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The tree-ring fire scar stands as a pivotal proxy for reconstructing historical wildfire occurrences, providing invaluable context for comprehending contemporary wildfire activities during the Anthropocene era. Precise identification of fire scars often necessitates sampling complete tree disks. Yet, stringent forest resource protection policies limit such collection in certain regions, thus curtailing the application of tree-ring-based fire reconstruction. While current methods based on tree-ring cores can ascertain the age range of fire events, pinpointing the exact year remains challenging. In this study, we propose a novel approach for detecting fire occurrence years by recognizing abrupt shifts in the tree-ring geometric center (TRGC). This method entails extracting a minimum of three tree-ring cores from the uninjured side of the tree and in proximity to the fire scar. We validated this method's efficacy using samples from Transbaikal of Russia, in northeastern Asia, where fire years have already been documented. Our results show that this method accurately identified the fire year in nine fire scars with a 67 percent probability of exact agreement with the actual fire year. It is noteworthy that this method particularly excels in cases of trees with a single fire scar. We recommend employing the traditional method of collecting tree-ring cores near the fire scar to establish the age range of the fire scar. Subsequently, within this determined range, we suggest detecting the shifts in the TRGC to accurately pinpoint the exact year of the fire scar. [ABSTRACT FROM AUTHOR]

Hydroclimatic change across China has received considerable attention due to its vital significance for regional ecosystem stability and economic development, yet the spatiotemporal dynamics of its nonlinear trends and complexity have not been fully understood. Herein, the spatiotemporal evolution of Dai's self-calibrating Palmer drought severity index (scPDSI) trends in China during the period from 1951 to 2014 is diagnosed using the ensemble empirical mode decomposition (EEMD) method. A persistent and noticeable drying has been identified in North and Northeastern China (NNEC) since the 1950s. Significant wetting in the north of the Tibetan Plateau (TP) and the south of the western parts of Northwestern China (WNWC) started sporadically at first and accelerated until around 1980. A slight wetting trend was found in Southwest China (SC) before 1990, followed by the occurrence of a dramatic drying trend over the following decades. In addition, we have found that the scPDSI variations in WNWC and the TP are more complex than those in NNEC and SC based on our application of Higuchi's fractal dimension (HFD) analysis, which may be related to complex circulation patterns and diverse geomorphic features. [ABSTRACT FROM AUTHOR]

Humid subtropical China is an "oasis" relative to other dry subtropics of the world due to the prevailing of the East Asian summer monsoon (EASM). Although many long climate sensitive tree-rings have been published to understand the historical climate change over various regions in China, long tree-ring chronologies in humid subtropical China are rare due to the difficulty to find old growth trees. This study established a tree-ring chronology spanning from 1776 to 2016 from Cryptomeria fortunei Hooibrenk ex Otto et Dietr in Liancheng area of humid subtropical China, which is also currently the longest chronology in Fujian province. Similar to the climate-growth relationships in neighboring regions, our tree-ring chronology is limited by cold temperature in winter and spring and drought in summer. In addition, a drought stress before the growing season also played a role in limiting the growth of our tree rings. Our climate sensitive tree rings showed different correlations with the Pacific Decadal Oscillation (PDO) in different periods, possibly via modulation of the EASM. [ABSTRACT FROM AUTHOR]