October 3, 2016 Subject: Short-Rotation Trees Technical

MEMORANDUM

Date: October 3, 2016

Subject: Short-Rotation Trees Technical Memorandum

From: U.S. Environmental Protection Agency, Office of Transportation and Air Quality

To: Docket ID No. EPA-HQ-OAR-2016-0041

In this memo EPA details the lifecycle analysis (LCA) results and important considerations in support of the proposed determinations for short-rotation hybrid poplar and short-rotation willow in the Renewables Enhancement and Growth Support (REGS) proposed rulemaking. Detailed results and calculations of lifecycle greenhouse gas (GHG) emissions are provided in spreadsheets available in the docket.1

I. Introduction

This document focuses on our assumptions related to the various stages in the short- rotation hybrid poplar and short-rotation willow biofuel lifecycle, including fuel and feedstock production and distribution. The general system boundaries for lifecycle GHG analysis of biofuels under the Renewable Fuel Standard (RFS) program were determined as part of the RFS2 final rule.2 Applying these system boundaries to our analysis of biofuel produced from short- rotation hybrid poplar and short-rotation willow was straightforward because the lifecycle system for short-rotation hybrid poplar and short-rotation willow biofuels is similar to those of other biofuels that were analyzed in the RFS2 final rule.

To analyze the indirect agricultural and land use change impacts, we used the same agricultural economic models that were used for the RFS2 final rule. The Forest and Agricultural Sector Optimization Model (FASOM), developed by Professor Bruce McCarl of Texas A&M University and others, provides detailed information on domestic agricultural and GHG impacts of renewable fuels. The Food and Agricultural Policy Research Institute international models, maintained by the Center for Agricultural and Rural Development at Iowa State University (FAPRI-CARD), consist of a number of econometric models that provide detailed information on the impacts on international agricultural markets from the wider use of renewable fuels in the U.S.

1 See “Hybrid Poplar FASOM Data for the Docket.xlsx,” “Willow FASOM Data for the Docket.xlsx,” “Hybrid Poplar LCA Calculations.xls,” and “Willow LCA Calculations.xls,” available in Docket ID No. EPA-HQ-OAR- 2016-0041. 2 See 75 FR 14670 (March 26, 2010).

1 II. Background on Short-Rotation Hybrid Poplar and Short-Rotation Willow

A. Populus

The genus Populus contains poplar species of varying biological characteristics grown in several regions of the world including North America, Europe, and Asia. Populus is comprised of 25-30 species across six sections3 on the basis of leaf and flower characteristics. In addition to a bioenergy feedstock, they provide a variety of benefits including protection against erosion, serving as noise barriers, use as natural water pumps, for pulp production in the paper industry, and for production of transport packaging (Isebrands and Richardson, 2014). Combined with willows, poplars account for more than 95 million hectares (ha) of natural (82 million ha) and planted forest systems (13 million ha) globally (International Poplar Commission, FAO).

Natural hybridization within a given section of Populus is common; hybrids between taxa in the Aigeiros and Tacamahaca sections also occur readily in nature. Additionally, artificial hybridization efforts have been ongoing for decades to maximize desirable characteristics in a cultivar. The most common of these commercial hybrids is P. deltoides × P. nigra (P. × canadensis) (Isebrands and Richardson, 2014).

B. Salix

Salix is a diverse and much larger genus than Populus, comprising 330–500 willow species worldwide of deciduous or, rarely, semi-evergreen trees and shrubs (Argus, 1999). Willows are tolerant of a wider range of climates than poplars. Willows are predominantly found in temperate and arctic zones, with some occurrence in the subtropics and tropics; most willows grow in the northern hemisphere (Isebrands and Richardson, 2014). Physically, willows take on many forms. They occur as upright trees, shrubs, prostrate plants or groundcovers, with the majority of taxa occurring as shrubs. As is the case with Populus, a large number of Salix hybrids have been bred through artificial cross-pollination.

III. Modeling Assumptions

The FASOM model makes a number of assumption about the categories detailed below, which may affect the results of modeling short-rotation hybrid poplar and willow.

A. Land Coverage in FASOM

FASOM represents private timberlands and all agricultural activity across the conterminous (“lower 48”) United States, broken into 11 market regions. The model tracks both area used for production and idled (if any) within each land category (Beach 2010). The land use categories in FASOM are:

• Cropland is actively managed cropland, used for both traditional crops (e.g., corn and soybeans) and dedicated energy crops (e.g., hybrid poplar, willow, switchgrass).

3 “Section” is the taxonomic rank below genus and above species.

2 • Cropland pasture is managed pasture land used for livestock production, but which can also be converted to cropland production without additional improvement.

• Pasture is land used only for pasture or grazing that cannot be converted into cropland.

• Forestland contains a number of sub-categories, tracking the number of acres of private forestland existing at the starting point of the model that remain in standing forests (i.e., have not yet been harvested), the number of acres harvested, the number of harvested acres that are reforested, and the area converted from other land uses (afforested). Public forestland area is not explicitly tracked because it is assumed to remain constant over time, although exogenous estimates of forest products production from these lands are included in the model.

• Rangeland is unmanaged land that can be used for livestock grazing production. While the amount of rangeland idled or used for production may vary, it is assumed that rangeland may not be used for any other purpose than for animal grazing due to its low productivity. In addition, much of the rangeland in the U.S. is publicly owned.

• Developed (urban) land is assumed to have an inherently higher value than land used for any other use. Thus, the rate of urbanization is assumed to be exogenous based on projections of population and income growth and does not change between the cases analyzed.

• Conservation Reserve Program (CRP) refers to land that is voluntarily taken out of crop production and placed in the USDA CRP. Land in the CRP is generally marginal cropland retired from production and converted to vegetative cover, such as grass, trees, or woody vegetation to conserve soil, improve water quality, enhance wildlife habitat, or produce other environmental benefits.

This allocation of land types has been updated since the RFS2 final rule, and has been employed for more recent EPA analyses (e.g., grain sorghum). Hybrid poplar and willow are grown on “cropland” in FASOM, where they can compete with traditional crops as well as other energy crops (e.g., switchgrass). While we are defining hybrid poplar and willow as “planted trees,” which come from “tree plantations,” per the renewable biomass definition, they are not grown on forestland as it is characterized in FASOM. The assumption in FASOM that hybrid poplar and willow will be cultivated on agricultural lands and not forest lands is consistent with historical data and expectations for future patterns. We expect that future production of hybrid poplar and willow will be on less productive agricultural land because they are unlikely to generate the returns per acre needed to economically compete with other options on more productive agricultural (or forest) lands. Current research is consistent with the assumption that hybrid poplar and willow will be produced on less productive agricultural land. For example, demonstration plots of hybrid poplar, primarily in the states of Washington, Oregon, and Minnesota, are being developed on less productive agricultural lands as are willows in upstate

3 New York through the Willow Project at SUNY-ESF, which is the largest dedicated willow operation in the United States with over 1100 acres planted.4

B. Representation of Short-Rotation Hybrid Poplar and Short-Rotation Willow in FASOM

Hybrid poplar and willow are unique in FASOM in that their end products can be allocated to either the forest sector in the form of pulp, or the agricultural sector in the form of bioenergy feedstock. Other crops represented in FASOM can only be consumed in one sector or the other (i.e., there is no means for agriculture to be consumed in the forest sector, and no means for forest products to be consumed in agriculture). If the price of pulp products reaches a certain level, FASOM will cultivate hybrid poplar and willow systems to help generate pulp supply. However, this does not occur to any appreciable degree as the returns for hybrid poplar and willow are inferior under normal circumstance. We allowed for the possibility of hybrid poplar and willow to contribute supply for the forest sector in our modeling, but none of this supply occurred.

On the agricultural side, hybrid poplar and willow are allowed to compete with annual crops in FASOM. In order for them to be widely adopted, they need to provide high enough returns to farmers to induce them to switch from alternative land uses to hybrid poplar and willow. Under baseline conditions, there is very little willow or hybrid poplar acreage5 due to the relatively poor opportunity for returns.

There are two additional assumptions in FASOM that distinguish hybrid poplar and willow (and other dedicated energy feedstocks) from other agricultural crops.

First, by definition in FASOM, perennial crops such as switchgrass, hybrid poplar, and willow are produced under zero tillage. This is a reasonable assumption because perennial crops are not tilled on an annual basis, resulting in less soil disturbance relative to annual crops. For example, a short-rotation willow coppice growth system in New York State can go over 20 years between site reestablishment (up to 7, 3-4 year cycles).6 This has important implications for the amount and timing of carbon released from soils. The longer rotation length of short-rotation trees results in greater carbon accumulation in soil and below-ground biomass (i.e., roots). Further, in FASOM willow and hybrid poplar are assumed to be produced under non-irrigated conditions and do not compete for irrigation water.

Second, in FASOM, the maximum concentration of hybrid poplar or willow is constrained at 10% of agricultural lands in a given region to reflect their nascent stages of development, and limitations for large scale deployment given their relative returns against other crops.

4 Willow Brochure. The Willow Biomass Project. State University of New York – College of Environmental Science and Forestry (SUNY-EST). http://www.esf.edu/pubprog/brochure/willow/willowbrochure.pdf 5 In the baseline in 2022, there are 0 acres of willow and 33,000 acres of hybrid poplar in production. 6 Willow Biomass Crop Production Cycle. Heavey, Justin P., Volk, Timothy A. 2015. The Willow Project at SUNY- ESF http://www.esf.edu/willow/documents/6CropProductionCycle.pdf

4 Another noteworthy update that has been made in FASOM since the RFS2 final rule was completed is the addition of “storage loss” representation for all feedstocks. Storage loss was included to more accurately reflect the realities of agricultural and forestry supply-chains. Storage loss is assumed to occur between field and bio-refinery, including both indoor and outdoor storage at either site. Storage loss in this circumstance also considers loss due to fermentation and carbohydrate breakdown. The amount of storage loss assumed in FASOM is 4% for all feedstocks. This translates to an additional 4% of feedstock quantity required to produce a given quantity of biofuel. This assumption is based off of work by Kim (2011).

C. Agricultural Inputs and Yields

The yields of hybrid poplar and willow are different in each region of the model. Because the model produced additional hybrid poplar or willow only in the regions with the highest yields, we present only those yields here. The Pacific Northwest East had the highest hybrid poplar yield of 6.62 wet tons per acre per yr in 2022.7 This was calculated by assuming a yield of 5.8 wet tons per acre per yr in 2000 (Walsh et al. 2003) and a yield growth of 1% per year starting in 2010.8 The 2020 yield was used for 2022. The dry matter content of hybrid poplar was assumed to be 69%, so the dry matter yield in 2022 is 4.57 dry tons per acre per yr. Our assumed yield is within the range of yields estimated by more recent studies of hybrid poplar, which used climate and soil data to predict productivity. In Wisconsin and Minnesota, Zalesny et al. (2012) estimated a yield of 9.5 to 11.9 dry Mg per ha per yr (4.2 to 5.3 dry tons per acre per yr), with a mean of 10.0 dry Mg per ha per yr (4.5 dry tons per acre per yr). In the same region, Headlee et al. (2013) estimated a yield of 4.4 to 13.0 dry Mg per ha per yr (2.0 to 5.8 dry tons per acre per yr). Because these yields ranges are based on model assumptions, we used a value on the lower end of the range as a conservative estimate.

The assumed willow yield was highest in the Northeast, at 5.47 wet tons per acre. This was also calculated by starting with the 2000 yield of 4.8 tons per acre from Walsh et al. (2003), and assuming a yield growth of approximately 1% per year starting in 2010.9 The dry matter content was assumed to be 66.7%, so the dry matter yield is 3.65 dry tons per acre. A 2010 study by Bucholz and Volk modeled willow profitability, and used a base yield of 12 oven-dried tons (odt) per ha per yr (4.9 odt per acre per yr) in their model, and also tested yields from 7.5 to 25 odt per ha per yr (3.0 to 10.1 odt per acre per yr). These yields are based on information on farming practices in New York. A 2014 update to this model, using more recent data on willow production in North America, assumes a yield of 10 wet tons per acre per yr with an assumed moisture content of 45% (5.5 dry tons per acre per yr).10 Our assumed yield is on the low end of the range used in these models, and therefore provides a conservative assumption of willow yield.

7 In FASOM, the Pacific Northwest East Region consists of Washington and Oregon east of the Cascade Mountains. 8 Alig et al. (2000) also assume a short-rotation hybrid poplar yield increase of 1% per year from 2005-2030, based on data from Oak Ridge National Laboratory. 9 This is the same yield increase as we assumed for hybrid poplar. Neuhauser et al. (1996) suggest that willow yield could increase by 50% over time. 10 See “Crop Production Scenarios Using EcoWillow 2.0” and “Summary of Updates to EcoWillow 2.0” available at: http://www.esf.edu/willow/download.htm. Accessed February 9, 2016.

5 Agricultural input assumptions for the hybrid poplar in the Pacific Northwest East and willow in the Northeast are shown in Table 1. Diesel use is supported by the ranges reported by Spineli et al. (2012) for hybrid poplar (6-10 lbs per acre), and Heller et al. (2003) and Stolarski et al. (2014) for willow (6 gal per acre and 5-17 gal per acre, respectively). Nitrogen fertilizer use for hybrid poplar and willow is consistent with the fertilizer application (60 kg N/ha, or 54 lb N/acre) that gave the highest yield for willow in Sevel et al. (2014), and is the value recommended by Aronsson et al. (2014).

Table 1: Yield and Input Assumptions for Hybrid Poplar and Willow in Model Region with the Highest Yield Hybrid Poplar Willow (Pacific Northwest East) (Northeast) Yield (wet tons per acre per yr) 6.62 5.47 Dry matter content 69.0% 66.7% Nitrogen fertilizer (lbs N per acre) 54 54 Diesel (gal per acre) 4.8 7.7

D. Fuel Production

We analyzed three types of fuel production processes: enzymatic, thermochemical, and Fischer-Tropsch (F-T). These processes produce either ethanol or diesel. We assumed that the fuel yield per ton of feedstock and the energy balance would be the same for hybrid poplar and willow as for switchgrass (Table 2). Fuel yields for different production processes are from Tao and Aden (2008). According to Aden (2009), the expected ethanol yield of hybrid poplar should be higher than that for switchgrass, because of the greater cellulose content of hybrid poplar relative to switchgrass. Aden estimated an ethanol yield of 94.6 gallons/ton for hybrid poplar and other farmed trees. However, we used the lower switchgrass yields as a conservative estimate. We also assumed that enzymatic production of fuel results in excess electricity sold to the grid, because lignin from the feedstock is used to produce electricity. The energy balance was combined with emission factors from The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model11 to calculate the upstream and on-site emissions associated with fuel production.

11 Energy Systems, Argonne National Laboratory. https://greet.es.anl.gov/index.php

6 Table 2: Energy Balance and Fuel Yield for Fuel Production Biomass Diesel Fuel Purchased Sold Use Use Electricity Electricity (BTU/gallon (BTU/gallon (BTU/gallon (BTU/gallon Fuel Yield Fuel Production fuel fuel fuel fuel (gallons/ton Process produced) produced) produced) produced) feedstock) Cellulosic Ethanol – 102,734 337 -- 18,391 92.3 Enzymatic Cellulosic Ethanol – 90,935 177 -- -- 74.9 Thermochemical Cellulosic Diesel 168,220 327 17 -- 58.6 – F-T

IV. LCA Analysis Results

A. Domestic Emissions

1. Hybrid Poplar

In order to produce 400 million gallons of biofuel in 2022, FASOM projects that approximately 6.3 million tons of additional hybrid poplar will be produced. All of the additional production is in the Pacific Northwest East, which is the region with the highest hybrid poplar yield.

In FASOM, hybrid poplar is treated like an agricultural crop, and must be grown on cropland. The scenario we ran requires 948,000 additional acres of cropland for hybrid poplar. Most of this land comes from cropland for other crops, but there is also some conversion of cropland pasture and forests to cropland (Table 3). The total national increase in cropland in 2022 including active and idle land is 129,000 acres.

Table 3: Change in National Land Cover in 2022 – Hybrid Poplar Scenario Land Type Thousand Acres Cropland for hybrid poplar 948 Cropland for other crops -688 Idle cropland -131 Active cropland 260 Pasture 44 Cropland pasture -116 Forest -57

In the Pacific Northwest East, there is no change in total cropland acres. Hybrid poplar acres increase at the expense of wheat, barley, and hay. As a result, production of wheat shifts to the Rocky Mountains and Great Plains, barley shifts to the Pacific Southwest and Rocky Mountains, and hay shifts to the Great Plains, Great Lake States, and Southwest. However, the

7 total national wheat production decreases (Table 4). As a result, exports of wheat decrease. In addition, prices of barley and wheat increase by up to 6.6% in 2022.

Table 4: Changes in Production, Exports, and Prices of Major Crops Production change Export change Crop (million tons) (million tons) Price change (%) Corn -0.007 -0.028 0% Soybeans -0.027 -0.027 0% Barley -0.094 -0.004 6.4% Wheat -0.520 -0.524 -0.9-6.6%a a Range of price changes for four types of wheat (soft white wheat, hard red winter wheat, soft red winter wheat, and hard red spring wheat).

Domestic land use change emissions are -2,481 g CO2e/mmBTU ethanol. Some of the decreased emissions are because conversion from annual crops, like wheat, to hybrid poplar leads to the greater amounts of belowground biomass and greater carbon storage in undisturbed soil than with the production of annual crops. Some of the decreased emissions are also due to forest intensification. The decrease in forest acres causes pressure on forest resources, which results in intensification on remaining forest acres and net carbon sequestration. Because of FASOM’s forward-looking approach, land-owners maximize returns over the lifetime of the simulation, not just in a given time period. For forest systems with temporal dynamics (versus an annually rotated agricultural crop), this means that decisions of how intensively to manage stands and harvest rotation lengths can be impacted. In our results, forest plantations in the Southcentral U.S. experience pressures, current and future, on forest lands from the expansion of willow and hybrid poplar acres in the agricultural system. The model responds to the expected pressures on forest inventories by enhancing inventories in the near term to meet later demand, leading to an increase in total forest carbon stocks in 2022.

In 2022, there is slightly increased production of broiler chickens (0.2%), and decreased production of beef (-0.1%). The emissions due to domestic livestock are -1,049 g CO2e/mmBTU ethanol.

FASOM also calculated emissions from rice methane, farm inputs, and fertilizer N2O under the hybrid poplar scenario. These emissions can be found in a spreadsheet available in the docket.12

2. Willow

FASOM projects that approximately 6.5 million tons of additional willow will be needed to produce 400 million gallons of biofuel in 2022. All of the additional production is in the Northeast, which is the region with the highest willow yield.

Like hybrid poplar, willow is grown on cropland in FASOM. In 2022, the production of 6.5 million tons of willow requires 1.2 million acres of cropland. Also, like hybrid poplar, this

12 See “Hybrid Poplar LCA Calculations.xls,” available in Docket ID No. EPA-HQ-OAR-2016-0041.

8 cropland comes from cropland for other crops as well as conversion of cropland pasture and forest to cropland (Table 5). The total national increase in cropland in 2022 including active and idle land is approximately 303,000 acres.

Table 5: Change in National Land Cover in 2022 – Willow Scenario Land Type Thousand Acres Cropland for willow 1,187 Cropland for other crops -824 Idle cropland -60 Active cropland 363 Pasture 172 Cropland pasture -262 Forest -212

In the Northeast, there is a small (2000 acre) expansion of cropland. There is a reduction in cropland devoted to hay, soybeans, corn, and wheat. Production of these crops shift to the Great Plains (for corn and soybeans), but the total national production decreases (Table 6). Exports of corn, soybeans, and wheat also decrease. Prices of corn, soybeans, and wheat increase by less than 2%.

Domestic land use change emissions are -2,596 gCO2e/mmBTU ethanol. Willow domestic land use change emissions decrease for the same reasons as hybrid poplar.

Table 6: Changes in Production, Exports, and Prices of Major Crops Production change Export change Crop (million tons) (million tons) Price change (%) Corn -1.224 -0.931 1.56% Soybeans -0.226 -0.226 0.38% Barley 0.034 0 -0.38% Wheat -0.115 -0.093 -0.87-0.53%a a Range of price changes for four types of wheat (soft white wheat, hard red winter wheat, soft red winter wheat, and hard red spring wheat).

In 2022, there is 0.2% increased production of broiler chickens while the production of beef decreases by 0.1%. The emissions due to domestic livestock are 948 g CO2e/mmBTU ethanol.

FASOM also calculated emissions from rice methane, farm inputs, and fertilizer N2O under the willow scenario. These emissions can be found in the spreadsheet available in the docket.13

13 See “Willow LCA Calculations.xls,” available in Docket ID No. EPA-HQ-OAR-2016-0041.

9 B. International Emissions

We based the international emissions associated with hybrid poplar and willow on the switchgrass analysis in the RFS2 final rule. Switchgrass, short-rotation hybrid poplar, and short- rotation willow are all energy crops, and are expected to grow on the same types of land and cause the same types of crop displacement. For analysis of hybrid poplar and willow, we started with the switchgrass international emissions from land use change, farm inputs, livestock, and rice methane. We converted these emissions from g CO2e/mmBtu to g CO2/acre using the yield of switchgrass per acre (7.8 tons/acre), the percent dry matter content (88.01%), and the yield of fuel per ton of switchgrass (see Table 2). We assumed that the international emissions per acre of U.S. production would be the same for hybrid poplar and willow as for switchgrass. We then converted the emissions per acre to emissions per mmBTU using the yield and percent dry matter of hybrid poplar and willow (Table 2). The international emissions are shown in spreadsheets available in the docket.14

C. Fuel Production

The emissions associated with fuel production from hybrid poplar and willow feedstocks range from -53,116 g CO2eq/mmBtu for ethanol produced via an enzymatic process to 835 g CO2eq/mmBtu for Fischer-Tropsch diesel. Enzymatic ethanol production results in lignin that can be burned to produce electricity. As shown in Table 2, we assumed that this results in large amounts of sold electricity, for which there is an emissions credit. Thermochemical ethanol and Fischer-Tropsch diesel processes do not result in sold electricity. We assumed that the Fischer- Tropsch process uses more fuel inputs than the thermochemical process, resulting in higher emission. Calculations and emission factors are available in the spreadsheets available in the docket.15

D. Sensitivity Analysis

To test the sensitivity of the results to the amount of ethanol production, we ran additional scenarios where short-rotation hybrid poplar or willow produced 200 MG of ethanol rather than 400 MG. In these scenarios, short-rotation hybrid poplar or willow were produced in the same regions as the 400 MG scenarios. There were also similar changes in the production of other crops and in the shifting of land from cropland-pasture and forest to cropland. These scenarios also resulted in similar lifecycle GHG impacts. Spreadsheets with data from these scenarios are provided in the docket. 16

14 See “Hybrid Poplar LCA Calculations.xls” and “Willow LCA Calculations.xls,” available in Docket ID No. EPA- HQ-OAR-2016-0041. 15 See “Hybrid Poplar LCA Calculations.xls” and “Willow LCA Calculations.xls,” available in Docket ID No. EPA- HQ-OAR-2016-0041. 16 For data and calculations from the 200 MG scenario runs, see “Hybrid Poplar 200MG LCA Calculations.xls,” “Willow 200MG LCA Calculations.xls,” “Hybrid Poplar 200MG FASOM Data for the Docket.xlsx,” and “Willow 200MG FASOM Data for the Docket.xlsx,” available in Docket ID No. EPA-HQ-OAR-2016-0041.

10 V. Definitions of Short-Rotation Hybrid Poplar and Short-Rotation Willow

There are three key components to the definition of qualifying short-rotation hybrid poplar and willow that EPA is proposing. One – which applies to all biofuel feedstocks under the RFS – is related to the renewable biomass definition, which is enumerated in 40 CFR 80.1401, and described in more detail in Section V.B below. Two, EPA is proposing to permit a specific set of species within these two genera as qualifying for renewable fuel feedstocks under the RFS. In Section V.A we provide background on the species and further detail on why we think including subsets of the species Populus and Salix is appropriate. Three, the definitions of short- rotation hybrid poplar and willow that we are proposing include a 10 year limit on the rotation length of the feedstock used.17 We included this provision for the following reasons.

In our analysis, we only consider hybrid poplar and willow grown in short-rotations of seven years. The results of the analysis are reflective of these systems. Therefore, we do not believe our analysis captures the impacts of traditional forest systems. Longer rotation forest systems –with 30 plus year harvest rotations –have different lifecycle characteristics which can produce very different GHG implications. For one reason, over longer periods of time, trees grow and accumulate greater amounts of carbon. If forest owners change their harvest schedules due to economic, policy, or environmental circumstances, there can be large changes in the amount of terrestrial carbon stored or released. For this reason, it is important to think about traditional forest systems, and the consequential amount of carbon stored in them, through a more dynamic approach. For short-rotation systems, the potential fluctuations in terrestrial carbon is limited; there is not a large, potentially volatile, stock of carbon that could be released depending on economic or policy circumstances. We are thus drawing a clear line between short- rotation and longer rotation hybrid poplar and willow systems in our proposed determination and believe a 10 year limit on rotation lengths is a reasonable place to make the distinction.

A. Qualifying Species

Given the great diversity of biological characteristics as well as cultivation practices existing among the Populus and Salix species, as described Section I, we think it is appropriate to define a subset of the species as qualifying biofuel feedstock under the RFS program so as not to include species with characteristics different than what we have considered. The basis for the set of species and crosses EPA is proposing to determine as qualifying is primarily those species and crosses that have already been researched for bioenergy purposes. By nature, these are species and crosses that exhibit qualities desirable in a feedstock such as high growth rates (e.g., P. deltoides, S. purpurea), disease and insect tolerance (e.g., P. deltoides x P. nigra, S. purpurea, S. caprea hybrid), and coppicing ability (e.g., S. eriocephala, S. viminalis). These are qualities that are also desirable from a GHG and environmental perspective, as the ability to grow rapidly augments carbon sequestration, while robust rooting systems enhances soil retention.

Other species may not possess these characteristics, which could result in greater LCA GHG emissions if used as a bioenergy feedstock. Also, there could be crosses yet to be developed that would display undesirable and new characteristics, beyond what we have

17 For coppice systems, we consider the rotation lengths as reset after each cut (i.e., if a willow is harvested after 10 years and regrown from coppice, in another 5 years we consider the rotation length to be 5 years, not 15 years).

11 analyzed. Therefore, we think it is appropriate to include a subset of Populus and Salix species and crosses between them as specified In Section IV.D.2 of the REGS preamble, rather than the entire Populus and Salix genera.

B. Renewable Biomass Provisions

To qualify as an allowable feedstock under the RFS, short-rotation hybrid poplar and willow must be grown on land that was actively managed on December 19, 2007, per the RFS program definition of renewable biomass in 40 CFR 80.1401. By these requirements, short- rotation hybrid poplar and willow are “planted trees” that are grown on “tree plantations” – a stand composed primarily of trees established by hand- or machine-planting of a seed or sapling, or by coppice growth from the stump or root of a tree that was hand- or machine-planted. This definition excludes hybrid poplar and willow grown on land that was naturally forested or not actively managed on December 19, 2007, which would not meet the RFS program definition of renewable biomass at 40 CFR 80.1401.

There are a number of different types of land that may be suitable to grow hybrid poplar on from an agronomic or economic perspective, but that would not align with the RFS regulatory definition for renewable biomass. For example, all of the following types of land would not meet the renewable biomass definition (note, this is not intended to be an exhaustive list):

• Land that was not previously cleared or cultivated prior to December 19, 2007. • Land that was naturally forested on December 19, 2007. • Land that was not actively managed on December 19, 2007.

C. Cellulosic content

For hybrid poplar and willow-derived biofuels to qualify as cellulosic biofuel under the RFS program, the fuel must achieve a 60% lifecycle GHG reduction as compared to the 2005 baseline fuels, and must also be derived from cellulose, hemicellulose, and lignin.18 In the Pathways II rule,19 EPA determined that fuel generated from feedstocks with an average adjusted cellulosic content20 of 75% or more is eligible to generate cellulosic biofuel RINs for the entire fuel volume. In that rulemaking, EPA also explained that we would apply the 75% threshold to feedstocks that we evaluated in the future. Consistent with that rulemaking, we have evaluated the cellulosic content of hybrid poplar and willow. Data and calculations can be found in the spreadsheet posted to the docket.21

In the Pathways II rule, we provided data showing that the average adjusted cellulosic content of wood, based on data from several types of trees, is 92%.22 Table 7 shows the

18 For simplicity, these three chemicals are hereafter referred to as “cellulose,” and their presence in feedstock as the feedstock’s “cellulosic content.” 19 See 79 FR 42128 (July 18, 2014). 20 Adjusted cellulosic content is the percent of organic material that is cellulose, hemicellulose, and lignin. 21 See “Hybrid Poplar and Willow Cellulosic Comp.xlsx,” available in Docket ID No. EPA-HQ-OAR-2016-0041. 22 See “Cellulosic Content of Various Feedstocks – 2014 Update,” available in Docket ID No. EPA-HQ-OAR-2012- 0401.

12 cellulosic content for hybrid poplar and willow. The data show that both hybrid poplar and willow contain well above the minimum 75% adjusted cellulosic content.

Table 7: Composition of Hybrid Poplar and Willow, Including Percentages as Reported (Raw and Unadjusted) for Total Cellulosic Content, Other Organic Materials, and Inorganics (Ash). Reported Composition Adjusted Cellulosic Other Inorganics Cellulosic Content Organics (Ash) Content23 Source Hybrid Poplar 89% 4% 1% 96% DOE Database Willow 91% n.d. 2% 93% Sassner et al. (2006)

VI. References

• Aden, A. 2009. “Feedstock Considerations and Impacts on Biorefining.” National Renewable Energy Laboratory (NREL).

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