Closed mcgregorian1 closed 5 years ago
EDIT: 4 days later, realized I included year as a random effect when it's a fixed effect. I have changed it.
the r-squared for the top model is 0.16.
definitely more of a significant effect of the interaction compared with the results in P3a.
Adding in dbh_ln separately to this gives pretty much the same picture. Inherently, dbh_ln*elev_m includes the effects of having dbh_ln and elev_m as separate effects along with the interaction.
which direction is the interaction?
The direction is negative, though the individual effects are both positive
also my bad on the original - I had included year as a random variable even though I don't have enough groups to consider it random
Okay, so it indicates that drought response increases with both elevation and dbh, but elevation has less impact on larger trees, supporting P2b.
Regarding a metric of distance to the stream, I'd think either of the suggestions above should give us a preliminary idea (and if its borderline or significant it may be worth improving the map). For the second option (distance to stream), you'd want to use ln[distance].
I've now calculated the distance for each point to water and added it as the ln[distance] (option 2 from above).
Running the model dbh_ln*distance_ln plus random effect, I get:
Here is the interaction summary:
Thanks! Could you please try it without the interaction (and give the coefficient)?
Running with no interaction yields:
These are the coefficients for the top three models:
Running without log-transformed distance gives an even weaker signal:
For the record, running dbh_ln + elev_m*distance_ln gives me almost the same result as above, with dbh_ln + (1|sp/tree) the best model by 2, but the next best model has the same r-squared (0.16) and is the full model
@teixeirak both H2 and H3 include a test for dbh*elev interaction, but in the table you listed it as height*elev (just want to make sure this was intentional - I'm assuming this is because height has the larger effect?).
Otherwise, the response we're seeing in the updated table (as of 12.30 today) is what I'm getting for running identical models
use height x elev for both. Note that the different hypotheses predict different directions of interaction.
Ok, sounds good. That's what the script is currently doing so I think it can stand as is
I think we're done with this issue.
H3- Rooting volume/depth relative to water sources are critical in drought response. Effects of drought on larger trees are mediated by the fact that large trees have better access to water.
P3a- drought response increases with elevation and/or distance from stream (it would be nice if we knew more about the site hydrology!)
Next step:
P3b- There is a dbh*elev interaction, elevation (relative to stream?) matters less for big trees with larger (and potentially deeper) root system.
Next step:
Originally posted by @teixeirak's writing in issue #7