phase.zg {dendRoAnalyst}

Application of the zero-growth approach to calculate different phases, their duration and to plot them.

Description

This function analyses data using the zero-growth approach. Initially, it divides the data in two categories: 1) Tree water deficiency (TWD), i.e. the reversible shrinkage and expansion of the tree stem when the current reading is below the previous maximum and, 2) Increment (GRO), the irreversible expansion of the stem when the current reading is above the previous maximum. Then it calculates the TWD for each data point as the difference between the modelled "growth line" and the observed measurement. See Zweifel et. al.,(2016) for details.

The severity value of each TWD was introduced in version 0.1.4 of the package.

Usage

phase.zg(df, TreeNum)

Arguments

df

dataframe with first column containing date and time in the format yyyy-mm-dd HH:MM:SS. It should contain data with constant temporal resolution for best results.

TreeNum

numerical value indicating the tree to be analysed. E.g. '1' refers to the first dendrometer data column in df.

Value

A list of two dataframes. The first dataframe ZG_cycle contains the cyclic phases along with various statistics and the second dataframe ZG_phase with assigned phases for each data point.The contents of ZG_cycle are:

Columns		Description
DOY		Day of year for the corresponding phase.
Phase		TWD for tree water deficit and GRO for irreversible expansion.
start		Time when the corresponding phase starts.
end		Time when the corresponding phase ends.
Duration_h		Duration of the corresponding phase in hours.
Magnitude		Radial/circumferential change in millimeters.
rate		Rate of Radial/circumferential change in micrometers per hour.
Max.twd		Maximum TWD recorded for the corresponding TWD phase.
twd.severity		The severity of the individual TWD period (see description below).
Max.twd.time		Time of occurrence of maximum TWD value for each TWD phase.
Avg.twd		Average of TWD values for each TWD phase.
STD.twd		Standard deviation of TWD values for each TWD phase.

References

Zweifel R, Haeni M, Buchmann N, Eugster W (2016) Are trees able to grow in periods of stem shrinkage? New Phytol 211:839–849. doi:10.1111/nph.13995

Examples

library(dendRoAnalyst)
data(gf_nepa17)
zg.phase<-phase.zg(df=gf_nepa17[1:600,], TreeNum=1)
head(zg.phase[[1]],10)
head(zg.phase[[2]],10)