Pollen-vegetation richness and diversity relationships in the tropics

Abstract

Tracking changes in biodiversity through time requires an understanding of the relationship between modern diversity and how this diversity is preserved in the fossil record. Fossil pollen is one way in which past vegetation diversity can be reconstructed. However, there is limited understanding of modern pollen-vegetation diversity relationships from biodiverse tropical ecosystems. Here, pollen (palynological) richness and diversity (Hill N 1 ) are compared with vegetation richness and diversity from forest and savannah ecosystems in the New World and Old World tropics (Neotropics and Palaeotropics). Modern pollen data were obtained from artificial pollen traps deployed in 1-ha vegetation study plots from which vegetation inventories had been completed in Bolivia and Ghana. Pollen counts were obtained from 15 to 22 traps per plot, and aggregated pollen sums for each plot were > 2,500. The palynological richness/diversity values from the Neotropics were moist evergreen forest = 86/6.8, semi-deciduous dry forest = 111/21.9, wooded savannah = 138/31.5, and from the Palaeotropics wet evergreen forest = 144/28.3, semi-deciduous moist forest = 104/4.4, forest-savannah transition = 121/14.1; the corresponding vegetation richness/diversity was 100/36.7, 80/38.7 and 71/39.4 (Neotropics), and 101/54.8, 87/45.5 and 71/34.5 (Palaeotropics). No consistent relationship was found between palynological richness/diversity, and plot vegetation richness/diversity, due to the differential influence of other factors such as landscape diversity, pollination strategy, and pollen source area. Palynological richness exceeded vegetation richness, while pollen diversity was lower than vegetation diversity. The relatively high global diversity of tropical vegetation was found to be reflected in the pollen rain.

Patterns of modern pollen and plant richness across northern Europe

“…A series of earlier studies have found similar positive correlations between pollen and plant richness in Europe (Birks, ; Felde et al, ; Matthias et al, ; Meltsov et al, ; Odgaard, ). However, investigations from the tropics (Gosling et al, ; Jantz, Homeier, & Behling, ) or from temperate western North America (Goring et al, ) have not found such positive correlations. Evaluating pollen–plant diversity relationships not only depends on the nature of pollen data but also on the spatial scale and quality of plant data (Birks, Felde, Bjune et al, ).…”

“…Among the landscape variables, openness and elevation have positive correlations with pollen richness and, as discussed above, earlier studies have also shown that both variables can have a positive effect on pollen richness (but not necessarily through an increase in plant richness) (Felde et al, ; Meltsov et al, ; Odgaard, ). In two modern pollen–plant richness studies from the tropics, where there is no clear link between pollen and plant richness, the gradient of openness is involved: Gosling et al () described the diversity from closed evergreen forests to wooded savanna and Jantz et al () involved elevational gradients. Openness, at high elevations or latitudes, in naturally open dry areas or human‐influenced landscapes is known to have a positive effect on pollen richness through the increased pollen‐source area in open conditions (Felde et al, ; Seppä, ; Sugita et al, ) and through higher pollen evenness that allows more taxa to be detected (Odgaard, ).…”

“…However, investigations from the tropics (Gosling et al, 2018;Jantz, Homeier, & Behling, 2014) or from temperate western North America (Goring et al, 2013) have not found such positive correlations.…”

“…There are several studies that have investigated modern pollen-plant diversity relationships (e.g. Felde, Peglar, Bjune, Grytnes, & Birks, 2016;Matthias, Semmler, & Giesecke, 2015;Meltsov, Poska, Odgaard, Sammul, & Kull, 2011;Meltsov, Poska, Reitalu, Sammul, & Kull, 2013) and the results usually show a positive relationship between modern pollen and plant diversity estimates (but see Goring, Lacourse, Pellatt, & Mathewes, 2013;Gosling et al, 2018). Most of these modernday pollen-plant studies are done at relatively local scales where climate variation is small and the diversity relationships mainly depend on landscape factors (e.g.…”

“…). In two modern pollen-plant richness studies from the tropics, where there is no clear link between pollen and plant richness, the gradient of openness is involved:Gosling et al (2018) described the diversity from closed evergreen forests to wooded savanna andJantz et al (2014) involved elevational gradients.…”