Fire and stand history in two limber pine (Pinus flexilis) and Rocky Mountain bristlecone pine (Pinus aristata) stands in Colorado

Abstract

We developed fire-scar and tree-recruitment chronologies from two stands dominated by limber pine and Rocky Mountain bristlecone pine in central and northern Colorado. Population structures in both sites exhibit reverse-J patterns common in uneven-aged forests. Bristlecone pine trees were older than any other at the site or in the limber pine stand, with the oldest tree dating to 780 AD and several dating to the 1000s and 1100s. The oldest trees in the limber pine stand date to the 1400s, with a majority of recruitment after an apparent bark beetle outbreak in the early 1800s. Spatial patterning in the limber pine suggests that the oldest trees established from seed caches left by corvid birds. Fire scars present in the early part of each chronology document that surface fire regimes dominated during certain periods. Decreased fire frequency, increased tree recruitment, and changes in species composition from the 1600s to1800s in the bristlecone pine may be reflective of cooler and wetter conditions during the Little Ice Age. Results suggest that a recent (1978) severe fire in the bristlecone pine stand that caused complete tree mortality was outside the historical range of variability in fire severity for at least the past ~1000 years.