Tree failures along State Road A1A tied to saltwater intrusion; CRA to replace select palms and pilot alternative plantings

CRA staff and consultants told the board on April 2 that clusters of recently planted Montgomery palms along State Road A1A are failing because of standing wet, saline soil in the small sidewalk planting pits.

Jonathan Hague of Kimley‑Horn presented project history and planting layout along the A1A streetscape, noting that constrained sidewalk widths required trees to be planted in 36‑inch tree‑grate pits to preserve ADA passing clearances. He described extreme wind and flood events since installation (late 2023–2024), then introduced consulting arborist Lisa Hammer, who detailed field and laboratory findings.

Hammer said soil cores and a water sample from several failed pits showed very high sodium, chloride and soluble salt levels consistent with seawater. In one sampled pit inspectors found standing water and an old irrigation sleeve that retained water; root systems were heavily decayed in pits where trees had died. Hammer concluded that saltwater intrusion from below and persistently saturated soils were the most likely cause of clustered palm decline. She noted some pits with better drainage and healthier root systems nearby, indicating heterogeneous subsurface conditions.

Based on the investigation, staff recommended the following interim actions: remove 30 dead palms where soils are continuously saturated and not replace them; replant 22 dead but salvageable locations where pits are adjacent to healthy trees and soils are more favorable; fill the permanently wet pits with structural fill and restore pavers; and run a pilot in one problem pit testing a soil‑volume vault and geotextile salinity barrier (a subsurface vault approach shown to limit salt intrusion in other coastal projects). For a planned future southern phase with wider sidewalks, staff recommended introducing a different, more flood‑ and salt‑tolerant street tree (green buttonwood) in locations that allow larger soil volume.

Board members asked for additional investigation steps before removing every location: several suggested short‑term monitoring of water rise and percolation in representative pits (after tides/rain) and testing a mature root ball or larger planting in one location. Commissioners also asked staff to check for abandoned irrigation lines or other infrastructure in pits that could retain water, and to explore whether failure correlates with the status of nearby flap gates and other coastal drainage infrastructure.

Susan Goldberg said the CRA has been coordinating with public utilities and has contracts planned to investigate flap gates in the district; board members asked staff to examine those data for correlation with failing pits. Members asked that staff pursue the pilot design (a subsurface vault with geotextile barrier) on one test pit before committing to large‑scale reconstruction. Several board members also suggested outreach to adjacent private property owners to see whether private‑side planting could be an alternative in some blocks.

The board did not take a formal vote to approve an immediate large‑scale structural vault solution but directed staff to proceed with the recommended removals and replacements targeted at locations where trees are salvageable, to fill permanently saturated pits, and to design and test a subsurface pilot (cost and feasibility to be returned to the board). Staff will also coordinate with public utilities and the city’s flap‑gate work to see whether broader drainage solutions affect tree survivability.