Rainforest's next generation of trees threatened 30 years after logging
IMAGE:
AN UNLOGGED TROPICAL FOREST IN DANUM VALLEY, MALAYSIAN BORNEO.
view moreCREDIT: DAVID BARTHOLOMEW
Rainforest seedlings are more likely to survive in natural forests than in places where logging has happened – even if tree restoration projects have taken place, new research shows.
Scientists monitored over 5,000 seedlings for a year and a half in North Borneo.
They studied a landscape containing both natural forest and areas logged 30 years ago – some of which were recovering naturally, while some had been restored by methods including tree planting.
A drought had triggered “mast fruiting” across the region, with trees simultaneously dropping fruit en masse and new seedlings emerging.
At first, both natural forest and restored forest had similarly high numbers of seedlings, compared to naturally recovering forest – suggesting restoration activities enhanced fruit production.
But these benefits did not last: low seedling survival in the restored forest meant that, by the end of the study, similarly low numbers of seedlings remained in restored and naturally recovering forest. Seedling populations remained higher in natural forest.
Together, these results show that regeneration may be challenged by different factors depending on the restoration approach – seed availability in naturally recovering sites and seedling survival in sites where planted trees have matured. These differences may have longer-term implications for how forests can deliver key ecosystem services such as carbon sequestration.
Dr Robin Hayward, who undertook this research during their PhD at the University of Stirling, said: “We were surprised to see restoration sites having lower seedling survival. After such a productive fruiting event in the restored forest, it’s disappointing that so few were able to survive – and to think what this might mean for the long-term recovery of different tree species.”
Whilst restoration has been shown to benefit biomass accumulation (the total amount of growth) in these forests, the research indicates this is not yet enabling full establishment of the next generation of seedlings.
Dr David Bartholomew, based at the University of Exeter during the study and now at Botanic Gardens Conservation International, said: “Our findings suggest that seedlings are experiencing stress in logged forests. This could be due to changes to the canopy structure, microclimate and soil, with current restoration treatments insufficient to eliminate this stress. In particular, highly specialised species seem to struggle to survive, leaving communities with reduced species diversity compared to intact forest.”
Daisy Dent of ETH Zürich, Switzerland and the Smithsonian Tropical Research Institute, Panama said: “Rainforests are complex systems and there are many possible explanations for our results. For example, animals that eat seeds – like bearded pigs – may be drawn into restored forest patches to eat the more abundant seeds and seedlings, rather than moving into adjacent poor-quality logged forest. In natural forests, animals potentially move more freely and so do not exhaust seed supplies in the same way.”
Selective logging of forests is prevalent throughout the tropics, and long-term recovery is crucial to maintaining carbon stocks and high biodiversity. Low rates of survival among seedlings three decades after logging therefore raise concerns about potential regeneration failure in future generations of trees.
Dr Lindsay F Banin of the UK Centre for Ecology & Hydrology, said: “Together, these results reveal there may be bottlenecks in recovery of particular elements of the plant community. We are now progressing this research into the various stages of the regeneration process – fruiting, germination, establishment and causes of mortality – to help understand which mechanisms are driving the patterns we have observed and how we can better assist forest regeneration and support the long-term sustainability of degraded forests.”
The study highlights the importance of carefully designing, monitoring and adaptively managing restoration projects so that they can recover both biodiversity and carbon in biomass over the long-term. This is key to restoring degraded landscapes and achieving global targets such as those outlined in the UN Kunming-Montreal Global Biodiversity Framework and the UN Decade on Ecosystem Restoration.
Local environmental conditions may differ between restored areas with higher biomass and canopy cover than in degraded areas with no restoration. Plant traits, or characteristics that determine how plants function, may be the key to understanding the low survival rates of seedlings – they can reveal which resources the plants are struggling to access.
The study observed differences in traits of the plants in logged areas compared to intact forest, showing that some species may be struggling to survive in disturbed areas, and some have to adapt how they grow to accommodate. This could lead to differences in biodiversity and ecological functioning in the long-term.
This study captures just 18 months after one fruiting event. Longer-term research is required to understand the full effects of historic disturbance, and how to enhance seedling survival.
The study was conducted in the Danum Valley Conservation Area and the surrounding Ulu Segama landscape of North Borneo.
Here, intact forests are dominated by a tree family, the Dipterocarpaceae, which along with many other tree families, fruits in large inter-annual episodes known as masting events.
These cyclical events have important cascading effects on food availability for animal species.
The study, published in the journal Global Change Biology, is entitled: “Bornean tropical forests recovering from logging at risk of regeneration failure Running Title: Seedling responses to logging and restoration.”
In this study, over 5,000 seedlings were individually tagged and monitored for 1.5 years
Logged forests have reduced seedling density, reducing the probability for the next generation to emerge
Logged forests have reduced seedling density, reducing the probability for the next generation to emerge
CREDIT
David Bartholomew
David Bartholomew
JOURNAL
Global Change Biology
ARTICLE TITLE
Bornean tropical forests recovering from logging at risk of regeneration failure Running Title: Seedling responses to logging and restoration.
ARTICLE PUBLICATION DATE
12-Mar-2024
Revolutionizing forest management: unveiling understory saplings with advanced airborne LiDAR technology
IMAGE:
FLOWCHART OF METHODS USED IN THIS STUDY.
view moreCREDIT: PLANT PHENOMICS
The regeneration of forest saplings is pivotal for maintaining biodiversity and ecosystem productivity, necessitating innovative management techniques for continuous forest coverage. Traditional 2-dimensional remote sensing struggles to accurately capture the complex, understory sapling dynamics. To address this, researchers are exploring the use of aerial laser scanning (ALS) for its potential in providing detailed 3-dimensional insights. However, despite progress in using ALS data to estimate tree metrics, accurately identifying and quantifying the phenotypic parameters of understory saplings remains a challenge. The current research gap lies in refining and applying algorithms that can effectively distinguish understory saplings within ALS datasets, a critical step towards enhancing forest management and understanding sapling regeneration processes.
In February 2024, Plant Phenomics published a research article entitled by “Identifying Regenerated Saplings by Stratifying Forest Overstory Using Airborne LiDAR Data”.
In this study, researchers developed a comprehensive methodology to extract phenotypic parameters of understory regeneration saplings using advanced high-density airborne LiDAR data. Initially, they fused data from multiple flights to generate a dense laser point cloud, which was then processed using a Nyström-based spectral clustering algorithm for segmenting upper mature trees. To address the common issues of oversegmentation and undersegmentation, a novel postprocessing method was introduced, prominently enhancing the positional accuracy of mature trees.
The results were impressive, showing a notable improvement in the detection and matching rates of tree segmentation after implementing the postprocessing steps; the detection rate for the Nyström-based spectral clustering postprocessing (NSCP) method reached 110.21%, with a matching rate of 96.69%. This optimization reduced trunk position errors, indirectly benefiting the accuracy of understory sapling detection. Utilizing the local adaptive mean shift algorithm, saplings under mature trees were successfully detected, achieving a matching rate of approximately 83% with an extraction rate between 102% to 105%, when the kernel bandwidth parameter was optimally set.
Further validation using multisource reference data confirmed the method's efficacy. Comparisons between airborne LiDAR (ALS) and terrestrial laser scanning (TLS) data revealed a strong correlation (R2 = 0.79) for tree height, demonstrating a notable improvement in RMS error after accounting for the ALS's inability to detect terminal leader shoots. This adjustment led to a more accurate representation of sapling heights, with an overall R2 of 0.71 and RMSE of 0.26 m when comparing ALS-extracted sapling heights against field measurements. Additionally, sapling crown widths estimated from ALS data, when matched against TLS measurements, yielded an acceptable R2 of 0.64 and RMSE of 0.24 m, despite the challenges posed by upper canopy obstruction.
In conclusion, the study not only demonstrated a successful application of high-density ALS data for understory sapling characterization but also highlighted the potential of this technology to enhance forest management and sapling growth studies. The proposed method distinguishes itself by accurately segmenting and measuring understory saplings offering a significant step forward in the use of remote sensing technologies for detailed forest inventory and analysis.
###
References
Authors
Liming Du1,2 and Yong Pang1,2*
Affiliations
1Institute of Forest Resource Information Techniques, Chinese Academy of Forestry, Beijing 100091, China.
2Key Laboratory of Forestry Remote Sensing and Information System, National Forestry and Grassland Administration, Beijing 100091, China.
About Yong Pang
He is currently a Professor with the Research Institute of Forest Resource Information Techniques, Chinese Academy of Forestry. His research interests include surface height and vegetation spatial structure from InSAR and LiDAR, modeling of LiDAR waveforms from forest stands, and development of algorithms for forest parameter retrieval from remote sensing data.
JOURNAL
Plant Phenomics
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Identifying Regenerated Saplings by Stratifying Forest Overstory Using Airborne LiDAR Data
No comments:
Post a Comment