Stand dynamics of the drought-affected floodplain forests of Araguaia River,Brazilian Amazon

Background： The floodplain forests of Araguaia River, a clear-water river in the southeastern Amazon（Tocantins State, Brazil）, are characterized by seasonal flooding up to 3.5 m height, low nutrient levels in the water, and seasonal drought periods of 4–5 months.Methods： We studied the forest dynamics（tree diameter growth, tree mortality and recruitment） of this unique forest ecosystem over a 5-year period by repeated censuses in 12 permanent plots established along a flooding gradient.Results： The cumulative basal area in the plots increased by 0.84（±0.45） m^2·ha^-1·yr^-1（mean ±SD） in the annual y-flooded（AF） plots in lower terrain and by 0.69（±1.00） m^2·ha^-1·yr^-1 in the higher non-annual y flooded（NAF） plots, corresponding to an aboveground biomass increase of 0.81（±0.57） and 0.69（±1.58） Mg·ha^-1·yr^-1 in the AF and NAF plots, indicating a recent carbon sink in the biomass. Mean diameter growth rate was 1.8（±0.44） mm·yr^-1 in the AF and 2.0（±0.56） mm·yr^-1 in the NAF plots（corresponding to a coarse wood production of 1.53（±1.29） and 2.02（±0.52） Mg·ha^-1·yr^-1）,indicating no flooding effect on radial growth. Mean mortality rates in the 5-year period were 1.9（±0.37）·yr^-1 in the AF plots and 1.8（±0.87）%·yr^-1 in the NAF plots with no differences along the flooding gradient. Highest mortalities were registered in the AF plots for the 10–20 cm dbh class（2.4%·yr^-1）, likely as a consequence of flooding,and in the NAF plots for the 40–50 cm dbh class（3.0%·yr^-1）, probably mainly caused by ENSO-related droughts.Conclusions： We conclude that these drought-affected tropical floodplain forests have a lower standing biomass and aboveground productivity than central Amazonian floodplain forests in more humid climates, and the imprint of the flooding gradient on stand dynamics is relatively weak, which may result from the lower flooding height and the interaction of flooding with low nutrient supply and periodic drought.

Asynchronous recruitment history of Abies spectabilis along an altitudinal gradient in the Mt. Everest region

Aims Forest growth and recruitment and their relationships to climate are complex.The aims of our study are(i)to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt.Everest region and(ii)to identify the climatic factors that are responsible to the observed patterns in tree growth and recruitment.Methods Four plots,each 30360 m in size,were established from the lower to upper limits of the eastern Himalayan fir forest in Dingjie County of the Mt.Everest Nature Reserve,China.Dendrochronological techniques were applied to obtain information about the radial growth and age of the trees in the plots.Correlation analysis was used to identify the relationships between radial growth and recruitment of trees and climatic variables,i.e.monthly mean temperature and Palmer Drought Severity Index(PDSI).The population age structure was analyzed to investigate the recruitment history.Important Findings The timberline plot was characterized by significant tree recruitments in the recent three decades and sporadic recruitments in earlier periods.The other three plots showed recruitment pulses during 1880–1910 in Plot 3700 m,during 1870–80 and 1920–30 in Plot 3520 m and during 1900–40 in Plot 3410 m.The recruitment of fir trees in the timberline was sensitive to summer(June–September)temperatures,but it was mainly controlled by episodic disturbances in lower altitudes.Fir radial growth in the upper two plots was positively correlated with previous winter and current August temperature.Fir radial growth at the two lower plots was positively correlated with PDSI from previous September to current September.