Due to variable expressions of physical and cultural phenomena, if we take a particular place on the landscape we might get one forest type, and if we pick another we might get something entirely distinct. The distribution of these assemblages is not random, however, nor do natural phenomena often adhere to discrete, clear-cut boundaries. And so, it is important to think about the range of different plant associations as a continuum across the landscape, and consider that similar associations of plants occur wherever comparable ecological and historical conditions are dominant.
The dominant natural community association found throughout Putney and all of southeastern Vermont is made up of northern hardwood trees such as sugar maple, yellow birch, and American beech. This association of plants is typically referred to as the region’s ‘matrix’ community, meaning that it makes up about 80% of the total landscape forest type. Yet Putney, being located along the low-lying Connecticut River valley, also has a southern influence consistent with the forests of Massachusetts. Consequently, mixed in with the maple, birch, and beech are healthy additions of red oak and white pine. Among the matrix of oak-pine northern hardwoods we can find scattered, smaller pockets responding to characteristics of the local landscape. One notable community in Putney is the black gum swamp, which can be found in a few low-lying pockets of water that persist on the top of Bear Hill. They tend to form in the depressions between bedrock ridges which accumulate acidic waters and deep organic matter. This swamp is characterized by the black gum tree, a plant associated with more more southern climes, and is therefore rare in this part of the world. It is believed to be a remnant from a time when the earth’s climate was warmer and the tree had a broader geographic distribution.
Even in your own backyard, there may be a high degree of vegetative variability owing to localized differences in topography, how much sunlight is received, and the resulting soil moisture. Take Putney Mountain, Bear Hill, and Rocky Ridge, for instance. The south-facing slopes on each of these hills tend to be warmer and drier and support associations of oaks, beech, and hickories with an understory of shrubs and flowers, while the heavily shadowed north-facing slopes remain cool and damp, providing good habitat for hemlocks and yellow birch, and an understory largely devoid of vegetation. The availability of soil nutrients can also significantly affect the local vegetative expression because plant roots uptake water and nutrients directly from the soil substrate. In general, soils that develop from schist and slate – such as those that predominate on the eastern side of town – tend to be acidic and relatively low in nutrient value, supporting trees like maples, birch, beech, and white pine, shrubs such as honeysuckle and witch hazel, and heaths like blueberry. Limestone substrates on the other hand – as are found mixed in as impure marbles more abundantly on the western side of Putney – weather to make soils ‘sweet’ or ‘rich,’ and have a higher capacity to grow an diversity of plants such as white ash, basswood, and sugar maple trees, as well as maidenhair fern, blue cohosh, wild columbine, and wild ginger in the herb layer. Human and natural influences together lead to dynamic and perpetual processes of vegetative change. Windy gusts and the accumulated weight of ice and snow can topple trees and snap off large branches, opening up holes in the forest canopy that are quickly colonized by sunlight-seeking shrubs and herbs. Shallow, dry soils and sandy ridge tops are susceptible to occasional fire outbreaks that leave the land bare; steep, saturated slopes are prone to landslides that prevent plants from getting a firm foothold, and low-lying wetland communities are frequently inundated by floodwaters that only specially adapted plants can withstand. Insects, too, can infest and devastate whole patches of forest.
As for humans, changes in landuse have led to dramatic vegetation changes and distribution patterns throughout Putney. Today the hillsides are predominantly forested, yet as we walk through the woods we can still see remnants that tell the story of the town’s agricultural past. For example, it is not uncommon to encounter solitary, thick-trunked trees with wide-spreading branches that grow in the midst of several younger, slimmer, vertical stems. Such trees developed in open fields, providing shade for cattle. Another dominant pattern we see is the presence of white pine in large patches. Pine thrive in full sunlight, and cows don’t really like to eat them. Consequently they are good colonizers of abandoned pastures. As regional farms have dwindled throughout town and the region, many young woodlands have grown back with a dense mosaic of white pines, indicative of parcels that were formerly pasture. However, historical studies show that when settlers arrived in Putney the landscape was heavily dominated by beech, while white pine comprised only a small component of the overall forest assemblage. Looking to the future, then, it is likely many of the pines will eventually succumb to other long-lived, shade-tolerant species. In short, what we see on the landscape today has not always been, nor will it always be, for disturbance and variability are inherent qualities of of the earth’s ecosystem functions.