Impacts of Myrtle Rust Induced Tree Mortality on Species and Functional Richness within Seedling Communities of a Wet Sclerophyll Forest in Eastern Australia

Austropuccinia psidii is an introduced plant pathogen known to have caused significant declines in populations of several Australian native Myrtaceae species. However, limited research has focused on the impacts of the pathogen on plant communities in the aftermath of its invasion. This study investigated the relationship between disease impact level, plant species diversity, and functional richness in seedling communities in a wet sclerophyll forest in southeast Queensland. A clear shift was found from early colonizer Myrtaceae species in the mid- and understory to a more diverse non-Myrtaceae seedling community indicative of secondary succession. Comparisons of key Myrtaceae species and the seedling community suggest that there may also be a shift towards species that produce drupes and larger seeds, and overall, a current reduction in fruit availability due to the dramatic loss of previously dominant species. Seedling diversity showed no significant correlation with tree mortality, possibly due to favorable rainfall conditions during the study period. The more subtle changes in forest composition, such as changes in fruit type and availability due to myrtle rust, however, could affect the visitation of local bird species in the short term and certainly reduce the store of early colonizing native shrub and tree species

Seedling diversity in actively and passively restored tropical forest understories.

Phylogenetic and functional diversity data beneath different reforestation types within Leyte, Philippines

Tropical tree leaf trade-offs are stronger for sub-canopy trees: leaf traits reveal little about growth rates in canopy trees

Tree species leaf traits&nbsp

Next generation tropical forests: recruitment of species and functional diversity underneath reforestation types in a human dominated landscape

Seedling recruitment data beneath different reforestation types within Leyte, Philippines

Next-generation tropical forests: reforestation type affects recruitment of species and functional diversity in a human-dominated landscape

1. In tropical countries where little natural forest remains, such as the Philippines, smallholder monocultures and mixed-species plantations potentially provide conservation values by providing habitat for local fauna and recruiting diverse understorey species. However, little information exists as to whether monocultures offer a framework to kick-start understorey species recruitment and how this compares to mixtures. 2. In this study, species and trait diversity were measured within the understories of three different forest types on the Island of Leyte, Philippines: mixed-species forests (known as ‘Rainforestation Farming’), Swietenia macrophylla monocultures and regenerating selectively logged forests. All plants less than 2 m in height were identified, and dispersal type, fruit type, seed and fruit size were extracted from literature and online data bases. 3. We found that overall seedling richness and diversity were lower within the monoculture forests compared with the regenerating selectively logged forests, with the Rainforestation forests showing intermediate seedling diversity, including trait diversity. Monoculture understories had a higher proportion of large fruited domesticated species that are likely dispersed by people and significantly lower wind-dispersed native seedlings than the other forest types. Higher understorey diversity was generally negatively correlated with soil nutrients and positively correlated with increased leaf area index, that is more canopy cover. 4. Our results confirm that mixed-species plantations and regenerating selectively logged forests recruit higher species diversity, but we also found evidence that monocultures can recruit diverse species in the understorey. However, monoculture understories were depauperate of native wind-dispersed traits that are often important emergent species in tropical rain forests. 5. Synthesis and applications. Overall, our results show that just having trees in a cleared landscape provides conservation value, but if monocultures are used as less costly and technically simpler solutions for initiating recruitment, then wind-dispersed native species (e.g. species from the Dipterocarpaceae family) in addition to other limited functional traits (e.g. large-seeded species

Seedling diversity in actively and passively restored tropical forest understories

Alternative methods for restoring tropical forests influence the ecological processes that shape recruitment of understory species. In turn, the traits of species recruited will influence the ecological processes the forests provide now and over the long term. We assess the phylogenetic and functional structure of seedlings beneath monoculture plantations, mixed-species plantations (both active restoration) and regenerating selectively logged native forests (passive restoration), considering traits of specific leaf area (SLA, including within-species variation), leaf nitrogen and phosphorus content, life-form, potential plant height, and dispersal type. Monoculture plantations comprised seedlings that were more closely related then would be expected by chance (i.e., phylogenetically clustered), and regenerating forest contained species more distantly related then would be expected by chance (i.e., phylogenetically overdispersed). This suggests that seedlings beneath monocultures assemble through environmental filtering and through the dispersal limitation of predictable functional guilds. However, dispersal limitation is frequently overcome by human-assisted dispersal, increasing trait diversity. Comparing SLA values revealed that regenerating forests recruit seedlings with both high and low mean and variation of SLA, leading to higher overall diversity. Regenerating forest seedlings showed signs of environmental filtering, only based on within-species variation of SLA. Regenerating forest understories appear to favor species that show a high intraspecific variation in SLA values (e.g., Pterocarpus indicus Willd.) and at the same time provided habitat for later successional seedlings that show a lower intraspecific variation in SLA (e.g., Canarium luzonicum (Blume) A.Gray). This trait diversity suggests limiting similarity or competitive exclusion may be reduced because of niche differences, allowing species with different traits to coexist. Phylogenetic and functionally distinct species are restricted in their regeneration capacity, many of which are of conservation significance (under the IUCN Red List). Reforestation projects should maximize desired ecological services (including conservation value) by actively managing for the recruitment of species that are phylogenetically and functionally (including intraspecifically) distinct. This management aim will increase the probability of fulfilling a wider array of niche spaces and potentially increase the diversity of ecosystem services provided.</p

Imminent Extinction of Australian Myrtaceae by Fungal Disease

Myrtle rust is a fungal disease that has spread rapidly across the globe, arriving in Australia in 2010. The tree species Rhodomyrtus psidioides is nearly extinct in the wild as a result of the disease, leading to potential disruption of ecosystem function. Many other Myrtaceae may also be threatened and unprecedented impacts of the disease are predicted

Recovery of species composition over 46 years in a logged Australian tropical forest following different intensity silvicultural treatments

Currently, more than 400 million hectares of tropical forests worldwide are now being managed for timber production. Understanding the long-term responses of tropical forests to management practices is critical for managing tropical forests sustainably. To investigate the responses of tropical forest dynamics to different silvicultural treatment intensities, permanent plots were established in 1967 in an Australian tropical forest with four treatments: selective logging only as a control and selective logging followed by three differing intensity silvicultural treatments in 1969. We investigated changes in the number of species, species dominance, and species composition of trees (DBH >= 10 cm) from 1967 to 2015. Before selective logging, the number of tree species did not differ between the treatments, ranging from 70 to 75. Selective logging alone had small immediate effects on the number of species and species abundance distributions. After silvicultural treatment, the number of species in the low-intensity treatment, medium-intensity treatment and high-intensity treatment were reduced to 48, 42, and 18 respectively. The number of species in the control, low-intensity, and medium-intensity treatments recovered to their pre-logging levels within 46 years, but recovery in the high-intensity treatment was incomplete due to much greater initial species loss through silvicultural treatment. Silvicultural treatments increased species dominance, with the differences being progressively more marked as the level of treatment intensity increased. Over 46 years, tree species abundance distribution in the silvicultural treatments became more even and largely returned to pre-logging conditions, with more rapid recovery after low and intermediate silvicultural treatments. Following silvicultural treatments, species composition in the logging only, low-intensity and medium-intensity silvicultural treatments did not change markedly, whereas species composition was substantially altered by high-intensity silvicultural treatment and was subsequently distinct from the other treatments. Within 46 years following treatments, species composition in the high intensity treatment showed a recovery trajectory towards pre-logging conditions, leading to increased species compositional similarity among the four treatments. Increasing the intensity of silviculture treatment led to greater time required for recovery of species diversity, composition and compositional similarity. We recommend that high intensity silvicultural treatments should be avoided if rapid recovery of species diversity and composition is the desired management outcome in tropical rainforests similar to those in our study area

Soil organic carbon recovery in tropical tree plantations may depend on restoration of soil microbial composition and function

Soil organic carbon (SOC) supports essential functions in terrestrial biomes and global biogeochemical cycles, and tropical tree plantations are often called upon to reverse deforestation-induced SOC loss. Yet the comparative efficacy of different plantation types and associated drivers of SOC restoration remain unclear. Theory suggests that higher chemical and spatial heterogeneity of plant litter should promote greater efficiency of soil microbial communities involved in SOC formation, so we hypothesised that more species-diverse tree plantations should be more effective in accelerating recovery of SOC. To test this, we compared developmental recovery of SOC and soil microbial communities between monoculture (Swietenia macrophylla King, mahogany) and highly diverse and mostly native species plantations (termed “rainforestation”). All plantation types, which were aged 15 to 20 years, only restored the composition of the soil microbial community to 20–30% of the reference, selectively logged old-growth rainforest. Contrary to our hypothesis, mahogany plantations, but not rainforestation, restored SOC and microbial function. Rainforestation shifted soil microbial composition and the composition of the understory vegetation closer to reference conditions. Soil microbial composition at all plantation sites was correlated with plant composition and functional traits, and better explained variation in SOC than land use. In particular, soil fungal PLFA biomass displayed a strong positive correlation with topsoil SOC concentration. This suggests that belowground restoration with tropical reforestation is slow relative to typical rotation times of tropical plantations (15–20 years). We conclude that reliable and rapid restoration of SOC may depend on interventions both above and below ground to re-instate the soil microbial community. This may require careful selection of plant species in combination with microbial inoculations