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Forest Change Queries

This directory contains SQL queries for analyzing forest condition changes over time using FIA's remeasurement data and change matrices.

Overview

Forest change analysis tracks how forest conditions evolve between measurement cycles. These queries use: - SUBP_COND_CHNG_MTRX table for condition-level changes - Previous plot linkages (PREV_PLT_CN) to connect remeasurements - Change evaluation types (EVALID ending in 03) for proper temporal analysis

Query Inventory

Missouri Forest Type Change

Calculates forest area changes by forest type group for Missouri's 2024 evaluation. - EVALID: 292403 (Missouri 2024 Change) - Focus: Net forest area by type group - Key Finding: Oak/hickory dominates with 11.8M acres

Key Concepts

Change Matrix (SUBP_COND_CHNG_MTRX)

  • Tracks proportion of each condition that changed between measurements
  • Links current and previous conditions through plot CNs
  • SUBPTYP_PROP_CHNG indicates the proportion changed (divided by 4 for per-plot basis)

Evaluation Types

Change evaluations (ending in 03) specifically support temporal analysis: - Include previous plot linkages - Have longer remeasurement intervals - Support growth, removal, and mortality calculations

Common Patterns

-- Link current and previous conditions
JOIN COND pcond ON pcond.PLT_CN = plot.PREV_PLT_CN
JOIN SUBP_COND_CHNG_MTRX sccm ON
    sccm.PLT_CN = cond.PLT_CN
    AND sccm.PREV_PLT_CN = pcond.PLT_CN

Best Practices

  1. Always filter both current and previous conditions for validity
  2. Apply appropriate adjustment factors based on subplot type
  3. Use change-specific EVALIDs (ending in 03)
  4. Account for the 4-subplot design when using proportion fields