chillR - Statistical Methods for Phenology Analysis in Temperate Fruit
Trees
The phenology of plants (i.e. the timing of their annual
life phases) depends on climatic cues. For temperate trees and
many other plants, spring phases, such as leaf emergence and
flowering, have been found to result from the effects of both
cool (chilling) conditions and heat. Fruit tree scientists
(pomologists) have developed some metrics to quantify chilling
and heat (e.g. see Luedeling (2012)
<doi:10.1016/j.scienta.2012.07.011>). 'chillR' contains
functions for processing temperature records into chilling
(Chilling Hours, Utah Chill Units and Chill Portions) and heat
units (Growing Degree Hours). Regarding chilling metrics, Chill
Portions are often considered the most promising, but they are
difficult to calculate. This package makes it easy. 'chillR'
also contains procedures for conducting a PLS analysis relating
phenological dates (e.g. bloom dates) to either mean
temperatures or mean chill and heat accumulation rates, based
on long-term weather and phenology records (Luedeling and
Gassner (2012) <doi:10.1016/j.agrformet.2011.10.020>). As of
version 0.65, it also includes functions for generating weather
scenarios with a weather generator, for conducting climate
change analyses for temperature-based climatic metrics and for
plotting results from such analyses. Since version 0.70,
'chillR' contains a function for interpolating hourly
temperature records.
