Tree lifespans in a warming world: unravelling the universal trade-off between growth and lifespan in temperate forests

Tree growth and lifespan are key determinants of forest dynamics, and ultimately control carbon stocks. Warming and increasing CO2 have been observed to increase growth but such increases may not result in large net biomass gains due to trade-offs between growth and lifespan. A deeper understanding of the nature of the trade-off and its potential spatial variation is crucial to improve predictions of the future carbon sink. This study aims to identify key drivers of growth and lifespan, assess the universality of tree growth-lifespan trade-offs, explore the possible latitudinal patterns of trade-off strengths and their determinants, and project growth and lifespan under future climate scenarios. We analyzed 21,193 trees of 69 species (48 included in further analysis) at 445 sites (417 included in further analysis) in temperate forests in northeastern China to estimate early growth rate and tree lifespan. We find that temperature and human pressure enhance tree growth and reduce lifespan, while altitude increases lifespan. We further find evidence for growth-lifespan trade-offs at all studied levels, i.e. among trees, among species and communities, and within species and communities. Trade-offs are stronger at colder, higher latitudes compared to warmer sites, because of larger variation in tree growth and climate, larger range sizes for individual species and lower species’ diversity for communities at high latitudes. We predict future increases in growth and reductions in tree lifespan in response to climate change for the 2050s. Taking growth lifespan trade-offs into account resulted in even larger predictions of decreases in tree lifespan of up to 8%. In conclusion, growth-lifespan trade-offs are universal, but the strengths may vary by environment and between different forests. Its effects are important to include in predictions of forest responses to global change and need to be considered more widely.树木生长与寿命是森林动态的核心决定因子，并最终调控碳储量。已有研究表明，气候变暖与二氧化碳浓度升高可促进树木生长，但由于生长与寿命间存在权衡关系，此类生长提升未必能带来显著的净生物量增量。深入理解该权衡关系的本质及其潜在空间变异规律，对提升未来碳汇的预测精度至关重要。本研究旨在明确树木生长与寿命的关键驱动因子，评估树木生长-寿命权衡关系的普适性，探究权衡强度的潜在纬度格局及其驱动机制，并预估未来气候情景下的树木生长与寿命变化。为估算树木早期生长速率与寿命，我们针对中国东北温带森林的445个样地（其中417个样地纳入后续分析）内69个树种的21193株个体（其中48个树种纳入后续分析）开展了分析。研究结果显示，气温与人类活动压力可促进树木生长并缩短其寿命，而海拔升高则会延长树木寿命。进一步分析证实，在所有研究尺度下均存在生长-寿命权衡关系，具体涵盖个体间、物种间与群落间，以及物种内和群落内的权衡。相较于温暖区域，寒冷高纬度地区的权衡强度更强，这是由于高纬度地区的树木生长与气候变异程度更大、单物种种群分布范围更广，且群落物种多样性更低。我们预估，到21世纪50年代，气候变化将推动树木生长量提升，但会缩短其寿命；若纳入生长-寿命权衡关系，对树木寿命降幅的预估可达8%，降幅更为显著。综上，树木生长-寿命权衡关系具有普适性，但其强度会因环境条件与森林类型的差异而有所不同。在预测森林对全球变化的响应时，必须纳入该权衡关系的影响，且需进一步推广其应用场景。