According to Roberts (2008), the origin of the 7 degree difference in summer temperatures was a study in Alaska involving a forested site with an O horizon and very little seasonal amplitude in temperatures versus an open area lacking an O horizon. The Roberts (2008) study, in contrast, shows that the difference is not always this great in Maine, and that cover vegetation type can have an effect iby greg.schmidt - Soil Taxonomy Forum
How much difference does O horizon thickness make regarding summer soil temperatures? Soil Taxonomy defines a 50 cm soil summer temperature threshold of 15°C for mineral soils lacking an O horizon, and having a mean annual temperature of less than 8°C. If an O is present, the summer temperature requirement drops to 8°C. Our office has collected preliminary data suggesting that one of ourby greg.schmidt - Soil Taxonomy Forum
What is the most appropriate method of averaging the pH of soil horizons? A straight weighted average of the horizons, such as 10 cm of a pH 4.5 soil averaged with 10 cm of pH 6, would be 5.25. But there are some who suggest that pH should be exponentially transformed with the rationale that pH is really hydrogen concentrations. However, this seems to skew the distribution towards acidity. Doing iby greg.schmidt - Soil Taxonomy Forum
Ortstein and densic horizons should also count as root limiting, as they are physical limitations.by greg.schmidt - Soil Taxonomy Forum
By a similar reasoning, strongly contrasting layers (fine loamy over sandy) should not be considered root limiting. There may be some sort of hydrotropic reasoning for this depending on plant species, but there is no actual barrier to penetrating the layer. There are some states in the US for which this is considered root restrictive, while across the border in another state, the same soil is notby greg.schmidt - Soil Taxonomy Forum
Just in case the PRISM map products are not trusted for one’s area of interest (i.e. wrong elevation gradient or lake effect gradient), or if my use of archived temperature didn’t correctly weigh missing data, I created maps from data from a couple other independent sources. First, I calculated annual air temperatures from the newly released 1 km temperature grids from WorldClim Version 2:by greg.schmidt - Soil Taxonomy Forum
The latitudinal trends in these Lower 48 data are consistent with the overall pattern of the arctic warming at a much faster rate than the tropics. This was also true with ice age climate, wherein northern regions were much colder, while the Gulf Coast remained almost as warm as it is today but was less seasonal. Instead of moving has as a unit, the vegetation belts essentially compressed southwarby greg.schmidt - Soil Taxonomy Forum
To illustrate my previous point, I've constructed a few maps of average annual air temperatures that combine the PRISM 2010 normals with interpolated anomalies from the 1881-1910 station records. I plotted the mesic zone as ranging from 7 to 14 °C in annual air temperature, assuming that the soil is 1 degree warmer (8-15 °C). 1910 Normals: https://drive.google.com/open?id=0B3NKeT9nHj0Raby greg.schmidt - Soil Taxonomy Forum
Another example of where we are considering whether subaqueous soils apply is the estuary-like Great Lakes marshes. These wetlands have hydroperiods of decades combined with the normal annual and daily storm-surge fluctuations, based on the levels of the Great Lakes. In some cases the emergent vegetation may be pretty deep. I don't know if such emergents are established on exposed bottoms atby greg.schmidt - Soil Taxonomy Forum
That is very interesting. Many non subaqueous soils like inceptisols and entisols, are already without the diagnostic horizons. So there must be something else besides soil processes to justify the recognition of subaqueous soils. Of course there is the one process which would seem very much tied to subaqueousness, which would be limnic processes. Probably more a geological rather than a soil procby greg.schmidt - Soil Taxonomy Forum
My question is whether semi-permanently submerged sites that are only intermittently exposed only during exceptionally dry years could be considered subaqueous by Soil Taxonomy (e.g. Wassents). Currently, such sites are mapped as undifferentiated ponded map units or as water. It would seem that Wassents and Wassists would have been logical replacements for such map units, but the truth is, some ofby greg.schmidt - Soil Taxonomy Forum
Ken, Thanks. If I am to interpret your response correctly, we are not mapping stationary land units that are subject to climate change (>30 or 100 years), but rather fluid systems that move along the landscape with climate change. The implication is that ecological sites and soil series may themselves come in and out of existence as environmental parameters change. I guess this would be the saby greg.schmidt - Soil Taxonomy Forum
Is there a reference timeframe for mapping soil climate? Is it the most recent 30 year normals, which shift forward every ten years? Is it a longer period? Is it a fixed period or a moving average? I ask because soil temperature and moisture regimes are subject to change over long periods. I am responsible for developing provisional ecological site concepts for northern Lower Michigan where a mby greg.schmidt - Soil Taxonomy Forum
This probably gets tricky at the isothermic California coast where vegetation may still take on a sclerophyllic characteristics and have a phenology like plants in the non-iso climate inland. In this case, day length would still tell the plants what time of year it is, which could still mean something different for a species that evolved in the xeric regime than for a plant which evolved in a non-by greg.schmidt - Soil Taxonomy Forum
What is the standard timeframe for soil climate? Is it the most recent 30 year normal, which shifts forward every ten years? Is it a longer period? Is it a fixed period of time or a moving average? I ask because soil temperature and moisture regimes are subject to change over long periods. If it were simply cyclical changes, then a long enough running average should suffice. But if climate changeby greg.schmidt - Soil Taxonomy Forum
Thank you for your thoughtful response. For the same reasons as you mentioned for the organic matter in floodplain sands, I wonder if the same applies to the fertility in spodisols under cultivation.by greg.schmidt - Soil Taxonomy Forum
I have always wondered why sandy floodplain soils with evidence of irregularly decreasing carbon are lumped in with Udipsamments (as Aquic and Oxyaquic subgroups in southern Michigan series Abscota and Algansee) , but are not afforded the additional fluventic modifier as one would in other suborders. These soils are fertile and express forests with floodplain tree species (as the fluventic subgrouby greg.schmidt - Soil Taxonomy Forum