Post-harvest natural regeneration and vegetation dynamics across forest gaps in Central Finland

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Title: Post-harvest natural regeneration and vegetation dynamics across forest gaps in Central Finland
Author: Downey, Margot
Contributor: University of Helsinki, Faculty of Agriculture and Forestry, Department of Forest Sciences
Publisher: Helsingfors universitet
Date: 2015
Language: eng
Thesis level: master's thesis
Discipline: Skoglig ekologi och resurshushållning
Forest Ecology and Management
Metsien ekologia ja käyttö
Abstract: The creation of forest gaps in disturbance emulation forestry alters local environmental conditions, which causes variability in natural seedling regeneration. Understory vegetation plays an important role in early seedling regeneration success and is sensitive to variations in topography and resource availability. Its analysis can uncover the finer-scale impacts of gap characteristics and competition on the patterns of tree regeneration. The objective of this study was to examine the impact of gap characteristics on patterns of natural vegetation and tree seedling regeneration 5 years post-harvest across 18 gaps in Norway spruce (Picea abies (L.) Karst.) dominated forests of Central Finland. Gap characteristics included distance from edge (into residual forest and gap interior), cardinal position in the gap (N, S, E or W), microsite type and dominant topography. All seedlings (≤5m) were counted and measured on 1m2 plots situated along linear strips (2 for each N-S and E-W orientations). On these same plots, vegetation and microsite types were assessed by percent cover for several key categories. Results show that distance from gap edge was the most influential gap characteristic, especially in the ±10m zone. The 0–15m zone inside the gap supported the greatest abundance of seedlings, as well as the highest diversity of both vegetation types and seedling species. The edge zone inside the forest supported shade-tolerant species (dwarf shrubs, mosses). Gap centers (~15m+) supported shade-intolerant species (grasses, shrubs, herbs), creating a highly competitive growing environment. The position within the gap was also an influential characteristic. The N gap positions showed the most statistically significant difference from the others; they had fewer birch seedlings, a greater percent cover of grasses and dwarf shrubs, and a smaller percent cover of ferns. This effect was generally more pronounced in the gap interior. The results of this study support that natural regeneration of seedlings in gaps is quite variable. The mean number of seedlings per ha inside the gaps were 20 360 for Norway spruce, and 6 820 for birch spp. combined; up to 62% were germinants (≤3cm). In the 15m+ region from the gap edge towards the gap center, the mean number of seedlings per m2 was on average ~58% smaller than for the rest of the strip. The presence and abundance of different vegetation species clearly demonstrate that distance from edge and within-gap position strongly affect resource availability and competition. The most significant gap characteristics affecting these patterns of early regeneration for Norway spruce and birch were revealed with the help of generalized additive models (GAMs). Since these gaps are in their early stages of regeneration, the future dynamics and final outcome are still fairly uncertain. However, the current mean number of seedlings inside the gaps suggests a promising potential for natural regeneration. These models point to management actions which could facilitate long-term natural regeneration in similar forest gaps.
Subject: Picea abies
Betula pendula
Betula pubescens
gap felling
partial felling
boreal forest
natural regeneration
understory vegetation

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