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Canopy disturbance events in forests often increase light availability and growth rates for surviving trees. Using ring widths, release-detection methods identify the initiation of rapid growth associated with these events enabling reconstructions of forest disturbance history. Conversely, dendroclimate reconstructions minimize these rapid growth responses by detrending entire ring-width time series to resolve underlying climate signals. Incorporating advantages from both of these approaches, we present a canopy disturbance detrending method that quantifies the subsequent, additional growth from release events as a discrete time series. Our method uses radial-growth averaging to detect release events and then power transformation and age-dependent smoothing splines to detrend individual release events, separating canopy disturbance responses from climatic effects. We test our canopy disturbance detrending method on both a coniferous and a broadleaf ring-width chronology from two contrasting temperate forests in eastern North America with known disturbance histories. The resulting disturbance growth time series agrees with the documented forest histories for each forest. Removing the effects of canopy disturbance from the ring-width series in each chronology improves climate correlations with monthly values of temperature and precipitation and may recover more low-frequency variation with past climate compared to other common detrending methods. Our method provides an alternative approach for detrending disturbance events in closed-canopy forests that should be accessible and useful for both ecological and climatological reconstructions.

Most information on the ecology of oak-dominated forests in Europe comes from forests altered for centuries because remnants of old-growth forests are rare. Disturbance and recruitment regimes in old-growth forests provide information on forest dynamics and their effects on long-term carbon storage. In an old-growth Quercus petraea forest in northwestern Spain, we inventoried three plots and extracted cores from 166 live and dead trees across canopy classes (DBH ≥ 5 cm). We reconstructed disturbance dynamics for the last 500 years from tree-ring widths. We also reconstructed past dynamics of above ground biomass (AGB) and recent AGB accumulation rates at stand level using allometric equations. From these data, we present a new tree-ring-based approach to estimate the age of carbon stored in AGB. The oldest tree was at least 568 years, making it the oldest known precisely-dated oak to date and one of the oldest broadleaved trees in the Northern Hemisphere. All plots contained trees over 400 years old. The disturbance regime was dominated by small, frequent releases with just a few more intense disturbances that affected ≤20% of trees. Oak recruitment was variable but rather continuous for 500 years. Carbon turnover times ranged between 153 and 229 years and mean carbon ages between 108 and 167 years. Over 50% of AGB (150 Mg·ha-1) persisted ≥100 years and up to 21% of AGB (77 Mg·ha-1) ≥300 years. Low disturbance rates and low productivity maintained current canopy oak dominance. Absence of management or stand-replacing disturbances over the last 500 years resulted in high forest stability, long carbon turnover times and long mean carbon ages. Observed dynamics and the absence of shade-tolerant species suggest that oak dominance could continue in the future. Our estimations of long-term carbon storage at centennial scales in unmanaged old-growth forests highlights the importance of management and natural disturbances for the global carbon cycle.

The Colchic rainforest of the Western Caucasus is one of the few temperate rainforests dominated by broadleaf deciduous trees. Understanding natural dynamics of broadleaf-dominated temperate rainforests is essential for their conservation and management. Here, we investigate for the first time the structure, natural disturbance, and recruitment dynamics of a mixed Colchic old-growth rainforest, dominated by Fagus orientalis and Picea orientalis. We used forest inventories and dendrochronological analysis of tree growth in five 30-m-radius plots to quantify forest structure, growth, and disturbances. For the last 400 years, the forest experienced a mixed disturbance regime dominated by frequent small gaps superimposed onto medium disturbances with about a 25-year recurrence period, with no evidences of stand-replacing disturbances. This disturbance regime favored the dominance of shade-tolerant, late successional species with slow tree canopy access through multiple growth releases. These dynamics impose low growth rates and continuous recruitment of spruce and beech, and contributed to a high heterogeneity of tree ages and sizes that result in stable forest structure, as suggested by the low stand slenderness. Spruces were the oldest (up to 427 years) and fastest growing trees in the forest, suggesting that their low presence in the forest is due to low disturbance rates that limit their recruitment. Spring climate conditions that promoted beech growth were detrimental for spruce growth, suggesting that interspecies interactions may condition the effect of climate on forest growth and development. The dynamic equilibrium state we reconstructed in this old-growth forest could likely be disrupted by anthropogenic disturbances or management.

The impact of ecological and climatological factors on individual organisms over time and space is inherently complex and creates substantial uncertainty about how climate change will influence the global biosphere. To understand some of this complexity, we investigated the factors influencing individual growth of Chamaecyparis thyoides over 61 years within 18 populations across the ca 1500 km and 11 degrees of latitude. We then applied a vulnerability framework to understand how the variability of tree growth response to climate varies between populations and regions across our network. Surprisingly, we found the growth of trees in the central portion of our network responded more synchronously to warming and drought than trees in the southern end of our network, suggesting greater vulnerability in the central populations with continued warming. Our analyses and framework approach revealed substantial complexity in growth responses to climate within and between populations. We found potential resiliency within all populations, but higher inter-population than intra-population variability in response to climate. We found that latitude was an important proxy for the growth response to temperatures during the non-growing season and spring, but that ecosystem structure can modify the growth response and vulnerability to drought during the summer. The range of growth responses to warming is greater in the southern populations than in more northernly populations. This asymmetrical distribution of growth response across our study network provides evidence for a kind of ecological hysteresis, more southerly populations could be more resilient with warming. Despite the fact that this species primarily lives in wetlands, we found drought stress to be an important constraint on growth. Our study and analyses help to explain the disparities between forecasts of how climatic change might impact tree species and ecosystems over space.

The retrospective study of abrupt and sustained increases in the radial growth of trees (hereinafter 'releases') by tree-ring analysis is an approach widely used for reconstructing past forest disturbances. Despite the range of dendrochronological methods used for release-detection, a lack of in-depth comparison between them can lead researchers to question which method to use and, potentially, increases the uncertainties of disturbance histories derived with different methods. Here, we investigate the efficacy and sensitivity of four widely used release detection methods using tree-ring width series and complete long-term inventories of forest stands with known disturbances. We used support vector machine (SVM) analysis trained on long-term forest census data to estimate the likelihood that Acer rubrum trees experiencing reductions in competition show releases in their tree-ring widths. We compare methods performance at the tree and stand level, followed by evaluation of method sensitivity to changes in their parameters and settings. Disturbance detection methods agreed with 60-76% of the SVM-identified growth releases under high canopy disturbance and 80-94% in a forest with canopy disturbance of low severity and frequency. The median competition index change (CIC) of trees identified as being released differed more than twofold between methods, from −0.33 (radial-growth averaging) to −0.68 (time-series). False positives (type I error) were more common in forests with low severity disturbance, whereas false negatives (type II error) occurred more often in forests with high severity disturbance. Sensitivity analysis indicated that reductions of the detection threshold and the length of the time window significantly increased detected stand-level disturbance severity across all methods. Radial-growth averaging and absolute-increase methods had lower levels of type I and II error in detecting disturbance events with our datasets. Parameter settings play a key role in

[Aim], The Caucasus is a global biodiversity hotspot that includes a wide diversity of temperate forests, from xeric to mesic and rain forest. Little is known about their vulnerability to climate change. We aimed to identify the major climate constraints on tree growth. Location: Western Caucasus of Georgia, Russia and Turkey (40–43° N, 41–43° E). Time period: Twentieth century. Major taxa studied: Trees, angiosperms and gymnosperms. [Methods], We used a new network of 35 tree‐ring width chronologies from four angiosperm and four gymnosperm species across an elevational gradient of > 2,000 m. We used correlations to identify the major climate factors (temperature, precipitation and drought) at monthly and seasonal scales affecting tree growth and to assess whether their effects change over time. To explore common response patterns among species, we used self‐organizing maps, a type of artificial neural network. [Results], Spring or summer drought reduced radial growth of most tree species, despite large differences in elevation. As expected, drought was particularly detrimental at warm, low‐elevation sites. Besides drought, growth of conifers at high elevations was also limited by cold winters and summers. Important species‐specific climate– growth responses were also evident. In general, climate–growth relationships were stable over time, except at some cold‐limited sites, where positive responses to summer and winter temperatures have diminished over the last few decades. [Main conclusión], Growth responses to precipitation and drought among species were more similar than they were to temperature, even at humid sites, providing further evidence of drought vulnerability in mesic forests. The productivity of highelevation conifer forests, limited by summer drought and low temperatures, will depend on the balance between temperature and precipitation. Given that climate change is expected to induce larger climatic gradients in the region, the potential reduction of f