High density planting: positive interactions in thornforest restoration

Edgar Damian Vasquez, Graduate Student Oral Presentation

Authors: Vasquez, E., Fierro-Cabo, A.

Affiliation University of Texas Rio Grande Valley

Natural habitats in the Rio Grande valley (RGV) have been degraded and lost through the conversion of thornscrub and other habitats to agricultural and urban land. Exotic African grasses me becoming dominant species in abandoned fields targeted for reforestation and are now a major impediment to successful thornforest restoration efforts as they tend to easily outcompete planted seedlings. High density plantings may favor seedlings under grass competition and abiotic stresses (e.g. Miyawaki method). A two-factor experiment is conducted to determine the effects of high-density thornforest seedling planting on subsequent survivorship, growth, and invasive grass cover. Thornscrub seedlings were planted at high (15,428 seedlings/ha) and low (2,571 seedlings/ha) densities and in three different species mixes (monospecific anacua (Ehritia anacua), monospecific elbow bush (Forestiera angustifolia}, and a mix of nine thornscrub foundation species} Invasive grass cover, seedling growth and leaf chloroophyll content are being measured every four months, with seedling survival being assessed eve1y six months. Hypotheses are 1) higher planting densities will yield taller plants with greater basal diameters, 2) chlorophyll content in seedlings planted in high density plots will be higher than those in low density plots, and 3) seedling survival will be higher in high density plots Invasive grass cover is less extensive in high density mixed plots. Survival rates for anacua are greater in high-density plots when compared to low-density plots. Growth of anacua and elbow bush seedlings appears to be favored by high density planting.

Research is part of The Nature Conservancy’s Sabal Palm/Thornscrub Research Project funded by the Robert J. Kleberg, Jr. and Helen C. Kleberg Foundation.  For further information, contact Sonia Najera at snajera@tnc.org.