W. Andrew Hartman of Sturgeon Bay, owner/operator of Acorn Services of Door County, LLC, recently earned the ISA Certified Arborist credential by successfully completing the Certified Arborist exam administered by the International Society of Arboriculture (ISA) and the local chapter of ISA. The ISA Credentialing Program is a voluntary program designed to test an individual’s degree of knowledge in the field of arboriculture. Individuals are required to pass an exam that certifies their knowledge about tree care and maintenance. Certification is valid for three years, and individuals are required to obtain continuing education units. The program is designed to increase the standard of practice in the tree care industry and to promote the professional development of individual practicing arborists. Credentialing also assists the public in identifying qualifying tree care professionals. Verification of credential holders is available at isa-arbor.com.