Invasive plants on the move; what will you do?

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rodophoto

Rodolpho “Rodo” Quiros is a biologist, adventurer, and man of mystery at Las Cruces Biological Station and Wilson Botanical Garden. The garden and station are a combination botanical garden and natural reserve. Rodo is an expert on both the plants of the natural reserve and the botanical garden, a true polymath to the plants. Around ten years ago he began to wonder if the exotic plants from the botanical garden might colonize the adjacent reserve. Running a botanical garden next to a natural reserve, although worthwhile, is a recipe for trouble. The Wilson Botanical Garden houses thousands of exotic plants! There’s bound to be at least a few which have the potential to escape and become become invasive.

This is exactly what Rodo addressed in his 2007 master’s thesis. He found around ten exotic plant species growing in the forest. Most of these plants were at their densest right on the edge of the forest, and became rarer as he went in.

Like so

Like so

This is called an invasion front pattern. Rodo found this by surveying exotic plants at four distances (50m, 270m, 360m, and 630m) from the botanical garden. He made six plots at each of the four distances. Here’s a map of his plots.

picturesheep

However, Rodo’s research, although amazing, represents only a snapshot in time. To see if plants are actually spreading through the forest, we need to see how populations are changing across time. But let’s back up a second. Why exactly do you need to see population changes across time? Here’s a helpful and extra-professional video to explain.

Here’s where Aviv and I come in. To see how populations of exotic plants in the Las Cruces Biological Station changed after seven years, we decided to make plots at the same distances Rodo did and count the same exotic plants he did.

However we knew next to nothing about the plants around here, so first we had to learn how to ID all these plants. Let’s meet the gang.

ginger

First on our list is Zingiber spectabile. This ginger was the most common invasive plant that Rodo found and is easily distinguishable by its distinctive flowers, leaf structure and lovely aroma. Rodo found these everywhere.

banana

Next up is Musa velutina, the pink banana. This was the second most common plant that Rodo observed and he only observed them in the middle two distances. For those who are curious, those bananas are disgusting.

caryota

Caryota urens, or the fish-tail palm, can be distinguished by its fish-tail shaped leaflets and crazy spaghetti seed things. Rodo found these most commonly near the edge of the garden and with increasing rarity as he moved away. This suggests an invasion front pattern.

raphia

Raphia taedigera is a palm with incredibly long leaves that Rodo found a few of. Their distribution also suggested an invasion front pattern.

phytelephas

Finally there’s Phytelephas aequatorialis, a plant that Rodo did not observe in his plots. However, we got confused and thought we needed to look for it.

Now that we knew our plants, we were ready to go. We decided we would look at four 10m x 10m plots at each of the distances that Rodo sampled. Wait! There’s one more thing. We only had one day to do it!

We started bright and early at 7:30. Our goals were to count plants in 4 plots at 4 distances, not get bit by snakes, and to do it all before dark. The first distance we did was 50m away from the botanical garden. We tried to keep our plots 50m apart following the border of the garden. In each plot we counted every invasive stem we could recognize. As it turns out all of our plots fell on slopes with 50 degree angles full of spiky plants. Needless to say it was a lot of fun.

The trick was not getting spiked

The trick was not getting spiked

By 10:30 we moved on to the 270m plots. Now these were much less steep, and we got those suckers done by lunch. These plots had a lot of light gaps, and a lot of bananas and gingers.

Much, much less murdery

Much, much less murdery

The 360m distance we got done by 2:00, but that fourth distance. That 630 distance was out to get us. The 630 meter plots were in the beginning of the primary forest of the reserve, and were characterized by 60 degree slopes, tree fall gaps and nightmarishly dense vegetation. We had to traverse it on hands and knees and slide down on our butts. I was convinced we were going to slip and fall onto a viper or a spike or something. But in the end, we got it done by 3:30.

Also, Aviv made a little friend!

Also, Aviv made a little friend!

Now I know what you’re all thinking. What about the invasive species? What did you find? Before we can get to it, we gotta show you a picture of how bad the chiggers got Aviv.

Poor guy really got munched. Check out them calves!

Poor guy really got munched. Check out them calves!

ginger

We found that the ginger had increased in density since 2007, but did not show an invasion front pattern. They especially increased in density in the primary forest.

banana

In the 270m plots we found incredible densities of Musa velutina in treefall gaps. There was no invasion front pattern with this one either. However the dense monocultures we observed were disturbing.

caryota

Caryota urens showed up a little in the 50m plots, but overall we saw a lot less than Rodo. Because we did not see any increase since 2007, we don’t think that this palm is spreading into the reserve.

raphia

We didn’t see heads or tails of Raphia taedigera. It too probably is not spreading into the forest.

phytelephas

Remember Phytelephas auquatorialis, the palm we weren’t even supposed to look for? Well we found a few at every distance we looked at. We don’t know how they got there in 7 years. Perhaps Rodo missed them, but that guy’s a pro. We don’t think he would have missed anything. The seeds of these palms are dispersed by rodents. What have these rodents been doing in 7 years? This one really baffled us.

As you may have noticed, we found no invasion fronts. The Wilson Botanical Garden has been around for 52 years. In that time you might think that any invasive plant that could have invaded would have. Zingiber spectabile and Musa velutina seem to have. They already are a part of the forest, having colonized suitable areas. More disturbingly, they seem to be increasing in density. Serious removal programs need to start for these plants before it gets worse. Their invasion fronts probably swept through this stretch of forest ages ago. The Phytelephas is more confusing. Seven years seems like too short a time for a slow-growing palm to have spread so far. All three of these species are ones that we need to keep an eye on.

What our results in combination with Rodo’s tell us is that there does not seem to be any invasions that are currently spreading through the area we studied. More research needs to go into how these plants are colonizing tree fall gaps and other suitable areas within the area they have already invaded. If we can understand the distribution of plants like Zingiber spectabile and Musa velutina within their colonized area we can better understand how they affect forest structure. It’s too late to prevent them from colonizing the forest, so future research should focus on how they affect the forest.

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