Internal and edge-effect environmental monitoring to assess the threats facing intact tropical peat swamp forest in Central Kalimantan

Peat swamp forest (PSF) provides vital environmental benefits, including carbon storage. However, almost half of the Indonesia’s PSF areas are extensively degraded. Internal threats such as drainage contribute to peat drying, vegetation damage and heightened fire risk. Equally, forest edges are threatened from human activity and fire spread, leading to forest edge regression. This study assesses biophysical changes within an area of intact tropical PSF and along their edges in Central Kalimantan. To assess these threats, we established seven transects perpendicular to the forest edge, transitioning from degraded to intact forest. Forty-nine dipwells, and three loggers were installed to assess drainage and subsidence. We established seed traps and seedling plots along three transects at three distances from the forest edge (three replicates per distance) to assess forest edge regeneration potential. Furthermore, we are analysing historic remote sensing data from the last two decades to study land cover change and forest edge loss related to fire. Equipment was established February 2022, with data collection underway for 12 months. Here, we present our initial findings. The results will provide quantitative and qualitative data analysis to describe potential threat levels facing this forest and give recommendations for developing a targeted conservation action plan.


Introduction
Tropical peatlands are a critical global ecosystem; their environmental services provide important carbon storage.Indonesia hosts the greatest global extent of tropical peatlands, yet, less than 7% of its natural-state peat swamp forest (PSF) is still classified as intact [1].Without targeted management, these remaining remnants will be lost.
Arguably, the most valuable elements of the tropical peatland landscape are its rare intact forest fragments.They are the instruction manual for forest restoration establishing its critical baseline or reference system [2].They also provide the source biota for plant and animal recolonization during the restoration process [3,4].Finally, they are a refuge for extraordinary biodiversity, which also supports local livelihoods [5].In their natural state, the forest above protects the vast carbon store below the peat surface, as well as providing nutrient and hydrological regulation for the region [6].
A prevalent threat currently facing many tropical peatland forests is that of drainage systems, leading to changes in the hydrology and the peat -even when under the forest canopy, ultimately causing drying.Research has shown that drainage leads to peat drying, subsidence, oxidation, and indirectly affects vegetation damage and increased fire risk [8][9][10].Differences across gradients within a hydrological system between intact forest and the drained, degraded areas constitutes grave risk to the intact forest, its below-ground carbon stores, and the subsequent ecological integrity of the system [7].Forests play a crucial role in rehabilitating degraded areas whilst also providing stability for the forest system.The forest regulates the microclimate; humidity, temperature, water and nutrient cycling whilst providing a source for seed and seedling recruitment.Forest edge becomes key in protecting the remaining forest fragments and facilitating potential regeneration.This important forest zone can therefore act as an indicator for forest integrity and stability, as well as its capacity to re-encroach the degraded surrounding area [8].
This study aims to assess the internal and edge threats facing a large, intact PSF area in Central Kalimantan.Internal threats will be assessed by establishing environmental peat and hydrology monitoring within the forest and across the forest edge.The security of the forest edge will be assessed through detailed historic remote sensing plus the establishment of ecological regeneration plots.

Study site
This study is taking place in the protected and conserved tropical peatland Mawas area (309,000 ha) in the Kapuas district of Central Kalimantan.The intact peat swamp forest covers the northern half of the Mawas area, north of the main east-west canal.Environmental monitoring has taken place across this area since 2010, however, additional transects were established perpendicular to the canals adjacent to the intact forest, across the forest edge (Figure 1).

Timing and duration
The study began field activities in Feb 2023.This paper presents the methods and initial results from March to May 2023.The project will continue to collect field data until January 2024.

Internal threat assessment
There are two major canals (SP7 -north-south, and SPI -east-west), and numerous minor canals within and bordering the remaining intact PSF [9].The internal impacts of drainage are being assessed using hydrology and peat subsidence monitoring techniques.This study established seven new hydrology and peat transects, each 2 km long, positioned perpendicular to its focus canal, and moving across the forest edge into the intact forest (Figure 1).Seven dipwells were established along each transect, at a spacing of 50, 100, 150, 300, 500, 1000, and 2000 m from each respective focus canal.Each dipwell is inserted down to the mineral soil (peat depth in this area is approximately 8 m deep), such that the dipwell casing can also serve as a measure for peat subsidence.Where the transect meets the canal, there are also staff gauges installed to monitor water depth in the canal.The water table in the peat, the peat subsidence, and the water depth in the canals is measured every two months.In the area, there are also three additional automated water loggers to monitor rapid-change fluxes, and one barometer to measure atmospheric pressure.

Edge threat assessment
Threats to the forest edge of the study area are being assessed in two ways.Firstly, using methodology already developed to analyse remote-sensing data to create maps of land cover in degraded tropical peatland forests [10].These techniques are being applied to this study areas to quantify forest cover loss due to fire over the last 30 years.Secondly, small regeneration plots were established in the region of the forest edge, alongside the hydrological and peat monitoring locations, to record seed dispersal and natural regeneration (seedling recruitment and growth) to quantify forest edge health and potential.Seedling plots and seed dispersal traps were established at three specific distances from the intact forest, those being: forest edge (0 m), open-canopy degraded forest (50 m), and degraded forest (200 m) (Figure 2).
Ecology and regeneration study areas were chosen to represent the seven transects.These three ecological 'regions': SP7 West, SP7 East and SPI, were determined based on their spatial distribution, but also, crucially, the influence of wind direction on seed dispersal (Figure 1).Every two months the seeds and fruits are collected from the seed traps and sorted by number and species, with trees overhanging the traps having their species recorded, and then the seedlings' survival and growth in the natural regeneration seedling plots is recorded.

Results
Data collection for this study is still underway.Here we present some initial findings from the hydrology transects and regeneration plots.

Hydrology measurement
The data shows that the average groundwater level in March tends to be higher than in May, given that May is entering the start of the dry season.The data also shows the water table is higher with increasing distance from canal (DFC): being close to the surface at 2 km DFC, whilst sometimes more than -20 cm adjacent to the canal, showing the negative impact of drainage.Some fluctuations in the data require further exploration in relation to other environmental variables.

Regeneration plot
Initial findings from the regeneration plots showed some early differences as one moved further into the degraded area from the forest edge: For the seedling plots, along the forest edge, the dominant seedling species were Syzygium sp. and Stemonorus scorpiodes with six species being recorded in total, while Syzygium sp. and Shorea balangeran dominated the seven species recorded in the open-canopy forest (50 m DFFE -distance from forest edge), and Shorea balangeran, Syzygium sp. and Antidesma coriaceum seedlings were most common in the degraded forest area with seven species in total recorded (200 m DFFE).
Regarding the seed dispersal, a total of eight tree species were observed in the traps (made up from both fruits and seeds) at the forest edge zone with Combretocarpus rotundatus, a wind-dispersed species, being most dominant.For the open canopy and degraded forest zones, Combretocarpus rotundatus also remained the most dominant, with only four and then three other tree species being observed in these respective zones.The majority of seeds and fruits observed in the traps did not have same-species overhanging adult trees in the immediate vicinity, and many were bird-dispersed suggested a degree of animal dispersal.Initial results suggest some difference between the ecological regions, and require further analysis.

Discussion
Initial findings from this study already illustrate that this intact primary peat swamp forest in Central Kalimantan has great conservation value, and potential for recovery along its forest edges, but also, that it is facing threats from its surrounding canals and edge-effects.Both the regeneration plots and the hydrology data show that distance from canal and distance from forest edge are important factors in determining the level of risk and the capacity of recovery for this important ecosystem [8].
Upon completion of data collection, the hydrology and peat data will be used to facilitate direct comparison of the water tables and rates of peat subsidence in the degraded versus intact forest areas, and the role of DFC.This will build upon recent research which suggests that the difference within single hydrologic systems and the hydrological gradient between the intact forest and the drained, degraded areas constitutes grave risk to the intact forest, its below-ground carbon stores, and the subsequent ecological integrity of the system [7].
Equally, the results from the regeneration plots and the remote sensing analysis will assess the in detail the continued threats to this critical buffer area both historically and currently, and equally, its capacity for recovery and re-encroachment into the degraded areas, and what can be done to prevent the former and support the latter [8].
This study aims, after 12 months of data collection, that a quantitative and qualitive analysis will be developed which describes the threat levels facing this forest, giving recommendations for the development of a targeted conservation action plan.We also hope this can provide guidelines and lessons learned to serve as a model that can be repeated across other forest fragments and direct management to the most immediate threats to the intact PSF remnants at BOSF-Mawas to ensure the conservation of this crucial resource.

Conclusions
Indonesian holds some of the world's most extensive tropical peatlands, which host some of extraordinary biodiversity, including orangutans and hornbills.Indonesia is taking a proactive approach in protecting and restoring these unique ecosystems, which also works towards mitigating the effects of the global climate crisis.Understanding the threats these precious remaining intact tropical peatland forest areas currently face, internally through drainage, and along their edges, and their capacity for recovery will be key to ensuring the successful sustainable management of these ecosystems.

Figure 1 .
Figure 1.Location of the environmental monitoring transects: Environmental monitoring transects established before the start of this project (dark blue), new transects established for this study (pale blue), dominant wind direction (red arrows), distinct ecological regions within the study area (yellow ovals).

Figure 2 .
Figure 2. The design layout for the seed traps and seedling plots: peat and hydrology transect (blue dotted line), forest edge (red dotted line), seed dispersal traps (small white squares), seedling plots (large white squares).

Figure 3 .
Figure 3.The water level in the study area, shown with distance from canal, across March (dotted line) and May (solid line) for the three ecological regions (SPI, SP7 East and SP7 West, pale blue, grey and dark blue respectively).