Conclusions (so far)
Since this project is still considered a, work in progress, these are the most recent results as of 2005. To date, four of the eight sampled tree species,representing four different genera have been processed:
White fir (Abies concolor)
Englemann spruce (Picea englemannii)
Pondersosa pine (Pinus ponderosa)
Douglas fir (Pseudotsuga menziesii)
The tree-ring data for each elevation zone (high,medium, low) have been pooled across species to determine if a signal consistent with increased water-use efficiency (WUE) can be detected. If present, we would expect the hotter/drier low-elevation sites to show a greater WUE signal.
The tree-ring chronologies separate out by elevation in a consistent way (i.e., below-average growth is less so with increasing elevation and vice-versa) (fig.1). No convergence between high and low-elevation chronologies is evident in the late 20th century (fig.2). This latter observation suggests that an increasing water-use efficiency signal is not evident in the tree-ring width variations
Figure 2. Species mean growth departures over the last century display no significant trend or level differences. What is clear from these results is the negative influence of moisture stress at different elevations. Drought conditions have a much more dramatic impact on the low elevation trees than it does on the high elevation trees.
Which is older??, which is respiring more??? hmmm.