Drivers Grass-Shrub Competition in Grassland Ecosystems
Shrub encroachment into grassland driven by climate changes and anthropogenic distur-bances,poses a significant threat to ecosystem structure and function.This study aimed to identify key fac-tors influencing grass-shrub competition across various grassland ecosystems.Precipitation,temperature,nutrient availability,grazing management and fire regimes were considered as potential drivers.The results showed that:Increased growing season precipitation favored grasses in arid grasslands,while reduced growing season precipitation and altered precipitation(increased non-growing precipitation,intensity,and decreased frequency)promoted shrub encroachment.Nitrogen and phosphorus availability may be crucial factors driving grass-shrub competition in moist grasslands.Rising temperature in polar and alpine regions promoted shrub expansion,although long-term warming induced drought can mitigate this effect.Tempera-ture impacts on grass-shrub competition in temperate steppe remain inconsistent.Overgrazing inhibited grasses growth,but enclosure could reverse this effect within 5-10 years.Prolonged enclosure or enclosure in non-degraded grasslands could paradoxically lead to shrub encroachment.Heavy-intensity,frequent fires suppressed shrubs and benefited grasses,while low-intensity,infrequent fires favored shrub expan-sion.The relative importance of these factors varies across different grassland ecosystems.Multi-factor experiments are necessary to fully understand the complex interactions driving grass-shrub competition in specific environments.
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