Species-specific responses to restoration interventions in a Tamaulipan thornforest

In the Lower Rio Grande Valley (LRGV) of south Texas, native thornscrub forest restoration has been ongoing for the past four decades, yet few assessments of their efficacy exist, and no study has yet quantified species-specific responses. Seedling transplantation in conjunction one or more restoration interventions (RIs) remains the method of choice at most sites, and thus the initial months following transplantation, when seedlings are especially vulnerable to drought and animal damage, are a critical time for determining restoration success. To this end, we evaluated the survival, growth, and animal damage of 3600 native seedlings of 24 thornforest species in response to RIs incorporating a combination of seedling shelters and slow-release moisture, as well as a mycorrhizae-biostimulant admixture (MBS). We surveyed seedlings on a bi-monthly basis over one year following planting at a semi-arid upland site in the LRGV. We found that while shelters had a pronounced and lasting impact on height growth (increased by 15–27% on average), reduction of mortality by seedling shelter RIs was only modest (reduced on average by 5–12% per species), with significant benefits accruing from cocoon shelters only, which provide slow-release moisture to the seedling roots during the initial month after planting. Species-specific responses were the most variable, with mortality ranging from 8 to 69%. While shelters in some cases reduced mammalian herbivory, the growth of leggier stems and degradation of biodegradable shelters may reduce their overall efficacy. We conclude that thornforest restoration may be most effective when seedling performance is considered in species selection and costly restoration interventions are applied on species-specific basis. These results contribute an important first step towards optimizing forest restoration efforts in the LRGV on the basis of species identity and kickstart a species-specific database of seedling demographic responses in semi-arid forest restoration.