Background
The authors write that "for caribou in Greenland earlier springs have been suggested to result in a lower reproductive success," based on the assumption that "Rangifer (caribou/reindeer) might be unable to adjust their timing of reproduction to the earlier surge of high quality food," which potential failure could "cause a mismatch between optimal forage conditions and the timing of reproduction." And, therefore, they state that "concerns have been raised regarding the future viability of Rangifer in Arctic and sub-Arctic tundra ecosystems."

What was done
In a study designed to further explore this unsettled situation, Tveraa et al. "analyzed a 10-year dataset of satellite derived measures of vegetation green-up, population densities, calf body masses and female reproductive success in 19 reindeer (Rangifer tarandus) populations in Northern Norway."

What was learned
The four Norwegian researchers found that "an early onset of spring and high peak plant productivity had positive effects on calf autumn body masses and female reproductive success," and that "the quantity of food available, as determined by the onset of vegetation green-up and plant productivity over the summer, were the main drivers of body mass growth and reproductive success." Hence, they found no evidence for a negative effect of the speed of spring green-up, nor did they detect "a negative mismatch between early springs and subsequent recruitment."

What it means
Very simply, Tveraa et al. concluded that the "effects of global warming on plant productivity and onset of spring are likely to positively affect sub-Arctic reindeer."