Fig 1.
Location of five Callitris columellaris tree-ring sites in relation to annual rainfall and rainfall seasonality zones of Australia.
Coloured shading indicates the 1961–1990 mean annual (January to December) rainfall amount (Data sourced from the Australian Bureau of Meteorology: http://www.bom.gov.au/jsp/ncc/climate_averages/rainfall/index.jsp). Dashed lines indicate boundaries between areas with summer-dominated, uniform (both summer and winter) or winter-dominated rainfall distributions (Data sourced from the Australian Bureau of Meteorology: http://www.bom.gov.au/jsp/ncc/climate_averages/climate-classifications/index.jsp?maptype=seasb#maps). Solid lines indicate state and territory boundaries and white dots indicate the location of some state capital cities.
Table 1.
Summary of climate and rainfall data for each of the five Callitris columellaris sites and the annual and growing season periods used in further analyses.
Fig 2.
Pearson correlations between ring-width index (RWI) and monthly (columns) and seasonal (lines) rainfall (a-e), maximum (f-j) and minimum temperatures (h-o) at each of the five Callitris columellaris sites. The x-axis indicates the starting month of the seasonal period while the colours of the lines correspond to the length of the seasonal period (the number of consecutive months) rainfall was summed over or temperature was averaged over. Shaded boxes indicate the ‘best’ (highest correlation) season; dashed boxes indicate the best annual period for each site. Numbers inside or next to boxes are the Pearson correlation values for the respective season or annual period. Lower case ‘p’ indicates months in the calendar year prior to the main growing season. LDE showed no significant correlation between RWI and minimum temperature for any period > 3 months.
Table 2.
Rainfall variables used to examine the relationship between growth of Callitris columellaris and rainfall amount, intensity, frequency, and intermittency.
Fig 3.
Relationship between ring-width index (RWI) and (a) annual or (b) growing season rainfall amount at the five Callitris columellaris sites. Each point represents data for one year. Lines represent fitted models; simple linear models for CJD, LDE and LTY and quadratic polynomial models for KOR and CHR. The fit of simple linear models for KOR and CHR are also shown in grey in (a).
Fig 4.
Distribution of annual rainfall attributes and their relationship with Ring Width Index (RWI) of Callitris columellaris across semi-arid (yellow-red) and tropical (blue) biomes in Australia.
(a-b) mean rain intensity (mm/rain day), (c-d) number of rain days (>0 mm), (e-f) length of wet season (number of days) and (g-h) mean number of consecutive rain days (>0 mm). Boxplots show the median (50th percentile) as the centre horizontal line, the interquartile range (25th to 75th percentile) as the bottom and top horizontal line, the range (0.3–99.7th percentile) as vertical lines, and extreme values (<0.7 or >99.3 percentile) of mean monthly temperatures as dots. Lines in b), d), f), and h) represent simple linear models.
Table 3.
Parameter estimates for regression models predicting ring-width index (RWI) from a) annual rainfall amount and b) “growing season” rainfall amount.
Table 4.
Slope parameter estimates and variance in ring-width index (RWI) explained by annual rainfall variables.