Leading Consulting Arborists

for the Pacific Northwest

Leading Consulting Arborists for the Pacific Northwest

A balanced approach to tree management.

With over 40 years of experience, we provide expert consulting services for all your tree management needs. From protecting trees during development to expert witness services, our team is here to ensure your projects succeed while preserving the beauty and benefits of urban trees.

Our Services

ISA Board Certified Master Arborists

ISA Qualified Tree Risk Assessors

ASCA Members and Registered Consulting Arborist

Trees along our streets, in our parks, and on our properties provide critical social, environmental, and economic benefits, enhancing our quality of life. As trees grow, their benefits increase, but so can their potential for failure. To ensure tree safety and longevity, a comprehensive Tree Risk Assessment can help reduce the risk of unexpected failures. Our consultants are Tree Risk Assessment Qualified by the International Society of Arboriculture (ISA). Whether you are concerned about a single tree or a grove, we offer basic, intermediate, and advanced risk assessments to determine overall risk ratings and recommend effective risk reduction solutions.
TREE PROTECTION PLANS
NEW DEVELOPMENT – PROPERTY DIVISIONS – LANDSCAPE RENOVATIONS
Teragan & Associates specializes in creating comprehensive tree protection plans for a range of projects. Whether it’s a large-scale development or a landscape renovation, we have extensive experience in assessing trees and adhering to local codes and best practices. Our in-depth knowledge and established relationships with city staff across the Portland-Vancouver Metro area ensure precise and professional tree reports that support your project's success.
Trees add significant value to properties and communities. Our tree appraisal process determines the dollar value of a tree, often used for tax deductions, insurance claims, or legal disputes. We provide a neutral, detailed assessment considering species, condition, and benefits, delivering the accurate reports you need for your claims.
Trees play a prominent role in many legal claims, from disputes between neighbors to assessing damage liability. Our consulting arborists are experts in arboriculture and provide specialized tree expertise for legal situations. Whether you need to determine the cause of tree damage or assess responsibility, Teragan & Associates offers reliable expert witness services.

Consult Our Arborists Now

Meet the Team

Terrence P. Flanagan

PRINICPAL, CONSULTING ARBORIST
Recently recognized as a "True Professional" by the International Society of Arboriculture (ISA), Terry Flanagan has dedicated his life to arboriculture. As a Board Certified Master Arborist® with Tree Risk Assessment Qualification, Terry brings over 40 years of experience to Teragan & Associates. His career has included significant contributions to the industry, including pioneering tree risk assessment standards and leading innovative tree management practices.

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Peter van Oss

SENIOR ASSOCIATE
With a family history in horticulture, Peter van Oss has a deep-rooted passion for trees. After relocating from the Netherlands, he has built 13 years of field experience and 4 years as a consulting arborist in the Pacific Northwest. Peter is ASCA Registered Consulting Arborist #826, ISA Certified Arborist, Tree Risk Assessment Qualified, and ASCA Tree and Plant Appraisal Qualified, bringing a wealth of knowledge and enthusiasm to every project.
Tom Feitl

ASSOCIATE
Tom Feitl’s career as an arborist began in Minnesota and has since expanded to the Pacific Northwest. An avid tree climber and outdoor enthusiast, Tom combines his love of nature with his professional expertise. With 8 years in the field, Tom is an ISA Certified Arborist and Tree Risk Assessment Qualified, dedicated to preserving and understanding trees in their natural state.