Agroforestry is to have indeed a positive effect on overall biodiversity. However, this won't account for every part of the broader concept for biodiversity.
Some species could show some decline in abundance (farmland birds for instance), while others will show a positive trend (isopods for example).
The biodiversity effects of agroforestry are thus depending of the region you implement it in and the species groups you are interested in. It may play a major role as connectivity patches between remnant forest patches.