Overview
This project explores how neighborhood street trees change over time in residential areas of San José, CA. Public street trees in park strips were the focus because these spaces depend on both city systems and adjacent property stewardship.
Two groups were reviewed: recently planted young trees from the 2020 inventory, and a separate group of dead planting-site records from the same inventory. Together, they offer a pilot look at establishment, replacement, and canopy continuity.
Young Trees: Five-Year Outcomes
This group includes public street trees that were small in 2020 and likely represented relatively recent plantings. In 2025, each site was checked to determine whether the original tree was still present, whether a new tree had replaced it, or whether the site was vacant.
Site-Adjusted Survival Rates Among Common Species
Because some species were planted in groups at the same address, survival rates below were adjusted so repeated same-species plantings at one property counted as one site.
| Species | Sites (n) | Trees (n) | Survival |
|---|---|---|---|
| Ulmus propinqua (Sunshine elm)* | 12 | 12 | 100.0% |
| Lagerstroemia indica (crape myrtle) | 287 | 437 | 88.3% |
| Pistacia chinensis (Chinese pistache) | 102 | 112 | 87.7% |
| Ginkgo biloba (ginkgo) | 69 | 81 | 83.8% |
| Acer × freemanii (Freeman maple) | 41 | 54 | 73.6% |
| Zelkova serrata (Japanese zelkova) | 13 | 18 | 69.2% |
| Tristaniopsis laurina (water gum) | 20 | 23 | 62.5% |
| Prunus serrulata (flowering cherry) | 10 | 11 | 40.0% |
* Ten of twelve observed Ulmus propinqua sites occurred along one residential street segment.
Observed Replacement Trees After Young Tree Loss
Where original young trees were absent, replacement plantings were recorded when visible from the public right-of-way. Lagerstroemia indica (crape myrtle) was by far the most common observed replacement.
| Species | Sites (n) |
|---|---|
| Lagerstroemia indica (crape myrtle) | 23 |
| Pistacia chinensis (Chinese pistache) | 6 |
| Zelkova serrata (Japanese zelkova) | 5 |
| Prunus cerasifera (purple-leaf plum) | 4 |
| Acer palmatum (Japanese maple) | 3 |
Are Neighborhood Trees Getting Smaller?
From the 2020 District 10 dead-tree inventory, I reviewed all 83 records where a known former dead park strip street tree had been replaced by a live tree by 2025. Using locally observed canopy spread values from the District 10 inventory, I compared the typical canopy size of former and replacement species.
Canopy Size Class Shifts
To make canopy-size changes easier to compare, species were grouped by their median observed canopy spread in District 10 park strips. These are local size classes, not maximum possible species sizes. The table below uses one address as one site, so repeated tree replacements at the same property do not outweigh other sites.
| Canopy Class | Local Median Spread |
|---|---|
| Compact | 15 ft or less |
| Mid-canopy | 16–24 ft |
| Broad canopy | 25 ft or more |
| Former Site Size | Sites (n) | Shifted Smaller | Stayed Similar | Shifted Larger |
|---|---|---|---|---|
| Broad canopy | 18 | 94.4% | 5.6% | N/A |
| Mid-canopy | 14 | 78.6% | 7.1% | 14.3% |
| Compact | 38 | N/A | 78.9% | 21.1% |
N/A indicates a shift direction that is not possible from that starting class under this three-class system.
Confidence in Size Estimates
| Confidence | Reference Trees (n) |
|---|---|
| High | 30+ |
| Medium | 10–29 |
| Low | 1–9 |
The smaller-canopy trend remained when limited to medium- and high-confidence species comparisons.
Replacement Trees at Dead, Stump, and Vacant Sites
Lagerstroemia indica (crape myrtle) again appeared as the most common replacement taxon. It was also the most common species in the younger planting cohort, where it showed strong five-year survival. In the District 10 inventory, its median observed canopy spread was 12 feet—illustrating how a successful and frequently selected species can still represent a smaller canopy choice than many former shade trees.
| Replacement Taxon | Sites (n) |
|---|---|
| Lagerstroemia indica (crape myrtle) | 16 |
| Acer × freemanii (Freeman maple) | 5 |
| Cercis canadensis (redbud) | 5 |
| Jacaranda mimosifolia (jacaranda) | 5 |
| Pistacia chinensis (Chinese pistache) | 4 |
Future Questions
- How do these patterns compare across other San José districts?
- Which species and site factors best predict survival?
- How long do vacant street tree sites typically remain empty?
- Are replacement choices shifting toward smaller or larger canopy trees over time?