Impact of Site Conditions Changes on the Tree Ring Records Suitability as Climate Proxies in the Brazilian Amazon

ABSTRACT The increment zones width in the xylem of Swietenia macrophylla King was investigated by dendrochronological methods in an undisturbed and a strongly disturbed tropical site near Aripuanã, Mato Grosso, Brazil (10°09’ S, 59°26’W). The study aimed to assess the impact of forest disturbance on the relationship between precipitation and the cambial growth of this species. Tree-ring width chronologies were developed for both sites from cross-dated increment curves. Simple correlations were computed between monthly precipitation records and the annual increment of Swietenia for the period between 1870 and 2000. Logging activities and altered land use caused a significant decrease of the water supply of the Swietenia trees grown in the disturbed area compared to trees grown in the undisturbed area. Consequently, the precipitation of almost the total growing season had a significant influence on the tree ring width of Swietenia grown in the disturbed area, while in the undisturbed forest area the significant correlation between monthly precipitation and the tree ring width of Swietenia was restricted to the beginning of the growing season (November to January). However, the reconstruction of monthly precipitation data from the tree ring width records was more precise using the chronology developed from tree ring width records of undisturbed trees compared to the chronology developed from tree ring widths from the disturbed area. It was concluded that the use of the tree ring widths of Swietenia as climate proxies is restricted to certain months of the year and requires tree ring width chronologies developed from trees grown in undisturbed or only slightly disturbed forest areas without severe anthropogenic changes in microclimate.摘要 本研究采用树木年代学方法，对巴西马托格罗索州阿里普阿南附近一处未受干扰与一处受严重干扰的热带样地（南纬10°09′，西经59°26′）内的大果桃花心木（Swietenia macrophylla King）木质部生长带宽度展开了调查。本研究旨在评估森林干扰对降水与该树种形成层生长之间关系的影响。研究基于交叉定年的生长曲线，为两处样地分别建立了树轮宽度年表。针对1870年至2000年期间的月度降水记录与大果桃花心木的年生长量，计算了简单相关系数。伐木活动与土地利用方式改变导致干扰样地内的大果桃花心木水分供给较未受干扰样地的树木出现显著下降。因此，几乎整个生长季的降水均对干扰样地内大果桃花心木的树轮宽度产生了显著影响；而在未受干扰的林区，月度降水与树轮宽度的显著相关仅局限于生长季初期（11月至次年1月）。不过，相较于基于干扰样地树轮宽度建立的年表，利用未受干扰样地树轮宽度建立的年表对月度降水数据的重建精度更高。研究结论表明，将大果桃花心木的树轮宽度作为气候代用指标的应用范围仅限于一年中的特定月份，且需要基于未受干扰或仅受轻微干扰、微气候未发生显著人为改变的林区内树木所建立的树轮宽度年表。