Disentangling Climate and Disturbance Effects on Regional Vegetation Greening Trends

Emmett, Kristen; Renwick, Katherine M.; Poulter, Benjamin

doi:10.1007/s10021-018-0309-2

Cited by 29 publications

(21 citation statements)

References 91 publications

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“…However, other factors such as prolonged fire return interval (Aakala 2018) and atmospheric nitrogen deposition (Henttonen et al 2017) have also influenced forest growth and dynamics during the same time period. Consequently, attributing canopy cover increase to a particular driver is more complex than attributing canopy cover decrease to disturbances (Emmett et al 2019).…”

Section: Discussionmentioning

confidence: 99%

The structure of boreal old-growth forests changes at multiple spatial scales over decades

et al. 2020

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Context Changes in the structure of boreal oldgrowth forests are typically studied at a specific spatial scale. Consequently, little is known about forest development across different spatial scales. Objectives We investigated how and at what spatial scales forest structure changed over several decades in three 4 km 2 boreal old-growth forests landscapes in northeastern Finland and two in Quebec, Canada. Methods We used canopy cover values visually interpreted to 0.1-ha grid cells from aerial photographs taken at three time points between the years 1959 and 2011, and error distributions quantified for the interpretation. We identified the spatial scales at which canopy cover changed between the time points, and examined the credibility of changes at these scales using the error distributions in Bayesian inference. Results Canopy cover changed at three to four spatial scales, the number of scales depending on the studied landscape and time interval. At large scales (15.4-321.7 ha), canopy cover increased in Finland during all time intervals. In Quebec, the direction of the large-scale change varied between the studied time intervals, owing to the occurrence of an insect outbreak and a consequent recovery. However, parts of these landscapes also showed canopy cover increase. Superimposed on the large-scale developments, canopy cover changed variably at smaller scales (1.3-2.8-ha and 0.1-ha). Conclusions Our findings support the idea that the structure of boreal old-growth forests changes at discernible spatial scales. Instead of being driven by gap dynamics, the old-growth forests in the studied regions are currently reacting to large-scale drivers by an increase in canopy cover.Landscape Ecol (2020) 35:843-858 https://doi.org/10.1007/s10980-020-00979-w( 0123456789().,-volV) (0123456789().,-volV)

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Section: Discussionmentioning

confidence: 99%

The structure of boreal old-growth forests changes at multiple spatial scales over decades

et al. 2020

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“…To the best of our knowledge, abrupt changes have not been taken into account while studying greening trends in the Alps. Furthermore, Emmett et al [22] showed the importance of disentangling climate and disturbance effects when studying greening trends. One of the most prominent tools for the analysis of trends and abrupt changes in time series of vegetation indices is the Breaks For Additive Seasonal and Trend (BFAST) method [23,24], which was successfully used in global and regional analyses.…”

Section: Introductionmentioning

confidence: 99%

Climatic Drivers of Greening Trends in the Alps

et al. 2019

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Since the 1980s, vegetated lands have experienced widespread greening at the global scale. Numerous studies have focused on spatial patterns and mechanisms of this phenomenon, especially in the Arctic and sub-Arctic regions. Greening trends in the European Alps have received less attention, although this region has experienced strong climate and land-use changes during recent decades. We studied the rates and spatial patterns of greening in an inner-alpine region of the Western Alps. We used MODIS-derived normalized difference vegetation index (NDVI) at 8-day temporal and 250 m spatial resolution, for the period 2000-2018, and removed areas with disturbances in order to consider the trends of undisturbed vegetation. The objectives of this study were to (i) quantify trends of greening in a representative area of the Western Alps; and (ii) examine mechanisms and causes of spatial patterns of greening across different plant types. We show that 63% of vegetated areas experienced significant trends during the 2000-2018 period, of which only 8% were negative. We identify (i) a climatic control on spring and autumn phenology with contrasting effects depending on plant type and elevation, and (ii) land-use change dynamics, such as shrub encroachment on abandoned pastures and colonization of new surfaces at high elevation. Below 1500 m, warming temperatures promote incremental greening in the transition from spring to summer, but not in fall, suggesting either photoperiod or water limitation. In the alpine and sub-alpine belts (>1800 m asl), snow prevents vegetation development until late spring, despite favorable temperatures. Instead, at high elevation greening acts both in summer and autumn. However, photoperiod limitation likely prevents forested ecosystems from fully exploiting warmer autumn conditions. We furthermore illustrate two emblematic cases of prominent greening: recent colonization of previously glaciated/non vegetated areas, as well as shrub/tree encroachment due to the abandonment of agricultural practices. Our results demonstrate the interplay of climate and land-use change in controlling greening dynamics in the Western Alps.

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“…However, also the fast processes induce spatial variation in forest structure (Kuuluvainen et al 2014). Hence, discerning the influence of a particular driver based on the landscape pattern is difficult (Emmett et al 2019). While identifying the drivers of change requires careful consideration, the landscape patterns are still effective in analyzing how forest structure varies in space and changes in time.…”

Section: Forest Structure Changes At Different Spatial Scalesmentioning

confidence: 99%

“…These examples indicate that the scale-dependent variability in forest structure is ultimately caused by interactions between multiple driving factors. Hence, similar to an analysis of forest ecosystem change, the linkages between the driving processes and forest structural variability should be interpreted carefully (Emmett et al 2019).…”

Section: Scale-dependent Processes Caused Variation In Forest Structumentioning

confidence: 99%

“…However, other factors such as changes in disturbance regime (particularly prolonged fire return interval; Wallenius 2011; Drobyshev et al 2017; Aakala 2018) and atmospheric nitrogen deposition (Henttonen et al 2017) have also influenced forest growth and dynamics during the same period of time. Because multiple factors drive changes in forest ecosystems, the influence of a particular driver is difficult to differentiate (Emmett et al 2019), and the drivers of the canopy cover increase cannot be explicitly determined based on the results. Superimposed on the changes at large spatial scales, changes in canopy cover were identified at two smaller hierarchical scales (1.3-2.8 ha, mid-scale; 0.1 ha, small-scale) in all landscapes and during all time intervals (III).…”

Section: Large Scale Processes Drove Canopy Cover Increase In Most Lamentioning

confidence: 99%

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Analyzing spatial variation and change in the structure of boreal old-growth forests

Kulha¹

2020

Diss. For.

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Global environmental change and other anthropogenic changes, such as changes in disturbance regimes alter the structure and dynamics of boreal old-growth forests (boreal forests with negligible human impact, henceforth natural boreal forests). Changes in these forests greatly influence key ecosystem properties such as biodiversity and carbon cycle. Hence, understanding the development of the remaining natural boreal forests is particularly important. This thesis examines how boreal forest structure varies in space and changes over time. Forest structure was examined in three natural boreal forest landscapes (2 km × 2 km each) in northern Fennoscandia and two landscapes in eastern North America. Canopy cover that was visually interpreted from stereopairs of aerial photographs taken between the years 1959 and 2011 was used as a surrogate measure of forest structure to quantify and examine spatial variation and/or temporal change, and Bayesian inference was used to separate credible ecological phenomena from the noise caused by visual interpretation error. This thesis presents and applies a novel methodology to study changes in forest structure. We calibrated visual canopy cover interpretations made from time series of aerial photographs with canopy cover reconstructions that were based on field-and tree-ring measurements. We successfully identified credible changes in forest structure in each studied landscape, but also noted that the visual interpretation of canopy cover was prone to systematic and random error that depended on, e.g., aerial photo quality. Due to this error, changes that occurred at the level of an individual tree could not be credibly discerned. Still, the methodology can be used to detect both abrupt and slow continuous changes in forest ecosystems. The methodology was extended to examine spatial variation in forest structure. The results revealed variation in forest structure at multiple spatial scales which showed similarities despite the differences in dominant tree species and disturbance regimes between the studied landscapes. The variability was connected with scale-dependent driving processes that also showed similarities among the landscapes. Last, the methodology was applied to study how varying scale of observation influences how changes in forest structure are perceived over different periods of time. This multi-scale change analysis revealed a synchronous and prevalent cover increase at large spatial scales in the majority of the studied landscapes, and canopy cover decrease and increase in areas that were subjects to disturbances. Changes of variable direction and magnitude were detected at smaller spatial scales in each studied landscape. The results indicated that historical aerial photographs are a valuable resource in studying how forest ecosystems develop, but the notable errors in their visual interpretation need to be taken into account in analysis of change. The results aligned with the hierarchy theory and the hierarchical patch dynamics concept by showing that the structur...

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Disentangling Climate and Disturbance Effects on Regional Vegetation Greening Trends

Cited by 29 publications

References 91 publications

The structure of boreal old-growth forests changes at multiple spatial scales over decades

The structure of boreal old-growth forests changes at multiple spatial scales over decades

Climatic Drivers of Greening Trends in the Alps

Analyzing spatial variation and change in the structure of boreal old-growth forests

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