pyFVS

Forest growth modeling in Python

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A Python implementation of the Forest Vegetation Simulator (FVS) supporting multiple regional variants. Simulate individual tree growth and yield across the United States.

Supported Variants

Variant	Region	Species Count	Key Species
SN	Southern US	90	Loblolly Pine, Shortleaf Pine, Longleaf Pine, Slash Pine
LS	Lake States (MI, WI, MN)	67	Red Pine, Jack Pine, Sugar Maple
PN	Pacific Northwest Coast	39	Douglas-fir, Western Hemlock, Sitka Spruce
WC	West Cascades (OR, WA)	37	Douglas-fir, Western Hemlock, Western Red Cedar
NE	Northeast (13 states)	108	Red Maple, Sugar Maple, Northern Red Oak
CS	Central States (IL, IN, IA, MO)	96	White Oak, Black Walnut, Yellow-Poplar
OP	ORGANON Pacific Northwest	18	Douglas-fir, Red Alder

Southern Yellow Pines (SN Variant)

Code	Species	Scientific Name
LP	Loblolly Pine	Pinus taeda
SP	Shortleaf Pine	Pinus echinata
LL	Longleaf Pine	Pinus palustris
SA	Slash Pine	Pinus elliottii

Quick Start

pip install pyfvs

from pyfvs import Stand

# Initialize a planted stand
stand = Stand.initialize_planted(
    species="LP",
    trees_per_acre=500,
    site_index=70
)

# Simulate 50 years of growth
stand.grow(years=50)

# Get results
metrics = stand.get_metrics()
print(f"Final volume: {metrics['volume']:.0f} ft³/acre")

Growth Models

pyFVS implements individual tree growth models from FVS documentation:

Height-Diameter (Curtis-Arney)

height = 4.5 + p2 × exp(-p3 × DBH^p4)

Large Tree Diameter Growth

ln(DDS) = β₁ + β₂×ln(DBH) + β₃×DBH² + β₄×ln(CR) + β₅×RH + β₆×SI + ...

Small Tree Height Growth (Chapman-Richards)

height = c1 × SI^c2 × (1 - exp(c3 × age))^(c4 × SI^c5)

Architecture

Tree Initial State
       │
       ▼
   DBH >= 3.0? ──No──► Small Tree Model
       │                    │
      Yes                   ▼
       │            Height Growth
       ▼                    │
  Large Tree Model          ▼
       │            Height-Diameter
       ▼                    │
  Predict ln(DDS)           ▼
       │              Update DBH
       ▼                    │
  Calculate DBH Growth      │
       │                    │
       └────────┬───────────┘
                ▼
        Update Crown Ratio
                │
                ▼
        Crown Competition
                │
                ▼
        Updated Tree State

Configuration

Species parameters are stored in YAML configuration files:

# cfg/species/lp_loblolly_pine.yaml
species_code: "LP"
common_name: "Loblolly Pine"
height_diameter:
  p2: 243.860648
  p3: 4.28460566
  p4: -0.47130185
bark_ratio:
  b1: -0.48140
  b2: 0.91413

Output

pyFVS generates yield tables with standard forest metrics:

Age	TPA	QMD	Height	BA	Volume
0	500	0.5	1.0	0.7	0
10	485	4.2	28.5	47.2	892
20	420	7.8	52.1	139.8	3,241
30	310	10.4	68.3	182.5	5,128
...	...	...	...	...	...

References

• FVS Southern Variant Documentation
• Bechtold & Patterson (2005) "The Enhanced Forest Inventory and Analysis Program"

Citation

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

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_{Built by Chris Mihiar}