Shekhar R. Biswas

Disturbance effects on species diversity and functional diversity in riparian and upland plant communities

Understanding disturbance effects on species diversity and functional diversity is fundamental to conservation planning but remains elusive. We quantified species richness, diversity, and evenness and functional richness, diversity, and evenness of riparian and upland plants along 24 small streams subjected to a range of anthropogenic disturbances in the boreal forest of northwestern Ontario, Canada. We included a total of 36 functional traits related to productivity, competitive ability, reproduction, disturbance tolerance, life history, and tolerance to habitat instability. Using nested ANOVA, we examined the response of diversity indices to disturbance and whether it followed the intermediate disturbance hypothesis (IDH) and varied with habitat stability. We found that, like species richness and diversity, functional richness and diversity reached peaks at moderate disturbance intensity; functional diversity followed the predictions of the IDH. Second, disturbance-habitat-stability coupling has very little effect on overall species and functional diversity, but the effect on particular life forms and functions may be significant. Since species richness and diversity patterns are context and system dependent, our findings should be most applicable to similar temperate riparian systems.

A unified framework for the restoration of Southeast Asian mangroves—bridging ecology, society and economics

The effect of intensive human intervention, poor socio-economic conditions and little knowledge on mangrove ecology pose enormous challenges for mangrove restoration in Southeast Asia. We present a framework for tropical mangrove restoration. Our proposed restoration framework addresses the ecology, economy and social issues simultaneously by considering the causes of mangrove degradation. We provide a step by step guideline for its restoration. We argue that although, ecological issues are of prime importance, economic and social issues must be considered in the restoration plan in order for it to be successful. Since mangrove ecology is not adequately studied in this region, local ecological knowledge can be used to fill the baseline information gaps. Unwanted human disturbance can be minimized by encouraging community participation. This can be ensured and sustained by facilitating the livelihood of the coastal community. We translated the restoration paradigm into a readily available practical guideline for the executors of the plans. We provide an example of mangrove restoration project that is closely related to our proposed framework. We are optimistic that this framework has the potential for universal application with necessary adjustments.

Edge influence on vegetation at natural and anthropogenic edges of boreal forests in Canada and Fennoscandia

Although anthropogenic edges are an important consequence of timber harvesting, edges due to natural disturbances or landscape heterogeneity are also common. Forest edges have been well studied in ...

Species diversity and functional diversity relationship varies with disturbance intensity

The relationship between species diversity and functional diversity is a fundamental topic in conservation ecology but its direct evaluation in naturally heterogeneous systems and its relationship with disturbance intensity is limited. We examined the relationship between taxonomy-based species diversity (in terms of richness and evenness) and trait-based functional diversity of riparian and upland vegetation and determined if the slopes of this relationship vary with disturbance intensity. We used data from riparian and upland plant communities subjected to three categorical disturbance intensities (low = uncut mature forests, intermediate = riparian buffers around clearcuts and riparian buffers around clearcuts + soil scarification, and high = clearcuts and clearcuts + soil scarification) along 24 small streams of boreal forests in northwestern Ontario, Canada. For all disturbance intensities and habitat types (riparian vs. upland), the relationships between species diversity and functional diversity were positive and non-zero, but the slopes of these relationships varied significantly with disturbance intensities. In species richness vs. functional richness relationship, the slopes were steep at low and high disturbances and relatively less steep at moderate disturbance; however, patterns were less clear in species evenness vs. functional evenness relationship. Differential distributions of species richness per trait were, in part, associated with this variation in slope. In richness (opposite for evenness), less steep slopes were associated with relatively uniform distribution of species richness per trait compared to non-uniform distribution at steep slopes, where competitive (low disturbance) and disturbance-tolerant (high disturbance) traits dominated. Our results confirm that species diversity is a good indicator of ecosystem stability but it depends on ecosystem disturbance history. More importantly, this study suggests that different components of species diversity (e.g., richness and evenness) and the distribution of species richness per trait together can summarize the stability of an ecosystem more accurately than prediction made from species diversity alone.

Context-dependent patterns, determinants and demographic consequences of herbivory in an invasive species

Non-native invasive plants often lose many of their specialist herbivores in their invaded ranges, but new enemies may be recruited from the local generalist fauna, or from enemies themselves introduced to the same region. As a result, few invaders are free of herbivore damage; however, the incidence of this herbivory and its consequences for plant demography may depend on an array of biotic and abiotic factors. In Alliaria petiolata, a non-native invasive forb in Canada, we quantified the incidence of leaf herbivory, rosette survival and seed production along with conspecific plant density and environmental site conditions in wild populations in mesic forest understory and moist grasslands. We complemented the field survey by a laboratory experiment with Trichoplusia to test whether the palatability of leaf tissue of A. petiolata varies with plant life stage and habitat type. Incidence of herbivory was significantly higher in adults than in rosettes, and significantly higher in grasslands than in forest understory. The palatability experiment confirmed that leaves of adults were more palatable to a generalist herbivore than leaves of rosettes. Path analysis revealed negative plant density-dependent herbivory of adults in forest understory but positive density-dependent herbivory in grasslands. Incidence of herbivory in rosettes was positively associated with soil moisture in grasslands, but not in forest understory. Seed production was significantly positively associated with herbivory in adults and soil moisture, whereas rosette survival was significantly negatively associated with conspecific plant density. We conclude that the patterns, determinants and demographic consequences of herbivory in invasive Alliaria may strongly depend on a plant’s life stage and plant density and may further be confounded by landscape heterogeneity.

Tree species diversity and regeneration traits of the dominant species in a dipterocarp forest in Bangladesh: implications for conservation

Forests dominated by dipterocarps are one of the few remaining terrestrial areas with high biodiversity in Bangladesh. This study was conducted in a remnant dipterocarp forest reserve to identify tree species diversity in the reserve and key regeneration traits of the dominant species. Vegetation in transects and quadrats was measured, and regeneration traits (weight, length, diameter and dispersal distance) were investigated using seed trap experiments. We identified 66 tree species, belonging to 27 families and 45 genera with four clearly defined strata. Tree density was 384.05 ± 12.76 stems/ha and Dipterocarpus turbinatus alone contributed 23.45% to the total forest area. Trees in the intermediate diameter class (30.10–40.00 cm dbh) have high regeneration potential. We developed regression models to predict seed dispersal for different diameter classes. We found problems in recruitment for the dominant species. We suggest planting of native species to aid natural regeneration and for better management and conservation of biodiversity in the reserve. Similar management approaches may be applicable for other dipterocarp-dominated forests in Bangladesh.

Reclamation strategies for mined forest soils and overstorey drive understorey vegetation

1.Understorey vegetation accounts for the majority of plant diversity in forest ecosystems and contributes to ecosystem functioning. In restoration of degraded forested ecosystems, however, understorey vegetation is often restored passively, contrasting to clear strategies such as informed species choice and site improvement intervention for overstorey vegetation. The choice of overstorey-centred restoration strategy may have important consequences for understorey vegetation. 2.We examined the effects of substrate material, overstorey type and time since reclamation (age) on understorey vegetation following reclamation of oil sands mining in Alberta, Canada. We sampled cover, richness, evenness and composition of understorey vegetation at 94 sites of conifer, mixedwood and broadleaf overstorey types on three reclamation substrates (overburden, secondary overburden and tailings sand), with age ranging from 4 to 30 years. 3.Total, woody and non-woody understorey cover and species richness were the highest on secondary overburden and the lowest on tailings sand, and total cover also decreased with age. Woody cover and richness were the highest under broadleaf overstorey, while non-woody cover and richness were the lowest under conifer overstorey. Overall species evenness was not significantly affected by substrate type, overstorey type or age, but woody evenness was the highest on secondary overburden and the lowest on tailings sand, and non-woody evenness showed overstorey-dependent responses to age. Species composition varied with substrate type, overstorey type and age. Indicator species analysis revealed that tailings sand with conifer overstorey favoured grasses, while overburden and secondary overburden supported a mix of grasses, forbs and shrubs. 4.Synthesis and applications. Our study demonstrates that overstorey-centred reclamation strategies impact the abundance, diversity and composition of understorey plant communities following oil sands mining. Landforms constructed with secondary overburden substrates and revegetated with mixedwood or broadleaf tree species provide the most favourable habitats for understorey vegetation, while tailings sand to be a poor substrate for understorey species diversity and composition. We therefore recommend utilizing secondary overburden and overburden substrate material during landform construction, and employing revegetation prescriptions that target mixedwood and broadleaf overstorey types to promote productive and diverse understorey plant communities on the reclaimed landscape. This article is protected by copyright. All rights reserved.