Biology subjects

Maxwell, T. L.

Publications and source records attributed to Maxwell, T. L..

3 recordsLinked to original sources

bioRxiv2026

Tree species composition and nutrient uptake influence soil nutrient availability, even under contrasted levels of water availability

Temporal asynchrony within a vegetation period, such as when mixing trees with contrasting leaf phenology (i.e. deciduous and evergreen species), may play an important role in accelerating belowground nutrient cycling in mixed-species forests. However, forests are increasingly impacted by drought, and how mixing effects may be modified by changes in water availability is unknown. Using an 11-year-old experimental plantation in southwestern France, we tested the interactive effect of stand composition (monocultures of each Pinus pinaster and Betula pendula, and the mixture of the two species) and water availability (via irrigation) on various belowground processes. We quantified soil nitrogen (N) and phosphorus (P) availability with ion-exchange resins in the growing vs dormant periods, net mineralization with an in situ soil incubation method every 4-6 weeks from April to September, and N uptake by trees using two in situ 15N soil labeling campaigns, one at budburst and one at peak leaf expansion in summer. The methods were implemented at several time points, in order to elucidate potential temporal complementarity in the mixture. We found differences in soil nutrient availability between different species compositions, with pure pine generally having higher mineral N, and pure birch having higher available P under high water availability. These differences were unlikely due to increases in net nutrient mineralization, as these rates were similar among treatments. Instead, differences in tree growth and canopy covering between species compositions, and thus different nutrient uptake needs may be the main drivers for the soil nutrient availability trends. The 15N labeling experiment revealed a competitive advantage for pine in the mixture at budburst, with higher N uptake than pine in monocultures, without negatively impacting birch uptake. This advantage was then lost once birch's leaves were out in the early summer. We conclude that the timing of nutrient needs and uptake of species within a mixture, such as between a broadleaf deciduous and an evergreen conifer, may be a stronger driver than mineralization for soil nutrient availability in a mixture, even under two contrasted levels of water availability.

ecology↗

bioRxiv2024

Soil carbon in the world's tidal marshes

Tidal marshes are threatened coastal ecosystems known for their capacity to store large amounts of carbon in their water-logged soils. Accurate quantification and mapping of global tidal marshes soil organic carbon (SOC) stocks is of considerable value to conservation efforts. Here, we used training data from 3,710 unique locations, landscape-level environmental drivers and a newly developed global tidal marsh extent map to produce the first global, spatially-explicit map of SOC storage in tidal marshes at 30 m resolution. We estimate the total global SOC stock to 1 m to be 1.44 Pg C, with a third of this value stored in the United States of America. On average, SOC in tidal marshes 0-30 and 30-100 cm soil layers are estimated at 83.1 Mg C ha-1 (average predicted error 44.8 Mg C ha-1) and 185.3 Mg C ha-1 (average predicted error 105.7 Mg C ha-1), respectively. Our spatially-explicit model is able to capture 59% of the variability in SOC density, with elevation being the strongest driver aside from soil depth. Our study reveals regions with high prediction uncertainty and therefore highlights the need for more targeted sampling to fully capture SOC spatial variability.

ecology↗

bioRxiv2023

The distribution of global tidal marshes from earth observation data

AimTidal marsh ecosystems are heavily impacted by human activities, highlighting a pressing need to address gaps in our knowledge of their distribution. To better understand the global distribution and changes in tidal marsh extent, and identify opportunities for their conservation and restoration, it is critical to develop a spatial knowledge base of their global occurrence. Here, we develop a globally consistent tidal marsh distribution map for the year 2020 at 10-m resolution. LocationGlobal Time period2020 Major taxa studiedTidal marshes MethodsTo map the location of the worlds tidal marshes we applied a random forest classification model to earth observation data from the year 2020. We trained the classification model with a reference dataset developed to support distribution mapping of coastal ecosystems, and predicted the spatial distribution of tidal marshes between 60{degrees}N to 60{degrees}S. We validated the tidal marsh map using standard accuracy assessment methods, with our final map having an overall accuracy score of 0.852. ResultsWe estimate the global extent of tidal marshes in 2020 to be 52,880 km2 (95% CI: 32,030 to 59,780 km2) distributed across 120 countries and territories. Tidal marsh distribution is centred in temperate and Arctic regions, with nearly half of the global extent of tidal marshes occurring in the temperate Northern Atlantic (45%) region. At the national scale, over a third of the global extent (18,510 km2; CI: 11,200 - 20,900) occurs within the USA. Main conclusionsOur analysis provides the most detailed spatial data on global tidal marsh distribution to date and shows that tidal marshes occur in more countries and across a greater proportion of the worlds coastline than previous mapping studies. Our map fills a major knowledge gap regarding the distribution of the worlds coastal ecosystems and provides the baseline needed for measuring changes in tidal marsh extent and estimating their value in terms of ecosystem services

ecology↗