Urban trees more than numbers

The number of trees does not necessarily determine how much shade a city has. The most important factor for street shade, urban cooling and the quality of public spaces is the canopy cover built up over years of growth. When mature trees disappear, planting replacements does not immediately restore the shade that was lost. The changes to Taipei’s urban trees in the past few years are not merely a landscaping issue, but a urban environment and public governance matter.

To understand what is happening to Taipei’s tree cover, we can look at two sets of numbers: the number of trees removed and the extent of canopy cover shown in satellite imagery. This reflects the area of ground covered by leaves and branches when viewed from above.

Publicly available data show that Taipei removed 1,425 trees in 2024. That number rose to 3,164 last year — an increase of 1,739 trees, or about 122 percent in a single year. In total 4,589 trees were removed over two years.

Satellite imagery provides the canopy cover data. Shen Sheng-feng (沈聖峰), a researcher at Academia Sinica’s biodiversity research center, uses imagery from the European Space Agency’s Sentinel-2 satellites to analyze urban areas and surrounding mountain forests separately. The results showed that Taipei’s urban tree canopy covered approximately 628 hectares in 2024, falling to about 615 hectares this year. This net decline of approximately 13.7 hectares over two years is equivalent to almost 20 soccer fields.

Canopy covers figures are significant because even planting new trees does not mean that urban shade immediately increases. Newly planted saplings need years to provide a comparable amount of shade to mature trees with large canopies.

The 13.7 hectare decline in tree canopy cannot be directly attributed to trees being cut down by the city government. Tree removal, land development, heavy pruning, transplantation and natural disasters all cause changes in tree canopy.

We do have clear records for some cases. This year, a 40-year-old rosewood tree near Dongmen Market was scheduled to be transplanted, but was instead cut down by a contractor. The authorities penalized the contractor and sought NT$325,000 in compensation.

The number of trees removed annually in Taipei increased by about 122 percent in one year, while during the same period, satellite data showed a decline in urban tree canopy.

Data on each of the 3,164 trees need to be made available. It should be established what their species, ages and trunk diameters were; why they had to be removed; whether safety assessments had been carried out; and which among them could have been transplanted or preserved in place.

Urban tree management should establish a system that can be monitored over the long term. It should include itemized records of tree removals, transplants, assessments and replacement plantings, and publish annual tree-canopy coverage rates and changes for each administrative district. Long-term standard indicators for mature tree canopy should be established, ensuring that different city administrations can be compared with the same standard across the years.

We already know about the 13.7 hectare decline in Taipei’s urban tree canopy over two yearsthrough satellite imagery. Why 3,164 trees were removed, and exactly how much those removals contributed to the decline in tree canopy should be answered through complete and publicly accessible data.

Urban greening should not be measured simply by how many trees have been planted. What matters more is how much mature tree canopy — capable of providing shade, cooling the city, and continuing to grow — the city would have in the years to come.