What was done
In 1930-31, Jorgensen (1933) recorded the presence of all species of vascular plants he encountered from approximately 1500 m to the tops of 25 peaks of the Jotunheimen mountains (61°N) of central Norway, which comprise the highest massif in the Fennoscandian range.  The authors repeated this feat in 1998 on 23 of the 25 mountains, resurveying 265 of the 320 original locations studied by Jorgensen.

What was learned
Over the 68-year interval between the two surveys, species richness increased on 19 of the 23 mountains studied.  In fact, the authors report that "new species (not recorded by Jorgensen) [were] found on all mountains."  They also note that nearly 25% of the species observed in 1998 "exceeded their altitudinal limits in Norway compared to previous records."

What it means
The authors note that "the 'Little Ice Age', the coldest period over the last millennium, induced major glacial advances in Jotunheimen," and that the mountains' vegetation "might still be recovering from this period."  Hence, they propose that "climatic warming is the major driving force for the changes observed [i.e., increased species richness and upward expansion of ranges], and [that] the upward shift of the vegetation belts may continue in the coming decades."

Is this response good or bad?  Increased species richness would probably be considered by most people to be good.  However, the authors note that "with a simple response to warmer climate, high-altitude species might be driven upwards, eventually becoming locally extinct," which most people would probably deem to be bad.

Fortunately for Norway's most cold-adapted - and, therefore, most threatened - plants, the air's CO2 content is also on an upward course; and this environmental change will likely hold the bad consequences at bay.  On the basis of both theory (Long, 1991; Cannell and Thornley, 1998) and a host of experimental observations (Idso and Idso, 1994), a 300-ppm increase in the atmosphere's CO2 concentration typically increases the temperatures at which plants grow best by several degrees C, so there is no biological imperative for plants to migrate towards cooler regions as temperatures rise when the air's CO2 content is rising concurrently.  Hence, vascular plant biodiversity should continue to increase on Norway's mountains - and in all analogous places on earth - as long as the air's CO2 content does not level off before the warming does.  And that is why Cowling (1999) has rightly warned: "maybe we should be less concerned about rising CO2 and rising temperatures and more worried about the possibility that future atmospheric CO2 will suddenly stop increasing, while global temperatures continue rising."

Yes, nature needs more CO2 in the air in a warmer world; and it would thus be unwise to implement measures to reduce anthropogenic CO2 emissions in the midst of what many claim to be the most dramatic global warming of the entire past millennium. If we are serious about wanting to maintain the planet's species richness, we must not do anything to encourage atmospheric CO2 concentrations to decline.

References
Cannell, M.G.R. and Thornley, J.H.M.  1998.  Temperature and CO2 responses of leaf and canopy photosynthesis: a clarification using the non-rectangular hyperbola model of photosynthesis.  Annals of Botany 82: 883-892.

Cowling, S.A.  1999.  Plants and temperature - CO2 uncoupling.  Science 285: 1500-1501.

Idso, K.E. and Idso, S.B.  1994.  Plant responses to atmospheric CO2 enrichment in the face of environmental constraints: a review of the past 10 years' research.  Agricultural and Forest Meteorology 69: 153-203.

Jorgensen, R.  1933.  Karplantenes hoidegrenser I Jotunheimen.  Nyt magazin for naturvitenskaberne 72: 1-128.

Long, S.P.  1991.  Modification of the response of photosynthetic productivity to rising temperature by atmospheric CO2 concentrations: has its importance been underestimated?  Plant, Cell and Environment 14: 729-739.