Forest StewardshipBasics of soils

Rob Harrison, Professor of Forest SoilsCollege of Forest ResourcesUniversity of WashingtonSeattle, WA 98195-2100

http://www.forestsoils.org/ForestSteward/

Forest Land Stewardship includes a faith in the future, and that what you do today will benefit and be enjoyed by people a long time from now.

To quote Aldo Leopold…

"We abuse land because we regard it as a commodity belonging to us. When we see land as a community to which we belong, we may begin to use it with love and respect."

"A thing is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends otherwise."

If you think you're owning forest land for the money, you may want to think again. However, many people should be able to pay the cost of owning their land (taxes, etc.) and enjoy some financial benefit from the land by growing and selling trees. That may not be among your goals, and often isn't, but it is a very worthy goal for many landowners.

Tree growth expression is a factor of:

1) Tree genes2) environment, including edaphic, or soil factors

An “Edaphologist” focuses on the soil as a habitat for living things, particularly plants

Soil provides (or doesn’t):

1) physical support2) air, CO2 to green, O2 to roots3) water4) temperature moderation5) protection from toxins (buffering)6) nutrient elements

Often not included:Home for plant-beneficial organisms (mutualists)

That said….

Trees do NOT need soil to get any of those

Trees can grow without soil

However, if that was the case, what would the poor soil scientists do?

Also important, though some of the processes of soil formation create better conditions for plant growth, many don’t, and soil development doesn’t necessarily coordinate with optimizing plant growth.

A typical elemental content life of granitic soil development

RobHarrison:whole soil structure texture

sand

sand

sandsilt

silt

siltsilt

RobHarrison:whole soil structure texture

Soil: (1) A dynamic naturalbody composed of mineraland organic materials andliving forms in which plantsgrow. (2) The collection ofnatural bodies occupyingparts of the earth’s surfacethat support plants and thathave properties due to theintegrated effect of climateand living matter acting uponparent material, as condi-tioned by relief, over periodsof time.

Soil Texture: The sizedistribution of individualparticles of a soil.

21% O2

0.033 % CO2

Soil aeration: The processby which atmospheric airenters the soil. The rate andamount of aeration dependson the size and continuity ofpore spaces, the degree ofwater logging, and the activ-ity of soil microorganisms.

< or = 21% O2

> or = 0.033 % CO2

Ectomycorrhizae

Endo-mycorrhizae

N Cycle of 38-y old DF (Wash State) vs. 22-y-old Eucalyptus grandis plantation, S. Brazil

Soil360

kg/ha

tree uptake90 kg/ha/y

return toforest floor45 kg/ha/y

leached fromforest floor15 kg/ha/y

understory0 kg/ha

trees1024 kg/ha

forest floor22 kg/ha

leached from soil0.6 kg/ha/y

Soil2809 kg/ha

tree uptake39 kg/ha/y

return toforest floor16 kg/ha/y

leached fromforest floor5 kg/ha/y

understory6 kg/ha

trees320 kg/ha

forest floor175 kg/ha

leached from soil0.6 kg/ha/y