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Growing Season Index (GSI)

NFDRS header graphic. Decorative.

 

The Growing Season Index (GSI) In NFDRS 2016, controls live fuel moistures, replacing the 1000-hour and X1000 controls in the 1978/88 versions. The moisture bounds  (30-250 for herbaceous and 50-200 for woody shrubs) and behavior of annuals versus perennials are maintained.

nfdrs-gsi_us.png The Growing Season Index is a simple metric of plant physiological limits to photosynthesis. It is highly correlated to the seasonal changes in both the amount and activity of plant canopies. It predicts the green-up and senescence of live fuels and the influence of water stress events on vegetation. Increasing values of GSI indicate periods of improving conditions for live fuels and decreasing values indicate periods of detrimental weather conditions. GSI is calculated as a function of the three indicators of important weather factors that regulate plant functions. These indicators are combined into a single indicator that integrates the limiting effects of temperature, water and light deficiencies. The importance of each of the three indicators is explained below and a summary of the Growing Season is given at the conclusion.

Minimum Temperature

Many of the biochemical processes of plants are sensitive to low temperatures. Although ambient air temperatures certainly influence growth, constraints on phenology appear to be more closely related to restrictions on water uptake by roots when soil temperatures are sub optimal and many field studies show variable ecosystem responses over a range of minimum temperatures.

Vapor Pressure Deficit (VPD)

Water stress causes partial to complete stomatal closure, reduces leaf development rate, induces the shedding of leaves, and slows or halts cell division. Although models are available to calculate a soil water balance, they require knowledge of rooting depth, soil texture, latent heat losses, and precipitation. As a surrogate, we selected an index of the evaporative demand, the vapor pressure deficit (VPD) of the atmosphere.

Photoperiod or Daylength

Photoperiod provides a plant with a reliable annual climatic cue because it does not vary from year to year at a given location. We assume that photoperiod provides the outer envelope within which other climatic controls may dictate foliar development. Studies have shown that photoperiod is important to both leaf flush and leaf senescence throughout the world.

Upper and lower limits of the indicator functions used to calculate the Growing Season

Input Variable Unconstrained (1) Completely Limiting (0)
Minimum Temperature 5ºC /41º F -2ºC /28º F
Vapor Pressure Deficit (Pascals) 900 Pascals 4100 Pascals
Photoperiod (Daylength) 11 hours 10 hours

Learn more about the Growing Season Index (GSI)

 

NWCG Latest Announcements

NWCG Equipment Technology Committee Releases Safety Warning: 25-001 Non-specification fire shelters

Date: January 15, 2025
Contact: Equipment Technology Committee

The Equipment Technology Committee (ETC) has released Safety Warning: 25-001 Non-specification fire shelters. Non-specification fire shelters claiming to meet Forest Service (FS) fire shelter specification 5100-606 were first found in February of 2023. As of September 2024, non-specification shelters are again being advertised and sold on the open market.

This Safety Warning outlines details and recommended procedures to purchase FS specification shelters made with materials and components that meet performance criteria and toxicity testing requirements outlined in FS Specification 5100-606. 

For additional information on identifying non-specification shelters, please view ETC Safety Warning 23-01.

References:

ETC Safety Warning 25-001: Non-specification fire shelters

NWCG Equipment Technology Committee

ETC Safety Warning 23-01

Paul Gleason Lead by Example Awards

Date: January 14, 2025
Contact: Leadership Committee

The NWCG Leadership Committee has awarded the 2023 Paul Gleason “Lead By Example” awards to individuals in the categories of Initiative and Innovation, Mentoring and Teamwork, and Motivation and Vision, as well as a Lifetime Achievement Award.

Congratulations to the awardees:

  • Sam Bowen, Superintendent of the Mark Twain Veteran Crew with the U.S. Forest Service.
  • Greg Titus, Zone Fire Management Officer for the St. Marks National Wildlife Refuge with U.S. Fish and Wildlife Service.
  • Renae Crippen, Manager of the Blue Mountain Interagency Dispatch Center with the U.S. Forest Service.
  • Eric Carlson, Instructor with OMNA International.

References:

Paul Gleason Lead by Example Award

Wildland Fire Leadership Development Program

Interview with Paul Gleason

Updated NWCG Standards for Water Scooping Operations, PMS 518

Date: December 19, 2024
Contact: Water Scooper Operations Unit

The NWCG Standards for Water Scooping Operations, PMS 518 establishes the standards for dispatching, utilizing, and coordinating water scooping aircraft on interagency wildland fires. These standards should be used in conjunction with the NWCG Standards for Aerial Supervision (SAS), PMS 505, and any local, state, or geographic/regional water scooping plans.

References:

NWCG Standards for Water Scooping Operations, PMS 518

Updated NWCG Standards for Aerial Supervision, PMS 505

Date: December 19, 2024
Contact: Interagency Aerial Supervision Subcommittee

The Interagency Aerial Supervision Subcommittee has updated the NWCG Standards for Aerial Supervision, PMS 505. PMS 505 establishes standards for aerial supervision operations for national interagency wildland fire operations. 

References:

NWCG Standards for Aerial Supervision, PMS 505