Let $G$ be a graph on $>1$ vertices. Recall that its maximum average degree is defined to be $$M(G) = \max\left\{\frac{2|E_H|}{|V_H|} \colon H \subseteq G, |V_H| > 1\right\},$$ and its arboricity is equal to $$A(G) = \max\left\{\left\lceil\frac{|E_H|}{|V_H|-1}\right\rceil \colon H \subseteq G, |V_H| > 1\right\}.$$

In [https://arxiv.org/pdf/1802.05582.pdf, near the end of page 2] it is stated that "it is not difficult to show that $2A(G) - 2 \le \lceil M(G)\rceil$". However, I am not sure what is the reasoning.