Simply put, the faster a tree grows and gains mass, the faster that tree increases wood product market value or environmental service value. Any tree species can be planted and harvested in 15 to 20 years, but not all tree species yield the same mass in that period of time (Figure 11).

Some conventional forestry systems cost very little to establish but do require long rotation times to yield value. Leaving land fallow to naturally regenerate with trees has low input costs but requires 60 to 80 years to yield wood-market product value. Economic structures to provide landowners revenue for the value can occur of the forest stand (forest carbon, water, wildlife habitat, and stormwater mitigation) are not yet universally available and potential loss of value due to extreme events. Tree species selection for short-rotation forests should be carefully considered for desired wood quality characteristics, biomass yields, services, market products, distance to market opportunities, and site conditions (Table 2).

Why Populus vs. other species?

For North Carolina, several tree species [poplar (Populus spp), willow (Salix spp.), pine (Pinus spp.), and American sycamore (Plananus occidentalis)] are often used for short-rotation forestry (Figure 12). Eastern cottonwood (Populus deltoides) is native to North Carolina and the Southeast. Unlike most genera, poplar species can interbreed and create interspecies crosses known as hybrids. Throughout the northern hemisphere, twenty-five or more poplar species provide a diverse genetic base from which tree breeders can create and evaluate hundreds of poplar clones or hybrid clones. Poplars from a specific breeding cross can be readily reproduced by harvesting and planting branch cuttings; these cuttings create a reproducible unique clone and is one distinct difference from other tree species that require seed collection and nursery production to create plantable trees. Poplars are an ideal candidate for short-rotation forestry because of the many clones that can be matched to site-specific conditions and ease of propagation once established (Figure 13).

Figure 12. Established plantation of bald cypress (left) and sycamore (center) at 25 years of age in the Piedmont area of North Carolina. Sweetgum plantation (right) at 6 years in the North Carolina coastal plain.

Figure 13. Hybrid poplar trees at two years (left) and at seven years (right) after establishment.