Small Heat Shock Protein Responses Differ between Chaparral Shrubs from Contrasting Microclimates

Small heat shock protein (sHsp) responses were studied for two evergreen perennial shrubs in the northern California chaparral; one common on warm, south-facing slopes (Ceanothus cuneatus), and the other on cooler, north-facing slopes (Prunus ilicifolia). Small Hsp expression was induced experimentally for field collected leaves. Leaf collections were made where the species co-occur. Small Hsp expression was quantified using two antibodies, one specific to a chloroplast 22 kD sHsp and another that detects a broad range of sHsps. Differences between chloroplast sHsp accumulation, which protects thermally labile proteins in PSII, and the general sHsp response were examined. The species from the cooler microclimate, Prunus, had a lower induction temperature and accumulated greater levels of sHsps at low temperatures. Both Prunus and Ceanothus reached peak sHsp expression at 42∘C. The species from the warmer microclimate, Ceanothus, had greater sHsp expression at higher temperatures. Chloroplast sHsp expression generally tracked sHsp expression in Ceanothus, but in Prunus general Hsps were elevated before chloroplast sHsps. Variation between species for sHsp expression (induction temperatures, accumulation levels, and the duration of expression) coupled with the costs of Hsp synthesis, may contribute to differences in the abundance and distribution of plants across environmental gradients.

Post-fire regeneration strategies and flammability traits of California chaparral shrubs

Fire behaviour is strongly influenced by fuel load and structure; however, efforts to describe fuel patterns have largely ignored differences among species or post‐fire regeneration strategies. In California chaparral, evergreen shrubs can be grouped into three post‐fire regeneration strategies that correlate with a wide variety of physiological and demographic characteristics including seasonal water status and the timing of reproduction in response to fire. To test if regeneration strategy is also associated with flammability, we compared the fuel loads and structure of two post‐fire seeders, Adenostoma fasciculatum and Ceanothus cuneatus, and two obligate resprouters, Heteromeles arbutifolia and Prunus ilicifolia. Species and post‐fire regeneration strategies did not differ in total fuel per area, or bulk density. The proportion of fuels smaller than 6 mm in diameter differed among species, but not consistently with regeneration strategy. However, species with a post‐fire seeding regeneration strategy had higher proportions of dead branches. We discuss how this difference could have arisen from evolutionary, demographic, or physiological processes.

Evaluation of Growth, Flowering, and Cold Hardiness of Ceanothus in Western Oregon

Thirty-eight species, cultivars, and hybrid selections of ceanothus (Ceanothus spp.) were evaluated for growth, flowering, and cold hardiness in a landscape trial in Silverton, OR, from 2001 to 2005. Plants were only irrigated for establishment in Summer 2001 and were not pruned or fertilized throughout the trial. Several cultivars showed dieback and leaf damage after 22 °F cold events in late October and early Nov. 2002 and 2003, the most severely affected of which were Ceanothus thyrsiflorus var. griseus, C. thyrsiflorus var. griseus ‘Yankee Point’, Ceanothus hearstiorum, and C. thyrsiflorus ‘Snowflurry’. Among the cultivars evaluated, those recommended for early bloom are ‘Ray Hartman’ and ‘Blue Jeans’. Several cultivars are effective drought-tolerant groundcovers, including ‘Wheeler Canyon’, ‘Joyce Coulter’, and ‘Joan Mirov’. Among the smaller-growing plants, Ceanothus cuneatus var. rigidus ‘Snowball’ and Ceanothus gloriosus ‘Heart's Desire’ made effective groundcovers only 0.6 and 0.2 m tall, respectively.