• Puhlick, J.
  University of Maine, Center for Research on Sustainable Forests
  joshua.puhlick@maine.edu
  
• Weiskittel, A.
  University of Maine, Center for Research on Sustainable Forests
  aaron.weiskittel@maine.edu
  

In Maine, a system of long-term monitoring plots was established on state-owned Ecological Reserves and preserves owned by The Nature Conservancy (TNC). The first vegetation monitoring plots were established on state and TNC lands in 2002 and 2004, respectively. Plots in forest ecosystems were remeasured approximately 10 years after initial measurement. This study uses plots (n = 682) from 37 reserves with repeated measurements of forest attributes. We also used 10,503 USDA Forest Service Forest Inventory and Analysis (FIA) subplots across managed forests in Maine to compare carbon (C) stocks and sequestration between Maine’s managed forests and reserves.

The most recent inventory of forest reserve plots had aboveground C in live trees, standing dead trees, and downed coarse woody debris of 89.4 ± 37.7 (mean ± SD) Mg ha-1. Mean aboveground C increased 11% over the 10-year interval between plot measurements. C stocks significantly varied between some Natural Community Types and Ecological Reserves. For example, the Hemlock Forest type had greater C stocks than the Pitch Pine - Scrub Oak Barren and Early Successional Forest types. Average annual net change in C (AAC) in live trees, standing dead trees, and downed coarse woody debris was 0.894 ± 1.949 Mg ha-1 yr-1.

For reserve and FIA plots, dominant Forest Type Groups were Aspen - Birch, Elm - Ash - Cottonwood, Maple - Beech - Birch, Oak - Hickory, Oak - Pine, Spruce - Fir, and White - Red - Jack Pine. For plots from these groups, C in live trees, standing dead trees, downed coarse woody debris, and harvested wood products was 90.2 ± 37.1 and 67.7 ± 36.3 Mg ha-1 for Ecological Reserve Monitoring (ERM) and FIA programs, respectively. Our models indicated that the difference in C stocks between programs was dependent on Forest Type Group. For these same plots, AAC in live trees, standing dead trees, downed coarse woody debris, and harvested wood products was 0.901 ± 1.957 and 0.581 ± 3.661 Mg ha-1 yr-1 for ERM and FIA programs, respectively. Program, Forest Type Group, and their interactions only explained 1% or less of the variation in ACC.

We modelled projections of live tree C stocks and sequestration on the reserves to 2040. From the most recent inventory to 2040, AAC in the aboveground portions of live trees was 1.096 ± 0.539 Mg ha-1 yr-1. We used the Natural Resources Conservation Service (NRCS) Gridded Soil Survey Geographic (gSSURGO) Database to estimate and compare soil C among Natural Community Types and Ecological Reserves. Overall, soil C represented 67 ± 13% of the total forest C stock, and forested plots on hydric soils had some of the greatest C stocks. Finally, we compared aboveground biomass estimates for individual Ecological Reserves using plot data and Light Detection and Ranging (LiDAR) data. Forest C objectives can be achieved with forests managed using silvicultural treatments to maintain or enhance C accumulation and with Ecological Reserves where timber is not harvested. The benefits of C storage in Maine’s Ecological Reserves lends support for the expansion of reserves in Maine and the establishment and monitoring of reserves in other states.