For the Umatilla NF Collaborative (from B. Bormann; 7-10-2013)
Pre-synthesis on effects of hardwood shrubs and trees on mineral soil organic matter (and hence, waterholding capacity, infiltration, and nutrients)—an initial set of knowns and unknowns (a full synthesis is
needed). Heavy to personal work (easily accessible given lack of time)
Knowns (not necessarily specific to Umatilla Forest soils)

Starting with low levels (primary succession), shrubs and hardwoods build mineral-soil organic
matter quickly (and more quickly than conifers); references: Glacier Bay, AK: Ugolini 1968;
Bormann and Sidle 1990; New Hampshire glacial outwash: Bormann et al. 1993.

Conifers such as Douglas-fir and pines, growing rapidly can deplete mineral-soil OM in SE US,
presumably in search for soil nutrients (Wells and Jorgenson 1975) and in southwestern OR
(Bormann et al. 2008; see p. 2780)
Wells, C.G., Jorgensen, J.R., 1975. Nutrient cycling in loblolly pine plantations. In: Bernier, B.,
Winget, C.H. (Eds.), Forest Soils and Forest Land Management. In: Proceedings of the Fourth
North American Forest Soils Conference. Laval University Press, Quebec, Canada, pp. 137158.







Alders have large positive effects on mineral soil (synthesis): Bormann et al. 1994.
Starting with intermediate levels, shrubs and hardwoods build mineral-soil organic matter
quickly (and more quickly than conifers). References: agriculture to forest: Poulton 2003); Red
alder compared to Douglas-fir: Bormann and DeBell 1981;
Mineral soil OM can build under conifers after soil disturbance from windthrow: Bormann et al.
1995.
Deciduous trees and shrubs alter upper mineral soil layers by dropping more litter and cycling
nutrients faster than conifers (e.g., Cole et al. 1978).
Deciduous trees and shrubs support different soil organisms than conifers with generally mode
species that mix soil layers (e.g., earthworms).
Conifers are associated with podsolization which can clog upper mineral soil layers and build
thick organic layers. In wet, cool locations this can lead to lateral flow through organics resulting
in “brown water” streams: Bormann et al. 1995.
Many hardwood shrubs and trees root far deeper than conifers: Zweineiki and Newton 1995
and can perhaps capture and use more water than conifers (may not get to stream as much;
e.g., Juniper?)
Unpublished paper in review:
Managed early-seral stands aid long-term productivity and biodiversity
in fire-prone “conifer” forests in southwestern Oregon
Decadal change (Mg ha-1)
Bernard T. Bormann, Robyn L. Darbyshire, Peter S. Homann,
Brett A. Morrissette, S. Mark Nay, and Susan N. Little
10
5
B horizon soil organic matter
Tukey 0.05
a
a
0
-5
a
b
0.2
0.1
B horizon nitrogen
Tukey 0.10
ab
ab
a
b
0.0
-10
-15
-20
-0.1
-0.2
Figure R7. Change in B horizon organic matter and N masses (mean ± 90% CI) over a
decade (8 or 11 years). B horizon is defined by the equivalent-layer approach as the
layer containing 600 Mg <4-mm inorganic matter ha-1 that underlies the surface layer
which contains 300 Mg <4-mm inorganic matter ha-1. Sample size is 5, 8, 6, 4 for
mature Control and Thinned, Early-seral, and Douglas-fir plantation, respectively.
Notes re this unpublished paper:



Mature stands are 80-110 year old Douglas-fir stands (pretreatment condition)
Early seral plantations are dense hardwood shrubs and young trees with a scattering of Douglasfir and knobcone pines
Douglas-fir plantations are 10 by 10 planted fir with hardwood slashing (not completely
eliminated).
Good questions


Is larch more like pines and Douglas-fir or hardwoods since it is deciduous?
Need to scour the hyro literature for direct measures of effects on infiltration, WHC,
aggregation, soil depths