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* Metric Name: Early Seral Stage  

* Tier: 2  

* Data Vintage: 04/2023  

* Unit Of Measure: Categorical 1 - 3 (seral stage), continuous variable 0-1 representing percentage of a HUC (early and late seral stage)  

* Represent element and pillar: No  

* Type and distribution of data: Zero-inflated, right-skewed beta-like distribution representing proportions. Raw data values range from 0 to 0.4 for early seral stage.  

* Translation: Where is proportion of early seral within the historical range? ****  

* Translation method and outcome: Raw data values translated to range from +1 to -1 representing more favorable and less favorable conditions, respectively. The proposition of more favorable is based on the objective of the proportion of the HUC12 sub watershed being within the historical range of early seral forest. We used two-tailed smooth (Gaussian) scoring, reflecting the perspective that a landscape could have both too little and too much early seral condition to support forest ecosystem functions. More favorable (translated to +1) set at 0.15 to 0.25 proportion of the sub watershed, and less favorable (translated to -1) represented in two ways (two-tailed test): too little early seral (-1 score) set at 0 proportion of the sub watershed; and too much early seral set at >40% of the sub watershed. Alternative translations could have a broader favorable range and higher or lower values for too much early seral. 

Figure . Histogram and scoring of early seral stage in Southern California

Figure . Histogram of translated early seral stage in Southern California

Figure . Maps displaying raw metric and translated metric early seral stage in
Southern California

  

* Metric Definition and Relevance: 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.  

* Credits: FVEG 2023 \--CALFIRE, CDFW, LANDFIRE, California Forest Observatory (SALO), USDA Forest Service