woodland area to its north showcases a dozen species of native mosses and companion plants. The Native Butterfly and Moth House opened June 1, 2018. The 2,160 square-foot hoop house features a planting scheme dedicated to supporting the entire life cycle of moths and butterflies native to Maine and New England. Slater Forest Pond was built in a naturally low-lying area well-suited to a small pond. The pond, excavated, lined, and replanted with native shrubs, trees, and pond plants in 2006, is filled with frogs and aquatic insects. Notable exhibits in 2021, Guardians of the Seeds, by Thomas Dambo, Danish "recycle art activist", opened to the public. It is the first Dambo exhibit to open in New England, and features five trolls with a theme of biodiversity and sustainability. Each troll has its own Danish name — Roskva, Birk, Gro, Lilja, Søren — and represents a different part of a tree. The tallest of the group is about 28 feet high. These trolls continue the story from Thomas Dambo's trolls around the world, from China to Puerto Rico. Expansion controversy In February 2017, the Gardens were warned of violations found the previous month at the site during a $30-million expansion — plans for which were made public in April 2016 Five months later, in July 2017, the State of Maine issued a formal Notice of Violation of four federal environmental laws: the Natural Resources Protection Act, the Erosion and Sedimentation Control Law, the Protection and Improvement of Waters Act and the Site Location of Development Act. On at least four occasions, a third-party inspector witnessed "instances of unclean water in protected wetlands and significant vernal pools", as well as "inadequate steps being taken to prevent erosion; and the unlicensed construction of a 'plunge pool' in a freshwater wetland area". By the end of June 2017, erosion-control measures were in place, and a restoration plan for a wetland area was in progress. The Department of Environmental Protection notice stated that sets of the contractor's construction plans for the project were never approved by the State. The constructor was Wright-Ryan Construction. The expansion included a new visitor center with gift shop along with formal gardens and trails. Parking was also expanded, with the loss of a large number of white pine trees. To make the expansion possible, large areas of wetlands (including of "critical terrestrial habitat of eight significant vernal pools") were