Alternative Restoration Treatments to Maximize Growth and Survival of Tamaulipan Thornscrub Species During Seeding Establishment

Anthropogenic activities that destroy, degrade, or fragment terrestrial ecosystems have long-lasting detrimental impacts on ecosystem function, services, and biodiversity. The Tamaulipan thornscrub ecoregion of south Texas and northeastern Mexico has sustained considerable loss, degradation, and fragmentation due land conversion for agriculture, urbanization, and introduction of invasive flora and fauna. In an attempt to restore habitat for endangered and migratory animals, United States Fish and Wildlife Service has undertaken a large-scale thornscrub revegetation effort in south Texas. The goal of this study was to develop effective restoration techniques to promote growth and survival of Tamaulipan thornscrub species during seedling establishment. Beginning March 2014, this study assessed the effects of pre-planting severe burning, seedling shelter tubes, and high (0.5 m-2), medium (1.0 m-2), and low (2.0 m-2) planting densities, both individually and in various combinations, on seedling height, basal diameter, and survival in relation to percent cover of surrounding invasive grasses and mammalian browse severity. Treatments were selected to target major environmental and biotic factors believed to inhibit seedling establishment in revegetation efforts, while utilizing three species to reduce variations in growth and survival rates of mixed-species planting schemes. After one year of treatment in March 2015, seedlings receiving only a single or no treatments decreased in overall mean height, increased by 24% in mean basal diameter from ~0.35 cm at planting, displayed an 87% survival, low herbivory, and high percent grass cover. Seedlings receiving shelter tube treatments in combination with burn, increased density, or both more than doubled in overall mean height from ~30 cm at planting, increased basal diameter up to 42% from ~0.35 cm at planting, maintained a 98% survival, increased browse, and developed a high percent grass cover. A key knowledge gap was filled by providing baseline data that demonstrates the importance of utilizing seedling shelter tubes in combination with a pre-planting severe burning of the revegetation site to promote seedling success during early stages of establishment in harsh semiarid environments. A cost-benefit analysis of treatment combinations was performed in order to aid land managers in adjusting current restoration practices for preparing and planting thornscrub in degraded habitats