Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Environmental studies regularly use the net present value (NPV) to value benefits and costs of projects. However, the NPV disregards whether the stream of net benefits is steady or volatile and ignores the distribution of net benefits among different groups of people. Here we test alternatives to NPV, building on two example cases: 1) We use discounted utility (DU) to evaluate land-use projects and calculate opportunity costs for avoided deforesta-tion. 2) We simulate decision-making on tropical deforestation, whereby we use multiple decision criteria to consider the distribution of net benefits between two groups: farmers and conservationists. Results show considerable differences in the ranking of projects between DU and NPV, when projects are not marginal. Compared to DU, NPV regularly overestimates the value of forest plantations. Moreover, NPV tends to overstate the opportunity costs of avoiding deforestation in terms of saved carbon emissions. Not accounting for the distribution of net benefits in optimizing land-use allocation leads to suboptimal simulated deforestation scenarios. We therefore suggest that future studies should either also use DU to value economic consequences of projects or that they use the NPV as only one among several socio-economic and ecological decision criteria.

Abstract:

Diversified agricultural landscapes have been shown to provide a wide range of ecosystem services. It is often stated that the main motivation behind growing multiple crops within a farm is to buffer farm income against market and climate risks. However, household characteristics, particularly the amount of off-farm income may also influence farm diversity. While the drivers of diversifying farm income have been investigated extensively,the ecologically important level of land-use diversity on a farm has seldom been used as a dependent variable. Based on data from 163 households, this paper analyzes the impact of social, economic and demographic household characteristics on crop diversification for farms located around the Laipuna Reserve in the dry forests of southern Ecuador. Using a Heckman two-step regression model, we identified factors that influence a) the probability that a farm will be diversified (PD) and b) the degree of diversification at the farm level (LUD), quantified by the Shannon index. We found that PD is positively related to the percentage of household members who depend on family income but do not work (economic dependence ratio), as well as river access and available family labor force. PD is inversely related to access to financial support (i.e. social payments and credits) and off-farm income. LUD is positively related to the number of household members and the age of the head of the household, and correlates negatively with labor force, financial support and off-farm income. Our results demonstrate that land-use diversification is not only a strategy to reduce risk, but it is also driven by farmers’ efforts to meet household, mainly subsistence, needs. Moreover, we also demonstrate that when households have access to financial support and off-farm income, the pressure to diversify their crops diminishes. Finally, we argue that forest and agricultural policies should impose instruments to support land-use diversification financially, while acknowledging the importance of financial support and off-farm income for household economies. Strategies to reduce poverty should be accompanied by direct support of land-use diversification, infrastructure development and agricultural training.

Abstract:

In tropical regions insect herbivores are considered one of the key players in the ecosystem function by effecting the nutrient cycle as well as the carbon sequestration of these systems. However, their feeding is strongly influenced by abiotic factors, like temperature, leading to a lower performance and abundance of herbivores under lower temperature, as well as biotic factors, like plant defence mechanisms (e.g. tougher leaves or a higher concentration of secondary metabolites). But plants are facing a constant trade-off between growth and defence, which is stronger under harsher environmental conditions. The resulting differences in defence further lead to a big variability in the rate of herbivory between the plants. Although several studies investigated the interaction between herbivory, biotic and abiotic factors, most of them concentrate on single species and systems. However, since herbivory varies between species and has high impacts on the whole ecosystem by influencing plants viability and the carbon sequestration, it is crucial to investigate the interaction on community level. We therefore assessed herbivory across an elevational gradient of 1000 m to 3000 m a.s.l. on a community level, i.e. by measuring 313 representative tree species. To determine the biotic interaction we measured leaf traits using both conventional and remote sensing methods, to look for the applicability of remote sensing for extrapolation of community patterns. Our study shows, that herbivory decreased with increasing elevation. Furthermore, sulphur showed a positive association with herbivory and SLA, nitrogen and tannin showed a negative association. The influence of carotenoid on herbivory changed from a positive to a negative one with elevation and anthocyanin showed the opposite pattern. Phylogeny thereby had the same effect on both conventional and remote sensing measured leaf traits. Our results showed, that the influence of the abiotic factors especially at higher elevations were strong, leading to the conclusion, that community level herbivory is more effected by the abiotic interaction along the elevational gradient than the biotic interaction. Moreover, the models of conventionally and remote sensing determined leaf traits had a strong congruence regarding the influence of abiotic and biotic factors on herbivory, although they comprise different leaf traits. Consequently we can state, that remote sensing can be used to predict herbivory on a community level in a tropical mountain forest.

Abstract:

The new issue of the Tabebuia Bulletin of the RESPECT Research Unit presents the new biodiversity land surface model Hydroatmo Unified Model of BiOtic interactions and Local Trait Diversity (HUMBOL-TD) and how it integrates hydrologic, biodiversity-related and atmospheric parameters. The bulletin summarises the research results of the individual projects that could be achieved despite the COVID-19 pandemic which overshadowed the entire work. Researchers report about responses and feedback effects of climate and land-use changes on abiotic drivers, biodiversity and ecological processes in this hotspot area. In details this Bulletin covers: • Hyperspectral data products that can be used to parameterize and test the LSMAtmo model • Partitioning net ecosystem exchange into gross primary productivity and ecosystem respiration • Simulating response and effect mechanisms of global change on hydrological processes • Response of nutrient supply to climate and land-use changes • Implementing biotic interactions into a process-based dynamic vegetation model • Functional traits: Effects of phylogeny and elevation and the relation to tree growth • Plant functional types that can be differentiated by their response to transitory drought events • Radial variability of wood functional traits in the pioneer tree Heliocarpus americanus • Evapotranspiration as an essential variable bridging climatology, soil science and plant ecophysiology • Reproductive traits of fleshy-fruited plants • How plant traits and arthropod communities influence herbivory Beyond, the bulletin reports on establishment and repair of field infrastructure, recent advances of the data warehouse and the reconstruction of climate time series. Finally, research projects from Ecuadorian counterparts and milestones reached by the infrastructure providers round off the issue.

Abstract:

Tropical dry forests (TDFs) are often degraded and fragmented through human impact, which is also the case in Southern Ecuador, where land-use pressure is high. In this context we studied tree species composition and forest structure in a protected and adjacent disturbed TDF at altitudes between 560-1080 m asl. Fabaceae and Malvaceae were identified as the most important tree families in both forest types. The disturbed forest displayed lower tree species richness than the protected forest, and the gap in species richness between the two forest types increased with increasing altitude. Ten species of the protected forest were not recorded in the disturbed forest, two of them endemic. The disturbed site was further characterized by a lower number of stems but with larger diameters, in comparison with the protected forest. The majority of the most abundant tree species in the disturbed forest had rather low wood densities, but also the combination of high wood density with browsing tolerance and high resprouting capacity was encountered, and seems to be advantageous for getting established in such sites. Although certain tree species were well represented in the disturbed forest, some endemic species with relatively low abundances (e.g. Simira ecuadorensis, Prockia crucis) should receive more conservation attention.

Abstract:

Many forests restoration programs and efforts depend on seeds. Particularly in the Andes, further information regarding seed germination requirements and seed storage behavior is necessary. The aim of this study was to evaluate the effects of storage conditions on the germination percentage, the viability and the coefficient of velocity of germination for seeds of three native tree species (Cedrela montana, Weinmannia fagaroides and Oreocallis grandiflora). Under controlled conditions, the seeds were exposed to three levels of seed moisture content and storage temperatures (5 °C, 10 °C and room temperature at approx. 19 °C) for 3, 6 and 12 months. The results showed that at 3–6 months of seed storage under temperatures of 5 and 10 °C, the seeds had a high percentage of germination, viability and germination speed for C. montana and W. fagaroides compared to those stored at room temperature. At 12 months of storage, there was a marked reduction in seed germination in all treatments for both species. Furthermore, the seed germination and viability of O. grandiflora was not influenced by any of the above storage treatments. However, at the end of the experiment a slight decrease was observed, hence this species might be tolerant to medium- and long-term storage conditions. Though limited to just three co-occurring species, the study provided insight into the variability in responses to storage, with preliminary indications of appropriate storage conditions to maximize storability of seeds for restoration programs. Importantly, the study demonstrated the need for empirical testing of storage responses (temperature and duration) of seeds before subjecting untested species to a particular storage regime.

Abstract:

In nutrient-poor tropical forests litter decomposition is essential for the supply of nutrients to plants. This process is in turn controlled by nutrient availability. Beside nitrogen (N) and phosphorus (P) other elements may co-limitate litter decomposition. Studies revealed a relationship between sodium (Na) shortage and reduced litter decomposition which can decrease the mineralization of stored carbon (C). Investigations of element fluxes of a Na-poor tropical montane rainforest in southern Ecuador have shown low atmospheric deposition rates since 1998. Additionally, Na was retained in different parts of the ecosystem. A study found that the Na-retention in the canopy was related to the Na demand of the microorganisms in the phyllosphere. Because the Na budget of the organic layer was also positive, it was assumed that decomposers may experience a lack of Na due to low atmospheric deposition. Thus, one main goal was to investigate whether Na fertilization accelerates litter decomposition. Based on the assumption of a higher Na demand of soil fauna than of microorganisms, it was also tested whether the stimulation of soil organisms by Na is limited to the soil fauna. To test these hypotheses, a combined litter decomposition and Na fertilization experiment was conducted in an evergreen premontane rainforest and a montane rainforest in south Ecuador. Fresh litter was incubated in the field and fertilized weekly with different Na concentrations which were similar to the natural deposition rates. Litterbags with different mesh sizes allowed to study the effects of Na fertilization on microbes and mesofauna separately. Additionally, a bait lamina experiment was installed in the organic layer to study the uptake of Na fertilized baits by soil organisms. Differences of the bait loss between the fertilized and the control group should indicate a potential stimulation of the soil organisms by a Na-addition. The statistical analysis confirmed the stimulation of litter decomposition by Na additions. The comparison of both sites revealed a slightly stronger effect of Na additions in the premontane forest than in the montane forest. The accelerated litter decomposition was related to an increased activity of the soil fauna. However, a significant stimulation of microorganisms by Na additions could not be detected. The bait lamina experiment confirmed the results of the litter decomposition experiment and showed a marginally significant increase of the activity of soil organisms by Na fertilization. Sodium can stimulate the decomposition of the organic layer in the studied premontane and montane rainforest, thus affecting ecosystem functioning. Na supply is of higher importance in the ecosystem than usually assumed and its relevance for the C turnover in the organic layer may increase if the atmospheric Na deposition remains on the present low level.

Abstract:

Herbivores play a key role for ecosystem functioning, but the current destruction of late-successional primary forests might negatively affect herbivore-mediated ecosystem processes. Understanding herbivore patterns between different succession stages is crucial for setting conservation priorities. Here we examined insect herbivore biomass and functional community composition along a successional gradient in a tropical montane rainforest in southern Ecuador. The insects were sampled off 42 tree individuals via canopy fogging. The trees comprised three succession stages (9 early, 25 intermediate, 18 late) and 16 species. Insect herbivores were identified on order level and assigned to one of three feeding guilds (leaf chewers, rostrum chewers, sapsuckers). Overall, we collected almost 16 000 herbivore individuals. Herbivore dry mass was not significantly affected by tree succession stage for almost all groups surveyed, except for caterpillars which weighed less on late- than on early-successional tree species. Furthermore, herbivore community composition was neither explained by tree succession stage nor by tree phylogeny. We conclude that solely conserving forests of late succession is not always expedient and that factors need to be identified which predict herbivory and herbivore community composition in tropical montane rainforests.

Abstract:

Being the most important herbivores in the tropics, insects play a key role in the trophic cascades and nutrient cycles of rainforest ecosystems. It is not fully understood, however, which drivers influence the biomass, abundance, individual size and functional community structure of these secondary consumers. In this study, we investigate the effects of morphological leaf traits such as leaf thickness, water content, physical resistance and specific leaf area on folivorous insect communities in the canopy of a primary tropical montane rainforest in South Ecuador. Via canopy fogging, we collected 52 community samples. Insects were assigned to five feeding guilds and their total and relative biomass, abundance and individual weights were modelled using leaf traits of the respective trees. We found that tree species identity was the main predictor of community structure. Leaf thickness and water content also played a significant role, the latter especially reducing the share of caterpillars within the community. Feeding guilds were differently affected by leaf characteristics: e.g. coleoptera and orthoptera showed no significant reaction to food quality parameters. Caterpillars again were the only group in which individual sizes were affected by leaf parameters. We assume that they respond more directly because of their need for efficient energy extraction and fast biomass accumulation rates. As water content was a main predictor in many of our models, we suggest that it be used as a measure of food quality in future research rather than N levels per dry mass because it better predicts nutrient levels in the fresh weight of leaves and it is fresh leaves that canopy-inhabiting folivorous insects consume.

Abstract:

Due to the high deforestation and climate change, the forests of Ecuador are endangered. In the future, there will be increasing drought, which is why the necessary afforestation have to be carried out with native tree species that meet these requirements. Therefore, it has to be clarified which tree species and provenances are suitable for this purpose. This thesis deals with the drought tolerance of Cedrela montana and Juglans neotropica in the greenhouse. The seeds of the plants come from four different regions in Ecuador. Ger-mination was carried out in two different temperature chambers. In the greenhouse, the two-year-old plants were divided into three groups that were supplied with different amount of water. During the drought stress-experiment group A received 100% of its water require-ment, group B 50% and group C 25%. After 14 weeks all groups were supplied with 100% of their water needs during the resilience-experiment. After three times of rehydration the desiccation-experiment started, in which the trees of all groups were no longer supplied with water. During the experiment series, water consumption, predawn and afternoon leaf water-potential and leaf status were documented. In addition, at the end of the test series, the growth and the root-shoot ratio were determined. Both tree species reacted very similar to the drought. There were hardly any differences in water consumption and water-potential. Only Cedrela montana had a higher number of leaves. The provenance and different germination temperatures had no significant influence. All groups reacted quickly to irrigation, so the afternoon water-potential were very similar in all groups. In the leaf status the gradation of the groups was still visible, but group B and C formed more leaves as the irrigation continued. Cedrela montana also had a higher number of leaves than Juglans neotropica. The germination treatment or provenance did not signif-icantly affect resilience. In the subsequent desiccation-experiment Group C of Juglans was best at dealing with the renewed dryness. This was evident in all parameters taken. All groups of Cedrela continued to behave similar. Significant differences could now be noted between germination treatments and provenances. In the aboveground growth, the grading of the groups was clearly recognizable, so in both tree species group A grew the most and group C the least. The root-shoot ratio behaved exactly the other way round. Group A had the lowest value on average, group C the highest. Again, significant differences between provenances and germination treatments were found.Both tree species showed a similar reaction over the course of the experiment, therefor both can be recommended for reforestation. The effects of germination conditions on the response to drought are not clear. For the species Cedrela montana, the provenance Barabon, and for Juglans neotropica, the Provenance Jipiro are considered to be suitable. As these have the largest root-shoot ratio, what makes them better equipped for increasing drought.

Abstract:

Tropical and subtropical dry forests make up the world’s largest terrestrial ecosystem. However, these forests have been used to establish several productive activities, such as growing crops, rearing livestock, and using the forest resources, due to their ease of access and climatic conditions, which has led to this ecosystem becoming highly threatened. Therefore, this research assessed the effects of anthropogenic pressures and a number of abiotic variables on natural regeneration in dry forests in the Tumbesian region by addressing three research questions: (a) What is the status of natural regeneration in terms of abundance and diversity? (b) Does livestock grazing and the anthropogenic pressure affect the abundance and diversity of natural regeneration? (c) Does seasonality or grazing have the greatest influence on the regeneration dynamics? Data were obtained from 72 samples (36 fenced and 36 unfenced) during five surveys spanning a 2-year period, and the seedling abundance, mortality, recruitment, species richness and diversity were evaluated using linear mixed models. Natural regeneration was most positively affected by rainy season precipitation, but soil conditions also played an important role. Short-term fences had a major effect on reducing mortality but did not improve the abundance or diversity, whereas cattle grazing significantly affected the abundance of seedlings.

Abstract:

The dry forest of southern Ecuador and northern Perú (called the Tumbesian region) is known for its high diversity, endemism, and healthy conservation state. Nevertheless, the forest is exposed to many threats linked with human activities. To understand the effects of these threats, which have not been appropriately assessed, we pose two questions: (a) What are the diversity and structural situations of the forest? (b) Are anthropogenic activities affecting the composition and structure of the forest? The assessed factors were species richness, diversity, species similarity, abundance, and density. Forest information was obtained from 72 plots (total area 25.92 ha) randomly placed to cover a wide range of stand densities (from 200 to 1100 m a.s.l.). After constructing linear mixed models and selecting the most influential one, we determined the individual influences of 12 predictors. The human pressure index (HPI) was the most negative predictor of forest health, and annual precipitation was the most important abiotic predictor of good health conditions. Livestock grazing did not significantly change the diversity and structure of mature forest. The mean annual temperature and stoniness influenced only the basal area and number of individuals, respectively. The species composition in our study area was not affected by the HPI, but was strongly predicted by annual precipitation.

Abstract:

Few studies have analysed the effect of silvicultural treatments on tree growth in tropical montane forests (TMF). These forests have strong topographic gradients, which influence growth rates and can potentially interact with silvicultural treatments. The present study investigated the relative effects of silvicultural treatments and topography on growth rates at the tree level in a TMF. For this, we combined two distinct data sources: (1) field data from a silvicultural experiment in the Andes of southern Ecuador where liberation thinnings, i.e. the removal of the strongest crown competitors, were applied to potential crop trees (PCT) in 2004; and (2) topographic variables obtained from a high-resolution digital terrain model created from an airborne LIDAR survey. We fitted all data in a single linear mixed-effect model. Based on monitoring data from 174 released and 200 reference PCTs of 8 timber species, we calculated periodic annual increment (PAI) in DBH 6 years after the silvicultural treatment as our outcome variable. As topographic predictors, we used elevation and a topographic position index. To control for the by-species growth variability we included random intercepts for species and random slopes for the effect of treatment on species in our model. PAI was significantly influenced by the topographic predictors. Over the elevational gradient, growth rates declined on average by 0.73 mm a−1 per 100 m increase in elevation. For the topographic position, PCTs in valleys had an average PAI of 2.02 mm a−1 compared to 1.04 mm a−1 on ridges. The effect of the silvicultural treatment across all species was only marginally significant, but its effect size was nevertheless within the range, but at the lower end of values reported for other tropical forest ecosystems (reference trees: 1.35 mm a−1; released trees: 1.60 mm a−1). Between species, baseline growth rates as well as the treatment effect varied considerably. Best linear unbiased predictions of species effects suggested that 5 species responded positively to the silvicultural treatment, whereas 3 species showed no treatment effect. Overall, tree growth varied substantially as indicated by the large residual variance that remained unaccounted for in the model. Our findings indicate that positive effects of silvicultural treatments in TMF are likely to exist, but that they are possibly obfuscated by strong topographical gradients and large between-tree growth variability. Overall, our results suggest that “broad-brush” management prescriptions are not suited for sustainable forest management of TMF. Instead, granular and spatially explicit prescriptions that take the strong impact of topography on diameter growth as well as species-specific responses to silvicultural treatments into account should be favoured.

Abstract:

Background: The impact of selective thinning on forest diversity has been extensively studied in temperate and boreal regions. However, in the tropics, knowledge is still poor regarding the impacts of this silvicultural treatment on functional diversity, especially in tropical mountain forests, which are considered to be highly biodiverse ecosystems and also endangered by human activities. By evaluating the changes on functional diversity by using different indicators, hypothesizing that selective thinning significantly affects (directly or indirectly) tropical mountain forests, this work promotes sustainable ecosystem use. Methods: A total of 52 permanent plots of 2500 m2 each were installed in a primary mountain forest in the San Francisco Biological Reserve to assess the impact of this silvicultural treatment. Selective thinning can be defined as a controlled process, in which trees that compete with ecologically and/or valuable timber species are progressively removed to stimulate the development of profitable ones, called potential crop trees (PCT). In doing so, the best specimens remain in the forest stand until their final harvest. After PCT selection, 30 plots were chosen for the intervention, while 22 plots served as control plots. The thinning intensity fluctuated between 4 and 56 trees ha−1 (average 18.8 ± 12.1 stems ha−1). Functional Diversity (FD) indices, including the community weighted mean (CWM), were determined based on six traits using the FD package implemented in R software. The difference between initial and final conditions of functional richness (FRic), functional divergence (FDiv), functional evenness (FEve), functional dispersion (FDis), and Rao quadratic entropy (RaoQ) was modeled using linear mixed models (LMM). As fixed factors, we used all the predictors inherent to structural and ecological forest conditions before and after the selective thinning and as a random variable, we used the membership to nested sampling units. Results: Functional Richness (FRic) showed significant changes after selective thinning, the other indexes (FEve, FDis, FDiv, RaoQ) were only influenced by predictors related to ecological conditions and characteristics of the community.

Abstract:

Abstract: Research Highlights: This study determined that treatment “release from competitors” causes different reactions in selected timber species respective to diametrical growth, in which the initial size of the tree (diametric class) is important. Also, the growth habit and phenological traits (defoliation) of the species must be considered, which may have an influence on growth after release. Background and Objectives: The objective of the study was to analyze the diametric growth of nine timber species after their release to answer the following questions: (i) Can the diametric growth of the selected timber species be increased by release? (ii) Does the release cause different responses among the tree species? (iii) Are other factors important, such as the initial diameter at breast height (DBH) or the general climate conditions? Materials and Methods: Four-hundred and eighty-eight trees belonging to nine timber species were selected and monitored over a three-year period. Release was applied to 197 trees, whereas 251 trees served as control trees to evaluate the response of diametrical growth. To determine the response of the trees, a linear mixed model (GLMM, R package: LMER4) was used, which was adjusted by a one-way ANOVA test. Results: All species showed a similar annual cycle respective to diametric increases, which is due to the per-humid climate in the area. Precipitation is secondary for the diametric growth because sufficient rainfall occurs throughout year. What is more important, however, are variations in temperature. However, the species responded differently to release. This is because the initial DBH and growth habit are more important factors. Therefore, the species could be classified into three specific groups: Positive, negative and no response to release. Conclusions: Species which prefer open sites responded positively to release, while shade tolerant species and species with pronounced phenological traits responded negatively. The initial DBH was also an important factor for diametric increases. This is because trees of class I (20 cm to 30 cm DBH) responded positively to the treatment, whereas for bigger or older individuals, the differences decreased or became negative.

Abstract:

Models of global climate change generally predict higher rainfall variability, with more intense rainfall events separated by extended dry periods. We experimentally studied the effects of prolonged droughts on diverse ant assemblages found at three elevations in an Ecuadorian montane rainforest. We hypothesized that most species will be negatively affected directly (physiological stress) or indirectly (less food or suitable nesting resources) by drought. We thus expected a decrease in species richness as well as changes in assemblage composition. As the decrease of moisture content was expected to be more marked above ground than in soil, its impact on ants should differ according to their nesting site (dead wood, leaf litter, soil). After 6-month treatments, dead wood, leaf litter and soil samples were on average 53%, 46% and 4% drier under tents than controls, respectively. The drought did not alter overall species richness in the three nesting situations. However, species composition was significantly modified, mostly in dead wood and in leaf litter. Camponotus in dead wood, Strumigenys in leaf litter and Solenopsis in all three microhabitats were more abundant under tents. In contrast, Pheidole in dead wood, and Pachycondyla in leaf litter, were less abundant than in controls. Similar trends were observed at the three study sites. To conclude, after 6-month droughts dominant ant genera in the assemblages were affected differently. In the longer term, alteration of the rainfall regime is therefore expected to have an important impact on ants, as well as on their ecosystem functions and services, through shifts in species dominance and composition. Zusammenfassung Die Modelle des globalen Klimawandels prognostizieren im Allgemeinen variablere Niederschläge mit intensiveren Regenfällen, denen ausgedehnte Trockenperioden folgen. Wir untersuchten experimentell die Auswirkungen von längeren Trockenphasen auf verschiedene Ameisengemeinschaften auf drei Höhenstufen im Bergregenwald von Ecuador. Wir stellten die Hypothese auf, dass Trockenheit sich auf die meisten Arten negativ auswirken würde, sei es direkt (physiologischer Stress) oder indirekt (weniger Futter oder geeignetes Nistmaterial). Wir erwarteten daher eine Abnahme des Artenreichtums sowie Veränderungen in der Zusammensetzung der Arten. Da zu erwarten war, dass die Abnahme der Feuchtigkeit über dem Boden deutlicher sein würde als im Boden, sollten die Auswirkungen auf Ameisen je nach Nistplatz (Totholz, Laub, Erdreich) verschieden sein. Nach sechsmonatiger Behandlung waren die Totholz-, Laub und Erdproben unter den Abdeck-Zelten jeweils durchschnittlich 53%, 46% und 4% trockener als an den Kontrollpunkten. Die Trockenheit hat den Artenreichtum insgesamt in den drei Nist-Situationen nicht verändert. Die Zusammensetzung der Arten hatte sich jedoch signifikant verändert, vor allem in Totholz und Laub. Camponotus in Totholz, Strumigenys in Laub und Solenopsis in allen drei Mikrohabitaten waren unter den Zelten häufiger. Andererseits waren Pheidole in Totholz sowie Pachycondyla in Laub weniger häufig als auf den Kontrollflächen. Ähnliche Tendenzen wurden an allen drei untersuchten Orten beobachtet. Zusammenfassend lässt sich sagen, dass die dominanten Ameisengattungen nach sechsmonatigen Trockenphasen unterschiedlich betroffen waren. Langfristig ist daher zu erwarten, dass eine Veränderung der Niederschlagsmuster durch Veränderungen in der Arten-Dominanz und –zusammensetzung wichtige Auswirkungen auf Ameisen hat, sowie auf ihre Funktionen und Dienste im Ökosystem.

Abstract:

The tree species Alnus acuminata and Morella pubescens, native to South America, are candidates for soil quality improvement and afforestation of degraded areas and may serve as nurse trees for later inter-planting of other trees, including native crop trees. Both species not only form symbioses with arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF), but also with N2-fixing actinobacteria. Because tree seedlings inoculated with appropriate mycorrhizal fungi in the nursery resist transplanting stress better than non-mycorrhizal seedlings, we evaluated for A. acuminata and M. pubescens the potential of inoculation with mycorrhizal fungi for obtaining robust tree seedlings. For the first time, a laboratory-produced mixed AMF inoculum was tested in comparison with native soil from stands of both tree species, which contains AMF and EMF. Seedlings of both tree species reacted positively to both types of inocula and showed an increase in height, root collar diameter and above- and belowground biomass production, although mycorrhizal root colonization was rather low in M. pubescens. After 6 months, biomass was significantly higher for all mycorrhizal treatments when compared to control treatments, whereas aboveground biomass was approximately doubled for most treatments. To test whether mycorrhiza formation positively influences plant performance under reduced water supply the experiment was conducted under two irrigation regimes. There was no strong response to different levels of watering. Overall, application of native soil inoculum improved growth most. It contained sufficient AMF propagules but potentially also other soil microorganisms that synergistically enhance plant growth performance. However, the AMF inoculum pot-produced under controlled conditions was an efficient alternative for better management of A. acuminata and M. pubescens in the nursery, which in the future may be combined with defined EMF and Frankia inocula for improved management practices.

Abstract:

Tropical montane forests, particularly Andean rainforest, are important ecosystems for regional carbon and water cycles as well as for biological diversity and speciation. Owing to their remoteness, however, ecological key-processes are less understood as in the tropical lowlands. Remote sensing allows modeling of variables related to spatial patterns of carbon stocks and fluxes (e.g., biomass) and ecosystem functioning (e.g., functional leaf traits). However, at a landscape scale most studies conducted so far are based on airborne remote sensing data which is often available only locally and for one time-point. In contrast, multispectral satellites at moderate spectral and spatial resolutions are able to provide spatially continuous and repeated observations. Here, we investigated the effectiveness of Landsat-8 imagery in modeling tropical montane forest biomass, its productivity and selected canopy traits. Topographical, spectral and textural metrics were derived as predictors. To train and validate the models, in-situ data was sampled in 54 permanent plots in forests of southern Ecuador distributed within three study sites at 1000 m, 2000 m and 3000 m a.s.l. We used partial least squares regressions to model and map all response variables. Along the whole elevation gradient biomass and productivity models explained 31%, 43%, 69% and 63% of variance in aboveground biomass, annual wood production, fine litter production and aboveground net primary production, respectively. Regression models of canopy traits measured as community weighted means explained 62%, 78%, 65% and 65% of variance in leaf toughness, specific leaf area, foliar N concentration, and foliar P concentration, respectively. Models at single study sites hardly explained variation in aboveground biomass and the annual wood production indicating that these measures are mainly determined by the change of forest types along with elevation. In contrast, the models of fine litter production and canopy traits explained between 8%–85% in variation depending on the study site. We found spectral metrics, in particular a vegetation index using the red and the green band to provide complementary information to topographical metrics. The model performances for estimating leaf toughness, biochemical canopy traits and related fine litter production all improved when adding spectral information. Our findings therefore revealed that differences in fine litter production and canopy traits in our study area are driven by local changes in vegetation edaphically induced by topography. We conclude that Landsat-derived metrics are useful in modeling fine litter production and biochemical canopy traits, in a topographically and ecologically complex tropical montane forest.

Abstract:

Habitat loss and landscape fragmentation are important drivers of changes in biodiversity. In fragmented landscapes, bird species are able to use multiple forest patches that may therefore share an important portion of the regional biodiversity. In turn, these patches are linked through their shared bird diversity (i.e. species-habitat networks). Identifying the importance of nodes (e.g. forest patches) in species-habitat networks is increasingly important to improve conservation planning. within this network approach, the relative importance of patches for birds can be identified via centrality indices-measures of the magnitude of shared bird diversity of patches across the entire network (i.e. patch centrality). here, we tested for changes in patch centrality within bird species-patch networks of two habitat guilds, forest specialists and generalists, in relation to patch area, patch shape irregularity and within-patch habitat characteristics across 15 Polylepis woodland patches in a páramo landscape of southern Ecuador. Patch centrality for forest specialists decreased with greater influence of surrounding páramo plants, i.e. an increasing proportion of bunch-grasses and small shrubs, in the within-patch habitat and was unaffected by either patch area or patch shape irregularity. On the other hand, patch centrality for generalists was positively influenced by patch shape irregularity but was unaffected by patch area or the influence of surrounding páramo plants in the within-patch habitat. Patch centrality reveals that the relative importance of Polylepis woodlands lies in their habitat quality. Forest specialists are dependent on mature Polylepis woodland patches, while generalists benefit from the natural irregular shape of the woodlands. Finally, a species-habitat network approach facilitates the recognition of important Polylepis patches and their characteristics for conservation of the Andean bird communityat a landscape scale.

Abstract:

Anthropogenic atmospheric deposition can increase nutrient supply in the most remote ecosystems, potentially affecting soil biodiversity. Arbuscular mycorrhizal fungal (AMF) communities rapidly respond to simulated soil eutrophication in tropical forests. Yet the limited spatio-temporal extent of such manipulations, together with the often unrealistically high fertilization rates employed, impedes generalization of such responses. We sequenced mixed root AMF communities within a seven year-long fully factorial nitrogen (N) and phosphorus (P) addition experiment, replicated at three tropical montane forests in southern Ecuador with differing environmental characteristics. We hypothesized (i) strong shifts in community composition and species richness after long-term fertilization, (ii) site- and (iii) clade-specific responses to N versus P additions depending on local soil fertility and clade life history traits respectively. Fertilization consistently shifted AMF community composition across sites, but only reduced richness of Glomeraceae. Compositional changes were mainly driven by increases in P supply while richness reductions were observed only after combined N and P additions. We conclude that moderate increases of N and P exert a mild but consistent effect on tropical AMF communities. To predict the consequences of these shifts, current results need to be supplemented with experiments that characterize local species-specific AMF functionality.

Abstract:

Our knowledge about the structure and function of Andean forests at regional scales remains limited. Current initiatives to study forests over continental or global scales still have important geographical gaps, particularly in regions such as the tropical and subtropical Andes. In this study, we assessed patterns of structure and tree species diversity along ~ 4000 km of latitude and ~ 4000 m of elevation range in Andean forests. We used the Andean Forest Network (Red de Bosques Andinos, https://redbosques.condesan.org/) database which, at present, includes 491 forest plots (totaling 156.3 ha, ranging from 0.01 to 6 ha) representing a total of 86,964 identified tree stems � 10 cm diameter at breast height belonging to 2341 identified species, 584 genera and 133 botanical families. Tree stem density and basal area increases with elevation while species richness decreases. Stem density and species richness both decrease with latitude. Subtropical forests have distinct tree species composition compared to those in the tropical region. In addition, floristic similarity of subtropical plots is between 13 to 16% while similarity between tropical forest plots is between 3% to 9%. Overall, plots ~ 0.5-ha or larger may be preferred for describing patterns at regional scales in order to avoid plot size effects. We highlight the need to promote collaboration and capacity building among researchers in the Andean region (i.e., South-South cooperation) in order to generate and synthesize information at regional scale.

Abstract:

The anthropogenic deposition of nitrogen (N) and phosphorus (P) into terrestrial ecosystems has an influence on the leaf morphology and leaf properties of vegetation as well as on interactions within an ecosystem. In this context, the increased availability of nutrients has an impact on herbivory. In addition to the availability of nutrients, sea level has also been shown to influence these parameters. The shown work deals with the quantification of herbivory under the influence of N- and P-fertilization and differences in certain leaf parameters (leaf area, specific leaf area, leaf toughness, leaf nitrogen content and leaf area loss) between three altitudinal levels (1000 m, 2000 m, 3000 m). The study area was located in a tropical mountain rainforest in Southern Ecuador. In a nutrient manipulation experiment (NUMEX) 48 plots within the study areas were fertilized with either N, P or NP twice a year. Per plot 50 leaves were collected, examined for various parameters and then subjected to a nutrient analysis. The aim of this study was to figure out to what extent sea level influences the leaf morphology, nitrogen content and the leaf area loss of the vegetation within the control areas and to what extent fertilization with nitrogen, phosphorus or both elements changes these leaf properties. Finally, it was investigated whether possible changes in feeding rates resulted from an increased leaf nitrogen content. Sea level had a major influence on leaf strength, which increased with increasing height gradients, and on the specific leaf area and the mean leaf area, which decreased with increasing sea level. Many of the values differed significantly between the altitudinal levels. This suggests that not only the soil becomes nutrient-poorer with rising sea level, but also that the mineralisation of the few available nutrients is slower than at lower altitudes. The climatic environmental conditions, which become more extreme as the sea level rises, also explain the changes in the leaf parameters mentioned. Fertilisation instead did not have an influence as strong as sea level on the studied parameters. There were hardly any significant differences between the plots with different fertilisation. Since tropical forests are considered nutrient-limited, the addition of nitrogen led to the formation of large and soft leaves, which was expected. The correlations between leaf nitrogen content and SLA or leaf strength were positive and significant. Leaf area loss did not correlate with nitrogen content, which was unexpected. This can be attributed to the fact that plants show highly species-specific reactions to nutrient availability, which manifest themselves in very different plastic changes in growth and defence mechanisms against herbivore species. In this work a strong influence of the sea level on the leaf parameters could be determined. An increasing influence of fertilization on the feeding rate of herbivorous species was not found.