Loss of total phenols from leaf litter of two shrub species: dual responses to alpine forest gap disturbance during winter and the growing season

Aims Alpine forest gaps can control understory ecosystem processes by manipulating hydrothermal dynamics. Here, we aimed to test the role of alpine forest gap disturbance on total phenol loss (TPL) from the decomposing litter of two typical shrub species (willow, Salix paraplesia Schneid., and bamboo, Fargesia nitida (Mitford) Keng f.). Methods We conducted a field litterbag experiment within a representative fir (Abies faxoniana Rehd.) forest based on ‘gap openness treatments’ (plot positions in the gap included the gap center south, gap center north, canopy edge, expanded edge and closed canopy). The TPL rate and litter surface microbial abundance (fungi and bacteria) of the two shrub species were measured during the following periods over 2 years: snow formation (SF), snow cover (SC), snow melting (ST), the early growing season (EG) and the late growing season (LG). Important Findings At the end of the study, we found that snow cover depth, freeze–thaw cycle frequency and the fungal copies g−1 to bacterial copies g−1 ratio had significant effects on litter TPL. The abundances of fungi and bacteria decreased from the gap center to the closed canopy during the SF, SC, ST and LG periods and showed the opposite trend during the EG periods. The rate of TPL among plot positions closely followed the same trend as microbial abundance during the first year of incubation. In addition, both species had higher rates of TPL in the gap center than at other positions during the first winter, first year and entire 2-year period. These findings suggest that alpine forest gap formation accelerates litter TPL, although litter TPL exhibits dual responses to gap disturbance during specific critical periods. In conclusion, reduced snow cover depth and duration during winter warming under projected climate change scenarios or as gaps vanish may slow litter TPL in alpine biomes.

Spatial scale and sampling resolution affect measures of gap disturbance in a lowland tropical forest: implications for understanding forest regeneration and carbon storage

Treefall gaps play an important role in tropical forest dynamics and in determining above-ground biomass (AGB). However, our understanding of gap disturbance regimes is largely based either on surveys of forest plots that are small relative to spatial variation in gap disturbance, or on satellite imagery, which cannot accurately detect small gaps. We used high-resolution light detection and ranging data from a 1500 ha forest in Panama to: (i) determine how gap disturbance parameters are influenced by study area size, and the criteria used to define gaps; and (ii) to evaluate how accurately previous ground-based canopy height sampling can determine the size and location of gaps. We found that plot-scale disturbance parameters frequently differed significantly from those measured at the landscape-level, and that canopy height thresholds used to define gaps strongly influenced the gap-size distribution, an important metric influencing AGB. Furthermore, simulated ground surveys of canopy height frequently misrepresented the true location of gaps, which may affect conclusions about how relatively small canopy gaps affect successional processes and contribute to the maintenance of diversity. Across site comparisons need to consider how gap definition, scale and spatial resolution affect characterizations of gap disturbance, and its inferred importance for carbon storage and community composition.