Hundred year projected carbon loads and species compositions for four National Forests in the northwestern USA

Patrick A Fekety,Nicholas L Crookston,Andrew T Hudak,Michael J Falkowski,Jody C Vogeler,Steven K Filippelli

doi:10.1186/s13021-020-00140-9

Abstract

BackgroundForests are an important component of the global carbon balance, and climate sensitive growth and yield models are an essential tool when predicting future forest conditions. In this study, we used the dynamic climate capability of the Forest Vegetation Simulator (FVS) to simulate future (100 year) forest conditions on four National Forests in the northwestern USA: Payette National Forest (NF), Ochoco NF, Gifford Pinchot NF, and Siuslaw NF. Using Forest Inventory and Analysis field plots, aboveground carbon estimates and species compositions were simulated with Climate-FVS for the period between 2016 and 2116 under a no climate change scenario and a future climate scenario. We included a sensitivity analysis that varied calculated disturbance probabilities and the dClim rule, which is one method used by Climate-FVS to introduce climate-related mortality. The dClim rule initiates mortality when the predicted climate change at a site is greater than the change in climate associated with a predetermined shift in elevation.ResultsResults of the simulations indicated the dClim rule influenced future carbon projections more than estimates of disturbance probability. Future aboveground carbon estimates increased and species composition remained stable under the no climate change scenario. The future climate scenario we tested resulted in less carbon at the end of the projections compared to the no climate change scenarios for all cases except when the dClim rule was disengaged on the Payette NF. Under the climate change scenario, species compositions shifted to climatically adapted species or early successional species.ConclusionThis research highlights the need to consider climate projections in long-term planning or future forest conditions may be unexpected. Forest managers and planners could perform similar simulations and use the results as a planning tool when analyzing climate change effects at the National Forest level.

Highlights

Forests are an important component of the global carbon balance, and climate sensitive growth and yield models are an essential tool when predicting future forest conditions
The probability of a fire occurring on the Gifford Pinchot National Forest (NF) is low (p = 0.012; Table 2), yet when a fire occurs a large proportion of the trees are affected (Fig. 2)
Results from the dClim Off simulations reflect mortality caused by changes in the maximum carrying capacity and future climate being outside speciesspecific climatic envelopes calculated from the species carbon estimates, change in species composition, and plot-level basal area shifting to lower densities

Summary

Introduction

Forests are an important component of the global carbon balance, and climate sensitive growth and yield models are an essential tool when predicting future forest conditions. Precipitation in the northwest USA is dominated by inter-annual fluctuations (e.g., El Niño–Southern Oscillation) and while downscaled climate projections predict slight increases in future precipitation on average (approximately 2% increase per decade), these increases are not as noteworthy as the inter-annual variations, the timing of precipitation may change resulting in drier summers and wetter winters [5, 6]. These changes have already begun to affect forests. The effects of climate change have been linked with the decline of quaking aspen (Populus tremuloides) across the western USA [10]

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