LANDIS-II PnET Impacts of Warming on Forest Net Primary Productivity in New England 2010-2100

Climate warming is expected to lengthen growing seasons of temperate forest ecosystems and increase gross primary productivity. Simultaneously, warming is expected to increase summer ecosystem respiration, which could offset gains accrued from longer growing seasons. These responses have been observed during anomalously warm years, but the role of future climate change on phenological trade‐offs and how they affect net primary productivity (NPP) at regional scales in temperate forests remain unexplored. We simulated scenarios of climate change on monthly forest NPP throughout 18 million hectares of temperate forests in New England, USA, through year 2100. Using an ecophysiological model coupled to a forest landscape model, we simulated scenarios of climate change on monthly NPP. A high emission scenario (RCP 8.5), resulted in longer growing seasons that offset midsummer ecosystem respiration costs and produced greater annual NPP throughout the study landscape compared to simulations using the current climate. In spring and autumn months, temperature was positively associated with greater NPP; in summer months, the relationship was negative. Spatially, the greatest increase in NPP occurred in the warmer southern region under a warm climate scenario with increased precipitation. Under a warm scenario with drier conditions, the greatest increase in NPP occurred in the cooler northern region. Phenological trade‐offs will affect NPP of future forests and their potential to serve as a negative feedback to climate change. Barring other limitations, longer growing seasons will offset greater respiratory demands and contribute to increases in NPP throughout the temperate forests of New England in the future.

气候变暖预计将延长温带森林生态系统的生长季，并提升总初级生产力（gross primary productivity，GPP）。与此同时，气候变暖还将加剧夏季生态系统呼吸作用，进而抵消生长季延长所带来的生产力增益。上述响应已在异常暖年中被观测到，但目前尚未明确未来气候变化对物候权衡的调控作用，以及其如何影响温带森林区域尺度的净初级生产力（net primary productivity，NPP）。本研究借助耦合了森林景观模型的生态生理模型，针对美国新英格兰地区1800万公顷温带森林，模拟了截至2100年的气候变化情景下的逐月森林净初级生产力。相较于当前气候情景的模拟结果，高排放情景（RCP 8.5）下生长季更长，抵消了仲夏生态系统呼吸的能耗，且研究区域整体的年净初级生产力显著提升。在春、秋两季，气温与净初级生产力呈显著正相关；而在夏季，二者关系则呈显著负相关。从空间分布来看，在降水增加的暖化气候情景下，净初级生产力增幅最大的区域为气候更温暖的南部地区；而在暖化且降水减少的情景下，净初级生产力增幅最大的区域则为气候较凉爽的北部地区。物候权衡将影响未来森林的净初级生产力，以及其作为气候变化负反馈的潜力。若无其他限制因素，未来新英格兰地区温带森林的生长季延长将抵消更高的呼吸消耗，并推动区域净初级生产力整体提升。