Novel planting regimes for herbivore reduction in the tropics
Plantations of native timber species established on former pasture are considered as an eligible strategy to reduce the logging pressure on remnant natural forests in the tropics. Such plantations may help to mitigate or reverse the negative impacts of land degradation, and they may contribute to the long-term livelihood of livestock farmers. Planting native trees is, however, perceived as a risky activity due to limited knowledge on their performance and due to marked losses of newly established seedlings attributed to insect pests.
We study the effects of different planting schemes (monoculture, tree mixture, companion planting with multipurpose trees, insecticide treatment) on survival and growth of native timber trees planted on former pasture. In addition, we quantify the effects of planting schemes on tree-associated arthropods as well as on damage by insect herbivores, with the goal to assess top-down (impact of beneficials) and bottom-up (impact of defensive plant traits) pest management options as a basis for a cost-effective and sustainable protection of native tropical timber trees in plantations on former tropical pasture. Plant traits and environmental parameters with high potential to support beneficials in suppressing pests are determined and experimentally manipulated in parallel to assessments of herbivores and beneficials in the plantation. Published findings from these studies are listed under “Publications” on this website. They reveal how beneficials as well as innovative planting regimes can be used as natural, locally available resources to limit pest damage and to enhance growth of high-value trees. Ultimately, the findings are expected to enhance reforestation efforts and to contribute to improved income generation of small-scale farmers in Central America.
|Fig. 1: Monoculture and mixed plantations of the timber trees Anacardium excelsum, Tabebuia rosea and Cedrela odorata four years after establishment.||Fig. 2: Damage to Tabebuia rosea by chrysomelid beetles.|
|Fig. 3: Mirco Plath collecting insects at night.||Fig. 4: Judith Riedel heading for arthropod sampling in tree canopies.|
Department of Geography, McGill University
M.Sc. student Muriel Abraham and I are examining soil properties in the field converted from pasture to plantation, in the control pasture field and in a undisturbed forest at Barro Colorado Island National Monument. The purpose is to define the soil properties before the plantation was installed, to compare them with soils developed under forest and to provide a detailed data base to evaluate what changes have been brought about by the plantation.
Soil sampling was conducted in July 2001 and in the following summer. Samples from 0 – 10 cm were collected on a 15 m grid in the plantation field, with nested clusters down to 0.25 m spacing. A similar scheme was employed in the pasture and forest. Seven soil profiles down to 1 m were sampled in the plantation field, covering the major topographic/soil units. This sampling will allow the detailed mapping of soil properties and the use of geo-statistics to define spatial variability. Soil samples will be archived.
Analyses include bulk density, water content, pH and C and N content and mass. 13C signatures of selected soil samples and plant tissues are being determined to allow us to establish the origin of the soil organic matter and to define the end member inputs as the soils change. Earlier work in an adjacent field has shown that most of the surface soil organic matter in the plantation field was derived from the grasses, mainly C4, but that when converted to a teak plantation, there was rapid replacement with organic matter from C3 plants. Organic matter turnover times were estimated to be between 18 and 30 years, in these clay-rich soils, similar to estimates by Giardina and Ryan (2000).
Our early work at the Sardinilla biodiversity experiment focused on litter production and litter decomposition, a key process in nutrient cycling (Scherer-Lorenzen et al. 2007, Oikos 116: 2108-2124). We found that tree diversity could increase litter production, especially at the intermediate 3-species richness level in cases where species with contrasting life histories were combined. We observed no overall effect of litter diversity if the entire litter mixtures were analyzed, i.e. mixing species resulted in pure additive effects and observed decomposition rates were not different from expected rates. However, the individual species changed their decomposition pattern depending on the diversity of the litter mixture, i.e. there were species-specific responses to mixing litter.
A later study investigated the effects of increasing tree species richness on nutrient cycling, focusing on nitrogen (N) and phosphorus (P), done in cooperation with Jan Jansa and Fabienne Zeugin (Institute of Plant Sciences, ETH Zurich). Our results showed a positive but not consistent net effect of biodiversity on the N and P pools, mainly explained by the complementarity effect (Zeugin et al. 2010, Forest Ecology and Management 260: 1424-1433). N and P use efficiencies strongly varied among the investigated tree species and the species richness gradient. Although the environmental conditions explained a large part of the variation in the N and P pools (58%), we argue that incorporating tree mixtures in the management can bring additional benefits and improve tree growth and nutrient uptake as compared to the monocultures.
Additional analyses included an isotope-based quantification of uptake of different nitrogen forms at various depths to detect niche differentiation and complementary resource use among coexisting tree species. Finally, we examined to what extent P-uptake can be modulated by tree diversity and the presence or absence of mycorrhizal (Zeugin 2010.PhD dissertation, ETH Zurich).
Recently, we are collaborating in a joint effort to quantify nutrient pools and fluxes after 10 years of growth, using nutrient concentrations in the Xylem sap as a proxy for short-term nutrient availability in the soil.
The ETH Zurich team at the field site (April 2006)
From left to right: Michael Scherer-Lorenzen, Carole Grob, Fabienne Zeugin and Jan Jansa
Jan Jansa digging for roots
Root sorting: Carole Grob & Fabienne Zeugin
Stem coring: Michael Scherer-Lorenzen
Tree diversity as a control of the element cycles of individual trees in experimentally assembled mixtures in Panama (funded by the German Research Foundation [DFG], Grant # Wi 1601/6-1)
Yvonne Oelmann, (Geography, Eberhard-Karls-University Tuebingen, Germany)
Wolfgang Wilcke, (Geographic Institute, University of Berne, Switzerland)
It has been shown that species identity and composition are important drivers of element fluxes. Model approaches introducing species identity into ecosystem models, which traditionally treat biota as a black box, are rare. To include diversity effects into ecosystem models, the influence of individual species on element cycles must be known. Therefore, we study the effect of tree diversity on element cycling. Our objectives are: (1) to set up element budgets for five tree species in monoculture, and (2) to assess the effect of tree diversity (1-, 3-, and 6-species mixtures) on the element budget of each tree species, and (3) to introduce diversity effects into an existing model of biogeochemical cycles in forests based on the interaction between neighboring trees.
With these goals we plan to test the following hypotheses:
1. Element fluxes of individual trees differ between species as a result of species-specific traits ("species identity matters").
2. Element fluxes and storages of individual trees and of soil increase with increasing diversity of neighboring trees.
We will determine element storage in all relevant ecosystem compartments and the main element fluxes.
The effect of tree species and tree diversity on ecosystem respiration in a tropical tree plantation
Norbert Kunert, Max Planck Institute for Biogeochemistry, Jena, Germany and Luitgard Schwendenmann, School of Environment, The University of Auckland, Auckland, New Zealand
The establishment of tropical tree plantations is of increasing importance to meet the demand for timber and to rehabilitate degraded sites. Tree plantations often consist of a single exotic fast growing species. There is increasing concern about non-sustainable water and soil nutrition use by such mono-specific plantations. Recent approaches to reforestation in the tropics emphasize the establishment of mixed stands because of higher productivity and hence enhanced carbon storage. The proposed project will analyze heterotrophic and autotrophic respiration (leaf, stem and soil respiration measurements)within stands varying in tree species richness (1-, 3-, and 6-species mixtures). Overall, the project will improve our understanding of the components contributing to overall ecosystem respiration in mono-specific and mixed native species stands in a tropical tree plantation.
The role of biodiversity on decomposition and nutrient cycling in forest ecosystems
Tanya Handa, Université du Québec à Montréal
As part of my broader interest on the role of biodiversity on decomposition and nutrient cycling in forest ecosystems, in collaboration with Michael Scherer-Lorenzen, Catherine Potvin and several graduate students, we aim to quantify decomposition of detrital pools (leaf litter, root litter and coarse woody debris) in the Sardinilla plantation and understand ultimately, how functional diversity of the detritus and detritivores impact the decomposition process within and between trophic levels. Specifically, we seek to understand:
a) the relation between tree species diversity and decomposition rates in the experimental plots and whether functional diversity of detritus can explain any observed net biodiversity effects (Master student Nathaly Guerrero with current focus on roots);
b) the extent of colonisation by detritivorous soil macrofauna in the plantation plots after a decade, whether their presence alters decomposition rates and if functional trait dissimilarity of the fauna can be used to explain process rates and colonization success (sub-project of PhD student Pierre-Marc Brousseau).
We hypothesize that:
(H1) increasing tree species diversity will result in overall faster decomposition of leaf litter, root litter and coarse woody debris based on positive complementary interactions when functional dissimilarity of litters is the highest;
(H2) soil macrofauna will be more abundant and diverse in plots with higher tree species richness due to more available niche space (chemical and structural diversity of litter);
(H3) the presence of functionally dissimilar detritivores will accelerate decomposition and
(H4) increasing functional dissimilarity at the detritus and detritivore level will interactively result in faster litter decomposition.
Last update: Jan. 16, 2013