Outplanting establishment within a contaminated and nonnative invaded semiarid desert riparian corridor

Abstract

Protected riparian ecosystems crucially important for wildlife habitat and maintaining water resources are often compromised by land use activities, such as mining, in or surrounding protected areas, creating challenges for conservation. Legacies of land use, contamination, and plant invasions can reduce vegetation community quality and hinder conservation and restoration efforts. In a semiarid riparian ecosystem in a US national monument, we conducted experimental outplantings to assess restoration techniques on native perennial species among sites with variable conditions and disturbance histories. Atriplex canescens and Encelia frutescens seedlings were planted at two coarse-textured soil sites that differed in surface exposure (sparse versus moderate woody perennial canopy cover) and disturbance histories (downstream from mine wastes and activities). For both species, exposed soils closer to mine wastes and with several years of active nonnative plant treatments had higher survival, although all E. frutescens died by one year after planting. After two years, A. canescens survival was 87.5%, or 50% higher, than survival in less exposed soils farther downstream from mine wastes. For four native understory perennials, Bothriochloa barbinodis, Bothriochloa saccharoides, Brickellia floribunda, and Tridens muticus, we tested the effects on planting microsite survival of two supplemental restoration treatments, partial buried container irrigation and tube shelters. For the first three species, planting microsites were located at sites with exposed coarse-textured soils (one site) and fine-textured (two sites) soil that differed in exposure. Tridens muticus was planted at the two fine soils sites, but most plants had died by five months after planting. Two years after planting, shelters improved survival of B. barbinodis, B. saccharoides, and B. floribunda by 20.8, 29.2, and 6.25%, respectively, and improved the probabilities of survival by 30.3, 40.4, and 21.3%, respectively. Survival differed among sites, with more plant microsites surviving in fine soils with lower surface exposure, and survival among supplemental treatments differed among sites and species. Outplanting failures often occur within the first few months to years after planting. Assessing short-term plant establishment is important to determine how plants will respond to site conditions, which are more difficult to manage than species selection and supplemental treatments. Continuing to monitor outplants and natural colonization may inform what species will remain viable options for riparian restoration as site and climate conditions change over time.