Leaf senescence (aging) and abscission (fall) in temperate deciduous forests can influence the rate and extent of important nutrient cycles, available soil nutrients and features of fungal and microbial communities, as well as the amount of nutrients resorbed by trees. Patterns of abscission have been shown to vary between species, across sites and over years (see figures). In each case, the variance explained across these groupings proved potentially critical to the community dynamics of the species. Furthermore, as leaf fall is thought to respond to local climate variability such as temperature and precipitation, changing climate may further influence how leaf fall varies across species, sites and years.
The x-axis shows the day of the year (fall). The y-axis shows the percent of total litter falling that year that has fallen up to the date on the x-axis (the cumulative distribution of litter fall). Differently colored curves are collections from different sites at SERC. In the top panel, one year of tulip poplar can be shown to have a very different form across sites. The middle and bottom panel show that the form can change both across sites collectively and return to a varied format, with new sites showing different forms. Answering the patterns of variance across the major forest species, sites and years allows the use of covariates at these distinct 'levels.'