Brenner Silva

Afforestation or intense pasturing improve the ecological and economic value of abandoned tropical farmlands

Increasing demands for livelihood resources in tropical rural areas have led to progressive clearing of biodiverse natural forests. Restoration of abandoned farmlands could counter this process. However, as aims and modes of restoration differ in their ecological and socio-economic value, the assessment of achievable ecosystem functions and benefits requires holistic investigation. Here we combine the results from multidisciplinary research for a unique assessment based on a normalization of 23 ecological, economic and social indicators for four restoration options in the tropical Andes of Ecuador. A comparison of the outcomes among afforestation with native alder or exotic pine, pasture restoration with either low-input or intense management and the abandoned status quo shows that both variants of afforestation and intense pasture use improve the ecological value, but low-input pasture does not. Economic indicators favour either afforestation or intense pasturing. Both Mestizo and indigenous Saraguro settlers are more inclined to opt for afforestation.

Bracken fern frond status classification in the Andes of southern Ecuador: combining multispectral satellite data and field spectroscopy

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.

Dynamic Mapping of Evapotranspiration Using an Energy Balance-Based Model over an Andean Páramo Catchment of Southern Ecuador

Understanding of evapotranspiration (ET) processes over Andean mountain environments is crucial, particularly due to the importance of these regions to deliver water-related ecosystem services. In this context, the detection of spatio-temporal changes in ET remains poorly investigated for specific Andean ecosystems, like the paramo. To overcome this lack of knowledge, we implemented the energy-balance model METRIC with Landsat 7 ETM+ and MODIS-Terra imagery for a paramo catchment. The implementation contemplated adjustments for complex terrain in order to obtain daily, monthly and annual ET maps (between 2013 and 2014). In addition, we compared our results to the global ET product MOD16. Finally, a rigorous validation of the outputs was conducted with residual ET from the water balance. ET retrievals from METRIC (Landsat-based) showed good agreement with the validation-related ET at monthly and annual steps (mean bias error <8 mm·month−1 and annual deviation <17%). However, METRIC (MODIS-based) outputs and the MOD16 product were revealed to be unsuitable for our study due to the low spatial resolution. At last, the plausibility of METRIC to obtain spatial ET retrievals using higher resolution satellite data is demonstrated, which constitutes the first contribution to the understanding of spatially-explicit ET over an alpine catchment in the neo-tropical Andes.

Mapping Two Competing Grassland Species from a Low-Altitude Helium Balloon

This paper describes a method of low-altitude remote sensing in combination with in situ measurements (leaf area, spectroscopy, and position) to monitor the postfire canopy recovery of two competing grassland species. The method was developed in the Andes of Ecuador, where a tethered balloon with a digital camera was deployed to record a time series of very high spatial resolution imagery (nominal resolution=2 cm ) of an experimental plot covered by two competing species: 1) the pasture grass, Setaria sphacelata; and 2) the invasive southern bracken, Pteridium arachnoideum. Image processing techniques were combined to solve geometric issues and construct high-quality mosaics for image classification. The semiautomatic and object-oriented classification method was based on geometrical and textural attributes of image segments and showed promising results for detecting the invasive bracken fern in Setaria pastures (performance by area under the curve, AUC = 0.88). Valuable insights are given into vegetation monitoring applications using unmanned aerial vehicles, which produces a time series of species-specific maps, including foliage projective cover (FPC) and leaf area index (LAI). This new method constitutes an important and accessible tool for ecological investigations of competing species in pastures and validation of remote sensing information on mountain environments.

Impacts of Local Land-Use Change on Climate and Hydrology

Land-use change has a potentially large impact on local water resources and climatic conditions in montane rainforest ecosystems of the Andes. Based on local meteorological observations and site-specific simulation studies involving a coupled hydrological model and a soil–vegetation–atmosphere transfer scheme, we are able to predict likely changes of water and energy fluxes for different land-use categories. To anticipate the effect of future land-use change on the water and energy budgets of the study area, we use results of statistically derived land-use scenarios and a coupled plot scale model representing the dominant land-use types for further upscaling. After assessing the impact of land-use change on ecosystem services we conclude that climate regulation will be decreasing due to a likely increase in drought vulnerability and that the discharge will remain stable or even slightly increase, thereby positively effecting provisioning and regulating hydrological services.

Remote sensing of vegetation in a tropical mountain ecosystem: Individual tree-crown detection

The hotspot of biodiversity in the Andes of Southern Ecuador has been severely threatened by climate change and unsustainable land use. The high biodiversity requires strategies for conservation and management of natural resources to be developed at both individual and area-wide levels. In this paper we focus on the development of an automatic treecrown detection and classification approach, which is in line individual-based investigations in the tropical mountain environment. Airborne laser scanning of discrete type was used with a very high granularity (<10 returns per square meter). The individual tree crown detection reached an accuracy of 51% while supervised classification of palm-trees reached an accuracy of 69%. Accuracy measurements are given in the paper. The detection and characterization of individual tree crowns is the first step in the development of a monitoring approach for the tropical mountain forest.

Future Provisioning Services: Repasturisation of Abandoned Pastures, Problems, and Pasture Management

More and more pastures in the Rio San Francisco valley were and still are abandoned as a result of ecologically unbalanced pasture management, which promotes the invasion of weeds like bracken. Under the common pasture management, using fire as an agricultural tool, bracken by virtue of several ecophysiological traits can outcompete the grass. Competition of both species was investigated by the growth model SoBraCoMo. Vegetation development after burning of a bracken-infected pasture was followed by automated monitoring, using a balloon. To rehabilitate abandoned pastures, a three-step experiment was performed. Bracken control was followed by planting of the pasture grass Setaria sphacelata. Subsequently, different strategies for pasture management were examined. Fertilisation was crucial for the achievement of reasonable yields as well as for bracken suppression. Additionally, the prevention of negative nutrient balances of active pastures was investigated in an extended pasture fertilisation experiment (FERPAST). A specific combination of N and P is necessary to maintain soil productivity and to increase fodder quality.

Climate Change and Its Impact on Current and Future Vegetation Dynamics and Carbon Cycling

In this chapter, pasture and forest productivity and dynamics are investigated under global climate change impacts. Due to unsustainable management, pasture areas, mostly covered by Setaria sphacelata, are invaded by the aggressive Southern Bracken (Pteridium arachnoideum). The Southern Bracken Competition Model (SoBraCoMo) was applied to predict the development of the pasture-weed competition under IPCC-SRES A1B conditions. The model and respective physiological observations reveal an equal gain in performance of Setaria and bracken under global warming. In the forest, a potential increase in precipitation could boost landslide activity and thus affect growth dynamics. The forest-gap FORMIND model predicts a higher fraction of early successional species in tree species composition, which would reduce the aboveground carbon stocks. In summary, climate warming might not only improve regulating and supporting services on the pasture side (increased carbon sequestration, higher pasture yield), but also lead to a reduction of aboveground carbon stocks in the natural forest.

Who will win where and why? An ecophysiological dissection of the competition between a tropical pasture grass and the invasive weed Bracken over an elevation range of 1000 m in the tropical Andes

In tropical agriculture, the vigorously growing Bracken fern causes severe problems by invading pastures and out-competing the common pasture grasses. Due to infestation by that weed, pastures are abandoned after a few years, and as a fatal consequence, the biodiversity-rich tropical forest is progressively cleared for new grazing areas. Here we present a broad physiological comparison of the two plant species that are the main competitors on the pastures in the tropical Ecuadorian Andes, the planted forage grass Setaria sphacelata and the weed Bracken (Pteridium arachnoideum). With increasing elevation, the competitive power of Bracken increases as shown by satellite data of the study region. Using data obtained from field measurements, the annual biomass production of both plant species, as a measure of their competitive strength, was modeled over an elevational gradient from 1800 to 2800 m. The model shows that with increasing elevation, biomass production of the two species shifts in favor of Bracken which, above 1800 m, is capable of outgrowing the grass. In greenhouse experiments, the effects on plant growth of the presumed key variables of the elevational gradient, temperature and UV radiation, were separately analyzed. Low temperature, as well as UV irradiation, inhibited carbon uptake of the C4-grass more than that of the C3-plant Bracken. The less temperature-sensitive photosynthesis of Bracken and its effective protection from UV radiation contribute to the success of the weed on the highland pastures. In field samples of Bracken but not of Setaria, the content of flavonoids as UV-scavengers increased with the elevation. Combining modeling with measurements in greenhouse and field allowed to explain the invasive growth of a common weed in upland pastures. The performance of Setaria decreases with elevation due to suboptimal photosynthesis at lower temperatures and the inability to adapt its cellular UV screen.

Monitoring and modelling competing grassland species using very-high and high-resolution remote sensing in the Andes of Ecuador

A method is presented for monitoring and modeling of two competing grassland species (the southern bracken fern and the pasture grass Setaria). The method consists of estimating leaf area index for each species by using field observations and measurements, very-high and high-resolution images. The higher level of information at very-high resolution is used for identification of homogenous cover, on which a single species predominates. Consequently, ground measurements are used with high-resolution data to calculate species-specific regression functions between the normalized difference vegetation index and leaf area index. These data are used in a simulation run to extend the knowledge on occurrence and competition of bracken fern and Setaria pasture in the southern Ecuador.