* Metric Name: Seral Stage  

* Tier: 2  

* Data Vintage: 2023  

* Unit Of Measure: Integer 1 - 3, continuous variable 0-1

The seral stages are categories that represent the developmental progression
of forest ecosystems from initial establishment or following a stand replacing
event (e.g., high severity fire) to a forest dominated by trees in the upper
age classes for a given forest type. Late seral forests are also often
characterized by multiple ages of forest trees and dead and dying trees in
some form of equilibrium. Seral conditions across landscapes were highly
variable prior to major European settlement in the western US. These patterns
were highly attuned to dominant disturbance regimes and the multi-scaled
variability in environmental conditions across topographic and climatic
gradients. These patterns helped to reinforce fire regimes dominated by low-
to moderate-severity fire across much of the region and provided for multiple
habitat requirements for a wide variety of species.

This metric contains three related data layers. The first is an assignment to
each 30 meter pixel of the seral stage it is currently in, either early, mid,
or late seral stage. The other two layers represent the proportion of a HUC 12
watershed that is in 1) early seral stage or 2) late seral stage.

* Creation Method: The FVEG data, used in characterizing vegetation and habitat conditions for a number of metrics in this kit, contain data on tree size (see FVEG discussion above). Seral stages for forested lands are binned into one of three categories of tree size (Early, Mid, Late) and those are defined by tree diameter, per the CWHR system. 

**Size Class**

|

 **Size (inches DBH)**

|

 **Seral Stage**  
  
---|---|---  
  
1 Seedling

|

less than 1

|

Early (1)  
  
2 Sapling

|

1 – 6

|

Early (1)  
  
3 Pole

|

6 – 11

|

Mid (2)  
  
4 Small

|

11 – 24

|

Mid (2)  
  
5 Medium to Large

|

24+

|

Late (3)  
  
6 Multi-storied

|

36 – 48

|

Late (3)  
  
Late Seral conditions have been lumped into a single classification (24” and
up).

The first layer provided here assigns a early, mid, or late seral value to
each cell based on dominant tree size in the canopy. The second and third data
layer provided identify the proportion of the HUC12-scale (typically
10,000-30,000 acres in size) that is either early seral forest or late seral
forest, respectively. These patterns can be highly variable at finer-scales so
we used a HUC 12 watershed as the unit for expressing relative abundance. For
each HUC12, the proportion of the watershed covered by the evaluated seral
stage has been calculated.

  

* Credits: FVEG \--CALFIRE, CDFW, LANDFIRE, California Forest Observatory (SALO), USDA Forest Service