Ecosystem Recovery Following Disturbance chaired by Craig Delong

Ecosystem recovery after disturbance: thresholds for biodiversity and resiliency indicators

J. Chandler — Wed, 24 Jun 2009 11:10:00 PDT

This project uses long-term (20 yr) research installations established and maintained by the BC Ministry of Forests and Range and that extend across north-central British Columbia, Canada. Vegetation structure (% cover and height) was measured at regular intervals (1, 2, 3, 5, 10 and 20 yrs) after clearcut or slashburning disturbances. These measurements are being used to develop indicators of biodiversity (composition, richness and biomass) and define response curves for measuring ecological resilience of Sub-boreal Spruce, Engelmann Spruce-Subalpine Fir, and Interior Cedar Hemlock forest ecosystems. We hypothesize that the rate of recovery, as measured by the three biodiversity indicators, varies significantly among ecosystems and across environmental gradients. We also expect that site productivity and the historical fire regime are important in determining vegetation recovery rates after burns of varying severity. To test these hypotheses, we will use post-burn vegetation repeated measures and environmental data collected in the summers of 2007/08 to develop a structural equation model. Our model will be tested using plant community composition first by species and then according to plant functional types. This research will support BC’s Future Forest Ecosystems Initiative, which aims to protect and enhance the resilience of BC’s forests through an adaptive management strategy.

Regeneration Dynamics in Mountain Pine Beetle-Disturbed Forests: Lessons From the Current and the 1978-82 Flathead Epidemics

Dave Coates — Tue, 23 Jun 2009 15:40:00 PDT

There are two dominant mechanisms for development of a new tree layer and subsequent canopy recruitment after major canopy mortality events. First, regeneration may develop from a pulse of new post-disturbance recruitment. Alternatively, regeneration can be from the existing seedling bank that survived the canopy mortality event. The timing and extent of post-disturbance recruitment from seed and the relative importance of the existing seedling bank is poorly understood in MPB-disturbed forests. The recruitment of post-MPB seedlings is a function of seed-source availability, seedbed substrate, overstory structure, and time since MPB attack. In the northern interior, post-MPB recruitment was sparse in stands impacted by beetle 3-10 years earlier. Subalpine fir comprised the majority of the post-MPB recruitment. It increased with local parent tree basal area and increased strongly with proximity to a major seed source, resulting in a patchy distribution. Lodgepole pine post-MPB recruitment was limited by overstory shading; pine regeneration decreased as the total overstory basal area increased. Spruce regeneration was similarly limited by total overstory basal area. Seedbed substrates were dominated by undisturbed moss layers and changed little (in the 3-10 yr post-MPB attacked stands). There was a weak trend to increased regeneration in older stands (7-10 years). Based on destructive sampling and stand reconstruction, regeneration post-beetle attack in the Flathead was often, but not always, delayed by 5-10 years. In most stands, this was followed by a strong pulse of regeneration for about 10 years. Twenty years after the outbreak there was an abrupt decrease in recruitment. In 2007, densities of post-beetle regeneration in all but 2 of the 22 stands were adequate for stocking. Based on age of understory trees in 2007, there was little advance regeneration in these forests at the time of the beetle attack. Virtually all stands are well-stocked with regeneration today.

Ecosystem Recovery Following a Mountain Pine Beetle Outbreak in Northern British Columbia: A Case of Shifting Values

Craig DeLong et al. — Tue, 23 Jun 2009 16:00:00 PDT

The massive Mountain Pine Beetle (MPB) outbreak in northern British Columbia created a unique opportunity to examine ecosystem change over time in response to this disturbance. Prior to this outbreak, the dominant disturbance agents were wildfire and harvesting. A key question is how timber and habitat value will change over time in response to this disturbance and how this might be impacted by extensive clearcut salvage harvest. We have established 48 permanent sample plots in MPB impacted stands. Changes in stand structure, vegetation and functional wildlife habitat along with tree mortality and growth are being monitored. There has been almost complete mortality (98%) of larger lodgepole pine (>22cm DBH) and the current focus of forest operations has been minimize the loss of timber value represented by these stems. However, in many stands there is considerable live understory and significant height and radial release of these stems representing an important future timber value that is lost through clearcut harvest. In addition there are larger live trees in most of these stands and they represent a shrinking habitat resource on these pine dominated landscapes. The larger dead pine are continuously losing timber value through checking and tree fall. At the same time the fallen stems represent valuable habitat. Accounting for the shifting timber and habitat values and determining appropriate management strategies, including no harvest, will be a key challenge for forest managers in these landscapes.

Structure and Composition of Post-Fire Regeneration on Upland Sites in Alberta

S. Gartner et al. — Tue, 23 Jun 2009 16:20:00 PDT

Although a good deal of post-fire vegetation development research has been done, there is a lack of information showing how western boreal mixedwoods regenerate after fire. The objective of our study was to conduct a broad survey using standard regeneration assessment protocols and evaluate regeneration attributes for fires 10 to 20 years after the fire disturbance. The heterogeneity in stand structure within the different fires was also of interest as well as the how late successional species Picea glauca is regenerating. Five fires in central and northern Alberta within the Lower Foothills and the Central Mixedwoods ecological subregions were selected. To compare the impact of different pre-fire composition on post-fire regeneration, we stratified the stands within the fires into broad classes (pure conifer, conifer dominated, deciduous dominated and pure deciduous stands) based on pre-fire regional forest inventory maps. Only post-fire stands with no anthropogenic disturbance were chosen. Within each stand we applied a systematic sampling design involving a 30 m inter-plot distance. For each 10 m2 circular plot we recorded tree species, measured stump height diameter and the height of the tallest conifer and deciduous tree. Additionally, at every fourth plot ten individuals of each species were measured for height and diameter. A total of 506 plots were sampled in 22 stands. A variety of nonparametric comparisons have been performed. Preliminary results suggest that there is no significant difference between the two ecological subregions. The number of plots with at least one conifer seedling in conifer and in conifer dominated stands increased with the time since fire. The most common species found were Populus tremuloides and Populus balsamifera while the most common conifers were Pinus contorta and Pinus banksiana. Our preliminary results suggest that pre-fire stands dominated by Picea glauca regenerate as deciduous stands post fire.

A Retrospective Study of Spatial and Temporal Recruitment Dynamics of Spruce in a Boreal Mixedwood Forest of BC

C. Maundrell et al. — Tue, 23 Jun 2009 16:40:00 PDT

Understanding post fire white spruce recruitment and natural regeneration in mixed aspen spruce stands in the boreal forests of Northeast British Columbia has proved difficult. Proximity to seed source is generally considered to have one of the greatest influences on natural regeneration of these forests following disturbance by fire. In order to increase our understanding of the dynamics of recruitment following fire, we measured white spruce regeneration within a 59 year old aspen spruce stand in Northeast BC. One meter wide linear transects, 75 m in length, were established perpendicular to the forest edge seed source: three transects were oriented to the southeast and three were oriented to the west (into prevailing wind). The number of white spruce encountered along transects were counted at one meter intervals along each transect. Remnants and co-dominant spruce trees producing seed within a tree length distance (25m) of transects were identified to establish internal stand seed sources. No post fire internal spruce seed sources were detected near transects. White spruce regeneration declined with distance from the fire edge for both sampling orientations. Seedling recruitment was negatively correlated to the direction of the prevailing winds. This resulted in more spruce recruitment on the eastern edge of the stand than the western. However remnants of the original stand or germinant seedlings that maintained co-dominance in the regenerating stand may have contributed spruce seed resulting in internal recruitment. This would result in isolated internal patches of white spruce with densities similar to those found at the forest edge. White spruce seed sources external and internal to the regenerating spruce aspen stand contribute to observed stand dynamics and succession processes. The recruitment and regeneration of spruce in these stands determines the complex nature (species and structural), spatially and temporally, of mixed aspen white spruce stands in Northeast BC.

Ecosystem Recovery : How Have Interior Cedar-Hemlock Forests in North-Western British Columbia Responded to Disturbance?

B. H. Heemskerk et al. — Wed, 24 Jun 2009 08:40:00 PDT

In British Columbia, ecosystem-based management initiatives are being implemented for a variety of forest management and harvesting practices often without adequate data on how forests have responded to past disturbances. The overall objective of this project is to quantify selected second growth Interior Cedar Hemlock forest ecosystem attributes to provide a field-based assessment of ecosystem recovery following disturbance. This objective is being accomplished through a retrospective examination of existing second growth forest stands that have developed after man-caused and natural disturbances. The intent is to characterize the ecological condition and level of ecosystem recovery toward 'old-growth' stand conditions. Ecosystem attributes being assessed include overstory and understory species composition and cover, forest growth, epiphytic lichen and bryophyte composition, soil properties, and stand structure including snags and CWD. These data provide a basis for comparison with the same attributes in old-growth plots that have been collected largely within the provincial Biogeoclimatic Ecosystem Classification Program over the past 30 years. Initial results indicate that at 81 to 140 years and 141 to 200 years after disturbance, vegetative characteristics have re-established with roughly 50% and 80% similarity, respectively, to that of old-growth stands (>200yrs). Second growth stands (<40yrs) throughout the study area contain less western redcedar, western hemlock and true firs with higher levels of spruce and pine when compared to older stands. With current management scenarios assuming rotation lengths of +/- 100 years this could result in decreased levels of species diversity and structural complexity, in turn limiting ecosystem integrity and resilience. The results of this study should aid in establishing future forest management practices including reforestation and harvesting methods that meet the challenges of climate change and ecosystem based management.

Assessment of Prescribed Burning Effects in Paludified Black Spruce Forests in Ontario’s Clay Belt Region

Sebastien Renard et al. — Wed, 24 Jun 2009 09:20:00 PDT

Paludification, the accumulation of poorly decomposed organic matter principally originating from Sphagnum, transforms black spruce forests to forested peatlands in the prolonged absence of fire. High-severity wildfires reverse this process by burning the organic matter layer and thus restart forest succession; in contrast low severity wildfires remove only the tree layer and do not reduce paludification. On the Ontario Clay Belt, a physiogeographic region prone to paludification due to its cold climate and poor drainage, current forest harvest practices (Careful Logging Around Advanced Growth; CLAAG) mimic low severity fires by removing trees but lacking forest floor and soil disturbances caused by fire. Historically, prescribed burning after clear cut (PB) was used as a site preparation technique, and may also be used for controlling paludification as it burns part of the organic soil layer and enhances soil fertility by releasing nutrients. Our retrospective study examines three hypotheses; compared to CLAAG and clear cut, 1) PB has positive effects on soil conditions, 2) controls sphagnum colonisation and 3) results in better growth of black spruce. We sampled 24 sites, using ecological forest classification and harvest records to ensure site equivalency. Results show a significant positive effect of PB on soil decomposition, nutrient contents and pH values. PB reduces Sphagnum establishment and growth. PB significantly increases black spruce growth (terminal shoots), however no difference in mean tree height is observed among treatments. We put forth that these contradictory results could be explained by a time lag in natural regeneration after PB as suggested by forest vertical structure. While not a high severity fire, prescribed burning after clear cut in paludified stands on the Ontario Clay Belt emulates some of its effects. Therefore we conclude that unlike CLAAG, prescribed burning after clear cut facilitates the development of unpaludified stands in a managed landscape.

Using Repeat Landscape Photography to Assess Vegetation Changes in Rural Communities of the Appalachian Mountains

L. Hendrick et al. — Wed, 24 Jun 2009 09:00:00 PDT

Repeat photography is a useful tool for evaluating landscape change and patterns over a long period of time in areas that lack scientific landscape information. The objective of this study was to use ground based repeat photography to quantify and identify landscape vegetation changes over the period 1880 to 2008 and to identify strengths and weaknesses in repeat photography techniques. The historical photograph collection used for this study contained 237 landscape photographs taken in 1880. Fifty-five photographs were successfully relocated and the photograph pairs were analyzed for changes in cover classes and changes by topographic position. From 1880 to 2008, forest land was the most stable cover type (98% of forested land in 1880 remained forested in 2008). Some of the main patterns of land conversion over this time period were (1) agricultural land converted to forest (19%), (2) residential and commercial land converted to forest (18%), (3) transportation systems converted to forest or agricultural land (57%), and (3) lands covered with water in 1880 converted to agriculture or forest lands (15%). Repeat photography when combined with other historical land-use methods can yield a detailed reconstruction of the historical profile of an area; however, if the original locations of the photographs are unknown repeat photography is a very time-intensive technique.

Structural and Compositional Resilience in Second-Growth Relative to Primary Northern Hardwood Stands

E. Zenner et al. — Wed, 24 Jun 2009 10:30:00 PDT

Effective implementation of natural-disturbance based silviculture requires an understanding of if, and how, structural and compositional patterns across multiple scales have been altered in second-growth forests relative to primary forests. We examined averages and heterogeneity of compositional and structural characteristics and diversity in primary stands and nearby second-growth stands that were cutover at the time of Euro-American settlement. Overstory trees and snags, coarse woody debris, understory vegetation, and light transmittance were sampled in four primary and eight second-growth stands along the North Shore of Lake Superior, Minnesota, USA. Primary and second-growth stands differed in both overstory and understory compositional characteristics but less so in structural characteristics. Primary stands were distinguished from second-growth stands by higher abundances of yellow birch (Betula alleghaniensis, Britt.) and conifers and greater variability in tree sizes and abundances, duff depth, understory composition, and decayed coarse woody debris despite the fact that second-growth stands encompassed a broader range of developmental stages. Similarity in structural conditions indicates that second-growth stands may have been relatively resilient to the original cutover 70-100 years ago, whereas composition differences arose during subsequent high-grading.

Weakened Biotic-Environmental Relationships in the Herb Layer After a Hundred Years of Recovery From Logging Disturbance

J. Wyatt et al. — Wed, 24 Jun 2009 09:40:00 PDT

A central debate in community ecology has been the degree to which communities bear the mark of history in their composition and structure. Modern forests have unique species compositions that are decoupled from gradients of temperature, precipitation, and soil types. We do not know how long it takes for the relationship between species composition and the environment to return. The intensity of disturbance may effect the time it takes for environmental coupling to return. Previous studies have addressed environmental coupling on former agriculture land. In contrast, logging disturbance has a lesser impact on the environment and has affected more of the Eastern North American landscape. Given that logging is a lower intensity disturbance than agriculture and that these communities have had a century of recovery time, does environmental coupling play an equal role in old growth and previously logged forests? This study was conducted on the understory herbaceous community of old growth and hundred year old rich cove hardwood forests in the Nantahala National Forest, North Carolina. Herbaceous diversity and abundance along with 24 environmental variables and a spatial dataset based on principal coordinates of neighbor matrices (PCNM) were used in a partial canonical correspondence analysis (CCA). The results show that understory herbs in old growth forests have a strong biotic-environmental relationship. However, this relationship is decoupled in hundred year old forests. The environmental model explained 37.2% of the variation in species composition in old growth forests with Mn, Mg and total exchangeable cations significant predictors. In hundred year old forests, Zn was a significant predictor, but it only explained 11.1% of the variation in community composition. Logging disturbance a century ago retains a mark on species composition by decoupling the biotic-environmental relationship. A hundred years of recovery is inadequate for species to reach equilibrium with the environment.