fvs-python 0.3.0

Python implementation of the USDA Forest Vegetation Simulator (FVS) with 10 regional variants, taper-based volume, and 500+ species configurations

pyFVS

Forest growth and yield simulation in Python

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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

Variant	Region	Species	Key Species	Volume Model
SN	Southern US	90	Loblolly Pine, Longleaf Pine, Slash Pine	Clark (R8)
LS	Lake States (MI, WI, MN)	67	Red Pine, Jack Pine, Sugar Maple	Clark (R9)
NE	Northeast (13 states)	108	Red Maple, Sugar Maple, Northern Red Oak	Clark (R9)
CS	Central States (IL, IN, IA, MO)	96	White Oak, Black Walnut, Yellow-Poplar	Clark (R9)
PN	Pacific NW Coast (WA, OR)	39	Douglas-fir, Western Hemlock, Sitka Spruce	Flewelling
WC	West Cascades (OR, WA)	37	Douglas-fir, Western Hemlock, Western Red Cedar	Flewelling
OP	ORGANON Pacific NW	18	Douglas-fir, Red Alder	Flewelling
CA	Inland California	—	White Fir, Ponderosa Pine	—
OC	ORGANON SW Oregon	—	Douglas-fir, Tanoak	—
WS	Western Sierra Nevada	—	White Fir, Giant Sequoia	—

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)

Age	TPA	QMD	Height	BA	Volume
0	500	0.5	1.0	0.7	0
10	485	4.2	28.5	47	892
20	420	7.8	52.1	140	3,241
30	310	10.4	68.3	183	5,128

Volume System

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

Model	Region	Method
Clark	Eastern (SN, NE, CS, LS)	3-segment profile with analytic integration
Flewelling	Western (PN, WC, OP)	4-segment variable-shape profile
Combined-variable	Fallback	V = a + b * D²H (Amateis & Burkhart 1987)

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:

Variant	Equation	Variables
SN	ln(DDS)	DBH, CR, RELHT, SI, BA, ecounit
LS, CS	DDS (linear)	DBH, CR, RELDBH, SI, BA, BAL
PN, WC	ln(DDS)	DBH, CR, RELHT, SI, BA, BAL, elevation, slope, aspect
NE	BA growth (iterative)	DBH, SI, BAL, CR
OP	ln(DG) direct	DBH, CR, SI, BA, BAL

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

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_{Built by Chris Mihiar}