Structure and Sustainability of Sacramento's Urban Forest

The urban forest of Sacramento County, California, contains approximately 6 million trees. Tree density and basal area decrease along an urban-rural gradient from city (73 trees/ha, 13.4 m/ha), to suburban (64 trees/ha, 4.5 m/ha), to rural (10 trees/ha, 0.9 m/ha) sectors. Within the city and suburban sectors, where 90% of all residents live, approximately 75% of total tree numbers, basal area, and leaf area occurs on residential land. Sacramento's urban forest is relatively sustainable. Seventy percent of the trees are in excellent or good condition, the population is well distributed by age and species, and the most abundant species are reasonably well suited to local conditions. Factors likely to trigger change in Sacramento's urban forest during the next 50 years are described (e.g., water conservation, development patterns, landscape maintenance issues) and species with potential to thrive in these conditions are listed for future planting and evaluation. A comparison of canopy cover, density, and basal area of trees in the city sectors of Sacramento and Chicago, Illinois, reveal surprising similarities. However, in Sacramento these values decrease along the urban-rural gradient, while in Chicago they increase. As human influences wane along the gradient, such factors as climate, soils, competition, and natural regeneration become more important forces in causing urban forest structure to approach presettlement conditions.