Future Work

While my work has shown that perennial biofuel crops should be a central consideration in land management strategies due to their potential for increasing global productivity and mitigating climate change, there are still several aspects of land management choices that deserve further investigation.

Using intentional LUC such as planting perennial biofuel crops needs to be carefully vetted. This effort should include mutually supportive model simulations and field observation campaigns. Field experiments should be chosen based on areas of uncertainty or unexpected findings from regional model simulations. Data from field experiments should then be used to make the model parameterizations more realistic.

A library of sustainable climate-smart scenarios should be developed that include various permutations of crop varieties, planting locations, and agronomic details. These will include an outline of best management practices including planting density, planting and harvest dates, fertilizer and irrigation levels, and tillage type. These suggestions will be tailored by region, future climate scenario, and agro-economic situation. Climate-mitigation guidance could also be included, such as when to harvest perennial biofuel crops so as to take advantage of surface cooling via higher snow albedo but without removing the crop before it’s able to translocate vital nutrients to below ground (Miller et al., 2015).

Among the future scenarios that are imperative to understand, hydroclimate shifts caused by climate or LUCs are of particular concern to the future of agro-ecosystems. Currently the

majority of agricultural land is not irrigated and so relies on precipitation, yet precipitation patterns are likely to change and become more unpredictable (Andresen et al., 2013; Rosenzweig et al., 2002; Wuebbles & Hayhoe, 2004). Expanding irrigation is logistically difficult in some regions and economically or environmentally too costly in other regions (Foley, 2005). Therefore, details regarding changes to hydrology caused by planting perennials should be further elucidated so as to not cause detrimental consequences to critical water reserves and potential yields. The evaporation of water is a highly energy-intensive process (Bernacchi & Vanloocke, 2014). Vegetation exerts strong control over latent heat fluxes via controlling the movement of water between the surface and the atmosphere through transpiration and also surface evaporation. Therefore vegetation has a direct influence on the global energy and water balance.

When considering various climate-smart management scenarios, it is important to understand how potential biofuel crops affect evapotranspiration (ET) on a more detailed level. Specifically, it is important to understand patterns of ET partitioning, or the separation of ET into plant transpiration and soil evaporation, for different crops, different hydro-climate zones, and different management practices. Transpiration is a more direct measure of crop physiology than ET. Therefore transpiration is a better proxy for predicting yields or the rate at which nutrients are utilized. Knowledge of how ET partitioning shifts in different situations can be used to adjust management techniques such as planting density, fertilization, or irrigation scheduling. Therefore, understanding ET partitioning is a crucial step in developing climate-smart

management strategies.

Below ground changes to biomass (roots) and soil nutrients caused by transitioning to perennial biofuel crops should be examined further. Planting perennial biofuel crops generally

sequesters CO2 from the atmosphere (Post et al., 2012). Observational evidence confirms the primary mechanism, the increase of soil organic carbon (Kantola et al., 2017), by which this sequestration occurs. However, the question remains whether this increase will diminish over time and lead to a detrimental effect on the carbon sequestration potential of perennial biofuel crops.

Experiments should be conducted that test the sensitivity of candidate biofuel crops to extremes of temperature and moisture. Initial findings suggest that extended periods below freezing can cause irreversible damage to young rhizomes (Zeri et al., 2011). Drought can also damage miscanthus crops (Ings et al., 2013). While miscanthus is much more resilient than annual crops to short-term drought-like conditions, tentative studies suggest a long-term impact on miscanthus stand health with a lag in future growth (Joo et al., 2016; Joo et al., 2017). Including upper and lower limits to climate sensitivity in integrated models discussed above would ensure long-term sustainability of land use decisions.

The research represented by this thesis and countless other studies like it can be useful for guiding future climate-smart science and informing those that make land management decisions. However, dissemination is a challenge. For example, some researchers still naively claim that the impact of, “…LUC-driven differences in albedo, evapotranspiration, and surface roughness to biophysical forcing of surface climate remain unclear (Burakowski et al., 2017)”.

Government agencies (e.g. USDA, EPA, DOE), non-governmental agencies (e.g. Soil Science Society of America, The Nature Conservancy, etc.), and university extension programs should spread scientifically based information related to climate-smart management techniques via their publicly available documents and extension agents.

Careful study of a broad-range of land use diversification strategies is important for ensuring a sustainable and economically resilient agro-economic sector. Historically, rapid LUC associated with agricultural intensification and expansion has led to dramatic environmental problems such as the Dust Bowl, water body eutrophication, Gulf of Mexico hypoxia, aquifer contamination, wildlife destruction, chemical spills, accidental spill-over of agrochemicals into nearby fields, and soil degradation. Of these, soil degradation is perhaps the most worrisome and long-term problem. Since the turn of the century Midwest U.S. soils have lost about 50% of their original carbon due to agriculture (Fig. 5.1, Matson et al., 1997). Soil erosion compounded with intensive agriculture is continuing to deplete soil quality (Pimentel et al., 1995).

Furthermore, pests and weed outbreaks are increasing in severity and intensity (Meehan et al., 2011). In response, herbicides, pesticides, and fertilizers are being used in increasing amounts (Fig. 5.2, Howarth et al., 2002; Matson et al., 1997). Land diversification offers alternative solutions to agro-economic challenges and can help avoid many environment problems.

We have tools available to help guide wise land use and management decisions that maximize productivity and minimize deleterious effects on our land and climate. Lest we want to repeat past environmental disasters, we should heed President Roosevelt’s warning, “The nation that destroys its soil destroys itself,” (Baveye et al., 2011). Society is at a crossroads with regards to global food and energy production. By drawing on the full breadth of scientific and socio-economic tools at our disposal, we can chart a wise path for sustainable land management.

5.4 Figures

Fig. 5.1: Total soil carbon in central U.S. corn belt simulated from beginning of large-scale conversion to agriculture. Source: Matson et al., 1997.

Fig. 5.2: Nitrogen inputs and fixation in U.S. agriculture. Source: Howarth et al.,

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