| The response of wood properties to climate variation at the macro and micro level was carried out to better understand the potential influence of changing climate on tree growth and wood property variation. The knowledge generated will provide scientific instruction for forest management and provide a scientific basis for developing forestry strategies that deal with ongoing climate change, and help to inform international negotiations on climate change issues.Annual variability was assessed in fourteen different wood properties of Picea crassifolia, measured by SilviScan-3(?), growing at three elevations (2600m, 2800m and 3000m) at Qilian Mountain, northwestern China. The fourteen parameters were ring, earlywood and latewood width, wood density, microfibril angle and modulus of elasticity, and ring tracheid radial diameter and tracheid wall thickness. Chronologies (42 chronologies) of wood property were constructed based on the investigation of the climate change features in the study area and variation of wood properties with three elevations and with tree cambial age. Responses of wood properties to main climate elements (temperature and precipitation) were analyzed using correlation and response function methodologies.The major achievements of this study are summarized as follows:1. Temperature had positive effect on cell wall thickness, wood density and modulus of elasticity, and a negative influence on cell radial diameter; ring width and microfibril angle. Correlations between wood properties and temperature indicated that temperatures during the growing season (May to September) have strong influence on wood properties. The temperature sensitivity of wood properties growing at the three elevations was similar. Temperature sensitivity of earlywood properties was similar to that of latewood properties. Temperature information recorded in earlywood and latewood properties were registered in ring properties.Cell wall thickness of P.crassifolia growing at elevations of 2600m, 2800m and 3000m positively correlated with temperature in February and May to September of current year, in December of previous year and September of current year, and in December of previous year and January, May to September of current year, respectively. Ring density of P.crassifolia growing at elevations of 2600m, 2800m and 3000m positively correlated with temperature in June to September, in December of previous year and June to September of current year, and in December of previous year and June and September in current year, respectively. Earlywood density growing at elevations of 2600m, 2800m and 3000m positively correlated with temperature in June to September, in December of previous year and June to September of current year, and in December of previous year and January, and June to September in current year, respectively. Latewood density growing at elevation of 2800m positively correlated with temperature in April, August and September. Correlation of latewood density growing at elevations of 2600m and 3000m was non significant. Ring modulus of elasticity of P.crassifolia growing at elevations of 2600m, 2800m and 3000m positively correlated with temperature in July to September, in December of previous year, and in May and July, respectively. Both earlywood modulus of elasticity growing at elevations of 2600m and 3000m positively correlated with temperature in June and July. Correlation of earlywood modulus of elasticity growing at elevation of 2800m was non significant. Latewood modulus of elasticity growing at elevation of 2600m negatively correlated with temperature in June to July. Both latewood modulus of elasticity growing at elevations of 2800m and 3000m positively correlated with temperature in August.All cell radial diameter of P.crassifolia growing at elevations of 2600m, 2800m and 3000m negatively correlated with temperature in June to July. Ring, earlywood and latewood width of P.crassifolia growing at elevations of 2600m and 3000m negatively correlated with temperature in June and July. The correlation of ring and earlywood width growing at elevation of 2800m was not significant. Latewood width at 2800m elevation was negatively correlated with temperature in July. Ring microfibril angle at 2600m, 2800m and 3000m elevation was negatively correlated with temperature in May to July, in June to July, and in June to July, respectively. The correlation between earlywood microfibril angle and temperature was similar to that of ring microfibril angle. Latewood microfibril angle at 2600m, 2800m and 3000m elevation was negatively correlated with temperature in April and August; in August; and in April, July to August, respectively.2. Precipitation had a positive influence on cell radial diameter; ring width and microfibril angle, and an negtive effect on cell wall thickness, wood density and modulus of elasticity. Correlations between wood properties and precipitation indicated that precipitation in spring of the current growing season (March to September) has strong influence on wood properties. Precipitation sensitivity of wood properties increased with decreasing of elevation and was stronger in earlywood compared to latewood properties. Precipitation information recorded in earlywood and latewood properties were almost registered in ring properties.Cell radial diameter of P.crassifolia growing at elevations of 2600m and 2800m positively correlated with precipitation in May and June and in June, respectively. The correlation of cell radial diameter with precipitation at 3000m was not significant. Ring width grown at 2600m elevation positively correlated with precipitation in March, May and June. At elevations of 2800m and 3000m, the correlation was not significant. Earlywood width at 2600m elevation was positively correlated with precipitation in March, May and June. The correlation between earlywood width growing at 2800m and 3000m was not significant. The correlation between latewood width growing at the three elevations was also non-significant. Ring microfibril angle growing at elevations of 2600m and 2800m were positively correlated with precipitation in May and June and in June, respectively. The correlation between ring microfibril angle and precipitation growing at 3000m elevation was not significant. Earlywood microfibril angle at three elevations was positively correlated with precipitation in May. The earlywood microfibril angle at the three elevations was positively correlated with precipitation in August.Cell wall thickness was negatively correlated with precipitation in March at all three elevations, as was ring wood density. Earlywood density growing at elevation of 2600m was negatively correlated with precipitation in June. The correlation between earlywood density and precipitation growing at elevations of 2800m and 3000m was not significant, as was the correlation between latewood density and precipitation at 2600m and 2800m elevation. Latewood density growing at 3000m was positively correlated with precipitation in January and August. Ring modulus of elasticity growing at 2600m elevation was negatively correlated with precipitation in June. Both ring modulus of elasticity of growing at elevations of 2800m and 3000m was positively correlated with precipitation in October of the previous year. Earlywood modulus of elasticity growing at elevations of 2600m, 2800m and 3000m negatively correlated with precipitation in June, in January and June, and in May, respectively. Latewood modulus of elasticity growing at elevations of 2600m, 2800m and 3000m negatively correlated with precipitation in July, in April and in August, respectively.3. Climate explained 22%～41% of the variance in ring cell radial diameter, cell wall thickness, ring width, wood density, microfibril angle and modulus of elasticity (cell radial diameter > microfibril angle > cell wall thickness > wood density > modulus of elasticity > ring width).4. The increasing trend of temperature over the period 1987-2009 is obvious. No trends are evident in temperature over the period 1957-1986 and for precipitation over the period 1957-2008. If global warming continues, the cell radial diameter, microfibril angle and wood density could be significantly affected. According to the significant response function of the ring cell radial diameter, ring microfibril angle and ring wood density over period 1987-2008, the ring cell radial diameter could decrease by 2.33μm, the ring microfibril angle could decrease by 2.44°and the ring wood density could increase by 0.13 g/cm~3 when temperature increased 1℃. These results indicated that trees would adapt to climate change by decreasing cell diameter and wood microfibril angle and increasing wood density. |
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