Climate change facilitated the early colonization of the Azores Archipelago during medieval times

Abstract

Humans have made such dramatic and permanent changes to Earth's landscapes that much of it is now substantially and irreversibly altered from its preanthropogenic state. Remote islands, until recently isolated from humans, offer insights into how these landscapes evolved in response to human-induced perturbations. However, little is known about when and how remote systems were colonized because archaeological data and historical records are scarce and incomplete. Here, we use a multiproxy approach to reconstruct the initial colonization and subsequent environmental impacts on the Azores Archipelago. Our reconstructions provide unambiguous evidence for widespread human disturbance of this archipelago starting between 700-60+50 and 850-60+60 Common Era (CE), ca. 700 y earlier than historical records suggest the onset of Portuguese settlement of the islands. Settlement proceeded in three phases, during which human pressure on the terrestrial and aquatic ecosystems grew steadily (i.e., through livestock introductions, logging, and fire), resulting in irreversible changes. Our climate models suggest that the initial colonization at the end of the early Middle Ages (500 to 900 CE) occurred in conjunction with anomalous northeasterly winds and warmer Northern Hemisphere temperatures. These climate conditions likely inhibited exploration from southern Europe and facilitated human settlers from the northeast Atlantic. These results are consistent with recent archaeological and genetic data suggesting that the Norse were most likely the earliest settlers on the islands.

Reply to Elias et al.: Multiproxy evidence of widespread landscape disturbance in multiple Azorean lakes before the Portuguese arrival

“…As stated in ref. 1 , we acknowledge the point raised by Elias et al. ( 2 ) that the Portuguese arrival led to more extensive changes in the landscape.…”

“…The age model from Peixinho (figure S6C of ref. 1 ) included two tephra layers at 650 and 700 CE, which correspond to the dates of the tephra layers found in the record of Pico Bog (see figure 2 of ref. 5 ).…”

Long-term hydroclimate variability in the sub-tropical North Atlantic and anthropogenic impacts on lake ecosystems: A case study from Flores Island, the Azores

“…Rising sea levels, changing precipitation patterns, and warmer temperatures threaten island ecosystems that are already under pressure from anthropogenic land use changes (Frias, 2000;Santos et al, 2004;Hoegh-Guldberg et al, 2018). Portuguese settlers shaped the landscape of the Azores Archipelago by replacing dense native laurel forests with exotic plants and agricultural fields, which led to increased soil erosion and left only a few places with native flora and fauna (Dias et al, 2005;Connor et al, 2012;Rull et al, 2017;Raposeiro et al, 2021b).…”

Is there solid evidence of widespread landscape disturbance in the Azores before the arrival of the Portuguese?

“…Raposeiro et al. ( 1 ) conclude that human occupation of the Azores islands began between 700 and 850 CE, causing widespread landscape disturbance and raising doubts about the islands’ presumed pristine nature when the Portuguese arrived. However, previous paleoecological studies from Flores, Pico, and São Miguel Islands ( Table 1 ) show that permanent changes in the vegetation occurred only after the early 15th century.…”

“… Arboreal pollen trends and tephra layers at Lagoa do Peixinho (LP, ref. 1 ) and Pico Bog (PB, ref. 3 ) showing the mismatch between chronologies based on pollen concentrates (LP) and macrofossils/bulk dates (PB).…”