The deciduous forests of northeastern United States are currently experiencing an invasion of the exotic plant species Japanese barberry (Berberis thunbergii). This recent and rapid invasion leads to rising concern about its potential threats to native species as well as natural ecosystems, demanding a better understanding of its invasion mechanisms and potential responses to climate change. Unfortunately, few studies have been conducted to understand the influence of climate on the growth of B. thunbergii, largely because of the absence of long-term growth records. In this study we demonstrate growth rings of B. thunbergii are annually resolved and crossdatable. The first ring-width chronology of B. thunbergii was therefore developed using samples collected from the Black Rock Forest (BRF), New York. Climate-growth relationship analysis indicates the growth of B. thunbergii in the BRF is positively correlated with precipitation in prior October, current February and May–August, but is negatively correlated with current March precipitation. The growth of B. thunbergii is also negatively correlated with temperatures in prior winter (November–January) and current summer (June–July), but is positively correlated with current spring temperature (March–May). These dendrochronological results on B. thunbergii, together with further physiological studies, will improve our understanding on how the growth of this invasive species is affected by local climate dynamics, as well as the long-term invasion potential that is tied to its responses to climate change.

One of the main elements of dendrochronological standardization is removing the biological trend, i.e. the progressive decline of ring width along a cross-sectional radius that is caused by the corresponding increase in stem size and tree age over time. The ‘‘conservative’’ option for removing this biological trend is to fit a modified negative exponential curve (or a straight line with slope ≤ 0) to the ring-width measurements. This method is based on the assumption that, especially for open-grown and/or shade-intolerant species, annual growth rate of mature trees fluctuates around a specific level, expressed by a constant ring width. Because this method has numerical and conceptual drawbacks, we propose an alternative approach based on the assumption that constant growth is expressed by a constant basal area increment distributed over a growing surface. From this starting point, we derive a mathematical expression for the biological trend of ring width, which can be easily calculated and used for dendrochronological standardization. The proposed C-method is compared to other standardization techniques, including Regional Curve Standardization (RCS), of tree-ring width from ponderosa pines (Pinus ponderosa Douglas ex P.Lawson & C.Lawson) located at the Gus Pearson Natural Area (GPNA) in northern Arizona, USA. Master ring-index chronologies built from ring area, RCS, and C-method reproduced stand-wide patterns of tree growth at the GPNA, whereas other standardization options, including the ‘‘conservative’’ one, failed to do so. In addition, the C-method has the advantage of calculating an expected growth curve for each tree, whereas RCS is based on applying the same growth curve to all trees. In conclusion, the C-method replaces the purely empirical ‘‘conservative’’ option with a theory based approach, which is applicable to individual ring-width measurement series, does not require fitting a growth curve using nonlinear regression, and can be rigorously tested for improving tree-ring records of environmental changes.