Quantified moorland vegetation and assessment of the role of burning over the past five millennia

Abstract

Aims To apply the Landscape Reconstruction Algorithm (LRA) to pollen count data from multiple sites to estimate local vegetation abundance and compare with charcoal‐derived records of burning. Location Exmoor, southwest England, UK. Methods Pollen count data from 16 sites were transformed to estimates of distance‐weighted vegetation abundance using the LRA (REVEALS and LOVE models), correcting for bias in pollen production and dispersal. Charcoal concentration data from six sites were normalized using Box‐Cox transformation to produce z‐scores. Moving‐window correlation was undertaken to compare pollen percentage values for key taxa (Calluna, Poaceae) and localized burning. Estimates of distance‐vegetation abundance (LRA output) and time‐averaged charcoal z‐scores were compared to assess the role of burning as a driver for upland vegetation cover. Results Comparison of pollen percentage and normalized charcoal z‐scores show little correlation between vegetation cover and burning. Estimates of distance‐weighted vegetation abundance and normalized charcoal data show relationships between vegetation change and burning at four of the six sites. The relationships are site‐specific: three sites suggest burning promoted grass‐dominated vegetation, at one site burning promoted heather‐dominated vegetation, and in two sites there is no apparent relationship. Conclusions The patterning of vegetation within uplands is a crucial part of ecosystem service delivery, and contemporary and future management benefits from understanding of ‘long‐term’ development, i.e. patterns over millennia. The correction of biases within pollen production and dispersal to produce local vegetation estimates has demonstrated spatial heterogeneity in vegetation cover on Exmoor that is not otherwise evident in the pollen percentage data (which retain a strong influence of the regional vegetation cover). The relationship between LRA‐derived vegetation cover and burning is not apparent in comparisons between pollen percentage data and charcoal records. This implies that studies that use pollen proportional data alone can misrepresent the relationship between vegetation cover and fire. This study demonstrates that fire has been an important part of the development of this cultural landscape.

Spatial and temporal patterns of upland vegetation over the last 200 years in the northern pyrenees: Example from the Bassiès valley, Ariège, France

“…Those two taxa have higher LOVE estimates around peat bog sites compared to lake sites. Several studies have excluded both or one of them from the pollen records in recognition of their likely strong local signal (Fyfe et al, 2018;Nielsen et al, 2012), however Calluna and Cyperaceae are widespread across our study area and are not restricted to peat bogs. Therefore, they have been included as important components of the upland vegetation.…”

“…Previous studies have already demonstrated vegetation patterning and composition differences using pollen percentages only (Davies and Tipping, 2004;Fyfe, 2012;Fyfe and Woodbridge, 2012;Poska et al, 2008a) or LRA-based estimates (Cui et al, 2014(Cui et al, , 2013Fyfe et al, 2018;Hultberg et al, 2014;Mehl et al, 2015;Mehl and Hjelle, 2016;Poska et al, 2018;Prøsch-Danielsen et al, 2020). Few studies have focused on the last centuries, with a temporal and spatial resolution high enough to capture the short-term land-use changes that occurred during certain critical time intervals such as the last two hundred years (Allen et al, 2020;Marquer et al, 2020a;Mazier et al, 2015).…”

Whither scientific debate? A rebuttal of “Contextualising UK moorland burning studies: geographical versus potential sponsorship-bias effects on research conclusions” by Brown and Holden (bioRxiv 2019; 731117)

“…For example, there are multiple studies in which burning has a negative effect, but the mean differences between burning treatments, while significant, are minimal (e.g. a few percentage points of vegetation cover or <1 o C temperature difference) (see, for example, Noble et al 2017b;Noble et al 2018;Grau-Andrés et al 2019a;Grau-Andrés et al 2019b) 15 . Such nuance is not accounted for by B&H's classification, and we wonder if such small differences are ecologically relevant.…”

Millennial to centennial vegetation change

“…Although fire is an important disturbance agent and its frequency can determine vegetation patterns, it does not play an important role for the regional vegetation change in Fennoscandia (Kuosmanen et al., ). Fyfe, Ombashi, Davies, and Head (), as well as Hjelle et al. (), apply models to the pollen data in order to translate pollen percentages to vegetation cover.…”

“…() show that open areas existed in the region prior to the introduction of agriculture. Correcting for pollen production biases and comparing the vegetation reconstructions to charcoal data reveals that fire is more strongly associated with vegetation structure of Exmoor moorlands than is evident from pollen percentage–charcoal associations (Fyfe et al., ). Shumilovskikh, Novenko, and Giesecke () evaluate the degree of forest cover based on modern analogues documenting changes in location and composition of the East European forest‐steppe ecotone over the last 7,000 years.…”