Small biodiversity effects on leaf litter production of a seasonal heath vegetation

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By José L.A. Silva, Alexandre F. Souza, Louis S. Santiago, Anderson R. Gripp, Ana E.B. Asato, Gabriel H.S. Silva, Mery I.G. Alencar and Adriano Caliman

Seasonal heath vegetation in the Barreira do Inferno Lauch Center, Parnamirim municipality, Rio Grande do Norte state, Brazil (5º54’S, 35º10’W, December 2015). Photo credit: José L.A. Silva.

Most of the white-sand coastal areas in Brazil are covered by heath vegetations, which in North-eastern Brazil suffer seasonal drought. The term ‘heath’ is used to describe a vegetation type that develops as an edaphic climax, in which plant growth is limited by well-drained and nutrient-poor soils rather than by climatic conditions. The term ‘seasonal’ is added to ‘heat’ to describe the temporal dynamics in the forest production, controlled mainly by the rainfall regime of the region. In these areas, the forest production decreases extensively during the hot, dry season, which is marked by a peak of leaf litter production through the synchrony of leaf shedding events. Trees and shrubs lose leaves to conserve water, and litterfall is frequently the main flux of biomass and nutrients from the vegetation to the soil, functioning as a key ecosystem process.

Not only climate and soil fertility control the leaf litter production, but also the diversity of species and their functions, known as biodiversity. Other studies have shown that the increase in biodiversity has a positive effect on the increase of forest production, with its effect comparable to climate and soil fertility. In our study, we compared the relative importance of biodiversity facets and abiotic conditions for the leaf litter production in seasonal heath vegetation in North-eastern Brazil. The area contains tall sandy dunes near the sea, and relatively flat areas further inland. Litterfall production was collected at monthly intervals throughout one year using several plastic basins established in 41 plots.

Data collection of leaf litter through plastic basins as litter traps in the Barreira do Inferno Lauch Center, Parnamirim municipality, Rio Grande do Norte state, Brazil (5º54’S, 35º10’W, December 2015). Photo credit: Ana Asato.

We found that leaf litter production was promoted by a few dominant species that enhanced the overall production due to their abundance. This means that sites with higher species richness had higher chances of presenting high-yielding or dominant species in the community composition, which increased leaf litter production without the need for these species to differ in function. In the perspective of management or restoration, if the interest is that the vegetation serves as a carbon sink (absorbs more carbon than it releases), then the number of species may be prioritized with a reduced focus on the understanding on how species functionally complement each other.

We also found that the rainfall regime imposed greater influence on leaf litter production than any asynchronous leaf-shedding behaviour between species, which could result from functional differentiation. The key role of climate-mediated controls on leaf litter production led us to believe that the positive biodiversity effect on ecosystem functioning should lose importance in ecological contexts where the entire plant community responds similarly to abiotic pressures. The particularities of the seasonal heath vegetation seem to offer an excellent opportunity for further studies to conduct hypothesis-oriented experiments and observational works in the related research field.

This is a plain language summary for the paper by Silva et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12908). The post was prepared by José L.A. Silva.