川西亚高山不同年龄紫果云杉径向生长对气候因子的响应

运用树木年轮气候学的基本方法,建立王朗自然保护区紫果云杉在集中分布上限区域的年轮宽度年表,选取差值年表分析不同年龄云杉的径向生长同逐月气候因子的相关及响应关系,结果显示:幼龄组云杉年表的敏感度高于中龄组和老龄组云杉,幼龄组云杉对生长季前及生长季的气温状况显著正相关;中龄组云杉年表仅与当年4月份和7月份的月平均最低气温显著正相关;老龄组云杉的年轮宽度指数同上年生长季(上年8月份)的月平均气温和月平均最低温显著负相关,上年生长季高温的"滞后效应"在老龄组云杉体现的更为突出;幼龄组与中龄组云杉对当年6月份降水持续增加显示出明显的负相关关系,上年12月份的降水会对幼龄组和老龄组云杉径向生长不利。研究表明幼龄组云杉包含的气候信息要优于中龄组和老龄组云杉,在该区域进行相关研究时应根据研究需要选取不同年龄跨度的云杉年表。

Age-dependent radial growth responses of Picea purpurea to climatic factors in the subalpine region of Western Sichuan Province, China

Although tree growth is mainly dependent on natural climate conditions, factors such as microclimate, growth of the previous year, tree age, and others may also affect tree growth. In dendroclimatological studies, it is generally assumed that the relationships between tree growth and climate factors are age-independent after removing the biological growth trends related to tree age. However, in some multi-aged forest stands, climate-growth relationships may be biased, because the trees'' chronologies respond differently to climate factors depending on their age or size. To assess this age-dependent effect, in this study, we tested the consistency of climate-growth responses in tree-ring series from Picea purpurea trees of different age classes in the Wanglang Nature Reserve, Sichuan province. In the concentrated distribution area of the upper limit, spruces were grouped into three age classes: trees younger than 100 years (young age class, YAC), trees 100-200 years of age (middle age class, MAC), and trees older than 200 years (old age class, OAC). Residual chronologies of the three age classes were built to analyze the climate-growth relationships using correlation and response functions. Correlation analysis indicated that the radial growth of the YAC was significantly and positively correlated with mean monthly temperature of the previous November and current February, June, and September; mean monthly maximum temperature of the previous November and current February and September; and mean monthly minimum temperature of the current February, March, April, June, July, August, and September, and it was significantly and negatively affected by monthly precipitation of the previous December and current June. The ring width of the MAC was positively correlated with mean monthly minimum temperature of the current April and July, and was negatively correlated with monthly precipitation of the current June. The residual chronology of the OAC was significantly and negatively affected by mean monthly temperature of the previous August, mean monthly minimum temperature of the previous August and current September, and monthly precipitation of the previous December. Response analysis showed that radial growth of the YAC was significantly and positively correlated with mean monthly maximum temperature of the current February, and mean monthly minimum temperature of the current February and April. There was no significant correlation between radial growth of the MAC and climate factors. The ring width of the OAC was significantly and negatively affected by monthly precipitation of the previous December.Overall, our results revealed that with an increase in tree age, the sensitivity of spruce to climate factors was reduced. The responses of young spruce were significantly correlated with temperature before the growing season and in the growing season. The chronology of the middle-aged spruce showed a significant and positive correlation with monthly mean minimum temperatures in the current April and July. The ring-width index of old spruce was significantly negatively correlated with monthly mean temperature and monthly mean minimum temperature of the previous August. The "lag effect" of high temperatures in the previous growing season was prominent in the old spruce. Spruce within the young and middle-aged groups showed a significant negative correlation with current June precipitation. Adequate precipitation in December was not beneficial for the radial growth of young and old spruce. Our study may demonstrate that future studies should consider the adaptive chronology of age span for spruce in this area to avoid losing or magnifying the climate signals.