acornwt = function(dbh, species)
{
#  Function to calculate mean acorn weight (in lb) from dbh and species and trees per acre
# by David R. Larsen, Copyright October 9, 2012
# Creative Commons http://creativecommons.org/licenses/by-nc/3.0/us/

  if( (species == "black") && (dbh > 9.9) && (dbh < 36.1) ){
    acornwt = -1.9065 + 0.2973 * dbh
  }else if((species == "chestnut") && (dbh > 9.9) && (dbh < 36.1)){
    acornwt = 0.0008271 * dbh ^ 3 - 0.08157 * dbh ^ 2 + 2.692 * dbh - 18.85
  }else if(species = "red" && dbh > 9.9 && dbh < 36.1) {
    acornwt = 0.0004016 * dbh ^ 4 - 0.0349937 * dbh ^ 3 + 0.9864357 * dbh ^ 2 - 9.5233885 * dbh + 27.32720516
  }else if (species = "scarlet" && dbh > 9.9 && dbh < 36.1) Then
    acornwt = 0.0005975 * dbh ^ 4 - 0.05325 * dbh ^ 3 + 1.651 * dbh ^ 2 - 19.97 * dbh + 84.71
  }else if(species = "white" && dbh > 9.9 && dbh < 36.1){}
    acornwt = 0.0001987 * dbh ^ 4 - 0.02027 * dbh ^ 3 + 0.694 * dbh ^ 2 - 8.768 * dbh + 37.36
  }else{}
    acornwt = 0.0
  }
  acornwt
}