Demographic rates of plants commonly vary along elevation gradients due to the associated gradients in environmental factors. However, there is little information yet on how such spatial trends may be changing temporally under the influence of recent climate change. Detection of change would be a positive test of the hypothesis that plants are responding to climate change through changes in demographic rates or shifts in elevation distribution. Towards this end, we provide a detailed analysis using measurements of diameter at breast height (dbh) of all woody plants (dbh ≥ 5cm) from 716 permanent plots in eastern China between 1989 and 2009 at 5-year intervals. We calculated the relative growth rate of each stem and the recruitment rates of new trees into the dbh ≥ 5cm class for each plot for every 5-year interval to examine the growth and recruitment rates along the elevation gradient and the responses of these elevation-related patterns to regional climate change. Further, we calculated elevation migration as the rate of change of the mean of the elevation distribution of 32 genera during the period from 1989 to 2009. Our objective was to detect changes that might be due to climate change over that period.
Results/Conclusions
We found significant strong negative relationships between relative growth rate with elevation for all the 5-year intervals (1989-1994; 1994-1999 and 2004-2009), though the relationship for the interval 1999-2004 was weak. Relative recruitment rate significantly decreased with elevation gradient between 1989 and 1999, but there appears to be no relationship since 1999, possibly due to the impact of rising temperature over that period. We found elevation shifts occurred during the past 20 years and 40.6% of the general shifted upward between 1989 and 2009, while 46.9% shifted downwards and 12.5% stayed within ±1 m of their initial mean elevation. We found there is a trade-off between growth and recruitment, which slower growth genus tend to have higher reproductive rate. Furthermore, this trade-off is related to elevation shift, that the genera which migrated father upslope, had relatively lower growth rate and higher recruitment rate.