Kristin Roos

Growth of Tropical Bracken (Pteridium arachnoideum): Response to Weather Variations and Burning

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. Nomenclature: Bracken, Pteridium aquilinum agg. (L.) Kuhn; tropical bracken (bracken of the southern hemisphere), e.g., neotropical Pteridium arachnoideum (Kaulf.) Maxon and Pteridium caudatum (L.) Maxon

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.

Forest Clearing by Slash and Burn

Burning is still the common method used by settlers (Colonos ; see Chapter 3 in this volume) to clear the primary forest for new farming areas. Every fire , irrespective of being lit inside or at the edge of the forest, kills the trees by burning or by the emerging heat. A fringe of dead, but not charred, trees is always found where forest has been cleared by fire. Later, when these heat-killed trees have completely dried up, they can be used to start a new fire.

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.

Current Provisioning Services : Pasture Development and Use, Weeds (Bracken) and Management

This chapter reports on the historical expansion and current state of the pastures in the Rio San Francisco valley. Its major part is inhabited by the Mestizos, who do not have a long-standing pasture tradition. Three types of pastures were identified by the dominant grass species: the “pastos azules” (Holcus lanatus), the Yaragua pastures (Melinis minutiflora) and the dominating “pastos mieles” (Setaria sphacelata). The peculiarities, species composition, soil dynamics and agricultural values of these pastures are discussed. Except for the pastos azules on small flattenings in the otherwise steep slopes of the valley, pastures in the area suffer from invasion by aggressive weeds, mainly the tropical bracken fern. Abandonment of pastures is fostered by the use of fire to combat weeds and stimulate grass growth. This type of low-yield pasture farming is not sustainable. The earnings of livestock farming are not sufficient for subsistence. Diversification of the income portfolio is necessary.

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.