Using experimental manipulation to assess the roles of leaf litter in the functioning of forest ecosystems

Abstract

The widespread use of forest litter as animal bedding in central Europe for many centuries gave rise to the first litter manipulation studies, and their results demonstrated that litter and its decomposition are a vital part of ecosystem function. Litter plays two major roles in forest ecosystems: firstly, litterfall is an inherent part of nutrient and carbon cycling, and secondly, litter forms a protective layer on the soil surface that also regulates microclimatic conditions. By reviewing 152 years of litter manipulation experiments, I show that the effects of manipulating litter stem from changes in one, or both, of these two functions, and interactions between the variables influenced by the accumulation of litter can result in feedback mechanisms that may intensify treatment effects or mask responses, making the interpretation of results difficult.Long-term litter removal increased soil bulk density, overland flow, erosion, and temperature fluctuations and upset the soil water balance, causing lower soil water content during dry periods. Soil pH increased or decreased in response to manipulation treatments depending on forest type and initial soil pH, but it is unclear why there was no uniform response. Long-term litter harvesting severely depleted the forests of nutrients. Decreases in the concentrations of available P, Ca, Mg, and K in the soil occurred after only three to five years. The decline in soil N occurred over longer periods of time, and the relative loss was greater in soils with high initial nitrogen concentration. Tree growth declined with long-term litter removal, probably due to lower nutrient availability. Litter manipulation also added or removed large amounts of carbon thereby affecting microbial communities and altering soil respiration rates.Litter manipulation experiments have shown that litter cover acts as a physical barrier to the shoot emergence of small-seeded species ; further, the microclimate maintained by the litter layer may be favourable to herbivores and pathogens and is important in determining later seedling survival and performance. Litter manipulation altered the competitive outcomes between tree seedlings and forbs, thereby influencing species composition and diversity ; changes in the species composition of understorey vegetation following treatments occurred fairly rapidly. By decreasing substrate availability and altering the microclimate, litter removal changed fungal species composition and diversity and led to a decline in populations of soil fauna. However, litter addition did not provoke a corresponding increase in the abundance or diversity of fungi or soil fauna.Large-scale long-term studies are still needed in order to investigate the interactions between the many variables affected by litter, especially in tropical and boreal forests, which have received little attention. Litter manipulation treatments present an opportunity to assess the effects of increasing primary production in forest ecosystems; specific research aims include assessing the eff...

Macrofungal diversity in community-managed sal (Shorea robusta) forests in central Nepal

“…The removal of litter affects fungal growth and diversity (Eaton et al 2004; Sayer 2005). Species richness of macrofungi therefore increased with increasing litter cover (Figure 3(b)).…”

A new approach to trenching experiments for measuring root–rhizosphere respiration in a lowland tropical forest

“…Interestingly, the greatest differences in soil water content between trenched and untrenched soil during the dry season (84% higher in trenched subplots) were observed in the Lþ plots where the thick litter cover protected the soil from evaporation and drying (Marthews et al, 2008), and the smallest difference (32% higher in trenched subplots) was observed in the LÀ plots (Fig. 3), where the lack of litter probably lead to greater evaporation from the soil surface (Walsh and Voight, 1977;Sayer, 2006).…”

“…For example, litter exclusion can result in soil drying caused by greater evaporation from the unprotected soil surface and differences in soil water balance (Walsh and Voight, 1977;Sayer, 2006). Reviews and meta-analyses of respiration partitioning studies highlight the difficulties involved in the different methods employed and generally agree that isotopic labelling is the most accurate method with the fewest methodological artefacts (e.g.…”

Alterations in forest detritus inputs influence soil carbon concentration and soil respiration in a Central-European deciduous forest

“…The differences in soil CO 2 emissions among treatments during winter and summer periods are likely due to altered insulation and soil moisture conditions, which influence soil microclimate and biological processes both directly and indirectly (Sayer, 2006;Veres et al, 2013). Numerous studies have documented the dominant role of temperature in controlling decomposition and soil CO 2 emissions (Chen et al, 2000;Knorr et al, 2005;Kotroczó et al, 2008;Bond-Lamberty and Thomson, 2010;Smith and Fang, 2010).…”