R. I. 2003. Spatial synchrony of the two-year cycle budworm outbreaks in central British Columbia, Canada. -Oikos 102: 146-154.Outbreaks of forest defoliating insects are usually synchronized over a large spatial scale. Observed records of past outbreaks are usually short and incomplete, therefore long proxy data are useful for better understanding of the spatial synchrony. In this study, we developed tree-ring proxy records of two-year cycle spruce budworm (Choristoneura biennis Freeman) outbreaks in central British Columbia, Canada, and examined the spatial patterns of past outbreaks. This budworm is a major defoliating insect of the interior spruce (Picea engelmannii Parry × P. glauca Moench) and subalpine fir (Abies lasiocarpa [Hook.] Nutt.) forests in the Prince George Region of British Columbia. Four outbreaks occurred in relatively close synchrony over the entire region in the period 1880-1999, however, the initiation year, the intensity and extent of outbreaks varied spatially and from one outbreak to another. In some instances, the occurrence of outbreaks was restricted to only one area. The general synchrony of outbreaks suggested that a large-scale extrinsic factor, such as weather, was at play. However, the imperfect synchrony of outbreaks suggested that local stand characteristics, such as canopy structure, composition of tree species and host plant quality, probably played a major role in preconditioning outbreaks. Dispersal might play a role in synchronizing outbreaks, but the extent to which it contributed to the synchrony was limited in this mountainous region.Q. Cold and Arid Regions En6ironmental and Engineering Research Institute, Chinese Academy of Sciences,

Forests in the Tibetan Plateau are thought to be vulnerable to climate extremes, yet they also tend to exhibit resilience contributing to the maintenance of ecosystem services in and beyond the plateau. So far the spatiotemporal pattern in tree resilience in the Tibetan Plateau remains largely unquantified and the influence of specific factors on the resilience is poorly understood. Here, we study ring‐width data from 849 trees at 28 sites in the Tibetan Plateau with the aim to quantify tree resilience and determine their diving forces. Three extreme drought events in years 1969, 1979, and 1995 are detected from metrological records. Regional tree resistance to the three extreme droughts shows a decreasing trend with the proportion of trees having high resistance ranging from 71.9%, 55.2%, to 39.7%. Regional tree recovery is increasing with the proportion of trees having high recovery ranging from 28.3%, 52.2%, to 64.2%. The area with high resistance is contracting and that of high recovery is expanding. The spatiotemporal resistance and recovery are associated with moisture availability and diurnal temperature range, respectively. In addition, they are both associated with forest internal factor represented by growth consistence among trees. We conclude that juniper trees in the Tibetan Plateau have increased resilience to extreme droughts in the study period. We highlight pervasive resilience in juniper trees. The results have implications for predicting tree resilience and identifying areas vulnerable to future climate extremes.

El Niño–Southern Oscillation (ENSO) affects various components of the Earth's climate systems but its role on the Tibetan Plateau remains poorly understood. Hydroclimatic changes in Asia's water tower can have substantial effects on the functioning and productivity of agricultural and natural ecosystems, and thus the wellbeing of many millions of people. Here, we use well‐replicated ring‐width chronologies from 10 juniper sites on the southern Tibetan Plateau to associate variations in tree growth with ENSO events between 1645 and 2001 CE. An empirical orthogonal function (EOF) was applied to emphasize regional growth coherency and climate sensitivity. May–June moisture availability was found to be most important for ring‐width formation, and most growth anomalies coincided with documentary evidence of hydroclimatic extremes. The superposed epoch analysis (SEA) and the composite analysis showed an increased ENSO sensitivity in tree growth on the southern Tibetan Plateau since the 1970s, possibly due to global warming, calls for integration of large‐scale ocean–atmosphere climate feedbacks into regional forest management strategies in future warming scenarios.