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Windthrow is a typical gap phrase disturbance that changes forest composition but rarely alter succession trajectories of a forest stand. Catastrophic windthrow such as typhoons is a large but infrequent disturbance that can have long-lasting effects on forest ecosystems. Whether catastrophic windthrow resets successional pathways of forest ecosystems remains inconclusive. We compared forest structure and regeneration patterns between undisturbed and disturbed stands 30 years after a typhoon event in the treeline ecotone of the Changbai Mountains, Northeastern China. Measurements were made using WorldView-1 satellite imaging and fieldwork in two types of large plots, one located in areas affected by the typhoon event and the other in adjacent undisturbed areas. Results showed that community divergence at landscape scale occurred following the typhoon. In non-wind–disturbed stands, forest development followed the successional pathway of both broadleaved and coniferous trees. By contrast, the late-successional coniferous rather than the early successional broadleaved trees occupied the wind–disturbed stands. The alteration mechanism on the forest succession pathway was that herbs formed tall, dense, and persistent mono-dominant thickets after the typhoon, which inhibited the regeneration of broadleaved trees. In contrast to the common knowledge that forest would return to initial successional stage after catastrophic disturbance, we concluded that catastrophic windthrow, different from gap phase windthrow, altered forest successional trajectory. [ABSTRACT FROM AUTHOR]

Vegetation in the alpine tundra area of the Changbai Mountains, one of two alpine tundra areas in China, has undergone great changes in recent decades. The aggressive herb species Deyeuxia angustifolia (Komarov) Y. L. Chang, a narrow-leaf small reed, was currently encroaching upon the alpine landscape and threatening tundra biota. The alpine tundra of the Changbai Mountains has been experiencing a warmer climate and receiving a high load of atmospheric nitrogen deposition. In this study, we aimed to assess the respective roles of climate warming and atmospheric nitrogen deposition in promoting the upward encroachment of D. angustifolia . We conducted experiments for three years to examine the response of D. angustifolia and a native alpine shrub, Rhododendron chrysanthum , to the conditions in which temperature and nitrogen were increased. Treatments consisting of temperature increase, nitrogen addition, temperature increase combined with nitrogen addition, and controls were conducted on the D. angustifolia communities with three encroachment levels (low, medium, and high levels). Results showed that 1) D. angustifolia grew in response to added nutrients but did not grow well when temperature increased. R. chrysanthum showed negligible responses to the simulated environmental changes. 2) Compared to R. chrysanthum , D. angustifolia could effectively occupy the above-ground space by increasing tillers and growing rapidly by efficiently using nitrogen. The difference in nitrogen uptake abilities between the two species contributed to expansion of D. angustifolia . 3) D. angustifolia encroachment could deeply change the biodiversity of tundra vegetation and may eventually result in the replacement of native biota, especially with nitrogen addition. Our research indicated that nutrient perturbation may be more important than temperature perturbation in promoting D. angustifolia encroachment upon the nutrient- and species-poor alpine tundra ecosystem in the Changbai Mountains. [ABSTRACT FROM AUTHOR]

Pronounced climate warming has resulted in a significant reduction of snow cover extent, as well as poleward and upslope shifts of shrubs in Arctic and alpine ecosystems. However, it is difficult to establish links between changes in snow cover and shrub distribution changes due to a lack of in situ and long-term snow records in relation to abundance shifts of shrubs at their leading (i.e., cold) and trailing (i.e., warm) edges. We used remote sensing to extract long-term changes in both snow cover and shrub distributions in response to climate change in the alpine tundra of the Changbai Mountains in Northeast China. First, we analyzed spatio-temporal changes in snow cover during the snowmelt period (April 1st to June 15th) over the past 54 years (1965–2019). Then, we analyzed distribution changes of the dominant evergreen alpine shrub, Rhododendron aureum , using 31 years (1988–2019) of Landsat NDVI archives. We applied a novel approach by analyzing NDVI data from autumn only, when R. aureum is green yet most of the surrounding plants are already brown. Finally, we tested the relationship between snowmelt date and the distribution of R. aureum. We found that the fraction cover of R. aureum experienced greater loss than gain in the last 30 years. R. aureum expanded at the leading edge, establishing in snow-rich habitats, yet retracted further at the trailing edge due to loss of snow habitats. We identified the preferred snowmelt regime (habitats with snowmelt date of 20 April or later) of this shrub species and found that further advances in snowmelt dates would lead to the upward range shift of R. aureum in a warming climate. Our results indicate that spring snow cover change affected distribution changes of R. aureum. Our study highlights that long-term changes in snow cover due to climate change have already had marked impacts on plant species distributions in alpine ecosystems. • The fraction cover of R. aureum in the Changbai Mountains experienced greater loss than gain in the last 30 years. • Changes in leading and trailing edges of R. aureum related to snow cover trends in the last 50 years. • Further advance in snowmelt dates would lead to the upward range shift of R. aureum. [ABSTRACT FROM AUTHOR]

Global environmental changes continuously result in plant migration from lower elevations or latitudes into alpine or arctic tundra ecosystems. In response to global environmental changes, the alpine shrubby tundra on the Changbai Mountain in northeastern China has been invaded by a low-elevation herb species Deyeuxia angustifolia over the past several decades. In this experiment, we studied the effects of D. angustifolia migration, Nitrogen (N) deposition (ambient N vs. N-addition of 10 g/m2/yr), and elevation (a higher elevation of 2200 m vs. a lower elevation of 2050 m a.s.l.) on soil properties and soil microbial communities to better understand the consequences of this migration for soil microbes and obtain feedback on the likelihood of further migration. We found that the migration of D. angustifolia decreased the soil available phosphorus (AP) and microbial biomass (particularly the biomass of Gram-positive bacteria (Gp) and Actinobacteria) at 2200 m a.s.l. N addition enhanced the availability of soil N, the nitrogen: phosphorous (N: P) ratio, and reduced the fungal: bacterial (F: B) ratio at 2200 m a.s.l. There was a higher Gram-positive: Gram-negative bacterial (Gp: Gn) ratio at 2200 m a.s.l. than those at 2050 m a.s.l. Our results suggest that the upward migration of D. angustifolia into the shrubby tundra combined with N deposition will substantially change the soil microbial community composition on the one hand, and result in a shortage of soil P on the other hand, especially at higher elevations. These changes may increase the competitive ability of D. angustifolia , and further benefit its migration, and suppress the shrubby species that currently exist in that habitat. This study helps to understand the mechanisms for the upward migration of D. angustifolia and facilitates the management of the Changbai alpine tundra in a changing world. • Increasing elevation increased soil Gram-positive:Gram-negative ratio. • D. angustifolia migration (D) decreased soil microbial biomass and Gram-positive:Gram-negative ratio. • N addition (N) decreased soil fungal biomass and fungi:bacteria ratio. • Soil P limitation and the proportion of Gn increased with D and N. • The microbial responses to D and N were more pronounced at higher elevations. [ABSTRACT FROM AUTHOR]

Enhanced frequency and intensity of freeze-thaw cycle (FTC) owing to global climate change may influence soil carbon (C) and phosphorus (P) cycling in terrestrial ecosystems. However, a comprehensive understanding of soil C and P cycling in response to FTC is still lacking. Here, we compiled data of 2471 observations from 75 publications and conducted a meta-analysis on the responses of soil C and P cycling and the stoichiometry of C, N and P cycling to FTC. Results showed that experimental FTC significantly increased soil dissolved organic C (+38%), instant and cumulative CH 4 (+41% and +59%, respectively), dissolved organic C leaching (+62%), total salt-extractable P (+27%), dissolved organic P (+9.4%), leaching of dissolved total P (+312%), dissolved organic P (+30%), and dissolved inorganic P (+115%), and the ratio of available N to P (+21%). In contrast, soil microbial biomass C (−10%), cellulase activity (−16%), microbial biomass P (−10%), and the ratio of microbial biomass C to nitrogen (−8.1%) significantly decreased under FTC treatments. The likely reason for the increases in soluble soil C and P after FTC is the C and P release from dead soil microorganisms and changes in soil structure enhancing organic matter availability. The mean effect size of FTC generally increased with increasing FTC intensity, which was probably also the main reason for higher responses of soil C and P pools and fluxes to FTC observed in laboratory than in field experiments. However, mean effect sizes of FTC generally decreased with increasing duration and frequency of FTC, very likely due to substrate depletion through microbial uptake and leaching. The results of this meta-analysis contribute to a better understanding of the overall responses of soil C and P pools and fluxes to FTC, providing the basis for more accurate prediction of the impacts of future global climate change on biogeochemical cycles. • We conducted a meta-analysis on the responses of soil C and P cycling to FTC. • FTC significantly increased soil soluble C and P. • FTC decreased enzyme activities, microbial biomass, and the ratio of MBC to MBN. • The FTC effect was higher in laboratory than in field experiments. • The FTC effect decreased with increasing duration and frequency of FTC. [ABSTRACT FROM AUTHOR]

Regions at high latitudes and high altitudes are undergoing a more pronounced winter warming than spring warming, and such asymmetric warming will affect chilling and forcing processes and thus the spring phenology of plants. We analyzed winter chilling and spring forcing accumulation in relation to the spring phenology of three tree species (Ulmus pumila , Populus simonii , and Syringa oblata) growing in a cold region (CR) compared with trees in a warmer reference region (WR), using the Dynamic Model and the Growing Degree Hour (GDH) model. We tested that forcing rather than chilling affects the spring phenology of trees in CR (hypothesis I), and that trees in CR have both lower mean chilling and forcing temperature and thus longer accumulation periods than trees in WR (hypothesis II). The modeling results confirmed that chilling and forcing occur simultaneously during the early spring when temperature gradually increases. In line with our hypotheses, forcing played a crucial role in spring phenology in CR, but chilling and forcing combined to determine spring phenology in WR. The temperature during the chilling and forcing periods was lower and the accumulation period started earlier and ended later in CR than in WR. Moreover, the chilling accumulation was broken into two periods by the low deep winter temperature in CR, and that interruption will be removed by future strong winter warming. Future asymmetric warming, with a stronger temperature increase in winter than in spring, could decrease the forcing accumulation effects and increase the chilling effects on the spring phenology of plants in CR. This change in the balance between chilling and forcing will lead to a shift in plant phenology, which will further have major impacts on biogeochemical cycles and on ecosystem functions and services. Unlabelled Image • Spring forcing is the main driver of tree spring phenology in cold regions (CR). • Chilling accumulation of spring phenology (SP) is broken into two periods in CR. • Forcing and chilling combine to determine SP in warmer regions (WR). • Chilling and forcing occur in parallel in eraly spring. • Forcing and chilling accumulation start earlier and end later in CR than in WR. [ABSTRACT FROM AUTHOR]

Aeolian desertification is one of the most serious environmental issues negatively impacting society. Assessing the spatiotemporal changes in desertification and determining its driving factors are crucial to preventing and controlling desertification. In this study, Landsat remote sensing images from 1980 to 2015 are used to extract the information of aeolian desertified land (ADL) in the Hulunbuir Grassland. We analyse the spatiotemporal dynamic changes in desertification using an intensity analysis, the gravity centre change model, and GIS spatial analysis and discuss the driving factors of these changes. The results show that the ADL area in the Hulunbuir Grassland increased during both 1980–2000 and 2000–2015. The ADL is mainly distributed in the central and western Hulunbuir Grassland. The gravity centres were distributed from west to east in the order of light, moderate, extremely severe, and severe ADL. ADL area and intensity changes were the highest during 1990–2000. The gain intensity of all ADL levels was active during 1980–2015. Excluding the severe ADL from 1980 to 1990 and the extremely severe ADL from 1990 to 2000, the loss intensity of other ADL levels was active. All ADL levels transformed to one level lower after 2000. The increasing annual average temperature, population, farmland area, and number of livestock promoted aeolian desertification during 1980–2000. Environmental protection policies and climate change contributed to the reversal of ADL during 2000–2015. In summary, Hulunbuir Grassland desertification has been controlled to a certain degree and has improved. The development and reversal of ADL were affected by the combined effects of climate change and human activities in the Hulunbuir Grassland. The results can provide meaningful information for the prevention and control of aeolian desertification in the Hulunbuir Grassland. • Desertification from 1980 to 2015 in study area was monitored using Landsat images. • The spatial-temporal distribution of ADL in different stages was identified. • The changes in the ADL area and intensity were the highest during 1990–2000. • Desertification has been controlled to a certain degree and has improved. • Ecological protection policies and climate change contributed to the reversal of ADL. [ABSTRACT FROM AUTHOR]