Multiple filters affect tree species assembly in mid-latitude forest communities

Area of Science:

• Ecology
• Forest Ecology
• Community Ecology

Background:

• Species assembly patterns are determined by abiotic/biotic filters and dispersal, influencing community structure.
• Functional assembly knowledge reveals the interplay of deterministic and stochastic processes in shaping species composition.

Purpose of the Study:

• To evaluate the roles of alpha (α) and beta (β) niches in tree species assembly.
• To analyze the influence of environmental filtering and functional traits on geographical patterns in mid-latitude forests.

Main Methods:

• Examined alpha niche traits (leaf, wood) and beta niche properties (cold/drought tolerance) using forest plot datasets.
• Tested trait assembly non-randomness (clustering/over-dispersion) using null models with regional species pools.
• Assessed latitudinal patterns of trait assembly in relation to climate.

Main Results:

• Most plots showed species assembly within random expectations.
• Significant deviations from randomness were frequent for cold/drought tolerance (β niche properties).
• Non-random clustering of β niche traits was predominant in higher latitudes with harsh climates.

Conclusions:

• Both randomness and non-randomness in trait assembly result from α and β niches.
• Dispersal and/or trait equalization may contribute to the prevalence of randomness.
• Clustering of functional traits along climatic gradients provides evidence for species sorting via environmental filtering.