Enhancing Plant Diversity in Secondary Forests

Ana C Palma,Susan G W Laurance,Pablo R Stevenson,Miriam Goosem

doi:10.3389/ffgc.2020.571352

Ana C Palma, Susan G W Laurance + Show 2 more

Open Access

https://doi.org/10.3389/ffgc.2020.571352

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Abstract

Dispersal, recruitment and establishment limitations are crucial processes shaping forest composition. In secondary forests these mechanisms may operate differently than in mature forests, because young and isolated secondary forests may suffer stronger limitations due to a lack of suitable dispersers and harsh environmental conditions— such as the elevated competition of exotic grasses. To assess establishment limitations in these forests, we undertook transplant experiments involving seeds and seedlings along a chronosequence of secondary forests in tropical Australia. The experiments included six species that varied in seed size (6–50 mm in length) and successional status (early to late successional). Seeds of five species were placed in one of three treatments: (1) exposed seeds, (2) fenced seeds, and (3) buried seeds, and multiple seedlings of six species were transplanted in block treatments. After 14–17 months, seed from all plant species germinated across all ages of secondary forests. However, in young secondary forest sites (4–12 years) fewer germinated seeds survived. The highest survival rates were observed for buried seeds (27.2%) compared to the low survival of exposed seeds (6.0%). Planted seedlings (6 spp) had the greatest overall survival (63.1%) and the highest growth rates in older secondary forests. We found that species identity was important for growth and survival in both experiments, but detected no effect of successional status or seed size. A crucial finding of this study was that the buried seeds of all species germinated and had relatively high survival irrespective of variation in site conditions or successional status, suggesting that seed availability may be a greater barrier to recovery of secondary forests in the region than the establishment limitations imposed by environmental conditions.

Highlights

Rapid transformation of mature tropical forests puts at risk the high biodiversity and the varied ecosystem services these forests provide
Survival for B. tooram, E. bessaphila and L. leefeana was greater when seeds were buried in old secondary forests (43.75 ± 27.51, 33.75 ± 16.52, and 53.75 ± 19.31, respectively), whilst C. oblata and G. lasioneura were more successful if sown in intermediate-aged forests (12.5 ± 15.54 and 8.75 ± 6.29, respectively)
We did not find a clear pattern relating to functional traits such as seed size or successional status

Summary

Introduction

Rapid transformation of mature tropical forests puts at risk the high biodiversity and the varied ecosystem services these forests provide. Some models focus on the physiological and morphological traits of the first colonists (e.g., Egler, 1954; Connell and Slatyer, 1977) and highlight that most of the species that will dominate later in succession are present since the onset of succession (Egler, 1954). These species will either prevent or facilitate the colonization of other species according to their life-spans and stress tolerances (Drury and Nisbet, 1973; Connell and Slatyer, 1977). Species with larger seeds present at the onset of succession should outcompete small-seeded plants because larger seed reserves provide higher per capita recruitment and survival (Moles and Westoby, 2004) increase resource provisioning (Westoby et al, 1996), stress tolerance (Muller-Landau, 2010) and improve seedling performance (Moles and Westoby, 2002, 2004)

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