Hybrid poplar plantations are becoming increasingly important as a source of income for farmers in northwestern Spain, as rural depopulation and farmers aging prevent landowners from planting other labor-intensive crops. However, plantation owners, usually elderly and without formal forestry background, lack of simple tools to estimate the size and volume of their plantations by themselves. Therefore, farmers are usually forced to rely on the estimates made by the timber companies that are buying their trees. With the objective of providing a simple, but empowering, tool for these forest owners, simple equations based only on diameter were developed to estimate individual tree volume for the Órbigo River basin. To do so, height and diameter growth were measured for 10 years (2009–2019) in 404 trees growing in three poplar plantations in Leon province. An average growth per tree of 1.66 cm year−1 in diameter, 1.52 m year−1 in height, and 0.03 m3 year−1 in volume was estimated, which translated into annual volume increment of 13.02 m3 ha−1 year−1. However, annual volume increment was different among plots due to their fertility, with two plots reaching maximum volume growth around 11 years since planting and another at 13 years, encompassing the typical productivity range in plantations in this region. Such data allowed developing simple but representative linear, polynomial and power equations to estimate volume explaining 93%–98% of the observed variability. Such equations can be easily implemented in any cellphone with a calculator, allowing forest owners to accurately estimate their timber existences by using only a regular measuring tape to measure tree diameter. However, models for height were less successful, explaining only 75%–76% of observed variance. Our approach to generate simplified volume equations has shown to be viable for poplar, but it could be applied to any species for which several volume equations are available.

Hybrid poplar plantations are becoming increasingly important as a source of income for farmers in the Duero Basin (northwestern Spain), as rural depopulations and aging prevent farmers from planting other labor-intensive crops. However, forest owners, usually elderly and without formal forestry backgrounds, lack simple tools to estimate the size and volume of their plantations by themselves. Therefore, farmers are usually forced to rely on the estimates made by the timber companies that are buying their trees. With the objective of providing a simple but empowering tool for these forest owners, simple equations based only on the diameter to estimate individual tree height and volume were developed for the region. To do so, growth in height, diameter, and volume were measured for 10 years (2009–2019) in 404 trees planted in three poplar plantations in Leon province (northern Spain). An average growth per tree of 1.66 cm year−1 in diameter, 1.52 m year−1 in height, and 0.03 m3 year−1 in volume was estimated, which translated into annual volume growth of 13.02 m3 ha−1 year−1. However, annual volume growth was different among plots due to their fertility, with two plots reaching maximum growth around 13 years of tree age and another at 15 years, encompassing the typical productivity range in plantations in this region. Such data allowed developing simple lineal, polynomic, and power equations to estimate height and volume explaining 76% to 97% of the observed variability. Such equations can be easily implemented in any cellphone with a calculator, allowing forest owners to accurately estimate their timber existences by using only a regular measuring tape to measure tree diameter.