How Does Soil and Climate Impact the Forest Investor?
Derek Dougherty - Saturday, April 27, 2019
For this blog, I want to highlight some operationally applicable collaborative work completed through the University of Tennessee. A recent study published by Perdue et al. in the August 2017 edition of Forest Policy and Economics and titled, “Profitability potential for Pinus taeda L. (Loblolly Pine) Short-rotation bioenergy plantings in the Southern USA“, highlights and summarizes the impacts of both soil and climate on loblolly pine biomass production and economic feasibility in the southeast US. As an investor, more fully understanding the impacts of soil and climate on growth is important because 1) we can choose where we invest in timberland, and 2) it allows us to frame the operational expectations for the land that we already own or manage. Coupling the estimates of soil and climate based potential with forest product market levels, genetic options, silvicultural options and associated contractor availability and costs, allows us to make strong estimates of investment return potential.
At the foundational-level of the published biomass profitability project are summarized process model (utilizing 3-PG) yield estimates that we completed in-house at our Center of Forestry Research and Applied Management. The model estimates consider a myriad of detailed climate variables, species specific growth variables, and a matrix of soil texture and slope impacts on water and nutrient availability. The 3PG model (Landsberg and Waring, 2001) has been effectively used for modeling the growth of many species around the globe and was pivotal for the full UT biomass project which included not only evaluating the feasibility of loblolly pine for biomass feedstock, but also that of using willow, cottonwood, Eucalyptus benthammii and E. grandis.
The loblolly pine model runs utilized a non-thinned regime planting of around 500 trees per acre and grown for 14 growing seasons before final clearcut. The estimated annual biomass production (dry weight tons) for operationally intensive loblolly pine plantations grown on a lowland clay soil are summarized for visual review in Figure 1
below. Here, with the soil type and slope position fixed, you can see the relative effects of regional climate on yield potential. In general, the coastal sites have increased growth potential as compared to the more inland, ‘continental’ sites. Another trend is for the growth potential to increase going from north to south. Both trends make good sense. Coastal sites generally receive increased frequency of and amounts of rainfall, and increased cloudiness, all of which decrease evaporative demand and reduce growing season water deficits. Also, the farther north you go, the growing season days decrease.
What should further jump out at you is just how strong operational production growth potential is across almost our entire southeast US operational loblolly pine range. Excepting in those extreme areas along the western and northern fringes, operational potential generally ranges from 4 to 8 dry tons of biomass per acre per year, which would convert to around 8 to 16 green tons/acre/year of pulpwood production. This assumes that great silviculture is prescribed and executed and also assumes that the land manager has access to exceptional genetic and morphological seedling stock.
Figure 2 here shows the productivity potential for the same geographic areas, but this time for a sandy textured, upland soil, i.e. the opposite end of the soil productivity spectrum. Here the estimated productivity for the range falls to 3 to 7 dry tons/acre/year; or basically 6 to 14 green tons/acre/year. This decrease in growth potential due to a soil texture gradient (changing from clay to sand) and slope position (from lowland to upland) makes intuitive sense as well, with the coarser sand particles holding less nutrients and water, and the better drained uplands having increased past erosion and lessened soil depth and water holding capacity.
The productivity levels estimated here are for operationally intensive production. They are below the absolute full potential of the species but above that of extensive (low intensity) forest management. So, intensity and execution quality matter. Realized growth rates below potential are generally due to falldown in some area, i.e. either missed site analyzation, less-than-optimal silviculture prescription or genotype allocation, or poor activity execution. But what about if you are growing on a sawtimber regime with one or more thinnings? In those cases, the anticipated yield drops by some percentage depending on the initial planting density, the post-thinning residual basal area, the mid-rotation competition, nutrient management, and the length of rotation. But on average, the decrease may be around 20-40% from the biomass production potential estimated here in these attached figures.
In conclusion, our production potential is generally greater than believed and greater than often achieved. Projects like these centered at the University of Tennessee and published for the forestry community empower investors to benchmark their production within a region when operating on specific soil types and slope positions. They further empower investors to quantify and subsequently manage production fall-down.
Optimizing the strategy, execution, and ‘fall-down’ management is the business of forestry. For the investor, the business is just as crucial as the biology of forestry. Welcome to FORTE’s Progressive Forest Investor’s Blog!
Derek Dougherty, Director
Forest Owners Research & Technology Exchange, LLC
References
Landsberg, J., Waring, R., 2003. Performance of the forest productivity model 3-PG applied to a wide range of forest types. Forest Ecology and Management 172:199-214
Perdue, J., Stanturf, J., Young, T., Huang, X., Dougherty, D., Pigott, M., Guo, Z., 2017. Profitability potential for Pinus taeda L. (loblolly pine) short-rotation bioenergy plantings in the southern USA. Forest Policy and Management 83: 146-155
Figure 1. Estimated loblolly pine plantation biomass productivity (oven-dry tons) for Lowland Clay soils across the Southeast US Loblolly pine range. *Assumes operationally intensive management for 500 TPA, non-thinned, 14- year rotation regime.
Figure 2. Estimated loblolly pine plantation biomass productivity (oven-dry tons) for Upland Sand soils across the Southeast US Loblolly pine range. *Assumes operationally intensive management for 500 TPA, non-thinned, 14- year rotation regime.
