A reconstruction and comparison of Grand Bahama pine forest age during the pre-major hurricane era using ridge regression and nested linear mixed-effects model

Abstract

Early historical-ecological records of the pine forest on Grand Bahama indicated that large-scale commercial removal of the mature pine trees from the island during logging in The Bahamas substantially reduced the pine population in Grand Bahama from 1944 to 1960. Additional losses of the pine population on the island were results of the major hurricanes in the post-logging era. There were ca. 43 million pine trees in Grand Bahama before the 2004 and 2005 major hurricanes. This study uses ridge regression and a nested linear mixed-effects model (with a random intercept included as the variance-covariance structure) to reconstruct and compare Grand Bahama pine forest age across different domains (pre-Dorian dead, post-Dorian dead, and post-Dorian live pine areas). Statistical results revealed that the mature pine forest (DBH ≥ 10 cm) in Grand Bahama in 2004 ranged in age from 38 to 49 years old. These are the pine seedlings that germinated between 1950 and 1970 during and at the end of the logging era in Grand Bahama. The intraclass correlation coefficient (ICC [1]) indicated that the nesting effect (survey plots within domains) in the linear mixed-effects model (LMM) explained 33.8% (ICC [1] = 0.338) of the total variance captured by the grouping effect of pine forest age. Both the fixed and random factors (predictors) explained 48.8% ($R_c^2$ = 0.488) of the total variance of the mean pine forest age across domains. This compared better to the fixed-effects factor, which alone explained a much smaller percentage of the variation of the response variable ($R_m^2$ = 0.227). The mean pine forest age was statistically significant across domains (F _{2, 300.34} = 79.94; p < 0.0001), indicating age-specific variation in pine tree age across the pine landscape.

From 1950 to 1970, Grand Bahama pine forest age underwent radical shifts due to extensive commercial harvesting during the logging era (1944–1960). The major hurricanes in 2004, 2005, and 2019 further changed the pine forest age structure, resulting in discrete fragments of dead pine forests scattered throughout Grand Bahama Island. Small-scale deforestation from urban growth continues to impact the pine forest age structure in Grand Bahama. Given that both logging and hurricanes result in structural changes to landscapes, the pine forest in Grand Bahama should consist of uneven-aged pine vegetation. The presence of uneven-aged pine trees should occur in areas with a repeated history of logging and along the north shore, where the effects of the 2004 and 2005 major hurricanes were the most impactful. This study provides historical contexts of Grand Bahama pine forest in the pre-major hurricane era. The findings presented here add to our understanding of the Bahamian pine forest by providing critical information on the pine tree density and pine forest age in Grand Bahama in the pre-major hurricane era, an era of significant importance.