Average (a) and mean deviations (b) of precipitation and temperature from their long-term (1956–2011) mean values for all the missing ring events of the composite chronology.

<p>Average (a) and mean deviations (b) of precipitation and temperature from their long-term (1956–2011) mean values for all the missing ring events of the composite chronology.</p

Trend surface for cambial age, elevation (m), tree-ring width (mm/100) (a) and radial ring-width growth trends (mm/100) (b) at MNT, Delingha, China.

<p>The surface is interpolated from four original unsmoothed curves of radial ring width (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0079362#pone-0079362-g005" target="_blank">Figure 5</a>) using inverse distance weighting.</p

Four standardized chronologies (a), four residual chronologies (b) and the composite chronology (All) and their sample depth at different elevations from MNT.

<p>The regional chronology is derived by using all available ring-width series from the four sub-chronologies. The thick line is the 11-year Fast Fourier Transform (FFT) smoothed series. To the right of the vertical dotted line the chronology EPS value is above 0.85, which indicates a statistical reliable series. The light yellow shaded area shows the number of series. The numbers in the upper left corner of all subfigures are the elevation ranges of each zone.</p

Characteristics of the radial tree-ring biological growth trends at different elevations: (a) H (3900 m–4015 m), (b) MH (3790 m–3899 m), (c) ML (3701 m–3789 m), and (d) L (3550 m–3700 m), based on Hugershoff functions fitted to the means measurement data.

<p>The thin line is a mean curve for radial tree-ring biological growth at different elevations. The thick line is a curve fitted to the Hugershoff function. The 95% confidence interval is shown by light yellow shading.</p

Comparison between missing ring ratio and the temperature (a) and precipitation (b) instrumental records at Delingha during 1956–2011.

<p>Temperature is the mean from previous September to current March. Precipitation is the total from previous July to current June.</p

Response surface regression results and their F values at the four different elevations and the composite site.

<p>The response surface was defined by a quadratic surface function: .</p><p>Here, Z = Z score value of standardized tree ring index at different elevations and the whole site; X = Z score value of mean precipitation (previous July to current June); Y = Z score value of mean temperature (previous September to current March). The F value is calculated by , with notation as follows. : regression sum of squares, : residual sum of squares, <i>p</i>: degrees of freedom of the regression function, here <i>p</i> = 5, n: number of active data, here n = 55. If , the response surface regression is significant at the α level.</p>**<p>F value is significant at p = 0.01 level.</p

Scatter diagram showing relationships between the elevation and mean ring width after Z score transformation using 265 trees.

<p>The Pearson's correlation coefficient is −0.29, which is significant at the p = 0.01 level.</p

Comparison of low-frequency variability in four STD chronologies at different elevations and the composite chronology during 1110–2011.

<p>Comparison of low-frequency variability in four STD chronologies at different elevations and the composite chronology during 1110–2011.</p

Comparison of altitude-related effects on standardized tree ring series (a) and residual tree ring series (b), which separately constitute the STD and RES chronologies during six typical periods (three high-value periods and three low-value periods).

<p>Euclidean distance is defined as the distance between each TRW series (50-dimensional vectors) and the mean TRW series (50-dimensional vector) of all the TRW series in the given periods. Both the elevation (m) and Euclidean distance are transformed to Z scores. R(1204–1253): high precipitation during 1204–1254; P(1254–1303):low precipitation during 1254–1303; SE: standard error; RSS: residual sum of squares; Prob>F: the probability that the null hypothesis for the full model is true (i.e., that all of the regression coefficients are zero).</p

Correlation coefficient matrix between the four STD (upper right corner) and RES (lower left corner) chronologies and the composite chronology during 1956–2011 and 1110–2011.

<p>All the values are significant at the p = 0.01 level.</p