Contrasting resistance and recovery of co‐occurring conifers to larch caterpillar defoliation in a Northeast China temperate forest

Climate change has been linked to the intensification of forest pest outbreaks, posing a serious threat to non‐coevolved tree species because of their potentially weak defensive capabilities. However, unlike broad‐scale climatic disturbances such as drought and heatwaves, insect outbreaks are highly heterogeneous in space and among host species, and the response of occurring conifers to such outbreaks remains poorly understood. The core area of the Changbai Mountain Nature Reserve in northeastern China was severely defoliated in 2019 by larch caterpillars ( Dendrolimus superans Butler)—a conifer‐feeding defoliator that prefers larch but also attacks other conifers. In this region, a vegetation transition zone between the broadleaf‐Korean pine and spruce–fir forests hosts multiple conifer species co‐existing within short distances under similar defoliation intensities. We monitored 1,837 trees in 2019 (pre‐disturbance), 2021 and 2024, and sampled needles of healthy individuals of each species in 2024 to obtain species‐level proxies of intrinsic foliar traits. Results revealed that: (i) mortality of attacked Korean pine peaked within 2 years, with little subsequent increase, resulting in a cumulative mortality rate of 31.3%; in contrast, mortality of spruce and fir continued to increase until the fifth year, reaching a combined cumulative rate of 78.6%, while larch exhibited nearly 100% survival. (ii) a deciduous habit, low needle biomass allocation and low carbohydrate concentrations enhanced survival by reducing canopy regeneration costs. (iii) regarding radial growth responses, spruce showed stronger compensatory growth but weaker recovery ability than fir and Korean pine, likely due to its limited carbon and nutrient reserves. Considering these findings, prioritizing the protection of non‐coevolved conifers is recommended to minimize biomass loss during pest outbreaks. This study also provides important insights for temperate and boreal conifer forest conservation, highlighting the high vulnerability of spruce–fir forests to larch caterpillar outbreaks.