Kenny Helsen

Weforest

Invasive alien plant effects on ecosystem functions are often difficult to predict across environmental gradients due to the context-dependent interactions between the invader and the recipient communities. Adopting a functional trait-based framework could provide more mechanistic predictions for invasive species' impacts. In this study, we contras...

Invader success and ecosystem impact are both expected to be largely driven by the functional trait distinctiveness of the resident species relative to the invaded communities. To understand the importance of trait distinctiveness for plant invasions, and the native community's trait response to the invasion, it is key to measure multiple traits si...

1. Functional traits can help elucidate and predict the impact of invasive plant species on ecosystem functioning. Yet, this approach requires comprehensive and labor-intensive trait collection campaigns, covering intraspecific trait variation of both the invader and native species in the invaded community. One potential way to overcome these logis...

Leaf mass per area (LMA), leaf dry matter content (LDMC) and leaf water content/ equivalent water thickness (EWT) are commonly used functional plant traits in ecology. Whereas spectroscopy has recently proven to be a powerful tool to collect such functional trait information across large scales, it remains unclear whether these reflectance-based tr...

Alien plant species invasiveness and impact on diversity (i.e. species richness and composition) can be driven by the altered competitive interactions experienced by the invader in its invaded range compared to its native range. Trait‐based competition effects on invasiveness can be mediated through size‐asymmetric competition, i.e. a trait suit of...

Questions: Woody plant encroachment is known to adversely affect the biodiversity and functioning of savannah ecosystems, yet removal strategies have been shown to have variable success. Here we evaluated the effectiveness of three woody removal methods or treatments for controlling the leguminous thorny shrub Dichrostachys cinerea, and assessed pl...

Ethiopian Arabica coffee is produced in different agroforestry systems which differ in forest management intensity. In forest coffee systems (FC), coffee shrubs grow naturally in the understory of Afromontane forests with little human intervention, whereas in semi-forest coffee systems (SFC) thinning of the canopy and removal of the understory is a...

Although the relative importance of climate in abiotic filtering is higher for woody than herbaceous species assemblages, it is unclear whether this pattern is also reflected between the woody overstory and herbaceous understory of forests. The understory might respond more to small‐scale soil variation, next to experiencing additional abiotic filt...

Background Attempts to restore degraded highlands by tree planting are common in East Africa. However, up till now, little attention has been given to effects of tree species choice on litter decomposition and nutrient recycling. Method In this study, three indigenous and two exotic tree species were selected for a litter decomposition study. The...

Community weighted means (CWMs) are widely used to study the relationship between community-level functional traits and environment variation. When relationships between CWM traits and environmental variables are directly assessed using linear regression or ANOVA and tested by standard parametric tests, results are prone to inflated Type I error ra...

While the relative importance of climate filtering is known to be higher for woody species assemblages than herbaceous assemblage, it remains largely unexplored whether this pattern is also reflected between the woody overstory and herbaceous understory of forests. While climatic variation will be more buffered by the tree layer, the understory mig...

While functional trait-trait and trait-environment relationships are well studied in angiosperms, it is less clear if similar relationships, such as the leaf economics spectrum (LES), hold for ferns and lycophytes. Similarly, studies exploring potential differences in trait-trait and trait-environment relationships between terrestrial and epiphytic...

Context Evidence for effects of habitat loss and fragmentation on the viability of temperate forest herb populations in agricultural landscapes is so far based on population genetic studies of single species in single landscapes. However, forest herbs differ in their life histories, and landscapes have different environments, structures and histori...

Aims The aim of the study was to explore whether the encroachment of an East-African savannah ecosystem by the invasive shrub Dichrostachys cinerea L. Wight & Arn has resulted in changes in the Arbuscular Mycorrhizal Fungus (AMF) communities which are associated with roots of the extant herbaceous plant communities. We hypothesized that this could...

This paper presents all current knowledge on the biology of the invasive therophyte Impatiens glandulifera Royle (Himalayan Balsam), and covers aspects of taxonomy, morphology, distribution, habitat requirements, ecology, life cycle, genetics, history of invasive spread, ecological impact and management. Although a few review papers have been publi...

Invasieve uitheemse soorten worden gezien als een van de grote bedreigingen voor onze biodiversiteit. Aan de Belgische kust blijkt ondertussen 60% van de flora uitheems te zijn. Een aantal van deze soorten beginnen zich invasief te gedragen. Een van de meest problematische invasieve uitheemse soorten in de duinen is Rimpelroos Rosa rugosa, waarvan...

Worldwide, invasive alien plant species (IAS) threaten the biodiversity and the functioning of ecosystems. Most invasion research so far has focused on the properties underlying species invasiveness and community invasibility, yet IAS impact and the underlying causal pathways remain largely unknown. Here we dealt with this knowledge gap by extendin...

Our ability to measure plant characteristics across space and time is crucial for understanding and tracking the diversity and functioning of ecosystems. Ecological approaches to synthesize these characteristics have evolved from allocating species to predefined conventional plant functional types (cPFTs) to describing vegetation through delineatin...

Questions: Woody encroachment is increasingly affecting biodiversity and ecosystem functioning of savannah ecosystems worldwide, yet the direction and magnitude of these impacts often seem context‐dependent. Here, we investigated the potential of a trait‐based framework to understand the effect of the encroaching shrub Dichrostachys cinerea on plan...

1. This account presents information on all aspects of the biology of Poa nemoralis L. (Wood Meadow-grass) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic...

• Background and Aims It remains unclear whether invasive species can maintain both high biomass and reproductive output across their invaded range. Along latitudinal gradients, allocation theory predicts that faster flowering onset at high latitudes results in maturation at smaller size and thus reduced reproductive output. For annual invasive pla...

Background and aims-Deforestation and forest degradation have hugely affected the Southern Ethiopian Rift Valley, jeopardizing biodiversity conservation and ecosystem service provisioning. Quantifying the impacts of human activities on the remaining woody plant communities and recognizing vegetation-environment relationships provide the basis for t...

Linear landscape elements such as hedgerows and road verges have the potential to mitigate the adverse effects of habitat fragmentation and climate change on species, for instance, by serving as a refuge habitat or by improving functional connectivity across the landscape. However, so far this hypothesis has not been evaluated at large spatial scal...

1.Climate change will increase the level of drought stress experienced by plant communities, but the spatial distribution of projected changes in dryness remains highly uncertain. Species can, to some extent, deal with climate uncertainty through natural variation in adaptive responses to environmental heterogeneity and predictability. Biodiversity...

Background: The observation that many alien species become invasive despite low genetic diversity has long been considered the ‘genetic paradox’ in invasion biology. This paradox is often resolved through the temporal buildup genetic diversity through multiple introduction events. These temporal dynamics in genetic diversity are especially importan...

Agricultural expansion and intensification threaten pollinator populations worldwide, potentially jeopardizing crop pollination. Although the highest rates of cropland expansion are currently found within the tropics, quantifying effects of landscape composition on tropical pollinator communities and the provided pollination services to crops has r...

Climate change is expected to increase the level of drought stress experienced by many plant populations, yet the spatial distribution of changes in dryness remains highly uncertain. Species can, to some extent, adapt to climate uncertainty through evolving increased trait plasticity. Biodiversity conservation could capitalize on such natural varia...

Background and aims Grasslands are expected to experience droughts of unprecedented magnitude and duration in this century. Plant traits can be useful for understanding community and ecosystem responses to climate extremes. Few studies, however, have investigated the response of community-scale traits to extreme drought on broad spatial/temporal sc...

Ploidy level in plants may influence ecological functioning, demography, and response to climate change. However, measuring ploidy level typically requires intensive cell or molecular methods. We map ploidy level variation in quaking aspen, a dominant North American tree species that is usually diploid or triploid and that grows in spatially extens...

Extensive green roofs (EGRs) are novel ecosystems and essential tools in mitigating the negative effects of urbanization. However, the extent to which traditional community assembly insights apply to spontaneous plant and trait diversity and composition on EGRs and novel ecosystems in general is unclear: (1) Is a dispersal filter present because of...

Invasive alien plant effects on ecosystem functions are often difficult to predict due to the context-dependent interactions between the invader and the recipient communities. Adopting a functional trait-based framework could provide more mechanistic predictions for invasive species' impacts. Recent advances in hyperspectral spectroscopy have furth...

Tropical deforestation and effects on biodiversity and ecosystem services are relatively well studied, but the extent and impact of forest degradation remains much more cryptic. Most of the remaining Ethiopian moist Afromontane forests are currently being degraded due to forest management for coffee production. So far, effects of degradation on bio...

Coffea arabica is native to the Afromontane forests of southwestern Ethiopia, the leading African country in Arabica coffee production. The intensity of coffee leaf rust (CLR), a fungal disease of growing concern to coffee farmers, was assessed in eight coffee berry disease-resistant C. arabica varieties planted at three different altitudes. Diseas...

Het Sigmaplan werd opgesteld na de watersnoodramp van 1976 om het overstromingsgevaar in het Schelde-estuarium te minimaliseren. Robuuste erosiebestendige dijken vormen dan ook een belangrijk onderdeel van het Sigmaplan. Deze erosieweerstand wordt voornamelijk gegarandeerd door de natuurlijke vegetatie op de dijkwanden. In deze studie tonen we dat...

Concentrated flow erosion resistance of herbaceous vegetation is known to be closely linked to the vegetation-level root length density (RLD). However, RLD measurements involve destructive and time-consuming sampling. Since plant species richness, functional diversity and functional composition are expected to affect RLD through either non-additive...

The relationships between functional traits are thought to be strong at global global scales and consistent across species and biomes. However, leaf economic spectrum (LES) relationships may not express the same relationships at smaller scales, because factors and processes affecting traits locally might be different, that in turn can blur the LES...

Predicting when invasive species will affect ecosystem functioning remains problematic, with strong contingency upon both the invasive species and the recipient community's identities. Adopting a functional trait-based approach might overcome this context-dependence. As an early exploration of this approach, we used a greenhouse experiment to asses...

Background: The importance of intraspecific trait variation (ITV) is increasingly acknowledged among plant ecologists. However, our understanding of what drives ITV between individual plants (ITVBI) at the population level is still limited. Contrasting theoretical hypotheses state that ITVBI can be either suppressed (stress-reduced plasticity hypo...

Invasive alien plant effects on ecosystem functions are often difficult to predict across environmental gradients due to the context-dependent interactions between the invader and the recipient communities. Adopting a functional trait-based framework could provide more mechanistic predictions for invasive species’ impacts. In this study, we contras...

The emerging plant communities on restored semi-natural grasslands are generally species poor subsets of the ancient target communities. Soil inoculation experiments suggest that the lack of suitable microbial communities, and especially of Arbuscular Mycorrhizal Fungi (AMF), may contribute to the low restoration success. To understand the limiting...

Spatial expansion, which is a crucial stage in the process to successful biological invasion, is anticipated to profoundly affect the magnitude and spatial distribution of genetic diversity in novel colonized areas. Here we show that, contrasting common expectations, Pyrenean rocket (Sisymbrium austriacum), retained SNP diversity as this introduced...

We investigated how the establishment of sown target species for ecological restoration is affected by the early introduction of either dominant or subordinate species during the assembly of a restored topsoil stripped nutrient-poor grassland. Do dominant or subordinate species exert different priority effects on either wanted target species or unw...

During species invasion, changes in ecosystem functioning are theoretically believed to be mediated by changes in the functional trait set of the species present in these ecosystems. These trait changes can occur directly through the introduction of novel traits by the invasive species, or indirect through shifts in the identity and abundance of th...

Aims: Concentrated flow erosion resistance of herbaceous vegetation is linked to vegetation-level root length density (RLD). However, RLD measurements involve destructive and time-consuming sampling. Since plant species richness, functional diversity and functional composition are expected to affect RLD through either non-additive diversity effects...

Background It is known that during plant community assembly, the early colonizing species can affect the establishment, growth or reproductive success of later arriving species, often resulting in unpredictable assembly outcomes. These so called ‘priority effects’ have recently been hypothesized to work through niche-based processes, with early col...

Gene flow can counteract the loss of genetic diversity caused by genetic drift in small populations. For this reason, clearly understanding gene flow patterns is of the highest importance across fragmented landscapes. However, gene flow patterns are not only dependent upon the degree of spatial isolation of fragmented populations, but are also depe...

The long-term establishment success of founder plant populations has been commonly assessed based on measures of population genetic diversity and among population genetic differentiation, with founder populations expected to carry sufficient genetic diversity when population establishment is the results of many colonists from multiple source popula...

Question: Unlike above-ground plant community assembly, the processes that govern assembly of the soil seed bank following severe habitat disturbance are poorly understood. Two hypotheses have been put forward in this context: (1) the ‘ecological palimpsest hypothesis’ assumes a gradual accumulation of species in the seed bank; and (2) the ‘communi...

The genetic consequences of species colonization following calcareous grassland restoration.

Increasing soil nutrient loads of European semi-natural grasslands strongly alter plant functional diversity independently of species loss.

Human activities have increasingly introduced plant species far outside their native ranges under environmental conditions that can strongly differ from those originally met. Therefore, before spreading, and potentially causing ecological and economical damage, non native species may rapidly evolve. Evidence of genetically based adaptation during t...

The earth is facing a worldwide decline in biodiversity, with land-use change identified as one of the most important drivers. There is evidence that the loss of diversity has a significant impact on ecosystem functioning. Earlier research focused on species richness, but more recent, functional and phylogenetic diversity came into the picture as t...

Anthropogenically increased input of nitrogen (N) and phosphorous (P) have led to a severe reduction of plant species richness in European semi-natural grasslands. Although it is well established that this species loss is not trait neutral, a thorough analysis of the effects of nutrient addition on trait based func-tional diversity and functional c...

In an attempt to halt species and habitat loss across the continent, many restoration projects have been established across Europe. However, clear scientific insight in the processes governing the success of these restoration projects is currently limited, as traditional ecological restoration research mainly focuses on the species level and the ef...

In most landscapes the success of habitat restoration is largely dependent on spontaneous colonization of plant species. This colonization process, and the outcome of restoration practices, can only be considered successful if the genetic makeup of founding populations is not eroded through founder effects and subsequent genetic drift. Here we used...

Pairwise genetic differentiation among Origanum vulgare populations. Lower left triange: FST estimates; Upper right triange: G’ST estimates. Significant values are shaded in grey. (XLS)

Inferred ancestry of individual plants. Analysis based on the Bayesian clustering of STRUCTURE 2.3.3 for K = 4, using the admixture with correlated alleles model with LOCPIOR option. qg = the probability of individual ancestry from group g. Each individual was assigned to the group with the highest qg value (assigned group). (XLS)

Pairwise genetic differentiation among Origanum vulgare populations. Lower left triangle: Jost’s D estimates Significant values are shaded in grey. (XLS)

Many restoration projects have been set up across Europe, in an attempt to halt species and habitat loss across the continent. However, clear scientific insight in the processes governing the success of these restoration projects is currently limited, with traditional ecological restoration research focusing mainly on the species level and the effe...

Ecological restoration schemes often assume that after reinstating appropriate abiotic conditions, plant communities will assemble following a single predictable pathway towards a fixed target state. This idea has recently been challenged, with increasing evidence that plant community assembly can only be considered deterministic at the plant trait...

Grassland restoration leads to founder populations of Origanum vulgare in the Viroin valley. Successful population establishment, however, depends on good genetic makeup and the resilience against strong genetic founder effects. Theory predicts the occurrence of reduced genetic diversity and increased genetic differentiation in founder populations.

In SW Ethiopia, the moist evergreen Afromontane forest has become extremely fragmented and most of the remnants are intensively managed for coffee cultivation (Coffea arabica), with considerable impacts on biodiversity and ecosystem functioning. Because epiphytic orchids are potential indicators for forest quality and a proxy for overall forest bio...

Community assembly or succession was traditionally thought of as being deterministic and directional, leading to a clearly defined climax state. The alternative view, however, keeps gaining attention. This view states that community assembly is influenced by historical processes, where differences in the sequence and timing of species arrival resul...