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Charster is designed to ease the
exploratory analysis of lake-sediment or bog/peatland charcoal records
when the purpose is to identify peaks in the charcoal record that
result from nearby fires. Charster provides a few statistical tools
that help characterize the variability in the charcoal record and
whether identification of peaks is warranted. Charcoal time series may
be manipulated in various ways before placing a threshold to identify
peaks.
Charster is most helpful for analysis
of charcoal records that display distinct peaks. Recent collaboration
among several labs has led to agreement on the conditions that yield
such a record (see also Whitlock and Larsen 2002; Whitlock and Anderson
2003):
- Sampled contiguously, typically at least every 1 cm, corresponding to deposition times of 30 years or less.
- The fire regime is of infrequent but
intense stand-replacing fires. Such a regime will deliver charcoal to
lakes in infrequent pulses such that subsequent delivery to the lake
bottom and mixing does not remove the fire signal.
- Lakes or bogs are small in size
(< ca. 10 ha), and if lake sediment is analyzed, that the lakes are
fairly deep (>2 m) to limit sediment disturbance.
- Charster requires age estimates on
the top and base of each sample where charcoal was quantified. It is
not possible to use the software on undated records.
The general approach of this analysis is to "decompose" a time series into two components: a slowly varying background and a high frequency peak component
(Long et al., 1999). One may make different assumptions regarding the
behavior of these two components (i.e., nature of variability over
time, relationship to local fires, etc.), prompting different methods
of analysis. The purpose of Charster is to allow one to easily explore
these options and their impact on the final interpretation.
It is recommended that first-time users
read through these help pages before delving into analyzing a record.
Please email me with any suggestions.
Some analyses are described in:
Gavin, D.G., F.S. Hu, K.P. Lertzman and P. Corbett. 2006. Weak
climatic control of forest fire history during the late Holocene.
Ecology 87:1722-1732.
CharAnalysis,
by Phil Higuera, grew out of the analyses in Charster.
CharAnalysis provides many more diagnostic statistics for
evaluating peaks
in charcoal records, including the ability to define thresholds using
local criteria and analyze fire-interval distributions. Some
other practical differences between the programs are 1) Data input
format and treatment of missing data-gaps, 2) Charster's capacity to do
simple analyses on non-interpolated data (while interpolation is
necessary for more complex analyses in Charster and is the default in
CharAnalysis), and 3) Many useful graphs produced by CharAnalysis.
This software was written by Daniel Gavin. Please read my software disclaimer.
Charster is based on CHAPS (Charcoal Analysis Programs) by Patrick Bartlein.
The United States Geological Survey
(USGS) funded this work. Craig Allen greatly facilitated this project.
Critical feedback was provided by Jenn Marlon and Phil Higuera.
The software is written in REALBasic, and the REALBasic project is available for those who wish to inspect the code.
updated 25 April 2008
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