What are some threats to the boreal shield?

Answer 1

Some threats to the boreal shield are Insects and diseases - essential ecological influences: Together, fire, forest tent caterpillar, lodge pole pine dwarf mistletoe, spruce budworm, and jack pine budworm, typically affect millions of hectares of forests each year in this Ecozone. Although they cause tree mortality, and reduction in growth amounts to tens of millions of cubic meters of wood annually, these agents of change are essential to the ecological well-being of these forests. However, volume losses due to these disturbances, which exceed volumes harvested, have implications for the available timber supply in the region. Disturbances may become more frequent, persistent, and severe if predictions of global climate change are realized. Insects and fungi are capable of adapting quickly to a changing environment because of their genetic makeup and short generation times, but trees are much slower to adapt .This difference in adaptive abilities would lead to an increased risk of insect and fungal infestation with a changing climate. Fragmentation of the aspen forest: Northward expansion of agriculture over the last 100 years has resulted in the loss of much of the most productive aspen forests in the southern portion of this ecozone. A belt of land ranging in width from a few to over 100 km has been converted from trembling aspen and mixedwood forests to agricultural land. This deforestation has resulted in fragmented forests that are in poor condition and prone to degradation. One such decline, caused by drought, occurred in trembling aspen stands in the 1960s (Zoltai et al. 1991). In the early 1990s, aspen decline again became prevalent as a result of forest tent caterpillar defoliation and drought. In contrast, trembling aspen stands in the continuous boreal forest portion of this ecozone have not been affected to the same degree by similar climatic conditions. This fact suggests that the fragmented aspen forests of the southern Boreal Plains ecozone are more predisposed to natural stressors. Roland (1993) states that large-scale forest fragmentation increases the duration of outbreaks of forest tent caterpillar. In addition, remnant forests, wetlands, and other `unimproved lands' within the agricultural belt of this ecozone are being converted to croplands or `improved' pasture lands. Increasing numbers of livestock are also being pastured within the remnant forests. Finally, many of the remaining wooded areas are being cleared. All these agricultural activities have tremendous net adverse health implications for large portions of the remaining aspen-dominated forest ecosystems.