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Quantitative studies of mangrove leaf functional traits will help us understand the adaptive evolutionary strategies of mangrove plants and the relationship between mangrove biodiversity and ecosystem functions. Because of the special environment of the intertidal zone where mangroves are located, it is very difficult to obtain the functional traits of mangrove canopies from the ground, and relevant studies are lacking. The maturity of Unmanned Aerial Vehicle (UAV) hyperspectral remote sensing technology provides a new means of conducting such research. This study considered mangroves on Qi'ao Island, Zhuhai, as the research object. Based on UAV hyperspectral data, two UAV hyperspectral data processing methods, which combined Partial Least Squares Regression with Normalized Difference Vegetation Index (PLSR+NDVI) and Partial Least Squares Regression with Continuous Wavelet Transform (PLSR+CWT), were used to estimate the 10 canopy leaf functional traits of mangroves on Qi'ao Island. The results showed that the PLSR + NDVI method was more suitable for the inversion of mangrove canopy-specific leaf weight (LMA), phosphorus content per unit mass (Pmass), and nitrogen content per unit area (Narea), whereas the PLSR + CWT method was more suitable for the estimation of the nitrogen/phosphorus ratio (N/P), chlorophyll content (Cab), and carotenoid content (Cxc). However, the results of the above two methods for retrieving the nitrogen content per unit mass (Nmass), potassium content per unit mass (Kmass), phosphorus content per unit area (Parea), and potassium content per unit area (Karea) were not ideal (R2

Biodiversity plays an important role in providing ecosystem services and maintaining ecosystem stability, which are closely related to human welfare. The identification of biodiversity hotspots and analysis of their threats provide effective ways for biodiversity conservation and restoration. Current studies generally combine species diversity and its threat situation to determine hotspots for priority protection. However, in-depth analysis of threats to biodiversity hotspots is still lacking. Guangdong Province is one of the key biodiversity areas in the world, but it faces great challenges in biodiversity preservation. To understand biodiversity hotspots and their threats in Guangdong Province more completely, this study developed a heat index for terrestrial biodiversity by considering plant species diversity, animal species diversity, and landscape diversity based on multi-source data of plant and animal species, ecosystem stand types, and land use. Then, the heat index was used to identify biodiversity hotspots, and their threat levels and controlling factors were analyzed according to the major threats to biodiversity. The results showed that areas with high values of terrestrial biodiversity heat index were mainly distributed in mountainous regions with relatively few human disturbances, whereas most areas with low values were concentrated in estuarine plains and intermontane basins with heavy human activities. Based on the zonation of the heat index, four biodiversity hotspots were identified, Yunwu Mountain, Nanling Mountain, Luofu Mountain, and Lianhua Mountain, with area percentages of 15.54%, 44.90%, 17.66%, and 21.90%, respectively. The area of biodiversity hotspots was 59,931.82 km2, accounting for 33.58% of the total land area of Guangdong Province. The 122 nature reserves within hotspots had an area of 6,594.39 km2, covering 61.33% of the whole area of the total 204 terrestrial nature reserves in Guangdong Province. This proportion gradually decreased with reduction of nature reserve grade, indicating that the nature reserves in hotspots were principally at a higher grade (nation and province levels) rather than at a lower grade (city and county levels). However, the area of these nature reserves in hotspots was only 11.00% of the whole area of hotspots, and most of the nature reserves that were not distributed in hotspots were located in the northeastern cities of Heyuan and Meizhou. Therefore, a large number of potential demands for biodiversity conservation still exist. For the four hotspots, the biodiversity in Yunwu Mountain was primarily under moderate to severe stress, with the intensity of economic development as the controlling factor. The biodiversity of the other three hotspots mainly underwent slight to moderate stress. The most important threat was the extensive economic development of the central part of Nanling Mountain and the southern parts of Luofu Mountain and Lianhua Mountain, whereas the periphery of Nanling Mountain and the northern parts of Luofu Mountain and Lianhua Mountain were more threatened by habitat quality or geological hazards. In addition, extreme stress on biodiversity occurred in all four hotspots, although within very small areas. Thus, more targeted management strategies for biodiversity should be proposed according to the stress levels and controlling threats. The results of this study provide a scientific reference for the comprehensive conservation and precise restoration of biodiversity hotspots in Guangdong Province.

There is a close quantitative relationship between crown traits and trunk traits and the relationship can be used to invert each other, calculate forest biomass and stock volume, and guide afforestation practice. The correlation between tree crown and trunk traits is quite different in different regions, and relevant research on the Nanling mountains is lacking. To find out the correlation between canopy and trunk traits and its relationship with altitude in the Nanling mountains, as well as to explore the feasibility of retrieving trunk traits and calculate forest biomass and stock in these mountains, forests with broad-leaf trees distributed at different altitudes (600, 800, 1000, 1400, and 1600 m) in these Mountains were selected as the research objects for this study. Unmanned aerial vehicle remote sensing was used to obtain canopy traits such as crown width, crown circumference, and crown area (CA) of canopy tree species. The correlation between basal diameter (BD) and tree trunk traits-Diameter at breast height (DBH), diameter at 2 m height (D2), and diameter at 4 m height (D4)-were investigated and regression equations were established. A high correlation was observed between crown traits and trunk traits in the Nanling mountains, and the correlation was statistically significant to invert trunk traits from crown traits. The correlation between tree crown traits and trunk traits significantly differed with elevation in these mountains, revealing an "M" shaped change with elevation. Among the crown traits selected in this study, the correlation between crown area and trunk traits was the highest, implying that it could be used solely for inversion of trunk traits. The specific equations were as follows:

Dicranopteris is the most representative pioneer species, dominant species and key species in degraded slope land in South China. Dicranopteris could quickly form dense synusia of a single and dominant species. In contrast to the traditional view that Dicranopteris hinders forest regeneration, we found that there are a few species that could settle down in Dicranopteris synusia. We proposed a hypothesis that Dicranopteris synusia could act as an ecological filter. In this study, we transplanted 12 target species seedlings under Dicranopteris synusia with 4 treatments to explore the ecological filtering effect of Dicranopteris synusia, and analyzed the mechanism with soil characteristics. The 4 treatments included the understory removal treatment (UR), the aboveground of Dicranopteris synusia were kept (AF), the root blanket of Dicranopteris synusia were kept (AR) and all of the Dicranopteris were kept (CK). The results showed that: 1) Compared with the red soil under Dicranopteris synusia of Eucalyptus plantation and bare ground, the contents of soil organic matter, total nitrogen, hydrolyzed nitrogen, available phosphorus, available potassium, and exchangeable base ions in the root blanket of Dicranopteris synusia were significantly higher. 2) The majority of the tree species and all of the herbaceous species could not survive with the root blanket of Dicranopteris synusia kept (AR and CK). The species that could survive with the root blanket of Dicranopteris synusia kept were Schima superba, Rhodomyrtus tomentosa, Ilex asprella and Melastoma candidum. The results indicated that Dicranopteris synusia could act as an ecological filter. The key lies in the role of root blanket of Dicranopteris synusia, and not in the improvement of soil nutrients. Theoretically, Dicranopteris synusia, especially the root blanket of Dicranopteris synusia, is closely related to the breakthrough of biological threshold for ecological restoration. In the future, it is necessary to further analyze the structure and function of the root blanket of Dicranopteris synusia. In terms of application, there are a large number of plantation types (such as Eucalyptus plantation) that Dicranopteris occupied as a single dominant understory species in South China. Therefore, we should pay more attention to the ecological filtering effect of Dicranopteris synusia in structural optimization and stand transformation. This study could provide a reference for the restoration and reconstruction of degraded slope land in South China.