Long-Term Vegetation Dynamics in a Megadiverse Hotspot: The Ice-Age Record of a Pre-montane Forest of Central Ecuador

Abstract

Tropical ecosystems play a key role in many aspects of Earth system dynamics currently of global concern, including carbon sequestration and biodiversity. To accurately understand complex tropical systems it is necessary to parameterise key ecological aspects, such as rates of change (RoC), species turnover, dynamism, resilience, or stability. To obtain a long-term (>50 years) perspective on these ecological aspects we must turn to the fossil record. However, compared to temperate zones, collecting continuous sedimentary archives in the lowland tropics is often difficult due to the active landscape processes, with potentially frequent volcanic, tectonic, and/or fluvial events confounding sediment deposition, preservation, and recovery. Consequently, the nature, and drivers, of vegetation dynamics during the last glacial are barely known from many non-montane tropical landscapes. One of the first lowland Amazonian locations from which palaeoecological data were obtained was an outcrop near Mera (Ecuador). Mera was discovered, and analysed, by Paul Colinvaux in the 1980s, but his interpretation of the data as indicative of a forested glacial period were criticised based on the ecology and age control. Here we present new palaeoecological data from a lake located less than 10 km away from Mera. Sediment cores raised from Laguna Pindo (1250 masl; 1°27′S, 78°05′W) have been shown to span the late last glacial period [50–13 cal kyr BP (calibrated kiloyears before present)]. The palaeoecological information obtained from Laguna Pindo indicate that the region was characterised by a relatively stable plant community, formed by taxa nowadays common at both mid and high elevations. Miconia was the dominant taxon until around 30 cal kyr BP, when it was replaced by Hedyosmum, Asteraceae and Ilex among other taxa. Heat intolerant taxa including Podocarpus, Alnus, and Myrica peaked around the onset of the Last Glacial Maximum (c. 21 cal kyr BP). The results obtained from Laguna Pindo support Colinvaux’s hypothesis that glacial cooling resulted in a reshuffling of taxa in the region but did not lead to a loss of the forest structure. Wide tolerances of the plant species occurring to glacial temperature range and cloud formation have been suggested to explain Pindo forest stability. This scenario is radically different than the present situation, so vulnerability of the tropical pre-montane forest is highlighted to be increased in the next decades.

Four centuries of vegetation change in the mid-elevation Andean forests of Ecuador

“…The relatively steep slopes and lack of marshy vegetation surrounding both lakes would have increased the probability that charcoal resulting from fires, if any, within the watershed would have been deposited into the lakes. Because sediment cores from the wet regions of the Andes and Amazonia often contain charcoal (Loughlin et al 2018;Montoya et al 2018), we do not think taphonomic processes affected our results.…”

Forests protect aquatic communities from detrimental impact by volcanic deposits in the tropical Andes (Ecuador)

“…The raw radiocarbon dates were calibrated using IntCal13.14c and SHCal.13.14c for L. Baños and L. Pindo respectively (Hogg et al 2013;Reimer et al 2013). The results were used to construct age-depth models in R using the statistical package 'clam.R' (Blaauw 2010), that have been published elsewhere (Matthews-Bird et al 2017;Montoya et al 2018), and are included in the Supplementary material (Figs. S1 and S2).…”

Capítulo 24: Resiliencia de la selva amazónica a los cambios globales: Evaluación del riesgo de puntos de inflexión

“…Regions like the southern and southeastern Amazon have shifted between forest and open savanna vegetation in relatively recent periods of colder and drier LGM climate (Absy and Hammen 1976), whereas the Andean flank in the western (van der Hammen and Absy 1994) and eastern portions of the Amazon (Wang et al 2017) seem to have persisted as forest. Long-term ecological data from pollen analysis have shown the prevalence of various types of rainforests, both in the southwestern cloud forests and northwestern pre-montane forests of the Amazonian highlands, showing the importance of cloud cover in buffering forests when facing climate change (Urrego et al 2010;Montoya et al 2018). The presence of forests with distinct composition during the LGM has also been observed in the northwestern Brazilian Amazon (Bush et al 2004;D'Apolito et al 2013).…”

“…When a forest is disturbed, the rates of ecosystem change observed in sedimentary archives depend on the ecological scale, being abrupt (decadal) at the species level, but gradual (centennial) at the community level (Montoya et al 2018(Montoya et al , 2019. In a tropical meta-data analysis of forest recovery rates after disturbances based on pollen records, Cole et al (2014) observed that South American forests required an average of 325 years to recover from disturbances (natural and human-induced).…”