A significant carbon sink in temperate forests in Beijing: based on 20-year field measurements in three stands

Impacts of Cross-Sectoral Climate Policy on Forest Carbon Sinks and Their Spatial Spillover: Evidence from Chinese Provincial Panel Data

This paper examines the impact of cross-sectoral climate policy on forest carbon sinks. Due to the complexity of the climate change issue and the professional division of labor among government departments, cross-sectoral cooperation in formulating climate policy is a desirable strategy. Forest carbon sinks play an important role in addressing climate change, but there are few studies focusing on forest carbon sinks and cross-sectoral climate policies. Thus, based on the panel data of 30 provinces and cities in China from 2007 to 2020, this paper establishes a benchmark regression model and a spatial panel model to analyze the impact of cross-sectoral climate policies on forest carbon sinks. We find that cross-sectoral climate policies positively impact forest carbon sinks. Under the influence of the "demonstration effect", we find that cross-sectoral climate policies have a positive impact not only on the forest carbon sinks in the region but also on those in the neighboring region. Further analysis shows that for provinces with less developed forestry industry and small forest areas, the positive effect of cross-sectoral climate policies on forest carbon sinks is more obvious. Overall, this paper can serve as an important reference for local governments to formulate climate policies and increase the capacity of forest carbon sinks.

N-P utilization of Acer mono leaves at different life history stages across altitudinal gradients

The relationship between plants and the environment is a core area of research in ecology. Owing to differences in plant sensitivity to the environment at different life history stages, the adaptive strategies of plants are a cumulative result of both their life history and environment. Previous research on plant adaptation strategies has focused on adult plants, neglecting saplings or seedlings, which are more sensitive to the environment and largely affect the growth strategy of subsequent life stages. We compared leaf N and P stoichiometric traits of the seedlings, saplings, and adult trees of Acer mono Maxim and different altitudes and found significant linear trends for both life history stages and altitude. Leaf N and P content by unit mass were greatly affected by environmental change, and the leaf N and P content by unit area varied greatly by life history stage. Acer mono leaf N-P utilization showed a significant allometric growth trend in all life history stages and at low altitudes. The adult stage had higher N-use efficiency than the seedling stage and exhibited an isometric growth trend at high altitudes. The N-P utilization strategies of A. mono leaves are affected by changing environmental conditions, but their response is further dependent upon the life history stage of the plant. Thus, this study provides novel insights into the nutrient use strategies of A. mono and how they respond to the environmental temperature, soil moisture content along altitude and how these changes differ among different life history stages, which further provide the scientific basis for the study of plant nutrient utilization strategy on regional scale.

The response of tree growth to nitrogen and phosphorus additions in a tropical montane rainforest

Rapid increase of global nitrogen (N) deposition has greatly altered carbon cycles and functioning of forest ecosystems. Previous studies have focused on changes in carbon dynamics of temperate and subtropical forests through N enrichment experiments; however, the effects of N deposition on tree growth remain inconsistent, especially in tropical forests. Here, we conducted a five-year N addition experiment (0 and 50kgNha^-1yr^-1) in a tropical montane rain forest in Hainan Island, China, to explore the effects of enhanced N deposition on growth of trees. We also set phosphorus (P) treatment (50kgPha^-1yr^-1) and N+P treatment (50kgNha^-1yr^-1+50kgPha^-1yr^-1) to examine potential P limitation driven by N deposition. Our results showed that N addition has not significantly influenced tree growth, while P addition significantly increased the relative growth rate of small (diameter at breast height, DBH≤10cm) and medium (10<DBH≤20cm) trees. The combined N and P addition accelerated the growth of small trees, but did not affect the growth of medium and large (20cm<DBH) trees. These contrasting effects of N and P addition on tree growth indicate that the tropical montane forest is mainly limited by P, which suggests the importance of P in regulating growth of trees in tropical forests.

Carbon stocks and changes of dead organic matter in China's forests

Forests play an important role in global carbon cycles. However, the lack of available information on carbon stocks in dead organic matter, including woody debris and litter, reduces the reliability of assessing the carbon cycles in entire forest ecosystems. Here we estimate that the national DOM carbon stock in the period of 2004-2008 is 925 ± 54 Tg, with an average density of 5.95 ± 0.35 Mg C ha^-1. Over the past two decades from periods of 1984-1988 to 2004-2008, the national dead organic matter carbon stock has increased by 6.7 ± 2.2 Tg carbon per year, primarily due to increasing forest area. Temperature and precipitation increase the carbon density of woody debris, but decrease that of litter. Additionally, the woody debris increases significantly with above ground biomass and forest age. Our results can improve estimates of the carbon budget in China's forests and for better understanding of effects of climate and stand characteristics on dead organic matter distribution.Reliable estimates of the total forest carbon (C) pool are lacking due to insufficient information on dead organic matter (DOM). Here, the authors estimate that the current DOM C stock in China is 925 ± 54 Tg and that it grew by 6.7 ± 2.2 Tg C/yr over the past two decades primarily due to increasing forest area.