CONTINUATION

The project was continued in 2011 by re-sampling soil of some tree

locations and in additional sample sites not associated with trees. Recent

samples were also analyzed for lead concentrations.

• Statistical analysis revealed soil parameter correlations between:

pH and nitrogen (p=0.000), C:N (p=0.003), SRP (p=0.016)

NO3 and NH3 (p=0.000), temperature (p=0.003)

Nitrogen and carbon (p=0.000), C:N (p=0.000)

Carbon and moisture (p=0.007)

Moisture and salinity (p=0.000); gravimetric H2O (p=0.029)

Longitude and carbon (p=0.045), temperature (p=0.001)

Latitude and compaction (p=0.023)

SRP with both longitude (p=0.011) and latitude (p=0.000)

• Spatial Interpolation

SRP reveals a gradient from both north to south and east-west

directions that support the statistical correlations reported above.

(Fig. 4b)

Pb and pH interpolations display an overlap between low pH and

high Pb concentrations (Fig. 3 a & b)

High NO3 values display as “islands” that may suggest associations

with particular land management regimes (i.e. high fertilizer input, no

management, etc.) (Fig. 4a)

Figure 3 : Interpolated surfaces for Pb (a), and pH(b). Surfaces were generated from average values

from each sample site using the ArcGIS 9.3 Krig function.

Figure 4: Interpolated surfaces for NO3(a), SRP (b). Surfaces were generated from average values

from each sample site using the ArcGIS 9.3 Krig function.

CONCLUSIONS

• Soil function in this urban forest may vary due to geographical associations with individual tree species.

• The distinct disconnection between health condition and soil runs counter to associations typically found in agro-ecology concepts where soil quality drives plant production.

• Our results linking soil patterns with tree species supports previously identified mechanisms in temperate savannah & tropical rainforest, where aboveground processes appear to alter associated soil properties.

• GIS technology can help manage large amounts of heterogeneous data required to assess ecosystem and landscape level patterns through easily accessible databases that can be used to generate practical tools.

• Spatial trends of Pb were most pronounced on soils collected under the elevated train tracks.

GEOGRAPHICAL ANALYSIS

Spatial Interpolation

In order to identify possible geographic spatial patterns, associated properties were

grouped together for possible visual correlations in Figure 1, with health condition

labeled for each sample tree. Total nitrogen (Fig. 1a) and Phosphate (Fig. 1b) display

gradient patterns with largest concentrations toward the southeast corner of the

study area near Oz park. Infiltration (Fig. 1c) and compaction (Fig. 1d) reveal

seemingly related and inverse patterns. Proximity to the eastern border (Lake

Michigan shore) increases infiltration values and decreases compaction. Properties

were not run across species due to inadequate sample size for the analyses.

Figure 1 (a-d): Interpolated surfaces for 4 of the 9 tested soil parameters; Total N (a), PO4 (b), infiltration rates (c), and

soil compaction (d). Surfaces were generated from average values from each sample site using the ArcGIS 9.2 Krig

function. Distribution of the three tree health conditions is also shown. Chi-squares were also performed using Figure 1

and the other five parameter interpolation maps to assess the randomness of condition distributions throughout the

various interpolated value ranges. No significant difference in health distributions were found for any soil property.

BACKGROUND: Urban trees are increasingly being valued for their economical contributions based on the environmental functions they provide to urban ecosystems. Based on 2002 data, total value for urban forests in the

U.S. was estimated at $2.4 trillion. Forest value increases when a greater proportion of forest trees are healthy with large diameters yet, maintaining urban tree longevity is met with a vast array of challenges (e.g. diverse

management, limited root space, soil compaction, etc.). Although maximizing tree growth is recognized as a critical urban forestry objective, few forest health preservation programs exist. Including urban soil function and

integrating urban soils into forest management can help managers understand the effects of tree management decisions.

METHODS: This study tested for presence of feedbacks between soil quality & tree health, as well as between soil quality and tree species in Chicago, IL. Samples were taken from an area of approximately 4,000 trees, using

36 random individuals in a blocked sampling design, accounting for health categories (good, fair, poor, dead) across the four most common tree species (Gleditsia triancanthos, Acer saccharinum, Acer platanoides, and Tilia

americana). Nine soil properties were measured, statistical analysis was performed using univariate, multivariate, and geospatial statistical tests: NH4, NO3, Total PO4, Total N, Total C, pH, infiltration, compaction & moisture.

GEOSPATIAL STATISTICS

Moran’s I analyses reported significant clustering of DBH

values and additional General G analyses revealed that all

significant clusters consisted of high DBH values for the good

trees (Fig. 2a) and for each study species (Fig. 2b-e).

Figure 2 (a-e): General G tests revealed high DBH values to be significantly clustered for

trees with Good condition (a). Other significant clustering was found in the high DBH

values for each of the four tree species included in the study (b-e).

STATISTICAL ANALYSIS

•No patterns were found linking any of the nine soil properties to tree conditions

(p>0.05)

•In contrast, tree species did show differences in the values for the soil

macronutrients nitrate (F=3.85; p=0.022) and phosphorus (F=4.60; p=0.012), as

well as for soil pH (F=3.42; p=0.033)

Acknowledgements to the support from DePaul University, College of Liberal Arts & Sciences, College of Science & Health, Environmental Science & Studies Dept., & CIRRUS

b c

a

d e

3a 3ab

4a 4b