September 2022 science summary

Hi,

First I wanted to say how sorry I was to hear that one of the lead authors I highlighted last month (Jonathan Higgins) has since passed away. Higs was a force of nature and he will be missed by many. I'm very glad that my last email exchange with him was about how useful his paper was and the impact I thought it would have, which made him very happy.

This month I am summarizing three articles on climate change, one on tropical forest recovery, and one on conservation and human well-being. If you know someone who wants to sign up to receive these summaries, they can do so at http://bit.ly/sciencejon (no need to email me).

CLIMATE CHANGE:
Gopalakrishna et al. 2022 highlights the need for local studies of climate mitigation potential. They found that if you avoid conflict w/ ag lands, forest restoration potential is lower in India than global estimates (and they suspect the same would be true in other tropical countries with lots of ag lands). They found 1.6 million ha of lands that could be restored; the plurality was degraded forest followed by scrub. If those lands were restored, they estimate it could provide 61.3 Mt (million tons) of carbon sequestration. They also roughly estimate 14.7 million ha of ag lands could incorporate agroforestry practices for up to another 98 Mt of carbon over 30 years. So the key take-aways here are a) we can't rely on global estimates for in-country work and b) if we can find ways to add trees to lands producing food w/o impacting food production (which is sometimes possible) there is a lot of opportunity there.

Noon et al. 2022 is a fantastic resource mapping global priority habitats for conservation to protect and/or manage to slow climate change. They focus on "irrecoverable carbon" - meaning carbon that will take 30+ years to recover after it is lost due to conversion or degradation. Fig 1 has a global map of irrecoverable carbon with a few hotspots highlighted (or use this web map which has slightly different symbology https://irrecoverable.resilienceatlas.org/map). But more useful is Fig 2 which splits out the carbon by how it's threatened (by land conversion, climate change, both, or neither) to identify where protection vs. management makes sense. Note that in Fig 2 darker colors mean more carbon within each of the four risks, but they are not consistent across the four risks (to see the highest total carbon you still need Fig 1). Fig 3 highlights how uneven irrecoverable carbon in, 50% of it is in just 3% of global land area! If you work on carbon in nature, read the whole paper. Many thanks to the authors who kindly answered my questions and sent me their data so I could make my own maps!

Reed 2021 tackles the thorny issue of how montane meadowns in California (wet grasslands in mountains) mitigate or worsen climate change. They found that a) these ecosystems store a lot of carbon, b) on net they can be either a big carbon source (10/13 sites) or a big carbon sink (3/13 sites) c) the sites that were a source had similar plant species to sink sites, but typically had groundwater closer to the surface, more root biomass, and less bare ground, d) methane emissions were consistently low, and e) they're not sure what caused most meadows to become net carbon sources (the high carbon stock indicate they all used to be sinks) but think it depends mostly on how much water and dissolved carbon flows into the meadows from uplands and thus upland forest loss is a likely culprit. The discussion is interesting - they hypothesize that hydrologic restoration in the meadow and upland forest management could slow carbon losses but think it's a safer bet to try and maintain sites that are currently net carbon sinks.


FOREST RESILIENCE / RECOVERY:
Poorter et al. 2021 look at how long it took for tropical forests (in Central & South America plus West Africa) to recover after deforestation, finding them pretty resilient. They found recovery to 90% of old growth values took 1-9 yrs for soil, plant function took 3-27 yrs, forest structure took 27-119 (tree size variation 27, max tree size 49, biomass 119), species diversity took 37-59, and species composition took 120 years. They thus argue secondary (regrowing) forests are still ecologically important and deserve conservation (protection, restoration, and management). Note that most of their sites had low to mid intensity land use after deforestation like swidden agriculture, so soil degradation was relatively minor. It's short and worth the read, but as is common w/ papers in Science I found the figures hard to decipher but useful once you put in the time. Fig 1B shows roughly how quickly different attributes recover over time (soil is brown, plant function is purple, structure is green, and diversity is turquoise); Fig 2 is similar but breaks out sub-indicators and is more precise; and Fig 3D is my favorite (how long it takes each attribute to return to 90% of old growth values). Here are the abbreviations since they are not defined in a single place! 
AGB=aboveground biomass
BD=soil bulk density
C=soil carbon
DMAX=maximum tree diameter
N=soil nitrogen
NF=proportional basal area of nitrogen-fixing species
SC=species composition (how similar abundance of each species is to old growth)
SD=Simpson diversity (~diversity of common species)
SH=structural heterogeneity (variation in tree size)
SR=species richness (number of species present)
SLA=community-weighted mean specific leaf area
WD=community-weighted mean wood density


NATURE & PEOPLE:
Huynh et al. 2022 is a global literature review of 300 peer-reviewed papers on the many intangible ways nature impacts people (what they call "cultural ecosystem services" or CESs). So it leaves out physical effects like providing food, clean water, reducing storms, etc. (which are well studied) and focuses on things like recreation, spiritual fulfillment, aesthetics, etc. If you enjoy taxonomies / classifications you will like this paper, and if not, you will find it a slog, since the heart of it is a framework to classify many ways people and nature interact (see Table 1 and Figure 2). But it's worth at least reading through Table 1 and pondering a bit. Ssome like how nature can help people bond ('Cohesive') were new to me but rang true; others felt like splitting hairs (e.g., splitting spiritual experiences into 'Intuitive' and 'Transcendentive'). Beyond the framework, they found 86% of over 1,000 observations positively impacted people (more studies looked at this and there is likely bias in the lit - it's not necessarily that nature is inherently overwhelmingly beneficial). Their expert judgment is that the biggest benefits come from mental and physical health, particularly from recreation (including tourism) and aesthetic values (the size of boxes in Fig 3 shows how many studies they had for each of 227 'pathways').The biggest negative impacts came from concern about safety ('Apprehensive'), or the loss of ecosystem services when nature is damaged or lost ('Destructive' - although it seems odd to me to mix that in with actual harms from nature itself), with only a few 'Irritative' (annoyance or disgust, e.g., from wildlife noise or excrement). In the end the paper gave me 'Cognitive' benefits but was not very 'Satisfactive.' The Washington Post has an overview of the paper here: https://www.washingtonpost.com/climate-solutions/2022/08/05/nature-study-impact-hiking-outdoors/


REFERENCES:

Gopalakrishna, T., Lomax, G., Aguirre‐Gutiérrez, J., Bauman, D., Roy, P. S., Joshi, P. K., & Malhi, Y. (2022). Existing land uses constrain climate change mitigation potential of forest restoration in India. Conservation Letters, December 2021, 1–11. https://doi.org/10.1111/conl.12867

Huynh, L. T. M., Gasparatos, A., Su, J., Dam Lam, R., Grant, E. I., & Fukushi, K. (2022). Linking the nonmaterial dimensions of human-nature relations and human well-being through cultural ecosystem services. Science Advances, 8(31), 1–22. https://doi.org/10.1126/sciadv.abn8042

Noon, M. L., Goldstein, A., Ledezma, J. C., Roehrdanz, P. R., Cook-Patton, S. C., Spawn-Lee, S. A., Wright, T. M., Gonzalez-Roglich, M., Hole, D. G., Rockström, J., & Turner, W. R. (2022). Mapping the irrecoverable carbon in Earth’s ecosystems. Nature Sustainability, 5(1), 37–46. https://doi.org/10.1038/s41893-021-00803-6

Poorter, L., Craven, D., Jakovac, C. C., van der Sande, M. T., Amissah, L., Bongers, F., Chazdon, R. L., Farrior, C. E., Kambach, S., Meave, J. A., Muñoz, R., Norden, N., Rüger, N., van Breugel, M., Almeyda Zambrano, A. M., Amani, B., Andrade, J. L., Brancalion, P. H. S., Broadbent, E. N., … Hérault, B. (2021). Multidimensional tropical forest recovery. Science, 374(6573), 1370–1376. https://doi.org/10.1126/science.abh3629

Reed, C. C., Merrill, A. G., Drew, W. M., Christman, B., Hutchinson, R. A., Keszey, L., Odell, M., Swanson, S., Verburg, P. S. J., Wilcox, J., Hart, S. C., & Sullivan, B. W. (2021). Montane Meadows: A Soil Carbon Sink or Source? Ecosystems, 24(5), 1125–1141. https://doi.org/10.1007/s10021-020-00572-x

 

p.s. the photo shows a goldfinch amidst my cutleaf coneflowers, watching me watch him (these flowers are only ~5 ft from a living room window)