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To assess potential causes of woody plant encroachment into desert grassland systems using a 5500‐yr‐old sediment record from a ciénega in New Mexico.

Cloverdale Ciénega, southwestern New Mexico.

Utilizing fossil pollen and charcoal preserved in wetland sediments, a long‐term record of variations in vegetation composition and fire activity was generated. The record was compared to published data on drought, the El Niño/Southern Oscillation (ENSO), carbon dioxide concentrations and known dates of grazing impacts to evaluate various hypotheses regarding the timing and causes of woody plant encroachment in desert grasslands.

The woody plant encroachment observed in the past 200 yrs is unprecedented in the context of the previous 5500 yrs of vegetation history. The observed increase in woody plant abundance was not related to droughts or changes in …