scholarly journals Variability in Mixed Conifer Spatial Structure Changes Understory Light Environments

Forests ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 1015 ◽  
Author(s):  
Jeffery B. Cannon ◽  
Wade T. Tinkham ◽  
Ryan K. DeAngelis ◽  
Edward M. Hill ◽  
Mike A. Battaglia
Keyword(s):  
Spatial Patterns ◽  
Ponderosa Pine ◽  
Spatial Scales ◽  
Light Availability ◽  
Structural Complexity ◽  
Tree Regeneration ◽  
Conifer Forests ◽  
Mixed Conifer ◽  
Regeneration Dynamics ◽  
Wide Range

In fire-adapted conifer forests of the Western U.S., changing land use has led to increased forest densities and fuel conditions partly responsible for increasing the extent of high-severity wildfires in the region. In response, land managers often use mechanical thinning treatments to reduce fuels and increase overstory structural complexity, which can help improve stand resilience and restore complex spatial patterns that once characterized these stands. The outcomes of these treatments can vary greatly, resulting in a large gradient in aggregation of residual overstory trees. However, there is limited information on how a range of spatial outcomes from restoration treatments can influence structural complexity and tree regeneration dynamics in mixed conifer stands. In this study, we model understory light levels across a range of forest density in a stem-mapped dry mixed conifer forest and apply this model to simulated stem maps that are similar in residual basal area yet vary in degree of spatial complexity. We found that light availability was best modeled by residual stand density index and that consideration of forest structure at multiple spatial scales is important for predicting light availability. Second, we found that restoration treatments differing in spatial pattern may differ markedly in their achievement of objectives such as density reduction, maintenance of horizontal and tree size complexity, and creation of microsite conditions favorable to shade-intolerant species, with several notable tradeoffs. These conditions in turn have cascading effects on regeneration dynamics, treatment longevity, fire behavior, and resilience to disturbances. In our study, treatments with high aggregation of residual trees best balanced multiple objectives typically used in ponderosa pine and dry mixed conifer forests. Simulation studies that consider a wide range of possible spatial patterns can complement field studies and provide predictions of the impacts of mechanical treatments on a large range of potential ecological effects.

scholarly journals Quantifying Understory Complexity in Unmanaged Forests Using TLS and Identifying Some of Its Major Drivers

2021 ◽  
Vol 13 (8) ◽  
pp. 1513
Author(s):  
Dominik Seidel ◽  
Peter Annighöfer ◽  
Christian Ammer ◽  
Martin Ehbrecht ◽  
Katharina Willim ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Structural Equation Models ◽  
Light Availability ◽  
Structural Complexity ◽  
Basal Area ◽  
Ecosystem Functions ◽  
Canopy Openness ◽  
Seasonal Precipitation ◽  
Wide Range ◽  
Precipitation And Temperature

The structural complexity of the understory layer of forests or shrub layer vegetation in open shrublands affects many ecosystem functions and services provided by these ecosystems. We investigated how the basal area of the overstory layer, annual and seasonal precipitation, annual mean temperature, as well as light availability affect the structural complexity of the understory layer along a gradient from closed forests to open shrubland with only scattered trees. Using terrestrial laser scanning data and the understory complexity index (UCI), we measured the structural complexity of sites across a wide range of precipitation and temperature, also covering a gradient in light availability and basal area. We found significant relationships between the UCI and tree basal area as well as canopy openness. Structural equation models (SEMs) confirmed significant direct effects of seasonal precipitation on the UCI without mediation through basal area or canopy openness. However, annual precipitation and temperature effects on the UCI are mediated through canopy openness and basal area, respectively. Understory complexity is, despite clear dependencies on the available light and overall stand density, significantly and directly driven by climatic parameters, particularly the amount of precipitation during the driest month.

The effects of burn entry and burn severity on ponderosa pine and mixed conifer forests in Grand Canyon National Park

2015 ◽  
Vol 24 (4) ◽  
pp. 495 ◽  
Author(s):  
Anna M. Higgins ◽  
Kristen M. Waring ◽  
Andrea E. Thode
Keyword(s):  
Ponderosa Pine ◽  
National Park ◽  
Forest Type ◽  
Grand Canyon ◽  
Burn Severity ◽  
Conifer Forests ◽  
Mixed Conifer ◽  
Grand Canyon National Park ◽  
White Fir ◽  
Mixed Conifer Forests

Over a century of fire exclusion in frequent-fire ponderosa pine and dry mixed conifer forests has resulted in increased tree densities, heavy surface fuel accumulations and an increase in late successional, fire-intolerant trees. Grand Canyon National Park uses prescribed fires and wildfires to reduce fire hazard and restore ecosystem processes. Research is needed to determine post-fire vegetation response thus enabling future forest succession predictions. Our study focussed on the effects of burn entry and burn severity on species composition and regeneration in two forest types: ponderosa pine with white fir encroachment and dry mixed conifer. We found no difference in tree composition and structure in a single, low-severity burn compared with unburned areas in the white fir encroachment forest type. We found no white fir seedlings or saplings in a second-entry, low-severity burn in the white fir encroachment forest type. Second-entry burns were effective in reducing white fir densities in the white fir encroachment forest type. There was significant aspen regeneration following high-severity fire in the dry mixed conifer forest type. This research suggests that repeated entries and an increase in burn severity may be necessary for prescribed fire or wildfire to be effective in meeting management objectives.

Woody debris and tree regeneration dynamics following severe wildfires in Arizona ponderosa pine forests

2012 ◽  
Vol 42 (3) ◽  
pp. 593-604 ◽  
Author(s):  
John P. Roccaforte ◽  
Peter Z. Fulé ◽  
W. Walker Chancellor ◽  
Daniel C. Laughlin
Keyword(s):  
Pinus Ponderosa ◽  
Forest Fires ◽  
Ponderosa Pine ◽  
Woody Debris ◽  
Climatic Conditions ◽  
Pine Forest ◽  
Tree Regeneration ◽  
Forest Recovery ◽  
Regeneration Dynamics ◽  
Ponderosa Pine Forests

Severe forest fires worldwide leave behind large quantities of dead woody debris and regenerating trees that can affect future ecosystem trajectories. We studied a chronosequence of severe fires in Arizona, USA, spanning 1 to 18 years after burning to investigate postfire woody debris and regeneration dynamics. Snag densities varied over time, with predominantly recent snags in recent fires and broken or fallen snags in older fires. Coarse woody debris peaked at > 60 Mg/ha in the time period 6–12 years after fire, a value higher than previously reported in postfire fuel assessments in this region. However, debris loadings on fires older than 12 years were within the range of recommended management values (11.2–44.8 Mg/ha). Overstory and regeneration were most commonly dominated by sprouting deciduous species. Ponderosa pine ( Pinus ponderosa C. Lawson var. scopulorum Engelm.) overstory and regeneration were completely lacking in 50% and 57% of the sites, respectively, indicating that many sites were likely to experience extended periods as shrublands or grasslands rather than returning rapidly to pine forest. More time is needed to see whether these patterns will remain stable, but there are substantial obstacles to pine forest recovery: competition with sprouting species and (or) grasses, lack of seed sources, and the forecast of warmer, drier climatic conditions for coming decades.

Silvicultural implications from analyzing light induced height growth development of eight North American juvenile tree species in mixed-conifer forests

2019 ◽  
Vol 92 (5) ◽  
pp. 616-626 ◽  
Author(s):  
Peter Annighöfer ◽  
Dominik Seidel ◽  
Christian Ammer ◽  
Scott L Stephens ◽  
Robert A York
Keyword(s):  
Sierra Nevada ◽  
North American ◽  
Tree Species ◽  
Light Availability ◽  
Height Growth ◽  
Light Environment ◽  
Conifer Forests ◽  
Conifer Forest ◽  
Mixed Conifer ◽  
Mixed Conifer Forests

Abstract Modern silviculture is based on simulating natural disturbance regimes on the one side and reducing their impact on the other side. Disturbances modify light regimes of forests along complex spatial patterns, and species participating in the ecosystem tend to have unique adaptations to the multitude of light conditions found in forests. We studied the height growth reaction of saplings from eight native North American tree species to different light availabilities in a Sierra Nevada mixed conifer forest. Large height growth differences occurred between species. Height growth increased for most species with increasing light availability. However, black oak but also incense cedar and tanoak reached an optimal value or saturation point of light availability at intermediate light levels, above which their growth stayed the same or slightly declined on average. A variety of stand conditions, representing the range from early to late successional stages, are beneficial to maintain tree species diversity across stands. Such a gradient of conditions can be achieved by diversifying silvicultural regimes and using regeneration approaches that mimic a range of disturbance intensities. The results add to knowledge on the species’ ecology by specifying their height growth in dependence of a quantified light environment. The quantification of the light environment can directly be linked to % canopy cover and a range of regeneration methods, respectively. With this, the results may help achieve a more precise and target-oriented management of Sierra Nevada mixed conifer forests.

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