Transplanted Ginkgo growth rates indicate common Chinese nursery techniques may severely limit urban ecosystem services

China has experienced history's largest rural-to-urban migration. The social, economic, and environmental challenges brought about by urbanization are diverse and complex. Given China's national goal to achieve carbon neutrality by 2060 and commitment to urban sustainability, large cities have focused on urban greening initiatives. Yet, studies seeking to quantify ecosystem services and disservices only assess healthy, mature trees, rather than those with severe damage, declining health, or lack of vitality due to poor management. In this short communication, we conducted a case-study in one of China's major nursery stock-producing cities, Chengdu, on a common street tree, Ginkgo biloba, to assess the long-term impact of one of the most common yet extreme nursery transplant practices on tree growth (traumatic root-cutting of 'super-large' nursery stock). We used tree-ring data collected in a typical urban greenspace from 23 Ginkgo trees, including 18 trees transplanted as 'super-large' nursery stock and a control group (5 trees) transplanted as small-caliper trees. We found the trees transplanted as 'super-large' nursery stock experienced declining tree growth with decades of lost landscape potential likely due to traumatic root-cutting at the time of transplant from nursery to landscape. The control group allowed contrast between the growth patterns of 'super-large' transplanted trees with those that remained healthy, being transplanted as smaller-caliper trees. For the 'super-large' trees, we found a decrease in carbon sequestration from 7.6 kg C yr-1 on average per tree in 2001 to about 1.5 kg C yr-1 on average per tree in 2021, while no decreasing trends were observed among the control trees. This implies a negative impact on multiple expected ecosystem services including carbon sequestration, shade, canopy coverage, and pollutant mitigation. These results highlight the unrecognized costs of common Chinese nursery and transplant techniques on urban landscape trees, necessitating more research, science-based policies, and better management techniques.

Reducing spatial resolution increased net primary productivity prediction of terrestrial ecosystems: A Random Forest approach

Net primary production (NPP) is a pivotal component of the terrestrial carbon dynamic, as it directly contributes to the sequestration of atmospheric carbon by vegetation. However, significant variations and uncertainties persist in both the total amount and spatiotemporal patterns of terrestrial NPP, primarily stemming from discrepancies among datasets, modeling approaches, and spatial resolutions. In order to assess the influence of different spatial resolutions on global NPP, we employed a random forest (RF) model using a global observational dataset to predict NPP at 0.05°, 0.25°, and 0.5° resolutions. Our results showed that (1) the RF model performed satisfactorily with modeling efficiencies of 0.53-0.55 for the three respective resolutions; (2) NPP exhibited similar spatial patterns and interannual variation trends at different resolutions; (3) intriguingly, total global NPP varied greatly across different spatial resolutions, amounting 57.3 ± 3.07 for 0.05°, 61.46 ± 3.27 for 0.25°, and 66.5 ± 3.42 Pg C yr-1 for 0.5°. Such differences may be associated with the resolution transformation of the input variables when resampling from finer to coarser resolution, which significantly increased the spatial and temporal variation characteristics, particularly in regions within the southern hemisphere such as Africa, South America, and Australia. Therefore, our study introduces a new concept emphasizing the importance of selecting an appropriate spatial resolution when modeling carbon fluxes, with potential applications in establishing benchmarks for global biogeochemical models.

Reconstruction of heavy metal(loid) pollution history based on dendrochemistry in Jiuzhaigou World Natural Heritage site, southwestern China

Heavy metal(loid)s are widely regarded as important environmental pollutants and have attracted extensive attention. In addition to such areas with frequent human activities as cities and industrial areas, the heavy metal(loid) pollution in remote areas lacking long-term monitoring data also deserves attention. In this study, Chinese pine (Pinus tabuliformis) in Jiuzhaigou World Natural Heritage was sampled to analyze concentration of Pb, Zn, Cu, As, Cd, Co, Cr, and Ni and to reconstruct pollution history. Source analysis and evaluation of the potential ecological risk of heavy metal(loid)s were also performed. Results showed that Jiuzhaigou has been polluted by heavy metal(loid)s at a relatively high level and concentrations were the highest at the location with intensive human activities (Nuorilang). Tree growth was inhibited by increased heavy metal(loid) concentration and this situation was more pronounced at high concentrations. The increased heavy metal(loid) concentrations were attributed to human activities such as forest logging, infrastructure construction, and tourism development. Heavy metal(loid) pollution reached a very high level of ecological harm at Nuorilang and a high level of ecological harm in Shuzheng and Heye villages. Overall, even at low concentrations, we demonstrated that Chinese pine can be used not only as a bioindicator for heavy metal(loid) pollution but also to infer pollution history over a relative long-term period and to enhance our understanding of the biogeochemical cycle of heavy metal(loid)s in forest ecosystems.

Declining tree growth rates despite increasing water-use efficiency under elevated CO2 reveals a possible global overestimation of CO2 fertilization effect

Though rising atmospheric CO₂ concentrations (C_a) harm the environment and society, they may also raise photosynthetic rates and enhance intrinsic water-use efficiency (iWUE). Numerous short-term studies have investigated tree growth under elevated CO₂ (eCO₂) conditions, but no long-duration study has investigated eCO₂ impacts on tree growth and iWUE under natural conditions. Utilizing a new dendrochronological experimental design in a heavily-touristed nature preserve in Southwest China (Jiuzhaigou National Nature Reserve), we compared tree growth (e.g., basal area increment) and iWUE in two biophysically and environmentally similar valleys with contrasting anthropogenic activities. Trees in the control valley with ambient CO₂ benefited from increasing C_a, possibly due to the CO₂ fertilization effect and optimal environmental conditions. However, trees in the treatment valley with intensive tourism experienced comparatively higher localized eCO₂ and growth rate declines. While iWUE increased (1959–2017) in the control (25.3%) and treatment sites (47.8%), declining tree growth rates in the treatment site was likely because comparatively extreme CO₂ exposure levels encouraged stomatal closures. As the first long-term study investigating eCO₂ impacts on tree growth and iWUE under natural conditions, we demonstrate that increased forest iWUE is unlikely to overcome negative drought stress and rising temperature impacts. Thus, forest potential for mitigating eCO₂ and global climate change is likely overestimated, particularly under dry temperate conditions.