The Pit and Mound Earthcache
This EarthCache lesson shows the rolling land shape typical of forestland and explains how it gets that way.
When I was about ten years old, one of my older brothers and I were walking in the woods and I noticed that the land was very rolling with little holes and hills. And I asked my brother why the ground was like that in the woods but not out in the fields. He didn't have an answer for me but the question stuck with me for years. About 12 twelve years later I got my answer when I attended a graduate student soil science seminar at Cornell University. This cache is an explanation of why the ground surface is more rolling in the woods.
All of the sites referred to in this cache can be seen from the trail and no bushwhacking is necessary. The coordinates at the top of the page take you to Stage 1, an area where you can see the beginning of the process of formation of Pit & Mound Topography. This is where the story of Pit and Mound Topography begins.
How Pits and Mounds Form - Windthrown trees, or trees blown over by wind, are a common sight in mature woods. As trees get older their crowns (tops) gets bigger and increases its chance of catching the wind and being blown down. Often the trees are literally ripped out by their roots and the tree plate (the major roots nearest the trees' base) is tipped up on edge like the ones you will see at stage 1. This creates the pit or hole where the roots and soil were. And over time the roots decay and soil falls down to form a small hill or mound below the tree plate. This location shows examples of windthrown trees from recent times and this is how the area looks at the beginning of the process of forming pit and mound topography.
Coordinates are given for the Trail Head for the section of the North Country Trail that this cache is on for you convenience. We recommend that you walk from the Trailhead into stage 1 and then visit stage 2 and 3 on your way back out.
At Stage 1 (N 41* 42.548 W 078* 54.070) You are in the area of three relatively new tree plates. Find the largest one, it’s furthest off the trail to the west. Estimate the average diameter and average thickness of the tree plate.
At Stage 2 At this location, look around you. You can see several old pits and mounds as they often appear in the woods. This is typical pit and mound topography (shape of the land) of a mature forest. How many mounds can you identify?
At Stage 3 (N 41* 42.503' W 078* 55.025') stand on the trail and look west. You will see the results of a fallen tree from very long ago. This is a large pit and mound indicating a very large tree was blown down here. The roots and trunk of the tree that created this mound are decayed away leaving only the pit and the mound of largely mineral soil. There are also small pole size (approximately 4-6 inch diameter) trees growing on the mound indicating its older age. Do you see any signs of the tree or roots from the original tree?
The pits and mounds create micro-topography or small scale variations in the land surface. These features provide sites for greater biodiversity. The pits often fill with water which can serve as vernal (temporary spring-time) pools in which frogs, toads and salamanders can breed. Other wildlife use these areas for drinking. In catching rainfall or snowmelt, the pits also serve to store water which will seep into the ground to water the trees and other vegetation as well as recharge (replenish) the water table. The pits also collect eroded soil and keep it from leaving the area. The pits gather leaves and other debris which gives them higher organic matter levels which in turn provides more nutrients, but are also wetter. Plants that need those conditions like wetland plants grow well in the pits.
In the photo above you can see the downed tree on the left and the root ball or tree plate on the right. The pit is at the base of the root plate on the right. Judging by the rooted tree seedlings on top of the root ball, this plate developed about 10 years ago.
But generally, trees don't grow well in the pits. The trees grow better on the mounds. The mounds collect less leaf litter which allows certain plants to grow easier. They provide a greater rooting depth of better drained soil because the water can drain off and out of them better thus providing a different microclimate (small scale variations in the conditions of the area) which is dryer. The mounds provide greater rooting depth just like a raised bed in a garden does. Other types of plants prefer these dryer locations.
The formation of pits and mound has an important impact on the soil. It acts to mix the soil. It mixes organic matter deeper into the soil and brings minerals up from below to the surface. It slows the formation of the natural layers called horizons that form in the soil. Pit and mound formation is a major factor in the development of forest soils.
If you see mature trees growing on top of mounds then that forest is relatively very old. If you see a forest with very smooth ground, chances are that it was disturbed by man. From first settlers to the current time, man has been cutting the trees down for various reasons and much of that land was then farmed. The activities of logging, pasturing and plowing slowly smoothed the ground surface out and removed most of this micro-topography.
This is a photo of the older mound and pit at Stage 3. It is difficult to see in this photo, but you can see a very old mound on the middle left and the pit is in the middle of the photo. Judging by the fact that there are no remnants of the tree that created this pit and mound and the size of the trees on top of the mound, this mound is probably 30 to 50 years old.
To claim this cache you need to send answers to my questions to me via my profile at geocaching.com:
1) How many mounds do you see at Stage 2?
2) At Stage 1, estimate the size of the root ball (average diameter and average thickness).
3) Calculate the volume and weight of the soil in the root plate (ball) at Stage 1. (You can use the formula for volume of a cylinder. Figure out the cubic feet of the root plate. Assume the root plate is 50% soil by volume. Silt Loam soil, which is the soil at the site, weighs 81 lbs per cubic foot.)
Photos of yourself and/or your GPSr next to any other tree plate (root ball) in the area or anything else interesting you see are welcome and appreciated. (THIS IS OPTIONAL)
To complete this Earthcache visit the three stages and answer the questions given and send them to me via my profile email. If this information is not emailed to the owner, the log will be deleted in fairness to those who do the work and calculations. PLEASE DO NOT PUT THE ANSWERS IN YOUR LOG or they will be deleted also.
