Flooding × tree fall gap interactive effects on blackwater forest floristics and physical structure in the Peruvian Amazon

Abstract

To better understand how flooding and tree fall structure forests in the Amazon, I sampled vegetation plots within three blackwater forests (least flooded, medium flooded, highest flooded) and their tree fall gaps in the Peruvian Amazon. I found (1) increased flooding decreased family richness in the closed-canopy forests but increased it in their gaps, with no trends for no. of unique species, (2) flooding decreased stem size everywhere as did the number of stems as size increased especially for larger stems, (3) Green's index showed clumping only for least-flooded forests with the closedcanopy forest showing more than its tree fall gap, and (4) both flooding and tree fall gap creation decreased canopy coverage perhaps as an additive effect. Further among the stem size classes, only the smallest stems were significantly affected by openness and by type of forest, with a significant interaction term where flooding significantly decreased the number of these smaller stems in all forests and their gaps, except those with the highest level of flooding. Also tree fall gaps had significantly more, smaller stems than their forests in the two most-flooded forests, but not in the least-flooded forest. I conclude that flooding is a greater stressor and influence on the structure of these forests than tree fall, and so, in these forests, gradients and disturbances overlap in their traditional roles.

Primary and Secondary Igapó Forests in the Peruvian Amazon: Floristics, Physical Structure and the Predictive Value of Soil Bulk Density

“…In addition to the structural parameters reported here, I also found in the ACRCTT 1 o forests tree stems and canopy coverage declined as flooding increased, more so than reductions due to tree-fall, trees were clumped only in the gaps for wet forest, and there were smaller stems in gaps compared to all adjacent forests (Myster, 2007;Myster, 2010;Myster, 2015). Flooding was a greater stressor than the tree-fall, but flooding and tree-fall may present plants with similar cues.…”

“…Finally, linear regression analysis (SAS, 1985) was performed using soil bulk density as the independent variable and six different structural parameters as the dependent variables. Structural parameters from this study and from previously published data collected at ACRCTT were used (Myster, 2007;Myster, 2010;Myster, 2015). Each regression was graphed and expressed as: (1) the Y-intercept of the best-fit regression line, (2) the slope of that line, (3) the amount of variation explained by that line (R 2 ), and (4) the p-value of the best-fit line.…”

“…In June 2001 we sampled two plots of the same size (250 m 2 ), using the same protocol as above (for both plants and soil), in three 1 o igapó which are subject to predictable, annual flooding at the ACRCTT. This design sufficiently samples floristics and physical structure of these forests (data published in Myster, 2007;Myster, 2010;Myster, 2015) and so I reuse that data here to address other questions. One 1 o igapó forest was flooded 1-2 month per year (dry), one 1 o igapó forest was flooded 3-4 months every year (wet) and one 1 o igapó forest was flooded over 4 months per year (very wet).…”

“…And so, in order to better understand the floristics and physical structure of both 1 o and 2 o igapó, and to explore which aspects of that structure (if any) can be predicted by soil bulk density, I expanded on my own past plot samplings of Amazon flooded forests (Myster, 2007;Myster, 2010;Myster, 2015;Myster, 2016;Myster, 2018a;Myster, 2018b) by sampling 16 1 o and 2 o igapó forest plots in the Peruvian Amazon. I first use that sampling data to compile floristics (species, genera, families) and compute physical structure parameters (stem density, mean stem diameter at breast height [dbh], species richness, Fishers α, stem dispersion pattern, canopy closure, basal area and above-ground biomass) for each of the igapó forests, and then explore if soil bulk density can predict any of these structural parameters.…”

Comparison of gap formation and distribution pattern induced by wind/snowstorm and flood in a temperate secondary forest ecosystem, Northeast China

“…The trees in smaller sizes have less resistant to uprooting of single tree duo to their undeveloped root systems (Myster 2007). Moreover, the flood produced dead standing trees due to the mechanical damages and insufficient supplement of soil oxygen (Iles and Gleason 1994;Myster 2015). Small trees died in this way had few impacts on canopy openness, so only small gaps were created by the flood.…”