Indirect interactions between browsers and seed predators affect the seed bank dynamics of a chaparral shrub

Abstract

Interactions between herbivores and seed predators may have long-term consequences for plant populations that rely on persistent seed banks for recovery after unpredictable fires. We assessed the effects of browsing by deer and seed predation by rodents, ants and birds on the densities of seeds entering the seed bank of Ceanothus cuneatus var. rigidus, a maritime chaparral shrub in coastal California. Ceanothus produced many more seeds when protected from browsers in long-term experimental exclosures than did browsed plants, but the seed densities in the soil beneath browsed and unbrowsed Ceanothus were the same at the start of an intensive one-year study. The density of seeds in the soil initially increased in both treatments following summer seed drop: while densities returned to pre-drop levels within a few weeks under browsed plants, soil seed densities remained high for 5-8 months beneath unbrowsed plants. Rodent abundance (especially deer mice) was higher near unbrowsed plants than >30 m away, and rodents removed Ceanothus seeds from dishes in the experimental plots. At least in the short term, rodent density and rates of seed removal were inversely related to the intensity of browsing. Our data have management implications for maintaining viable Ceanothus populations by regulating the intensity of browsing and the timing, intensity and frequency of fires.

Seed limitation of woody plants in Neotropical savannas

“…In Neotropical savannas, seeds of most common woody species do not form persistent but seasonal transient soil seed-banks (Salazar et al 2011). Short-lived soil seed-banks further increase the magnitude of seed limitation because viable seeds do not accumulate in the soil over time and cannot recruit into the population even during a productive seed year for that species (Deveny and Fox 2006;Clark et al 2007;Zobel et al 2000;Moles and Westoby 2002). Although seed limitation does not necessary reduce seedling recruitment (Orrock et al 2006), it is highly likely that the combination of poor seed dispersal among sites, post-dispersal seed loss, and short-lived soil seed-banks enhance seed limitation reducing the potential seedling recruitment of woody species in tropical savannas.…”

Comparing seed removal of 16 pine species differing in invasiveness

“…The tube was fixed to the soil with U-shaped wire (Castro et al 1999;Deveny and Fox 2006;Jacob et al 2006;Fig. 1b).…”

Using Small-Scale Studies to Prioritize Threats and Guide Recovery of a Rare Hemiparasitic Plant: Cordylanthus rigidus ssp. littoralis

“…At the University of California, Fort Ord Natural Reserve, where we conducted our studies, abnormally heavy deer browsing limits population viability of Ceanothus cuneatus var. rigidus (Rhamnaceae), a shrub species of special concern [14]. Because a large proportion of C.r.l.…”

“…Fire suppression in Mediterranean-climates has changed the trajectory of many plant communities, threatening some natives that rely on post-fire habitats ([16]). The Monterey Bay area was subjected to frequent (yearly) intentional burning by Native Americans [17], but aerial photographs indicate that the Fort Ord area has not burned for at least 60 years [14]. We are not aware of previous work on fire-dependency in C.r.l.…”