Urban Road Landscape Planting

Urban Road: Landscape and Planting

Overview

Road-fronting planting is where a landscape architect's design meets the urban-road code. This skill carries the planting dimensions and the species classification needed to apply them, plus the qualitative landscape-and-ecology provisions that belong in the design narrative.

Before applying any value, confirm which instrument and version govern via urban-road-code-fundamentals, and note the live standard-versus-code discrepancy on the tree pit recorded there. The 應/不得/宜/不宜 wording rules from that skill apply throughout: "shall" renders 應 or 不得, "should" renders 宜, "should not" renders 不宜. 不宜 is a default prohibition (do not do it unless justified), not a soft hint, so a 不宜 breach carries a heavier burden to justify than a plain 宜.

A tree pit also consumes sidewalk width, so a planting check and a clear-width check are two halves of the same drawing. The width side lives in urban-road-pedestrian-accessibility.

Planting Design (§16.2)

• Tree pit clear area shall exceed 1.5 m², with priority given to crown development space and continuous linear configuration (item 6). Note 設計標準 §21(4) states area "1.5 m² or more"; the standard outranks the code where they differ.
• The 1.5 m² floor attaches to the discrete pit (植穴). Item 6 names 植穴 and 植栽帶 separately and puts the numeric duty on the former, while naming continuous linear beds as the preferred configuration. In a continuous bed the qualifying area accrues along the run, so a bed narrower than a compliant square pit is not thereby non-compliant. Never back-convert 1.5 m² into a width floor of about 1.22 m; that inference holds only for a square discrete pit.
• Spacing: large-canopy species 8 m to 10 m; small-canopy species 4 m to 7 m (item 6).
• Planting shall not obstruct sight lines or driving safety (item 3).
• Within 25 m of the stop line at intersections, and at sidewalk intersection sections and vehicle crossings, beds should use ground flora or turf, with shrub height below 0.5 m (items 10, 11).
• Large-canopy trees should be planted on sidewalks 4 m wide or wider, or adjoining building setbacks (item 12).
• Species should favour native, tolerant, low-maintenance species and should avoid invasive, malodorous, toxic-pollen, heavy-sap or heavy-fruit-drop species (item 4). Shallow-, buttress- and prop-rooted species require assessment of long-term adverse effects (item 5).

Soil Depth (§16.2 items 7 and 8)

Two distinct sets. Always state which set is being applied; the gap reaches 60 cm.

Species Classification (Appendix 4 items 19 and 20)

Classify a proposed species first: canopy size drives the spacing and sidewalk-width rules, and root form drives the §16.2 item 5 assessment and the soil-depth table.

• Root form: shallow 小葉欖仁, 黑板樹, 莿桐; buttress 鳳凰木, 吉貝, 銀葉板根; prop 榕樹, 印度橡膠樹, 雀榕, 垂榕
• Large canopy (mature crown ≥ 6 m): 榕樹, 樟樹, 臺灣欒樹, 茄苳, 楓香, 欖仁樹, 風鈴木
• Small canopy (mature crown ≤ 5 m): 臺灣肖楠, 海檬果, 臺灣海桐, 福木, 厚皮香

Island Planting (§15.2)

• Planted median width should exceed 1.2 m (a planted median narrower than this is a WARNING).
• Channelising island area should be 7 m² or more, minimum 5 m²; planting must not compromise the sight triangle.

Qualitative Landscape and Ecology (§16.1, §16.3 to §16.8)

No numeric thresholds, mostly 宜. These support the design narrative and review comments, never a pass-or-fail finding.

• §16.1 principles: beautification, cultural landscape with resident participation, ecological conservation (habitat diversity, green-corridor networks, wildlife passages, native site-adapted species, soil permeability and retention), facility reduction and consolidation.
• §16.3 drainage: earth, grass or cobble channels from local materials where subgrade and sidewalk quality allow; planting to screen concrete slope structures; compound culvert sections as wildlife passages with diameter rising as length rises; less culverting and concreting, detention basins where the setting allows.
• §16.4 to §16.6 bridges, tunnels, slopes: slim structures, integrate form and texture, conceal deck drainage, reserve wall and three-dimensional greening space, retain natural landform and rock, reduce cut and fill, use porous materials for habitat.
• §16.7 lighting: combined poles at intersections, light and maintainable fittings, reduce light pollution, keep high-mast lighting clear of tree crowns. Numeric illuminance sits in Ch.19, held at chapter level in the fundamentals references.
• §16.8 noise barriers: integrate with landscape, reserve planting space, pattern transparent barriers against bird strike, treat terminal ends, anti-glare design.

Full clause text in ../urban-road-code-fundamentals/references/ch16-landscape-ecology.md.

Worked Example

Same drawing as the worked example in urban-road-pedestrian-accessibility; this skill checks the planting half, that skill checks the width half. Neither half is conclusive alone.

Input. A 3.2 m sidewalk on a 15 m secondary road, with a 1.0 m green strip running along the sidewalk centre. Proposed: 臺灣欒樹 in that strip at 6 m spacing, soil depth 60 cm, first tree 18 m from the intersection stop line.

Check.

1. Classify. 臺灣欒樹 is large canopy and deep-rooted (Appendix 4). This sets spacing to 8 to 10 m, sidewalk-width preference to 4 m, and soil depth to 90 cm survival / 150 cm growth.
2. Configuration and area. A 1.0 m continuous strip is a 植栽帶, not a discrete 植穴, and item 6 names continuous linear beds as the preferred form. Area per tree is 1.0 × 6 = 6 m², well over 1.5 m². PASS. The strip being narrower than a compliant 1.22 m square pit is not a finding: the 1.5 m² floor is an area duty on a discrete pit, not a width floor on a bed.
3. Spacing. Proposed 6 m against 8 to 10 m. WARNING, item 6 uses 宜. Widening to 8 m would also raise area per tree to 8 m².
4. Canopy versus sidewalk width. Large canopy on a 3.2 m sidewalk; item 12 wants 4 m. Uses 宜, so WARNING with a stated reason in the design report.
5. Soil depth. Deep-rooted needs 90 cm to survive; 60 cm is below even survival. ERROR against §16.2 item 7. This, not the strip width, is what makes the 1.0 m centre strip a poor host for a deep-rooted large-canopy species.
6. Sight line. 18 m is inside the 25 m zone. WARNING on item 10 wording, escalating to ERROR under item 3 (不得) if the crown or trunk blocks the sight triangle (Appendix 3 item 35).

Result. The planting rules yield one determinate violation (soil depth) and three items needing justification. Nothing here prohibits the centre strip. What kills it is §6.1: the two flanking clear widths total 2.2 m and the better side can only reach 1.2 m if the other drops to 1.0 m, breaching the 1.2 m per-side floor — checked in urban-road-pedestrian-accessibility.

The loop that matters. Moving the strip kerbside fixes the §6.1 failure, but it also converts the planting from a continuous bed back into discrete pits, at which point the 1.5 m² pit floor does bind: a 1.2 m by 1.2 m pit gives 1.44 m² and becomes an ERROR under §16.2 item 6 and 設計標準 §21(4). Changing the width answer changes the planting answer. Re-run both skills after any re-section.