A Python implementation of the USDA Forest Vegetation Simulator (FVS) supporting 10 regional variants, taper-based volume calculations, and 500+ species configurations for simulating individual tree growth and yield across the United States.

Features

• 10 Regional Variants — Southern, Lake States, Pacific Northwest, West Cascades, Northeast, Central States, ORGANON, and more
• Taper-Based Volume — Clark (Eastern) and Flewelling (Western) taper models with NVEL-compatible merchandising
• 500+ Species Configs — Individual species parameters for height-diameter, bark ratio, crown ratio, and growth
• Individual Tree Growth — Diameter, height, crown ratio, and mortality modeled per tree per cycle
• Stand Management — Thinning from below/above, selection harvest, clearcut, and custom prescriptions
• FIA Integration — Initialize stands directly from Forest Inventory and Analysis plot data
• Export Formats — Yield tables, CSV, Excel, and tree lists

Supported Variants

Variants marked with — use default (SN) infrastructure and are pending full implementation.

Installation

pip install fvs-python

Quick Start

from pyfvs import Stand

# Southern loblolly pine plantation
stand = Stand.initialize_planted(
    trees_per_acre=500,
    site_index=70,
    species="LP",
    ecounit="M231"
)
stand.grow(years=50)
metrics = stand.get_metrics()
print(f"TPA: {metrics['tpa']:.0f}  QMD: {metrics['qmd']:.1f}\"  "
      f"BA: {metrics['basal_area']:.0f} ft²  Volume: {metrics['volume']:.0f} ft³/ac")

Multi-Variant Examples

from pyfvs import Stand

# Pacific Northwest Douglas-fir (PN variant)
stand = Stand.initialize_planted(400, 120, "DF", variant="PN")
stand.grow(years=50)
# ~333 TPA, 14.5" QMD, 383 BA, 15,029 ft³/ac

# Lake States Red Pine (LS variant)
stand = Stand.initialize_planted(500, 65, "RN", variant="LS")
stand.grow(years=50)
# ~459 TPA, 10.4" QMD, 270 BA, 7,774 ft³/ac

# Northeast Red Maple (NE variant)
stand = Stand.initialize_planted(500, 60, "RM", variant="NE")
stand.grow(years=50)
# ~89 BA, 7.4" QMD

# Central States White Oak (CS variant)
stand = Stand.initialize_planted(500, 65, "WO", variant="CS")
stand.grow(years=50)
# ~283 TPA, 8.7" QMD, 117 BA

# ORGANON Douglas-fir (OP variant - highest yield)
stand = Stand.initialize_planted(400, 120, "DF", variant="OP")
stand.grow(years=50)
# ~323 TPA, 18.5" QMD, 601 BA, 28,395 ft³/ac

Thinning

stand = Stand.initialize_planted(500, 70, "LP", ecounit="M231")
stand.grow(years=15)
stand.thin_from_below(target_tpa=200)
stand.grow(years=35)

Yield Tables

from pyfvs import Stand

stand = Stand.initialize_planted(500, 70, "LP", ecounit="M231")
table = stand.grow(years=50, yield_table=True)
print(table)

Volume System

pyFVS uses a taper-based volume system matching NVEL (National Volume Estimator Library):

Merchandising supports Scribner Decimal C, International 1/4", and Doyle board-foot rules with per-log bucking.

Architecture

Stand.initialize_planted() --> Tree objects --> grow() cycles --> mortality / harvest
         |                         |
    StandMetrics              GrowthModels
    Competition               HeightDiameter
    Mortality                 CrownRatio
    HarvestManager            BarkRatio
    OutputGenerator           TaperVolume

Each Tree uses a size-dependent growth model:

• Small trees (DBH < 1"): Height-driven growth via Chapman-Richards
• Transition (1" - 3"): Weighted blend of small and large tree models
• Large trees (DBH > 3"): Diameter-driven growth via variant-specific DDS equations

Variant-specific diameter growth equations:

Configuration

Species parameters stored in YAML with variant-specific coefficient files in JSON:

src/pyfvs/cfg/
  species/*.yaml              # SN species configs (90 species)
  sn_*.json                   # SN variant coefficients
  ls/species/*.yaml           # LS species configs (67 species)
  ls/ls_*.json                # LS variant coefficients
  pn/, wc/, ne/, cs/, op/     # Other variant directories
  taper/                      # Taper model coefficients
    clark_r8_coefficients.json
    clark_r9_coefficients.json
    flewelling_coefficients.json

Testing

# Run all tests (~1000 tests)
uv run pytest

# Run specific variant tests
uv run pytest tests/test_ls_variant.py
uv run pytest tests/test_pn_variant.py
uv run pytest tests/test_taper.py

References

• FVS Documentation — USDA Forest Service
• FVS Essential Guide (GTR-WO-102) — Dixon (2023)
• Clark, A. et al. (1991). Stem profile equations for southern tree species. USDA-FS Research Paper SE-282.
• Flewelling, J.W. (1994). Stem form equation development notes. USDA-FS.
• Amateis, R.L. & Burkhart, H.E. (1987). Tree volume and taper. Forest Science 33(2).

Citation

@software{pyfvs2025,
  title = {pyFVS: Python Implementation of the Forest Vegetation Simulator},
  author = {Mihiar, Christopher},
  year = {2025},
  url = {https://github.com/mihiarc/pyfvs}
}

License

MIT