Trees and their leaves

I have a question concerning trees and their leaves:

I live in Helsinki, Finland and on my home street there are maples in a row between the street and a sportsground on the opposite side to where I live. I’m not sure when those trees were planted but I’m quite sure that they were planted all at the same time.

Now three of those trees are shorter than the others and they drop their leaves lot later than the others. It’s now 1:st of October and almost all leaves in the other trees are already red or yellow but those three trees still have green leaves and they normally drop them in late November or early December.

I think the reason for this is that the communal heating water ducts are laid cross my street at the point where these three trees are. The ground is definitely warmer there which can clearly seen when the snow falls.

So my question is that does the fact that these trees keep their leaves longer when there is not so much sunlight cause the fact that those trees are stunted in their growth?

We had a maple next to a pond that dropped its leaves later than others. The pond had a liner so it wasn’t getting pond water through the ground. We assumed it was capturing water vapor as it evaporated from the pond. Or the water vapor moderated the temperature around the tree.

ETA - Sorry, this doesn’t answer your question in the last paragraph.

One thing to consider is whether the maple trees are all the same species. It looks like the Norway maple is the only indigenous maple in Finland, but unless there are regulations prohibiting the planting of non native species, there are many ornamental maples someone could have planted along the street. There are different growth patterns, leaf shapes, and leaf colors across the different maple species. You might compare the bark color and texture, the shape of the the winged seed pods, and the shapes of the leaves to see if you think they are all indigenous Norway maples. The “stunted” trees might be perfectly normal maples, but a different species of maple.

Also, are they “stunted”, or are they doing well, just shorter? Plants can be stunted if they don’t get enough sunlight, but they also grow taller if they are competing for sunlight, and may settle in and turn more energy into reproducing if they have everything they need.

Do they all flower and fruit (seeds with wings) in the spring? How large are they?

I have 5 red maple hybrids in a row that I planted 20 years ago. 2 of them are very tall and full. One is a little less so because it’s fighting with an evergreen in my neighbors yard for air space. The two on the ends are much smaller, one is more shaded and getting less sunlight, the other is planted in some hard pack earth that was used as a driveway for many years. They also start out green in the spring and change to red at different rates apparently based on the amount of sunlight they receive. It’s not unusual to see differences in trees like that, especially for trees that young.

The Arboretum Mustila, which is about 114km northeast of Helsinki, lists 26 species of maples as growing at their location, so it would appear that many non native maples can survive and do exist in Finland. You could always take some photos and collect some leaves along your street and then take a drive to the arboretum to compare them with the maples there. That might help you figure out if they are all the same kind of maple, and what they might be if they are not Norway maples.

I doubt it, in fact I would think those trees would be larger because they have a longer growing period per year. On the other hand, could they be leafing out too soon in the spring, fooled by the warmer soil, but then getting frost damage? Or on another level, could they be stunted because of the extra heat or drying out of the soil during the summer, despite the longer shoulder seasons?

They are all same species (maybe the Norway Maple I’m not a botanic) and as far as I’ve notice they seed all the same time in spring.

I used the word stunted because they are shorter than the others. In every other way they are similiar and as they were planted by Helsinki park maintenance (established in 18??) I’m sure that they were planted at the same time. That has been their major sin as it has meant that in some places all the trees die at the same time and must be replaced and thus for years that area has no tall trees. They have changed their methods in 90’s though.

Could the ductwork be restricting root growth, resulting in shorter tree heights?

Are these trees by chance near any street lights? I once had an office with a window and could observe a row of trees across the parking lot. There was a light on the side of the building just beyond them. The branches nearest that light kept their leaves long after all the other had fallen.