Inventory strategies for monitoring and evaluation of forest damage

Under global change, increasing stresses on forests require strategies for monitoring and mitigation of damages caused by pests and diseases. While the threats to forests increase, so do the possibilities to set up efficient monitoring programmes and detect forest damage by utilising new technologies. This thesis focuses on strategies for forest damage inventories where different auxiliary data are combined to improve information for pest mitigation programmes. First, the efficiency of National Forest Inventories (NFIs; or similar inventories) for detecting and estimating state and change of forest damage across large regions was evaluated. NFIs were found efficient for assessing widely distributed damage, but unable to detect clustered and local outbreaks with adequate precision. Second, targeted forest damage inventories directed to areas with potential or suspected damage were investigated. It was found that two-phase sampling for stratification taking the first phase information from existing NFIs was an efficient strategy. Remotely-sensed auxiliary information and post-stratification was shown to further improve the precision. Third, the use of a new sampling design was evaluated: the local pivotal method (LPM), which spreads the sample in the multi-dimensional space of available auxiliary data. The LPM was found to be more efficient than simple random sampling in all scenarios and, depending on the allocation of the sample and the properties of the auxiliary data, it sometimes outperformed two-phase sampling for stratification. Thus, the LPM may be a valuable tool for practical forest damage inventories. Fourth, the cost-plus-loss method was applied to evaluate inventory strategies in a pest mitigation context. If inventory costs are large, it is especially important to quantify the inventory efforts necessary to evaluate the need for mitigation. The optimal sampling effort necessary for deciding whether or not a defoliator outbreak should be treated was quantified. Double sampling was found to be a cost-effective sampling strategy, i.e. the size of the second phase sample was determined based on the estimates from a small first phase sample. As an overall conclusion, the thesis points out the importance of making use of existing information in setting up effective inventories of forest damage and of using appropriate sampling strategies for making use of the information in the best possible way

Using longitudinal survival probabilities to test field vigour estimates in sugar maple (Acer saccharum Marsh.)

Tree mortality is a major force driving forest dynamics. To foresters, however, tree mortality is often considered a loss in productivity. To reduce tree mortality, silvicultural systems, such as selection cuts, aim at removing trees that are more likely to die. In order to identify trees with higher risks of mortality, field classifications are employed that assess vigour based on external characteristics of trees. We used a novel longitudinal approach for estimating survival probabilities based on ring-width measurements, initially developed by Bigler and Bugmann [Bigler, C., Bugmann, H., 2004. Predicting the time of tree death using dendrochronological data. Ecol. Appl. 14 (3), 902-914], to parameterize a survival probability model for sugar maple (Acer saccharum Marsh.) and to test whether field-assessed tree vigour classes are corroborated by survival probabilities determined from radial growth history. Data from 56 dead and 321 live sugar maples were collected in stands in western Quebec (Canada) that had undergone a selection cut ≈10 years prior to sampling. Our results showed that tree vigour established from external defects and pathological symptoms, using the classification of Boulet [Boulet, B., 2005. D

Slow carbon and nutrient accumulation in trees established following fire exclusion in the southwestern United States.

Increasing tree density that followed fire exclusion after the 1880s in the southwestern United States may have also altered nutrient cycles and led to a carbon (C) sink that constitutes a significant component of the U.S. C budget. Yet, empirical data quantifying century-scale changes in C or nutrients due to fire exclusion are rare. We used tree-ring reconstructions of stand structure from five ponderosa pine-dominated sites from across northern Arizona to compare live tree C, nitrogen (N), and phosphorus (P) storage between the 1880s and 1990s. Live tree biomass in the 1990s contained up to three times more C, N, and P than in 1880s. However, the increase in C storage was smaller than values used in recent U.S. C budgets. Furthermore, trees that had established prior to the 1880s accounted for a large fraction (28-66%) of the C, N, and P stored in contemporary stands. Overall, our century-scale analysis revealed that forests of the 1880s were on a trajectory to accumulate C and nutrients in trees even in the absence of fire exclusion, either because growing conditions became more favorable after the 1880s or because forests in the 1880s included age or size cohorts poised for accelerated growth. These results may lead to a reduction in the C sink attributed to fire exclusion, and they refine our understanding of reference conditions for restoration management of fire-prone forests

Why and where do adult trees die in a young secondary temperate forest? The role of neighbourhood

The density and identity of tree neighbourhood is a key factor to explain tree mortality in forests, especially during the stem exclusion phase. To understand this process, we built a logistic model for mortality in a spatially explicit context,including tree and neighbourhood predictors. Additionally, we used this model to build mortality risk frequency distributions. Finally, we tested this model against a random mortality model to predict the spatial pattern of the forest. Annual mortality rate was high for pedunculate oak (Quercus robur, 6.99%), moderate for birch (Betula celtiberica, 2.19%) and Pyrenean oak (Q. pyrenaica, 1.58%) and low for beech (Fagus sylvatica, 0.26%). Mortality risk models for pedunculate oak and birch included stem diameter, tree height, canopy position and neighbourhood. Mortality was affected by the specific nature of the neighbourhood showing a clear competitive hierarchy: beech > pedunculate oak > birch. Models based on random mortality and logistic regression model were able to predict the spatial pattern of survivors although logistic regression predictions were more accurate. Our study highlights how simple models such as the random mortality one may obscure much more complex spatial interactions

The discretely observed immigration-death process: likelihood inference and spatiotemporal applications

We consider a stochastic process, the homogeneous spatial immigration-death (HSID) process, which is a spatial birth-death process with as building blocks (i) an immigration-death (ID) process (a continuous-time Markov chain) and (ii) a probability distribution assigning iid spatial locations to all events. For the ID process, we derive the likelihood function, reduce the likelihood estimation problem to one dimension, and prove consistency and asymptotic normality for the maximum likelihood estimators (MLEs) under a discrete sampling scheme. We additionally prove consistency for the MLEs of HSID processes. In connection to the growth-interaction process, which has a HSID process as basis, we also fit HSID processes to Scots pine data

Ecological effects of prescribed burning, mechanical cutting, and post-treatment wildfire for restoration of Pinus albicaulis

The field of ecological restoration is growing rapidly, increasing the need for reliable and generalizable information on the impacts of management interventions aimed to be restorative. Prescribed burning and mechanical cutting have been proposed as primary strategies for restoration. However, there is limited information on their efficacy and effects in subalpine forest types, suggesting that monitoring to inform adaptive management is a priority need. I used data from a 15-year, replicated before-after-control-impact (BACI) study on Pinus albicaulis (whitebark pine) restoration to assess the ecological effects of prescribed burning and mechanical cutting, with and without subsequent unplanned wildfire, as well as the efficacy of the monitoring design. Mature tree mortality was high across all study units (77-100%), but neither treatment type nor wildfire were significant predictors of mortality. Similarly, I was unable to detect any effects of treatments or wildfire on P. albicaulis basal area, which declined over time across all study units. However, I found a significant effect of treatment on basal area for two (Pinus contorta and Picea engelmannii) of the three competing conifer species. At Bear Overlook, the site not affected by wildfire, P. contorta basal area change varied significantly between the two treatment units; it decreased by 2.1 m2ha-1 in the burn-only unit but increased by 2.4 m2ha-1 in the prescribed burn with mechanical cutting unit; however, neither treatment was significantly different from the control unit. In contrast, at Beaver Ridge, the prescribed burn with mechanical control treatments, both with and without wildfire, resulted in significant reductions of P. contorta basal area (by 9.8 m2ha-1 and 4.1 m2ha-1, respectively), compared to the untreated control (which did not experience wildfire), which increased by 1 m2ha-1. For P. engelmannii, at Bear Overlook, the site not affected by wildfire, basal area increased after treatment (by 10.3 m2ha-1 and 2.6 m2ha-1 in the burn-only and prescribed burning with mechanical cutting, respectively), but these increases did not differ from changes in the control unit (7.2 m2ha-1). Pinus albicaulis seedling density decreased across both sites and all treatments, however, response to treatment was not statistically significant, while response to wildfire was. The most precisely estimated variable was basal area with a 34% margin of error, followed by mortality (47%) and seedling density (71%). Overall, my findings reveal that the restoration treatments did not affect P. albicaulis mature tree mortality, basal area or seedling density, and were not consistently effective at reducing pressure from competing conifers 15-years after treatment. Although the study utilized best practice design (BACI) and had a relatively large number of replicates (n= 5), loss of study sites due to wildfire coupled with low precision of estimation in field measurements limited power of detection, and highlights the need for large-scale long-term monitoring networks and innovative sampling designs to improve understanding of the efficacy and effects of restoration treatments in P. albicaulis and other degraded forest ecosystems

GLOBAL CHANGE AND WHITEBARK PINE: RESTORATION, REFUGIA, AND ALPINE TREELINES

Whitebark pine is a major component of subalpine forests in western North America. The species occupies harsh high-mountain sites up to treeline, where it is often the dominant species. The species is ecologically important but is also a valuable species for studying the dynamics of alpine treelines. However, whitebark pine has experienced significant mortality in recent decades from mountain pine beetle outbreaks and white pine blister rust. This kind of rapid environmental change presents significant challenges to our understanding and management of the dynamics of ecological communities. On one hand, the effects of climate change on forest ecosystems could provide unique opportunities to study how species, populations, communities, and ecosystems respond to large-scale disturbance. On the other, prediction of future ecosystem behaviors and associated management decisions are complicated by a current lack of understanding of long-term dynamics. Managers are responding to indirect effects of climate change by expanding restoration activities into previously unmanaged, and often poorly understood, forest ecosystems. In this dissertation I investigated three aspects of whitebark pine ecology and conservation: 1) the ecological responses of whitebark pine stands to restoration treatment, 2) the potential of treeline habitats as refugia from mountain pine beetle attack, 3) and the climate-related processes that control growth form at treeline