Carbon Stocks and Climate Change: Management Implications in Northern Arizona Ponderosa Pine Forests

Benjamin Bagdon,Ching-Hsun Huang

doi:10.3390/f5040620

Abstract

Researchers have observed climate-driven shifts of forest types to higher elevations in the Southwestern US and predict further migration coupled with large-scale mortality events proportional to increases in radiative forcing. Range contractions of forests are likely to impact the total carbon stored within a stand. This study examines the dynamics of Pinus ponderosa stands under three climate change scenarios in Northern Arizona using the Climate Forest Vegetation Simulator (Climate-FVS) model to project changes in carbon pools. A sample of 90 stands were grouped according to three elevational ranges; low- (1951 to 2194 m), mid- (2194 to 2499 m), and high- (2499 to 2682 m.) elevation stands. Growth, mortality, and carbon stores were simulated in the Climate-FVS over a 100 year timespan. We further simulated three management scenarios for each elevational gradient and climate scenario. Management included (1) a no-management scenario, (2) an intensive-management scenario characterized by thinning from below to a residual basal area (BA) of 18 m2/ha in conjunction with a prescribed burn every 10 years, and (3) a moderate-management scenario characterized by a thin-from-below treatment to a residual BA of 28 m2/ha coupled with a prescribed burn every 20 years. Results indicate that any increase in aridity due to climate change will produce substantial mortality throughout the elevational range of ponderosa pine stands, with lower elevation stands projected to experience the most devastating effects. Management was only effective for the intensive-management scenario; stands receiving this treatment schedule maintained moderately consistent levels of basal area and demonstrated a higher level of resilience to climate change relative to the two other management scenarios. The results of this study indicate that management can improve resiliency to climate change, however, resource managers may need to employ more intensive thinning treatments than currently proposed to achieve the best results.

Highlights

Recent climatic changes have induced shifting forest ecotones and widespread mortality events in the southwestern United States (SW US) [1,2,3,4,5]
We used a set of baseline stand conditions to simulate the relative changes in stand structure between climate, management, and elevational differences over time
This study simulated ponderosa pine stand development in Climate-Forest Vegetation Simulator (FVS) to evaluate the likely impacts of various climate change scenarios

Summary

Introduction

Recent climatic changes have induced shifting forest ecotones and widespread mortality events in the southwestern United States (SW US) [1,2,3,4,5]. Drier conditions in the SW US have been linked to an increased frequency of catastrophic wildfires [4,8,9], bark-beetle outbreaks [4,10], and widespread mortality events [1,2,3,4,5,6,11]. These amplified rates of tree mortality and extensive mortality events result in large pulses of stored carbon being released into the atmosphere [1,12]. It is uncertain how carbon stocks within these forests will respond to different intensities of climate change

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