Edge effects enhance carbon uptake and its vulnerability to climate change in temperate broadleaf forests

Abstract

Forest fragmentation is a ubiquitous, ongoing global phenomenon with profound impacts on the growing conditions of the world's remaining forest. The temperate broadleaf forest makes a large contribution to the global terrestrial carbon sink but is also the most heavily fragmented forest biome in the world. We use field measurements and geospatial analyses to characterize carbon dynamics in temperate broadleaf forest fragments. We show that forest growth and biomass increase by 89 ± 17% and 64 ± 12%, respectively, from the forest interior to edge, but ecosystem edge enhancements are not currently captured by models or approaches to quantifying regional C balance. To the extent that the findings from our research represent the forest of southern New England in the United States, we provide a preliminary estimate that edge growth enhancement could increase estimates of the region's carbon uptake and storage by 13 ± 3% and 10 ± 1%, respectively. However, we also find that forest growth near the edge declines three times faster than that in the interior in response to heat stress during the growing season. Using climate projections, we show that future heat stress could reduce the forest edge growth enhancement by one-third by the end of the century. These findings contrast studies of edge effects in the world's other major forest biomes and indicate that the strength of the temperate broadleaf forest carbon sink and its capacity to mitigate anthropogenic carbon emissions may be stronger, but also more sensitive to climate change than previous estimates suggest.climate change | forest fragmentation | land cover change | terrestrial carbon cycle | tree growth D espite advances in measurement and remote sensing methods for carbon (C) accounting, considerable uncertainty remains in estimates of the global forest C sink and the C implications of deforestation (1-4). Expansion of agricultural and developed land has reduced global forest cover by one-third (5) and led to emissions of up to 146 Pg C to the atmosphere since 1850 (3). These changes in land cover and land use have also resulted in widespread landscape fragmentation, with 20% of the world's remaining forest within 100 m of a forest's edge (6). Compared with the forest interior, forest edges often experience altered growing conditions because of novel microenvironment conditions that typically include higher temperatures, vapor pressure deficit, wind, and availability of resources, such as light and nutrients (7-10). Consequently, the effects of deforestation on the terrestrial C cycle extend into adjacent forest fragments (10-12), with a growing body of research from tropical rainforests (10), temperate rainforests (11), and boreal forests (12) showing widespread increases in tree mortality and reductions in biomass near the forest's edge. Edges were recently associated with a 10% reduction in tropical forest C density (13), which highlights the importance of considering landscape fragmentation when quantifying regional C balance (14). Furthermore, the potentia...

Piecing together the fragments: elucidating edge effects on forest carbon dynamics

“…In the broadleaf forests of Quebec, Canada, no changes in aboveground C stocks were observed within 100 m of an edge, although stem density increased (Ziter et al . ); in contrast, in broadleaf forests of eastern Massachusetts, Reinmann and Hutyra () found a 64% increase in forest biomass within 20 m of an edge. Similarly, in montane temperate lodgepole pine ( Pinus contorta ) forests in British Columbia, Canada, biomass was 31% higher in edges adjacent to roads than in the forest interior (Bowering et al .…”

“…Quantifying changes in C sequestration at the forest scale requires an inventory of all trees, given that increases in biomass with proximity to the edge could be attained (1) through faster‐growing individual trees at the edge or (2) through a higher density of trees at the edge, with the growth rates of each tree equal to the growth rates of trees within the forest interior. To our knowledge, the only study that has examined forest growth rates in an edge‐to‐interior context found evidence for both of these mechanistic pathways, leading to an 89% increase in forest growth within 20 m of a forest edge relative to the forest interior (Reinmann and Hutyra ). Furthermore, enhancement of temperate forest edge growth was greatest in years with cool summers and lowest in years with warmer than average summers, with absolute rates of forest growth declining nearly three times faster at the edge than in the interior in response to early growing season heat stress (Reinmann and Hutyra ).…”

“…; Laurance et al . ; Reinmann and Hutyra ). However, the aggregate response of forest C dynamics may differ between biomes that vary in structural characteristics and limiting factors on productivity, such as climate.…”

“…() showed that tree mortality was considerably higher in fragmented as compared to intact stands. In contrast, biomass densities in a temperate broadleaf forest were 64% higher near the forest edge than the forest interior, scaling to a 10% increase in regional estimates of biomass through southern New England in the US (Reinmann and Hutyra ), and biomass density in a temperate coniferous forest was 31% higher near the edge relative to the interior (Bowering et al . ).…”

Quantifying energy use efficiency via maximum entropy production: A case study from longleaf pine ecosystems

“…Changes in climate and natural and human induced disturbances are becoming more frequent and severe (IPCC, 2014), demanding more predictive power about how changes in ecosystem structure and function will alter resilience to disturbances. Future policy, conservation or restoration applications depend on reliable theories such as the theory of MEP presented here, to maintain ecosystem services and 20 ecological function (Haddeland et al, 2014;Porter et al, 2012;Reinmann and Hutyra, 2016;Thom et al, 2017). This is especially critical for anthropogenically modified systems, as their land use history can affect changes in energy use efficiency and thus alter their ability to recover from disturbances (Bürgi et al, 2016;Foster et al, 2003).…”