Agriculture Reference
In-Depth Information
of nonnative species, but only when fire and seed addition were combined was
there an increase in the number of native species relative to nonnatives (Suding
and Gross 2006b).
Our understanding of how landscape factors regulate weed community dynam-
ics and composition in agricultural systems is still in its infancy (Gabriel et al.
2005). Much of the research in this area has been conducted outside of the United
States. In these studies, local plant species and genetic richness in agricultural fields
have been shown to be strongly affected by processes operating at landscape scales,
even across distances as short as 2 km (Gabriel et al. 2005, Poggio et al. 2010).
Recent studies in the midwestern USA have found evidence that weedy species in
the landscape surrounding an agricultural field may provide ecosystem services,
such as biocontrol and pollinator services (Isaacs et al. 2009, Gardiner et al. 2009,
Landis and Gage 2015, Chapter 8 in this volume). This has sparked interest in
understanding how an agricultural landscape that supports multiple functions and
ecosystem services can be established. Understanding the economic, social, and
ecological processes to promote this type of landscape is an important focus of
agroecological research in the United States (Jordan and Warner 2010).
Climate Change and Precipitation
At the global scale, there is a strong correlation between primary productivity
and mean annual precipitation (MAP) in terrestrial plant communities in gen-
eral (Melillo et al. 1993), and in grasslands in particular (Knapp and Smith 2001,
Cleland et al. 2013, Robinson et al. 2013). How plant communities respond to
altered precipitation patterns—particularly, increases in precipitation variability, as
predicted by global change models—has heightened interest in this relationship
(Knapp and Smith 2001, Huxman et al. 2004). Although in a cross-site analysis,
Knapp and Smith (2001) found a positive correlation between aboveground net
primary production (ANPP) and MAP across temperate biomes at a continental
scale, they found no relationship between interannual variation in productivity and
annual precipitation at the local scale. Their analysis revealed that some biomes—
specifically, temperate grasslands—were more responsive to pulses (maxima) in
precipitation than others and that this was driven by abundant, highly responsive
species in ecosystems where precipitation and evapotranspiration were approxi-
mately balanced. A more recent cross-site synthesis (Cleland et al. 2013) across a
broad range of grasslands showed that while species richness was strongly corre-
lated with MAP, only the most xeric sites were responsive to interannual variation
in MAP. Much of this response was driven by annual species whose emergence was
sensitive to precipitation variation, suggesting that annual and perennial communi-
ties may respond differently to changes in precipitation variability.
Although the relationship between MAP and productivity is well studied in
both grasslands and agricultural systems (e.g., Laurenroth and Sala 1992, Knapp
and Smith 2001, Motha and Baier 2005), considerably less is known about how
predicted changes in precipitation variability, particularly seasonal distribution,
will affect not only productivity but other ecosystem processes as well (Cleland
et al. 2013, Robinson et al. 2013). Only a few studies at KBS have manipulated
