Only just realized this when watching a diving video.

But why isn’t the ocean full of massive plants? The surface of the earth is covered is giant trees working to fight against gravity, wind, and fire.

But in the ocean you have little things like coral beds and sponges and maybe a kelp forest.

Seeing as weight is massively reduced, and the closer you get to the surface means more light, and water and nutrients are probably plentiful… Why isn’t the plant life more massive? What is the limiting factor to things evolving to be bigger?

Only thing I can think of is CO2 perhaps?

  • WoodScientist@lemmy.world
    462·
    11 hours ago

    Wind dominates the morphological structure of trees. Weight is not the limit to tree height. Trees could grow many times their current maximum height on a planet with no wind. You could hang iron weights on most trees much greater than the weight of the tree. As long as the wind wasn’t blowing hard, the tree would stand.

    Wind, the movement of something as light as air, is able to dominate the form land plants have evolved into.

    Now realize that water has a thousand times the density of air.

    There’s a reason all it takes to cause a local explosion of diversity in sea life is to dump something solid like a subway car into the sea. Water has so much momentum behind it that life struggles just to remain firmly fixed in one place while subject to waves and current.

    EDIT: Also one other major structural factor: soil! Dry well compacted soils are stronger than moist loose soils. The sea bed is an ever-churning bed of loose water logged mud and sand. So not only are ocean plants subject to much greater lateral loads due to the 1000x density of water over air, but those ocean plants also must cling to the worst foundation imaginable.

    • cogitase@lemmy.dbzer0.com
      6·
      10 hours ago

      Trees could grow many times their current maximum height on a planet with no wind.

      By analyzing the interplay between these forces, a team of biologists led by George Koch of Northern Arizona University calculated the theoretical maximum tree height, or the point at which opposing forces balance out and a tree stops growing. This point lies somewhere between 400 and 426 feet (122 and 130 m)…

      “As trees grow taller, increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth,” the biologists wrote in a 2004 article in the journal Nature. This limit lies at or just above 400 feet.

      • WoodScientist@lemmy.world
        9·
        10 hours ago

        That article is unfortunately devoid of the information we need.

        I however managed to find the Nature article that it appears to be based on.

        https://annas-archive.pk/scidb/10.1038/nature02417/

        Trees do face limits on their height due to the limits of the lengths capillary forces can draw water up through their cells. However, the figure quoted is from a regression analysis of living trees. It’s not a prediction of how tall trees could evolve if certain environmental stresses were removed. It’s a prediction of the maximum height achievable by California Redwoods.

        From the paper:

        At reserves further north and closer to the coast, stronger storms may explain the lower heights (,100 m), yet similar relationships of water potential and d13 C to height 27 as we observed in the tallest redwoods. At the drier inland margin of redwood’s natural distribution in northern California, maximum tree height is lower (,80 m), yet treetop values of minimum water potential (21.9 MPa) and maximum d13 C (222‰) are similar to those at 110 m in the tallest redwoods. Thus a similar physiological ceiling may be reached at different physical heights depending on water availability, with storm damage reducing realized heights at sites that are otherwise optimal

        So note that even though the trees on the coast have moisture conditions, they still reach lower heights than those further inland.

        The key thing to keep in mind is that the current maximum height achievable by living tree species is not the maximum height of trees allowable by physics. For example, instead of relying only on osmotic pressure, trees might evolve a staged-lift system, where they have upper reservoirs that feed one into the next. This is how tall skyscrapers handle their plumbing systems. A hundred story building will have water tanks at different levels rather than just one big tank on the roof. This prevents the need to have pipes at the base of the skyscraper capable of surviving 100 stories worth of water pressure.

        There’s no need for trees on our planet to evolve such mechanisms. The limits for wind kick in at similar heights to the limits of the water transport mechanisms trees have evolved. But other mechanisms would have different limits. There just isn’t any evolutionary pressure to develop them.

        Although, the paper does make being a tree scientist sound like an amazing job.

        We accessed tree crowns by shooting arrows trailing filament over branches with a powerful bow. Rope was then hauled over the branches and climbed via mechanical ascenders. Access to the treetop was achieved by arborist-style techniques. Heights were measured by lowering weighted fibreglass measuring tapes from the treetop to average ground level.