Trees and regeneration data for Sutton site.
dat_sutton
    A list of 5 objects:
trees that includes identity and position of trees;
regen2015 and regen2016 regeneration and favourability data for 2015 and 2016 respectively (note that favourability values are the same for both years);
lsdist a list of distances: for every plot it gives the distance of all surrounding tree including in the site;
iddist a list of logicals of the same format as lsdist that states whether the tree is included in the buffer.