Sullivan, M. J. P. | bioRxiv Science

bioRxiv2025

Lightning-caused disturbance frequency and severity varies with topography in an Afromontane forest

Lightning is an important agent of tropical tree mortality, but we know little about lightning-caused disturbances beyond one lowland tropical forest in Panama. Here we quantified variation in the frequency and severity of visually-detectable lightning-caused disturbances across topography in the montane forests of Nyungwe National Park, Rwanda. This was the first systematic assessment of lightning-caused disturbance in Africa and a preliminary test of the hypothesis that forest tolerance to lightning is higher where lightning disturbances are more common. Lightning-caused disturbances were observed six-times more frequently on ridges than in valleys, but lightning-caused disturbances in valleys tended to cause more tree-level damage than those on ridges. Overall, lightning disturbances tended to kill a lower proportion of trees in this Afromontane forest than in previously documented lightning disturbances in tropical America. We also observed less tree-level damage to Syzygium spp.(Myrtaceae) compared to the community-wide average, providing support for taxonomic differences in lightning tolerance. Our results indicate that lightning disturbance severity differs within and among sites, mediated in part by differences in lightning tolerance among tree species, and provide some support for the hypothesis that disturbance severity declines with disturbance frequency.

ecology↗

bioRxiv2021

Rapid carbon accumulation at a saltmarsh restored by managed realignment far exceeds carbon emitted in site construction

Increasing attention is being paid to the carbon sequestration and storage services provided by coastal blue carbon ecosystems such as saltmarshes. Sites restored by managed realignment, where existing sea walls are breached to reinstate tidal inundation to the land behind, have considerable potential to accumulate carbon through deposition of sediment brought in by the tide and burial of vegetation in the site. While this potential has been recognised, it is not yet a common motivating factor for saltmarsh restoration, partly due to uncertainties about the rate of carbon accumulation and how this balances against the greenhouse gases emitted during site construction. We use a combination of field measurements over four years and remote sensing to quantify carbon accumulation at a large managed realignment site, Steart Marshes, UK. Sediment accumulated rapidly at Steart Marshes (mean of 75 mm yr-1) and had a high carbon content (4.4% total carbon, 2.2% total organic carbon), resulting in carbon accumulation of 36.6 t ha-1 yr-1 total carbon (19.4 t ha- 1 yr-1 total organic carbon). This rate of carbon accumulation is an order of magnitude higher than reported in many other restored saltmarshes, and is higher although more similar to values previously reported from another hypertidal system (Bay of Fundy, Canada). The estimated carbon emissions associated with the construction of the site were [~]2-4% of the observed carbon accumulation during the study period, supporting the view that managed realignment projects in such settings are likely to have significant carbon accumulation benefits. We outline further considerations that are needed to move towards a full carbon budget for saltmarsh restoration.

ecology↗