Does Environment Filtering or Seed Limitation Determine Post-fire Forest Recovery Patterns in Boreal Larch Forests?

Wen H Cai,Jian Yang,Yuan Z Yang,Zhihua Liu

doi:10.3389/fpls.2018.01318

Abstract

Wildfire is a primary natural disturbance in boreal forests, and post-fire vegetation recovery rate influences carbon, water, and energy exchange between the land and atmosphere in the region. Seed availability and environmental filtering are two important determinants in regulating post-fire vegetation recovery in boreal forests. Quantifying how these determinants change over time is helpful for understanding post-fire forest successional trajectory. Time series of remote sensing data offer considerable potential in monitoring the trajectory of post-fire vegetation recovery dynamics beyond current field surveys about structural attributes, which generally lack a temporal perspective across large burned areas. We used a time series of the normalized difference vegetation index (NDVI) and normalized difference shortwave infrared reflectance index (NDSWIR) derived from Landsat images to investigate post-fire dynamics in a Chinese boreal larch forest. An adjacent, unburned patch of a similar forest type and environmental conditions was selected as a control to separate interannual fluctuation in NDVI and NDSWIR caused by climate from changes due to wildfire. Temporal anomalies in NDVI and NDSWIR showed that more than 10 years were needed for ecosystems to recover to a pre-fire state. The boosted regression tree analysis showed that fire severity exerted a persistent, dominant influence on vegetation recovery during the early post-fire successional stage and explained more than 60% of variation in vegetation recovery, whereas distance to the nearest unburned area and environmental conditions exhibited a relatively small influence. This result indicated that the legacy effects of fire disturbance, which control seed availability for tree recruitment, would persist for decades. The influence of environmental filtering could increase with succession and could mitigate the initial heterogeneity in recovery caused by wildfire.

Highlights

Wildfire is the primary natural disturbance in boreal forest ecosystems and plays a key role in regulating the carbon, water and energy exchange between the land and atmosphere via its influence on ecosystem structure and function in the region (Harden et al, 2000; Carcaillet et al, 2001; Conard et al, 2002; Kashian et al, 2006; Flannigan et al, 2009; Young et al, 2016)
Relatively little is known about the mechanisms that regulate post-fire community assembly in the Siberian light taiga dominated by Pinus sylvestris and Larix spp, because the results from North American boreal forests may not be applicable to Siberian larch forests due to differences in species’ life history traits, fire regimes, climate, and environmental conditions
We examined the effect of fire severity on an early post-fire vegetation recovery pattern using Landsat-derived timeseries normalized difference vegetation index (NDVI) and normalized difference shortwave infrared reflectance index (NDSWIR) as proxies of vegetation recovery

Summary

Introduction

Wildfire is the primary natural disturbance in boreal forest ecosystems and plays a key role in regulating the carbon, water and energy exchange between the land and atmosphere via its influence on ecosystem structure and function in the region (Harden et al, 2000; Carcaillet et al, 2001; Conard et al, 2002; Kashian et al, 2006; Flannigan et al, 2009; Young et al, 2016). In Central Siberian dark taiga forests dominated by Abies sibirica, Picea obovata, and Pinus sibirica, seed limitation plays a major role in determining postfire successional trajectories via the different dispersal abilities of deciduous hardwoods and conifers (Tautenhahn et al, 2016) These studies have offered insightful implications for how an intensified fire regime will affect future ecosystem structures and functions in similar boreal forest ecosystems. Relatively little is known about the mechanisms that regulate post-fire community assembly in the Siberian light taiga dominated by Pinus sylvestris and Larix spp, because the results from North American boreal forests may not be applicable to Siberian larch forests due to differences in species’ life history traits, fire regimes, climate, and environmental conditions Most of these studies are based on local observations and are spatially and temporally limited (Johnstone et al, 2004; Lecomte et al, 2006; Cai et al, 2013). Its application over multiple wildfires and large regions remains uncertain

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