Morphology and Genesis of Humus Profiles under Chaparral Shrubs in Southern California

Abstract

Core Ideas Litter layers of chaparral soils differ dramatically under different plant species. The rate of litterfall, balanced by the rate of decomposition, influences the type of litter layers that develop. Macrofauna, such as earthworms, are inhibited by dry conditions and have minimal effects on litter layer characteristics. Chaparral is the predominant wildland ecosystem adjoining many urban areas of California. The litter layers under this dense shrub cover are important because they modify soil climate, support soil fauna, provide nutrients, and protect against soil erosion. The objectives of this study were: (i) to understand how the morphology of chaparral litter layers changes with depth under different shrub species, and (ii) to determine the influence of shrub species and associated macrofauna on the genesis of humus profiles. Research was conducted within mature chaparral stands (38 yr after fire) on the San Dimas Experimental Forest under four common chaparral species: chamise (Adenostoma fasiculatum H. & A.), hoaryleaf ceanothus (Ceanothus crassifolius Torr.), bigberry manzanita (Arctostaphylos glauca Lindl.), and scrub oak (Quercus dumosa Nutt.). Increased litter decomposition with depth was expressed as decreasing C/N ratios, proliferation of fungal hyphae, and degradation of characteristic leaf features. Mineral matter content also increased with depth in the humus profiles, resulting from mixing by soil fauna. Earthworm densities were low throughout the chaparral, caused by seasonal moisture limitations, and were insufficient to consume manzanita leaf litter effectively, leading to thicker humus profiles and the development of Mor‐type humus. Moder‐type humus forms, with thinner litter layers, were found under scrub oak and ceanothus. Chamise litter was classified as a Rhizomull because of minimal litter accumulation, resulting from low and roughly equivalent litterfall and decomposition rates. Unique characteristics of the chaparral species led to different humus profiles and humus forms but macrofauna were not an overriding genetic influence.

A Bibliometric Analysis on Research Progress of Earthworms in Soil Ecosystems

“…Additionally, earthworm activities were observed to impact humus profile morphology. The mineral content of the soil humus profile increased with depth due to the mixing effect of earthworms in the soil [ 88 ]. Subsequently, the interactions among earthworms and other soil animals were paid more attention and ecological roles of earthworms were further reported.…”

Removal ofN‐fixing vs.non‐N‐fixing herbs in postfire chaparral: Competition and contributions to soil N and C cycling

“…California chaparral shrublands cover 7% of the state's land area and are susceptible to high‐intensity summer and fall fires (Keeley & Davis, 2007). Mature chamise chaparral generally has an understory bare of herbaceous species and is covered with a thin litter layer of dry twigs and chamise leaves (Haydu‐Houdeshell et al, 2017). Chaparral shrubs have been shown to decompose slowly due to high C:N and high lignin content, with the chaparral litter layer actually immobilizing N and P over the first three years of leaf decomposition (Schlesinger, 1985).…”