Deciduous Forests

INTRODUCTION

A deciduous forest, simply described is a forest that is leafless during the winter. Eury species make up this type of forest, meaning that the species can tolerate a wide range of conditions. In the extreme northern latitudes, the growing season is short causing the trees to be leafless the majority of the year. The deciduous forest is subjected to distinct weather cycles and temperature shifts. In this area of the northeast we experience four distinct seasons, and for a tree species to thrive it must adapt to the stresses corresponding to each season.

Of the three basic types of temperate broadleaf forests, (temperate deciduous forest, temperate woodlands, and temperate evergreen forest) our lab data deals with characteristics of the temperate deciduous forest. This forest type once covered large portions of Eurasia, South America, and North America. As with most native forests, they have been cleared so that the land could be used for farming or residential use. The temperate deciduous forests of North America were more diverse than the same type of forests in Europe due to glacial history. Glacial action dumped till as the ice edge retreated, and North America inherited a fertile soil base. Soil type is an important factor for which species of trees can thrive in an area. The general dominant tree species for temperate deciduous forests are Beech, Ash, Oak, and in our region also Tulip, Maple, Birch, and Hickory. Developed forests consist of four layers. The layers are: canopy, sub canopy, shrub, and ground cover. This layering affect benefits the diversity of the ecosystem by providing a rich variety of habitats. It is a result of adaptation and competition for sunlight and shows the continuing process of succession. The stratification of a forest, by intercepting the some of the available sunlight at various locations, also creates micro-climates with a wide range of temperatures and moisture conditions. The soil composition also greatly influences the amount of water that is available to the plant species. The composition of the soil, the various layer development and the nutrient content are major factors in the survival of specific species of trees. Climate and soil type are a-biotic factors, meaning they are outside and uncontrollable by the species itself. Insect infestations such as Gypsy moths and disease such as the Chestnut blight are also a-biotic factors that in a relatively short period of time can severely thin out or destroy a specific species of tree. It might just add enough stress to one species, where a competing species will then out-compete it and then dominate. The cycle of dropping the leaves when the days grow short is vital for the replenishment of nutrients in the soil. This litter layer decomposes and returns organic material to the trees through leeching and decomposition into the upper soil layers where they can be reused by re-absorption through the roots.

METHODS

This lab involved the investigation of a deciduous forest located on the undeveloped portion of the campus. The survey techniques used to collect data for the vegetation analysis portion of this lab were the quadrant and line intercept methods. Using pre-established 25 meter square plots, on opposite sides of a stream, the tree species and sizes were mapped and recorded. Breast height diameter measurements were made on the canopy and sub canopy trees in each quadrant. The types of trees found and the number per species was recorded and used to figure which species were dominate. Each quadrant also used a random line intercept of 10 meters in length to determine the density of the bush coverage of the quadrants. A soil analysis of both sides of the creek was also conducted to determine the effects of a-biotic conditions on the species recorded in the vegetation analysis. Multiple samples of the A1 and A2 horizons were collected and analyzed using standard screening and drying stages to determine soil particle size and moisture content. The measurement of the specific gravity using a hydrometer while the soil particles are settling out in a flask is used to calculate the percentages of sand, silt, and clay fractions of the soil samples. These sampling techniques were derived from exercises #14 and #40 located in: George W. Cox, Laboratory Manual of General Ecology, seventh edition, W.C. Brown Publishing, 1996.

RESULTS & DISCUSSION

The data for this lab was analyzed in stages. In the two charts provided, the overall differences between the two sides of the forest can be seen. The first chart compares the tree species found on each side of the forest and shows the relative dominance. Relative dominance compares the presence of one species to the total presence of all species located in the forest and expresses this value as a percentage. The overall trend in the relative dominance data shows a clear change from one side of the creek to the other. On the north side of the creek, the dominant tree species is the Beech tree, occupying over 50% of the canopy area. The Beech tree is also the most dominant tree species in the sub canopy layer as well. The data shows that the Beech species is doing well and has an assured future in the area as indicated as the dominance of the same species in the sub canopy. On the northern sites, the canopy is relatively well developed and has virtually no bushes, just saplings mostly of the parent dominant Beech. On the southern side of the creek, the Tulip tree is the dominant tree type in the canopy layer with almost half of the area occupied. In the sub canopy layer, the Sugar Maple is clearly dominant at 90%. It seems that the Tulip trees are at the end of their life cycle and are unable to produce any offspring to allow the species to continue to dominate that area, as there were no young Tulip saplings found in the sub canopy. The southern side is heavier in the bush layer due to the opportunities to gain sunlight through the failing canopy.

The second chart shows the soil analysis. The differences in the soil content are also clear. The total percent of water held in the A-1 horizon of the soil on the Beach side, is approximately 6% more moist than the Tulip side. The amount of organics in the Beech side are also higher by approximately one to two percent than the Tulip side soil. The specific gravity measurements indicated that the Tulip side is primarily sandy (A1 horizon) side but the Beech side data s does not show a clear composition. Both the amount of water and the amount of organic nutrients in the soil are important a-biotic factors that can affect the ability of any species to thrive in an area. The northern side also contains a high concentration of large rock, virtually not present in the Tulip side. This indicates that there is a difference in the soil construction, given that soil is produced by the breakdown of local parent material.

This lab showed how the species in a mixed forest are influenced by a-biotic factors. The general trend of the data does show that there are distinct differences in the construction of the forest. The differences in the soil composition may have pushed the beech tree into a dominant state in their location. However, it would be difficult to say that the decline in the Tulip tree population is due to soil depletion alone. It may be due to the natural life span of the species or a stress from a previous decease. The tulips are not producing any new seedlings, possibly suggesting that the conditions that once allowed the Tulip to thrive no longer exist, but the current conditions now favor the Sugar Maples.