Scientific studies conducted in Giant Forest by Richard Hartesveldt showed that development harmed mature sequoias where major roots had been pruned for road or building construction. In other situations, little or no negative effects were detected on survival or growth rate of individual mature sequoias, at least in the short term. There were likely longer-term effects of development on mature sequoias that had not been detected. Hartesveldt found that soils under asphalt or in highly compacted areas were wetter and warmer than in natural sites. This increase in soil moisture and temperature may increase soil pathogens, contributing to root-rot and tree failure in the long term.

Continued development in Giant Forest would have greatly increased the overall negative effect on the health of mature sequoias. Replacing underground water and sewer systems would have required additional cutting of mature sequoia roots. Young giant sequoias, as well as many other trees, shrubs,and wildflowers, would fail to regenerate because of impacts to the soil and the absence of fire. Future generations would see a forest radically different from what we see today. Although the overall effect of development on the Giant Forest grove is strongly negative, Hartesveldt found that in some cases development increased the growth rates of mature sequoias in the short term. He attributed this increased growth in heavily used areas to higher soil moisture and temperature. Soils are wetter and warmer in developed areas because covering by asphalt and soil compaction help to maintain soil moisture deep in the rooting zone throughout the growing season, both by reducing evaporation from the soil and by preventing growth of competing vegetation. In addition, many of the competing trees surrounding monarch sequoias were cleared when buildings and parking lots were constructed, making a greater proportion of the limited soil moisture and nutrients available for the mature sequoias.