Editorial- The Role of Complex Agroecosystems in Climate Change Mitigation
Authors: Oelbermann Maren 
Published: April 2014

The burning of fossil fuels in developed nations and the conversion of natural grasslands and forests to intensely managed
agricultural production systems are the single most important anthropogenic sources of greenhouse gases (GHGs) contributing
to global warming. Such activities do not only contribute to the accumulation of GHGs in the atmosphere, but also lead to the
depletion of the global soil organic matter (SOM) pool, further impacting soil fertility and crop productivity. Climate change
will likely affect the distribution and productivity of life-sustaining agricultural crops and livestock in different regions of the
world, including temperate and tropical biomes. As a result, the United Nations Development Program suggested that millions
of people may be facing shortages of food and continued degradation of their agricultural resources. Therefore, one of the
challenges is to maintain agricultural productivity to meet current and projected trends in food production, while at the same
time minimizing GHG emissions, increasing C (C) sequestration and maintaining soil fertility. This, coupled with large-scale
land, soil, and water degradation, will challenge the long-term and sustainable production of agricultural resources that promote
food security.

Traditional coping mechanisms, such as conventional agroecosystem management practices may not be an economically
feasible adaptation strategy, especially for those already experiencing socioeconomic adversity. Therefore, improvement and
refinement of ecologically-based land management practices are essential. Soft-path agricultural technologies such as the
complex agroecosystems, including agroforestry systems, may make a substantial contribution in the mitigation of GHGs, the
sequestration of C, and other ecological services while maintaining a long-term sustainable production of agricultural products.
Due to their multipart structure, complex agroecosystems are likely more resilient to climate change and provide a sustainable
alternative to conventional land management practices.

This special issue of the Agriculture Journal, on the role of complex agroecosystems in climate change mitigation,
encapsulates research from temperate and tropical biomes, with a special focus on agroforestry systems. In tropical regions,
Chesney et al. investigated the performance of cowpea (Vigna unguiculata L.) on alley cropping agroforestry systems with
Gliricidia sepium (Jacq.) Kunth ex Walp. and Leucaena leucacephala (Lam.) de Wit and a no-tree control on an infertile acidic soil in Guyana. Their goal was to evaluate the ability of fast-growing nitrogen (N2)-fixing trees (G. sepium, L. leucocephala) on cowpea yield. Such practice would maximize the cowpea crop yield but minimize the need for an external source of N
fertilizers. They suggested that such practices provide a sustainable source of food, and conserve soil resources but it will also
reduce the potential production of the GHGs over the long-term. They noted that these agroforestry practices would curb N2O
emissions, which has a global warming potential 296 times greater than that of CO2. Smith and Oelbermann used a qualitative
approach to evaluate the perception and knowledge of climate change by landowners in a remote Costa Rican agricultural
community. They also evaluated the type of sustainable agricultural practices already implemented that could also serve as a
strategy to climate change adaptation. Their study showed that community members were aware of climate change and already
observed changes in local weather patterns over the past decade that affected the distribution of vegetation and wildlife. As a
result, agricultural producers were continually striving to implement agroforestry practices which were viewed as more robust
and resilient to climate change by helping to maintain agricultural productivity while also providing economic and
socioecological needs.

In temperate regions, Evers et al. provided an overview of the potential of tree-based intercropping (agroforestry alley cropping) systems in climate mitigation through the reduction of GHG emissions. They outlined the most recent research
results from southern Ontario and Quebec and found that agroforestry systems could lower N2O emissions by 1.2 kg ha-1 y-1
compared to a conventional (monoculture) agroecosystem. They also suggested that the potential of agroforestry systems to
sequester C in the soil and tree component was greater than in conventional agroecosystems, especially if fast-growing tree
species for bioenergy production were used. Such practices may also provide an opportunity to receive payment for the
ecological services provided by the agroforest, making these production systems a better option than conventional systems for
agricultural producers in temperate regions. Isaac et al. investigated the internal accumulation and retention of nutrients in
nutrient-spiked pine seedlings commonly used in temperate agroforestry systems and hypothesized that nutrient-spiking would
lower seedling transplanting stress and reduce pressure on native soil resources and proposed that nutrient spiking would also
lead to an increase in nutrient availability for the growing crop and also minimize competition between trees and crops. They
found a favorable response in tree and crop root biomass accumulation in nutrient-spiked treatments and found that N,
phosphorus (P) and potassium (K) significantly increased in the pine tissue and resulted in a steady or increased uptake of these
nutrients by the crop (maize). Isaac et al. suggested that such specialized practices may be required when establishing
agroforestry systems for the benefit of nutrient regulation and enhanced capacity to sequester C for the long-term mitigation of
climate change.

The Argentine Pampa is one of the most fertile regions in the world and natural grasslands and forests continue to be
converted to intense agricultural production systems. Such practices have led to large losses in soil organic carbon (SOC) and contributed to the accumulation of GHGs in the atmosphere. The paper by Posse et al. outlines the absence of precise
quantitative data on the emission and sequestration of GHG, which impedes a better understanding of the mechanisms driving
CO2 emissions from agroecosystems. Although the paper by Posse et al. does not investigate CO2 fluxes from complex
agroecosystems, but instead it provides vital information on the emission of this GHG in one of the most rapidly expanding
agricultural frontiers in the world, which is also experiencing the effects of global warming on crop productivity. Posse et al.
aim to characterize the exchange of CO2, using eddy covariance techniques, in a monoculture soybean system during an
extreme dry summer which resulted in a high crop loss. They found that the greatest emission of CO2 occurred during premature
crop senescence (due to drought) but the field became a CO2 sink once the soil as covered by weeds. As such, changes
in crop phenology and botanical composition (weeds) coincided with changes in the flux of CO2.

The papers presented in this special issue of the Agriculture Journal provided an important insight into the potential of decreasing GHGs and maximizing C sequestration. These papers have also provided an important stepping stone by outlining
the future direction of research to further understand the importance and role of complex agroecosystems in mitigating climate
change. This research field is in its infancy but results are favorable by indicating that complex agroecosystems not only
enhance the cycling of nutrients and the productivity of agricultural crops and show greater resilience to climate change, but
they can also play an important role in the mitigation of climate change.