Leucaena leucocephalaand adjacent native limestone forest habitats contrast in soil properties on Tinian Island

Abstract

An ex situ germplasm collection of the endangered Cycas micronesica was established in a transition zone between biodiverse native forest and mature stands of the invasive species Leucaena leucocephala. Soil chemical properties were determined for the 2 tree cover types to inform management decisions. Total carbon, total nitrogen, calcium, and net ammonification were greater in native forest cover than in L. leucocephala patches. Net nitrification and net mineralization were greater under L. leucocephala cover. Trace metals also differed between the 2 forest cover types, with chromium, cobalt, and nickel accumulating to greater concentration under L. leucocephala cover and zinc accumulating to greater concentration under native forest cover. The results indicated that L. leucocephala cover generated substantial changes in soil chemical properties when compared with native forest tree cover, illuminating one means by which understory vegetation may be affected by changes in invasive tree cover.

Soil Chemistry Following Afforestation of Barren Coastal Soils in Southern Guam Does Not Conform to that of Continuously Vegetated Surfaces

“…Indeed, overlap of plant functional traits does not occur among the three sites comprised of graminoids (savanna), exotic trees with endosymbionts capable of biological nitrogen fixation (Acacia), or biodiverse tree community represented by numerous plant families (native forest). Differences between the Acacia forest and the native biodiverse forest concur with other reports where non-native tree species have generated soil traits that differ from those of native tree species [15,16].…”

Two Cycad Species Affect the Carbon, Nitrogen, and Phosphorus Content of Soils

“…The fieldwork and analyses were patterned after our previous methods [3,8]. The soils associated with the C. micronesica plants were collected at half the length of the pinnately compound leaves, and four subsample cores at each cardinal direction were collected in the 0-10 cm horizon for each specimen.…”

“…Enhanced conservation knowledge is especially needed for C. micronesica, which has been listed as endangered since 2006 [6]. Various in situ and ex situ conservation projects have been initiated and include a germplasm collection from Guam-sourced seeds that was planted in 2008 on the U.S. Commonwealth island of Tinian [7,8]. Soil samples were collected from the germplasm site during various years from 2008 to 2018 to understand how the introduction of the cycad plants to the native limestone forest habitat modified various attributes of the karst soils.…”

Passive restoration following ungulate removal in a highly disturbed tropical wet forest devoid of native seed dispersers

“…Understory cover percentages in degraded exclusion plots more closely reflected native limestone forest plots after 5 years. Decreased non‐native understory most likely resulted from reduced soil disturbance and environmental changes, such as available light or changes in soil chemistry, caused by the emerging dominance of Leucaena leucocephala (Marod et al ; Marler et al ). Thus, reductions in understory may have resulted from ungulate removal by allowing tree regeneration, which altered local environmental properties.…”