Karen Traviss began writing the Republic Commando series before The Clone Wars TV series started. Her series turned into what was going to be the Imperial Commando series (as a result of the in-universe transition from Republic to Empire), but only one book was published. The novel that would have been the second was canceled due to issues with Traviss' contract and continuity changes that were being introduced by the The Clone Wars. Traviss had taken the clones, Mandalore, Mandalorians, etc. in a different direction that The Clone Wars team decided to take, so her series was canceled and there are contradictory portrayals of Mandalore.
In an interview she gave for io9.com she states that she was not in communication with the Clone Wars team:
You ask if I discussed the direction the Mandalorian canon would take with the TV team, and fans have asked me that same question - no, I had no direct access to or discussion with the Clone Wars team while I was writing the Clone Wars tie-ins or the Commando series, and that's common practice in the tie-in industry. Whatever information I was given came through the publisher, and I put my views on that information to the editor.
Also, Traviss has an FAQ page on her website about why she stopped writing Star Wars. In it, she discusses the canon change to the Mandalorian culture and history as well as the planet Mandalore itself:
When I was finishing 501st in January this year, I was told about a significant continuity change coming up in the Clone Wars cartoon. (As was mentioned and shown in a couple of books that came out in the summer - this is not confidential information of any kind now.) I was told that the Mandalorians were being revamped as long-standing pacifists who'd given up fighting centuries ago and that Mandalore was now a post-apocalyptic wasteland devastated by war. I was told not to refer to (recent) Mandalorian history because of that, as it was obviously at odds with the old continuity in my novels. That's fairly common procedure for any franchise - but unfortunately it wasn't that simple in practice. The two Commando series - and quite a few older books and comics, come to that - were based entirely on that original history, and basic logic meant that the fundamental plot of the series could never have existed if this had been a pacifist society. Neither could any of the characters or their motives have existed, because they were wholly based on a global warrior culture living on a non-nuked Mandalore.
Her portrayal of Mandalore was based on the Mandalorians' original warlike history (e.g. the Mandalorian Wars) and she assumed the Mandalorians remained warlike, but this contradicts the portrayal of the Mandalorians and Mandalore in The Clone Wars (which is canon).
The Wookieepedia Legends article on Mandalore does suggest that the two portrayals of Mandalore have been integrated:
Despite the radical departure from established canon the television series made use of for Mandalore, the later reference books The Essential Atlas and the Star Wars: The Clone Wars: New Battlefronts: The Visual Guide made several retcons that effectively integrated the new version of Mandalore with prior, more arboreal iterations, stating collectively that the barren desert is in fact only one aspect of Mandalore's varied ecosystems, and the previously established jungles and forests were still accepted as canon.
Essentially, Traviss' portrayal of Mandalore has been retconned as referring only to a different region of Mandalore not portrayed in The Clone Wars.