Under conditions of a warmer climate,the advance of the alpine treeline into alpine tundra has implications for carbon dynamics in mountain ecosystems.However,the above- and below-ground live biomass allocations among...Under conditions of a warmer climate,the advance of the alpine treeline into alpine tundra has implications for carbon dynamics in mountain ecosystems.However,the above- and below-ground live biomass allocations among different vegetation types within the treeline ecotones are not well investigated.To determine the altitudinal patterns of above-/below-ground carbon allocation,we measured the root biomass and estimated the above-ground biomass(AGB) in a subalpine forest,treeline forest,alpine shrub,and alpine grassland along two elevational transects towards the alpine tundra in southeast Tibet.The AGB strongly declined with increasing elevation,which was associated with a decrease in the leaf area index and a consequent reduction in carbon gain.The fine root biomass(FRB) increased significantly more in the alpine shrub and grassland than in the treeline forest,whereas the coarse root biomass changed little with increasing altitudes,which led to a stable below-ground biomass(BGB) value across altitudes.Warm and infertile soil conditions might explain the large amount of FRB in alpine shrub and grassland.Consequently,the root toshoot biomass ratio increased sharply with altitude,which suggested a remarkable shift of biomass allocation to root systems near the alpine tundra.Our findings demonstrate contrasting changes in AGB and BGB allocations across treeline ecotones,which should be considered when estimating carbon dynamics with shifting treelines.展开更多
The southeastern Tibetan Plateau has the highest timberlines in the world and climate change affects this area to a considerable extent. Quantification of vegetation biomass in the forests at the timberline is essenti...The southeastern Tibetan Plateau has the highest timberlines in the world and climate change affects this area to a considerable extent. Quantification of vegetation biomass in the forests at the timberline is essential for understanding carbon balance, forest structure and functional changes in the forests at timberlines. We describe biomass and its constituent components of a smith fir tim- berline forest occurring at an elevation of 4320 m on the Sergyemla Mountain in the southeastern Tibetan Plateau. The results show that, in the tree layer, the average diameter at breast height （DBH） was 35.6 cm, the density 251 trees per hectare with a total biomass of 309.9 t.ha 1. Of the total biomass, the tnmks accounted for 70.49%, branches for 9.09%, leaves for 5.57% and roots for 14.85%. The total biomass in the shrub layer was 77.9 t＇ha-~ of which the biomass of trunks, branches, leaves and roots accounted for 42.8, 14.9, 4.6 and 15.6 t.ha-1, respectively. The total biomass in the herb layer was 3.0 t.ha-1. The total vegetation biomass in the smith fir timberline forest was 390.9 t-ha-l, to which the tree layer contributed the most （79.3%）, followed by shrubs （19.9%） and herbs （0.8%）. We estimate that the smith fir forest stand at the timberline had a higher total biomass than other fir or spruce forest stands in the surrounding area.展开更多
基金supported by the National Natural Science Foundation of China (41561011)the Natural Science Foundation of Jiangxi Province, China (20151BAB213029)
文摘Under conditions of a warmer climate,the advance of the alpine treeline into alpine tundra has implications for carbon dynamics in mountain ecosystems.However,the above- and below-ground live biomass allocations among different vegetation types within the treeline ecotones are not well investigated.To determine the altitudinal patterns of above-/below-ground carbon allocation,we measured the root biomass and estimated the above-ground biomass(AGB) in a subalpine forest,treeline forest,alpine shrub,and alpine grassland along two elevational transects towards the alpine tundra in southeast Tibet.The AGB strongly declined with increasing elevation,which was associated with a decrease in the leaf area index and a consequent reduction in carbon gain.The fine root biomass(FRB) increased significantly more in the alpine shrub and grassland than in the treeline forest,whereas the coarse root biomass changed little with increasing altitudes,which led to a stable below-ground biomass(BGB) value across altitudes.Warm and infertile soil conditions might explain the large amount of FRB in alpine shrub and grassland.Consequently,the root toshoot biomass ratio increased sharply with altitude,which suggested a remarkable shift of biomass allocation to root systems near the alpine tundra.Our findings demonstrate contrasting changes in AGB and BGB allocations across treeline ecotones,which should be considered when estimating carbon dynamics with shifting treelines.
基金supported by an IFS research grant (No. D/4048-1)the National Natural Science Foundation of China (Grant No. 40701008)
文摘The southeastern Tibetan Plateau has the highest timberlines in the world and climate change affects this area to a considerable extent. Quantification of vegetation biomass in the forests at the timberline is essential for understanding carbon balance, forest structure and functional changes in the forests at timberlines. We describe biomass and its constituent components of a smith fir tim- berline forest occurring at an elevation of 4320 m on the Sergyemla Mountain in the southeastern Tibetan Plateau. The results show that, in the tree layer, the average diameter at breast height （DBH） was 35.6 cm, the density 251 trees per hectare with a total biomass of 309.9 t.ha 1. Of the total biomass, the tnmks accounted for 70.49%, branches for 9.09%, leaves for 5.57% and roots for 14.85%. The total biomass in the shrub layer was 77.9 t＇ha-~ of which the biomass of trunks, branches, leaves and roots accounted for 42.8, 14.9, 4.6 and 15.6 t.ha-1, respectively. The total biomass in the herb layer was 3.0 t.ha-1. The total vegetation biomass in the smith fir timberline forest was 390.9 t-ha-l, to which the tree layer contributed the most （79.3%）, followed by shrubs （19.9%） and herbs （0.8%）. We estimate that the smith fir forest stand at the timberline had a higher total biomass than other fir or spruce forest stands in the surrounding area.
