Establishment of microscale vegetation pattern in maritime chaparral after fire

Abstract

We quantified microscale pattern in vegetation and seed assemblages along a 24 m transect before and for two years following a controlled burn in chamise (Adenostoma fasciculatum) chaparral in central coastal California. Our objective was to document scale-dependent correlation between pre-burn seed assemblages, pre-burn canopy cover, microtopography, soil temperatures during burning, post-burn seed assemblages and post-burn vegetation. Scale-dependent correlations among pre-and post-burn seed densities, maximum soil temperatures during burning, microtopography and post-burn vegetation were measured based on two-term local covariance analysis.Seed distribution varied among species prior to fire, with seeds of some annual species concentrated in gap areas. Maxinmm soil temperatures during burning ranged from less than 50 °C to 225 °C, and were generally lowest in gaps in the pre-burn canopy. These gaps were associated with local topographic depressions. After burning, readily germinable seeds were concentrated in or near gaps in the pre-burn canopy. Germination of different species was variously enhanced, diminished or unchanged by the passage of fire. Post-burn vegetation was very patchy, with some areas nearly devoid of seedlings and other areas, especially pre-burn canopy gaps, supporting numerous seedlings. Seedling recruitment patterns in the second year were generally highly correlated with patterns in pre-burn seed banks and first year vegetation. Although many species exhibited similar recruitment patterns, several different mechanisms may have been responsible for the origin of those patterns.

Impacts of climate, disturbance and topography on distribution of herbaceous cover in Southern California chaparral: Insights from a remote‐sensing method

“…The dominant factor in determining the distribution of grasses and other herbaceous cover is site-specific moisture limitation. Thus, although differences in microclimate (Davis, Borchert, & Odion, 1989;Johnson-Maynard, Shouse, Graham, Castiglione, & Quideau, 2004), herbivory (Lambrinos, 2006) and extreme climate events that are not captured in this study may also impact invasion into chaparral, it is clear that differences in long-term moisture availability are essential to understanding and predicting the distribution of herbaceous cover and invasive grasses throughout chaparral at both highly local and broader scales. High aridity has been found to control the rate and extent of post-fire recovery by chaparral shrubs (Keeley et al, 2005b), while low-precipitation years may thin young shrubs significantly (Keeley, Baer-Keeley, & Fotheringham, 2005).…”

Peak Fire Temperatures and Effects on Annual Plants in the Mojave Desert

“…Desert fires can kill a high proportion of the seedbank which is concentrated beneath shrubs (Young and Evans 1978, Hassan and West 1986, Price and Joyner 1997), and may ameliorate undercanopy and drip line microhabitats that are favored by many native annual plants (Shreve 1931, Went 1942, Muller 1953, Halvorson and Patten 1975, Nelson and Chew 1977, Shmida and Whittaker 1981), thereby decreasing species richness. In contrast, chaparral fires kill relatively few seeds since relatively few are present beneath shrubs (Davis et al 1989), and expose undercanopy soil creating a regeneration niche for opportunistic species and obligate seeders (Keeley and Zedler 1978, Zammit and Zedler 1994, Odion and Davis 2000, thereby enhancing species richness. At the small scale represented by the shrub-intershrub gradient, fire can therefore decrease plant diversity in desert shrubland and increase plant diversity in chaparral shrubland.…”

“…Woody and fine fuels are highest beneath creosote bushes, intermediate at the canopy drip line, and lowest in the interspaces between shrubs. Heterogeneous fuel distributions often create variable peak fire temperatures (Davis et al 1989, Odion andDavis 2000), and spatially and seasonally heterogeneous peak fire temperatures should produce variable effects across the landscape.…”

Fire Severity and Ecosytem Responses Following Crown Fires in California Shrublands

“…Studies of prescribed burns have shown direct effects of fire intensity on ecosystem responses such as resprouting and seedling recruitment (Davis et al 1989, Borchert and Odion 1995, Tyler 1995. Understanding the manner in which variations in fire intensity affect ecosystem responses such as soil erosion and community recovery is important to managing these landscapes, particularly where urban development interfaces with these wildlands.…”