The Role of Leaf Litter

Let begin with the basics:

Leaf litter consists largely of the dead organic material that's shed by plants throughout the year but mostly at the end of the growing season. It accumulates in the understory of the forest, and covers the forest floor. Most people might not suspect, but leaf litter plays a crucial role in the overall health of terrestrial ecosystems. In many ecosystems, vegetative growth is largely dependent on leaf litter decomposition for a source of minerals that support development (Ewel, 1976). In essence leaf litter can be thought of as a natural fertilizer because as it decomposes it releases phosphorous, ammonium, carbon dioxide and water (Aerts, 1997). Though this is not the only thing worth noting, it may come as a surprise, but in addition to the role of fertilizer, leaf litter can influence the global carbon cycle. As I mentioned earlier, the process of decomposition produces carbon dioxide. This makes makes leaf litter an integral part of the global carbon cycle. It's estimated that leaf litter decomposition contributes to roughly 70% to the annual carbon flux (Raich and Schlesinger, 1992).

As I briefly stated earlier, the underlying mechanism that makes leaf litter so important is decomposition. Decomposition is a process which allows for the break down of organic material with the aid of detritivores, micro-organisms (bacteria and fungi) as well as temperature and precipitation, into inorganic molecules such as phosphate, nitrogen and carbon. This is a vital process which enriches the soil with inorganic molecules that plants use as a source of mineral nutrients.

 I've annotated the diagram below with the major steps of the cycles for a better illustration of the process.

  In addition here's a link to an animation provided by the Michigan Technological University which shows the major steps in the process of decomposition in real time.


Having discussed the basic purpose of leaf litter as well the process of decay, we can now look at which factors specifically contribute to litter decomposition rates. In the previous section I briefly mentioned temperature, precipitation, detritivores and micro-organisms (bacteria and fungi) as drivers of decomposition. However the process is actually controlled by a combination of the environmental conditions, the chemical composition of the litter, and the soil organisms. In general these factors are considered to be part of a hierarchical system where the magnitude of effects is presented as such: CLIMATE  >  LITTER CHEMISTRY  >  SOIL ORGANISMS. One of the main reasons why climate is considered to be higher in magnitude is because climate has the potential to affect both litter chemistry as well as soil organisms.

 Currently more research is being done to better understand how these factors interact, and how global CLIMATE CHANGE might affect the overall dynamic.