Vegetation control effects on the Vegetation control effects on the soil/plant/microbial system of soil/plant/microbial system of

loblolly pine plantationsloblolly pine plantations

Michael Blazier, Ph.D.Michael Blazier, Ph.D.

SFA Herbicide WorkshopSFA Herbicide Workshop

December 7, 2005December 7, 2005

Ecological function of herbicidesEcological function of herbicides

Reducing competing vegetation Reducing competing vegetation increasesincreases soil soil moisturemoisture– Important limitation to pine growth on sandy soils, areas Important limitation to pine growth on sandy soils, areas

with low rainfallwith low rainfall– Higher soil moisture in summer promotes growth of high-Higher soil moisture in summer promotes growth of high-

density, high-quality wooddensity, high-quality wood

Reducing competing vegetation Reducing competing vegetation re-distributes re-distributes nutrients to crop treesnutrients to crop trees– Allows soil to reach its fullest potential for meeting crop Allows soil to reach its fullest potential for meeting crop

tree nutrient demandtree nutrient demand– Most southern pine forest grows on nutrient-poor soilsMost southern pine forest grows on nutrient-poor soils

Ecological function of herbicidesEcological function of herbicides

Loblolly pine plantation N supply often out of sync with N Loblolly pine plantation N supply often out of sync with N demanddemand

0

20

60

100

80

40

0 3 9 126 15

Stand Age

demand

acquired

UPTAKE FROM SOIL

DEFICIT

REMOBILIZED

Nit

rog

en (

kg/h

a/yr

)

SOIL SUPPLY

Ecological function of herbicidesEcological function of herbicides

Improving crop tree growth with herbicide:Improving crop tree growth with herbicide:– Reducing underbrush = removal of main Reducing underbrush = removal of main

nutrient competition = better growth?nutrient competition = better growth?

Ecological function of herbicidesEcological function of herbicides

Improving crop tree growth with herbicide:Improving crop tree growth with herbicide:– Reducing underbrush = removal of main Reducing underbrush = removal of main

nutrient competition = better growth?nutrient competition = better growth?

NOT THE WHOLE ECOLOGICAL NOT THE WHOLE ECOLOGICAL STORY…STORY…