Herbivory limits recruitment in an old-field seed addition experiment.

Area of Science:

• Ecology
• Plant Community Dynamics
• Conservation Biology

Background:

• Environmental variability can support rare plant coexistence, but grassland homogenization may reduce diversity.
• Causes of species loss in transformed anthropogenic grasslands remain unclear.
• Two hypotheses for species loss are homogenization (loss of variability) or barriers (inaccessibility).

Purpose of the Study:

• To investigate the roles of environmental variability and barriers in limiting plant establishment in degraded grasslands.
• To test the homogenization and barrier hypotheses in the context of grassland restoration.
• To identify factors controlling the success of introduced plant species.

Main Methods:

• Manipulated environmental variability (fertility, disturbance, competition) and circumvented dispersal barriers in a degraded grassland.
• Introduced 1.2 million seeds of five distinct species.
• Excluded small native herbivores using exclosures to assess their impact.

Main Results:

• Small native herbivores acted as a significant barrier to the establishment of introduced plant species.
• Browsing by herbivores directly caused recruitment failure.
• Invasive plants, seemingly more herbivore-resistant, outcompeted introduced species indirectly.

Conclusions:

• Herbivory, rather than manipulated environmental variability, was the primary factor limiting the establishment of new plant populations.
• Herbivore resistance may be a key trait for invasive plant success in these systems.
• Restoration efforts must consider herbivore management to facilitate the establishment of desired species.