The wet meadow on the way to the Portal Bridge is a floodplain, which means that this land gets seasonally flooded with water from Sackett's Brook. The flooding is natural and has been happening here for many, many years. Some years see more flooding than others - this past winter (2020) the meadow flooded so much that for a few weeks it looked more like a frozen lake!
These photos show how the water ran over the land when it flooded, bringing mud up onto the meadow and depositing it there. The mud (also called sediments) from the river is filled with minerals that plants need to grow, so every time there is a flood this helps the plants living in the floodplain.
Another way to talk about the frequent flooding of Sackett's Brook is to call it a disturbance. Natural disturbances like ice storms, wind events, fire and flooding change forests, especially when they happen repeatedly. Here, at the Sackett's Brook floodplain, the water disturbance from flooding is what keeps this area as an open meadow, a place where grasses and wildflowers are abundant. Most trees can't stand being flooded, but the ones that can are also here, including sycamore, cottonwood, elm and willow.
Another natural disturbance is when wild animals make changes to the land. Take a look at the second photo, what do you see? These are willow stumps that beavers left behind. Beavers love willow; the inner bark is one of their very favorite foods. After they eat the bark they also use the wood to build their dams and lodges. That's why we don't see the cut down trees in this photo - they dragged them away for food and building projects. And these willow stumps may look dead, but they are not - their roots are still very alive and they'll quickly grow right back. In fact, willows and beavers get along just fine - both need the wet, flooded land, where they have been living together for millions of years.