Insect sampling in forest ecosystems

Forests have long been recognized as excellent model systems for studying insect ecology. The fact that many forests＇ ecosystems still function in a semi-natural state, with little influence from human disturbance, provides unique opportunities for understanding co-evolved community and population processes. Unfortunately the structural complexity of forests and the sheer size of trees often pose formidable problems when attempting to sample insects in forests. As such, any scientist embarking on a study of forest insect ecology would be well-advised to carefullv plan their sampling efforts.     

Does forest fragmentation cause an increase in forest temperature?

Forest fragmentation is considered by many to be a primary cause of the current biodiversity crisis. The underlying mechanisms are poorly known, but a potentially important one is associated with altered thermal conditions within the remaining forest patches, especially at forest edges. Yet, large uncertainty remains about the effect of fragmentation on forest temperature, as it is unclear whether temperature decreases from forest edge to forest interior, and whether this local gradient scales up to an effect of fragmentation (landscape attribute) on temperature. We calculated the effect size (correlation coefficient) of distance from forest edge on air temperature, and tested for differences among forest types surrounded by different matrices using meta-analysis techniques. We found a negative edge-interior temperature gradient, but correlation coefficients were highly variable, and significant only for temperate and tropical forests surrounded by a highly contrasting open matrix. Nevertheless, it is unclear if these local-scale changes in temperature can be scaled up to an effect of fragmentation on temperature. Although it may be valid when considering “fragmentation” as forest loss only, the landscape-scale inference is not so clear when we consider the second aspect of fragmentation, where a given amount of forest is divided into a large number of small patches (fragmentation per se). Therefore, care is needed when assuming that fragmentation changes forest temperature, as thermal changes at forest edges depend on forest type and matrix composition, and it is still uncertain if this local gradient can be scaled up to the landscape.     

Do riparian forest strips in modified forest landscapes aid in conserving bat diversity?

Agricultural practices lead to losses of natural resources and biodiversity. Maintaining forests alongside streams (riparian forest strips) has been used as a mechanism to minimize the impact of clearing for agriculture on biodiversity. To test the contribution of riparian forest strips to conserve biodiversity in production landscapes, we selected bats as a biodiversity model system and examined two dimensions of diversity: taxonomic and functional. We compared bat diversity and composition in forest, with and without stream habitat, and in narrow forest riparian strips surrounded by areas cleared for agriculture. We tested the hypothesis that riparian forest strips provide potential conservation value by providing habitat and serving as movement corridors for forest bat species. Riparian forest strips maintained 75% of the bat species registered in forested habitats. We found assemblage in sites with riparian forest strips were dominated by a few species with high abundance and included several species with low abundance. Bat species assemblage was more similar between sites with streams than between those sites to forests without stream habitat. These results highlight the importance of stream habitat in predicting presence of bat species. We registered similar number of guilds between forest sites and riparian forest strips sites. Relative to matrix habitats, stream and edge habitats in riparian forest strips sites were functionally more diverse, supporting our hypothesis about the potential conservation value of riparian forest strips. Results from this study suggest that maintaining riparian forest strips within cleared areas for agricultural areas helps conserve the taxonomic and functional diversity of bats. Also, it provides basic data to evaluate the efficacy of maintaining these landscape features for mitigating impacts of agricultural development on biodiversity. However, we caution that riparian forest strips alone are not sufficient for biodiversity maintenance; their value depends on maintenance of larger forest areas in their vicinity.     

Are habitat islands islands? Woodliving beetles (Coleoptera) in deciduous forest fragments in boreal forest

Modern forestry has changed the fire dynamics in the boreal forest and as a result the size and number of deciduous forest patches have been reduced as well as the number of deciduous trees within the coniferous forest This has exaggerated the insularity of deciduous forest patches within the boreal coniferous forest zone In this paper I examine whether the diversity of beetles living in dead stems of deciduous trees follows the relationship with patch area to be predicted from island biogeographic theory, and to what extent the species assemblages differ between large and small patches and single deciduous trees within managed coniferous forests Three larger patches of deciduous forest (>120 ha) arisen as successions after forest fires in the late 1880's are compared with 6 small (<20 ha) patches of similar origin No difference in diversity could be detected between large and small patches A statistically significant difference between assembly composition was detected using matrix regression between a matrix of observed assembly similarities and a hypothetical similarity matrix based on the type of area in which the plot was situated (large- small or matrix) Finally I examined the distribution of the 56 most common beetle species over the habitat types investigated Thirty four species did not show any Significant habitat preference, 12 were found more often in clear-cut areas than expected 5 were over-represented in small patches, and 4 in large areas My explanation to this apparent lack of insularity effects is the relative recent commencement of intensive forestry in these areas and the fact that the matrix is of rather high quality that is inhabitable for numerous beetle species Thus the patches may be viewed as incipient islands still exchanging biota with their surroundings     

Testing heterogeneity–diversity relationships in tropical forest restoration

Restoring small-scale habitat heterogeneity in highly diverse systems, like tropical forests, is a conservation challenge and offers an excellent opportunity to test factors affecting community assembly. We investigated whether (1) the applied nucleation restoration strategy (planting tree islands) resulted in higher habitat heterogeneity than more homogeneous forest restoration approaches, (2) increased heterogeneity resulted in more diverse tree recruitment, and (3) the mean or coefficient of variation of habitat variables best explained tree recruitment. We measured soil nutrients, overstory and understory vegetation structure, and tree recruitment at six sites with three 5- to 7-year-old restoration treatments: control (no planting), planted tree islands, and conventional, mixed-species tree plantations. Canopy openness and soil base saturation were more variable in island treatments than in controls and plantations, whereas most soil nutrients had similar coefficients of variation across treatments, and bare ground was more variable in control plots. Seedling and sapling species density were equivalent in plantations and islands, and were substantially higher than in controls. Species spatial turnover, diversity, and richness were similar in island and plantation treatments. Mean canopy openness, rather than heterogeneity, explained the largest proportion of variance in species density. Our results show that, whereas canopy openness and soil base saturation are more heterogeneous with the applied nucleation restoration strategy, this pattern does not translate into greater tree diversity. The lack of a heterogeneity–diversity relationship is likely due to the fact that recruits respond more strongly to mean resource gradients than variability at this early stage in succession, and that seed dispersal limitation likely reduces the available species pool. Results show that planting tree islands facilitates tree recruitment to a similar degree as intensive plantation-style restoration strategies.     

Is chloride a conservative ion in forest ecosystems?

Chloride (Cl^?) has often been assumed to be relatively unreactive in forest ecosystems, and is frequently used as a conservative tracer to calculate fluxes of water and other ions. Recently, however, several studies have detailed cycling of Cl^? in vegetation and soils. In this study Cl^? budgets are compiled from 32 catchment studies to determine the extent to which Cl^? is conserved in the passage through forest ecosystems. Chloride budgets from these sites vary from net retention (input?>?output) to net release (output?>?input). In the overall data set, including those sites with very high inputs of seasalt Cl^?, there was a strong correspondence between inputs and outputs. However, sites with low Cl^? deposition (<6?kg?ha^?1?year^?1) consistently showed net release of Cl^?, suggesting an internal source or a declining internal pool. The results indicate that Cl^? may be a conservative ion in sites with high Cl^? deposition, but in sites with low deposition Cl^? may not be conservative. We discuss the possible causes of the Cl^? imbalance and reasons why Cl^? may not be conservative in ecosystem functions.     

Litter decomposing and ectomycorrhizalBasidiomycetes in an igapó forest

An igapó forest near the confluence of Rio Tarumã Mirim (Tarumãzinho) and Rio Negro has been studied. It is a typical ectotroph forest with a raw humus layer and suppressed litter decomposing activity by Higher (i.e., carpophore-producing) Fungi. The number of the latter is about one-fifth of that observed in the (anectotrophic) terra firme forest. All ectotrophically mycorrhizal fungi observed belonged in three families:Amanitaceae, Boletaceae, Russulaceae. Leguminosae are dominant, and of theseAldina latifolia andSwartzia cf.polyphylla were demonstrably ectomycorrhizal. The scarcity of mineral nutrients in the soils of igapó, campinarana and campina is overcome by direct cycling through ectomycorrhizae. This is in contrast to other black- and white-water inundated forest communities in Amazonia.Litter Decomposition and Ectomycorrhiza in Amazonian Forests3. Previous contributions seeSinger & Araujo (1979) andSinger & al. (1983).     

Comparison of structure,regeneration and dead wood in virgin forest remnant and managed forest on Grmeč Mountain in Western Bosnia

This paper compares the forest structure, regeneration and distribution of dead wood in a virgin forest remnant and a close-to-nature managed beech–conifer mixture situated on Grme? Mountain in Western Bosnia. The investigations were carried out in a 1 ha permanent sample plot and 35 circular plots (20 m radius) in the virgin forest and in 17 circular plots (25 m radius) in managed forests. The number of trees in the managed forest was significantly (p = 0.05) higher than that in virgin forest and the distribution of the number of trees per diameter classes had a decreasing trend, but with a different shape in the virgin forest compared to the managed stands. In the lower diameter classes, the stock volume recorded in virgin forest was half of that in the managed forest, whilst for higher diameter classes the cumulated volume of the growing stock was almost double in virgin forest. The young crops had a significantly lower presence in the virgin forest and a larger volume of dead wood was identified in the virgin forest than in managed stands. The study results are important in assessing the consequences of close-to-nature management on the forest structure and regeneration when compared to the condition in virgin forests.     

Carbon–biodiversity relationships in a highly diverse subtropical forest

Carbon-focused climate mitigation strategies are becoming increasingly important in forests. However, with ongoing biodiversity declines we require better knowledge of how much such strategies account for biodiversity. We particularly lack information across multiple trophic levels and on established forests, where the interplay between carbon stocks, stand age, and tree diversity might influence carbon–biodiversity relationships. Using a large dataset (>4600 heterotrophic species of 23 taxonomic groups) from secondary, subtropical forests, we tested how multitrophic diversity and diversity within trophic groups relate to aboveground, belowground, and total carbon stocks at different levels of tree species richness and stand age. Our study revealed that aboveground carbon, the key component of climate-based management, was largely unrelated to multitrophic diversity. By contrast, total carbon stocks—that is, including belowground carbon—emerged as a significant predictor of multitrophic diversity. Relationships were nonlinear and strongest for lower trophic levels, but nonsignificant for higher trophic level diversity. Tree species richness and stand age moderated these relationships, suggesting long-term regeneration of forests may be particularly effective in reconciling carbon and biodiversity targets. Our findings highlight that biodiversity benefits of climate-oriented management need to be evaluated carefully, and only maximizing aboveground carbon may fail to account for biodiversity conservation requirements.     

Tropical forest fragmentation and nest predation – an experimental study in an Eastern Arc montane forest, Tanzania

When a habitat becomes fragmented and surrounded by another habitat this generally causes an increase in predation pressure at habitat transitions, often referred to as an edge effect. Edge effect in the form of enhanced nest predation intensities is one of the most cited explanations for bird population declines in fragmented landscapes. Here, we report results from a nest predation experiment conducted in a tropical montane forest landscape in the Uzungwa Mts., Tanzania. Using artificial nests with chicken eggs, we determined predation rates across a fragmentation gradient. The proportion of indigenous forest in four landscapes used in the study were 0.29, 0.58, 0.75 to 1.0. Nest predation intensities on artificial nests were about 19% higher inside intact forest than at edges in fragmented forest landscapes. Furthermore, predation intensities were relatively constant across a forest fragmentation gradient. Our results thus challenge the applicability and generality of the edge effect, derived from studies almost exclusively conducted in temperate regions rather than tropical forest ecosystems. Nest predation levels differences between tropical montane forest and that reported in other forest ecosystems are discussed.     

Topographic position affects the water regime in a semideciduous tropical forest in Panamá

The effects of topographic position on water regime in a semideciduous tropical forest on Barro Colorado Island in Panamá were assessed by measuring soil matric potential using the filter paper technique and by using measured soil water release characteristics to convert a long-term (20 years) gravimetric water content data-set to matric potential. These were also compared against predictions from a simple water balance model. Soil matric potentials on slope sites were significantly higher than on plateau sites throughout the measurement interval and slopes experienced a shorter duration of drought during the annual dry-season. Measured values of matric potential agreed with those predicted from converting the gravimetric measurements using water release characteristics. Annual duration of drought predicted by the simple water balance model agreed with values determined from the converted long term water content data-set and was able to predict the annual duration of drought on plateau sites. On slope sites, the water balance systematically and significantly overestimated the duration of drought obtained from the water content data-set, suggesting that slope sites were supplied with water from upslope. Predictions of annual drought duration from sites with higher annual rainfall than Barro Colorado Island (BCI), suggest that while plateau sites on BCI experience a water regime consistent with annual rainfall, slopes experience a water regime more similar to that of forests with much higher rainfall. We conclude that such large variations in water regime over small spatial scales may play a role in maintaining high species richness through providing opportunities for niche specialisation and by buffering slopes against possible climate change.     

Diversity–invasibility relationships across multiple scales in disturbed forest understoreys

Non-native plant species richness may be either negatively or positively correlated with native species due to differences in resource availability, propagule pressure or the scale of vegetation sampling. We investigated the relationships between these factors and both native and non-native plant species at 12 mainland and island forested sites in southeastern Ontario, Canada. In general, the presence of non-native species was limited: <20% of all species at a site were non-native and non-native species cover was <4% m⁻² at 11 of the 12 sites. Non-native species were always positively correlated with native species, regardless of spatial scale and whether islands were sampled. Additionally, islands had a greater abundance of non-native species. Non-native species richness across mainland sites was significantly negatively correlated with mean shape index, a measure of the ratio of forest edge to area, and positively correlated with the mean distance to the nearest forest patch. Other factors associated with disturbance and propagule pressure in northeastern North America forests, including human land use, white-tailed deer populations, understorey light, and soil nitrogen, did not explain non-native richness nor cover better than the null models. Our results suggest that management strategies for controlling non-native plant invasions should aim to reduce the propagule pressure associated with human activities, and maximize the connectivity of forest habitats to benefit more poorly dispersed native species.     

Beech forest communities in the Nordic countries – a multivariate analysis

In this study we present the first comprehensive multivariate analysis of beech (Fagus sylvatica) forest communities in the Nordic countries. The history of beech and beech forests in Scandinavia are described. In the north, the species is climatically restrained and, at present, restricted to Denmark and the southern parts of Sweden and Norway.More than 2000 sample plots were compiled, partly from literature, partly from new and unpublished data. The material included more than 20 studies of beech forests, often recorded by different non-standardised sampling designs. Therefore, prior to data analysis, a large number of plots had to be excluded to reduce the heterogeneity of the data. Only such sample plots were considered that showed a predominance of Fagus sylvatica in the canopy, that had a size within the interval of 16–100 m2, and that could be located by geographical coordinates. All species abundance values were transformed into simple species presences, and data from different vegetation layers were merged into one.A TWINSPAN cluster analysis resulted in 15 types. Three main communities with several sub-communities and varieties can be distinguished: (1) the Fagus sylvatica-Fraxinus excelsior-Stachys sylvatica community on the most basic and fertile soils, (2) the Fagus sylvatica-Corylus avellana-Galium odoratum community on moderately fertile and acid soils, and (3) the Fagus sylvatica-Sorbus aucuparia-Deschampsia flexuosa community on very acid and oligotrophic soils. Synonyms in the recent literature on Nordic beech forests to these communities are given. An ordination with the program DECORANA confirmed the primary significance of soil acidity and nutrient status for community differentiation.p>     

Factors influencing soil enzyme activity in China’s forest ecosystems

Enzyme activity (EA) mediates soil organic matter (SOM) degradation, transformation, and mineralization, thereby maintaining the biogeochemical cycles and energy flow of ecosystems. To determine the main factors explaining EA variations in China’s forest ecosystems, we created a database of soil EAs and relevant variables using data from the literature and analysed relationships between EAs and both climatic and edaphic variables. Catalase, phenol oxidase, acid (alkaline) phosphatase, and protease activities differed significantly among different types of forests. Catalase and urease activities were generally higher in primosols, cambisols, and argosols than in ferrosols. EA largely decreased with soil depth and increased with SOM. Phenol oxidase and urease activities were negatively correlated with mean annual temperature (MAT); in contrast, catalase, invertase, and protease activities first decreased (< 2.5 °C), increased (2.5–17.5 °C), and then decreased (> 17.5 °C) with increasing MAT. Although protease activity was slightly positively correlated with mean annual precipitation (MAP), catalase, phenol oxidase, and urease activities were all negatively related to MAP. Catalase, invertase, acid (alkaline) phosphatase, urease, and protease activities first increased (< 2000 m.a.s.l.) and then decreased (2000–4100 m.a.s.l.) with increasing elevation. Principal component analysis revealed most EAs to be correlated with climate conditions and soil pH. These findings suggest that climatic and edaphic variables directly and indirectly correlate with forest type and greatly impact soil EA.     

Quantifying the interannual litterfall variations in China’s forest ecosystems

凋落物是森林生物地化学循环和火险预测的关键参数。然而,森林凋落物如何随林龄变化仍不清楚。因此,量化森林生态系统凋落物年际变化对减少大尺度凋落物预测的不确定性至关重要。本论文基于中国人工林和次生林凋落物连续多年(≥2年)测定的数据集(N = 318),采用变异系数(CV)、变化百分比(V_P)和年际间比率量化凋落物的年际变化。研究结果表明,凋落物的年际变化随林龄增加(1–90年生)而呈下降趋势。其中,1–10年林龄的凋落物年际变化最大(平均CV = 23.51%,平均V_P= -28.59%~20.89%),其主要原因在于树木早期快速生长,即下一年与当年凋落物比率平均为1.20。11–40年林龄的凋落物年际变化逐渐减小,但CV平均值仍在18%左右,V_P平均值在-17.69%~21.19%之间。41–90年林龄的凋落物年际变化最小,CV平均值仅为8.98%,V_P平均值维持在8%左右。因此,大于40年林龄的凋落物量较低且稳定。这一结果与已有研究的认知不同：即当林龄大于30年、20年甚至15年时,森林凋落物量达到相对稳定。本研究结果将有助于我们深入理解森林凋落物生态学,并为大尺度碳收支和生物地化学循环模型提供基础。     

Phytosociological survey in Brazilian forest genetic reserve of Caçador

A phytosociological survey was carried out in the Forest Genetic Reserve of Caçador, which belongs to the Brazilian Agriculture Research Corporation – EMBRAPA. The Genetic Reserve comprises an area of 1120 ha and has been managed by the Agricultural Research and Extension Corporation of the State of Santa Catarina (EPAGRI). A restricted random sampling by plots, with units of 2500 m² (100 x 25 m) was used, allocating 40 plots to stands containing Araucaria angustifolia. All trees with diameter 20 cm at breast height were measured. Frequency, density, dominance, soil coverage, and importance value were evaluated, The most important species indicated by these parameters were Araucaria angustifolia, Ocotea porosa, Cupania vernalis, Matayba eleagnoides, Mollinedia elegans, Ocotea pulchella, Ilex paraguariensis and Prunus brasiliensis. In spite of the very high mean basal area (35.84 m² ha^-1), mean density (222 trees ha^-1) and mean volume outside bark (531.14 m³ ha^-1) for A. angustifolia it was found that understory had low commercial value and a very low natural regeneration rate in the priority species for in situ conservation: A. angustifolia, Cedrela fissilis, I. paraguariensis, Mimosa scabrella, P. brasiliensis and O. porosa. Simpson's index has shown in this case a low floristic diversity of species however, as was expected, the highest levels of abundance, dominance and frequency were found for Araucaria angustifolia.     

Woody species patterns at forest–grassland boundaries in southern Brazil

Vegetation mosaics of grassland/savanna and forest can be found in tropical and subtropical regions of the world, as in southern Brazil, where climate conditions are suitable for forest. Changes in intensity or frequency of disturbances could enable woody species encroachment in grassland communities; however, the processes are related to site conditions and life history of pioneer species. In this paper, we study transition patterns of forest to grassland in the absence of grazing, but under different site conditions related to aspect (landscape position) and time since the last burn. Data are based on shrub and tree species composition and soil variables at forest–grassland boundaries. We found 119 woody species of 42 families along transects of 27 m into the forest and 31.5 m into the grassland. Gradients from forest to grassland were analysed as compositional trajectories in ordination space and differences in the spatial patterns depicted between distinct site aspects. The time since the last fire did not influence these patterns. Inside the forest, tree species diversity was significantly higher close to the edge, independent of the density of individuals. Two main mechanisms may promote forest expansion into the grassland. First, a gradual tree encroachment near the edge and, second, a mechanism linked to the recruitment of isolated pioneer trees within the grassland matrix, most frequently near rocky outcrops, where a decrease in grass biomass leads to low-intensity fires. Despite vegetation patterns at boundaries differing according to aspect, the most important explanatory factor was the distance from the forest border, not just by itself, but with all correlated parameters that are changing along the gradient.     

Making a living in the tropical forest: Yuquí foragers in the Bolivian Amazon

Questions concerning the availability of resources in tropical rain forests have given rise to the current debate centering on whether human subsistence based solely on foraging is possible in these biomes without agricultural subsidies. This paper takes the position that changing perspectives on ecological pattern and process in tropical forests and the significant variation among tropical forests on a worldwide as well as regional scale must be taken into consideration. Human disturbance is also proposed as a cause of dependence on agriculture by modern human foragers rather than as a necessary precondition for successful exploitation of the tropical forest. These issues are discussed against the background of a case study of the Yuquí, who, until very recently, were true foragers in the Bolivian Amazon. For the Yuquí, the sustainability of their subsistence system depended on a finegrained knowledge of their environment and the freedom of movement over a large territory to access resources within it.