More than two decades of NASA satellite imagery across 346 city parks show that spring leaf-out in New York City is occurring later, not earlier. Spring was defined as when at least 15% of park trees leafed out. Warmer winters reduce the chilling that temperate trees need to reset, causing delayed leaf-out, shorter green seasons, and reduced urban shade. Medium-sized parks experience the largest delays, with spring arriving three to five days late; large parks see two-day delays and tiny pocket parks about one day. Delayed leaf-out reduces shade, increases heat exposure, disrupts wildlife food and shelter, and weakens native trees like oaks and maples.
The culprit is warmer winters that mess with the trees' internal clocks. Trees in temperate regions, including those in New York City, need a proper cold spell to reset for spring. Without that chill, they don't know when to wake up. So instead of bursting into bloom, they stall-resulting in delayed leaf-outs, shorter green seasons and less shade when we need it most.
Researchers analyzed more than two decades of NASA satellite images from 346 city parks. They defined spring's start as when at least 15% of the trees in a park leafed out. The results flipped expectations: Spring is actually coming later, not earlier and the effect is most pronounced in medium-sized parks like Bryant Park and City Hall Park. These spaces-too big to fully blend into the urban grid, too small to buffer against it-are caught in a heat trap.
'It's going to be really disruptive for a lot of wildlife that depend on these trees for food, for shelter,' Novem Auyeung of NYC Parks told Gothamist . Humans lose out, too, with less shade, hotter streets and fewer leafy canopies to soften the city's concrete edges. Over the past 50 years, NYC winters have warmed by more than three degrees Fahrenheit. That means less photosynthesis, weaker growth and native trees like oaks and maples losing ground
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