Biogeomorphic influence of soil depth to bedrock, volcanic ash soils, and surface tephra on silversword distribution, Haleakalā Crater (Maui, Hawai'i)

Clinal variation in drought resistance shapes past population declines and future management of a threatened plant

“…Total root length in 9‐ to 12‐month‐old greenhouse plants averaged over 43 m, with some individuals exceeding 100 m. Average root length per leaf area (RLLA, 0.7 m/cm 2 ) in these plants was substantially higher than the modal value measured for mature individuals of a large variety of perennial alpine forbs (Körner and Renhardt ). Pérez () found that silverswords preferentially grow on shallow cinder soils <0.4 m in depth at one study site, possibly because of the shorter distance to basalt bedrock that may channel or perch water. We suspect that rooting depth varies across sites according to subsurface geology and pedological properties and, in younger substrates, may correspond to the depth at which porous cinder deposits meet layers that hold or channel more reliable water supplies.…”

“…Silverswords appear to be highly adapted to their environment (Robichaux et al. ), and take advantage of favorable microsites such as nurse rocks that improve soil moisture and temperature status and increase seedling survival (Pérez , ). Nevertheless, a ~60% decline in the silversword population size in recent decades has been strongly tied to reduced rainfall, which has coincided with other atmospheric changes such as higher solar radiation and vapor pressure deficit that appeared to result from an upward shift in the incidence of the trade wind inversion (TWI) around 1990 (Krushelnycky et al.…”

Plant Organic Matter Really Matters: Pedological Effects of Kūpaoa (Dubautia menziesii) Shrubs in a Volcanic Alpine Area, Maui, Hawai’i

“…This structure provides low coherence, and loose soils remain unstable, prone to sliding even on gentle gradients; the name of the hiking path crossing the study site-Sliding Sands trail (SSt)-highlights the proclivity of soils for geomorphic instability. Several profiles in the crater at 2175-2725 m [59,70] evince Inceptisols (Typic, Lithic, Andic Lithic, and Aridic Lithic Haplustepts) and Andisols (Typic Haplustands) with andic properties, developed on heterogeneous pyroclastic deposits [71]. Multiple thin, finely grained subsurface horizons indicate volcanic sediments were reworked by post-depositional geomorphic events like pellicular mudflows, and rainwater or snowmelt runoff [59].…”

“…Pu'u o Māui ( Figure 2C) last erupted 2700 BP, when ashfall deposits and lava flows covered much of the crater; later explosions at Ka lu'u o Ka 'O'o and Halāli'i cones contributed additional ashfall deposits from 970 to 940 BP [72,73]. Several profiles at~2175 m exhibit deep, buried horizons with high SOM and fine-grain percentages, suggesting successive waves of plant invasion took place after pyroclastic events [70]. As these cinder cones lie upwind ≤0.5-1 km from the research site ( Figure 2C), this probably was extensively affected by deposition of pyroclastic debris, transported by NE trade winds, during the last millennium.…”

“…Both soils were comparably coarse and virtually had the same sand content; fines made up <8% of the soil fraction, thus all samples were classified as gravelly coarse sand [82]. The bulk of fine material was silt; contents of clay-sized particles were exceedingly low (<1%) and barely detectable by hydrometer; this is common for the young volcanic soils across Haleakalā crater [65,70]. Median grain size (D 50 ) was practically the same for both soil positions.…”