View source: R/interval.trend.R

interval.trend | R Documentation |

The function calculates year-to-year growth changes for individual tree-ring series and defines interval trends for (the population of) trees using the pointer interval method according to Schweingruber et al. (1990), which is also extensively described in Jetschke et al. (2019). The minimum percentual growth change and the minimum percentage of trees that should display a negative (or positive) trend for that year to be considered as negative (or positive) pointer year, can be adjusted.

```
interval.trend(data, period = NULL, trend.thresh = 0,
IT.thresh = 95, make.plot = FALSE)
```

`data` |
a |

`period` |
a |

`trend.thresh` |
a |

`IT.thresh` |
a |

`make.plot` |
a |

The function calculates year-to-year growth changes. For each tree and year, the interval trend is defined as 1 if a positive change exceeds `trend.thresh`

, as 0 if a negative change falls below minus `trend.thresh`

and as 0.5 if the absolute change is below `trend.thresh`

. `trend.thresh`

defaults to 0%. The interval trend for a population is defined as the average interval trend of the individual trees. A year is considered a negative (or positive) pointer year if the percentage of trees showing a decreasing (or increasing) trend exceeds `IT.thresh`

(defaults to 95%). Hence, in case of a negative pointer year the mean overall interval trend falls below 1 - `IT.thresh`

, for a positive pointer year the mean overall interval trend exceeds `IT.thresh`

.

The function returns a `list`

containing the following components:

`perc.diff` |
a |

`ITvalues` |
a |

`out` |
a |

`spec.param` |
a |

Marieke van der Maaten-Theunissen, Ernst van der Maaten and Gottfried Jetschke.

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 BrÃ¤ker, O.U. (1990) Identification, presentation and interpretation of event years and pointer years in dendrochronology. *Dendrochronologia* 8: 9-38.

```
## Calculate pointer years using interval.trend
## for a specified period and create a plot
data(s033)
IT <- interval.trend(s033, period = c(1950,2010), make.plot = TRUE)
## Calculate pointer years as years with at least 90% of the trees
## showing a positive/negative interval trend
data(s033)
IT <- interval.trend(s033, IT.thresh = 90)
IT$out[which(IT$out$nature == 1),"year"]
IT$out[which(IT$out$nature == -1),"year"]
```

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