Abstract
AbstractAimAt the elevational limit of forest distribution, montane forests show diverse responses to environmental change with upward shifts, increased tree density and lateral expansion reported. To enable informed analysis of the consequences forest advance will have on montane biodiversity, we quantify changes in the area and elevation of the tree line ecotone and identify how patterns of forest advance are modified by topography and over time.LocationCentral Mountain Range, Taiwan.Time period1963–2016.Major taxa studiedMontane Forests.MethodsChanges in the area and elevation of montane forest at the tree line ecotone were quantified using a stratified random sample of aerial photography captured in 1963, 1980, 2001 and 2016. Weighted estimates of habitat area and elevation for each time step were used to quantify the influence of slope aspect and inclination on tree line ecotone change and identify how the rate of habitat change varies over time.ResultsNon‐forest area declined by 29% between 1963 and 2016 driven by a 295.0 ha increase in forest area within the study region. Despite no change in mean forest elevation, the mean elevation of establishing forest has increased at a rate of 2.17 m/yr. Changes in forest area and elevation are spatially variable, driven by the complex montane topography. East and south facing slopes show the largest gains in forest area and 0–20° slopes show an increasing rate of forest establishment up to 2016, while slopes facing west or with incline > 46° show negligible change.Main conclusionsClimate‐linked montane forest expansion in the Central Mountain Range in Taiwan is dominated by infilling rather than increases in forest elevation. Forest expansion has significantly reduced non‐forest habitat area in this endemic species‐rich region. However, considerable terrain‐dependent variation in forest advance occurs, offering the potential that non‐forest species will continue to persist at high elevations with reduced population size.
Highlights
| MATERIALS AND METHODSThis research was conducted in the Central Mountain Range of Taiwan (Figure 1). Despite Taiwan spanning the Tropic of Cancer, high-elevation areas of the Central Mountain Range experience temperate conditions that support conifer-dominated forests at elevations higher than 2,400 m a. s. l
The integration of repeat aerial photography analysed with a change-sample assessment enables precise and unbiased estimates of forest change that could not be achieved in any other way
In Taiwan's Central Mountain Range, this approach reveals a complex pattern of tree line advance in which rates of forest advance vary according to topography and over time
Summary
This research was conducted in the Central Mountain Range of Taiwan (Figure 1). Despite Taiwan spanning the Tropic of Cancer, high-elevation areas of the Central Mountain Range experience temperate conditions that support conifer-dominated forests at elevations higher than 2,400 m a. s. l. Average rates of advance were calculated as the proportion of available area occupied by a change class divided by the length of the monitoring period (e.g. the proportion of the non-forest area in 1980 that has converted into establishing forest in 2001 divided by 21 years, returns the rate of recent establishment between 1980 and 2001). Two of the terrain strata considered here show increases in the proportion of area occupied by the establshing forest class, with establishing forest area increasing by 4.3% on west-facing slopes and by 3.0% on slopes with 0–20° between 1963 and 2016 (Figure 4). The rate of recent establishment (a change from non-forest to establishing forest within a single change period) peaked across the study area between 1980 and 2001 and remained stable between 2001 and 2016 (Figure 5a). Slopes > 46° show an inverse relationship to the landscape-scale pattern of advanced establishment with a strong decline in the rate of change between 1980 and 2001 and higher rates of advanced establishment during the 1963–1980 change period and the 2001– 2016 change period (Figure 5f)
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