I'm a postdoc at Aarhus University, working with Prof. J.C. Svenning (centre ECONOVO). Before that, I finished my Ph.D. with Prof. Mark Vellend, at Université de Sherbrooke. My research interests lie in species distributions, community ecology, forest dynamics, functional traits, and biological invasions.
Research
Trophic controls on vegetation dynamics
Nested fiting method is developed to estimate herbivore relative abundance at landscape scale
Herbivore effects on plant community are context dependent!
We map the diversity of native and alien large herbivores across North America
Nested fiting method is developed to estimate herbivore relative abundance at landscape scale
Large mammalian herbivores are crucial for maintaining plant diversity and regulating ecosystem functions, yet many populations have suffered significant declines. My postdoctoral research at Aarhus University focuses on understanding: (1) how environmental contexts and population density shape the effects of large herbivores on vegetation dynamics, with emphasis on forest regeneration and understory invasions; and (2) how the spread of native and alien herbivores might help restore the diversity and ecological functions of large herbivore communities, particularly in North America. To achieve objective (1), I am also developing a new tool, the 'nested fitting method,' to estimate the landscape-scale relative abundance of large herbivores—specifically white-tailed deer and wild pigs—across the US.
Soil effects on plant distributions and migration
Soil properties have important impacts on plant fitness, but we have little knowledge of how soil properties influence large-scale plant distributions and potential migration under climate change. Two studies in my Ph.D. address these questions – one studying soil effects along a latitudinal gradient (Eastern North America, see the paper in New Phytologist), and one along an elevational gradient (Mont-Mégantic, Québec, see the paper in Philosophical Transactions B). We found that soil properties had substantial effects on plant distributions on both the latitudinal and elevational gradients, and such influences could be more pronouncedly in colder environments. Furthermore, the unsuitable soil environments at high latitudes/elevations may represent a major constraint on plant migration under climate change (a review of this topic will come soon). I am also exploring the evolutionary mode and tempo of plant soil niches, to ask whether plants are likely to adapt to the high-latitude soils where future climates are likely to become suitable.
The relative importance of climate (grey) and soil (yellow) variables in predicting species distributions of plants(a), and soil effects for different plant growth forms (b) and habitats (c).
An example that high-latitude soil is not suitbale for trout lily in eastern North America.
The influence of soil pH and elevation on the abundance of an understory herb Trillium erectum at Mont-Mégantic. The pH effect changes from neutral at low elevation to positive at high elevation.
The relative importance of climate (grey) and soil (yellow) variables in predicting species distributions of plants(a), and soil effects for different plant growth forms (b) and habitats (c).
Forest dynamics under climate change
Differences in the geographic or niche distributions of juvenile and adult trees are often used to infer the impacts of climate change on tree range dynamics. Previous studies have suggested that juvenile trees have narrower distributions than adults, indicating range contraction. However, this conclusion may be biased by uneven sampling of adults and juveniles in forest inventories. We showed through spatial simulations that reduced sampling intensity can underestimate range and niche limits. Reanalyzing U.S. Forest Inventory and Analysis data for 92 tree species, we applied resampling procedures to control for sampling biases. These adjustments substantially altered range estimates, often reversing the original conclusion that juvenile ranges are narrower. More details in the Ni & Vellend, 2021.
Larger sampling areas in local plots can result in larger estimated latitudinal ranges by increasing the probability of detecting occurrences at the range edge.
The previous finding that juveniles’ trees had narrower latitudinal ranges than adult trees (original analysis) were likely caused by sampling biases. After controlling for sampling issues, juvenile trees generally had broader ranges than adult trees.
Larger sampling areas in local plots can result in larger estimated latitudinal ranges by increasing the probability of detecting occurrences at the range edge.
Introduction history, distributions, and invasiveness of alien plants in China
The Anthropocene has seen massive species exchanges, with some alien species causing significant environmental impacts. As a rapidly growing economy, China faces increasing invasion risks. During my M.Sc. research, I used herbarium and literature records to reconstruct the introduction history of alien naturalized plants in China. Our findings revealed that plant introductions were largely driven by intentional efforts, with botanic gardens playing a key role in shaping spatial patterns, particularly for ornamental species (Ni & Deane, 2022, Ni & Hulme, 2021). The determinants of invasiveness varied across invasion stages: evolutionary adaptation and population expansion influenced invasion success, while competitive traits predicted impact severity (Ni et al., 2021). Additionally, our work highlighted the critical role of root traits in shaping the competitiveness of invasive plants, an often-overlooked factor in invasion ecology (Ni et al., 2018; Ni et al., 2023).
The spatial pattern of alien plant introductions in China, which is mainly driven by the number of species in botanic gardens.
Root growth was measured in the lab, and fast root growth was found to explain the competitiveness of invasive plants.
The spatial pattern of alien plant introductions in China, which is mainly driven by the number of species in botanic gardens.