The Phenology Handbook - USA National Phenology Network

USA-NPN Monitoring System
Phenophase and Phenological Event Definitions
Phenophase: An observable stage or phase in the annual life cycle of a plant or animal that can be defined by
a start and end point. A phenophase generally has a duration of a few days or weeks. Examples include the
period over which newly emerging leaves are visible, or the period over which open flowers are present on a
plant.
Phenological event: A precisely defined point in the annual life cycle of a plant or animal, generally marking
the start or end point of a phenophase. The occurrence of a phenological event can be pinpointed to a single
date and time (in theory, if not in practice). Examples include the opening of the first flower on a plant, the
end of leaf fall on a tree, or the first appearance of a particular songbird species in spring.
Note: The definitions of the terms “phenophase” and “phenological event” have not yet been standardized and vary among
scientists. The definitions presented here reflect our usage of the terms in the USA­NPN National Coordinating Office.
Specific Phenophase Definitions
The tables on the following pages list the “phenophase” definitions in use by the USA‐NPN Monitoring
System for various plant groups, and define the important “phenological events” that mark the start and end
points of each phenophase. In observation data, these phenological events occur at the transition from an
answer of “No” to “Yes” or “Yes” to “No” for the question “Do you see…?” a given phenophase (Figure 1).
Phenological events defined by the USA‐NPN correspond to those defined in the BBCH scale1, a system for a
uniform coding of phenologically similar growth stages of plant species that is commonly used in Europe.
Please visit www.usanpn.org and click Observe! to see species profile pages which include
more specific definitions for some species. Note that definitions are subject to change slightly
for the 2010 monitoring season.
1 Meier, U. (editor). 2001. Growth stages of mono‐ and dicotyledonous plants. BBCH Monograph, 2. Edition. Federal
Biological Research Centre of Agriculture and Forestry. Germany.
A PDF version of the BBCH scale is available here: http://www.bba.de/veroeff/bbch/bbcheng.pdf
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