The function calculates the ratio of tree growth in year `t` and the average growth of `n` preceding years for individual trees. Resulting relative growth changes are used to identify event years for trees, and these event years to define pointer years for the site.

Following Schweingruber et al. (1990), `nb.yrs`, `rgc.thresh.pos`, `rgc.thresh.neg` and `series.thresh` are set to 4, 60, 40 and 75 respectively, meaning that a positive or negative pointer year will be defined when at least 75% of the tree-ring series display an event year with a growth increase or decrease of at least 60% or 40%, respectively, relative to the average growth in the four preceding years. Depending on the sensitivity of the tree-ring series, the thresholds `rgc.thresh.pos` and `rgc.thresh.neg` may be adjusted (e.g., lowered for more complacent series; Jetschke et al. 2019).

Note that the resulting time series are truncated by `nb.yrs` at the beginning inherent to the calculation method.

### Value

The function returns a `list` containing the following components:

 `rgc` a `matrix` with relative growth changes for individual tree-ring series `EYvalues` a `matrix` indicating positive (1), negative (-1) and non-event years (0) for individual tree-ring series `out` a `data.frame` containing the following columns: `year` - time stamp, `nb.series` - number of series considered, `perc.pos` - percentage of trees showing a positive event year, `perc.neg` - percentage of trees showing a negative event year, `nature` - number indicating whether the year is a positive (1), negative (-1) or no pointer year (0), `dev_mean` - mean growth deviation in percentage over the available series for each year, and `dev_sd` - standard deviation of the growth deviation for each year `spec.param` a `data.frame` specifying the arguments used in the calculation

### Author(s)

Marieke van der Maaten-Theunissen and Ernst van der Maaten.

### References

Jetschke, G., van der Maaten, E. and van der Maaten-Theunissen, M. (2019) Towards the extremes: A critical analysis of pointer year detection methods. Dendrochronologia 53: 55-62.

Schweingruber, F.H., Eckstein, D., Serre-Bachet, F. and Bräker, O.U. (1990) Identification, presentation and interpretation of event years and pointer years in dendrochronology. Dendrochronologia 8: 9-38.

In writing the function, the code of the dplR function `pointer` (Pierre Mérian) was used as a reference.

### Examples

``````## Calculate pointer years on tree-ring series
data(s033)
py1 <- pointer.rgc(s033)