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

Abstract:

With increasing elevation, trees in tropical montane forests have to invest larger frac-tions of their resources into their fine roots in order to compensate for increasingly unfavorable soil conditions. It is unclear how elevation and related edaphic changes influence the variability in tree fine root traits and belowground functional diversity. We measured six fine root traits related to resource acquisition on absorptive fine roots of 288 trees from 145 species along an elevational gradient from 1000 m to 3000 m a.s.l. in tropical montane forests of the Ecuadorian Andes. We analyzed trait relation-ships with elevation and soil nutrient availability, and tested whether root functional diversity varied along these gradients. Fine roots at higher elevations and at more nutrient-poor sites were thicker, had higher tissue densities, and lower specific root length and nutrient concentrations than at lower elevations. These trends were diluted by the coexistence of tree species with a broad range of different root traits within communities particularly towards lower elevations, where root functional diversity was significantly higher. We conclude that nutrient limitation and potentially further adverse conditions at higher elevations are strong environmental filters that lead to trait convergence towards a conservative resource use strategy, whereas different trait syndromes are equally successful at lower elevations.

Abstract:

Increased nutrient supply can have drastic effects on natural ecosystems, especially in naturally nutrient-poor ones such as most tropical rainforests. Many studies have focused on the reaction of trees to fertilization, but little is known about herbaceous plants. Ferns are a particularly common group in tropical forests, spanning all vegetation types and zones. Here, we assess how seven years of moderate addition of nitrogen (N), phosphorus (P), and N+P along an elevational gradient (1000–3000 m) have impacted richness and composition of fern and lycophyte assemblages in tropical montane rain forests growing on naturally nutrient deficient soils in the Ecuadorian Andes. We found that fertilization does not affect overall species richness, but that there were strong differences in species abundances (~60% of species), both negative and positive, that were apparently related to the systematic affiliations and ecological properties of the affected species. These diverse responses of ferns to fertilization provide insight into the sensitivity and complexity of the relationships of nutrient availability and community composition in tropical forests.

Abstract:

In the past two decades, the Amazon-exposed, tropical montane rain forests in south Ecuador experienced increasing deposition of reactive N mainly from Amazonian forest fires, episodic Ca and Mg inputs from Saharan dust, and a low but constant P deposition from unknown sources. To explore the response of this tropical, perhumid ecosystem to nutrient inputs, we established in 2007 a Nutrient Manipulation Experiment (NUMEX). Since 2008, we have applied 50 kg ha−1 year−1 of N as urea, 10 kg ha−1 year−1 of P as NaH2PO4·H2O, 50 kg ha−1 year−1 of N + 10 kg ha−1 year−1 of P and 10 kg ha−1 year−1 of Ca as CaCl2·H2O in a randomized block design at 2000 m a.s.l. in a natural forest of the south Ecuadorian Andes. Previous studies have shown that alkali and alkaline earth metals had beneficial effects on the functioning of N and P co-limited tropical forests occurring on acidic soils. Therefore, we determined the response of all major aqueous ecosystem fluxes of K, Ca, Mg and Na to nutrient amendments, to understand how increasing atmospheric deposition would affect their cycling in the future. Additions of N and P decreased K leaching from the organic layer and in the mineral soil, thus tightening K cycling. This suggests that increasing future N and P availability may result in K limitation in the long term. The leaching of Ca and Mg from the canopy increased in response to amendments of N and P and we observed an enhanced uptake of these nutrients also if Ca was amended alone. Although N was applied as urea, acidity of soil solutions and leaching of K, Ca, Mg and Na did not increase following separate N amendments. In spite of the acid soils and of its low cation-exchange competitivity, Na included in the P fertilizer was only partly leached from the organic layer. We suggest that it was probably required to cover an unmet Na demand of the soil fauna. Our results demonstrate the major role in the functioning of the tropical montane forests played by K, Ca and Mg as potential future growth-limiting elements and increasingly required nutrients in response to rising N and P availability, while they also support the importance of Na as a functional element in these ecosystems.

Abstract:

Theory predicts positive effects of species richness on the productivity of plant communities through complementary resource use and facilitative interactions between species. Results from manipulative experiments with tropical tree species indicate a positive diversity–productivity relationship (DPR), but the existing evidence from natural forests is scarce and contradictory. We studied forest aboveground productivity in more than 80 humid tropical montane oldgrowth forests in two highly diverse Andean regions with large geological and topographic heterogeneity and related productivity to tree diversity and climatic, edaphic and stand structural factors with a likely influence on productivity. Main determinants of wood production in the perhumid study regions were elevation (as a proxy for temperature), soil nutrient (N, P and base cation) availability and forest structural parameters (wood specific gravity, aboveground biomass). Tree diversity had only a small positive influence on productivity, even though tree species numbers varied largely (6–27 species per 0.04 ha). We conclude that the productivity of highly diverse Neotropical montane forests is primarily controlled by thermal and edaphic factors and stand structural properties, while tree diversity is of minor importance.

Abstract:

(1) We investigated the variation in tree fine root traits and their functional diversity along a local topographic gradient in a Neotropical montane forest to test if fine root trait variation along the gradient is consistent with the predictions of the root economics spectrum on a shift from acquisitive to conservative traits with decreasing resource supply. (2) We measured five fine root functional traits in 179 randomly selected tree individuals of 100 species and analyzed the variation of single traits (using Bayesian phylogenetic multi‐level models) and of functional trait diversity with small scale topography. (3) Fine roots exhibited more conservative traits (thicker diameters, lower specific root length and nitrogen concentration) at upper slope compared to lower slope positions, but the largest proportion of variation (40‐80%) was explained by species identity and phylogeny. Fine root functional diversity decreased towards the upper slopes. (4) Our results suggest that local topography and the related soil fertility and moisture gradients cause considerable small‐scale variation in fine root traits and functional diversity along tropical mountain slopes, with conservative root traits and greater trait convergence being associated with less favorable soil conditions due to environmental filtering. We provide evidence of a high degree of phylogenetic conservation in fine root traits.

Abstract:

Background: Tropical forests play an important role in the global carbon (C) cycle. However, tropical montane forests have been studied less than tropical lowland forests, and their role in carbon storage is not well understood. Montane forests are highly endangered due to logging, land-use and climate change. Our objective was to analyse how the carbon balance changes during forest succession. Methods: In this study, we used a method to estimate local carbon balances that combined forest inventory data with process-based forest models. We utilised such a forest model to study the carbon balance of a tropical montane forest in South Ecuador, comparing two topographical slope positions (ravines and lower slopes vs upper slopes and ridges). Results: The simulation results showed that the forest acts as a carbon sink with a maximum net ecosystem exchange (NEE) of 9.3 Mg C?(ha?yr)?1 during its early successional stage (0–100 years). In the late successional stage, the simulated NEE fluctuated around zero and had a variation of 0.77 Mg C?(ha?yr) –1. The simulated variability of the NEE was within the range of the field data. We discovered several forest attributes (e.g., basal area or the relative amount of pioneer trees) that can serve as predictors for NEE for young forest stands (0–100 years) but not for those in the late successional stage (500–1,000 years). In case of young forest stands these correlations are high, especially between stand basal area and NEE. Conclusion: In this study, we used an Ecuadorian study site as an example of how to successfully link a forest model with forest inventory data, for estimating stem-diameter distributions, biomass and aboveground net primary productivity. To conclude, this study shows that process-based forest models can be used to investigate the carbon balance of tropical montane forests. With this model it is possible to find hidden relationships between forest attributes and forest carbon fluxes. These relationships promote a better understanding of the role of tropical montane forests in the context of global carbon cycle, which in future will become more relevant to a society under global change.

Abstract:

Tropical forests and the trees as their principal components have been investigated in detail. However, due to its complexity, their interactions, adaptations and response to climate variations require much more research. In this study, dendrochronological techniques were applied to evaluate the potential of tree-rings from tropical tree species as climate records. Two ecosystems with very distinct climate scenarios were selected from a dry and humid forest in southern Ecuador. A comparative analysis between these two forest types was performed by applying three dendrochronological methods. First, Tree Ring Width (TRW) measurements from tree species with distinct ring boundaries were dated to develop ring-width chronologies. Second, stable carbon isotopes (?13C) were measured from whole-wood and alpha-cellulose of dated annual tree-rings. Finally, concentrations of more than 23 chemical elements were determined from individual dated tree-rings after dissolving the wooden material in HNO3. The results showed the high potential of tropical tree species as climate archives, Bursera graveolens and Maclura tinctoria for the dry forest and Cedrela montana for the humid forest. Radial growth variations in tree species from the dry forest revealed a strong and reliable precipitation signal. Then, for these tropical regions, the first ring-width based wet-season precipitation reconstruction over the past century was developed, and spatial correlations unraveled a strong connection to the climatic conditions of the central Pacific precipitation and temperature variability. Interseries correlations of the TRW from the trees of the humid forest revealed a weak common signal. Stable carbon isotopes evidenced higher climate sensitivity than TRW measurements in the humid forest. However, to infer a reliable climate reconstruction from stable carbon isotopes, more ?13C time series were needed. ?13C values from whole-wood and alpha-cellulose reflected local and regional signals of precipitation and humidity. Meanwhile, nutrient concentration in the wood was higher in the dry forest, but common patterns and trends of nutrients were more distinct in the humid forest. For both study sites, two groups of nutrients with opposite radial distribution were identified (Group 1: Ca, Sr, Ba, Ga; and Group 2: K, P, Rb). In conclusion, TRW of tree species from the dry forest have a high paleoclimate potential, especially to reconstruct precipitation amounts in arid zones of southern Ecuador. Stable carbon isotopes constitute a promising tool to perform climatic reconstructions in both ecosystems. Finally, the valuable historical information of nutrient concentration evidenced in tree-rings opens promising ways to study tree growth dynamics especially in the humid forest.

Abstract:

In the past two decades, the tropical montane rain forests in south Ecuador experienced increasing deposition of reactive nitrogen mainly originating from Amazonian forest fires, while Saharan dust inputs episodically increased deposition of base metals. Increasing air temperature and unevenly distributed rainfall have allowed for longer dry spells in a perhumid ecosystem. This might have favored mineralization of dissolved organic matter (DOM) by microorganisms and increased nutrient release from the organic layer. Environmental change is expected to impact the functioning of this ecosystem belonging to the biodiversity hotspots of the Earth. In 2007, we established a nutrient manipulation experiment (NUMEX) to understand the response of the ecosystem to moderately increased nutrient inputs. Since 2008, we have continuously applied 50 kg ha-1 a-1 of nitrogen (N), 10 kg ha-1 a-1 of phosphorus (P), 50 kg + 10 kg ha-1 a-1 of N and P and 10 kg ha-1 a-1 of calcium (Ca) in a randomized block design at 2000 m a.s.l. in a natural forest on the Amazonia-exposed slopes of the south Ecuadorian Andes. Nitrogen concentrations in throughfall increased following N+P additions, while separate N amendments only increased nitrate concentrations. Total organic carbon (TOC) and dissolved organic nitrogen (DON) concentrations showed high seasonal variations in litter leachate and decreased significantly in the P and N+P treatments, but not in the N treatment. Thus, P availability plays a key role in the mineralization of DOM. TOC/DON ratios were narrower in throughfall than in litter leachate but their temporal course did not respond to nutrient amendments. Our results revealed an initially fast, positive response of the C and N cycling to nutrient additions which declined with time. TOC and DON cycling only change if N and P supply are improved concurrently, while NO3-N leaching increases only if N is separately added. This indicates co-limitation of the microorganisms by N and P. The current increasing reactive N deposition will increase N export from the root zone, while it will only accelerate TOC and DON turnover if P availability is simultaneously increased. The Saharan dust-related Ca deposition has no impact on TOC and DON turnover.

Abstract:

Atmospheric nutrient deposition and climate change are expected to endanger the diversity of tropical forest ecosystems. Nitrogen (N) deposition might influence nutrient fluxes beyond the N cycle by a concomitant increased demand for other nutritional elements such as phosphorus (P). Organisms might respond to the increased P demand by enhanced activity of enzymes involved in releasing inorganic P from organic matter (OM). Our aims were to assess the effect of i) climate shifts (approximated by an altitudinal gradient), and ii) nutrient addition (N, P, N+P) on phosphatase activity (PA) in organic layer and mineral soil of a tropical montane rainforest in Southern Ecuador. A nutrient manipulation experiment (NUMEX) was set up along an altitudinal gradient (1000, 2000, and 3000 m a.s.l.). We determined PA and inorganic and total P concentrations. PA at 1000 m was significantly lower (mean ± standard error: 48 ± 20 µmol p-NP g-1 dm h-1) as compared to 2000 m and 3000 m (119 ± 11 and 137 ± 19, respectively). One explanation might be that very rapid decomposition of OM at 1000 m results in very thin organic layers reducing the stabilization of enzymes and thus, resulting in leaching loss of enzymes under the humid tropical climate. We found no effect of N addition on PA neither in the organic layer nor in mineral soil, probably because of the low nutrient addition rates that showed ambiguous results so far on productivity measures as a proxy for P demand. In the organic layers of P and N+P treatments, we found decreased PA and increased concentrations of inorganic P. This indicates that the surplus of inorganic P reduced the biosynthesis of phosphatase enzymes. PA in megadiverse montane rainforests is likely to be unaffected by increased atmospheric N deposition but reduced upon atmospheric P deposition.

Abstract:

South America hosts 22% of the world´s forests with its unique biological diversity. Among all countries Ecuador is considered being the country with the highest biodiversity. But unsustainable land use and forestry practices threaten this diversity. Up to today Ecuador has the highest deforestation rate of the South American continent. To combate against those high forest losses wide-ranged reforestation has to take place but is still lacking in Ecuador. The reforestation efforts up to now do not compensate the high losses in forest cover. 90% (3500ha) of the annual reforestation in Ecuador is taking place in the Andean region (FAO 2006, 2011). A common tool to reinstall the forest cover is plantings. To this day 140,000 ha of forest plantations exist in the Andes of Ecuador. The commonly used species are Eucalyptus globulus, Pinus radiata and Pinus patula. Just recently Ecuadorian organizations paid particular attention to tree species native to Ecuador and their reforestation potential. The major obstacle to use native species on a larger scale for reforestation is the lack of adequate knowledge about their physiological and silvicultural traits. Information about appropriate seed storage, propagation methods and silvicultural treatment options has to be acquiered, applied and its experience communicated. Tree seed programs provide a valuable framework to deal with such sets of questions and research needs. The Danish International Development Agency (DANIDA) has over 50 years of experience in the development and establishment of national tree seed programs. Their development framework is used as an orientation in the course of this thesis to frame a regional seed program for the provincial region of Loja. The general objectives of this thesis are to evaluate the current seed procurement and management methods in the Province of Loja and to develop a concept for regional seed program for the province of Loja which is practicable and adapted to the local circumstances. Data on the current practices was gathered through a questionnaire survey and structured observation among the provincial tree nurseries. National and regional forestry strategies and plans were revised to understand the encountered situation. To develop the regional seed program the national tree seed program framework from Danida was consulted. This study assesses the main areas of improvement of the provincial seed management and highlights local facts in need for special consideration in the scope of a regional seed program. Furthermore essential parts and how to best implement those in a regional seed program are discussed. Major results involve the formulation of four main areas of improvement common for all surveyed tree nurseries of the province: Infrastructure, workforce, documentation and seed handling itself. The individual performances of the nurseries were ranked to get a clearer picture about the production efficiency. The survey also revealed the variety of tree species produced. Regarding the regional seed program the results picture the Gobierno Provincial de Loja (GPL) as a suitable entity to be in charge of the program. Moreover important stakeholders beneficiary for the program were detected and an exemplary distribution of activities among them was conducted. The principal contributions of this thesis consist in conducting a systematic evaluation of the current status of the seed sector in southern Ecuador and particularly in the Province of Loja for the first time, and in providing the provincial government with an elaborated concept to improve the seed management. Additionally the developed ranking scheme can serve as a guideline for further nursery performance evaluations.

Abstract:

In tropical mountains, trees are the dominant life form from sea level to above 4,000-m altitude under highly variable thermal conditions (range of mean annual temperatures: <8 to >28C). How light-saturated net photosynthesis of tropical trees adapts to variation in temperature, atmospheric CO2 concentration, and further environmental factors, that change along elevation gradients, is not precisely known. With gas exchange measurements in mature trees, we determined light-saturated net photosynthesis at ambient temperature (T) and [CO2] (Asat) of 40 tree species from 21 families in tropical mountain forests at 1000-, 2000-, and 3000-m elevation in southern Ecuador. We tested the hypothesis that stand-level averages of Asat and leaf dark respiration (RD) per leaf area remain constant with elevation. Standlevel means of Asat were 8.8, 11.3, and 7.2 lmol CO2 m-2 s-1; those of RD 0.8, 0.6, and 0.7 lmol CO2 m-2 s-1 at 1000-, 2000-, and 3000-m elevation, respectively, with no significant altitudinal trend. We obtained coefficients of among-species variation in Asat and RD of 20?53% (n = 10?16 tree species per stand). Examining our data in the context of a pan-tropical Asat data base for mature tropical trees (c. 170 species from 18 sites at variable elevation) revealed that area-based Asat decreases in tropical mountains by, on average, 1.3 lmol CO2 m-2 s-1 per km altitude increase (or by 0.2 lmol CO2 m-2 s-1 per K temperature decrease). The Asat decrease occurred despite an increase in leaf mass per area with altitude. Local geological and soil fertility conditions and related foliar N and P concentrations considerably influenced the altitudinal Asat patterns. We conclude that elevation is an important influencing factor of the photosynthetic activity of tropical trees. Lowered Asat together with a reduced stand leaf area decrease canopy C gain with elevation in tropical mountains.

Abstract:

Caterpillar ensembles were sampled on 16 species of shrubs from the family Asteraceae and the genus Piper (Piperaceae) in open and forest habitats in the Andean montane forest zone of southern Ecuador between August 2007 and May 2009. Trophic affiliations of caterpillars to the host plants were confirmed in feeding trials. Overall, species richness of herbivorous caterpillars was high (191 species across all plants), but varied strongly between ensembles associated with different plant species (2–96 lepidopteran species per shrub species). Ensembles on Piper species were characterized by low effective species numbers and high dominance of one or two species of the Geometridae genus Eois Hübner. Low species number and high dominance were also found on latex-bearing Erato polymnioides, whereas ensembles on two other Asteraceae species were far more diverse and less strongly shaped by a few dominant species. The observed diversity patterns fit well to the concept that anti-herbivore defenses of plants are the major factors regulating associated insect ensembles. Local abundance and geographic range of host plants appear to have less influence. Lepidopteran species feeding on Asteraceae were found to be more generalistic than those feeding on Piper species. We conclude that caterpillar ensembles on most, but not all, studied plant species are defined by a small number of dominant species, which usually are narrow host specialists. This pattern was more distinct on Piper shrubs in forest understory, whereas Asteraceae in disturbed habitats had more open caterpillar ensembles.

Abstract:

Landslides are a hazard for humans and artificial structures. From an ecological point of view, they represent an important ecosystem disturbance, especially in tropical montane forests. Here, shallow translational landslides are a frequent natural phenomenon and one local determinant of high levels of biodiversity. In this paper, we apply weighted ensembles of advanced phenomenological models from statistics and machine learning to analyze the driving factors of natural landslides in a tropical montane forest in South Ecuador. We exclusively interpret terrain attributes, derived from a digital elevation model, as proxies to several driving factors of landslides and use them as predictors in our models which are trained on a set of five historical landslide inventories. We check the model generality by transferring them in time and use three common performance criteria (i.e. AUC, explained deviance and slope of model calibration curve) to, on the one hand, compare several state-of-the-art model approaches and on the other hand, to create weighted model ensembles. Our results suggest that it is important to consider more than one single performance criterion. Approaching our main question, we compare responses of weighted model ensembles that were trained on distinct functional units of landslides (i.e. initiation, transport and deposition zones). This way, we are able to show that it is quite possible to deduce driving factors of landslides, if the consistency between the training data and the processes is maintained. Opening the ?black box? of statistical models by interpreting univariate model response curves and relative importance of single predictors regarding their plausibility, we provide a means to verify this consistency. With the exception of classification tree analysis, all techniques performed comparably well in our case study while being outperformed by weighted model ensembles. Univariate response curves of models trained on distinct functional units of landslides exposed different shapes following our expectations. Our results indicate the occurrence of landslides to be mainly controlled by factors related to the general position along a slope (i.e. ridge, open slope or valley) while landslide initiation seems to be favored by small scale convexities on otherwise plain open slopes.

Abstract:

Shallow landslides are an important type of natural ecosystem disturbance in tropical montane forests. Due to landslides, vegetation and often also the upper soil layer are removed, and space for primary succession under altered environmental conditions is created. Little is known about how these altered conditions affect important aspects of forest recovery such as the establishment of new tree biomass and species composition. To address these questions we utilize a process-based forest simulation model and develop potential forest regrowth scenarios. We investigate how changes in different trees species characteristics influence forest recovery on landslide sites. The applied regrowth scenarios are: undisturbed regrowth (all tree species characteristics remain like in the undisturbed forest), reduced tree growth (induced by nutrient limitation), reduced tree establishment (due to thicket-forming vegetation and dispersal limitation) and increased tree mortality (due to post-landslide erosion and increased susceptibility). We then apply these scenarios to an evergreen tropical montane forest in southern Ecuador where landslides constitute a major source of natural disturbance. Our most important findings are (a) On the local scale of a single landslide tree biomass recovers within the first 80 years after landslides for most scenarios, but it takes at least 200 years for the post-landslide forest to reach a structure (in terms of stem size distribution) similar to a mature forest. On this scale forest productivity is reduced for most regrowth scenarios. Changes in different tree species characteristics produce distinct spatio-temporal patterns of tree biomass distribution in the first decades of recovery within the landslide disturbed area. These patterns can potentially be used for identifying the dominant processes that drive forest recovery on landslide disturbed sites. (b) On the larger scale of the landscape overall tree biomass is reduced by 9?15% due to landslide disturbances. Overall forest productivity is only slightly reduced (<6%), but landslides increase landscape heterogeneity and produce hotspots of biomass loss and ?blind spots? of forest productivity. Thus landslides have a strong impact on the distribution of biomass in tropical montane forests. This study demonstrates that dynamic forest models are useful tools for complementing field based studies on landslides; they allow for testing alternative hypotheses on different sources of heterogeneity across spatial scales and investigating the influence of landslides on long-term forest dynamics.

Abstract:

Catchment-scale runoff generation involves a complex interaction of physical and chemical processes operating over a wide distribution of spatial and temporal scales. Understanding runoff generation is challenged by this inherent complexity ? the more uncertain step of predicting the hydrologic response of catchments is that much more challenging. Many different hypotheses have been implemented in hydrological models to capture runoff generation processes and provide hydrologic predictions. These concepts have been developed based on extended field observations. Here we propose inferring water flux understanding and catchment exploring through the application of a variety of available hydrological models as a mechanism to build upon and extend models that have been developed to capture particular hydrological processes. We view this ensemble modeling strategy as particularly appropriate in ungauged catchments. The study is carried out in a tropical montane rainforest catchment in Southern Ecuador. The catchment is 75 km2 and is covered by forest in the south, while the northern slopes have been partly deforested for grazing. Annual rainfall is highly variable, reaching up to 5700 mm per year in the upper parts of the catchment. To explore the dominating runoff processes, an ensemble of 6 hydrological models with different structures applied over different levels of both spatial and temporal detail was developed. The ensemble includes spatially lumped (HBV-light), semi-distributed (HEC-HMS, CHIMP, SWAT, LASCAM) and a fully distributed model (HBV-N-D). The hydro-statistical toolkit WETSPRO was used to characterize simulated and observed hydrographs. Estimated baseflow indices, flow minima and maxima, flow duration curves and cumulative errors were generated and compared among the ensemble of models. This process facilitated the exploration of processes controlling runoff generation, enabled an evaluation of the applicability of the screened models to tropical montane rainforests, and provided the capacity to evaluate and explain where different models failed.

Abstract:

Stem diameter increments of the broadleaved deciduous tree species Tabebuia chrysantha were measured with high-resolution dendrometers in a tropical lower montane forest and in a dry forest in southern Ecuador, the latter showing a distinct dry season. Those analyses were complemented by wood anatomical studies on regularly collected microcores to determine the season of active cambial growth and the time of formation of annual growth boundaries. The length of the cambial active period varied between 3 and 7 months at the tropical lower montane forest and 2 and 4 months in the dry forest, respectively. During dry days, amplitudes of daily stem diameter variations correlated with vapour pressure deficit. During October and November, inter-annual climate variations may lead to dry and sunny conditions in the tropical lower montane forest, causing water deficit and stem diameter shrinkage in T. chrysantha. The results of the climate– growth analysis show a positive relationship between tree growth and rainfall as well as vapour pressure deficit in certain periods of the year, indicating that rainfall plays a major role for tree growth.

Abstract:

Soil-landscapes are diverse and complex due to the interaction of pedogenetic, geomorphological and hydrological processes. The resulting soil profile reflects the balance of these processes in its properties. Early conceptual models have by now resulted into quantitative soil-landscape models including soil variation and its unpredictability as a key soil attribute. Soils in the Andean mountain rainforest area of southern Ecuador are influenced by hillslope processes and landslides in particular. The lack of knowledge on the distribution of soils and especially physical soil properties to understand slope failure, resulted in the study of this particular soil-landscape by means of statistical models relating soil to terrain attributes, i.e. predictive soil mapping. A 24 terrain classes comprising sampling design for soil investigation in mountainous areas was developed to obtain a representative dataset for statistical modelling. The soils were investigated by 56 profiles and 315 auger points. The Reference Soil Groups (RSGs) Histosol, Stagnosol, Umbrisol, Cambisol, Leptosol and Regosol were identified according to the World Reference Base for Soil Resources (WRB). Classification tree models and a probability scheme based on WRB hierarchy were applied to include RSG prediction uncertainty in a digital soil map. Histosol probability depended on hydrological parameters; highest Stagnosol probability was found on slopes < 40° and above 2146 m a.s.l. Poor model performance, probably due to the prediction of complex categories (RSGs) and WRB inconsequence (absolute and relative value criteria), led to the proposal of ?incomplete soil classification? by relating the thickness of the WRB?s diagnostic horizons as percentage to the upper 100 soil centimetres, including the organic layer. Typical diagnostic horizons histic, humic, umbric, stagnic and cambic were regionalised in their thickness and occurrence probability by classification and regression trees (CART). Prediction uncertainty was addressed with hundredfold model runs based on different random Jackknife partitions of the dataset. Whether the first mineral soil horizon displays stagnic properties or not, likely depends on physical soil properties in addition to terrain parameters. Incomplete soil classification resulted in histic and stagnic soil parts dominating the first 100 cm of the soil volume for most of the research area. While soil profiles and auger points were described in their horizon composition, thickness, Munsell colour and soil texture by finger method (FAO, 2006), soil cohesion, bulk density and texture by pipette and laser were analysed in soil profiles only. Texture results by pipette compared to laser method, showed the expected shift to higher silt and lower clay contents. Linear regression equations were adapted. Pedotransfer functions to predict physical soil properties from the bigger auger dataset analysed by field texture method only, could not be developed, because field texture analysis did not provide satisfying results. It was therefore not possible to correct its results with the more precise laboratory data. Comparing CART and Random Forest (RF) in their model performance to predict topsoil texture and bulk density as well as mineral soil thickness by hundredfold model runs with random Jackknife partitions, RF predictions resulted more powerful. Altitude a.s.l. was the most important predictor for all three soil parameters. Increasing sand/ clay ratios with increasing altitude, on steep slopes and with overland flow distance to the channel network are caused by shallow subsurface flow removing clay particles downslope. Deeper soil layers are not influenced by the same process and therefore showed different texture properties. Terrain parameters could only explain the spatial distribution of topsoil properties to a limited extent, subsoil properties could not be predicted at all. Other parameters that likely influence soil properties within the investigation area are parent material and landslides. Strong evidence was found that topsoil horizons did not form from the bedrock underlying the soil profile. Parent material changes within short distance and often within one soil profile. Landslides have a strong influence on soil-landscape formation in shifting soil and rock material. Soil mechanical and hydrological properties in addition to terrain steepness were hypothesized to be the major factors in causing soil slides. Thus, the factor of safety (FS) was calculated as the soil shear ratio that is necessary to maintain the critical state equilibrium on a potential sliding surface. The depth of the failure plane was assumed at the lower boundary of the stagnic soil layer or complete soil depth, depending on soils being stagnic or non-stagnic. The FS was determined in dependence of soil wetness referring to 0.001, 0.01, 0.1 and 3 mm/h net rainfall rate. Sites with a FS &#8805; 1 at 3 mm/h (complete saturation) were classified as unconditionally stable, sites with a FS < 1 at 0.001 mm/h as unconditionally unstable. The latter coincided quite well with landslide scars from a recent aerial photograph.

Abstract:

The number of previous hydrological studies concerning water flow paths in tropical montane rainforest is small. However, due to the increasing pressure of deforestation and land use change comprehensive knowledge of these natural ecosystems is needed if sustainable land use strategies should keep negative effects of human impacts on water flow paths as low as possible. In this context, present work addresses the identification, characterisation, and modelling of water flow paths in soils of an undisturbed and landslide affected natural Andean forest ecosystem in the south of Ecuador whose deforestation rate is one of the highest in South America. In an investigation area situated in the Andes of South Ecuador, in gentler slopes and altitudes above 2100 m ASL mainly Stagnosols and Histosols with stagnic colour pattern and low to negligible rock fragment content prevail. With increasing altitude the abundance of these soils increase, while the presence of Cambisols and Regosols is most pronounced below 2100 m ASL and clearly correlated with the slope angle. Therefore, these soils were mainly encountered in steeper, particularly landslide affected sites often resembling a melange of fine soil and high contents of rock fragments. Aside the investigation of the influence of the rock fragment content on soil hydrological- and physical parameters such as the relationship between rock fragment content and saturated hydraulic conductivity of the soil, present study aims particularly to investigate flow paths of water in soils of landslide affected and unaffected hillslopes. Therefore, we employed conventional field- and laboratory methods, dye tracer experiments including an appropriate image processing technique, as well as statistical models. Results show that both rock fragment content and bulk density control significantly, but not largely the saturated hydraulic conductivity of the mineral soils. Dye tracer experiments and soil parameters document a deeper percolation in the landslide affected hillslopes than in the landslide unaffected hillslopes, where we found preferential flow in root channels with low soil matrix interaction as dominant flow mechanism. A surface near quasi impervious layer along the interface between topsoil and subsoil limits percolation of the water giving the prerequisites of a lateral shallow subsurface flow along the interface between topsoil and organic layer. This is in line with previous studies performed in the same investigation area which already proved indirectly the existence of this flow. However, in none of these studies the shallow subsurface flow was assigned to certain slope inclinations or altitudes. Due to a recently published digital soil map and the results we obtained from the landslide unaffected sites, we know that particularly in hillslopes of less than 30 ° above 2100 m ASL prerequisites are given for spatially extended shallow subsurface flow. However, even if these prerequisites are not evident for the landslide affected hillslopes, we cannot exclude the possibility of shallow subsurface flow occurrence here since soil cover of the steep terrain is relatively shallow while rainfall is high throughout the year. Therefore, and given that key parameters such as permeability of subsoil and bedrock, interception and evaporation remain unclear or were investigated exclusively such as the spatial variability of the saturated hydraulic conductivity, we conducted a series of virtual experiments in order to assess the potential occurrence of shallow subsurface flow in Cambisols below 2100 m ASL. In these experiments we also included the organic layer being highly abundant in the investigation area, whose hydraulic parameters were estimated by means of inverse numerical modelling. The virtual experiments were based on a two dimensional finite element model representing a steep forested hillslope transect of ~54 m length. Aside soil properties, evapotranspiration and interception, the model included the spatial variability of the saturated hydraulic conductivity, the pressure head and their spatial trends. The results of virtual experiment series show that a sound evidence of the key parameters aforementioned is obligate if process conceptualisation regarding shallow subsurface flow generation, but also landslide initiation, solute and matter transport is in the spotlight.

Abstract:

As part of an interdisciplinary research programme, the spatial and temporal variability of precipitation in southern Ecuador has been investigated since January 2002. The study site is located at the northern margin of the Podocarpus National Park in the vicinity of Loja, about 500 km south of Quito, at altitudes ranging from 1800 to 3200 m.a.s.l. Due to its low density, the conventional rainfall station network fails to register the highly variable spatial distribution of rain, whereas contributions by fog are not accounted at all. Hence, for the first time in a tropical montane forest setting, a weather radar was used, covering a radius of 60 km and reaching from the Amazon Basin to the coastal plains of the region. Furthermore, a network of sampling stations supplies data about the altitudinal gradient of fog and rainwater inputs. The precipitation distribution in the study area proves to be far more variable than previously thought and is strongly coupled to the orographic characteristics and the special topographical setting of the landscape. Maxima in precipitation occur especially in the eastern parts of the radar range on slopes exposed to advected moisture from the Amazon Basin, whereas the highest crests of the Andes receive less precipitation. The study area has two cloud condensation levels, occurring at 1500?2000 and 2500?3500 m.a.s.l., respectively. At 1800?2000 m.a.s.l., fog is estimated to contribute an additional input of 5% of conventionally measured rainfall, increasing to about 35% at the highest measurement station (3200 m.a.s.l.). In contrast to some other tropical mountains, there seems to be no maximum zone of water input, although the gradient remains positive up to the highest altitudes. The unusual precipitation distribution is thought to reflect the contrasting climatological influences operating in the study area.

Abstract:

Knowledge of the fate of deposited N in the possibly N-limited, highly biodiverse north Andean forests is important because of the possible effects of N inputs on plant performance and species composition. We analyzed concentrations and fluxes of NO3?N, NH4?N and dissolved organic N (DON) in rainfall, throughfall, litter leachate, mineral soil solutions (0.15?0.30 m depths) and stream water in a montane forest in Ecuador during four consecutive quarters and used the natural 15N abundance in NO3 during the passage of rain water through the ecosystem and bulk d15N values in soil to detect N transformations. Depletion of 15N in NO3 and increased NO3 fluxes during the passage through the canopy and the organic layer indicated nitrification in these compartments. During leaching from the organic layer to mineral soil and stream, NO3 concentrations progressively decreased and were enriched in 15N but did not reach the d15N values of solid phase organic matter (d15N = 5.6?6.7%). This suggested a combination of nitrification and denitrification in mineral soil. In the wettest quarter, the d15N value of NO3 in litter leachate was smaller (d15N = -1.58%) than in the other quarters (d15N = -9.38 ± SE 0.46%) probably because of reduced mineralization and associated fractionation against 15N. Nitrogen isotope fractionation of NO3 between litter leachate and stream water was smaller in the wettest period than in the other periods probably because of a higher rate of denitrification and continuous dilution by isotopically lighter NO3-N from throughfall and nitrification in the organic layer during the wettest period. The stable N isotope composition of NO3 gave valuable indications of N transformations during the passage of water through the forest ecosystem from rainfall to the stream.

Abstract:

Atmospheric nitrogen (N) and phosphorus (P) depositions are expected to increase in the tropics as a consequence of increasing human activities in the next decades. In the literature, it is frequently assumed that tropical montane forests are N-limited, while tropical lowland forests are P-limited. In a low-level N and P addition experiment, we determined the short-term response of N and P cycles in a north Andean montane forest on Palaeozoic shists and metasandstones at an elevation of 2100m a.s.l. to increased N and P inputs. We evaluated experimental N, P and N+ P additions (50 kg ha&#8722;1 yr&#8722;1 of N, 10 kg ha&#8722;1 yr&#8722;1 of P and 50 kg + 10 kg ha&#8722;1 yr&#8722;1 of N and P, respectively) and an untreated control in a fourfold replicated randomized block design. We collected litter leachate, mineral soil solution (0.15 and 0.30m depths), throughfall and litterfall before the treatment began (August 2007) until 16 months after the first nutrient application (April 2009). Less than 10 and 1% of the applied N and P, respectively, leached below the organic layer which contained almost all roots and no significant leaching losses of N and P occurred to below 0.15m mineral soil depth. Deposited N and P from the atmosphere in dry and wet form were retained in the canopy of the control treatment using a canopy budget model. Nitrogen and P retention by the canopy were reduced and N and P fluxes in throughfall and litterfall increased in their respective treatments. The increase in N and P fluxes in throughfall after fertilization was equivalent to 2.5% of the applied N and 2% of the applied P. The fluxes of N and P in litterfall were up to 15% and 3%, respectively, higher in the N and N+ P than in the control treatments. We conclude that the expected elevated N and P deposition in the tropics will be retained in the ecosystem, at least in the short term and hence, N and P concentrations in stream water will not increase. Our results suggest that in the studied tropical montane forest ecosystem on Palaeozoic bedrock, N and P are co-limiting the growth of organisms in the canopy and organic layer.

Abstract:

Cedrela montana is a deciduous broad-leaved tree species growing in the humid mountain rainforests of southern Ecuador. High-resolution dendrometer data indicate a regular seasonal growth rhythm with cambial activity during January to April. Amplitudes of daily radial stem diameter variations are correlated with the amount of the maximum daily vapour pressure deficit. During humid periods, daily stem diameter variations are considerably smaller than during drier periods. This indicates that cambial activity is limited by available moisture even in such a very humid mountain climate. Wood anatomical studies on microcores show the formation of a marginal parenchyma band at the beginning of the growth period. This parenchyma band can be used to delineate annual growth rings. We were able to establish the first ring-width chronology from Cedrela montana which covers the time until 1840. However, the chronology is presently statistically robust back to 1910 only. Correlation functions calculated with NCEP/NCAR data indicate a significantly positive relationship of tree growth with temperatures during the growth period during January to April. However, only 8% of the growth variance is explained by this climatic factor. In the future, this relationship may be useful to reconstruct past temperature conditions of the study area.

Abstract:

Soil landscape modelling is based on understanding the spatial distribution patterns of soil characteristics. A model relating the soil?s properties to its position within the landscape is used to predict soil properties in other similar landscape positions. To develop soil landscape models, the interaction of geographic information technology, advanced statistics and soil science is needed. The focus of this work is to predict the distribution of the different soil types in a tropical mountain forest area in southern Ecuador from relief and hydrological parameters using a classification tree model (CART) for soil regionalisation. Soils were sampled along transects from ridges towards side valley creeks using a sampling design with 24 relief units. Major soil types of the research area are Histosols associated with Stagnosols, Cambisols and Regosols. Umbrisols and Leptosols are present to a lesser degree. Stagnosols gain importance with increasing altitude and with decreasing slope angle. Umbrisols are to be found only on slopes <30°. Cambisols occurrence might be related to landslides.The CART model was established by a data set of 315 auger sampling points. Bedrock and relief curvature had no influence on model development. Applying the CART model to the research area Histosols and Stagnosols were identified as dominant soil types. Model prediction left out Cambisols and overestimated Umbrisols, but showed a realistic prediction for Histosols, Stagnosols and Leptosols.

Abstract:

The montane forests of Ecuador are part of one of the world?s hotspots of biodiversity and they also suffer the highest deforestation rate amongst South American countries. The processes that drive the dynamics of these highly diverse ecosystems are poorly understood. This is particularly true for transient dynamics, which are crucial for the protection and sustainable management of such forests. Dynamic simulation models can be used to analyse the growth of forests, but so far they have been applied mostly to temperate forests and to some few tropical lowland forests. In this study we investigate whether a process-based, individual-oriented simulation model like FORMIND is capable of reproducing the dynamics of tropical montane forests. For this purpose we develop a parameterisation for the model and validate the model against field observations of different (structural) patterns. We then analyse the predicted succession dynamics. The model is capable of reproducing the structure and dynamics of mature ridge forest on different levels of complexity. The main results indicate that, in terms of relative abundances of different species groups and stem size distribution in the tree community, our model predicts the observed patterns in the field. Additional field studies and model modifications are required to simulate the succession processes that follow different types of disturbances. FORMIND is a promising tool for the extrapolation of local measurements and for simulating the dynamics of tropical montane forests. Parameterisations of the model for further forest types within the research area are intended. The model has a number of potential applications, ranging from investigating the impact of (different) natural disturbances on forest structure and tree species diversity to analysing different potential management strategies.