Quantifying environmental limiting factors on tree cover using geospatial data

Area of Science:

• Ecology
• Environmental Science
• Forestry

Background:

• Environmental limiting factors (ELFs) define the thresholds for biological responses to environmental conditions.
• Quantifying ELFs typically requires large sample sizes, posing a challenge for ecological studies.

Purpose of the Study:

• To detect and spatially map ELFs influencing percent tree cover on the eastern slopes of the Lake Tahoe Basin.
• To determine the extent to which unmeasured environmental factors limit tree cover.

Main Methods:

• Utilized wall-to-wall geospatial data across a large spatial extent to ensure inclusion of rare data points.
• Tested mean temperature, minimum temperature, potential evapotranspiration (PET), and PET minus precipitation (PET-P) as potential ELFs.

Main Results:

• System-wide limitations on tree cover were observed, with temperature and evapotranspiration showing evidence of limitation.
• Only 1.2% of the study area was limited by the four tested environmental factors, indicating the influence of unmeasured factors.
• Non-forest sites (<25% tree cover) were limited by cold mean temperatures, open-canopy sites (25-60% tree cover) by evaporative demand, and closed-canopy forests showed no specific environmental limitation.

Conclusions:

• The detection of ELFs is crucial for understanding the full range of environmental limitations species face.
• Unmeasured environmental factors play a substantial role in limiting tree cover in the Lake Tahoe Basin.
• Specific environmental factors differentially limit tree cover depending on the existing canopy density.