Ecological Benefits of
Taipei's Street Trees

Estimated using a species-specific allometric equation. Above-ground biomass B_AG = a × DBH^b (species-specific a, b parameters calibrated from domestic and international urban-tree biomass literature; species without published parameters use generic values), plus a below-ground root-to-shoot ratio R = 0.25 (IPCC 2006 GL Vol. 4 Ch. 4 Table 4.4[1]) for total biomass, multiplied by a carbon fraction CF = 0.463 (within the IPCC 2006 range[1], consistent with Taiwan-specific timber carbon-content measurements — Lin et al. 2002[2]) to get carbon storage (kg C), then × 44/12 for the CO₂ equivalent. Annual carbon uptake is further multiplied by a 4% annual growth rate (a conservative value from domestic urban street-tree research). Trunk diameters come from surveys by the Taipei Public Works Department's Parks and Street Lights Office and Hydraulic Engineering Office; these are not field-measured carbon-inventory values.

The carbon figures shown all come from the backend /stats endpoint (total_carbon_tonnes, annual_co2_kg, etc.). When no backend value exists, an individual tree's detail page falls back to the Brown (1997)[14] biomass equation (a front-end fallback only, not the primary method).

Estimated from crown vertical projection area. Annual interception = crown projection area × Taipei's average annual rainfall of 2,400 mm × an interception coefficient of 0.08 (Xiao et al., 2000[4]). Crown projection area = π × (crown width ÷ 2)², preferring the government survey's field-measured crown width (about 94% of street trees, 100% of riverside park trees, and about 99% of park trees have a measured crown width); trees without a measurement use crown width ≈ height × 0.4 (Pretzsch et al., 2015[11]).

Unit conversion: 1 m² × 1 mm = 1 L; ÷ 1000 for m³. This method replaces an earlier version that used a DBH-based lookup table — street trees (94%), riverside trees (100%), and park trees (about 99%) now have measured crown widths.

First estimates net PM2.5 removal, then converts it to a health value. Annual removal = crown projection area × a net removal rate of 0.30 g/m²/yr (Nowak et al., 2013[5], measured at 0.13–0.36 g/m² across ten U.S. cities; this rate is per unit of crown projection and already accounts for leaf layers and resuspension, so it is not multiplied by LAI again; a value near the high end is used to reflect Taipei's higher PM2.5 levels and frequent rain-driven washout). The health value uses Nowak et al. (2013)[5]'s ten-city average of US$682,000/tonne (based primarily on statistical value of life from mortality data), converted at an exchange rate of 30 and ÷1000 to ≈ NT$20,000/kg.

Prefers the government survey's field-measured crown width; falls back to a height-based estimate otherwise. This method replaces an earlier version that multiplied leaf area by LAI and overestimated by roughly 1–2 orders of magnitude. The health value is a conservative reference based on an international VSL (value of statistical life) benchmark, not an officially certified Taiwan figure.

Estimates each tree's shaded area from its crown vertical projection area. Field studies show that surface temperature under tree shade can be 10°C or more lower than on unshaded pavement, with a noticeably lower perceived temperature, and can reduce summer air-conditioning load in nearby buildings (Armson et al., 2012[10]). Crown projection area is also the geometric basis for leaf-area and interception calculations across the i-Tree family of models.

When no measured crown width is available, it is estimated from height as crown width ≈ height × 0.4 (an empirical urban-tree crown-to-height ratio, Pretzsch et al., 2015[11]). Individual tree pages also show a "≈ N parking spaces" conversion (using 12.5 m² per standard car parking space) to help the public grasp the scale of the shade provided.