Demand for fossil fuels is increasing globally. The United States is pursuing an energy policy that aims to reduce our dependence on fossil fuels by expanding renewable energy sources. One important part of this effort is the use of bioenergy crops to produce heat, electricity, and transportation fuel. Meeting energy demands could have big implications for agricultural land use. Not only will land used to grow fuel not be available for growing food, but the choice of energy crop will have large consequences in the environment.
Few studies have considered the effects of bioenergy crops on biodiversity. Bioenergy crops can be broadly categorized as “high intensity, low diversity” (HILD, corn and soybean) or “low intensity, high diversity (LIHD, hay fields and prairies). HILD crops are characterized by high fertilizer and pesticide inputs and are generally annually replanted. LIHD require fewer inputs, are more perennial, and are composed of a mix of several different plant species.
The number of plant species in a field can influence the number of species on a landscape. In general, HILD crops are expected to support fewer species than LIHD crops. The number of bird species is often considered to be a good indicator of the number of animal species in a community. An active group of professional and amateur bird watchers involved with the North American Breeding Bird Survey have produced useful data on the number of bird species in landscapes across North America. Using this data, Meehan et al. developed a model to predict the number of bird species in different future land-use scenarios. Specifically, they contrasted two extremes scenarios for bioenergy crops on marginal lands in the Upper Midwest: (1) changing 9.5 million ha of LIHD into HILD and (2) changing 8.3 million ha of HILD into LIHD. These two scenarios represent opposite ends of the spectrum, moving to mostly perennial (LIHD) or mostly annual (HILD) bioenergy crops on marginal lands.
Their model predicted that changing to a more perennial landscape (hay fields and prairies that are not re-planted every year) would result in more species of birds (up to 200% more) in the landscape while a more annual landscape (corn and soybeans fields) would result in fewer species of birds (up to 65% fewer) in the landscape. This is especially the case for rare grassland birds of particular conservation interest. Which crops are used for producing bioenergy will have consequences for many aspects of the environment, including the number of bird species. It is important to consider all of the costs and benefits of our energy policies.