Litter inputs and standing stocks in riparian zones and streams under secondary forest and managed and abandoned cocoa agroforestry systems

Abstract

Background Cocoa is an important tropical tree crop that is mainly cultivated in agroforestry systems (AFS). This system, known as cabruca in northeastern Brazil, holds promise to reconcile biodiversity conservation and economic development. However, since cocoa AFS alters forest structure composition, it can affect litter dynamics in riparian zones and streams. Thus, our objective was to determine litter inputs and standing stocks in riparian zones and streams under three types of forest: managed cocoa AFS, abandoned cocoa AFS, and secondary forest. Methods We determined terrestrial litter fall (TI), vertical (VI) and lateral (LI) litter inputs to streams, and litter standing stocks on streambeds (BS) in the Atlantic Forest of northeastern Brazil. Litter was collected every 30 days from August 2018 to July 2019 using custom-made traps. The litter was dried, separated into four fractions (leaves, branches, reproductive organs, and miscellaneous material) and weighed. Results Terrestrial litter fall was similar in all forests, ranging from 89 g m−2 month−1 in secondary forest (SF) to 96 g m−2 month−1 in abandoned cocoa AFS (AC). Vertical input were higher in AC (82 g m−2 month−1) and MC (69 g m−2 month−1) than in SF (40 g m−2 month−1), whereas lateral input were higher in MC (43 g m−2 month−1) than in AC (15 g m−2 month−1) and SF (24 g m−2 month−1). Standing stocks followed the order SF > AC > MC, corresponding to 425, 299 and 152 g m−2. Leaves contributed most to all litter fractions in all forests. Reproductive plant parts accounted for a larger proportion in managed AFS. Branches and miscellaneous litter were also similar in all forests, except for higher benthic standing stocks of miscellaneous litter in the SF. Despite differences in the amounts of litter inputs and standing stocks among the forests, seasonal patterns in the abandoned AFS (AC) were more similar to those of the secondary forest (SF) than the managed AFS, suggesting potential of abandoned AFS to restore litter dynamics resembling those of secondary forests.

Species of leaf litter are more important than urbanization effects for litter mass loss in semi-arid river

“…N, F, temperature, dissolved oxygen and electrical conductivity), and iii) water ow abrasion power (Rezende et al 2014a). Also, the vegetation surrounding water bodies plays a fundamental role in supplying organic matter to the aquatic system (Bambi et al 2017), which can undergo anthropogenic alterations due to changes in land use (Bambi et al, 2022;Inhamuns et al, 2021;Brandão et al, 2022).…”

“…A mass loss of around 40% for both litter types in 30 days is a relevant result that supports this inference. After leaching (usually compounds against herbivory), the litter becomes less toxic and more palatable(Marsaro et al 2023), allowing for the colonization of the decomposer community(Biasi et al 2016), also justifying the higher invertebrate density on E. velutina and T. aurea (by increase of nitrogen and protein content) compared to other plant species litter, and consequently, its leaf litter breakdown(Rezende et al, 2018(Rezende et al, , 2014bBrandão et al, 2022).…”

Year-to-year variations have a more impact on leaf litter breakdown than the presence or absence of riparian vegetation in highland grasslands streams

“…The decomposer community transform organic matter into simpler and reusable compounds on the ecosystem (Rezende et al 2019). In this sense, the presence or absence of riparian vegetation may plays a crucial role in the composition and functioning of headwater streams (Lind et al 2019;Brandão et al 2022;Bambi et al 2023). On the other hand, highland grasslands often have natural open streams areas without riparian vegetation (Fernandes 2016).…”