In the process of researching understory vegetation for our urban ecology project, I came across a study by Sikorski et al. that was interested in the effects of visitor pressure on the understory vegetation of forests. Prior to this study, other research has been done on the factors that contribute to an urban park’s species diversity of understory vegetation. The factors associated with the presence of visitors, also known as visitor pressure, are assumed to be the greatest contributor to declines in species diversity. However, no one had compared how species diversity decreases in trampled parks in ancient vs. recent forest stands. The authors of this study hypothesized that understory vegetation in park forest stands exposed to visitor pressure will decrease in species diversity.
The researchers analyzed the effects of visitor pressure on vegetation at thirty-seven parks in Warsaw, Poland. The data was split into three groups: recent forest stands with public access to undergrowth (PR), recent forest stands with restricted access to undergrowth (RR), and old forest stands with restricted access to undergrowth (OR). Older forest stands have been maintained for over 150 years ago and recent forest stands were planted approximately 60 years ago on previously non-forest environments. In each of these forests, the trunks of randomly selected trees were used as a central point to sample from 3 1x1m quadrates that measured vegetation composition, soil samples, and other habitat parameters.
Recent forest stands with public access to undergrowth (PR) were found to have fewer native species and fewer species overall in comparison to restricted access area species (RR and OR). However, the biggest finding was that RR stands had 30 times more species richness than PR stands. Additionally, PR stands exhibited features that hamper the growth of understory plants like higher pH, more soil compaction, a greater percentage of light reaching the ground, more bulk density, and a greater difference in moisture.
The urban ecology project I’m working on with my group also focuses on the understory vegetation of trees, with the biggest difference from Sikorski et al.’s work being that our focus is on small groups of trees rather than forests. We’re also limiting our focus to measuring the radius of vegetation, the distance between trees in a group, and the understory vegetation species. With the paper’s findings on the effects of visitor pressure in mind, I think close together communities of trees will be better protected from foot traffic and have greater species richness.
Sikorski, P., Szumacher, I., Sikorska, D. et al. Effects of visitor pressure on understory vegetation in Warsaw forested parks (Poland). Environ Monit Assess 185, 5823–5836 (2013). https://doi.org/10.1007/s10661-012-2987-0
That is really interesting and something not many probably think about (or at least I haven't really thought about it). It makes sense that fewer species are present in undergrowth that people have access too; 30 species is a lot.
ReplyDeleteWere the forest stands Sikorski et al. was looking at mowed or otherwise treated? Are you looking at trees that have untouched undergrowth or have some of them been mowed or treated? (I'm not sure I phrased those questions very well).