in the RCP 3.4 case, U.S. harvests increase by an average of 27% over a 100-year period, while harvests in Southeast Asia and Russia only increase by 6 and 2%, respectively.
The increased demand for woody biomass encourages changes in forest management along several margins that are typically ignored in traditional life cycle analyses. First, the area of intensively managed plantations increases by up to 61 million hectares (Mha), or 60%, over the baseline (Fig. 1C). These plantations have rotation ages ranging from 10 to 30 years and, thus, can be used to ramp up timber and biomass supply relatively quickly. We calculate that for every 1% increase in timber price, the area of plantations increases by 0.32% globally.
This section illustrates the difference between an efficient carbon management approach, which incentivizes both sequestration and
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Fig. 2. Mean change in total regional harvests relative to the baseline, 2010–2100.
the baseline (Fig. 1C). These plantations have rotation ages ranging from 10 to 30 years and, thus, can be used to ramp up timber and biomass supply relatively quickly. We calculate that for every 1% increase in timber price, the area of plantations increases by 0.32% globally.
Second, forests that currently have limited management become more intensively managed via increased investment in harvesting and replanting, thinning, fertilizing, and other actions. Every 100 million m3 of additional woody biomass energy supply could create 5.6 Mha of more intensively managed forests. Higher prices provide a market signal to landowners, who will take steps to increase their forest stocks via expanding the area in managed forests and/or improving management activities (18, 35). Expenditures on forest management could increase by an average of 230 per hectare on managed forests due to the increase in woody biomass demand, nearly 70% greater than the mean baseline expenditure estimate (Fig. 1F). Some of the land that we project that will become intensively managed is currently ecologically sensitive and/or high in biodiversity. Assuming that there are no other forest carbon sequestration incentives or forest conservation policies in effect, we estimate that if woody biomass demand rises to 4 billion m3/year, as under RCP 1.9, about 15% of global natural forest area, or 250 Mha, could be converted to a more intensive management regime (fig. S5). These results confirm that “standard” bioenergy policy targeting woody biomass generally has a negative impact on the world’s natural unmanaged or inaccessible forests. However, these natural forests will not be converted to agriculture, as economic incentives offset losses through planting forests managed at different degrees of intensity and avoided deforestation of managed forests (fig. S5).
Third, other land will be converted to forests and, thus, increase the absolute area of forests globally. The largest demand scenario (RCP 1.9) estimates a potential increase in forest area by 1.1 billion ha, 30% more than the current forest cover by 2100 (Fig. 1B). This is within the bounds of the recent paper by Bastin et al. (36), who identify an area of 1.6 billion ha of additional land that could support forests, of which 0.9 billion ha are located outside valuable cropland and urban regions. For this study, we used the 1.6 billion ha as an upper bound for our simulations, and in the sensitivity analysis, we tested the results under the more stringent 0.9 billion limit. The 1.1 billion ha estimate is large but not an outlier (fig. S6). Our results are confirmed by integrated assessment models (IAMs) with land modules and crop prices, which suggest that global forest area could increase by up to 1.0 billion and that about 5.4 billion ha could be covered by forests under the RCP 1.9 stabilization scenario with approximately 1.9 billion ha new forestland (31, 33).
While we do not explicitly model crop production or prices, our model incorporates land rental functions that require paying higher prices to rent land as more land is used for forests. The increases in rents that we project are consistent with other studies in the literature. Under the RCP 1.9 scenario, our global average land rents between now and 2100 are estimated to be four times higher than the baseline rents. Popp et al. (37) similarly shows that agricultural land for food and feed production declines as more land is used for bioenergy and carbon sequestration. They do not present estimates of land rents, but they do show that crop prices could be between two to six times higher than the baseline under a high mitigation scenario.