Estimation of pollen productivity and dispersal: How pollen assemblages in small lakes represent vegetation

Abstract

Quantitative understanding of vegetation dynamics over timespans beyond a century remains limited. In this regard, the pollen-based reconstruction of past vegetation enables unique research opportunities by quantifying changes in plant community compositions during hundreds to thousands of years. Critically, the methodological basis for most reconstruction approaches rests upon estimates of pollen productivity and dispersal. Previous studies, however, have reached contrasting conclusions concerning these estimates, which may be perceived to challenge the applicability and reliability of pollen-based reconstruction. Here we show that conflicting estimates of pollen production and dispersal are, at least in part, artifacts of fixed assumptions of pollen dispersal and insufficient spatial resolution of vegetation data surrounding the pollencollecting lake. We implemented a Bayesian statistical model that related pollen assemblages in surface sediments of 33 small lakes (<2 ha) in the northeastern United States, with surrounding vegetation ranging from 10 1 to >10 5 m from the lake margin. Our analysis revealed three key insights. First, pollen productivity is largely conserved within taxa and across forest types. Second, when local (within a 1-km radius) vegetation abundances are not considered, pollen-source areas may be overestimated for some common taxa (Cupressaceae, Pinus, Quercus, and Tsuga). Third, pollen dispersal mechanisms may differ between local and regional scales; this is missed by pollendispersal models used in previous studies. These findings highlight the complex interactions between vegetation heterogeneity on the landscape and pollen dispersal. We suggest that, when estimating pollen productivity and dispersal, both detailed local and extended regional vegetation must be taken into account. Also, both deductive (mechanistic models) and inductive (statistical models) approaches are needed to better understand the emergent properties of pollen dispersal in heterogeneous landscapes.

Functional traits of fossil plants

“… * We use the concept pollen dispersal to refer to how far for example airborne pollen grains may travel before being deposited (Yao et al ., 2022). …”

“…The advantage consists of a rapid germination due to the short rehydration time (Pacini & Hesse, 2012) Terminology used for the six pollen traits (pollen size, shape, apertures, sculptures, dispersal unit, and wall thickness) follows the Palynological Database-PalDat (https://paldat.org) and Halbritter et al (2018). *We use the concept pollen dispersal to refer to how far for example airborne pollen grains may travel before being deposited (Yao et al, 2022).…”

Holocene land cover change in North America: continental trends, regional drivers, and implications for vegetation-atmosphere feedbacks

“…Others are process-based proxy system models (Evans et al, 2013) that attempt to represent the processes governing the atmospheric transport and deposition of pollen, such as the REVEALS and LOVE (Sugita, 2007a, c) or STEPPS (Dawson et al, 2019a). Efforts continue to test and refine the parameterizations of these models through paired analyses of pollen assemblages and forest composition at local to landscape scales (Liu et al, 2022).…”

Amazonian pollen assemblages reflect biogeographic gradients and forest cover

“…Quantifying the amount of deforested areas using pollen assemblages in Amazonia is also dependent on the source area of pollen (Liu et al, 2022). Studies in the forest-savanna ecotone areas of Bolivia suggested that anemophilous (wind-dispersed) pollen found in lake sediments may be derived from distances of over 40 km (Whitney et al, 2019).…”

“…One parameter that has been lacking, however, is quantifying the extent of deforestation that occurred alongside occupation and cultivation. Using pollen assemblages to quantify past land cover has been successful in temperate ecosystems (Dawson et al, 2019; Gaillard, Sugita, Bunting, Dearing, et al, 2008; Gaillard, Sugita, Bunting, Middleton, et al, 2008; Liu et al, 2022; Prentice, 1988; Sugita, 1993, 2007; Trondman et al, 2015). The only attempt to quantify land cover in Amazonia was performed in the savanna‐forest landscape of Bolivia, which revealed that deforestation was easier to detect in the closed‐canopy rainforests than in the savannas (Whitney et al, 2019).…”