Forest gaps, which are formed by small-scale disturbances that often occur in forest communities, are the most dominant form of disturbance in many types of forests around the world and play an essential role in the dynamics of forest regeneration, plant diversity conservation, nutrient cycling, and forest succession. Forest gaps are one of the vital directions in forest research. Dynamic disturbance and vegetation regeneration are important elements of forest gap research. The research on forest gaps has a history spanning over 70 years, but there is a lack of a systematic overview of the process. Therefore, this review outlines the spatial changes in the whole process of forest gap development by systematically analyzing the occurrence, basic characteristics, micro-environmental changes, and the effects of forest gap disturbance processes on understory animals, plants, soil microorganisms, and forest regeneration and succession. The results contribute to a better understanding of forest gaps and their impacts on forest regeneration and management. Based on this, we remapped the forest gap process during forest succession. We suggest directions and recommendations for improvements in response to the dilemmas and challenges facing the future of forest gaps.

The Populus euphratica desert riparian forest, predominantly distributed along the Tarim River in northwestern China, has experienced significant degradation due to climate change and anthropogenic activities. Despite its ecological importance, systematic assessments of P. euphratica stand structure across the entire Tarim River remain scarce. This study employed terrestrial laser scanning (TLS) to capture high-resolution 3D structural data from 2741 individual trees across 30 plots within six transects, covering the 1300 km mainstream of the Tarim River. ANOVA, PCA, and RDA were applied to examine tree structure variation and environmental influences. Results revealed a progressive decline in key structural parameters from the upper to lower reaches of the river, with the lower reaches showing pronounced degradation. Stand density decreased from 440 to 257 trees per hectare, mean stand height declined from 9.3 m to 5.6 m, mean crown diameter reduced from 4.1 m to 3.8 m, canopy cover dropped from 62% to 42%, and the leaf area index fell from 0.51 to 0.29. Age class distributions varied along the river, highlighting population structures indicative of growth in the upper reaches, stability in the middle reaches, and decline in the lower reaches. Abiotic factors, including groundwater depth, soil salinity, soil moisture, and precipitation, exhibited strong correlations with stand structural parameters (p < 0.05, R² ≥ 0.69). The findings highlight significant spatial variations in tree structure, with healthier growth in the upper reaches and degradation in the lower reaches, enhance our understanding of forest development processes, and emphasize the urgent need for targeted conservation strategies. This comprehensive quantification of P. euphratica stand structure and its environmental drivers offer valuable insights into the dynamics of desert riparian forest ecosystems. The findings contribute to understanding forest development processes and provide a scientific basis for formulating effective conservation strategies to sustain these vital desert ecosystems, as well as for the monitoring of regional environmental changes.

Improving the carbon storage in terrestrial ecosystems can effectively reduce atmospheric CO₂, which is one of the important ways of mitigating global climate change. The knowledge on terrestrial carbon stock research is relatively mature in the international community; however, the research pulse, hotspots, and trends in terrestrial ecosystems carbon stock research are not clear. To better understand the research focus and developmental directions of terrestrial ecosystems’ carbon storage, we conducted a bibliometric analysis of 6305 research articles between 2002 and 2022, which were gathered from the Web of Science Core Database. The temporal distribution, country/region distribution, co-citation network, keyword evolution and clustering, journals, and authors of the literature were analyzed, and the knowledge domain was mapped using the CiteSpace visualization software. This study established the following three observations: (1) The number of publications on carbon stock research in terrestrial ecosystems continues to expand, and the trend in the number of publications proves that carbon sinks in terrestrial systems remain an important research topic internationally. (2) Important issues concerning terrestrial ecosystem carbon stock research have evolved from monitoring the carbon stock changes in terrestrial ecosystems to the mechanism of carbon stock formation for the realization of monitoring and management under global climate change. Furthermore, the research methodology has evolved from small-scale, fixed-point instrumental observations to large-scale remote sensing and model simulations, with diversifications in research content and methodology. (3) In the future, academic research on carbon stocks in terrestrial ecosystems will focus more on international and interdisciplinary cooperations, increasing the intensity in surveying and monitoring carbon stocks in terrestrial ecosystems, and realizing the accurate monitoring, assessment, management, and enhancement of carbon stocks from the integrated carbon stock computation system for “sky, air, and land.” The results of this study comprehensively demonstrate the current status and development of the research on carbon stocks in terrestrial ecosystems worldwide, and provide a reference for future research on the sustainable management of terrestrial ecosystems within the context of global warming.

Populus euphratica is the only dominant tree species of desert riparian forest in the Tarim River Basin and faces a great threat of drought. Policy-based artificial water delivery projects are an effective engineering method to mitigate drought and reduce the degradation of desert riparian forests. Forest gaps have been shown to be the primary mode of forest regeneration. However, little is known about growth status of P. euphratica in various arid zone habitats, particularly in light of the complex and diverse microenvironmental alterations in the understory. This study quantified the effects of forest gaps and flooded areas on microenvironmental changes in the understory. The relationships between the microenvironmental changes, soil physicochemical properties, and physiological characteristics of P. euphratica were investigated through a cross-experiment that compared whether the water delivery process was flooded and whether forest gaps existed. The results revealed that the forest gap increased the diversity of light conditions on the ground; floods decreased the temperature of the forest gap by 1.94 °C while they increased the air humidity by 8.19%. Flooding improved the vertical distribution of soil physicochemical properties within the forest gap while also altering the content of soil indicators in different directions. In the research area, only the peroxidase activity (POD) exhibited significant differences (p < 0.05) in drought indicators between the forest gaps and understory of P. euphratica, while all of the drought indicators improved after flooding. Changes in the microenvironments and soil physicochemical features together play an important ecological role in mitigating the drought of P. euphratica. These results provide an actionable theoretical basis for the efficient management of riparian forests and a research basis for sustainable forest development in arid zones.