Spatial associations of humus, nutrients and soils in mixed dipterocarp forest at Lambir, Sarawak, Malaysian Borneo

Abstract

Discrete humus layers are common on podzols under temperate coniferous and tropical heath forests, and patchy layers also occur under some temperate broadleaved forests on non-podzolic soils. We used multiple data sets to test the reported association of humus with oligotrophic but non-podzolic soils under non-heath dipterocarp forest at Lambir, Sarawak. We examined the distribution, morphology and nutrient dynamics of necromass on soils derived from sandstone and shale. Concentrations of the main mineral nutrients were lower in fresh litter on the very oligotrophic sandstone soils than on shale. The rates of litterfall were similar, so that annual litterfall fluxes of all nutrients were lower on sandstone. The lower nutrient concentrations and fluxes in the litter on sandstone resulted in slower decomposition, longer residence times and larger standing crops of forest-floor necromass, with lower concentrations of nutrients. The necromass on sandstone sequestered significantly more N, K and Mg but less Ca and Mn than on shale, with no significant difference for P. The variations in necromass nutrient dynamics were associated with morphological differences. There were mats of densely rooted humus under the litter on sandstone, whereas litter lay directly over the mineral topsoil on shale. Spatial associations with soil nutrients were weak for necromass thickness, but clear for humus. The proportions of nutrients in the litterfall and necromass reflected the stoichiometric profiles of the soils. We attribute the differences in necromass nutrient dynamics and their association with soil reserve nutrients to lower rates of nutrient replenishment from the weathering of sandstone than from shale. Necromass characteristics are robust field indicators of multivariate edaphic differences in these and other tropical forests on Acrisols/Ultisols derived from Tertiary clastic sediments.

Nitrogen uptake strategies of edaphically specialized Bornean tree species

“…Sandstone-derived soils are humult utisols or sandy haplic acrisols with substantial surficial raw humus and root mat and relatively low nutrient and water retention. Shale-derived soils are clay-rich ultisols generally lacking a humus layer and root mat and have greater nutrient and moisture retention (Baillie et al 2006). Four soil types have been described based on differences in soil chemistry (C, N and P and exchangeable K, Ca and Mg) and elevation (Davies et al 2005).…”

“…Davies et al (2005) found that of the abundant species at Lambir, 73 % had distributions significantly aggregated on at least one of the four soil types. Here we focus on two soil types, clay and sandy loam, at the extremes of this gradient that differ most in soil properties (Baillie et al 2006). Supply rates of NH þ 4 and NO À 3 in surface soil (top 10 cm) of clay and sandy loam were quantified in the 52-ha plot over a 5-week period using anion and cation exchange resins as part of a separate study (Kochsiek et al 2013).…”

“…In this forest, most tree species' distributions are tightly correlated with soil resources, causing forest composition to vary dramatically between soil types along an edaphic gradient, resulting in high b diversity (Davies et al 2005) that contributes to the exceptionally high species richness of this region (Ashton and Hall 1992). We focused on the two soil types at the extremes of the edaphic gradient, clay and sandy loam (Baillie et al 2006). These soils share the same climate, due to their close proximity, but differ in supply rates of N-forms, with greater supplies of NO (Kochsiek et al 2013).…”

Covariation between understorey light environments and soil resources in Bornean mixed dipterocarp rain forest

“…In 1991, a 52-ha plot (hereafter, Lambir) was established in the Park following standardized methods (Condit 1998) and pegged with permanent markers at every 20-m grid corner (Figure 1). Floristic composition, stand structure, soils, soil nutrient and water contents, and geomorphology of Lambir are described elsewhere (Baillie et al 2006, Lee et al 2002, Russo et al 2010, Tan et al 2009). …”

“…We tested the hypothesis that regimes of PAR differ significantly in the understorey of rain forest growing on four soil types along an edaphic gradient in Borneo. Soils along this gradient range from coarse loams that are sandstonederived, nutrient-depleted and well-drained, to clays that are shale-derived, less nutrient-depleted and less welldrained (Baillie et al 2006, Russo et al 2010, Tan et al 2009), but the forests share the same rainfall regime, as they are located at one site. Variation in light regimes between and within forest types was characterized in terms of total daily PPFD and the frequency, duration and intensity of sunflecks and in terms of their seasonal variation between the non-monsoon season and the generally cloudier, early monsoon season.…”