Expanding forests and changing growth forms of Siberian larch at the Polar Urals treeline during the 20th century
Expanding forests and changing growth forms of Siberian larch at the Polar Urals treeline during the 20th century
复制标题
DOI：
10.1111/j.1365-2486.2008.01583.x
复制
发表时间：
2008-07-01
影响因子：
11.6
通讯作者：
Rigling, Andreas
中科院分区：
文献类型：
--
作者：
Devi, Nadezhda;Hagedorn, Frank;Rigling, Andreas
持续的气候变化可能会影响植物生长以及受温度限制的高海拔和高纬度生态系统的功能；然而，这些生物变化的速度和程度尚不确定。本研究的目的是在百年时间尺度上重建偏远极地乌拉尔未受干扰的森林-苔原生态交错带中西伯利亚落叶松 (Larix sibirica (Ledeb.)) 的林分结构和生长形态。将当前的生态交错带与 20 世纪 60 年代的历史照片进行比较，清楚地证明自那时起森林面积已显着扩大。同样，对从山谷森林到苔原的三个海拔梯度采样的300多棵树木进行的森林年龄结构分析表明，目前直立生长的树木70%以上的树龄<80年。由于同一地区存在数千棵树龄超过 500 年的亚化石树木，但 15-19 世纪的树木遗迹几乎完全消失，因此我们得出结论，森林在上个世纪一直向上扩展至以前没有树木的苔原，海拔高度约 20-60 m。森林的向上移动伴随着树木生长形态的显着变化：在少数树龄超过100年的树木中，36%是多茎树丛，而1950年以后出现的树木90%是单茎树。对多茎落叶松水平和垂直茎的年轮分析表明，这些树木自 15 世纪以来一直以匍匐生长的形式生长。 20世纪初，它们开始直立生长，每棵树有5-20个茎。初期的垂直生长导致径向生长突然增加三倍，从而导致生物量产量增加三倍。根据对挖出的33棵树的地上和地下生物量测量以及树高和直径的绘制，我们估计上个世纪森林扩张导致生物量增加40-75 t ha(-1)，碳积累约20-40 g C m(-2) yr(-1)。 20 世纪，森林扩张和生长形式的变化与夏季显着升温 0.9 摄氏度和冬季降水量增加一倍同时发生。总之，我们的结果表明，持续的气候变化已经对极地乌拉尔地区林线生态交错带的外观、结构和生产力留下了印记。
The ongoing climatic changes potentially affect plant growth and the functioning of temperature-limited high-altitude and high-latitude ecosystems; the rate and magnitude of these biotic changes are, however, uncertain. The aim of this study was to reconstruct stand structure and growth forms of Larix sibirica (Ledeb.) in undisturbed forest-tundra ecotones of the remote Polar Urals on a centennial time scale. Comparisons of the current ecotone with historic photographs from the 1960s clearly document that forests have significantly expanded since then. Similarly, the analysis of forest age structure based on more than 300 trees sampled along three altitudinal gradients reaching from forests in the valleys to the tundra indicate that more than 70% of the currently upright-growing trees are < 80 years old. Because thousands of more than 500-year-old subfossil trees occur in the same area but tree remnants of the 15-19th century are lacking almost entirely, we conclude that the forest has been expanding upwards into the formerly tree-free tundra during the last century by about 20-60 m in altitude. This upward shift of forests was accompanied by significant changes in tree growth forms: while 36% of the few trees that are more than 100 years old were multi-stem tree clusters, 90% of the trees emerging after 1950 were single-stemmed. Tree-ring analysis of horizontal and vertical stems of multi-stemmed larch trees showed that these trees had been growing in a creeping form since the 15th century. In the early 20th century, they started to grow upright with 5-20 stems per tree individual. The incipient vertical growth led to an abrupt tripling in radial growth and thus, in biomass production. Based on above- and belowground biomass measurements of 33 trees that were dug out and the mapping of tree height and diameter, we estimated that forest expansion led to a biomass increase by 40-75 t ha(-1) and a carbon accumulation of approximately 20-40 g C m(-2) yr(-1) during the last century. The forest expansion and change in growth forms coincided with significant summer warming by 0.9 degrees C and a doubling of winter precipitation during the 20th century. In summary, our results indicate that the ongoing climatic changes are already leaving a fingerprint on the appearance, structure, and productivity of the treeline ecotone in the Polar Urals.