Nitrogen deposition suppresses ephemeral post-fire plant diversity

Area of Science:

• Ecology
• Botany
• Environmental Science

Background:

• Mediterranean-type ecosystems, like California's coastal scrub, rely on fire for plant diversity.
• Many native species in these areas are ephemeral, emerging post-fire, making them vulnerable to threats like nitrogen deposition and invasive species.

Purpose of the Study:

• To experimentally evaluate the impact of nitrogen (N) deposition on post-fire vegetation cover and richness in coastal sage scrub.
• To understand how pre-fire invasion status influences vegetation dynamics under N deposition.

Main Methods:

• Experimental plots with four levels of N addition were established in recently burned coastal sage scrub.
• Vegetation cover and richness were monitored for three years.
• Areas with and without prior nonnative grass invasion were included to assess invasion status impact.

Main Results:

• Nitrogen addition reduced native forb cover and richness, particularly in previously invaded areas.
• Nonnative forb abundance increased with N addition.
• Species richness declined over three years, a process accelerated by N addition.

Conclusions:

• Nitrogen deposition poses a significant threat to native ephemeral species in post-fire coastal sage scrub.
• This can lead to the depletion of native species by suppressing post-fire bloom events.
• Management strategies should consider N deposition impacts on these sensitive ecosystems.