Final answer:
The growth rate of trees at different altitudes is influenced by the altitude above sea level, which affects temperature, moisture, net primary productivity, and aboveground biomass of the trees.
Step-by-step explanation:
The factor that influences the growth rate of certain trees at different altitudes is altitude above sea level. Altitude influences various abiotic factors that, in turn, affect tree growth. These include temperature and moisture, which are significant in determining plant productivity and biomass – both of which are indicative of growth rates in trees. As one ascends in altitude, temperature typically decreases and moisture patterns may change, leading to different biomes with distinct plant life adapted to those conditions.
For example, net primary productivity, which is the rate at which plants accumulate organic matter, can vary with altitude due to changes in temperature and moisture. Another example is variance in aboveground biomass, which refers to the total mass of living plants in an area, excluding the roots. Lower temperatures and different levels of moisture can reduce the biomass, thereby influencing the overall growth rate of trees.
Furthermore, factors such as increased or decreased evaporation rates related to changes in humidity can also be impacted by altitude. This alteration in water availability, combined with the likely changes in soil fertility and sunlight intensity, further impact plant growth.