Most urban soils have been disturbed, displaced, or compacted. This
partially or totally destroying structure, reduces pore space and
increases bulk density.
2. Low organic matter content which disfavors aggregation. The
aggregating effect of soil organism activity is also reduced.
3. Low frequency of wet-dry or freeze-thaw cycles which enhance
aggregation and structure formation.
4. Urban soils are subjected to various compressive forces over a range
of moisture conditions that contribute to compaction.
5. Vegetation is subject to damage and reduction of cover, leaving the
soil bare and susceptible to crust formation, compaction, and erosion.
All of these deterimentally influence other soil properties such as water
infiltration and permeability, water-holding capacity, aeration status and root
penetrability, especially of the upper soil layers where roots are concentrated.
Poor vigor and decline in general well-being of trees and shrubs follow from the
lack of water and oxygen and poor root development. Mortality is the final result
under the stressful conditions of the urban environment.
Soil compaction and loss of pore space arises from forces exerted on the
soil surface compressing and crushing the aggregates into smaller sizes
(Patterson and Mader, 1982). Foot and vehicular traffic exert the forces. Soil
with high silt or very fine sand components coupled with low organic matter
content tends to naturally compact under certain moisture conditions and the
presence of vibrational forces (Craul and Klein, 1980). This phenomenon is
one reason for the compaction of the lower soil layers beyond the influence of
surface compactive forces. Urban soils may have bulk densities that occur
within the range of natural soils, but most often they are at or exceed the higher
limit of the bulk density range. Patterson (1976) found average values ranging
from 1.74 to 2.18 Mg/m3 in four profiles of the Washington, D.C. Mall. Root
penetration is highly restricted at values exceeding 1.70 Mg/m3. Craul and
Klein (1980) found a range of 1.54 to 1.90 Mg/m3 with most centering on 1.82
Mg/m3. Values from New York’s Central Park (unpublished data) range from
less than 1 .OO to 1.34 Mg/m3 for undisturbed surface soil and 1.52 to 1.96
Mg/m3 for subsoils.
Most urban soils have been disturbed, displaced, or compacted. Thispartially or totally destroying structure, reduces pore space andincreases bulk density.2. Low organic matter content which disfavors aggregation. Theaggregating effect of soil organism activity is also reduced.3. Low frequency of wet-dry or freeze-thaw cycles which enhanceaggregation and structure formation.4. Urban soils are subjected to various compressive forces over a rangeof moisture conditions that contribute to compaction.5. Vegetation is subject to damage and reduction of cover, leaving thesoil bare and susceptible to crust formation, compaction, and erosion.All of these deterimentally influence other soil properties such as waterinfiltration and permeability, water-holding capacity, aeration status and rootpenetrability, especially of the upper soil layers where roots are concentrated.Poor vigor and decline in general well-being of trees and shrubs follow from thelack of water and oxygen and poor root development. Mortality is the final resultunder the stressful conditions of the urban environment.Soil compaction and loss of pore space arises from forces exerted on thesoil surface compressing and crushing the aggregates into smaller sizes(Patterson and Mader, 1982). Foot and vehicular traffic exert the forces. Soilwith high silt or very fine sand components coupled with low organic mattercontent tends to naturally compact under certain moisture conditions and thepresence of vibrational forces (Craul and Klein, 1980). This phenomenon isone reason for the compaction of the lower soil layers beyond the influence ofsurface compactive forces. Urban soils may have bulk densities that occurwithin the range of natural soils, but most often they are at or exceed the higherlimit of the bulk density range. Patterson (1976) found average values rangingfrom 1.74 to 2.18 Mg/m3 in four profiles of the Washington, D.C. Mall. Rootpenetration is highly restricted at values exceeding 1.70 Mg/m3. Craul andKlein (1980) found a range of 1.54 to 1.90 Mg/m3 with most centering on 1.82Mg/m3. Values from New York’s Central Park (unpublished data) range fromless than 1 .OO to 1.34 Mg/m3 for undisturbed surface soil and 1.52 to 1.96Mg/m3 for subsoils.
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