Calotriton arnoldi is an endemic amphibian inhabiting Montseny Natural Park and Biosphere Reserve (PNRBM), listed as “critically endangered (CR)” by IUCN. At the end of 2016, the Life Tritó del Montseny (LIFETM) project (LIFE15 NAT/ES/000757) was launched. The aim of the project was to promote around fifty actions to ensure the conservation of C. arnoldi and its natural habitat, and this entailed five strategic lines: (1) Increasing the scientific and technical knowledge with regard to C. arnoldi’s conservation status and its habitat management. (2) Expanding its geographic distribution. (3) Involving and engaging stakeholders in the conservation of the Montseny brook newt. (4) Eliminating or minimizing threats that exist in the riparian habitat. (5) Establishing proper legal coverage and defining long-term strategic planning. The successes and failures experienced throughout the process provide us with essential information that will enable us to develop an adaptive management of the habitat. In order to eliminate or minimize threats to the newt’s habitat, some of the actions that are currently being carried out are: (a) Land acquisitions and land exchanges with private properties. (b) Land stewardship procedures, with two custody agreements being signed. (c) Reduction of water withdrawal with nine water catchments and distribution being remodeled. (d) Improvement of water treatments and storage by installing ecological wastewater treatment facilities. (e) Ensuring ecological connectivity and riparian forest restoration. Here, we present an evaluation of the actions carried out to improve the habitat of this species, including the necessary considerations for them to be implemented correctly and to be successful in a natural area, which is under public-private management.

1. Optimization methods are routinely used for landscape-level conservation planning, but still underused in supporting species recovery programs. A possible barrier is the difficulty in representing and optimizing complex multidimensional problems: for example, many species recovery programs require management at the population level, but also allocation of effort and resources across populations and over time.Optimization methods can help, but they must strike a balance: too much realism can be computationally unfeasible, but too much simplification can limit relevance for complex programs, exactly where decision support might be most needed.2. We show how integer linear programming can be used to solve such a complex problem, combining multiple site-level demographic models with realistic management constraints under different sources of stochasticity and uncertainty.We apply this protocol to reintroduction planning for the critically endangered Montseny brook newt Calotriton arnoldi, optimizing site restoration efforts, captive releases from limited and variable stocks, and short-and long-term monitoring, all across 17 sites over 10 years.3. For C. arnoldi, the optimal solution was generally to open as many sites as possible, as soon as allowed by budget, and to reinforce sites with additional releases.The number of new populations that could be established was limited not only by the high initial costs of restoring and preparing sites for releases, but also because opening new sites would require subsequent monitoring, eventually adding up to unsustainable costs. 4. Synthesis and applications. Our results suggest releases of Calotriton arnoldi should be dictated first by habitat restoration capacity, then by long-term sustainability. More generally, our study shows how quantitative decision-support This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Calotriton arnoldi is an endemic amphibian inhabiting Montseny Natural Park and Biosphere Re-serve (PNRBM). It was recognized as a new taxon in 2005 by means of genetic and morphologi-cal analyses and, due to its small distribution range and population size, it was listed as “Criti-cally endangered (CR)” by IUCN. Its area of distribution is small and fragmented less than line-ar 5 km. The Montseny Brook Newt is adapted to mountain streams and requires a pristine hab-itat, one which is currently being affected by conservation issues linked to climate change and human activities (logging, water catchments, visitor’s frequency, among others). At the end of 2016, the Life Tritó del Montseny (LifeTM) project (LIFE15 NAT/ES/000757) was launched. This project’s aim was to promote around fifty actions to ensure the conservation of C. arnoldi and its natural habitat, in the Montseny SCI of the Natura 2000 Network, with five strategic lines: 1) To increase scientific and technical knowledge with regard to C. arnoldi conservation status and its habitat management. 2) To ensure its genetic conservation and expand its geographic distribu-tion 3) To eliminate or minimize threats that exist in the riparian habitat. 4) To Involve and en-gage stakeholders and local residents in the conservation of Montseny brook newt riparian hab-itats. 5) To establish proper legal coverage and define long-term strategic planning. Since 2017, several actions linked to the strategic lines 1 and 3 have been initiated. Many unforeseen events have been overcome and there have been some failures, but there have also been several satis-factory results that allow us to be optimistic about the future of the species. These achievements and failures obtained throughout the process provide us with essential information to develop an adaptive habitat management. Dozens of monitoring surveys have been carried out which allow us to understand the evolution of natural populations, to improve our knowledge re-garding their biology and to assess the impact of conservation actions. In relation to eliminating or minimizing threats to the newt’s habitat, some of the actions that are being carried out are: a) Land acquisitions and land exchanges with different private properties. b) Land stewardship with two custody agreements being signed. c) Reduction of water withdrawal with nine water catchments and distribution being remodeled. e) Improvement of water treatments and storage by installing ecological wastewater treatment facilities. f) Ensure ecological connectivity and ri-parian forest restoration by removing twenty-two river connectivity barriers removed and exe-cuting twelve forestry and bioengineering interventions within the riverside habitat. With re-gard to analyzing the conservation status, management activities and scientific and technical knowledge, active long-term monitoring of the newt population and hydrological conditions has begun. Here we present an evaluation of the actions carried out to improve the habitat of this species, including the necessary considerations for them to be implemented correctly and to be successful in a natural area, which is under public-private management.