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Northern forest soils are vital for climate change mitigation since upland sandy soils favor the net consumption/oxidation of atmospheric methane (CH4). We are studying biogeochemical CH4 cycle processes in a Northern Forest (Howland Research Forest, Maine), where upland soils are interspersed with wetland (Sphagnum bog), and upland-wetland transition soils along with hummock-hollow microtopography. This complex mosaic of microsites with sources and sinks of CH4 is subjected to change under future wet climates projected for this region, with a potential for these forests to shift from a net CH4 sink to a net CH4 source. Net CH4 emissions in a wet climate can increase either by inhibiting methanotrophs or favoring methanogens, or both. Thus, quantifying underlying processes of gross CH4 production and consumption can reduce the uncertainty of CH4 sink/source estimation in this critical ecosystem. We have collected baseline soil data across the forest's landscape including Total Carbon and Total Nitrogen with the Elemental Analyzer, Gravimetric Soil Moisture, and pH. Furthermore, stable isotope dilution method will serve as a proxy for methanogenic and methanotrophic activities to quantify gross rates of CH4 production and consumption from a flooding (wet-up) experiment in Howland Forest. We will differentiate between CH4 consumption and production by measuring both the change in the amount of CH4 and the ratio between labeled and unlabeled CH4 in a closed system. We will analyze the stable C isotope in 13CH4 to determine gross rates of CH4 production and oxidation in situ and within laboratory incubations. The in situ stable isotope dilution technique will be compared with the gas push-pull method, to test the suitability of a simple, low cost method to quantify gross CH4 oxidation rates. Novel data obtained in this study will constrain CH4 cycle processes in a biogeochemical model to quantify CH4 source-sink potential in Northern Forests under current and future climatic conditions. 

This data set documents the temporal and spatial variation of soil and deadwood moisture, and nearby microclimate, for the a four-month period from June to October 2018. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and main tained by the USDA Forest Service, Northern Research Station. 

Abstract Linking biometric measurements of stand‐level biomass growth to tower‐based measurements of carbon uptake—gross primary productivity and net ecosystem productivity—has been the focus of numerous ecosystem‐level studies aimed to better understand the factors regulating carbon allocation to slow‐turnover wood biomass pools. However, few of these studies have investigated the importance of previous year uptake to growth. We tested the relationship between wood biomass increment (WBI) and different temporal periods of carbon uptake from the current and previous years to investigate the potential lagged allocation of fixed carbon to growth among six mature, temperate forests. We found WBI was strongly correlated to carbon uptake across space (i.e., long‐term averages at the different sites) but on annual timescales, WBI was much less related to carbon uptake, suggesting a temporal mismatch between C fixation and allocation to biomass. We detected lags in allocation of the previous year's carbon uptake to WBI at three of the six sites. Sites with higher annual WBI had overall stronger correlations to carbon uptake, with the strongest correlations to carbon uptake from the previous year. Only one site had WBI with strong positive relationships to current year uptake and not the previous year. Forests with low rates of WBI demonstrated weak correlations to carbon uptake from the previous year and stronger relationships to current year climate conditions. Our work shows an important, but not universal, role of lagged allocation of the previous year's carbon uptake to growth in temperate forests.