Seeing beyond the trees: a comparison of tropical and temperate plant growth forms and their vertical distribution

Abstract

Forests are the most diverse and productive terrestrial ecosystems on Earth, so sustainably managing them for the future is a major global challenge. Yet, our understanding of forest diversity relies almost exclusively on the study of trees. Here, we demonstrate unequivocally that other growth forms (shrubs, lianas, herbs, epiphytes) make up the majority of vascular plant species in both tropical and temperate forests. By comparing the relative distribution of species richness among plant growth forms for over 3,400 species in 18 forests in the Americas, we construct the first high‐resolution quantification of plant growth form diversity across two ecologically important regions at a near‐continental scale. We also quantify the physical distribution of plant species among forest layers, that is, where among the vertical strata plants ultimately live their adult lives, and show that plants are strongly downshifted in temperate forests vs. tropical forests. Our data illustrate a previously unquantified fundamental difference between tropical and temperate forests: what plant growth forms are most speciose, and where they ultimately live in the forest. Recognizing these differences requires that we re‐focus ecological research and forest management plans to encompass a broader suite of plant growth forms. This more holistic perspective is essential to conserve global biodiversity.

Guidance for successful tree planting initiatives

“…Tree planting in some cases facilitates forest recovery, but tree planting and forest restoration are not synonyms (Table 2). In fact, trees represent less than a third of the plant species across a range of forest types (Spicer, Mellor, & Carson, 2020). Forests host a diverse suite of plants (e.g.…”

Disentangling the Ecological Determinants of Species and Functional Trait Diversity in Herb-Layer Plant Communities in European Temperate Forests

“…However, within the pan-European programme for monitoring forest health (i.e., the International Co-operative Programme on the Assessment and Monitoring of Air Pollution Effects on Forests-ICP Forests; [26][27][28]), previous studies rarely focused on ground vegetation. The herb layer should be a central part of forest diversity studies because herbaceous species majorly contribute to vascular plant species richness and overall forest biodiversity [29][30][31] and play a pervasive role in ecosystem functioning [21,32]. Vegetation records from ICP Forests monitoring plots (Level I or Level II; [33]) have been more frequently used for the research of possibilities and accuracy of different survey methods [34,35] or impacts of atmospheric nitrogen deposition [36][37][38] and forest disturbances [39].…”

Are we missing the forest for the trees? Conspecific negative density dependence in a temperate deciduous forest

“…Canopy plants were significantly more overdispersed than understory plants regardless of dispersal mechanism(n canopy-bird = 5, n canopy-wind = 12, n understory-bird = 18, n understory-wind = 5). Bird dispersal was emphasized here; however, plants did not differ significantly PLOS ONE of plant diversity in temperate deciduous forests [63] and are largely neglected with respect to their diversity maintenance [17]. Nevertheless, even by simply dividing the woody plant community into canopy trees and woody understory plants, we demonstrate that CNDD, which appears to maintain canopy tree diversity, may not be strong enough to overcome dispersal limitation and maintain understory woody plant diversity in this temperate forest.…”

“…In tropical forests, however, trees commonly represent 65% or more of the woody plant species diversity (e.g., [60,61]), and thus CNDD is still likely a powerful diversity maintenance mechanism. By contrast, CNDD may fail to maintain the majority of species diversity in temperate forests where canopy trees represent a small minority of species [62,63].…”