Climate change, ecosystems and smallholder agriculture in Central America: an introduction to the special issue - Imbach, Pablo; Beardsley, Megan; Bouroncle, Claudia; Medellin, Claudia; Läderach, Peter R.D.; Hidalgo, Hugo G.; Alfaro, Eric; Etten, Jacob van; Allan, Robert; Hemming, Debbie; Stone, Roger; Hannah, Lee; et al. (Springer, 2017)