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Harvard Forest Research Project 2023

• Title: How is spring warming altering temperate deciduous forest carbon allocation?
• Principal investigator: Kristina Anderson-Teixeira (TeixeiraK@si.edu)
• Institution: Smithsonian Tropical Research Institute - Center for Tropical Forest Science
• Primary contact: Kristina Anderson-Teixeira (TeixeiraK@si.edu)
• Team members: David Orwig
  Neil Pederson
• Abstract:

  Forests will strongly influence the course of climate change. Currently, sequestration of carbon (C) by forests worldwide offsets ~20% of anthropogenic emissions, dramatically slowing the pace of atmospheric CO2 accumulation and climate change. Of this important C sink, ~47% occurs in temperate forests, with temperate deciduous forests sequestering >0.3 Gt C yr-1. Yet, the future of C cycling in these forests remains uncertain. It has largely been assumed – including in global climate models—that warm springs and lengthening growing seasons increase C sequestration in the long-lived woody tissues of trees, paralleling known increases in annual CO2 uptake. Yet our recent work (in press at Nature) showed that despite causing earlier leaf-out and commencement of woody growth, warm springs do not increase total annual woody growth. This implies (1) that the future potential C sink of this biome has been overestimated and (2) that “extra” C fixation in years with warm springs must be allocated to a function other than woody growth (e.g., production of pollen, fruits, and nuts; belowground allocation aimed to relieve nutrient limitation). The fate of this extra C will have important implications for forest ecosystem function, animal populations, human health, and climate change feedbacks.
  Here, we seek to understand the fate of additional C in years with warm springs. Work will focus at three temperate deciduous forests with rich collections of relevant data from the Smithsonian-led Forest Global Earth Observatory (ForestGEO), the National Ecological Observatory Network (NEON), and other sources: the Smithsonian Conservation Biology Institute (Front Royal, VA), the Smithsonian Environmental Research Center (Edgewater, MD), and Harvard Forest (Petersham, MA). We will synthesize existing data on leaf phenology, ecosystem-atmosphere CO2 exchange, woody growth, foliage production, production of reproductive structures (flowers, pollen, and fruits/nuts), belowground allocation, and nutrient limitation. We will also analyze tree rings to obtain new data on C density and nitrogen limitation of woody growth, and we will initiate new automated measurements of the seasonality of tree growth. This will allow us to test hypotheses likely to result in high-impact findings, including that (1) warm springs result in increased C allocation to reproduction (pollen, fruits/nuts) and (2) warm springs result in increased belowground C allocation, but that this fails to relieve nutrient limitations.
  The proposed research will develop partnerships, build analytical infrastructure for working with NEON data, initiate critical new measurements, yield results that give important insight into forest functioning under climate change, and identify the most pressing questions for a larger proposal. We plan to develop a proposal to the NSF Macrosystems Biology and NEON-Enabled Science Program that would allow us to expand upon the work proposed here to cover more sites, biomes, global change drivers, and/or C allocation variables. As part of this project, we will mentor 2-3 early-career individuals, targeting minoritized groups.