For example, strategic satellite remote-sensing efforts have achieved good levels of accuracy in assessing the amount of canopy change over time in forested regions [ 25].
We use data from a birth cohort based in New York City to examine the relationship of total urban tree canopy coverage with childhood asthma, wheeze, rhinitis, and allergic sensitization at the individual level.
Regression models adjusted for covariates indicated a significant positive association of tree canopy coverage with diagnosed asthma at 7 years of age (adjusted RR = 1.17; 95% CI: 1.02, 1.33) consistent with a 17% increase in the prevalence of asthma with each SD increase in tree canopy coverage (for tree canopy coverage, the SD was 8%).
The proportion of children with allergic sensitization to tree pollen increased with increasing quartiles of tree canopy coverage (Table 3, p = 0.03).
Urban variables studied are: the extent of tree canopy coverage, traffic load, surfaces albedo modification, street deepening aspect and the street's ventilation.
Proportions of children with asthma, wheeze, or rhinitis did not appear to be related to quartiles of tree canopy coverage near the prenatal address (Table 3).
Associations of tree canopy coverage with asthma at 5 years, and with wheeze at 5 or 7 years, were similar in magnitude, but not statistically significant [ Table 4; see also Supplemental Material, Figure S1 (http://dx.doi.org/10.1289/ehp.1205513)].
We also measured the percentage of herbaceous vegetation (grass, forbs, and total herbaceous vegetation) canopy coverage using 20 × 50-cm Daubenmire plots (Daubenmire 1959).
We randomly selected five non-overlapping sampling points within each transect at which we recorded vertical density of vegetation and canopy coverage.
Conclusions: Results did not support the hypothesized protective association of urban tree canopy coverage with asthma or allergy-related outcomes.
