Table S3.

Distribution of memberships in professional organizations in 2020 UFP Survey. “% of Canada” and “% of US” each represent the percent of respondents employed in that country who are members of the indicated organization. “Mean # of memberships per member” represents the mean memberships held by members of the indicated organization (e.g., ISA members held on average 3.0 memberships in professional organizations). Overall, US and Canadian respondents hold a mean of 2.8 memberships (median is 3.0). Organizations that were not explicitly professional organizations (e.g., the Arbor Day Foundation) or do not offer memberships for individuals (e.g., Tree Care Industry Association) were excluded.

	Country of employment
	Canada respondents (n = 106)		United States respondents (n = 602)		Total respondents (n = 708)		Mean # of memberships per member
Organization	Count of Canada	% of Canada	Count of US	% of US	Count of total	% of total	Mean # of memberships per member
International Society of Arboriculture (ISA)	87	82.1	536	89.0	623	88.0	3.0
One or more ISA Chapters	55	51.9	450	74.8	505	71.3	3.3
Society of Municipal Arborists (SMA)	28	26.4	194	32.2	222	31.4	3.9
A local or regional urban forest networking group^*	20	18.9	153	25.4	173	24.4	3.9
A state urban forest council^*	2	1.9	150	24.9	152	21.5	4.1
Society of American Foresters (SAF)	2	1.9	68	11.3	70	9.9	4.1
American Society of Consulting Arborists (ASCA)	5	4.7	37	6.1	42	5.9	4.6
Utility Arborists Association (UAA)	2	1.9	33	5.5	35	4.9	4.6
Arboriculture Research and Education Academy (AREA)	4	3.8	29	4.8	33	4.7	6.0
American Public Works Association (APWA)	0	0.0	29	4.8	29	4.1	4.2
Provincial/state professional forestry organization^**	17	16.0	2	0.3	19	2.7	2.8
American Society of Landscape Architects (ASLA)	0	0.0	18	3.0	18	2.5	3.9
Canadian Institute of Forestry (CIF)	17	16.0	0	0.0	17	2.4	3.2
American Planning Association (APA)	0	0.0	12	2.0	12	1.7	4.4

↵* These organization types tend to be variable in terms of formality of membership structures.
↵** Variable grouped from write-in responses of provincial and state forestry professional organizations. This was the only organization type from write-in responses where n > 10.