Specifying the distance between levels in forest

Question

I would like to have more space between the first level and the second level in the tree below. In tikz-qtree I can use

\tikzset{level 1+/.style={level distance=3\baselineskip}} \tikzset{level 2+/.style={level distance=2\baselineskip}}

Is there something equivalent in forest?

\documentclass{minimal}

\usepackage{forest}

\forestset{
sn edges/.style={for tree={parent anchor=south, child anchor=north,align=center,base=bottom,where n children=0{tier=word}{}}}, 
background tree/.style={for tree={text opacity=0.2,draw opacity=0.2,edge={draw opacity=0.2}}}
}


\begin{document}

\begin{forest}
sn edges
[S
  [NP [er\\he] ]
  [NP
    [Det [das\\the] ]
    [N [Buch\\book] ] 
  ]
  [NP
    [Det [der\\the] ]
    [N [Frau\\woman] ] 
  ]
  [V [gibt\\gives] ]
]
\end{forest}

\end{document}

Answer 1

Do you want something like

l sep+=<some length>

which will reduce the distance between tiers by <some length>?

To restrict this increase to only the distance between the root node and the first tier, you can use

for children={
  l sep-=<some length>,
}

to reverse the increase. (There may be a more direct method - this is just what came most readily to hand.)

The following compares the default with increases of 1em and 2em respectively:

\documentclass{standalone}

\usepackage{forest}

\forestset{
sn edges/.style={for tree={parent anchor=south, child anchor=north,align=center,base=bottom,where n children=0{tier=word}{}}},
background tree/.style={for tree={text opacity=0.2,draw opacity=0.2,edge={draw opacity=0.2}}}
}


\begin{document}

\begin{forest}
sn edges
[S
  [NP [er\\he] ]
  [NP
    [Det [das\\the] ]
    [N [Buch\\book] ]
  ]
  [NP
    [Det [der\\the] ]
    [N [Frau\\woman] ]
  ]
  [V [gibt\\gives] ]
]
\end{forest}
\begin{forest}
sn edges,
l sep+=1em,
for children={
  l sep-=1em,
}
[S
  [NP [er\\he] ]
  [NP
    [Det [das\\the] ]
    [N [Buch\\book] ]
  ]
  [NP
    [Det [der\\the] ]
    [N [Frau\\woman] ]
  ]
  [V [gibt\\gives] ]
]
\end{forest}
\begin{forest}
sn edges,
l sep+=2em,
for children={
  l sep-=2em,
}
[S
  [NP [er\\he] ]
  [NP
    [Det [das\\the] ]
    [N [Buch\\book] ]
  ]
  [NP
    [Det [der\\the] ]
    [N [Frau\\woman] ]
  ]
  [V [gibt\\gives] ]
]
\end{forest}

\end{document}