Response of plant and gastropod species to knotweed invasion

Invasive species of the knotweed complex (Fallopia sp.) have repeatedly been shown to decrease diversity of native local biota. While effects on plant species richness are well established, effects on invertebrate and in particular gastropod species richness are less well understood. We recorded cover of plant species and diversity and abundance of gastropod species in four plots (1 m × 1 m) with Fallopia japonica and compared these to paired control plots without F. japonica at 15 sites along the river Birs (Switzerland) in early summer (June) and autumn (September). Knotweed and control plots did not differ in site characteristics and soil parameters.Average plant species richness in F. japonica plots was 50% lower compared to control plots. This reduction was significant for woody species as well as for herbaceous species. However, species richness of early flowering annuals did not differ significantly. Among the species most affected by knotweed were hop (Humulus lupulus) and European spindle tree (Euonymus europaeus) but also stand-forming species such as nettle (Urtica dioica) or ground elder (Aegopodium podagraria).Average snail species richness was significantly reduced in F. japonica plots. The reduction was pronounced in large (≥5 mm shell size) and long-lived (>2 years) snail species but not in slugs or small and short-lived snails. For example, large snails such as the Roman snail (Helix pomatia, ?85%) or the red-listed species Bradybaena fruticum (?93%), showed reduced abundances in F. japonica compared to control plots. In contrast, the red-listed but small Vertigo pusilla (+92%) had higher abundances in F. japoinca plots. Principal component analyses revealed little overlap in plant communities or community composition of large snail species between F. japonica and control plots. Taken together, knotweed invasion decreased the cover of most plant species and abundance of large and long-lived gastropods.     

Characteristics in coarse woody debris mediated by forest developmental stage and latest disturbances in a natural secondary forest of Pinus tabulaeformis

Coarse woody debris (CWD) characteristics are expected to reflect forest stand features. Few studies evaluated logging-induced stand characteristics of secondary coniferous forests by quantifying the quality and quantity in CWD. After selective logging, the form of secondary forest of Pinus tabulaeformis in the Qinling Mountains is inferior and the regeneration is poor. We measured the CWD characteristics of the forest which had an average CWD biomass amount of 12.56 t hm⁻², and was predominated by abundant logs (65.68%), followed by snags (33.13%). The CWD biomass of P. tabulaeformis and Toxicodendron vernicifluum was significantly higher than that of other species, which took up 85.51% of the total. Although there was no significant difference among different diameter sizes (P > 0.05), the CWD biomass of diameter 30–40 cm occupied 46.26% of the total (5.81 t hm⁻²). Similarly, the CWD biomass of decay class I and II accounted for 39.89% (5.01 t hm⁻²) and 33.04% (4.15 t hm⁻²) of the total CWD biomass respectively, despite no significant difference among those 5 decay classes (P > 0.05). The results indicated that the combination of young forest developmental stage caused by past selective logging and natural and anthropogenic disturbances such as strong wind, tapping lacquer, firewood collection, and illegal tree felling played a crucial role in distribution characteristics of CWD in this secondary forest of P. tabulaeformis.     

Strong influence of long-distance edge effect on herb-layer vegetation in forest fragments in an agricultural landscape

In agricultural landscapes in central Europe, species richness of the herbaceous plant community may be compromised by processes associated with forest fragmentation, habitat loss, and management practices. We examined variability in species richness and composition of the herbaceous layer in 229 plots located in 23 forest fragments (0.1 to 255 ha), in a representative upland agricultural landscape in central Bohemia, in relation to the most important site environmental factors, edge effects, and site history. The influence of environmental factors on the composition of vegetation in the herb layer was evaluated using generalized additive models, which enabled us to analyze highly non-linear and non-monotonic relationships. Total species richness and number of red-listed and ancient forest species were significantly influenced by type of forest vegetation, light quality, soil pH, slope aspect, and distance from the forest edge. Implications of the significant explanatory variables corresponded well to previous findings, with the exception of distance from the forest edge, for which we found a positive relationship with species richness for distances up to 200 m toward the forest interior. Plant species with low colonization ability occupied plots with increasing frequency from edge to forest interior, while fast-colonizing species showed the opposite trend. Apart from the edge effect, forest continuity should be considered for its important contribution to the richness of ancient forest and red-listed species, whereas the effect of forest fragment size appeared to be generally weak. These results do not negate the importance of large forest fragments for the maintenance of herb layer species richness, but specifically emphasize the essential contribution of the core habitats of these forests. In summary, we showed that the negative effects of habitat fragmentation on the richness of ancient forest and red-listed species and on herb layer species in total can be largely attributed to either the edge effect itself or to aggregate effects of forest edge and forest continuity.     

Extinction thresholds and negative responses of Afrotropical ant-following birds to forest cover loss in oil palm and agroforestry landscapes

Afrotropical ant-following birds are vulnerable to forest loss and disturbance, but critical habitat thresholds regarding their abundance and species richness in human-dominated landscapes, including industrial oil palm plantations, have never been assessed. We measured forest cover through Landsat imagery and recorded species richness and relative abundance of 20 ant-following birds in 48 plots of 1-km², covering three landscapes of Southwest Cameroon: Korup National Park, smallholder agroforestry areas (with farms embedded in forest), and an industrial oil palm plantation. We evaluated differences in encounter frequency and species richness among landscapes, and the presence of critical thresholds through enhanced adaptive regression through hinges. All species were detected in Korup National Park and the agroforestry landscape, which had similar forest cover (>85%). Only nine species were found in the oil palm plantation (forest cover = 10.3 ± 3.3%). At the 1-km² scale, the number of species and bird encounters were comparable in agroforests and the protected area: mean species richness ranged from 12.2 ± 0.6 in the park and 12.2 ± 0.6 in the agroforestry matrix to 1.0 ± 0.4 in the industrial oil palm plantation; whereas encounters decreased from 34.4 ± 3.2 to 26.1 ± 2.9 and 1.3 ± 0.4, respectively. Bird encounters decreased linearly with decreasing forest cover, down to an extinction threshold identified at 24% forest cover. Species richness declined linearly by ca. one species per 7.4% forest cover lost. We identified an extinction threshold at 52% forest cover for the most sensitive species (Criniger chloronotus, Dicrurus atripennis, and Neocossyphus poensis). Our results show that substantial proportions of forests are required to sustain complete ant-following bird assemblages in Afrotropical landscapes and confirm the high sensitivity of this bird guild to deforestation after industrial oil palm development. Securing both forest biodiversity and food production in an Afrotropical production landscape may be best attained through a combination of protected areas and wildlife-friendly agroforestry.     

The white-backed woodpecker: umbrella species for forest conservation planning?

In northern Europe, a long history of land use has led to profound changes within forest ecosystems. The white-backed woodpecker (Dendrocopos leucotos) is one of several specialised forest species whose populations have declined. Conservation management directed at this species’ habitat has made it a de facto umbrella species for conservation of the biodiversity associated with forests rich in deciduous trees and dead wood. We assessed empirically the value of the white-backed woodpecker as an indicator and umbrella species in central Sweden. Occurrence of the woodpecker in breeding bird atlas squares (5 × 5 km²) indicated high species richness of forest birds, particularly species of special conservation concern, which included on average 13% more species in squares with than without the woodpecker. The number of red-listed cryptogam species expected to benefit from conservation actions directed at white-backed woodpecker habitats was higher in squares where the woodpecker bred compared to where is was absent. However, no such pattern was found for red-listed beetles, a group with very few records in the studied squares. White-backed woodpecker occurrence was positively associated with the current area of deciduous and mixed forest of high conservation value. Considering its indicator value, its specialised habitat requirements and its potential as a communication tool, using the white-backed woodpecker as an umbrella species may provide a coarse filter for the conservation of several other deciduous forest species. However, focusing solely on white-backed woodpecker habitat may not provide for the conservation of all such species, which stresses the need for a suite of complementary planning approaches.     

Structural indicators of richness and rarity of epiphytic lichens on Corylus avellana in two different forest types within a nature reserve in south-western Norway

Abstract:Epiphytic lichens (and some non-lichenized fungi) on 34 coppices (204 stems) ofCorylus avellana were investigated in a 140 ha study area in south-western Norway. A total of 65 species were recorded on a total bark area of 63 m². Corylus in broad-leaved deciduous forest supported more species of macrolichens, and fewer species of microlichens, than Corylus in pine forest. The macrolichen flora of the deciduous forest differed from that of the pine forest by having a rich flora of species belonging to the Lobarion alliance. OldCorylus coppices with tall stems (>8 m), large girth (>8 cm diameter at breast height) and a noticeable cover of macrolichens (>10% of bark area) supported the highest number of rare species, and overall, species of macrolichens. More than 50% cover of microlichens indicated richness and rarity of microlichens on Corylus.     

Diversity and spatial clustering of shade trees affect cacao yield and pathogen pressure in Costa Rican agroforests

The importance of the spatial organisation of individuals in explaining species coexistence within a community is widely recognised. However, few analyses of spatial structure have been performed on tropical agroforests.The main objective of this study was to highlight the links between spatial organisation of shade trees on the one hand, and shade tree species richness and cacao yield on the other, using data from 29 cacao agroforests in Costa Rica.A method of spatial statistics, Ripley's K-function, was used to analyse the spatial organisation of shade and cacao trees in the study plots. For each stand, the X and Y coordinates of ≥2.5-m-tall trees were recorded. In each plot we also assessed shade tree species richness and cacao yield (with total number of pods = number of pods damaged by frosty pod rot + number of healthy pods).Three types of stands were identified: the first was characterised by significant clustering of shade trees, the highest shade tree species richness (S = 6), and the highest number of damaged pods (139 pods ha^?1 year^?1). The second type was characterised by random spatial organisation of shade trees. The third type showed a trend towards regular organisation. Species richness of shade trees did not differ significantly between the last two types (S = 4 for both), nor did the number of damaged pods (56 pods ha^?1 year^?1 and 67 pods ha^?1 year^?1 respectively).Although the trends were not statistically significant for all the variables in our data set, the clustered spatial structure appears to favour a synergy between environmental (tree species richness), and provisioning (cacao production) services.     

Structural–functional approach to identify post-disturbance recovery indicators in forests from northwestern Patagonia: A tool to prevent state transitions

The disruption of the natural post-disturbance recovery process, either by changes in disturbance regime or by another disturbance, can trigger transitions to alternative degraded states. In a scenario of high disturbance pressure on ecological systems, it is essential to detect recovery indicators to define the period when the system needs more protection as well as the period when the system supports certain use pressure without affecting its resilience. Recovery indicators can be identified by non-linear changes in structural and functional variables. Fire largely modulates the dynamic and stability of plant communities worldwide, and is this the case in northwestern (NW) Patagonia. The ultimate goal of this study is to propose a structural–functional approach based on a reference system (i.e. chronosequence) as a tool to detect post-disturbance recovery indicators in forests from NW Patagonia. In NW Patagonia (40–42°S), we sampled 25 Austrocedrus chilensis and Nothofagus spp. communities differing in post-fire age (0.3–180 years). In each community we recorded structural (woody species cover and height, solar radiation, air temperature, relative humidity) and functional (annual recruitment of woody and tree species) attributes. We modeled these attributes in function of post-fire age and analized the relationship between a functional attribute and a Structural Recovery Index (SRI). Communities varying in time-since-last-fire were structurally and functionally different. Moreover, response variables showed non-linear changes along the chronosequence, allowing the selection of recovery indicators. We suggest to use vegetation variables instead of environmental variables as structural recovery indicators. Horizontal and Vertical Vegetation Heterogeneity indices provided the information necessary to describe vegetation spatial reorganization after fire. Tree species annual recruitment was a good indicator of the functional recovery of forest communities. The relationship between a functional attribute and SRI allowed us to detect phases with high- and low-risk of degradation during post-fire succession. High-risk phases (<36 years old) had the highest horizontal vegetation heterogeneity and scarce tree seedling density (<7000 seedlings ha⁻¹ year⁻¹). Whereas, low-risk phases (>36 years old) had the highest vertical vegetation heterogeneity and tree species seedling density (>10,000 seedlings ha⁻¹ year⁻¹). Due to the low structural–functional levels, communities at high-risk phases would be more vulnerable to antropic pressure (e.g. livestock raising, logging) than communities at low-risk phases. The proposed approach contributes to the sustainable management of forest communities because it allows to estimate the minimum structural–functional levels from which forest communities could be harvested.     

Role of the Siberian flying squirrel as an umbrella species for biodiversity in northern boreal forests

One of the potentially useful indirect shortcut methods in biodiversity conservation is the umbrella species concept. An umbrella species can be seen relatively demanding for the size of the area and probably also for certain habitat types: conservation management for the umbrella species would thus encompass other species preferring similar habitats but with smaller area requirements. As such, it has a comprehensive spatial aspect for landscape planning. We tested the role of the Siberian flying squirrel (Pteromys volans) as an umbrella species for wood dependent species among red-listed and old-growth forest associated polypores, epiphytic lichens and beetles. Flying squirrels inhabit home ranges of several to tens of hectares, and prefer mature spruce-dominated (Picea abies) mixed forests, which often have high amounts of dead wood. We carried out species surveys and trappings during 1 year from 20 mature spruce-dominated forest stands (altogether 162 ha), of which 12 were occupied by the flying squirrel. The amount of dead wood was higher in occupied stands than in unoccupied stands. We also found a tendency for a higher number of species and number of records in occupied stands, a relationship mostly due to the polypore species. The presence of the flying squirrel may reflect the habitat availability for species depending on dead and living wood, and assist in site selection of conservation areas. We suggest that the flying squirrel has potential as an umbrella species to partly enhance maintenance of biodiversity in northern boreal forests in Finland.     

Modelling impacts of forest bioenergy use on ecosystem sustainability: Lammi LTER region,southern Finland

Increasing the use of forest biomass for energy production is an important mitigation strategy against climate change. Sustainable use of natural resources requires that these policies are evaluated, planned and implemented, taking into account the boundary conditions of the ecological systems affected. This paper describes the development and application of a quantitative modelling framework for evaluating integrated impacts of forest biomass removal scenarios on four key environmental sustainability/ecosystem service indicators: (i) carbon sequestration and balance, (ii) soil nutrient balances (base cations and nitrogen), (iii) nutrient leaching to surface waters (nitrogen and phosphorus), and (iv) dead wood biomass (used as proxy indicator for impacts on species diversity). The system is based on the use of spatial data sets, mass balance calculations, loading coefficients and dynamic modelling. The approach is demonstrated using data from an intensively studied region (Hämeenlinna municipality) encompassing the Lammi LTER (Long-Term Ecosystem Research) site in southern Finland. Forest biomass removal scenarios were derived from a management-oriented large-scale forestry model (MELA) based on sample plot and stand-level data from national forest inventories. These scenarios have been developed to guide future Finnish forest management with respect to bioenergy use. Using harvest residues for district heat production reduced fossil carbon emissions but also the carbon sink of forests in the case study area. Calculations of the net removal of base cations of the different scenarios ranged between −36 to −43 meq m⁻² a⁻¹, indicating that the supply of base cations (soil weathering + deposition) would be enough to sustain also energy-wood harvesting. Greatly increased nutrient removal values and increasing nitrogen limitation problems were however predicted. Clear-cuttings and site preparation were predicted to increase the load of total nitrogen (4.0%) and total phosphorus (4.5%) to surface waters, compared with background leaching. The amount of dead wood has been identified as a key factor for forest species diversity in Finland. A scenario maximising harvest residues used for bioenergy production, would decrease stem dead wood biomass by about 40%, compared with a business-as-usual scenario. Clear trade-off situations could be observed in the case study area between maximising the use of energy-wood and minimising impacts on species diversity, soil carbon and nutrient stores, and nutrient leaching. The developed model system allows seeking for optimised solutions with respect to different management options and sustainability considerations.     

How do evergreen and deciduous species respond to shade?—Tolerance and plasticity of subtropical tree and shrub species of South-East China

Different plant species make use of resource gradients such as light in different ways. First, plant species specialize in using different parts of the gradient, resulting in niche partitioning, Second, within the section of the gradient used by a species, plants respond to a different resource supply by plasticity. Our study addressed both of these strategies, with the main objective to relate mean responses and plasticity indices of seedlings of woody species to species characteristics such as leaf habit and to variation in branch lengths and local frequency of adult trees in forest communities.A greenhouse experiment with 36 deciduous and 35 evergreen subtropical tree and shrub species was carried out to test the influence of light and nutrient availability on trait expression and plasticity of the species. The greenhouse responses of seedlings were compared with adult individuals in the field, based on a set of 46 species that occurred also in the 27 permanent plots in a secondary subtropical broadleaved forest in Zhejiang Province (SE-China).In the greenhouse experiment, most variables showed significant differences between unshaded (250 μE m⁻² s⁻¹) and shaded (10 μE m⁻² s⁻¹) treatments as well as between high and low nutrient supply. Deciduous species were more plastic than evergreen species in their response to light. No significant correlations were detected in mean responses and plasticity between juvenile plants in the greenhouse and adult trees in the field. However, some trait values such as biomass and node density as well as plasticity of several traits were positively related to the species’ abundance in the field, suggesting that locally abundant species tend to be less “plastic” than locally rare species.     

Assessing forest fragmentation in northeastern region (NER) of India using landscape matrices

Northeastern region (NER) of India, one of the largest reserves of forests in India has so far been studied with a view to map the distribution of species or modeling the disturbance regimes and richness analysis. The present study focuses on the importance of regional level studies where the entire NER which is under the threat of forest fragmentation and degradation, is been assessed. In the present study, six historical data sets generated from remote sensing data (1972, 1982, 1987, 1989, 1993 and 1999) are used to assess forest cover loss, shape index and entropy to the degree of forest fragmentation over a multi-decadal period. The assessments have been carried out in the open (40–10% canopy density) and close (>40% canopy density) forest cover classes. The range of shape index and deviation from the actual mean in open forest and closed forest were computed separately. The patches among two categories were further analyzed based on patch area into six classes; ranging from <1 km² to >500 km². This also indicates variability of the forest patches. It is noteworthy that patches of area within 1–10 km² and 10–50 km² have been severely fragmented. This loss could be attributed to the shifting cultivation practice where the patches of moderate size are cultivated by group of families. The present study could give an insight to the patch configuration and composition in terms of shape index and the Shannon's entropy index.     

Agri-environment incentive payments and plant species richness under different management intensities in mountain meadows of Switzerland

We investigated whether agri-environmental incentive payments help to maintain biodiversity. We studied the effect of agricultural management intensity on vascular plant species richness and plant assemblages of mountain meadows in Switzerland. Other factors such as slope, altitude or accessibility (distance from farmyard) were also taken into account. Vegetation sampling was conducted at 69 sites representing five different management types, differing with respect to nutrient input and soil moisture: (i) dry extensive meadows; (ii) extensive meadows; (iii) dry low-intensive meadows; (iv) low-intensive meadows; (v) intensive meadows. There was a significant negative relationship between plant species richness and management intensity: The mean number of plant species per management type declined markedly when management intensity increased, although dry sites harboured slightly more species regardless of management intensity (dry extensive > dry low intensive > extensive > low intensive >> intensive meadows). Species richness was clearly affected by management intensity, but not so by slope, altitude or accessibility. There was a gradual shift in plant assemblages among management types with only intensive meadows differing from the other four types of differently managed meadows. We therefore found, in contrast to many studies done in the European lowlands, positive effects of incentive payments on plant species richness.     

An indirect method of estimating leaf area index in a tropical deciduous forest of India

Rapid, reliable and meaningful estimates of leaf area index (LAI) are essential to functional characterization of forest ecosystems including biomass and primary productivity studies. Accurate LAI estimates of tropical deciduous forest are required in studies of regional and global change modeling. Tropical deciduous forest due to higher species richness, multiple species association, varied phenophases, irregular stem densities and basal cover, multistoried canopy architecture and different micro-climatic conditions offers dynamism to the understanding of the LAI dynamics of different PFTs in an ecosystem. This investigation reports a new indirect method for measurement of leaf area index (LAI) in a topical moist deciduous forest in Himalayan foothills using LAI-2000 Plant Canopy Analyzer. We measured the LAI in two seasons (summer; leaf senescence stage and post-monsoon; full green stage) in three (dry miscellaneous, sal mixed and teak plantations) plant functional types (PFT) in Katerniaghat Wildlife Sanctuary, India. Ground LAI values ranged between 2.41 and 6.89, 1.17 and 7.71, and 1.92 and 5.19 during post-monsoon season and 1.36–4.49, 0.67–3.1 and 0.37–1.83 during summer season in dry miscellaneous, sal mixed and teak plantation, respectively. We observed strong correlation between LAI and community structural parameters (tree density, basal cover and species richness), with maximum with annual litter fall (R² > 0.8) and aboveground biomass (AGB) (R² > 0.75). We provided equations relating LAI with AGB, which can be utilized in future studies for this region and can be reasonably extrapolated to other regions with suitable statistical extrapolations. However, the relations between LAI and other parameters can be further improved with incorporation of data from optimized and seasonal sampling. Our indirect method of LAI estimation using litter fall as a proxy, offers repetitive potential for LAI estimate in other PFTs with relatively time and cost-effective way, thereby generating quicker and reliable data for model run for regional and global change studies.     

Hollow oaks and beetle conservation: the significance of the surroundings

In this study we investigated hollow oaks (Quercus robur, Q. petrea) situated in open landscapes and in forests in Norway in northern Europe, and compared their importance for rare and threatened beetles (Coleoptera). Old, hollow oak trees, both in parks and in forests, were extremely rich in red-listed beetles, and hosted a high proportion of threatened species. The proportion of oak associated species and the mean number of red-listed beetle species per tree was similar in the two site types, but rarefaction showed that for a certain number of individuals, oaks in forests had more threatened and near-threatened species than oaks in parks. The species composition also differed between site types: Park oaks had a higher proportion of species associated with hollows and animal nests, whereas in forests, there was a higher proportion of species depending on dead oak wood in general. Four factors were significant in explaining the richness of red-listed beetles in our study: Tree circumference, cavity decay stage, proportion of oak in the surroundings, and coarse woody debris (CWD) in the surroundings. Forest oaks were smaller, but they still trapped a species richness comparable to that of the larger park oaks—probably a result of high amounts of CWD in the surroundings. We show that oaks in open landscapes and oaks in forest have only partly overlapping beetle assemblages and, thus, cannot be substituted in conservation. Planning for conservation of red-listed beetles associated with this key habitat demands a large scale perspective, both in space and time, as the surroundings have important effects on associated threatened and near threatened species.     

Mapping tree species diversity of a tropical montane forest by unsupervised clustering of airborne imaging spectroscopy data

With the ongoing global biodiversity loss, approaches to measuring and monitoring biodiversity are necessary for effective conservation planning, especially in tropical forests. Remote sensing has much potential for biodiversity mapping, and high spatial resolution imaging spectroscopy (IS) allows for direct prediction of tree species diversity based on spectral reflectance. The objective of this study was to test an approach for mapping tree species alpha diversity that takes advantage of an unsupervised object-based clustering. Tree species diversity of a tropical montane forest in the Taita Hills, Kenya, was mapped based on spectral variation of high spatial resolution IS data.Airborne IS data and species data from 31 field plots were collected in the study area. Species diversity measures were obtained from the IS data by clustering spectrally similar image segments representing tree crowns. In order to do this, the image was segmented to objects that represented tree crowns. Three measures of species diversity were calculated based on the field data and on the clustering results, and the relationships were statistically analyzed.According to the results, the approach succeeded well in revealing tree species diversity patterns. Especially, tree species richness was well predicted (RMSE = 3 species; r² = 0.50) directly based on the clustering results. The optimal number of clusters was found to be close to the estimated number of tree species in the forest. Minimum tree size was an important determinant of the relationships, because only part of the trees are visible to the airborne sensor in the multi-layered closed canopy forest.In general, the object-based approach proved to be a viable alternative to a pixel-based clustering. The approach takes advantage of the capability of IS to detect spectral differences among tree crowns, but without the need for spectral training data, which is expensive to collect. With further development, the approach could be applied also for estimating beta diversity.     

Influence of Forest Management on the Species Richness and Composition of Wood-inhabiting Basidiomycetes in Swiss Forests

In order to investigate the diversity of wood-inhabiting aphyllophoroid basidiomycetes in Swiss forests, 86 plots of 50 m ² were established. They harboured a total of 3339 samples of woody debris, classified according to three categories (coarse, fine, and very fine woody debris), yielding 238 species of wood-inhabiting fungi. The selected sites cover the main forest types of Switzerland and various degrees of management intensity. A multiple linear regression analysis showed that substrate variation, i.e. differences in the quality of dead wood, including volume, age, degree of decomposition and host tree species, are the most important factors influencing diversity of wood-inhabiting fungi. In addition, a Principle Coordinate Analysis highlighted differences in the fungal communities in the different forest types. The greatest fungal species richness is found on thermophilic deciduous tree and woody shrub species. Fine and very fine woody debris, even present in intensively managed forests, often serve as important refuges for many species. Forests with a recent management intervention were found to be either species poor or species rich. Possible reasons for these differences may lay in forest size and landscape fragmentation, the distance to the nearest species pool or microclimatic factors. In Switzerland intensively managed forests harbour significantly less wood-inhabiting, aphyllophoroid fungi than non-managed or extensively managed forests. This is the case in both deciduous forests and in conifer forests. However, occasionally intensively managed forest will also harbour rare and endangered species.     

Tree species composition rather than diversity triggers associational resistance to the pine processionary moth

The reduction of insect herbivory is one of the services provided by tree diversity in forest ecosystems. While it is increasingly acknowledged that the compositional characteristics of tree species assemblages play a major role in triggering associational resistance to herbivores, underlying mechanisms are less well known. We addressed this question in the ORPHEE experiment by assessing pine processionary moth infestations (Thaumetopoea pityocampa) across a tree diversity gradient from pine monocultures to five species mixtures. We showed that tree species richness per se had no effect on the probability of attack by this pest. By contrast, the infestation rate was strongly dependent on plot composition. Mixtures of pines (Pinus pinaster) and birches (Betula pendula) were less prone to T. pityocampa infestations, whereas mixtures of pines and oaks (Quercus spp.) were more often attacked than pine monocultures. By taking into account the relative height of pines and associated broadleaved species, this effect could be explained by pine apparency. Pines were on average 343 ± 5 cm height. Birches, as fast growing trees, were slightly taller than pines (363 ± 6 cm), while oak trees were significantly smaller (74 ± 1 cm). Host trees of T. pityocampa were then partly hidden in mixtures of pines and birches but more apparent in mixtures with oaks. We suggest that reduced pine apparency disrupted visual cues used by female moths to select host trees prior to oviposition. This study highlights the need to take into account tree traits such as growth rate when selecting the tree species that have to be associated in order to improve forest resistance to pest insects.     

The effects of fire on woody plant encroachment are exacerbated by succession of trees of decreased palatability

The ingression of woody plants into the grassy layer of savannas and grasslands has become a global concern. The increase of woody plants has been primarily attributed over grazing, fire and more recently to the increase of atmospheric CO₂. We used long-term observations and analyses to assess changes in woody vegetation in Ithala Game Reserve (IGR), South Africa. Textural analysis of aerial photographs was used to detect changes in woody vegetation, from 1943 to 2007 in Ithala Game Reserve (IGR), South Africa. Daily rainfall data from 1905 to 2009 were used in a time-series analysis to determine if rainfall patterns have changed. The time-series analysis showed that the low magnitude (0–10 mm) rainfall events decreased from 1916 to 2009 and high magnitude rainfall events increased (10–20 and >20 mm). The mean annual rainfall increased from ～700 to ～850 mm from the 1930s to the 2000s. This change in rainfall was a key factor in the increase in woody vegetation from 1943 to 2009. We also used field data from the same reserve collected over 30 years to assess the increases in tree cover. Tree cover and density increased significantly by 32.5% and 657.9 indiv ha^?1 respectively, over 64 years. Before the proclamation of IGR in 1972, increases in woody vegetation from 1943 were non-significant. After the proclamation of IGR, herbivore population numbers and spatial distribution influenced the accumulation of grassy biomass required to fuel fires. In areas with reduced fuel loads, the consequential suppression of fire accelerated the rate of woody plant invasion into savannas. The increase in woody vegetation coincided with a decrease in palatable (e.g. Acacia gerrardii and Acacia davyi) and an increase in unpalatable woody plants. The avoidance of the unpalatable trees (e.g. Euclea and Searsia species) by large mammalian herbivores has allowed these trees to increase in density relatively unhindered.