FINAL

April 15, 2000

Abstract

Regeneration of the rare Morro manzanita (Arctostaphylos morroensis) is dependent on fire. This plant is an obligate seeder; that is, individuals do not resprout after fire, and the species maintains itself solely by reproducing from seed. Because fire in stands of A. morroensis will be controlled by land management decisions, it is imperative to consider the fire regime that will best maintain this rare shrub. In order to gain information about the factors affecting regeneration of this species, we conducted studies on its reproductive biology and response to prescribed burning. This report presents results of our studies conducted 1998 - 2000.

We completed studies on the reproductive biology and seed predation of A. morroensis. Our main findings were: 1) bumblebees were the most common pollinator, although these were not abundant; 2) A. morroensis does not self-pollinate; 3) plants produced an average of 57 flowers and 8 fruits per stem (on stems selected haphazardly), with a mean 18% fruit set; 4) we found no difference in flower or fruit characters among sites; 5) fruit predation was occurring at all 3 sites, and was especially high at the Elfin Forest (77% fruit lost within 3.5 weeks), and 6) the number of seeds added to the seed bank in 1999 ranged from 248 to 1008 per m^2. These studies confirm that a long fire interval is needed for seed to accumulate to the levels present in moderate-aged stands.

To examine regeneration of A. morroensis following fire, we conducted studies in a prescribed burn. The burn was carried out in a ten-acre parcel in Montaña de Oro in the fall of 1998. Soil heating during the burn varied considerably throughout the site. This, along with variation in pre-burn seed densities was likely responsible for the differences observed in seedling emergence among sample plots. Seedling recruitment overall was extremely low, and was not adequate to replace the pre-burn adult population. We discuss the importance of a long fire interval to the accumulation of a sufficient soil seed bank that will ensure successful post-fire regeneration.

We compared seed viabilities and germinabilities in litter vs. soil-stored seed to identify the best sources of seed for use in restoration efforts. We found that simulated burning enhanced the germination of both types of seed. The percent of intact seeds that germinated was lower for seeds collected in the litter compared to soil-stored seed, but the litter may be still provide a useful source of seed for restoration projects.

We conclude this report with a preliminary geographic information systems (GIS) analysis of the species distribution. Our results indicate that the present ~350 Ha of maritime chaparral and coastal scrub in which A. morroensis occurs are about 1/3 the estimated historical extent.