3-10: Land Use Issues

Underconstruction!!!

First: The rules of ecology (F.A. Bazzaz)

I. Global Carbon Cycle
II. Carbon Budgets of Landscapes
III. Species Diversity Issues

I. Global C cycle

• (Sundquist 1993)

  

  • Large pools with small turnover time
  • Small pools (atmosphere with fast turnover time
• (Schlesinger 1991)

  

  • Terrestrial impact

II. Carbon Budgets of Landscapes

• Why does land use impact atmospheric CO₂?
  • Production (C) flow-through vs. material recycling:
    • C storage on land due to production > respiration
    • Change in this balance changes net flux
  • Three major impacts:
    
    • Conversion of biomass C to CO₂
    • Conversion of soil OM to CO
    • Continued degradation of forest biomass
    • Note: there is no way to change a mature forest into a net C storage

Example 1: Comparison of C storage in temperate forest, grassland, crops

FOREST
	compartment	mass	carbon
	              (kg/m^2) (kg/m^2)
	------------------------------
	live biomass	28	14	(Ajtay et al. 1979)
	dead wood	2.66	1.33	(Harmon et al. 1986)
	litter		3	1.5	(Ajtay et al. 1979)
	soil OM			12	(Ajtay et al. 1979)
	TOTAL			29
	
GRASSLAND
	compartment	mass	carbon
		      (kg/m^2) (kg/m^2)
	------------------------------
	live biomass	2.1	1.05	(Ajtay et al. 1979)
	dead wood	0	0	
	litter		0.5	0.25	(Ajtay et al. 1979)
	soil OM			14	(Ajtay et al. 1979)
	TOTAL			15	

CULTIVATED LAND   


	compartment	mass	carbon
		      (kg/m^2) (kg/m^2)
	------------------------------
	live biomass	0.1	0.05	(Ajtay et al. 1979)
	dead wood	0	0	
	litter		00.5	0.025	(Ajtay et al. 1979)
	soil OM			8	(Ajtay et al. 1979)
	TOTAL			8

SUMMARY	
	compartment	forest	grassland	cropland
		       (kg/m^2)  (kg/m^2)	(kg/m^2)
	-------------------------------------------------
	live biomass	14	1.1		0.1
	dead wood	1.3	0		0
	litter		1.5	0.3		0.1
	soil OM		12	14		8
	TOTALS		29	15		8

Exmaple 2: Soils

• total C storage X years in cultivation (Mann 1986)
• carbon X years since clearing in tropical forests (Detwiler 1986)
• peat depth x year in Everglades cane fields (Allen and Chen 1984)

  

• soil C X time in Amazonian pasture (Cerri)

  

  • note potential for net storage with management
  • Note, though, that these were forests and are now grasslands

Example 3: Iowa's forest land areas increasing, wood volume decreasing because cut+mortality > growth

• Effects on atmosphere

  

• However, land use has not yet stopped (C flux by tropical country)

  

• Potential for land management: Table 1 from Samson et al (1993)

Part III: Species Diversity Issues

Note: many of the supporting images are not available at this time
• Global cycle of life diagram

  

• Modified production ---> species diagram

  

  • Global NPP = 225 PgOM/yr
• How many species??
• Best range of total estimate = 5-30 million species, 50% in tropical forests
• 225 Pg/year supports say 5 e6 species ---> 4.5 e10 gOM/species/yr
• average lifetime of species = 10e6 yr, assuming constante rate of population increase, net is 2.25e10 gOM/species/yr for maintaince and each species woth 4.5e10 +(10e6 * 2.25e10) = 2.25e17 gOM
• At minimum each species requires 4.5e10 gOM each year
• Modified life diagram including humans - removal of NPP form cycle and placement into human food chain (supporting ~ 1000 species) = removal of support for remaining 5e6 species
• How much NPP are humans using? Direct consumption table from Vitousek et al; co-opted table from Vitousek et al.
• More recent work on Marine systems suggests that , yes, marine total is small, but most of marine is from high-NPP coastal areas.

• ---

  Additional images not on the lecture

  Illustrates the factors that must be measured to estimate large-scale vegetation productivity. NASA Eos Science Steering Committee Report, Vol II, Figure 30.

  Relative intensity of vegetation over North America using AVHRR data integrated from April to November 1982. Ibid, Figure 32.