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

Abstract:

Ratios of stable oxygen isotopes in tree rings (δ18O) are a valuable proxy for reconstructing past climates. Such reconstructions allow us to gain better knowledge of climate dynamics under different (eg warmer) environmental conditions, which also forms the basis for effective risk management. The latter aspect is particularly relevant for our study site on the western flanks of the Andes in Southern Ecuador, since the region is frequently affected by droughts and heavy precipitation events during the rainy season (January to April), leading to enormous social and economic losses. In particular, we focus on precipitation amounts and moisture source regions as they are known to influence the δ18O signature of tree rings. Moisture source regions are based on 240 h backward trajectories that were calculated with the trajectory model LAGRANTO for the rainy seasons 2008 to 2017. A moisture source diagnostic was applied to the air parcel pathways. The resulting moisture source regions were analyzed by calculating composites based on precipitation amounts, season, and calendar year. The precipitation amounts were derived from data of a local Automatic Weather Station (AWS). The analysis confirms that our study site receives its moisture both, from the Atlantic and the Pacific Oceans. Heavy precipitation events are linked to higher moisture contributions from the Pacific, and local SST anomalies along the coast of Ecuador are of higher importance than those off the coast toward the central Pacific. Moreover, we identified increasing moisture contributions from the Pacific over the course of the rainy season. This change and also rain amount effects are detectable in preliminary data of δ18O variations in tree rings of Bursera graveolens. These signatures can be a starting point for investigating atmospheric and hydroclimatic processes, which trigger δ18O variations in tree rings, more extensively in future studies.

Abstract:

Abstract Conversion of tropical forests is among the primary causes of global environmental change. The loss of their important environmental services has prompted calls to integrate ecosystem services (ES) in addition to socio-economic objectives in decision-making. To test the effect of accounting for both ES and socio-economic objectives in land-use decisions, we develop a new dynamic approach to model deforestation scenarios for tropical mountain forests. We integrate multi-objective optimization of land allocation with an innovative approach to consider uncertainty spaces for each objective. These uncertainty spaces account for potential variability among decision-makers, who may have different expectations about the future. When optimizing only socio-economic objectives, the model continues the past trend in deforestation (1975–2015) in the projected land-use allocation (2015–2070). Based on indicators for biomass production, carbon storage, climate and water regulation, and soil quality, we show that considering multiple ES in addition to the socio-economic objectives has heterogeneous effects on land-use allocation. It saves some natural forest if the natural forest share is below 38%, and can stop deforestation once the natural forest share drops below 10%. For landscapes with high shares of forest (38%–80% in our study), accounting for multiple ES under high uncertainty of their indicators may, however, accelerate deforestation. For such multifunctional landscapes, two main effects prevail: (a) accelerated expansion of diversified non-natural areas to elevate the levels of the indicators and (b) increased landscape diversification to maintain multiple ES, reducing the proportion of natural forest. Only when accounting for vascular plant species richness as an explicit objective in the optimization, deforestation was consistently reduced. Aiming for multifunctional landscapes may therefore conflict with the aim of reducing deforestation, which we can quantify here for the first time. Our findings are relevant for identifying types of landscapes where this conflict may arise and to better align respective policies.

Abstract:

Trees in tropical dry forests (TDFs) have manifold drought coping strategies including succulence of different plant organs, wood anatomical traits and leaf phenology. As water availability to plants is the limiting factor for physiological activity, changes in precipitation patterns are assumed to have strong influences on tree phenology, growth and water turnover. Our objectives were to assess patterns in leaf phenology, radial stem circumference changes and sap flux responses to fluctuating moisture regimes of selected species. Based on these findings we evaluated the potential suitability as indicator species for climate change effects. The study was implemented at different elevational positions in a submontane dry forest of southern Ecuador. Annual rainfall is 600 mm with an eight months dry period; moisture availability slightly increases with altitude because of moist air coming from the Pacific. At three altitudes,we studied the tree species Ceiba trichistandra (leaf deciduous, stem succulent), Eriotheca ruizii (leaf deciduous, root succulent) and Erythrina velutina (leaf deciduous). Reversible stem swelling and shrinking was observed for all three species during the whole study period and at all positions at the altitudinal gradient. However, it was most pronounced and sensitive in the stem succulent C. trichistandra and at the lowest (driest) position. C. trichistandra flushed leaves at dry season intermittent rain events, and from dry to wet season leaf out was earlier, and in this period sap flux was high while stem circumference decreased. Length of the leaved periods of all species increased with altitude. Thus, clear differences among species, topographic positions, radial growth and tree water use patterns are revealed; especially C. trichistandra responded very sensitive to fluctuating moisture regimes with leaf phenology, sap flux and stem diameter variations, and can be regarded as a sensitive indicator for assessing climatic variations.

Abstract:

High landscape diversity is assumed to increase the number and level of ecosystem services. However, the interactions between ecosystem service provision, disturbance and landscape composition are poorly understood. Here we present a novel approach to include uncertainty in the optimization of land allocation for improving the provision of multiple ecosystem services. We refer to the rehabilitation of abandoned agricultural lands in Ecuador including two types of both afforestation and pasture rehabilitation, together with a succession option. Our results show that high compositional landscape diversity supports multiple ecosystem services (multifunction effect). This implicitly provides a buffer against uncertainty. Our work shows that active integration of uncertainty is only important when optimizing single or highly correlated ecosystem services and that the multifunction effect on landscape diversity is stronger than the uncertainty effect. This is an important insight to support a land-use planning based on ecosystem services.

Abstract:

We present the first multi-year long time series of local climate data in the seasonally dry tropical forest in Southern Ecuador and related growth dynamics of Loxopterygium huasango, a deciduous tree species. Local climate was investigated by installing an automatically weather station in 2007 and the daily tree growth variability was measured with high-resolution point dendrometers. The climatic impact on growth behaviour was evaluated. Hydro-climatic variables, like precipitation and relative humidity, were the most important factors for controlling tree growth. Changes in rainwater input affected radial increment rates and daily amplitudes of stem diameter variations within the study period from 2009 to 2013. El Nin˜o Southern Oscillation (ENSO) related variations of tropical Pacific Ocean sea surface temperatures influenced the trees’ increment rates. Average radial increments showed high inter-annual (up to 7.89 mm) and inter-individual (up to 3.88 mm) variations. Daily amplitudes of stem diameter variations differed strongly between the two extreme years 2009 (wet) and 2011 (dry). Contrary to 2009, the La Nin˜a drought in 2011 caused a rapid reduction of the daily amplitudes, indicating a total cessation (‘growth collapse’) of stem increment under ENSOrelated drought conditions and demonstrating the high impact of climatic extreme events on carbon sequestration of the dry tropical forest ecosystem.

Abstract:

From 10 selected tree species, Bursera graveolens and Maclura tinctoria exhibited distinct annual and crossdatable tree-rings. It was possible to synchronize individual tree-ring series and to establish two tree-ring chronologies of 203 and 87 years length, respectively. The characteristic ENSO frequency band is reflected in wavelet power spectra of both chronologies. Both species showa strong correlation between ringwidth and precipitation of thewet season (January–May). Strong El Niño events (1972, 1983 and 1998) lead to strong growth responses in the tree-ring chronologies, whereas ‘normal’ ENSO events do not trigger long-lasting growth responses. The first ring-width based wet-season precipitation reconstruction for the past 103 years was developed. Statistical and spatial correlation analysis verified the skills of the reconstructed precipitation which captures a great part of the Rainfall Index over the land area of Ecuador and the equatorial Pacific. Furthermore, teleconnections with central Pacific precipitation and SST patterns were found.

Abstract:

This paper presents a method to extrapolate wind-speed data and to calculate wind-speed and dynamic pressure maps for the complex topography of a mountain rainforest area in the tropical Andes of southeastern Ecuador. The spatial differentiation of dynamic wind pressure in this area is claimed to be a major determinant of the altitude of the tree-line ecotone and to affect the tree line’s physiognomy. The paper presents a hybrid method encompassing statistical data analysis using the Weibull distribution and a digital terrain analysis, taking topographical shelter effects into account. The method is used to derive mean and maximum wind-speed and dynamic pressure maps to reveal whether the tree-line ecotone is influenced by direct wind effects. On average, the tree-line ecotone on the eastern slopes shows a clear average depression of ~50 m. These slopes are affected by higher dynamic wind stress, so have a more disturbed canopy. These altered vegetation structures may be caused mainly by direct wind effects and to a smaller extent by indirect effects, such as high humidity.

Abstract:

The precise estimation of precipitation quantities in tropical mountain regions is in great demand by ecological and hydrological studies, due to the heterogeneity of the rainfall distribution and the lack of meteorological station data. This study uses radar images and ground station data to provide the required high-resolution precipitation maps. Also wind data are taken into account, due to its influence on the precipitation formation and to demonstrate the relation between synoptic wind, topography and the precipitation distribution inside small mountain valleys. The study analyses the rainfall distribution and amounts of 4 days inside the San Francisco Valley, a small catchment in the tropical Andes of southern Ecuador, representing different seasons and the typical atmospheric flows, which are correlated to the annual precipitation map. The results show that the rainfall distribution and amounts are generally defined by the wind direction and velocity, besides the topographic location in relation to the main barriers and pathways. The dominant wind direction causes a division of the catchment in a wetter eastern and a dryer western part. Moreover, the annual seasons are reversed; the main rainy season for the eastern part occurs between June and August, while the western part reaches the precipitation maximum between January and March. This may have influence on the species composition at the different slopes and the annual hydrological cycle inside the catchment.

Abstract:

Systematic investigations of the upper forest line (UFL) primarily concentrate on mid and high latitudes of the Northern Hemisphere, whereas studies of Neotropical UFLs are still fragmentary. This article outlines the extraordinary high tree diversity at the UFL within the Andean Depression and unravels the links between the comparatively low position of the local UFL, high tree-species diversity, and climate. On the basis of Gentry?s rapid inventory methodology for the tropics, vegetation sampling was conducted at 12 UFL sites, and local climate (temperature, wind, precipitation, and soil moisture) was investigated at six sites. Monotypic forests dominated by Polylepis were only found at the higher located margins of the Andean Depression while the lower situated core areas were characterized by a species-rich forest, which lacked the elsewhere dominant tree-species Polylepis. In total, a remarkably high tree-species number of 255 tree species of 40 different plant families was found. Beta-diversity was also high with more than two complete species turnovers. A non-linear relationship between the floristic similarity of the investigated study sites and elevation was detected. Temperatures at the investigated study sites clearly exceeded 5.5°C, the postulated threshold value for the upper tree growth limit in the tropics. Instead, quasi-permanent trade winds, high precipitation amounts, and high soil water contents affect the local position of the UFL in a negative way. Interestingly, most of the above-mentioned factors are also contributing to the high species richness. The result is a combination of a clearly marked upper forest line depression combined with an extraordinary forest line complexity, which was an almost unknown paradox.

Abstract:

Water-bound nitrogen (N) cycling in temperate terrestrial ecosystems of the Northern Hemisphere is today mainly inorganic because of anthropogenic release of reactive N to the environment. In little-industrialized and remote areas, in contrast, a larger part of N cycling occurs as dissolved organic N (DON). In a north Andean tropical montane forest in Ecuador, the N cycle changed markedly during 1998–2010 along with increasing N deposition and reduced soil moisture. The DON concentrations and the fractional contribution of DON to total N significantly decreased in rainfall, throughfall, and soil solutions. This inorganic turn of the N cycle was most pronounced in rainfall and became weaker along the flow path of water through the system until it disappeared in stream water. Decreasing organic contributions to N cycling were caused not only by increasing inorganic N input but also by reduced DON production and/or enhanced DON decomposition. Accelerated DON decomposition might be attributable to less waterlogging and higher nutrient availability. Significantly increasing NO3-N concentrations and NO3-N/NH4-N concentration ratios in throughfall and litter leachate below the thick organic layers indicated increasing nitrification. In mineral soil solutions, in contrast, NH4-N concentrations increased and NO3-N/NH4-N concentration ratios decreased significantly, suggesting increasing net ammonification. Our results demonstrate that the remote tropical montane forests on the rim of the Amazon basin experienced a pronounced change of the N cycle in only one decade. This change likely parallels a similar change which followed industrialization in the temperate zone of the Northern Hemisphere more than a century ago.

Abstract:

In the anthropogenic fire-disturbed ecosystem of the San Francisco Valley in the Andes of southeastern Ecuador, dense stands of an aggressive invasive weed, the southern bracken fern (Pteridium arachnoideum and Pteridium caudatum), dominate the landscape. To secure sustainable land management in the region, a comprehensive understanding of bracken spatial-distribution patterns and life cycle dynamics is crucial. We investigated the possibility of detecting bracken-infested areas and frond status (live, fungi-infected, and dead) by means of a high-resolution QuickBird scene from October 2010 and spectral signatures based on field spectroscopy. After image pre-processing, a two-step classification procedure first delineates the bracken-infested area by means of a maximum-likelihood hard classification. The probability-guided unmixing classifier with field-derived end-members is applied in the second step to obtain the fractional cover of the different frond statuses per pixel. The results showed that the areas infested by bracken could be distinguished from the other land-cover classes with high accuracy (overall accuracy of 0.9973). Also, the three frond statuses could be accurately classified at the sub-pixel level. The ‘dead’ class was the dominant frond status at the time of image acquisition (October 2010). We conclude that the extreme dry spell in October 2010 was particularly responsible for this dominance.

Abstract:

Areas with high landslide activity and diversity were encountered in the tropical Andes of Southern Ecuador under contrasting, semi-arid to perhumid climatic conditions. The objective of this study was to determine and compare geomorphic process rates of shallow landslides along this remarkable humidity gradient and subject to different types of human-made and natural environmental changes. Geomorphic work, geomorphic power and landslide mobilization rate (LMR) were therefore calculated for shallow landslides in two study areas with two separate geological or land use-related subareas each. While landslide ages were known in the perhumid Reserva Biológica San Francisco (RBSF) area, only an approximation of the frequency of critical landslide-triggering rainfall events was available for the semi-arid Masamanaca area. Landslide volumes were estimated by volume–area scaling. Generalized additive models (GAMs) were used as landslide susceptibility models in order to analyze the relative importance of topography, and to downscale LMR values to a fine spatial resolution. LMR in the perhumid RBSF area ranged from ˜2 mm yr-1 in the natural part of this area with tropical mountain rainforests to ˜5 mmyr-1 in the human-influenced part. The semi-arid Masamanaca area, though subject to greater estimation uncertainties, displayed LMR on the order of ˜0.4 to 4 mm yr-1 for shallow landslides. The results provide a basis for the spatially differentiated assessment of landscape evolution and degradation in an area with a close relation between landslide activity, natural vegetation succession and human land use.

Abstract:

The near surface humidity in a megadiverse mountain ecosystem in southern Ecuador is examined on the basis of Relative Humidity (RH) measurements inside the natural mountain forest and at open sites along an altitudinal gradient from 1700 to 3200 m. The main methodological aim of the current study is to generate a humidity regionalization tool to provide spatial datasets on average monthly mean, minimum and maximum RH, Specific Humidity (q) and Specific Saturation Deficit (DS) by using observation data of RH. The maps based on data of the period 1999–2009 are needed by ecological projects working on various plots where no climate station data are available. The humidity maps are generated by combining a straightforward detrending technique with a Digital Elevation Model and a satellite-based land cover classification which also provides the relative forest cover per pixel. The topical aim of the study is to investigate the humidity distribution and structure of both manifestations of our ecosystem (pastures and natural vegetation) with special considerations to the ecosystem regulation service by converting natural forest into pasture. The results reveal a clear differentiation over the year, partly triggered by the change of synoptic weather situation but also by land cover effects. Humidity amplitudes are particularly low during the main rainy season when cloudiness and rainfall are high, but markedly pronounced in the relative dry season when daily irradiance and outgoing nocturnal radiation causes distinct differences between the land cover units. Particularly the upper pasture areas gained by slash and burn of the natural forest exhibit the lowest humidity values while the humidity inside the mountain forest is significantly higher due to the regulating effects of the dense vegetation. Thus, clearing the forest clearly reduces the regulation function (regulating ecosystem services) of the ecosystem which might become problematic for reforestation under future global warming.

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:

The ecology of tropical bracken, which occurs in tropical regions, is not well known. We studied its response to weather variations and burning in the south Ecuadorian Andes, where this weed had already overgrown 40% of the pastureland. In field observations, a constant 1:1 ratio of emerging and dying leaves suggested limitation of frond density by nutrient shortage. Short-term deviations from that ratio could be related to weather variations. Spells of dry weather temporarily increased mortality but stimulated emergence of new fronds. Lifespan of the fronds produced immediately after a fire was longer than of those produced during unaffected bracken growth. A burst of frond development during the initial 2 to 3 mo was observed after a fire followed by self-thinning to a stable level. To analyze the effect of fire on bracken, rhizomes were treated with heat pulses. Rhizomes were heat tolerant up to 70 C, and frond production from short shoots was enhanced by elevated temperature. Burning apparently releases apical dominance of developed fronds, as does cutting, and stimulates bud break. The local practice of pasture maintenance in Ecuador of repeated burning favors growth of the fern.

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:

The thermal structure of a megadiverse mountain ecosystem in southern Ecuador is examined on the basis of temperature measurements inside the natural mountain forest and at open-sites along an altitudinal gradient from 1600 to 3200 m. The main methodological aim of the current study is to develop an air temperature regionalization tool to provide spatial datasets on average monthly mean, minimum and maximum temperature by using observation data. The maps, based on data of the period 1999?2007, are needed by ecological projects working on various plots where no climate station data are available. The temperature maps are generated by combining a straightforward detrending technique with a Digital Elevation Model and a satellite-based land cover classification which also provides the relative forest cover per pixel. The topical aim of the study is to investigate the thermal structure of both manifestations of our ecosystem (pastures and natural vegetation) with special considerations to the ecosystem temperature regulation service by converting natural forest into pasture. The results reveal a clear thermal differentiation over the year, partly triggered by the change of synoptic weather situation but also by land cover effects. Thermal amplitudes are particularly low during the main rainy season when cloudiness and air humidity are high, but markedly pronounced in the relative dry season when daily irradiance and outgoing nocturnal radiation cause distinct differences between the land cover units. Particularly the lower pasture areas gained by slash and burn of the natural forest exhibit the most extreme thermal conditions while the atmosphere inside the mountain forest is slightly cooler due to the regulating effects of the dense vegetation. Thus, clearing the forest clearly reduces the thermal regulation function (regulating ecosystem services) of the ecosystem which might become problematic under future global warming.

Abstract:

This paper deals with natural disturbances and their impact on vascular plant enrichment at two climatically contrasting Andean ranges, i.e. the perhumid Cordillera Real in southern Ecuador and the arid Cordillera de Atacama in northern Chile. In the first case, main triggers for an additional input of pioneer species during succession stages initiated by perturbations are landslides, mudflows, and, to a lesser extent, cohort mortality, floods, and wildlife damages. Droughts and wind are stressors, which reduce plant growth but hardly plant diversity, in contrast to enhanced UV radiation with its mutagen effect. Though stress effects are similar in the Atacama, disturbance regimes differ considerably in this dry mountain environment. Here, most perturbations are of small dimension such as nitrogen inputs by feces of Lamoids and burrow activities of tuco-tuco mice, both of them fostering nitrophilous plant communities. Flooding, gelifluction, and other denudation processes such as sheet wash occur too, however, do not charge species enrichment in the dry Andes. Although the perhumid study site represents one of the world’s plant diversity “hotspots” and, by contrast, the arid one a comparatively “coldspot”, pioneer species during successive stages after natural disturbances contribute in a similar percentage to the total plant inventories (appr. 10% of the species numbers). Relatively seen, natural disturbances are most important for species enrichment in the Atacama (200–500 species per 10 000 km2), while most other ecological factors delimit plant survival. Instead, plant life at the Ecuadorian study area benefits from many climatic and edaphic site conditions, and consequently, disturbances are considered only one of many driving forces for its hotspot status (>5000 species per 10 000 km2).

Abstract:

Long-term field studies in the scope of a multidisciplinary project in southern Ecuador revealed extraordinary high species numbers of many organismic groups. This article discusses reasons for the outstanding vascular plant diversity using a hierarchical scale-oriented top-down approach (Grüninger 2005), from the global scale to the local microscale. The global scale explains general (paleo-) ecological factors valid for most parts of the humid tropics, addressing various hypotheses and theories, such as the ?greater effective evolutionary time?, constant input of ?accidentals?, the ?seasonal variability hypothesis?, the ?intermediate disturbance hypothesis?, and the impact of soil fertility. The macroscale focuses on the Andes in northwestern South America. The tropical Andes are characterised by many taxa of restricted range which is particularly true for the Amotape-Huancabamba region, i.e. the so called Andean Depression, which is effective as discrete phytogeographic transition as well as barrier zone. Interdigitation of northern and southern flora elements, habitat fragmentation, geological and landscape history, and a high speciation rate due to rapid genetic radiation of some taxa contribute to a high degree of diversification. The mesoscale deals with the special environmental features of the eastern mountain range, the Cordillera Real and surrounding areas in southern Ecuador. Various climatic characteristics, the orographic heterogeneity, the geologic and edaphic conditions as well as human impact are the most prominent factors augmenting plant species diversity. On microscale, prevailing regimes of disturbance and environmental stresses, the orographic basement, as well as the general role on the various mountain chains are considered. Here, micro-habitats e.g. niches for epiphytes, effects of micro-relief patterns, and successions after small-sized disturbance events are screened. Direct effects of human impact are addressed and a perspective of possible effects of climate change on plant diversity is presented.