Functioning and Resilience of Ecosystem Services in Tropical Rainforests
OPEN ACCESS
Author / Producer
Date
2023
Publication Type
Doctoral Thesis
ETH Bibliography
yes
Citations
Altmetric
OPEN ACCESS
Data
Rights / License
Abstract
Tropical rainforests have undergone vast degradation in the past decades. Changes in forest structure through removal of trees affects ecosystem functionality on multiple levels. For instance, the carbon cycle is being altered, not only by the removal of biomass, but also by changing environmental conditions, leading to changes in, for example, decomposition processes. This lowers the carbon storage density of forests. Forest degradation also affects the hydrological cycle: interception and evapotranspiration change, and soils of degraded forests might not be equally capable of infiltrating rainfall. This can lead to overland flow, soil erosion, and to reduced recharge of the ground water. It has further been warned that forest degradation reduces biodiversity, which in turn is an important driver for various ecosystem functions.
Consequently, the restoration of ecosystems is on political agendas, as well as in eco-market mechanisms in private industry, directed by individual customers. Successful ecosystem restoration can address multiple Sustainable Development Goals (SDGs) at once: alleviation of poverty, increase in crop yield and fuelwood, reduction of involuntary migration and conflicts, and regeneration of biodiversity. Ecosystem restoration can be conducted in different forms, but generally it is differentiated into two categories. Natural regeneration (also known as “passive restoration”) describes the regrowth of forests with relatively little assistance, mainly focusing on prevention of further degradation (i.e., cessation of logging). Active restoration promotes forest restoration through various silvicultural restoration mechanisms, such as enrichment planting (i.e., tree planting), liana and climber cutting, or the creation of more favorable environmental conditions (e.g., light availability).
This PhD thesis aimed to better understand the recovery of selected ecosystem functions after degradation in tropical rainforests in Sabah, Malaysian Borneo. Namely, I compared the recovery of species community composition and diversity between actively restored and naturally regenerating forest sites (15 forest plots per restoration type) which were selectively logged between 1981 to 1991. Half of the forest plots were actively restored between 1993-2004 through enrichment planting and climber cutting. I assessed whether traces of silvicultural restoration interventions are detectable in the forest structure nowadays (i.e., higher density of species that were used during enrichment planting, and lower climber/liana density). This observational study was conducted for adult trees and seedlings to allow the assessment of long-term trajectories of forest recovery. I observed that adult tree diversity (expressed with the Shannon Diversity Index) was significantly higher in actively restored forest plots compared to naturally regenerating forest plots, and that rare species were more common in restored plots. Species communities of both, adult trees and seedlings, were dominated by late-succession species for both management practices and did not differ significantly between active restoration and natural regeneration. I further observed a higher number of adult tree individuals of species that were planted and a lower density of liana seedlings in actively restored than naturally regenerating forest sites. These results highlight the successful restoration of a key ecosystem function (i.e., biodiversity) and the effective implementation of silvicultural measures in the framework of forest restoration.
I measured throughfall in a landscape of logged-over, regenerating forest and identified influential structural forest characteristics. With throughfall being an influential factor on rainfall partitioning, it is important to understand how the recovery of formerly degraded forests might affect the regional water balance. I therefore monitored throughfall for seven months in twelve forest plots located in two areas with a different restoration history (i.e., active restoration and passive regeneration in one area for about 30-40 years, and natural regeneration in the other area for about 10-15 years). When describing throughfall models (i.e., relationship between throughfall and structural forest characteristics), I was particularly interested whether throughfall models perform better when measures of forest heterogeneity (i.e., tree diversity or coefficient of variation in DBH) were included. I also explored whether throughfall could be predicted with LiDAR-derived Top of Canopy (TCH) maps. I identified multiple influential forest characteristics on throughfall (i.e., tree density, basal area, Shannon Diversity Index, coefficient of variation of diameter at breast height (DBH)), but including measures of forest heterogeneity did not lead to a better in throughfall-model performance. I did not find a relationship between TCH and throughfall. The overall best performing throughfall-model simply included tree density. This finding will hopefully generate more awareness on how forest structure, and associated effects of restoration, influences throughfall.
Lastly, I assessed in an experimental study the influence of dung beetles as bioturbating insects on infiltration – a hydrological process relevant to prevent overland flow and to recharge soil and ground water. Using mesocosms and three treatments (control, dung only, dung and dung beetles) I assessed the increase in infiltration rates in three time steps (after 1 day, 5 days, or 10 days of dung beetle presence). I also assessed infiltration patterns by using a blue dye tracer to visualize the infiltration pathways. The novel implementation of blue dye tracer is widely used in hydrological method, but not yet in macrofauna-soil interaction studies. I indeed found an increase in infiltration rates after dung beetles were present for 10 days, and that water infiltrated to greater soil depth (measured after 5 days). These results emphasize the important role of dung beetles as ecosystem engineers and their potential as nature-based solutions in restoring hydrological processes.
Permanent link
Publication status
published
External links
Editor
Contributors
Examiner: Ghazoul, Jaboury
Examiner : van Meerveld, Ilja
Examiner : Philipson, Christopher D.
Examiner : Slade, Eleanor M.
Examiner : Pena-Claros, Marielos
Book title
Journal / series
Volume
Pages / Article No.
Publisher
ETH Zurich
Event
Edition / version
Methods
Software
Geographic location
Date collected
Date created
Subject
Organisational unit
03723 - Ghazoul, Jaboury / Ghazoul, Jaboury
Notes
Funding
ETH-36 16-2 - "FORESTeR: Functioning & Resilience of Ecosystem Services in Tropical Rainforests" (ETHZ)