de Meira Junior Milton Serpa, Pinto José Roberto Rodrigues, Ramos Natália Oliveira, Miguel Eder Pereira, Gaspar Ricardo de Oliveira, Phillips Oliver L
Department of Forest Engineering, University of Brasília, Brasília, Brazil.
Carbon Balance Manag. 2020 May 30;15(1):12. doi: 10.1186/s13021-020-00147-2.
Long-term studies of community and population dynamics indicate that abrupt disturbances often catalyse changes in vegetation and carbon stocks. These disturbances include the opening of clearings, rainfall seasonality, and drought, as well as fire and direct human disturbance. Such events may be super-imposed on longer-term trends in disturbance, such as those associated with climate change (heating, drying), as well as resources. Intact neotropical forests have recently experienced increased drought frequency and fire occurrence, on top of pervasive increases in atmospheric CO concentrations, but we lack long-term records of responses to such changes especially in the critical transitional areas at the interface of forest and savanna biomes. Here, we present results from 20 years monitoring a valley forest (moist tropical forest outlier) in central Brazil. The forest has experienced multiple drought events and includes plots which have and which have not experienced fire. We focus on how forest structure (stem density and aboveground biomass carbon) and dynamics (stem and biomass mortality and recruitment) have responded to these disturbance regimes.
Overall, the biomass carbon stock increased due to the growth of the trees already present in the forest, without any increase in the overall number of tree stems. Over time, both recruitment and especially mortality of trees tended to increase, and periods of prolonged drought in particular resulted in increased mortality rates of larger trees. This increased mortality was in turn responsible for a decline in aboveground carbon toward the end of the monitoring period.
Prolonged droughts influence the mortality of large trees, leading to a decline in aboveground carbon stocks. Here, and in other neotropical forests, recent droughts are capable of shutting down and reversing biomass carbon sinks. These new results add to evidence that anthropogenic climate changes are already adversely impacting tropical forests.
对群落和种群动态的长期研究表明，突然的干扰常常会引发植被和碳储量的变化。这些干扰包括林中空地的形成、降雨季节性变化、干旱，以及火灾和直接的人类干扰。此类事件可能叠加在干扰的长期趋势之上，比如与气候变化（变暖和干燥）以及资源相关的趋势。完整的新热带森林最近除了大气二氧化碳浓度普遍增加之外，还经历了干旱频率增加和火灾发生次数增多的情况，但我们缺乏对这类变化响应的长期记录，尤其是在森林和稀树草原生物群落交界处的关键过渡区域。在此，我们展示了对巴西中部一个山谷森林（潮湿热带森林飞地）进行20年监测的结果。这片森林经历了多次干旱事件，其中包括有火灾发生的样地和没有火灾发生的样地。我们关注森林结构（树干密度和地上生物量碳）以及动态变化（树干和生物量的死亡与补充）是如何对这些干扰状况做出响应的。
总体而言，由于森林中现有树木的生长，生物量碳储量增加，而树木的总数并未增加。随着时间推移，树木的补充尤其是死亡率都趋于上升，特别是长期干旱时期导致大树死亡率增加。这种死亡率的增加反过来导致在监测期结束时地上碳含量下降。
长期干旱影响大树的死亡率，导致地上碳储量下降。在此处以及其他新热带森林中，近期的干旱能够使生物量碳汇停止并逆转。这些新结果进一步证明了人为气候变化已经对热带森林产生了不利影响。
