{"id":32923,"date":"2020-01-31T08:47:39","date_gmt":"2020-01-31T08:47:39","guid":{"rendered":"https:\/\/blogs.agu.org\/landslideblog\/?p=32923"},"modified":"2020-01-31T08:47:39","modified_gmt":"2020-01-31T08:47:39","slug":"trees","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2020\/01\/31\/trees\/","title":{"rendered":"Do trees make slopes more stable?"},"content":{"rendered":"

Do trees make slopes more stable?<\/h4>\n

A common comment on this blog, or on Twitter, in the aftermath of a landslide is that it could have been prevented by the planting of trees.\u00a0 It is widely believed that trees increase slope stability, and thus reduce the likelihood of landslides.\u00a0 This feels logical, and of course there is a long history of landslides in the aftermath of wildfires<\/a> or in the period after deforestation<\/a>.\u00a0 However, the quantitative evidence that planting trees decreases landslide susceptibility is surprisingly poor, but some studies have suggested that tree planting can sometimes be detrimental to overall stability.<\/p>\n

In that context, a new paper published in the journal Landslides<\/em><\/a> (Lan et al.<\/em> 2020<\/a>), which reports a study that seeks to explore this topic, is particularly welcome.\u00a0 To do so, the authors built a model slope, 80 cm long and 20 cm wide, onto which they “planted” artificial trees, with a simulated root network.\u00a0 The slope was then sprayed with simulated rainfall via a nozzle system, and the likelihood of failure was determined.\u00a0 A range of conditions were investigated, with a variety of slope angles and with different patterns of tree planting.\u00a0 In total 12 experiments were conducted, and the behaviour of the slope was both observed and modeled.\u00a0 In each case an experiment was conducted with no trees present as a control, as shown in the figure below.<\/p>\n

\"Trees\"

The development of slope failure in a simulated slope – in this case on a 60 degree slope. From Lan et al.<\/em> (2020)<\/a>.<\/p><\/div>\n

.<\/p>\n

The results are interesting and perhaps surprising.\u00a0 For lower gradient slopes (20\u00ba and 35\u00ba in the model), tree planting increased slope stability.\u00a0 It should be noted that in the real world a 35\u00ba slope would be considered to be very steep.\u00a0 However, on steeper slopes (50\u00ba and 60\u00ba), tree planting reduced stability. \u00a0 The pattern of planting of the trees changed their effectiveness in terms of reducing landslides. The most effective pattern was found to be dense, wide bands of trees with spaces between the bands.\u00a0 This was found to be more effective than an even distribution of trees across the slope.<\/p>\n

There are caveats to a study like this, of course.\u00a0 The first is that scaling between model slopes and the real world is notoriously difficult.\u00a0 This is the reason that centrifuges are used to simulate slope behaviour – this study really needs such equipment to be reliable.\u00a0 Second, there is a problem with the grain size of the simulated soil, which does not scale properly. And finally, the model does not really simulate the complex relationships between trees and the soil – for example, to what degree does the presence of trees change the physical characteristics of the soil through time?<\/p>\n

But nonetheless, this is a really useful study in that it highlights that tree planting on slopes is a complex issue.\u00a0 It is clear that it can be beneficial in lower gradient slopes, assuming that the slope is sufficiently stable that the trees can become established (this is a big problem in active slopes, like those undergoing coastal erosion).\u00a0 But, effective planting is an expert task, and needs careful design.<\/p>\n

Reference<\/h4>\n

Lan, H., Wang, D., He, S. et al.<\/em> 2020.\u00a0Experimental study on the effects of tree planting on slope stability<\/a>. Landslides<\/em><\/a>. https:\/\/doi.org\/10.1007\/s10346-020-01348-z<\/a><\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

A new study (Lan et al 2020) explores whether planting trees increases slope stability. Spoiler alert: in general they do on lower angled slopes, but on steep slopes they can reduce stability.<\/p>\n","protected":false},"author":22,"featured_media":32926,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[367,831,469,484,17,28568],"class_list":["post-32923","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-deforestation","tag-experiment-2","tag-featured","tag-forest","tag-research","tag-trees"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/32923","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/comments?post=32923"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/32923\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/32926"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=32923"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=32923"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=32923"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}