How is lumbering bad for the climate? Don't final products still store that carbon? What do those calculations mean (example [ch. 3], methodology [ch. 4])? The report says it doesn't include in-use storage because of the low life-cycle of paper products. But if they imply that the carbon would be shortly released from a landfill or incinerator anyway, then I don't get why landfill emissions are so much lower from calculated carbon storage sequestration (sometimes, see p. 3-6, the emissions are negative, i.e. discarded paper products act as a sink). But speaking generally, what harm does deforestation do (unless the logged wood is burned, either intentionally or not)? The carbon would be stored either in soil (e.g. sawdust) or final products, wouldn't it?
Sometimes it is, sometimes it isn't.
If you have a forest that is cleared with no intention whatsoever to re-plant a new forest, that is bad for the climate. You can't make all of the trees into lumber, you will have waste products like small diameter treetops (too small to make lumber from it, can be used as pulpwood), roots, branches and lots of sawdust. Those waste products will eventually decompose or alternatively can be burned immediately for energy. Either way, they release their carbon dioxide into atmosphere and since no new forest was planted, the carbon dioxide won't be sequestered again. At least that part of lumber that was used to create furniture or build houses retains the carbon for some time but the forest wasn't re-planted so no new carbon will be sequestered.
However, let us consider a different kind of forestry: sustainable forestry. If you have a forest that is on the end of its growth cycle, so old that it is at equilibrium and the carbon stored in the forest won't increase. Now if you cut the forest, you make room for new forest to grow and store more carbon (some countries like Finland mandate that a new forest must be planted). Out of the cut trees, you get treetops and other small diameter wood (good for pulpwood to make packaging products like cardboard that displace plastic products made from oil), roots (you can burn to energy and return the ashes as fertilizer to accelerate growth of new forest), branches (the same), sawdust (the same). Out of the forest that had ceased to be a net carbon sink, you get lots of bioenergy (and return the ashes as fertilizer), lots of wood-based packaging material (that displace packaging materials made from oil), and lots of lumber that is used to build for example houses and furniture that act as a permanent carbon sink for >100 years. Some of the lumber is left over, but that can be burned to energy while returning the ashes back to the forest.
So it's a question of what kind of forestry you want to do. In the country where I live, Finland, sustainable forestry is the only kind of forestry. Unfortunately the European Union consisting of countries that have long time ago eliminated their forests is attempting to mandate what kind of forestry practices can be used in Finland, but fortunately Finnish politicians have had good success in telling European Union that no mandates are needed since we only have already sustainable forestry.