Body mass is correlated with lifespan
npr.org
npr.org
The paper just claims to support some known, quantifiable correlations with some data. The correlations pertain to mortality rates and birth rates, and certainly suggests no formula for when to die, or causation of any sort for that matter. E.g, is it that bigger plants die less often, or that plants that die less often can get bigger? Does it matter?
[0] http://www.pnas.org/content/104/40/15777.full
[1] "Whereas the action of selective processes on animal lifespan cannot extend through their entire lifespan because many lose reproductive capacity with age, this is not the case in plants, which generally remain reproductive throughout their lifespan, suggesting that lifespan could be under greater selective pressure in plants."
Plants can essentially live forever through cloning, where the plant lays new roots and isn't stuck on its former shell.
On the other hand stressed plants go to seed (a good evolutionary move) and statistically no plant lives forever in the wild, with fires and etc, so perhaps this data is more of a testament to how fragile a plant is... e.g. how easily it's killed. It makes sense that smaller = more fragile, more easily burnt/frozen to death, etc.
Even on a log-log graph, the data looks like a shotgun spread. Species of similar mass have lifetimes that vary by up to a factor of 1,000. Species with similar life-spans differ in mass by up to a factor of a trillion.
A formula that "tells us when it's time to die" would imply some sort of prediction about individuals, which they admit is not the case at all. That would actually be interesting.
Looks like the trees along the right have a half-life range of <10,000 to >1,000,000, even with nearly identical individual mass.
Make sure you correctly read a paper before spreading wrong conclusions. The article is about the relationship between death, birth and mass (which are obviously connected, the paper is about that relationship). Time is just the scope there.
That being said. The article states that this relationship governs "all life" but only gives data for plants. Even there, "some variation, but not a lot" is an extremely generous representation. For the same mass, a difference in mortality rate could be 10^3 or more if I'm reading the graph correctly. While the relationship might roughly follow a trend, I wouldn't call that "not a lot" of variation. It's interesting, but I think the authors are overselling the relationship.