Multiple stages of tree seedling recruitment are altered in tropical forests degraded by selective logging

Bornean tropical forests recovering from logging at risk of regeneration failure

Active restoration through silvicultural treatments (enrichment planting, cutting climbers and liberation thinning) is considered an important intervention in logged forests. However, its ability to enhance regeneration is key for long-term recovery of logged forests, which remains poorly understood, particularly for the production and survival of seedlings in subsequent generations. To understand the long-term impacts of logging and restoration we tracked the diversity, survival and traits of seedlings that germinated immediately after a mast fruiting in North Borneo in unlogged and logged forests 30-35 years after logging. We monitored 5119 seedlings from germination for ~1.5 years across a mixed landscape of unlogged forests (ULs), naturally regenerating logged forests (NR) and actively restored logged forests via rehabilitative silvicultural treatments (AR), 15-27 years after restoration. We measured 14 leaf, root and biomass allocation traits on 399 seedlings from 15 species. Soon after fruiting, UL and AR forests had higher seedling densities than NR forest, but survival was the lowest in AR forests in the first 6 months. Community composition differed among forest types; AR and NR forests had lower species richness and lower evenness than UL forests by 5-6 months post-mast but did not differ between them. Differences in community composition altered community-weighted mean trait values across forest types, with higher root biomass allocation in NR relative to UL forest. Traits influenced mortality ~3 months post-mast, with more acquisitive traits and relative aboveground investment favoured in AR forests relative to UL forests. Our findings of reduced seedling survival and diversity suggest long time lags in post-logging recruitment, particularly for some taxa. Active restoration of logged forests recovers initial seedling production, but elevated mortality in AR forests lowers the efficacy of active restoration to enhance recruitment or diversity of seedling communities. This suggests current active restoration practices may fail to overcome barriers to regeneration in logged forests, which may drive long-term changes in future forest plant communities.

Conservation implications of mapping the potential distribution of an Ethiopian endemic versatile medicinal plant, Echinops kebericho Mesfin

Echinops kebericho is a narrow-range multipurpose medicinal plant confined to Ethiopia. Intense land use change and overharvesting for traditional medicine have resulted in narrow distributions of its populations. It is a threatened species with a decreasing population trend. This study aims to map its potential distribution, which is key to guide conservation efforts and sustainable use. We modeled the potential distribution of E. kebercho using the maximum entropy model (MaxEnt) employing 11 less correlated predictor variables by calibrating the model at two complexity levels and replicating each model 10 times using a cross validation technique. We projected the models into the whole of Ethiopia and produced binary presence-absence maps by classifying the average map from both complexity levels applying three threshold criteria and ensembling the resulting maps into one for the final result. We mapped suitable habitat predicted with high certainty and identified local districts where E. kebericho can be cultivated or introduced to enhance its conservation. We estimated that E.kebercho has about 137,925 km² of suitable habitat, mainly concentrated in the western highlands of the Ethiopian mountains. Our models at both complexity levels had high average performances, AUC values of 0.925 for the complex model and 0.907 for the simpler model. The variations in performance among the 10 model replicates were not remarkable, an AUC standard deviation of 0.040 for complex and 0.046 for simple model. Although E. kebericho is locally confined, our models predicted that it has a remarkably wider potential distribution area. We recommend introducing E. kebericho to these areas to improve its conservation status and tap its multiple benefits on a sustainable basis. Locally confined threatened plants and animals likely have wider potential distributions than their actual distributions and thus similar methodology can be applied for their conservation.

Understorey Seedling Bank in Forest Areas with a Differing Period of Recovery in Mabira Central Forest Reserve, South Central Uganda

Seedling banks are very important in forest regeneration following forest disturbances such as crop cultivation. In 2011 and 2013 the Uganda National Forestry Authority (NFA) evicted encroachers from parts of Mabira Central Forest Reserve that had been under crop cultivation for over 40 years. This gave an opportunity for the vegetation to recover. In this study, we assessed the recovery process based on seedling bank diversity, richness and density in three blocks differing in recovery time. Two disturbed blocks, the Western Block (WB) (abandoned by encroachers 1-3 years), and the Eastern Block (EB) (abandoned 4-5 years) before this study and a nearby undisturbed area (intact) were included in the study. We recorded 48 seedlings species; 37 in WB, 30 in EB and 27 in intact. Differences in species richness were not statistically significant among blocks (F_{2, 88} = 1.2420, p = 0.294). All seedling species found in the intact were found in the EB and WB. There were statistically significant differences in species diversity (Shannon-Wiener: F_{2, 88} = 5.354, p = 0.006), density (P < 0.001) and composition (ANOSIM; R = 0.55, p = 0.001) among blocks. Apart from Broussonetia papyrifera, other species contributing to the dissimilarity (Acalypha neptunica, Antiaris toxicaria, Blighia unijugata, Funtumia elastica were late succession species. Animal dispersed species dominated intact. Seed-regenerating species were found in both WB and EB, but re-sprouts were more common in EB. These results show that proximity to intact forest aids forest recovery, even for areas with long-term cultivation history.

Limited contributions of plant pathogens to density-dependent seedling mortality of mast fruiting Bornean trees

Fungal pathogens are implicated in driving tropical plant diversity by facilitating strong, negative density-dependent mortality of conspecific seedlings (C-NDD). Assessment of the role of fungal pathogens in mediating coexistence derives from relatively few tree species and predominantly the Neotropics, limiting our understanding of their role in maintaining hyper-diversity in many tropical forests. A key question is whether fungal pathogen-mediated C-NDD seedling mortality is ubiquitous across diverse plant communities. Using a manipulative shadehouse experiment, we tested the role of fungal pathogens in mediating C-NDD seedling mortality of eight mast fruiting Bornean trees, typical of the species-rich forests of South East Asia. We demonstrate species-specific responses of seedlings to fungicide and density treatments, generating weak negative density-dependent mortality. Overall seedling mortality was low and likely insufficient to promote overall community diversity. Although conducted in the same way as previous studies, we find little evidence that fungal pathogens play a substantial role in determining patterns of seedling mortality in a SE Asian mast fruiting forest, questioning our understanding of how Janzen-Connell mechanisms structure the plant communities of this globally important forest type.

Forest Degradation: When Is a Forest Degraded?

The concept of forest degradation tends to be addressed in broad terms, and existing definitions are difficult to apply in practice. These definitions are based on a reduction in the production of ecosystem goods and services, but fail to address how, when and to what degree this reduction—which ultimately leads to degradation of a forest—occurs. Generally speaking, degradation is the result of a progressive decline in the structure, composition and functions upon which the vigor and RESILIENCE of a forest is based. A degraded forest is one whose structure, function, species composition, or productivity have been severely modified or permanently lost as a result of damaging human activities. So far, no guidelines have been developed for classification and evaluation of a degraded forest at the stand level, nor are there methodologies for assessing the degree of degradation found. The present work proposes stand-level guidelines for identification of a degraded forest according to a list of structural, compositional and regeneration criteria and characteristics. Emphasis is put on the need for local definitions of forest degradation, and identification of thresholds that determine the points where the processes of degradation finalize into degraded forests. Finally, the present work makes a call to move forwards in sustainable management in order to prevent degradation, and in implementation of restoration or rehabilitation practices in degraded forests.

Multiple stages of tree seedling recruitment are altered in tropical forests degraded by selective logging

Tropical forest degradation is a global environmental issue. In degraded forests, seedling recruitment of canopy trees is vital for forest regeneration and recovery. We investigated how selective logging, a pervasive driver of tropical forest degradation, impacts canopy tree seedling recruitment, focusing on an endemic dipterocarp Dryobalanops lanceolata in Sabah, Borneo. During a mast-fruiting event in intensively logged and nearby unlogged forest, we examined four stages of the seedling recruitment process: seed production, seed predation, and negative density-dependent germination and seedling survival. Our results suggest that each stage of the seedling recruitment process is altered in logged forest. The seed crop of D. lanceolata trees in logged forest was one-third smaller than that produced by trees in unlogged forest. The functional role of vertebrates in seed predation increased in logged forest while that of non-vertebrates declined. Seeds in logged forest were less likely to germinate than those in unlogged forest. Germination increased with local-scale conspecific seed density in unlogged forest, but seedling survival tended to decline. However, both germination and seedling survival increased with local-scale conspecific seed density in logged forest. Notably, seed crop size, germination, and seedling survival tended to increase for larger trees in both unlogged and logged forests, suggesting that sustainable timber extraction and silvicultural practices designed to minimize damage to the residual stand are important to prevent seedling recruitment failure. Overall, these impacts sustained by several aspects of seedling recruitment in a mast-fruiting year suggest that intensive selective logging may affect long-term population dynamics of D. lanceolata. It is necessary to establish if other dipterocarp species, many of which are threatened by the timber trade, are similarly affected in tropical forests degraded by intensive selective logging.