The Geocarto International Centre in Hong Kong wrote an article in the Aug 2018 Arborist News ("An Integrated Approach to Tree Stress Monitoring"), as a follow-up to the article they published in Apr 2017 ("A New Technology Warns of Stressed Trees").

I wrote a summary on the Apr 2017 article here: http://openplants.blogspot.com/2017/05/monitoring-at-risk-trees-using-spectral.html

In the Aug 2018 article, as mentioned before, the spectral reflectance data were collected from satellites to observe the following in trees:

• Drop in near-infrared band
• Drop/shift in red-edge band
• Rise in red band, which means a drop in chlorophyll absorption

So, how much drop or rise would warrent concern about the tree's health? The article went on to show the spectral reflectance curves in different trees collected within a 4 to 6 years period. Keywords here being "retrospective study" [emphasis mine], as the author would mention later.

 Arborist News, Aug 2018, page 29

Arborist News, Aug 2018, page 30

The author highlighted a case where a 400 years old Ficus benjamina in Kowloon Park, Hong Kong deteriorated due to park redevelopment, branch failure due to typhoon and brown root rot. A treatment of Trichoderma was applied presumably after Sep 2013 when its removal was withdrawn. The spectral reflectance chart below reflected the claim that the tree improved in its health.

Arborist News, Aug 2018, page 31

 According to this chart:

• Rise in near-infrared band <- Indicates better leaf cellular structure
• Rise and fall in red-edge band <- Indicates rise in chlorophyll absorption in 2011, dropped in the subsequent years (coincide with application of Trichoderma) and rised again in 2017
• Not much difference in red band <- Indicates no difference in chlorophyll absorption

In my opinion, the chart does not indicate that the Trichoderma treatment has definitely suppressed the brown rot fungus. And while the tree's physiological health seemed to be improving, it structural condition is uncertain due to the redevelopment, wind-throw (typhoon), and anything prior to its decline.

Gardens by the Bay, Flower Dome

Flower Dome in Gardens by the Bay opened in November 2011 to the public. South American, South African, Australian plants. Mediterranean cool and relatively lower in humidity. Chilean Wine Palms or Jubaea chilensis are from the South American nation of Chile. Overpruning of fronds and/or nutrient decifiency affects the trunk's taper; causing it to develop a bottleneck trunk, which is also known as "penciling". The narrower trunk could lead to fracturing. Makes fronds smaller and skinnier. Been 6, 7 years since the palms arrived in Singapore and they still have not overcame the penciling issue.

From the Palm Tree Doctor blog:
In addition to preventing malnutrition, proper maintenance fertilization provides the following benefits:

• More cost effective to keep palms healthy than replace
• Greatly increased size and fullness of the canopy
• Allows each frond to stay greener longer
• Allows self-cleaning palms to drop their dead fronds more rapidly
• Improves ability to survive hurricane force winds
• Accelerates recovery after storm damage
• Increases cold hardiness

 Penciling palms in differing severity. One in the background was in its death throes.

In order to harvest the sap to make wine, the whole palm have cut down, hence the name. Extremely slow-growing, making large specimens like these a rarity.

 A slightly narrow trunk would represent leaner days, quite usual for single trunk palms of larger girth - whether in the wild, nursery-grown or planted in the landscape.

I think this was the one in the middle of the Chilean wine palms' group photo. Has smaller and narrower fronds.