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:

The worldwide demand for large scale biodiversity monitoring systems is challenging for recent remote sensing techniques. For monitoring changes in species as well as functional diversity the consideration of ecosystem processes is crucial. Herbivory as a focal function in tropical forest ecosystems is therefore being investigated in this study. Aim of the study is to reveal the potential of remotely sensed image textures for predicting herbivory. For this leaf area loss (LAL) due to herbivory has been quantified in different vegetation layers of a tropical mountain forest in the Ecuadorian Andes. The study area is a structurally highly complex region along an elevation gradient from 1000 to 3000 m a.s.l. with undisturbed primary forest and disturbed forest fragments within agriculturally used land. It has been proven that LAL has similar patterns as herbivore abundance over the elevation gradient showing it to be a possible proxy for herbivore abundance. Further results show a correlation of LAL data and canopy cover thus local forest structure. Correlations between LAL and image textures as a proxy for vegetation structure were stronger than with pixel wise derived spectral values only. Unveiling the high potential of image textures as a surrogate for herbivory and ecosystem function.

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:

Within this chapter relative air humidity, evaporation, transpiration, evapotranspiration, hydrologic cycle and water balance are discussed for the Tropics. In general, atmospheric water is of high climatological importance due to its capacity to control precipitation as well as to its influence on absorption and reflection of solar and terrestrial radiation. When water changes its state of aggregation, energy is either produced or consumed. This is crucial for the tropical atmosphere where the condensation of large amounts of water vapor leads to the release of latent heat energy. The global hydrosphere consists of a couple of different water reservoirs which are connected by water fluxes in various phases. From these reservoirs, water moves in a great series of continuous interchanges of both physical state and geographical position, known as the hydrologic cycle. Evapotranspiration is one of the most important factors for the water budget and physical processes in the tropics. It specifies the total flow of water into the atmosphere which is composed of two processes: evaporation and transpiration.

Abstract:

Within this chapter the Hadley Circulation, the Monsoon System, Easterly Waves, Tropical Cyclones and the Walker Circulation are discussed. While the Hadley Circulation and the Monsoon System explain different air flow systems in a mainly meridional sense, a secondary system of latitudinal wind flow is governed by the Walker circulation which is decisive for the formation of La Niña and El Niño events. Apart from the long-term seasonal and nonseasonal variations of the tropical atmosphere, the climate of the Tropics is also affected by more frequent tropical weather disturbances. One of them are large-scale planetary waves which produce greater amounts of rainfall in many maritime tropical regions. These disturbance lines sprawl in a meridional direction from east to west and are called easterly waves.

Abstract:

A main character of the entire tropics are the very low longitudinal gradients of air temperature of only 1 °C/1,000 km. In Fig. 1 (above) this is indicated by the broad reddish sector around the equator between 30°N and S and even beyond. A closer look at the upper image reveals darker patterns and hence the globally "hottest ecozone" over the Sahel and southern Sahara to the SE of the Arabian Peninsula. By far most of this section is part of the outer tropics. This "heat crest" north of the equator represents a thermal asymmetry and is linked to the large dimension of landmass in the northern half of Africa. Vertical termperature gradients in tropical mountains as well as changing meridional gradients of temperature amplitudes between the outer and inner tropics are presented by Figs. 2 and 3, resp. Diurnal an seasonal cycles are illustrated by thermoisopleths for different altitudes and under arid up to perhumid conditons (Figs. 4 and 5), which are also exampled for soil and surface temperatures (Fig. 6). Impacts of cold as well as of dry air intrusions (Figs. 7-9) are related to plant reactions and phenological aspects (Fig. 10).

Abstract:

Within this chapter different aspects of radiation and heat are discussed for the tropics. On a global scale the amount of annual solar radiation reaching the Earth's surface is determined by atmospheric and astronomical factors and the average energy budget of the Earth could be explained by the global radiation budget. Within the tropics the net radiation varies clearly across the different climatic regions. In the humid tropics the amount of net radiation shows an almost uniform annual pattern with two maxima per annum. In contrast to this, the horizontal course of the isopleths in a radiation isopleths diagram for the marginal tropics still indicates a marked diurnal cycle. At the Earth's surface, the total incoming radiation is transformed into different heat fluxes which are either directed towards the ground or to the atmosphere. In the tropical rainforests, only 10 % of the incoming radiation reaches the ground, and only a weak flow of sensible and latent heat exists from the forest canopy towards the forest ground and vice versa.

Abstract:

Large scale moisture patterns subdevide the year-round tropics from perarid up to perhumid subzones, which are combined with different degrees of cloudiness (Fig. 1) with convective heap clouds being of most importance (Figs. 2, 3, 4 and 5). A rather clear seasonal distribution of rainfall frequency and intensity (Fig. 7) governs the rythm of plant growth. Areas of highest precipitation amounts on the globe are concentrated on the inner parts of the tropics (Fig. 8), where thunderstorms are a typical feature of weather occurence. Long enduring droughts in wet as well as extraordinary rainfall intensities in arid regions are concentrated on distinct areas (Figs. 11 and 12). Most of the tropical high mounts show obvious "bulges" of enhanced rainfall rates at mid-elevations (Fig. 15).

Abstract:

Microclimatic differences between site conditions of forest ecosystems and farmlands are accented to clarify the significant importance of tree canopies for ecosystem services and agroforestry. An analyis of the climate within a tropical rainforest and its impact on epiphytic structure is given by Fig. 2. After forest conversion into farmland, radiation turnovers and energy flows as well as precipitation rates change dramatically (Figs. 3 and 4). Furthermore, clear-cuts of tropical forests enhance in destructive erosion processes during tropical downpours (Figs. 5, 6, and 8), which can reach impressive amounts during hurricane events (Fig. 7).

Abstract:

One of the most important climate criteria of the tropics is the absence of thermic seasons. Thus, hygric seasons become more relevant for ecosystem functioning and are of special importance for plant growth. Within this chapter different climate types of the tropics are discussed on the basis of their annual water budget. The humid climate type appears across the rain equator within or close to the ITCZ. It is distinguished by a clear water surplus and all months show a positive water balance in the long-term mean. The semi-humid climate type prevails at a certain distance from the Equator and the ITCZ. It is characterized by a distinct rainfall seasonality and the occurrence of more than 3 -4 arid months. In terms of the arid climate type the arid period is in general longer than the humid period and precipitation amounts decrease almost towards zero within the desert areas.

Abstract:

In this chapter, different aspects of climate variability at different time and spatial scales and their possible influences on ecosystems and biodiversity are discussed. A comprehensive full survey on climate change is presented in the fifth IPCC(Intergovernmental Panel on Climate Change) assessment report 2013/2014.

Abstract:

Unlike the high latitudes and most of the mid-latitudes, the tropical ecozone benefits from a constant radiation surplus. In daytime, the sunrays descend at a steep angle up to 90° at noon between the tropics twice per year. Hence,long-term shaded slopes in mountain landscapes do not exist. Lengths of day and night stay almost the same at the equator (approx. 12 h.), while at the Tropics of Cancer and Capricorn, minimum and maximum day lengths vary within a time span from 10.5 to 13.5 h. As a result marked thermal seasons are absent in the tropical climates.

Abstract:

Differences in the thermic and hygric seasonalities cause decisive distinctions between extratropical and tropical plant growth features. Around the tropics of Capricorn and Cancer noticeable seasonal cycles of temperature still occur, which are of minor importance within the megatherm inner tropics. Two classification systems offer a subdivision of the tropical climates. Compared to the frequently used Koeppen-approach, that one of Lauer is prefered here due to its clearly defined hygrothermal regimes. Altitudinal climate belts in the tropics are presented by a general scheme, while climate and vegetation profiles reflect a realistic situation alongside the neotropical Cordilleras.

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:

Deforestation for gaining pastures and croplands is still advancing in the tropical Andes while vast agricultural areas are at the same time disused due to degradation (FAO 2011). In the research area in South Ecuador infestation by bracken (Pteridium spp.) plays an important role in this regard (Göttlicher et al. 2009), especially where fire is used for forest clearing or in pasture management (Hartig & Beck 2003, Roos et al. 2010). The focus of our study was: (1) the analysis of the infestation rate of bracken on agricultural land, (2) to reconvert bracken-infested areas into useful pastures, and (3) to find a sustainable management for the rehabilitated pastures. Bracken cover was analyzed using high resolution satellite data (QuickBird) on which bracken could be identified from the spectral reflection. Actually, almost 40% of the potential mountain pastures in the research area have been abandoned, because they are overgrown by the weed. An experiment extending over several years was conducted to reconvert these abandoned areas into pastures (Roos et al. 2011): A two-step strategy seemed to be successful. In a first step, the efficacy of 13 bracken control treatments was compared with the vegetation development in untreated plots. Two of the measures proved to be successful and at the same time affordable for the local farmers, namely periodical cutting of the weed with a machete or repeated spraying of a locally available herbicide ?Combo? (a mixture of metsulfuron methyl and picloram) (Figure 1A). However, due to brackens persistent rhizomes in various soil depths, only ponderable weakening of the weed could be achieved, but not complete eradication. In a next step, the common pasture grass Setaria sphacelata (a highly competitive C4-grass) was planted. About 1.5 years later, the grass had reached a cover of more than 70% suppressing the fern to a cover of less than 40% and grazing could start (Figure 1B). Growth of bracken and of Setaria was monitored monthly using cover and height of vegetation as variables. Different extensive and intensive management treatments (various grazing intensities in combination with fertilization regimes) were applied to the rehabilitated pasture plots, and the effects on biomass gain and protein content of Setaria were analyzed. Additionally, vegetation composition depending on the treatments was compared with existing pastures. Regrowing bracken fronds should be removed annually with the machete to maintain the weed on a low stage. Following the described protocol, repasturisation requires about 2.5 years until the pastures can be used. Applying a balanced management of fertilization and grazing can lead into a sustainable reutilization of the abandoned areas and thus alleviate the pressure on the natural forests.

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.