High stocks, but slow recovery, of ecosystem carbon in southern oceanic tussock grasslands

Abstract

Peat-forming large tussock grasslands on oceanic and sub-Antarctic islands are fundamentally understudied in terms of carbon (C) storage. Here we quantify both plant and soil C and nitrogen (N) storage for the large-tussock grass Poa flabellata in the Falkland Islands, at its most northerly range. In this study we adopt a spatially explicit sampling approach to account for tussock and inter-tussock (between tussocks) areas for three habitats; remnant stands (surviving clearance and overgrazing), restored stands (planted) and eroded bare peat sites. We found that remnant stands of P. flabellata have above-ground C densities of 49.8 ± 9.7 Mg C ha-1 , equivalent to temperate and boreal forests. The majority of aboveground C is stored within the pedestal, a compact accumulation of dead leaves, rhizomes and roots. By surveying restored stands of increasing age we found that such C accrual may take longer than two decades. Soil C stocks were horizontally and vertically spatially variable and did not differ between habitat types. Plant and soil C and N stocks were strongly coupled identifying the important role of N availability for C accrual in this system. Scaling-up our results, planting tussock grass could accrue up to 0.9 million Mg C on a decadal timescale across the islands, yet the impact of planting on soil C storage is likely to be more variable. Our results highlight the local and regional importance of large tussock grasslands as dense C stores and that land management and conservation of these communities needs to be more carbon-conscious.

Going native, going local: revegetating eroded soils on the Falkland Islands using native seeds and farmland waste

“…On the Falkland Islands, the successful native species in our trial are predominantly coastal and often receive significant nutrient inputs from marine mammal and sea bird colonies and the plant productivity benefits of such allochthonous (marine-derived) nutrient inputs has been observed on other island ecosystems (Bergstrom et al 2001;Ellis 2005). Furthermore, anecdotal evidence suggests that allochthonous nutrients can enhance planted P. flabellata tiller establishment and growth (Kerr 1994;Smith & Karlsson 2017). Thus, a nutrient source, however small in quantity (i.e.…”

“…Furthermore, anecdotal evidence suggests that allochthonous nutrients can enhance planted P . flabellata tiller establishment and growth (Kerr ; Smith & Karlsson ). Thus, a nutrient source, however small in quantity (i.e.…”

“…For example, individual P . flabellata tussocks can reach sizes of 1.5 m 2 area and 3 m tall (Gunn ; Smith & Karlsson ). Potentially only a handful of seeds would be necessary to revegetate each square meter.…”

“…We sowed seeds at densities of 200 seeds per species m −2 , yet many of the successful species form large tussocks (Moore 1968;Broughton & McAdam 2005). For example, individual P. flabellata tussocks can reach sizes of 1.5 m 2 area and 3 m tall (Gunn 1976;Smith & Karlsson 2017). Potentially only a handful of seeds would be necessary to revegetate each square meter.…”

Peatland initiation and carbon accumulation in the Falkland Islands

“…However, there are open questions around whether these peatlands are continuing to accumulate carbon and how their carbon stock has been affected by climate change and land management (Otley et al, 2008). The peatland landscapes of the islands are unusual and varied, including some highly atypical peatland habitats with very tall grasses and extensive influence from marine birds and mammals (McAdam, 2013;Smith and Karlsson, 2017). Prior to the first European settlement in the mid-18 th century there were no mammalian herbivores on the islands, and the introduction of extensive livestock grazing has therefore led to major ecological change.…”