Lianas?

About a year ago I took a trip to Costa Rica as part of a three-week plant systematics field trip with the University of Vermont. Lianas were present in nearly every forest type we explored. The word “liana” seemed exotic and their commonness was perhaps the most noticeable differences between northern temperate and tropical forests. Even the subtropical forests of southern Florida I became familiar with didn’t share such a pronounced abundance of these elegant climbing plants. I asked myself this question: Do northern temperate forest have lianas? The short answer is yes, but what follows here is the strange rabbit hole my mind traveled down in attempt to learn more. ( The picture on the left is a liana behind my uncle's house, the right is Bauhinia spp. in Costa Rica)

Google searches to a peer reviewed ecology papers will define lianas as a climbing woody vine. We definitely have these up north. As a kid I can remember swinging on big vines behind my uncle’s house, a place I visited recently. Although not as abundant, lianas exist in northern temperate forests. We know them as vines, which doesn’t sound as sexy.

In fact, there are about 215 liana species in the contiguous United States according to the USDA-NRCS (Londre and Schnitzer, 2006). The lianas behind my uncle’s house were likely of the genus Vitus, grapes, but other species I’ve regularly seen are Parthenocissus quinquefolia, Celastrus orbiculatus and Toxicodendron radicans (Virginia creeper, Oriental bittersweet and poison ivy). Liana studies done in northern forests almost always mention these species.

Apparently, one main reason why lianas don’t exist is such abundance in temperate forests is due to freezing xylems. However, a 0.94°C increase of average temperatures over the last 45 years in Wisconsin hasn’t increased liana abundance there (Londre and Schnitzer, 2006). However, in South Carolina, where increases in average temperatures could decrease the number of day below freezing per year, Allen at al’s 2007 study showed no convincing results that indicated increasing liana growth rates over a 12-year span.

According to Londre and Schnitzer (2006), we can expect to see more lianas along forest edges rather than interiors, which is what one might expect if they were in a tropical environment. Laurance et al (2001) did not observe higher liana abundances in fragmented area, but did find increases in diversity. Additionally, tropical forests being harvested have increased liana abundance and some by 40% in just 17 years (Schnitzer, 2011).

Lianas’ large canopies, high reproductive outputs (at the cost of structural support(Schnitzer and Bongers, 2002)) plus Zhu and Cao’s 2010 observation that lianas in South Western China have higher photosynthetic rates compared to trees of the same region, exemplify how lianas compete with trees for resources. Furthermore, underground competition for nutrients are thought to play a significant role in liana distributions and colonizations (Laurance et al 2001, Leight-Young et al, 2010), but are difficult to observe. Not only can they out compete trees for resources, but liana can climb up trees to steal their precious light!

There are many mechanisms employed by lianas to reach a forest canopy including, stem twining, clasping tendrils, thorns and spines, down-ward pointing hairs and adhesive adventitious roots (Schnitzer and Bongers, 2002). Leight-Young et al (2010), observed that the larger a tree’s diameter, the more root climbers were observed. Of course, tree architecture also plays a role in what kind of liana might colonize it.

Because of their ability to colonize disturbed areas there is concern about lianas suppressing forest regeneration by shading out plants important to succession. While having lower above ground biomasses than trees (lianas: 5-10%, trees: 90%), lianas can also slow tree growth. These factors: deforestation, colonization by lianas and decrease tree growth and regeneration suppression all decrease the amount of carbon being sequestered. Soil homogenization may also occur because of high foliar nitrogen and phosphorous as well as short leaf life-spans (Zhu and Cao 2010). Soil homogenization has the possibility of limiting growth of plants adapted to specialized soils (Schnitzer et al, 2011).

So, it would seem, from the information I’ve included, that lianas are bad. They take over light gaps, prevent other perhaps valuable trees from growing and regenerating the forest, decrease regeneration rates and facilitate soil homogenization. Lianas do provide structural diversity for forests, from which plant and animal life does benefit. They do contribute to biodiversity and may play an integral role in maintaining it because their ability to pull down trees and provide light gaps (Schnitzer et al, 2011).

Although this is my first foray into the world of existing liana research, it seems as though research does paint lianas in a negative light, despite acknowledgement of their cool ecology. Tropical inhabitants rely on their forest for income and sustenance. If lianas are portrayed as detriments to forests, it is possible their conservation may be neglected (despite their apparent increase in abundance, deforestation ultimately means less liana habitat). More research is likely needed into liana forest dynamics and their ecological role.

In my opinion, people are reluctant to change unless it has an economic benefit. By surveying ethnobotanical uses of lianas, results may garner support in effort for their conservation. For example, a survey conducted within a 1-ha plot of Amazonian Ecuador found 46 out of 98 liana species to have a use. The uses range from lamp fuel to music and construction material to edible material, and of course, ritualistic and medicinal uses. There is so much more to learn! I’ll end it here, but leave you with these questions in my head:

Is there a trend between lineage and liana climbing mechanism?

How are the different climbing mechanisms correlated to forest age, tree diameter and tree architecture?

Do lianas have host preferences and how do they range within a species?

Is there an ethnobotanical solution to liana conservation?

Works Cited:

Laurance, W.F., Perez-Salicrup, D., Delamonica, P.,Fearnside, P.M., D’Angelo, S., Jerozolinski, A., Pohl, L. and Lovejoy, T.E. 2001. Rain forest fragmentation and the structure of Amazonian liana communities. Ecology 82 (1): 105-116.

Leight-Young, S.A., Pavlovis, N.B., Frohnapple, K.J. and Grundel, R. 2010. Liana habitat and host preference in northern temperate forests. For. Ecol. And Management 260: 1467-1477.

Londre, R.S., and Schnitzer, S.A. 2006. The distribution of liana and their change in abundance in temperate forests over the past 45 years. Ecology 87(12):2973-2978.

Paz Y Mino C., G., Balslev, H. and Valencia, R. Useful liana of the Siona-Secoya Indians from Azmazonian Ecuador. Economic Botany 49 (3): 269-275.

Schnitzer, S.A. and Bongers, F. 2002. The ecology of lianas and their role in forests. Trends in Ecology and Evolutions 17 (5): 223-230.

Schnitzer, S.A., Bongers, F., and Wright, S.J. 2011. Community and ecosystem ramifications of increasing lianas in neotropical forest. Plant Signaling & Behavior 6:598-600.

Zhu, S. and Cao, K.F. 2010. Contrasting cost-benefit strategy between lianas and trees in a tropical seasonal rain forest in southwestern China. Oecologia 163: 591-599.