Are Soil
Characteristics Correlated with Piñon Pine Mortality in New Mexico?
Nope! But read
on to find out how I figured that out…
Photo: Robert Parmenter
Piñon-juniper woodlands are widespread in New Mexico, but
the recent drought has resulted in severe piñon mortality in some areas of the
state.
In
this project I used the State Soil Geographic Database (STATSGO)
to examine features of the soil which might be related to piñon death.
I
used USDA Forest Service data from 2003 as my dependent
variable.
In
ArcGIS, I clipped the STATSGO coverage of New Mexico to
the extent of the 2003 USFS survey and to the area where piñon mortality was
documented.
I assessed four soil characteristics to see if they
correlated with piñon mortality.
Click on the links below to learn more about each one
and see the maps I generated.
None of my variables differed between the areas where
piñons died and areas where they didn’t, as the table below shows.
This is an interesting case of visual assessments
being somewhat misleading; the maps linked to the variables above sometimes
seem to show a pattern.
|
|
Piñon Mortality |
No Piñon Mortality |
||
|
|
Mean |
Standard Deviation |
Mean |
Standard Deviation |
|
Surface Texture Proxy (0-40) |
15.6 |
5.9 |
15.8 |
5.9 |
|
Available Water Content (inches
per inch) |
1.9 |
0.7 |
1.8 |
0.8 |
|
Permeability (inches
per hour) |
35.7 |
36.1 |
37.0 |
43.5 |
|
Slope (degrees) |
21.2 |
13.8 |
21.2 |
15.4 |
Why didn’t I find an effect of soil type?
·
Poor soil data
resolution – SSURGO data would give more resolution, but isn’t available for
all of New Mexico yet
·
Mortality data
was only from one year – multiple years might have shown mortality
intensification
·
Mortality data
was listed as “dead trees per acre” but in reality there were only four
categories of data and I input it as a binary variable (presence/absence) –
more continuous mortality data might allow regression analysis
·
There really isn’t any effect!
o
Differences in
mortality could be due to precipitation patterns, bark beetle population
dynamics, aspect, or genetic variability among piñon pine populations
You can find out more about my: