The Spanish and Mexican Baseline of California Tree and Shrubland Distributions Since the Late 18th Century

Historical distributions of 31 tree species, chaparral, and coastal sage scrub described by Spanish land explorers in the late eighteenth and early nineteenth centuries (1769–1806) and in land grant diseños (1784–1846) are reconstructed at 634 localities across central and southern California. This baseline predates most formal botanical surveys by nearly a century, allowing for assessment of vegetation change over the broadest time frame for comparison with pre-historical evidences and future distributions. Spanish accounts are compared with historical sources in the Mexican era (1821–1848), American settlement (1848–1929), and modern range maps of the 1929–1934 Vegetation Type Map (VTM) survey. Among tree species that were recorded in Spanish explorations, the site-specific localities are consistent with VTM maps at the spatial resolution of the land expeditions. In contrast with massive deforestation across eastern North America since European colonization, hardwood and conifer forests in California sustained inconsequential cutting during Hispanic settlement. Spanish accounts and Mexican diseños occasionally provide remarkable detail of fine-scale distributions which have not changed over the past two centuries, including Pinus radiata forest at Cambria and Monterey, the eastern limit of Quercus lobata and Q. agrifolia woodlands with Aesculus californica in the Salinas Valley, as well as isolated stands of Cupressus macrocarpa and C. sargentii. Disjunct occurrences of trees in southern California were recorded at the same places they occur today, including an isolated grove of Q. engelmannii at the Baldwin Park Arboretum, and the Pinus coulteri stand in the mountains above Santa Barbara. The southern margin of mixed conifer forest in the San Bernardino Mountains has remained on the crest of the range since Garcés’ account in 1776. Long-term tree distributions are evaluated with respect to land use, grazing and climate change. We advocate the use of historical records as proxy data for climate change studies

Appendix A. Chaparral and coastal sage scrub mapped near Santa Ana, California, by the Weislander Vegetation Type Map survey in 1940 matches a similar distribution of this shrubland vegetation mapped in 1887.

Chaparral and coastal sage scrub mapped near Santa Ana, California, by the Weislander Vegetation Type Map survey in 1940 matches a similar distribution of this shrubland vegetation mapped in 1887

Appendix B. The reported origin of the 1889 wildfire near Santa Ana is shown on a map of Fremont Canyon in the Lomas de Santiago Rancho.

The reported origin of the 1889 wildfire near Santa Ana is shown on a map of Fremont Canyon in the Lomas de Santiago Rancho

Appendix C. Meteorological data is presented as reported by the Times for measurements registered every 12 hours at Los Angeles from 20 September to 20 October 1889.

Meteorological data is presented as reported by the Times for measurements registered every 12 hours at Los Angeles from 20 September to 20 October 1889

Soil morphology of a debris flow chronosequence in a coniferous forest, southern California, USA

Soils on a series of debris flow deposits, ranging from \u3c 1 to 244 years old, were described and sampled in order to investigate the early stages of soil development. The parent material at the site is debris flow regolith, composed mainly of gneiss, the soil moisture regime is xeric, and the vegetation is mixed coniferous forest. Ages of the deposits were assessed using dendrochronology. Morphologic trends in the organic horizons included a thickening of the humus form over time, along with the development of Fm and Hr horizons. The humus forms underwent a progression from Mormodors (20 years old), to Hemimors (26–101 years old), and finally Lignomors (163 years old) and Resimors (184–244 years old). Changes in physical properties of the uppermost mineral horizons as a function of increasing age included a decrease in the volume of coarse fragments, a linear decrease in bulk density, and a darkening and reddening of the soil color. No significant soil development took place in the subsoil during the time span of this chronosequence. The soils described were classified as Typic Xerofluvents and Typic Xerorthents (Regosols and Leptosols). Buried A horizons were observed in many of the soils. Where the A horizons could be linked to dendrochronology to assess the age of the buried surface, we found that the properties of the buried A horizons do not serve as a good indicator of the age of the surface. This study suggests rapid development of the humus form profile (organic horizons and A horizon) following debris flow deposition and rapid degradation of these horizons when the debris flow surface is buried