Anamorphic Site Index Curves for Central Appalachian Red Spruce in West Virginia, USA

Eric Yetter,Sophan Chhin,John Brown

doi:10.3390/f12010094

Abstract

Traditional site index curves are frequently produced for shade-intolerant species but are scarce for shade-tolerant species. Red spruce (Picea rubens Sarg.) can be found in three distinct geographic regions (northern, central, and southern) within the Appalachian Mountains. The one commonly used set of red spruce site index curves is over ninety years old. A definite need exists for a modern, regionally applicable set of site index curves. This research sampled 83 plots randomly located in the central Appalachians of West Virginia. Three sets of anamorphic site index curves were created after careful examination of height models built using Chapman-Richards and Meyer functions. One set of curves was constructed with traditional age height pairs. The second utilized a suppression-corrected age and height pair. The third set examined diameter at breast height (DBH) and height pairs. Fit statistics indicated better performance for the suppression-corrected age–height pair site index and the DBH–height pair site index versus the traditional age–height pair models. Site index conversion equations were also investigated for the red spruce age-corrected site index. Linear regression was used to determine significant geographic and climate variables and the utility of including site index values for red maple (Acer rubrum L.) and yellow birch (Betula alleghaniensis Britton) in the model to predict red spruce site index. Significant models were found for varying combinations of species site index, climate, and geographic variables with R2adj in the range of 0.139–0.455. These new site index curves and conversion equations should provide utility for site productivity estimation and growth and yield modeling while aiding in restoration efforts for this important central Appalachian species.

Highlights

Site index models are primarily developed using tree age and height for shadeintolerant species in even-aged stands
Central Appalachian red spruce (Picea rubens) is one such species which frequently experiences suppression periods, as it transitions through canopy classes [1] and is often found growing in uneven-aged stands for which few site index models have been developed [2]
Being able to quantify locations with predicted site index values for red spruce would be a major advantage in selecting lands for future restoration activities in order to ensure management activities occur on the sites most likely to optimize both ecological and economic outcomes [40]. These new Meyer 2P height models with guide curves should be useful for estimating central Appalachian red spruce site index values

Summary

Introduction

Site index models are primarily developed using tree age and height for shadeintolerant species in even-aged stands. One novel method of accounting for suppression in red spruce was developed by Seymour and Fajvan [9] This method involves using free-growth age of the tree instead of the true age of the tree by replacing time periods during lengths of suppression on tree cores with free-growth age of the same length following the suppressed period. Both age correction to account for suppression and the use of DBH instead of age are different methods to address the shade tolerance of red spruce when predicting height and site index

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Results

Discussion

Conclusion