Tree growth rates
Growth Rates of Selected Tree Species
We wanted to see how nutrient-enriched wastewater might influence the rate of growth of the three dominant tree species. To determine this, we needed to measure how big around some trees were and then remove cores from them. Cores are pieces of wood that are removed from the tree (they look like a pencil) that let us see how much growth occurs each year. The first figure shows that there was an increase in growth rate for all three tree species when exposed to wastewater. Although the increase was small for cottonwood and willow, there was a doubling of the growth rate in salt cedar. Next, we wanted to see if trees growing near to the wastewater channel were growing faster than trees far away. The reason for this question is that nutrient concentrations in groundwater (the water used by trees) should be higher near the channel and lower farther away.
The second figure shows that for cottonwood and willow, growth rates near the channel are more than twice that of trees growing far away from the channel. Salt cedar shows a greater growth rate far away, we are uncertain as to why this occurred. It is possible that salt cedar doesn't compete as well for the nutrients as does cottonwood and willow, so it must grow in less favorable conditions. More studies will help to address this issue. What these two figures tell us is that wastewater can be beneficial to the trees along rivers.